JP2021138850A - Heat storage material and heat storage power generator - Google Patents

Abstract

To provide a heat storage material which can be used at a high temperature and has excellent heat storage and heat radiation characteristics, and to provide a heat storage power generator which can be operated at a high temperature and has excellent power generating efficiency.SOLUTION: A heat storage material of the present invention comprises a Ge alloy. The Ge alloy is preferably an Fe-Ge alloy, and the Ge alloy preferably contains a eutectic alloy. Especially, the Ge alloy is preferably a hyper-eutectic Ge alloy containing excess Ge in addition to the eutectic alloy. A ratio of Ge in the Ge alloy is preferably 70 atom% to 99 atom%. Further, the heat storage material of the present invention is preferably used in a temperature range of 650°C or higher.SELECTED DRAWING: None

Description

The present invention relates to a heat storage material and a heat storage power generation device.

In recent years, as a measure against the depletion of fossil fuels and environmental destruction, non-stationary heat such as industrial waste heat such as factory waste heat and natural energy such as solar heat is stored in a heat storage device, and when necessary, it is used as an operating medium. Development of power generation and heat utilization technologies that are taken out and used as steam turbines, supercritical CO ₂ , Stirling engines, gas turbine power generation, hot water, etc. is underway.

As such a heat storage device, from the viewpoint of securing a large heat capacity per unit device, latent heat storage is performed by utilizing the latent heat at the time of phase change between solid and liquid as well as the heat accompanying the temperature change of the substance. Attention is being paid to those that apply materials (PCM). Conventionally, it has been proposed to use molten salts such as alkali metal chlorides, carbonates, fluoride salts and various nitrates as PCM (see, for example, Patent Document 1). However, the amount of heat that can be stored per unit amount is not always large. In particular, since the nitrate-based molten salt is thermally decomposed at about 600 ° C., its operating temperature range is limited to 500 ° C. to 550 ° C., and its thermal conductivity is low. Therefore, when it is used by filling it in a container. There is a problem that temperature deviation is likely to occur and the output response is slow.

On the other hand, as a means for solving the problem of the nitrate-based molten salt, an Al—Si-based alloy is known (Hokkaido University document: JP-A-2019-203128). In the Al—Si alloy, higher heat conduction can be obtained as compared with the nitrate molten salt, and it can be used as a heat storage material up to a higher temperature range.

In the process of using an Al—Si alloy as a PCM and solidifying the melted alloy to generate heat dissipation, the Al—Si alloy forms a eutectic, so that it is a primary crystal depending on its composition. After a certain Si phase (or Al phase) is precipitated and cooled with latent heat release of the same phase, when the eutectic temperature reaches around 580 ° C., the Al phase and the Si phase are precipitated while maintaining the eutectic temperature. Since all the latent heat of solidification is released, it is possible to operate in a higher temperature range than the above-mentioned nitrate-based molten salt. Further, since volume expansion occurs when a general metal melts, volume contraction occurs especially when Si melts. Therefore, by using an alloy containing Si as a PCM, melting and solidification occur. The Al—Si alloy also has an advantage as a PCM in that the volume change in the thermal cycle including the above can be reduced.

Further, the heat accumulated by using the PCM is generally converted into electric power by gas turbine power generation using steam turbine as a working medium or high temperature air as a working medium, for example. In this use, from the viewpoint of system management and thermal efficiency, heat caused by latent heat of solidification is continuously used while maintaining a constant temperature, such as the melting point in pure materials and the eutectic temperature in eutectic systems. It is hoped that it can be done. In this respect as well, the Al—Si alloy having a eutectic temperature near 580 ° C. has desirable characteristics as PCM.

Japanese Unexamined Patent Publication No. 2016-166705

When the heat accumulated by using the PCM is converted into electric power by steam turbine power generation using steam as a working fluid, it is preferable that there is a large heat transfer in the temperature range of 100 to 560 ° C. Further, in _{a supercritical CO 2 turbine using solar heat using CO 2} as a working fluid, it is preferable that a large amount of heat is transferred in a temperature range of 550 to 800 ° C. Further, when it is converted into electric power by gas turbine power generation using high temperature air as an operating medium and used, it is preferable that there is a large heat transfer in the temperature range of 850 to 1000 ° C. (National Research and Development Organization Research and Development Center (Overview Report of Research and Development) Environment and Energy Field (2019) / CRDS-FY2018-FR-01) Using PCM with a Stirling engine that uses temperature difference When the stored heat is converted into electric power and used, it is preferable that there is a large heat transfer in the temperature range of 50 to 900 ° C. In addition, high thermal efficiency is generally achieved by generating electricity in a high temperature range. On the other hand, when the PCM is heated to 1000 ° C. or higher by using the condensed sunlight as a heat source, heat dissipation from the heated PCM becomes remarkable, which causes a problem that the thermal efficiency is lowered.

In the current solar thermal power generation, power generation by a steam turbine is the mainstream, but in the state-of-the-art technology, it operates at a higher temperature than a steam turbine such as a _{supercritical CO 2 turbine, a gas turbine, a Stirling engine, etc. due to the high temperature technology of the operating medium.} Power generation technology is being developed. Considering the above-mentioned power generation using PCM, the eutectic temperature (around 580 ° C.) indicated by the above-mentioned Al—Si alloy is not necessarily in the desired temperature range, and the melting point or eutectic in a higher temperature range. It is desirable to use a material system with temperature as the PCM. That is, as a characteristic required for the next-generation PCM, the latent heat of solidification with respect to the total volume is obtained by having the maximum melting temperature (liquidus line temperature in the chemical composition) in which all the PCM materials are melted in a temperature range of about 1000 ° C. or less. Is available, and the minimum melting temperature such as melting point and eutectic temperature is higher, and especially in supercritical CO ₂ using solar heat, sterling engine, gas turbine power generation, high efficiency is expected at 650 ° C or higher. It is desirable to have a minimum melting temperature. _{More preferably, the supercritical CO 2} turbine is desired to have a minimum melting temperature of about 700 ° C. to 800 ° C. from the viewpoint of high thermal efficiency. More preferably, from the viewpoint of high thermal efficiency, it is desired that the power generation by the Stirling engine has a minimum melting temperature of about 800 to 900 ° C. More preferably, from the viewpoint of high thermal efficiency, it is desired that the gas turbine power generation has a minimum melting temperature of about 850 to 1000 ° C. Further, a PCM material having a larger amount of heat (total value of latent heat of solidification and specific heat) required for PCM per unit amount when heating from room temperature to the maximum melting temperature is desired.

An object of the present invention is to provide a heat storage material that can be used at a high temperature and has excellent heat storage and heat dissipation characteristics, and also to provide a heat storage power generation device that can operate at a high temperature and has excellent power generation efficiency. be.

Such an object is achieved by the present invention described below.
The heat storage material of the present invention is characterized by containing an alloy in which the Ge phase and the second phase are in equilibrium and the Ge phase and the second phase form a eutectic in a solidified state.

In the present invention, it is preferable that the second phase is an intermetallic compound containing Ge.

In the present invention, the intermetallic compound containing Ge that is in equilibrium with the Ge phase is K, Sc, Ti, Cr, Mn, Fe, Co, Ni, Mg, Sr, Rh, Pd, Hf, Pt, or a rare earth element. It is preferable that at least one of the elements is contained in the constituent elements.

In the present invention, the alloy is a eutectic composition between the Ge phase and the intermetallic compound containing Ge that is in equilibrium with the Ge phase, or a composition containing an excess of Ge with respect to the eutectic composition. Is preferable.

In the present invention, the eutectic temperature of the eutectic formed by the Ge phase and the second phase is preferably 650 ° C. or higher.

In the present invention, the content of Ge element in the alloy is preferably 40 atomic% or more.

The heat storage material of the present invention is characterized by containing a Ge alloy.

In the present invention, the Ge alloy is preferably a Fe—Ge alloy.

In the present invention, the Ge alloy preferably contains a eutectic alloy.

In the present invention, the Ge alloy is preferably a hypereutectic Ge alloy containing an excess of Ge in addition to the eutectic alloy.

In the present invention, the proportion of Ge in the Ge alloy is preferably 70 atomic% or more and 99 atomic% or less.

In the present invention, the latent heat storage capacity of the Ge alloy ^{is preferably 1.28 GJ / m 3} or more.

In the present invention, it is preferably used in a temperature range of 650 ° C. or higher.

The heat storage power generation device of the present invention is characterized by comprising a heat storage material.

In the present invention, the heat storage power generation device preferably stores heat obtained by condensing sunlight.

According to the present invention, it is possible to provide a heat storage material that can be used at a high temperature and has excellent heat storage and heat dissipation characteristics, and also provides a heat storage power generation device that can operate at a high temperature and has excellent power generation efficiency. can.

It is a state diagram (phase diagram) about the dual system of Fe-Ge at 1013 hPa (1 atm). It is a figure which shows an example of the use form of the heat storage material of this invention. It is a figure which shows another example of the use form of the heat storage material of this invention. It is a schematic diagram which shows an example of the solar thermal power generation apparatus. It is an XRD pattern of the heat storage material of Examples 1 and 2. It is a figure which shows the structure of the apparatus used for the evaluation of the heat storage heat dissipation characteristic. It is a figure which shows the result of the heat storage heat dissipation test performed on the heat storage material of Examples 1 and 2. It is a DSC curve about (a) the heat storage material of Example 1 and (b) the heat storage material of Example 2 in a heat storage mode and a heat dissipation mode. It is a figure which shows the specific heat capacity of a heat storage material, and the heat storage capacity per volume. It is a figure which shows the change of the time derivative (dT / dt) of the heat storage material temperature T with respect to time t in (a) heat storage mode and (b) heat dissipation mode in vacuum about Example 2. FIG. The change in the time derivative (dT / dt) of the heat storage material temperature T with respect to time t in (a) heat storage mode and (b) heat dissipation mode under the flow of the inert gas (N _{2) for Example 2 is shown.} It is a figure. It is a figure which showed the measurement result of the mass loss in the heat storage heat dissipation cycle under the inert gas flow about the heat storage material of Example 2. It is a BEI micrograph and an element mapping image of the cross section before and after the heat storage heat dissipation cycle about the heat storage material of Example 2. It is a BEI micrograph and a carbon mapping image of the cross section of the heat storage material of Example 2 after a heat storage heat dissipation cycle.

Hereinafter, preferred embodiments of the present invention will be described in detail.
[1] Heat storage material When the present inventor conducted various studies to solve the above problems, Ge (germanium) directly under Si on the periodic table was used, and Ge in an equilibrium state (solid phase). By using a predetermined alloy system containing a phase, it has a higher eutectic temperature than the above Al—Si system, can be completely melted at 1000 ° C. or lower, and is released between complete melting and complete solidification. We came up with the idea that a PCM with a large amount of heat can be constructed, and came up with the present invention.

Pure Ge has a melting point of about 938 ° C. and can be melted at a relatively low temperature. Further, the latent heat of melting of a normal metal is 10 to 18 kJ / mol (reference: aluminum; 8.4 kJ / mol; iron; 13.8 kJ / mol), whereas the latent heat of melting of Ge is 34.7 kJ / mol. It is known that it exhibits a particularly large latent heat of melting (Revised 4th Edition Metal Data Book, edited by the Japan Institute of Metals). Therefore, the alloy system containing the Ge phase is expected to be used as a PCM that exhibits a large amount of heat storage per unit amount in the temperature range in which the PCM is used.

In other words, the PCM has both the maximum melting temperature (the temperature at which all solids melt into a liquid, which corresponds to the liquidus temperature) and the minimum melting temperature (symbol temperature), which are supercritical CO ₂ , a sterling engine, and a gas. Where it is desired to be within a temperature range that can be used for turbine power generation, the present inventor adjusts the maximum melting temperature and the minimum melting temperature within a predetermined range with a small amount of addition in order to utilize the large latent melting heat of Ge. By adding a possible alloy element, we have come up with the idea that it is possible to provide a PCM that enables highly efficient power generation or the like using a Ge phase having a large latent heat of melting as a matrix phase.

Hereinafter, as an example of the heat storage material according to the present invention, an alloy containing a Ge phase and a FeGe2 phase as a second phase will be described. FIG. 1 shows an equilibrium phase diagram of the Fe-Ge system. As shown in FIG. 1, in the Fe-Ge system, the Ge phase and the FeGe2 phase exist in equilibrium in the composition range of Fe-66.6 to 99.9 at% Ge, and the two phases are substantially eutectic. It is known that there is a crystal (eutectic temperature: 838 ° C.) relationship. In the composition range, for example, in an alloy having a composition of Fe-70 at% Ge, which is a eutectic composition of a Ge phase and a FeGe2 phase, the entire alloy undergoes melting and solidification at the eutectic temperature of 838 ° C. It will result in the absorption and release of latent heat of melting. Then, at the time of the solidification (melting), a latent heat amount (30.0 kJ / mol) approximately corresponding to the weighted average of the solidification latent heat of Fe and Ge is released (absorbed).

Similar to the Fe-Ge system, the composition range in which the Ge phase and the second phase exist in equilibrium is sometimes referred to as "Ge phase-containing composition" in the present specification. Further, an intermetallic compound containing Ge that is in equilibrium with the Ge phase may be hereinafter referred to as a “Ge-containing intermetallic compound”. Further, in the case where a eutectic point exists between the two phases, the alloy composition at the eutectic point is particularly described as "Ge phase-containing eutectic composition" (or simply "eutectic composition"), and the "Ge phase" is described. The alloy in the "containing eutectic composition" may be referred to as a "Ge phase eutectic alloy". Further, in the present specification, the Ge phase means a metal Ge in which a second element or the like is solid-solved in the crystal structure.

That is, the alloy having the composition of Fe-70 at% Ge corresponds to the "Ge phase eutectic alloy", and the eutectic temperature of 838 ° C. is the maximum melting temperature and the minimum melting temperature of 30.0 kJ / mol. It functions as a heat storage material that shows the latent heat of solidification. By using the alloy as a heat storage material, the total amount of latent heat of solidification of the alloy can be taken out at the eutectic temperature. Therefore, as long as the liquid phase exists, the heat of 838 ° C. regardless of the change in the heat storage amount. Thermal energy can be taken out through a medium, and stable power generation can be performed.

In addition, even when heat is absorbed from a predetermined heat source at the same time as heat is dissipated, a part of the solid phase is melted and changed to the liquid phase by supplying heat from the outside within the range where the liquid phase and the solid phase coexist. Since the temperature of 838 ° C. is maintained, stable heat storage and power generation can be performed regardless of the temperature of the heat source.

For example, even in an Al—Si alloy having a eutectic temperature at 577 ° C., it is possible to store heat and dissipate heat while maintaining the eutectic temperature as described above, but in the heat storage material according to the present invention, It has an advantage in that it can utilize the eutectic temperature existing in a higher temperature range. Further, also in the heat storage material according to the present invention, by heating to an appropriate temperature equal to or higher than the eutectic temperature, it is possible to store sensible heat up to the temperature in addition to the latent heat of solidification, and a larger amount of heat can be stored. Heat can be stored.

Further, as the heat storage material according to the present invention, it is also possible to use an alloy having a composition richer in Ge than the Ge phase-containing eutectic composition (for example, Fe-87 at% Ge). When the alloy is used, the Ge phase and the FeGe2 phase (Ge-containing intermetallic compound) are in equilibrium in the solid phase state, and the two phases are substantially in a eutectic (eutectic temperature: 838 ° C.) relationship. In addition, it is known that Ge coexists in excess of the Ge phase-containing eutectic composition. In the process of extracting heat from the melted alloy, the temperature indicated by the liquidus line existing at around 900 ° C. is set as the maximum melting temperature, and the release of latent heat due to the precipitation of the Ge phase excessive from the Ge phase-containing eutectic composition starts. However, latent heat is released with a decrease in temperature up to the eutectic temperature, which is the minimum melting temperature. Then, at the eutectic temperature of 838 ° C., the entire amount of the liquid phase having the eutectic composition is solidified at a constant temperature in the same manner as described above, and the latent heat derived from the eutectic composition can be taken out at the constant temperature.

That is, when an alloy having a Ge content higher than that of the Ge phase-containing eutectic composition is used among the heat storage materials according to the present invention, the temperature difference between the maximum melting temperature and the minimum melting temperature is set according to the composition. On the other hand, due to the high content ratio of Ge, which has a large latent heat of solidification per unit amount, the amount of heat that can be stored between melting and solidification of the alloy is made larger than that of an alloy having a Ge phase-containing eutectic composition. Therefore, it can be preferably used for heat storage in applications where temperature changes are allowed in a certain range.

On the other hand, by using an alloy having a composition in which the proportion of Ge is lower than that of the Ge phase-containing eutectic composition, it is possible to precipitate an intermetallic compound containing Ge as a primary crystal during solidification, and the structure of the solidified structure. Its use is effective from the viewpoint of control and the like.

As a result, the latent heat of solidification can be used for the total volume by having the maximum melting temperature at which all the PCM materials are melted in the temperature range of about 1000 ° C. or less, which is a characteristic required for the next-generation PCM. The minimum melting temperature such as melting point and eutectic temperature is higher, and the latent heat of melting is absorbed at the minimum melting temperature of 650 ° C or higher, which is expected to be highly efficient especially in supercritical CO2 using solar heat, sterling engine, and gas turbine power generation. And the emission will be available for solar thermal power generation.

It is preferable that the alloy element X instead of Fe of the present alloy and the Ge alloy system (X-Ge alloy) also have a eutectic temperature according to the purpose. More preferably, it has an equilibrium state containing excess Ge rather than a Ge-containing eutectic composition. The X-Ge alloy preferably has a Ge-containing eutectic temperature of 650 ° C. or higher, which is expected to have high efficiency in _{supercritical CO 2 utilizing solar heat, Stirling engine, and gas turbine power generation.} In order to further increase the power generation efficiency, the supercritical CO ₂ turbine preferably has a Ge-containing eutectic temperature of about 700 ° C. to 800 ° C. More preferably, from the viewpoint of higher thermal efficiency, it is preferable to have a Ge-containing eutectic temperature at about 800 to 900 ° C. for power generation by a Stirling engine and 850 to 1000 ° C. for gas turbine power generation.

Table 1 shows an X-Ge alloy-based heat storage material containing an Fe-Ge system, which is an example of the heat storage material according to the present invention, and an alloy element X other than Fe and Ge. The compounds equilibrated with the Ge phase shown in Table 1 represent Ge-containing intermetallic compounds, and the eutectic composition shows the Ge phase-containing eutectic composition. The eutectic temperature indicates the melting and solidification temperature of the Ge phase-containing eutectic composition.

In Example 1, in the Ge phase eutectic alloy having the composition of Ni-67 at% Ge in Table 1, the Ge phase and the NiGe phase (Ge-containing intermetallic compound) are in equilibrium in the solid phase state, and substantially the two phases are present. Is in a eutectic relationship (eutectic temperature: 762 ° C.). At the eutectic point at 762 ° C., a latent heat amount (30.5 kJ / mol) approximately corresponding to the weighted average of the solidification latent heat of Ni and Ge is released. For example, while the upper limit of the operating temperature of a heat storage material containing sodium nitrate or the like is 500 to 550 ° C and the latent heat of solidification is about 13.81 kJ / mol, the heat storage material capable of releasing a large latent heat in a higher temperature range. Functions as.

In Example 2, when an alloy having a composition richer in Ge than the above Ge-containing eutectic composition (for example, Ni-90 at% Ge) is used, the Ge phase and the NiGe phase (Ge-containing metal-to-metal compound) are used in the solid phase state. ) Is in equilibrium, and the two phases are substantially in a eutectic relationship (eutectic temperature: 762 ° C.), and it is known that an excess amount of Ge phase coexists from the Ge-containing eutectic composition. ing. In the alloy having the composition, the Ge-phase eutectic alloy melts and solidifies at the eutectic temperature of 762 ° C., and in addition to absorbing and releasing the latent heat of melting, an excess amount from the Ge-phase eutectic composition. The Ge phase of the Ge phase undergoes melting and solidification at 762-938 ° C., resulting in the absorption and release of the latent melting heat of the Ge phase. As a result, the alloy absorbs and releases latent heat of melting in a higher temperature range than the Ge-phase eutectic alloy.

In Example 3, for example, in the Ge phase-containing eutectic alloy having the composition of Co-73 at% Ge in Table 1, the Ge phase and the CoGe2 phase (Ge-containing intermetallic compound) are in equilibrium in a solid phase state, and substantially The two phases are in a eutectic relationship (eutectic temperature: 817 ° C.). At the eutectic point at 817 ° C., a latent heat amount (31.3 kJ / mol) approximately corresponding to the weighted average of the solidification latent heat of Co and Ge is released. For example, while the upper limit of the operating temperature of a heat storage material containing sodium nitrate or the like is 500 to 550 ° C and the latent heat of solidification is about 13.81 kJ / mol, the heat storage material capable of releasing a large latent heat in a higher temperature range. Functions as.

In Example 4, when an alloy having a composition richer in Ge than the Ge phase-containing eutectic composition (for example, Co-90 at% Ge) is used, the Ge phase and the CoGe2 phase (between Ge-containing metals) are used in a solid phase state. The compound) is in equilibrium, and in addition to the fact that the two phases are eutectic (eutectic temperature: 817 ° C.), an excess amount of Ge phase may coexist from the Ge phase-containing eutectic composition. Are known. In the alloy having the composition, the Ge phase eutectic alloy melts and solidifies at the eutectic temperature of 817 ° C., and in addition to absorbing and releasing the latent heat of melting, an excess amount from the Ge phase eutectic composition. The Ge phase of the Ge phase undergoes melting and solidification at 817-938 ° C., resulting in the absorption and release of the latent melting heat of the Ge phase. As a result, the alloy absorbs and releases latent heat of melting in a higher temperature range than the Ge-phase eutectic alloy.

As described above, the heat storage material according to the present invention is a heat storage material containing an alloy having a Ge phase as a matrix phase, and is particularly used as various means for using the heat stored in the heat storage material. It is a heat storage material containing an alloy formed by mixing various alloying elements with Ge in order to cause the release and absorption of latent heat of melting of the alloy in a suitable temperature range. Further, as the alloying element, a eutectic point is formed between the Ge phase and the alloy element so that the maximum melting temperature of the alloy can be lowered by mixing with Ge and latent heat can be absorbed and released at a constant temperature. Elements are preferably used. Alloy elements that satisfy this requirement can be identified by examining various equilibrium phase diagrams including Ge.

Further, for example, when the heat stored in the heat storage material according to the present invention is used to generate power by a gas turbine or the like, the thermal efficiency can be increased by using the heat at a higher temperature. An alloy element having a eutectic temperature of about 650 ° C. or higher of the alloy formed by mixing the alloy elements is preferably used.

As an element that produces a eutectic temperature of about 650 ° C. or higher in a two-component system with Ge, for example, K, Sc among the elements having atomic numbers 19 to 28 included in the fourth period of the periodic table , Ti, Cr, Mn, Fe, Co, Ni, Mg, Sr among alkaline earth metals, elements Rh, Pd with atomic numbers 45 and 46 included in the 5th period of the periodic table, Elements Hf, Pt and rare earth metals (La, Pr, Nd, Sm, Ho, Tm, Yb, Lu, etc.) having atomic numbers 72 and 78 included in the sixth period are known. Further, when the element is mixed with Ge, an intermetallic compound phase containing Ge that exists in equilibrium with the Ge phase is generated, and a eutectic point exists between the intermetallic compound phase and the Ge phase. It is known to do.

Table 1 summarizes the eutectic temperature, eutectic composition, etc. generated when each of the above elements is mixed with Ge. As shown in Table 1, it is known that when each of the above elements is added to Ge, an intermetallic compound that is in equilibrium with the Ge phase is generated, and a predetermined eutectic point is generated between the intermetallic compound phase and the Ge phase. An element that gives a eutectic temperature or the like suitable for a power generation means or the like for using the heat stored in the heat storage material can be appropriately selected and used. Further, it is also effective to adjust the temperature of the eutectic point according to the power generation means or the like using the eutectic temperature by utilizing the fact that the temperature of the eutectic point generally generated by using a plurality of kinds of alloying elements is lowered.

On the other hand, since the latent heat of solidification of Ge is about three times as high as that of the elements shown in Table 1, from the viewpoint of securing the amount of heat storage per unit amount of heat storage material, the amount of added element added is smaller. Elements that produce eutectic points are preferably used. Further, the alloy constituting the heat storage material according to the present invention does not necessarily have to have a eutectic composition, and as described above, the heat capacity per unit amount is particularly increased by making the composition richer in Ge than the eutectic composition. Can be increased.

Within the temperature range in which the heat storage material according to the present invention is used, high temperature reactivity (high temperature corrosion) with the heat storage container (crucible material) that physically adheres to the heat storage material and stores the heat storage material may become a problem. The alloying elements to be mixed with Ge can be determined for the purpose of avoiding high temperature reactivity in consideration of chemical properties such as reactivity with the crucible material.

Further, a plurality of types of alloying elements may be contained to the extent that the effects of the present invention are not impaired.
Further, in order to facilitate nucleation during solidification, it is also possible to mix and use a component that does not melt and remains in a solid phase in the temperature range in which the heat storage material according to the present invention is used.

That is, the heat storage material of the present invention is characterized by containing a Ge alloy.
As a result, it is possible to provide a heat storage material that can be used at a high temperature and has excellent heat storage and heat dissipation characteristics.

As an alloy element (a metal element other than Ge that constitutes a Ge alloy) that satisfies the above requirements, an eutectic point exists between the Ge phase and an intermetal compound that is in equilibrium with the Ge phase in the equilibrium state diagram between the alloy element and Ge. By using an alloy element in which the temperature of the eutectic point (eutectic temperature) is approximately 650 ° C. or higher and the atomic ratio of Ge at the eutectic point (eutectic composition) is 40 atomic% or more. It is possible to form a PCM corresponding to a desirable temperature range in _{supercritical CO 2 to be} used, a sterling engine, and a gas turbine power generation using a Ge phase having a large latent heat of melting as a parent phase.

Examples of the alloying element added to the Ge include elements having an atomic number of 20 to 28 included in the fourth period of the periodic table (Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni). , Mg, Ca, Sr, and rare earth metals (La, Nd, Sm, Tm, Lu, etc.) among the alkaline earth metals. Table 1 shows an intermetallic compound that balances with the Ge phase when each of the above elements is added to Ge, and the eutectic temperature and eutectic composition between the intermetallic compound and the Ge phase. As shown in Table 1, when the above elements are added to Ge, eutectic points can be generated in the range where the atomic ratio of Ge is 40 atomic% or more, and the eutectic temperature can be set to 650 ° C. or higher. ..

As the alloy element, two or more kinds of elements may be used in combination.

The composition of the Ge alloy may be such that a compound equilibrating with the Ge phase and the Ge phase coexist, and preferably, the Ge content is higher than the eutectic composition.

The alloying elements, composition can be determined from the above range so as to provide the preferred maximum melting temperature and minimum melting temperature for the individual application.

While general metal elements cause volume expansion when they melt, Ge causes volume reduction when they melt. Therefore, the addition of the alloying element is also preferable in terms of reducing the amount of change in volume during melting.
In the following description, in the heat storage material of the present invention, the case where the Ge alloy is a Fe-Ge alloy will be mainly described.

Such a heat storage material of the present invention is an alloy-based material and has a solid-phase-liquid phase phase change temperature in a higher temperature range than a conventional molten salt-based heat storage material, and has heat resistance. Are better.

Thereby, in the present invention, it can be used at a higher temperature than the conventional one, for example, 650 ° C. or higher, and the usable temperature range can be expanded.
Further, the heat storage material of the present invention has a large heat storage capacity.

Further, the heat storage material of the present invention has a very high thermal conductivity as compared with the conventional molten salt type heat storage material. As a result, the heat responsiveness is excellent, that is, heat storage and heat dissipation can be performed quickly.

Further, the conventional heat storage material has a problem of changing from a solid phase to a liquid phase, that is, having a large volume expansion rate at the time of melting, whereas the heat storage material of the present invention has a volume change due to a temperature change, particularly. , The volume expansion rate at the time of melting can be reduced.

From the above, it can be said that the heat storage material of the present invention can be used at a high temperature and has excellent heat storage and heat dissipation characteristics.

Further, in the heat storage material of the present invention, the melting point of the alloy can be adjusted by changing the composition ratio of each element constituting the alloy, for example, Fe and Ge, and the characteristics such as the heat storage capacity and the heat storage temperature can be adjusted. Can be made to. Thereby, it can be suitably applied to the heat storage material in various usage forms.

On the other hand, if the above conditions are not satisfied, the above excellent effect cannot be obtained.

For example, when the heat storage material is a metal material containing no alloying element (Fe) other than Ge, for example, Ge as a simple substance metal, there arises a problem that the melting temperature cannot be changed. Further, in the case of alloys other than those listed in Table 1 described above, there arises a problem that eutectic is not formed with Ge and a problem that the Ge content is small.

FIG. 1 is a state diagram (phase diagram) of a dual system of Fe-Ge at 1013 hPa (1 atm). The horizontal axis of the phase diagram shows the content of Ge and Fe (mass% and atomic%), and the vertical axis shows the temperature (° C.).

In the figure, "L" indicates a liquid phase in which Ge and Fe are melted, and the others indicate a solid phase. However, the region between the liquid phase line l and the eutectic isotherm e indicates a solid phase / liquid phase coexistence region in which the solid phase and the liquid phase coexist. Regarding the solid phase, "α1, α2 and αFe" indicate an α phase having a cubic structure, and in particular, αFe indicates a ferrite phase. “Β” indicates a β phase having a body-centered cubic structure. “ΓFe” represents an austenite phase having a face-centered cubic structure. “Ε” indicates the ε phase, which is the intermediate phase in the change from the γ phase to the α phase. “Η” indicates an η phase having low phase stability. Then, "Tc" indicates the transition temperature (Curie temperature) at which the ferromagnet changes to a paramagnetic material.

The heat storage material of the present invention may contain a Ge alloy, but the Ge alloy preferably contains a eutectic alloy. More preferably, a chemical composition having a two-layer coexistence region in which a eutectic alloy and a hypereutectic Ge coexist is more preferable.

As a result, in addition to the latent heat storage due to the chemical composition of the eutectic alloy, the latent heat of melting due to Ge having a hypereutectic composition can be utilized for the latent heat storage.

In the phase diagram shown in FIG. 1, it can be seen that the Ge alloy has a eutectic composition with a Ge ratio of 70 atomic%. Line A shows the composition ratio of Fe and Ge at the eutectic point (30 atomic% Fe-70 atomic% Ge).

In the state diagram shown in FIG. 1, when the eutectic alloy absorbs heat from the surroundings near the eutectic temperature of 838 ° C., the phase changes from the solid phase to the liquid phase and stores the heat as latent heat, in other words, heat is stored. When heat is released to the surroundings, the phase changes from the liquid phase to the solid phase to release latent heat, in other words, it can dissipate heat.

When the Fe-Ge alloy contains a eutectic alloy, the Fe-Ge alloy reversibly stores / dissipates latent heat according to the equilibrium phase diagram shown in FIG.
As a result, the heat storage material is thermodynamically stable and has particularly excellent cycle characteristics.

The Ge alloy is preferably a hypereutectic Ge alloy containing an excess of Ge in addition to the eutectic alloy.

In the phase diagram shown in FIG. 1, when the proportion of Ge exceeds 70 atomic%, the Fe-Ge alloy becomes a hypereutectic Fe-Ge alloy containing excess Ge in addition to the eutectic alloy. The hypereutectic alloy is a mixture of the eutectic alloy (FeGe ₂ ) and excess Ge. Line B shows the composition ratio (23 atomic% Fe-87 atomic% Ge) of an example of a hypereutectic alloy.

In the state diagram shown in FIG. 1, the temperature indicated by the intersection of the line B and the liquidus line, that is, the temperature at which the metal Ge (excess Ge that does not form the eutectic alloy) solidifies when the liquid hypereutectic alloy is cooled. Is about 838 ° C to about 895 ° C, and in this temperature range, the ambient heat can be stored as latent heat by the solid-liquid phase change of the eutectic alloy, and the stored heat can be released as latent heat, and the metal can be released. The solid-liquid phase change of Ge (excessive Ge that does not form a eutectic alloy) can store ambient heat as latent heat and release the stored heat as latent heat.

By adjusting the Fe-Ge alloy to a hypereutectic composition in this way, it is possible to have a range in the phase change temperature at which the solid component and the liquid component coexist when the Fe-Ge alloy is heated or cooled. It becomes.

In the case of a hypereutectic Fe-Ge alloy, as shown in Examples described later, the temperature profile or dT / dt profile of the Fe-Ge alloy (see FIGS. 7, 10, 11) and the DSC curve (FIG. 8). (See), two peaks appear, one due to the phase change of the eutectic alloy and the other due to the excessive Ge phase change.

The proportion of Ge in the Ge alloy (particularly, Fe-Ge alloy) is preferably 70 atomic% or more and 99 atomic% or less, more preferably 75 atomic% or more and 98 atomic% or less, and 80 atomic% or more and 97. It is more preferably atomic% or less.

As a result, the thermal conductivity of the heat storage material can be effectively increased, and the thermal responsiveness can be made more excellent. In addition, the volume change at the time of melting can be suppressed more effectively.

The Fe-Ge alloy constituting the heat storage material of the present invention may contain elements other than Fe and Ge. Hereinafter, such an element is also referred to as "other elements".

The content of other elements in the Fe—Ge alloy is preferably less than 1.0% by mass, more preferably less than 0.5% by mass. However, when the Fe-Ge alloy contains a plurality of kinds of elements as other elements, it is preferable that the sum of the contents of the plurality of elements satisfies the above conditions.

The latent heat storage capacity of the Fe-Ge alloy at 1013 hPa (1 atm) ^{is preferably 1.28 GJ / m 3} or more, which is the heat storage capacity of _{Na 2} CO ₃ which is a typical carbonate-based molten salt, and Cu-Si. It is more preferable that the heat storage capacity of the alloy is 2.67 GJ / m ^{3 or more.}

As the value of the latent heat storage capacity of the Fe-Ge alloy described above, the measurement method and the measurement value at the time of heat storage (heat storage mode) under the measurement conditions can be adopted.

The Fe-Ge alloy is preferably used in a temperature range of 650 ° C. or higher, more preferably used in a temperature range of 700 ° C. or higher, and a temperature range of 800 ° C. or higher and 1000 ° C. or lower. It is more preferable that it is used in.

Since the Fe-Ge alloy has high heat resistance, it can be suitably used even in the high temperature range as described above. Further, as described above, the Fe-Ge alloy has a high phase change temperature and can be suitably used even in the above-mentioned high temperature range. Then, for example, by using the heat storage material from a low temperature region such as around room temperature to a high temperature region as described above, the amount of heat storage per unit volume of the heat storage material can be further increased, and the effect of the present invention is further exhibited. Can be made to.

The heat storage material of the present invention may contain the above-mentioned Fe-Ge alloy (alloy for heat storage material), but in addition to the Fe-Ge alloy, components other than the Fe-Ge alloy (hereinafter, "others"). It may also contain "components of").

Examples of other components include alloys other than the Fe-Ge alloy shown in Table 1 above, alumina, quartz, silica, SiC, and the like.

The content of other components in the heat storage material of the present invention is preferably 30% by mass or less, more preferably 20% by mass or less, and further preferably 10% by mass or less.

The Fe-Ge alloy is less likely to cause loss due to evaporation or the like even when the temperature is relatively high.
The heat storage material of the present invention, an inert gas (e.g., Ar, _{N 2,} etc.) under a stream of the mass change ratio when the heat storage / heat radiation was performed 360 cycles from 25 ° C. (room temperature) to 1000 ° C., less than 5% It is preferably present, and more preferably less than 3%.

As a result, the cycle characteristics and long-term reliability of the heat storage material are particularly excellent. Therefore, for example, even when the heat storage material of the present invention is applied to a heat storage power generation or the like that repeatedly stores and dissipates heat, stable operation can be guaranteed for a long period of time.

The heat storage material of the present invention is preferably used in a temperature range of 650 ° C. or higher, more preferably used in a temperature range of 700 ° C. or higher, and is used in a temperature range of 800 ° C. or higher. It is more preferable that the temperature is increased.

Since the heat storage material of the present invention has high heat resistance, it can be suitably used even in the high temperature region as described above. Further, as described above, the Fe-Ge alloy constituting the heat storage material of the present invention has a high phase change temperature, and the heat storage material of the present invention can be suitably used even in the high temperature region as described above. Then, for example, by using the heat storage material from a low temperature region such as around room temperature to a high temperature region as described above, the amount of heat storage per unit volume of the heat storage material can be further increased, and the effect of the present invention is further exhibited. Can be made to.

[2] Usage pattern of heat storage material Next, a usage pattern of the heat storage material of the present invention will be described.

In the latent heat storage type heat storage material, since it melts during heat storage, it may be used by filling it in a capsule in order to prevent leakage of the liquid heat storage material.

When a conventional heat storage material is filled in a capsule and used, there is a problem that the capsule cannot follow the volume change of the heat storage material and is damaged because the volume change rate at the time of phase change is large. Therefore, a gap for stress relaxation due to volume expansion during melting is required, and the heat storage material cannot be sufficiently filled in the capsule. Therefore, the heat storage capacity is lowered and the thermal resistance is increased. Alternatively, the volume change was absorbed by making a hole in the capsule. As described above, when the conventional heat storage material is used, the capsule cannot be sealed, so that there is a problem of evaporation or leakage of the filled heat storage material.

On the other hand, in the heat storage material of the present invention, since the volume change rate at the time of phase change is small, it is possible to seal the capsule without making a hole in the capsule. As a result, it is possible to more effectively prevent the occurrence of problems such as evaporation and leakage of the heat storage material, and it is possible to make the cycle characteristics and long-term reliability particularly excellent. Further, since the heat storage material can be filled without providing a gap in the capsule, it is possible to increase the heat storage density and make the heat storage container compact. In addition, the thermal resistance is reduced, and the heat exchange efficiency can be further improved.

FIG. 2 is a diagram showing an example of a usage pattern of the heat storage material of the present invention. More specifically, it is a figure which shows an example of the structure which holds the heat storage material of this invention in a capsule and uses it as a heat storage capsule. FIG. 2A is an exploded perspective view of the heat storage capsule, and FIG. 2B is a cross-sectional view of the heat storage capsule.

The heat storage capsule 1 includes a heat storage material 2 of the present invention and a capsule 3 that houses the heat storage material 2.

The capsule 3 has, for example, a hollow substantially spherical shape whose inner diameter is substantially the same as the outer diameter of the heat storage material 2, and includes a first semifield 3a and a second semifield 3b. The first half body 3a and the second half body 3b are shaped like a hollow capsule 3 cut in half, and male threads 4a and female threads 4b are formed on the annular edges, respectively, and are screwed together. When the inner diameter of the capsule 3 is formed to be larger than that of the heat storage material 2, a gap is generated between the capsule 3 and the heat storage material 2, but oxidation of the heat storage material 2 is prevented or excessive due to a temperature change. It is preferable that this void is evacuated in order to suppress the increase in volume.

In the illustrated configuration, one heat storage material 2 is housed in the hollow portion of the capsule 3, but for example, a plurality of heat storage materials 2 are housed in the hollow part of one capsule 3. May be good. For example, a powdery heat storage material may be used.

The size and shape of the heat storage material 2 and the capsule 3 are not particularly limited and may be appropriately selected depending on the intended use, but are preferably spherical. As a result, the thermal conductivity of the heat storage capsule 1 is not anisotropic, and it can be suitably applied to various heat storage devices.

As the constituent material of the capsule 3, for example, various ceramics can be preferably used.

Further, since the Fe-Ge alloy hardly reacts with the carbon-based material even if the heat storage and heat dissipation are repeated, a material containing carbon can be preferably used as the material of the capsule 3. Further, the material containing carbon can also be used as a passivation layer (liner material) of a heat storage material accommodating body (a housing such as a capsule or a storage tank) made of stainless steel or the like.

The material containing such carbon is not particularly limited, and examples thereof include carbon-based materials such as graphite (graphite carbon). Examples of the material containing carbon include carbon-based ceramic materials and alloy materials containing carbon atoms.

Further, the heat storage material of the present invention is not limited to the case where it is used by filling it in a capsule as described above. Further, the shape of the heat storage material and the housing is not limited, and any shape can be adopted depending on the applicable equipment.

FIG. 3 is a diagram showing another example of the usage mode of the heat storage material of the present invention. More specifically, it is a perspective view which showed an example of the heat storage body 10 provided with the heat storage material of this invention.

The heat storage body 10 includes a substantially cylindrical housing body 11 and a heat storage material 12 of the present invention housed in the housing body 11.

The accommodating body 11 has an outer cylinder 11a and a thin tube 11b coaxially arranged along the center line (central axis) of the outer cylinder 11a. A plurality of plate members 11c are provided on the outer peripheral surface of the thin tube 11b so as to extend radially outward in the radial direction, and are connected to the outer cylinder 11a. The plurality of plate materials 11c are arranged at equal intervals in the circumferential direction, and the axial cross section of the space surrounded by the thin tube 11b, the outer cylinder 11a, and the plate material 11c has a substantially fan shape. The heat storage material 12 of the present invention has a long shape having a substantially fan-shaped cross section, and is inserted into each of the above spaces.

As shown in FIG. 3, a plurality of heat storage bodies 10 configured in this way can be bundled and applied to a power generation system using waste heat, which is heat energy from the outside.

Since the heat storage material 12 has high heat conductivity and high heat storage capacity, waste heat is efficiently transferred from the outer cylinder 11a to the heat storage body 10 and conducted to water or high temperature gas flowing through the thin tube 11b. The heated steam or high-pressure high-temperature gas heated by the waste heat is used for power generation by being discharged from the other end of the thin tube to the turbine of the power generation unit, for example.

As described above, the heat storage material of the present invention can store / dissipate heat at a higher temperature than the conventional one by containing the Fe-Ge alloy. Further, for example, since the thermal conductivity is higher than that of molten salt or the like, efficient heat transport, heat exchange, etc. are possible. From these things, it is possible to have a high heat storage density and a high heat storage capacity. In addition, the amount of heat supplied and the amount of heat absorbed at the phase change temperature can be increased. Furthermore, since it basically only repeats the phase change of the substance, it can be used stably and repeatedly many times and is excellent in terms of durability.

Therefore, the heat storage material of the present invention can be suitably used in, for example, solar thermal power generation, waste heat utilization, and other energy fields.

For example, heat storage power generation is stable for 24 hours by converting renewable energy that fluctuates over time such as solar cells and solar heat into heat and storing it at low cost, and converting heat into electric power and leveling it as needed. It is a power generation method that can be used.

Further, examples of the use of waste heat include power generation using high-temperature factory waste heat. By effectively utilizing the waste heat from the factory, _{it is possible to effectively reduce the amount of CO 2} emitted from the factory, and it is also very effective from the viewpoint of energy saving.

In addition, other energy fields include, for example, a method of producing hydrogen by hydrothermal decomposition using heat obtained by condensing sunlight, reforming methane, gasifying biomass, and the like.

[3] Heat storage power generation device Next, the heat storage power generation device of the present invention will be described.
The heat storage power generation device of the present invention includes the heat storage material of the present invention as described above.

The heat storage power generation device converts non-stationary power such as a solar cell, inexpensive surplus power at midnight, etc. into heat to store heat, and converts the heat into electricity when necessary to generate electricity.

Further, the heat storage power generation device generates solar heat, that is, heat obtained by condensing sunlight, exhaust heat of a heat source such as a fuel cell, heat generated by combustion of industrial waste in a factory, etc., a boiler, etc. Heat, factory exhaust heat such as boiler and engine exhaust gas, or heat such as intermittently generated heat may be stored and generated.

By providing the heat storage material of the present invention in such a heat storage power generation device, it is possible to operate at a higher temperature, store more heat, and improve the power generation efficiency. Can be done.

The heat storage power generation device is preferably a so-called solar thermal power generation device that stores heat obtained by condensing sunlight.

As a result, it is possible to obtain the effect that a large temperature change can be mitigated by the heat release from the heat storage even when the clouds pass or the weather is suddenly bad. Further, in the nighttime when there is no solar radiation, the heat stored in the daytime can be continuously generated by releasing the heat from the heat storage device, and the power generation for 24 hours can be realized.

[3-1] Solar Thermal Power Generation Device The solar thermal power generation device provided with the heat storage material of the present invention will be described below.

Examples of the solar thermal power generation device include a parabolic dish type, a solar tower type, a parabolic trough type, a Frenel type, a beam down type, and the like, depending on the difference in the sunlight condensing method.
In the following description, a solar tower type solar thermal power generation device will be described as an example.

FIG. 4 is a schematic view showing an example of a solar thermal power generation device. FIG. 4A is a diagram schematically showing the overall configuration of the solar thermal power generation device, and FIG. 4B is a diagram showing an example of a heat storage device included in the solar thermal power generation device.

The solar thermal power generation device 200 includes a mirror 20, a solar heat storage device 100, and a generator 30. The energy conversion unit E that mediates between the solar heat storage device 100 and the generator 30 is composed of a heat exchanger.

The mirror 20 is composed of, for example, a reflecting mirror such as a heliostat, and plays a role of reflecting sunlight from the sun S and guiding it to a heat receiving portion 110 of the solar heat storage device 100. For example, a large number of mirrors 20 are arranged radially around the heat receiving portion 110. Further, a control device (not shown) sets the orientation of each mirror 20 to an optimum position according to the position of the sun S with the passage of time.

The solar heat storage device 100 includes a heat receiving unit 110 that absorbs the solar heat of sunlight guided by the mirror 20, a heat storage unit 120 that can store and release the heat of the heat medium, and an energy conversion unit E. Further, the solar heat storage device 100 includes a flow path pipe 130 that connects the heat receiving unit 110, the heat storage device 120, and the energy conversion unit E, and is a heat medium pipe through which the heat medium flows.

The heat receiving unit 110 is also called a receiver, and is composed of, for example, a ceramic structure that can withstand high temperatures while absorbing the solar heat of sunlight. The heat receiving unit 110 is provided on the top of a tall building such as a tower, and absorbs the solar heat of sunlight guided by the mirror 20. The heat receiving unit 110 is connected to the flow path pipe 130, and heat exchange is performed by heating the heat medium flowing through the flow path pipe 130. The arrangement position, type, etc. of the heat receiving unit 110 are not particularly limited.

The heat storage device 120 can store and release the heat of the heat medium flowing through the flow path pipe 130, and the details thereof will be described later. The energy conversion unit E is composed of a heat exchanger that exchanges heat (energy exchange) between the solar heat storage device 100 and the generator 30.

The flow path pipe 130 connects the heat receiving unit 110, the heat storage unit 120, and the energy conversion unit E to form a closed flow path. The heat medium circulates in the flow path pipe 130 along the path of the heat receiving unit 110 → the heat storage device 120 → the energy conversion unit E → the heat receiving unit 110. As the heat medium flowing through the flow path pipe 130, various ones such as air, water, oil, and molten salt are used.

The generator 30 is composed of, for example, a steam gas turbine generator or the like, heat is exchanged with the solar heat storage device 100 via an energy converter (heat exchanger) E, and is built in by a heated heat medium. The turbine is rotated to generate electricity. The type of the generator 30 is not particularly limited, and various types of generators capable of exchanging heat with the solar heat storage device 100 can be applied.

The solar heat storage device 100 includes a heat storage device 120 capable of appropriately storing the heat of the heat medium flowing through the flow path pipe 130, and absorbs output fluctuations due to fluctuations in the solar heat (sunlight) obtained from the sun S. Can be done. That is, even if the amount of solar heat (amount of sunshine) obtained from the sun S fluctuates due to a sudden change in weather, the output fluctuation can be suppressed by the action of the heat storage device 120.

As shown in FIG. 4B, the heat storage device 120 is provided between the heat receiving unit 110 and the energy conversion unit E in the flow path (flow path pipe 130) of the heat storage material 123. The heat storage device 120 includes a housing 121, a heat storage material 123 of the present invention sealed inside the housing 121, and a transfer device 124 for transferring the heat storage material 123 between the inside and the outside of the housing 121. There is.

The housing 121 is made of, for example, a material such as ceramics, metal, or concrete. Further, in the illustrated configuration, the housing 121 has a box shape, but the shape of the housing 121 is not particularly limited.

The heat storage material 123 is enclosed in the internal space of the housing 121. As the heat storage material 123, the heat storage material of the present invention is used. The heat storage material may be used, for example, in a state of being contained in the capsule 3 as described above, or may be used in a state of not being contained in the capsule 3.

The transfer device 124 includes a pump 125 for circulating the heat storage material 123 having fluidity between the inside and the outside of the housing 121, a reserve tank 126 capable of storing the liquefied heat storage material 123, and the housing 121 and the pump. Includes a pipe 127 connecting the 125 and the reserve tank 126. According to this configuration, the transfer device 124 can be constructed easily and inexpensively. The transfer device 124 makes it possible to easily circulate the liquefied heat storage material 123 between the inside and the outside of the housing 121. Here, "having fluidity" means, for example, when the heat storage material 123 is in a liquefied state or in a powder state, or when the heat storage capsule 1 in which the heat storage material 123 is housed in the capsule 3 is used. Includes a state in which the heat storage capsule 1 has fluidity even if the heat storage material 123 itself does not have fluidity.

Further, the control device 128 that controls the operation of the heat storage device 120 controls the operating state of the pump 125 of the transfer device 124. The control device 128 is a computer including a processor, a memory, and the like. Then, the control device 128 is connected to the temperature sensor S1 provided in the heat storage material 123, receives the temperature signal of the heat storage material 123 from the temperature sensor S1, and transmits the control signal based on the temperature signal to the pump 125. Feed and control the operation of the pump 125.

As shown in FIG. 4B, the flow path pipe 130 penetrates the space inside the heat storage device 120, and the flow path pipe 130 is composed of three sub-pipes 130a, 130b, and 130c. .. In order to increase the contact area of the heat storage material 123 with respect to the flow path pipe 130, the flow path pipe 130 is divided into a plurality (three) in the peripheral region of the heat storage device 120 including the inside of the heat storage device 120. However, the number of sub-pipes is not particularly limited. Further, in FIG. 4B, as an example of the arrangement position of the sub-pipes, all the sub-pipes are arranged in the upper part of the housing 121, but the position of the sub-pipes is not particularly limited.

In such a solar thermal power generation device, by using the heat storage material of the present invention as the heat storage material 123, it can be operated at a higher temperature than the conventional one, for example, 650 ° C. or higher, so that it is possible to generate steam at a higher temperature. As a result, the power generation efficiency can be improved.

Further, since the heat storage material of the present invention has a high heat storage capacity and heat storage density, it is possible to realize a small heat storage system and contribute to cost reduction of the solar thermal power generation device.

Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto.

For example, the heat storage power generation device of the present invention may be any one provided with the heat storage material of the present invention, and is not limited to the solar thermal power generation device as described above.

The present invention will be described in more detail with reference to specific examples below, but the present invention is not limited to these examples.
In the following description, the treatments and measurements that do not particularly indicate the temperature conditions were performed at room temperature (25 ° C.). Further, in the following description, the treatments and measurements that do not particularly indicate the pressure conditions were performed at 1013 hPa (1 atm).

[4] Production of heat storage material (Example 1)
Using high-purity Fe powder and Ge powder manufactured by High-Purity Chemical Laboratory Co., Ltd. as raw materials, an Fe-Ge alloy was produced as follows.

First, Fe powder: 30 atomic% and Ge powder: 70 atomic% were weighed and placed in an alumina boat and mixed.

Next, the alumina boat containing the mixed powder was heated in vacuum at 1400 ° C. for 2 hours to melt the mixed powder and form an ingot of Fe-Ge alloy.

Then, the ingot was cut into pellets and chemically washed to remove impurities and the like on the surface. As a result, an Fe-Ge alloy containing 30 atomic% of Fe and 70 atomic% of Ge (hereinafter, also referred to as FeGe70 alloy) was obtained.
In this example, the Fe-Ge alloy thus obtained was used as a heat storage material.

(Example 2)
A heat storage material was produced in the same manner as in Example 1 except that the weighed amount of the raw material powder was Fe powder: 23 atomic% and Ge powder: 87 atomic%. The heat storage material obtained in this example was a Fe-Ge alloy containing Fe in 23 atomic% and Ge in 87 atomic% (hereinafter, also referred to as FeGe87 alloy).

(Comparative Example 1)
A Cu—Si alloy ingot containing 80 parts by mass of Cu and 20 parts by mass of Si was prepared and purchased from Furuya Metal.

This ingot was cut into pellets and chemically washed to remove impurities and the like on the surface. As a result, a Cu—Si alloy containing 80% by mass of Cu and 20% by mass of Si was obtained.
In this comparative example, the Cu—Si alloy thus obtained was used as a heat storage material.

(Comparative Example 2)
In this comparative example, Li ₂ CO ₃ was used as the heat storage material. For Li ₂ CO ₃ , the thermodynamic data of the thermodynamic database FactSage was referred to.

(Comparative Example 3)
In this comparative example, K ₂ CO ₃ was used as the heat storage material. For K ₂ CO ₃ , the thermodynamic data of the thermodynamic database FactSage was referred to.

(Comparative Example 4)
In this comparative example, Na ₂ CO ₃ was used as the heat storage material. For Na ₂ CO ₃ , the thermodynamic data of the thermodynamic database FactSage was referred to.

[5] Identification of solid phase The solid phase of the heat storage material of each of the above examples was identified.
The solid phase was identified by an X-ray diffractometer (XRD: D2Phaser, Burker) at room temperature using CuKα radiation (λ = 0.15418 nm) (30 kV-10 mA).

Diffraction data were collected over an angle range of 10 ° <2θ <80 ° with a step size of 0.02 ° and a step interval of 1 second.

The crystal phase was identified by comparing the peak positions using ICSD (Inorganic Crystal Structure Database) and COD (Crystallography Open Database) as standard reference patterns.

The lattice constants of the precision structure of the solid phase were evaluated by Rietveld analysis of the structural model using the while pattern identification method of the FullProf package.

FIG. 5 shows the XRD patterns of (a) Example 1 (FeGe70 alloy) and (b) Example 2 (FeGe87 alloy). In FIG. 5, the vertical line shown below the XRD pattern indicates the peak position of the Fe—Ge alloy.

In the XRD pattern, a series of peaks corresponding to the Ge solid solution phase were clearly observed in both Example 1 and Example 2. Furthermore, _{a series of very strong peaks corresponding to the FeGe 2} phase (intermetallic compound defined by the integrated atomic ratio of the constituent elements) was observed. No other peaks were observed in the XRD pattern.

All diffraction peaks assigned as the Ge solid solution phase and the FeGe ₂ phase were indexed and the lattice constants of the solid phase were determined by the Rietveld method of the structural model. The results are shown in Table 2.

All peaks assigned as the Ge solid solution phase are indexed as a cubic unit cell (space group Pm-3m (227)), and _{peaks assigned as the FeGe 2} phase are tetragonal unit cells (space group I4 /). It was indexed as mcm (140)).

The lattice constant of the Ge solid solution phase is very high as the lattice constant (a = 5.657 (3) Å) described in "Wyckoff RWG. Second Edition. Interscience Publishers, New York, Crystal Structures 1963; 1: 7-83." It matched well with. Since the FeGe ₂ phase is a compound on the stoichiometric line, its lattice constant was specified by the heat storage material (Fe-Ge alloy) of each of the above examples.

These results mean that the Fe-Ge alloy was successfully produced without impurities and thermodynamically unstable phases according to the phase diagram of the Fe-Ge alloy shown in FIG.
In particular, the heat storage material of Example 1 _{contains a eutectic alloy (FeGe 2} ), and the heat storage material of Example 2 is a hypereutectic alloy composed of a mixture of a eutectic alloy and an excess Ge (Ge main phase). rice field.

[6] Characteristic evaluation The heat storage and heat dissipation characteristics of the heat storage materials obtained in each of the above Examples and Comparative Examples were evaluated.

[6-1] The storage material of Evaluation of the embodiments of the heat storage heat dissipation characteristics, as follows, under N _2, was evaluated heat storage and heat radiation characteristics.

FIG. 6 is a diagram showing a configuration of an apparatus used for evaluating the heat storage and heat dissipation characteristics, and FIG. 6A is a diagram schematically showing an overall configuration of the apparatus used for the evaluation, FIG. 6B. Is a figure showing a state in which a heat storage material is filled in a PCM container arranged in a test container of the apparatus used for evaluating the heat storage and heat dissipation characteristics.
The test container was made of stainless steel (SUS310S) and had a length (height) of 200 mm, an inner diameter of 93.6 mm, and an outer diameter of 101.6 mm.

The PCM container arranged in the test container and filled with the heat storage material was a crucible composed of graphite (graphite carbon), and had a length (height) of 35 mm, an inner diameter of 30 mm, and a thickness of 10 mm. ..

The heat storage materials of each of the Examples and Comparative Examples were filled in different PCM containers. The mass of the heat storage material filled in the PCM container was 28.0 g in Example 1, 23.0 g in Example 2, and 61.5 g in Comparative Example 1.

In the heat storage mode, the heating temperature is raised at a rate of 4 ° C./min to 6 ° C./min depending on the composition of the heat storage material, and after reaching a temperature equal to or higher than the liquidus temperature, the temperature is maintained for 2 hours. Heated.
Then, in the heat dissipation mode, the mixture was cooled at a rate of -4 ° C./min to −10 ° C./min depending on the composition of the heat storage material.

The heat storage and heat dissipation characteristics during heating and cooling were evaluated from the time derivative (dT / dt) of the heat storage material temperature T with respect to the time t during heating and cooling.

The heat storage material temperature T was measured by directly filling the graphite crucible inside the test vessel with the heat storage material and using a type K thermocouple (temperature resolution ± 0.0075 × | t | ° C.).

Hereinafter, the results of the heat storage mode shown in FIG. 7A will be described in detail.
For the heat storage material of Example 1, the temperature profile rose smoothly with almost no unevenness up to around 838 ° C, but one small plateau (stagnation region) was found in the range from around 838 ° C to around 950 ° C. It was observed. On the other hand, the dT / dt profile showed an almost constant value up to around 838 ° C, but decreased around 838 ° C and then rapidly increased around 895 ° C. It is considered that this is because the eutectic mixture started to melt at around 838 ° C, the melting of the eutectic mixture was completed at around 895 ° C, and the absorption as latent heat was completed.

On the other hand, with respect to the heat storage material of Example 2, the temperature profile showed the same behavior as that of Example 1 from around 650 ° C to around 838 ° C. In the range from around 838 ° C to around 950 ° C, one small plateau was observed in Example 1, whereas two small plateaus were observed in Example 2. The dT / dt profile also showed almost the same behavior as in Example 1 at a temperature lower than 895 ° C, but slightly increased at around 895 ° C and then decreased sharply. It is considered that this is because the Ge main solid phase began to melt rapidly around 895 ° C. and was absorbed as latent heat. Then, after the completion of melting of the Ge main solid phase, the dT / dt profile is increased. From this, it is considered that in Example 2, the heat supplied to the heat storage material was stored as sensible heat due to the temperature rise of the liquid phase of the eutectic mixture and latent heat due to melting of the Ge main solid phase.
The sensible heat and latent heat in the liquid phase / solid phase coexistence region continued from around 838 ° C to around 895 ° C, which is the liquidus temperature.

From the behavior of the dT / dt profile in the heat storage mode, it was confirmed that the sensible heat and latent heat of the eutectic mixture and the hypereutectic mixture have good followability to the phase diagram shown in FIG. rice field.

Further, as for the heat dissipation mode shown in FIG. 7B, the results corresponding to the state diagram of FIG. 1 were obtained as in the above heat storage mode.

In particular, since the Fe-Ge alloy constituting the heat storage material of the present invention has a phase change temperature at a high temperature, it can be suitably used as a heat storage material at a temperature higher than the conventional one, for example, 650 ° C. or higher. I can say.

Further, since the Fe-Ge alloy contains a eutectic alloy, the Fe-Ge alloy becomes thermodynamically stable, and for example, latent heat can be reversibly stored / dissipated according to the phase diagram shown in FIG. confirmed.

Further, since the Fe—Ge alloy is a hypereutectic alloy, it is possible to have a range in the phase change temperature.

In addition, similar results were confirmed for Examples other than Examples 1 and 2.

[6-2] Evaluation of Latent Heat Storage Capacity The latent heat storage capacity was evaluated for the heat storage materials of each of the above-mentioned Examples and Comparative Examples.
The latent heat storage capacity was evaluated using a differential scanning calorimetry device (DSC: NETZSCH DSC 404 F3 Pegasus, temperature resolution ± 0.0025 × | t | ° C.) under the condition of Ar flow rate: 20 ml / min. Further, in the heat storage mode, the heating temperature was raised at a rate of 20 ° C./min, and in the heat dissipation mode, the temperature was cooled at a rate of −10 ° C./min.

The latent heat capacity in the heat storage mode and the heat dissipation mode was calculated from the peak area of the DSC curve.

For each of the above examples, the latent heat storage capacity derived from the eutectic alloy and the latent heat storage capacity derived from the Ge main solid phase in the solid phase / liquid phase coexistence region were obtained, and the sum of these was taken as the total capacity. ..

FIG. 8 shows DSC curves for (a) the heat storage material of Example 1 and (b) the heat storage material of Example 2 in the heat storage mode and the heat dissipation mode.

As shown in FIG. 8A, in Example 1, two peaks were observed in the heat storage mode, a small peak from around 780 ° C to around 794 ° C and a large peak from around 841 ° C to around 898 ° C. rice field. Similarly, in the heat dissipation mode, two peaks were observed, a small peak near 794 ° C and a large peak near 780 ° C to 761 ° C. These peaks were reproducibly observed on the DSC curve. The large peaks corresponded to the melting of the eutectic mixture containing the Ge solid solution phase and the FeGe _{2 solid phase.} On the other hand, the small peak did not correspond to any phase change or magnetic transition in the state diagram shown in FIG. Therefore, this small peak may be associated with an unknown phase change in _{the FeGe 2 solid phase.} As described above, the DSC results for Example 1 indicate that the melting of the eutectic mixture proceeded in accordance with the phase diagram in the heat storage mode. The melting start temperature (around 841 ° C.) of the eutectic mixture was substantially the same as the liquidus temperature (838 ° C.) in the state diagram shown in FIG. On the other hand, in the heat dissipation mode, the solidification start temperature (around 794 ° C.) of the liquid phase was about 45 ° C. lower than the temperature shown in the state diagram of FIG. Further, this result was almost the same as the result of the heat storage heat dissipation test shown in FIG. 7 (b). Therefore, if the heat storage / heat dissipation rate is further reduced, the melting / solidification temperature is considered to approach the eutectic temperature in the phase diagram.

As shown in FIG. 8B, in Example 2, two large peaks were observed in the range from around 838 ° C to around 940 ° C in the heat storage mode. It is considered that the peak around 838 ° C corresponds to the melting of the eutectic mixture and the peak around 920 ° C corresponds to the melting of the Ge main solid phase. In the DSC curve, the starting temperature of melting of the Ge main solid phase was not clear because the two peaks overlapped. In the heat storage mode, the melting of the Ge main solid phase continued above the liquidus temperature of 895 ° C. to around 940 ° C. In the heat dissipation mode, solidification of the Ge main solid phase from the liquid phase started at about 900 ° C., and then shifted to solidification of the eutectic mixture at about 813 ° C. From these results, it can be seen that the latent heat of the Ge main solid phase and the eutectic mixture is stored or dissipated at the liquidus temperature and the eutectic temperature.

For the heat storage materials of each of the Examples and Comparative Examples, the latent heat storage capacities in the heat storage mode and the heat dissipation mode were determined, respectively.

In the DSC curve, since the two peaks overlapped in the heat storage mode or the heat dissipation mode, the latent heat storage capacity was calculated from the total capacity per volume of the Fe-Ge alloy. The results are shown in Table 3.

As is clear from Table 3, the heat storage material of the present invention has a large latent heat storage capacity.

[6-3] Evaluation of Temperature Dependence of Latent Heat Storage Capacity For the heat storage materials of the above Examples and Comparative Examples, the temperature dependence of the latent heat storage capacity and the specific heat capacity Cp in the temperature range of 200 ° C. to 837 ° C. Was measured.
Furthermore, the temperature dependence of the latent heat storage capacity was estimated using the Cp value of the heat storage material measured by DSC.

The heating / cooling conditions for DSC measurement are shown below.
(1) Heating was performed from room temperature to 150 ° C. at a heating rate of 20 ° C./min.
(2) It was held at 150 ° C. for 20 minutes.
(3) The temperature was raised to a maximum of 1000 ° C. at a heating rate of 20 ° C./min.
(4) It was held at 1000 ° C. for 20 minutes.
(5) The temperature was cooled from 1000 ° C. to 400 ° C. at a temperature lowering rate of 10 ° C./min.
The above heating / cooling cycle was repeated 3 times under an Ar flow at a flow rate of 100 mL / min.

FIG. 9 shows the specific heat capacity of the heat storage material and the heat storage capacity per volume. FIG. 9A is a diagram showing (a) specific heat capacity Cp calculated from the following approximate formula for the heat storage materials of Examples 1 and 2, and FIG. 9B is a diagram showing the heat storage of Examples 1 and 2. It is a figure which shows the heat storage capacity per volume of a material, and FIG. 9C is a figure which shows the heat storage capacity per volume of Comparative Examples 1 to 4.

In addition, in FIGS. 9 (b) and 9 (c), the heat storage capacity is shown with 500 ° C. as a reference temperature. In addition, FIG. 9B also shows the molten salts NaCl, KCl, and LiCl estimated by theoretical thermodynamic calculation for comparison.

The approximate expression was estimated from the quadratic fitting of the measured Cp value. ^{The coefficient of determination was R 2} = 0.968 for the heat storage material of Example 1 ^{and R 2} = 0.995 for the heat storage material of Example 2. The heat dissipation capacity of the liquid phase was determined using the Cp value measured in the liquid phase.

The latent heat storage capacity and heat dissipation capacity of the molten salts NaCl, KCl, and LiCl were theoretically calculated using a thermodynamic equilibrium software program (FactSage ver 6.4).

In Examples 1 and 2, the magnitude of the discontinuous change corresponds to the amount of latent heat radiated / stored at 838 ° C. of each Fe-Ge alloy, and the latent heat storage capacity of each melts. It was bigger than salt.

Further, in the range from about 838 ° C. to about 895 ° C., the heat storage capacity of the heat storage material of Example 2 was enhanced by the heat radiation from the Ge main phase in addition to the heat radiation from the eutectic mixture. When the liquidus temperature (895 ° C.) in the state diagram shown in FIG. 1 was exceeded, heat dissipation from the liquid phase contributed to an increase in the heat storage capacity of the Fe—Ge alloy.

As described above, it was confirmed that in the Fe-Ge alloy, the total heat storage capacity and the temperature range of the latent heat related to the Ge main phase can be suitably adjusted by changing the chemical composition.

[6-4] Evaluation of Heat Storage and Heat Dissipation Cycle Characteristics Regarding the heat storage materials of each of the above Examples and Comparative Examples, the reproducibility of the heat storage and heat dissipation cycle characteristics, particularly the short-term reliability, of the heat storage and heat dissipation characteristics under different atmospheres. The effects of the rate of temperature rise and the rate of temperature decrease were evaluated.

<Evaluation result of reproducibility of heat storage and heat dissipation characteristics>
The heat storage mode and the heat dissipation mode were performed in the same manner as in [6-2] above, except that the inside of the test container _{was evacuated instead of the N 2 atmosphere, and this was repeated for 10 cycles.}
In cycles 1 to 9, the rate of temperature rise and temperature decrease was set to 4 ° C./min, and in cycle 10, the rate of temperature increase and temperature decrease was dynamically changed from 4 ° C./min to 7 ° C./min.

FIG. 10 is a diagram showing a change in the time derivative (dT / dt) of the heat storage material temperature T with respect to time t in (a) heat storage mode and (b) heat dissipation mode in vacuum according to the second embodiment. be.
Note that FIG. 10 shows the second, fifth, seventh, and tenth cycles of the ten cycles.

From the viewpoint of thermodynamics, when the heat storage material does not chemically react with the PCM container in which the heat storage material is housed, for example, a graphite crucible, the heat storage material shows reproducibility in the cycle test based on the phase diagram shown in FIG. .. In terms of the kinetics of the phase change between the solid phase and the liquid phase, heat storage and heat dissipation respond rapidly in phase diagram-based cycle tests.

The heat storage and heat dissipation characteristics are affected by heat conduction and radiation without convection from the external heater to the heat storage material. As shown in FIG. 10A, in the dT / dt profile, a strong endothermic peak was observed around 840 ° C., and a wide and weak endothermic peak was observed around 900 ° C. to 940 ° C. in all cycles.
These peak temperatures were substantially the same as the eutectic temperature (838 ° C.) and the liquidus line temperature (895 ° C.) of the Fe—Ge alloy in the state diagram shown in FIG.

Therefore, it was found that the heat storage material of Example 2 can continuously store latent heat in a vacuum. Due to the end of heat storage, a large exothermic peak was observed from around 946 ° C to around 965 ° C. Changes in the dT / dt profile in the heat storage mode showed that the heat dissipation and heat storage of the heat storage material were reproducibly repeated without reacting with the vessel.

As shown in FIG. 10B, in the heat dissipation mode of cycles 1 to 9, a strong heat generation peak near 900 ° C. and a strong heat generation peak near 835 ° C. appeared with good reproducibility. The peak around 900 ° C. corresponded to the solidification of Ge from the molten alloy, and the peak around 835 ° C. corresponded to the precipitation of the eutectic alloy. This temperature was substantially the same as the start temperature of the two endothermic peaks observed in the heat storage mode of FIG. 10 (a).

The latent heat storage / heat dissipation of the eutectic mixture under thermodynamic equilibrium conditions at a constant pressure theoretically occurs at a constant temperature in the binary system. Therefore, the experimental results of the dT / dt profile showed that the melting or solidification of the eutectic mixture and the Ge main phase occurred with good reproducibility.

In cycle 10 shown in FIG. 10B, the temperature lowering rate in the heat dissipation mode was dynamically changed from 4 ° C./min to 7 ° C./min. The dT / dt profile of cycle 10 decreased to around 900 ° C., indicating that the cooling rate increased with the cooling time. In cycles 2, 5, and 7, heat dissipation was reproducibly generated at a constant temperature drop rate around 900 ° C, but in cycle 10, the start temperature of heat dissipation was around 893 ° C, compared to the cases of cycles 2, 5, and 7. Also shifted to the low temperature side.

Similarly, in cycle 10, the heat dissipation temperature due to solidification of the eutectic mixture shifted to a lower temperature side than the temperature observed in cycles 2, 5 and 7. The results of cycle 10 showed that the heat dissipation of the liquid Fe-Ge alloy was affected by the rate of temperature decrease. The major reasons for the delay in heat dissipation when the temperature drop rate is changed may be due to the slow solidification rate and the non-uniform thermal conductivity around the sample resulting from the temperature change.

From the above results, it was confirmed that the heat storage material of the present invention can obtain good reproducibility of heat dissipation characteristics without chemically reacting with the container to generate gas or the like.

<Effect of temperature rise rate and temperature decrease rate on cycle characteristics>
In the same manner as in [6-2] above, the heat storage mode and the heat dissipation mode were performed, and this was repeated for 20 cycles.

In the heat storage mode, the heating rate was dynamically changed from 3 ° C./min to 7 ° C./min. In the heat dissipation mode, the temperature lowering rate was set to 5 ° C./min in cycles 1 to 19, and was dynamically changed between 5 ° C./min and 10 ° C./min in cycle 20.

FIG. 11 shows the time derivative (dT / dt) of the heat storage material temperature T with respect to the time t in the (a) heat storage mode and (b) heat dissipation mode under the flow of the _{inert gas (N 2) for Example 2.} It is a figure which shows the change of.
Note that FIG. 11 shows 11, 15, 17, and 20 cycles out of 20 cycles.

Further, _{N 2} flow rate in cycle 1~19 0.1dm ³ / min was passed through the test containers in cycle 20 in 0.5 dm ³ / min flow rate, investigated the effect of flow rate.

From the results of FIG. 11 (a), the following was found.
(1) The heat storage by melting the eutectic mixture at around 838 ° C., which is the melting start temperature of the FeGe90 alloy according to the phase diagram of FIG. 1, and the heat storage by melting the Ge main solid phase at around 895 ° C. are the number of cycles and the heat storage. It was almost independent of the N ₂ flow rate.

(2) end temperature of the heat storage eutectic mixture under N ₂ flow, despite were similar to the heat storage completion temperature in a vacuum as shown in FIG. 10 (a), Ge in a stream of N ₂ The heat storage end temperature of the main solid phase (around 920 ° C.) was lower than the heat storage end temperature in vacuum (around 940 ° C.) and approached the liquidus temperature. Therefore, from these results, creating a convection stream of N ₂ is the test vessel, the melting of Ge principal solid phase in the solid / liquid phase coexisting region is shown to have been promoted.

In the heat dissipation mode shown in FIG. 11B, exothermic peaks were reproducibly observed for the start and end temperatures of solidification of the Ge principal phase and eutectic mixture in all cycles. These results are reproducibly operate based FeGe alloy in thermodynamic equilibrium, increase of the flow rate of N ₂ at cycle 20, the start temperature and end temperature of the coagulation for both Ge main phase and eutectic Indicates that it did not affect.

On the other hand, when compared with the results in vacuum shown in FIG. 10B, the start temperature of solidification of the Ge main phase and the start temperature of solidification of the eutectic mixture are on the liquidus temperature side, respectively. And shifted to the eutectic temperature side. This result, in the heat radiation mode, N ₂ flow of the test vessel, by discharging the heat storage of the heat storage material from the test vessel, indicating that coagulation of Ge main phase and the eutectic mixture has been promoted than vacuo ..
Thus, it was confirmed that the heat storage and heat dissipation characteristics are affected by the radiation from the heater under heat conduction, convection and inert gas flow to the heat storage material.
rice field.

[6-5] Evaluation of Mass Change Rate by Heat Storage and Heat Dissipation Cycle The mass change of the heat storage material before and after the heat storage and heat dissipation cycle was evaluated as long-term reliability up to 360 cycles for the heat storage materials of each of the above Examples and Comparative Examples. ..

The heat storage mode and the heat dissipation mode were repeatedly performed in a vacuum, and the change in the mass of the sample exposed to the repeated cycle of the heat storage and heat dissipation was evaluated.

In a standard state of 100 ml / min in an Ar stream, heating / cooling between 750 ° C. and 1000 ° C. at a temperature raising rate and a temperature lowering rate of 25 ° C./min is set as one cycle, and this 120 cycle is performed three times. , A cycle test of up to 360 cycles was performed.

Evaluation of the mass change rate uses simultaneous thermal analysis (STA2500 Regulus, Netzsch) that combines thermogravimetric analysis (TG) (TG resolution <0.03 g) and differential thermal analysis (DTA) (temperature accuracy 0.3 K). I went.

FIG. 12 is a diagram showing the measurement results of mass loss in the heat storage heat dissipation cycle under the flow of an inert gas for the heat storage material of Example 2.

As shown in FIG. 12, the mass change after the first execution of 120 cycles was less than 2%, but 1.3% after the second execution of 120 cycles and after the third execution of 120 cycles. A minimum mass reduction of 0.8% was seen. In both cases, the mass loss was kept small, confirming that there was no significant runoff and evaporation of the alloy during the 360 cycles. Therefore, for example, even when the heat storage material is applied to a heat storage power generation or the like that repeatedly stores and dissipates heat, stable operation can be guaranteed for a long period of time.

[6-6] Evaluation of metal structure and element distribution before and after the heat storage and heat dissipation cycle For the heat storage materials of each of the above Examples and Comparative Examples, the metal structure and element distribution of the heat storage material before and after the heat storage and heat dissipation cycle were evaluated.

The element distribution in the heat storage material before and after the heat storage heat dissipation cycle test was measured using an electron probe microanalyzer (EPMA, Shimadzu EPMA-1610) equipped with a wavelength dispersion type X-ray spectrometer (WDS, relative error <1%). The measurement was performed under the conditions of an acceleration voltage of 15 kV, a beam current of 200 mA, a beam size of 2 μm, a step size of 2 μm, and a sampling time of 30 ms.

Prior to the EPMA analysis, the microstructure analysis sample was mirror-finished by mechanical grinding and polishing using a resin-bonded diamond grinding disk (Struers, MD-Piano 1200, 2000 and 4000).

FIG. 13 is a BEI micrograph and an element mapping image of the cross section of the heat storage material of Example 2 before and after the heat storage heat dissipation cycle. FIG. 13 (a) is a reflected electron image (BEI) micrograph of a cross section of the heat storage material of Example 2 before the heat storage heat dissipation cycle test, and an element mapping image, and FIG. 13 (b) is an example. FIG. 13 (c) is a reflected electron image (BEI) micrograph and an element mapping image of a cross section of the heat storage material of No. 2 after a heat storage heat dissipation cycle test in vacuum, and FIG. 13 (c) shows the heat storage material of Example 2. the reflection electron image of a cross section after the cycle test under N ₂ flow (BEI) micrographs, and an element mapping images.

In addition, in FIG. 13A, FIG. 13B, and FIG. 13C, images of each element of Fe, Ge, and O are shown as element mapping images.

In FIG. 13 (a), a light gray region of the Ge main crystal having a particle size of less than 1 mm and a dark gray region of the matrix were observed in the BEI micrograph. The black area observed on the left side of the image corresponds to the epoxy resin used to mount the sample. Further, in the mapping image of the Fe element, a large number of microscopic spots characteristic of the metal structure of the eutectic structure, a needle-like region (FeGe ₂ phase), and a region of the Ge solid solution phase were observed. These corresponded to the dark gray areas of the BEI micrograph. _{These results indicate that the FeGe 2} phase and the Ge solid solution phase are uniformly distributed in the hypereutectic mixture of the alloy before the cycle test. In the mapping image of the Ge element, a coarse region (Ge main phase) of the Ge crystal was observed together with a region of the eutectic mixture. The count value per second (cps) shown in the mapping was correlated with the Ge element concentration using the standard sample calibration curve. The maximum intensities of Fe and Ge were 1222 cps and 5706 cps, respectively. In the O element mapping image, the Ge main crystal and eutectic mixture showed the detection limit level of O.

In FIG. 13 (b), the Ge principal phase (light gray) and the eutectic mixture (dark gray) reappeared as thermodynamically stable phases in the BEI micrograph. In contrast to the sample before the cycle test shown in FIG. 13 (a), both phases were observed as aggregated phases in FIG. 13 (b). This is believed to be due to the sample being exposed to a heating / cooling cycle at high temperatures. In the Fe element mapping, _{many spots of the FeGe 2} phase were closely aggregated and concentrated in the eutectic mixture. Furthermore, _{the Fe intensity (maximum value 1335 cps) of the FeGe 2-} phase spot was larger than that observed in FIG. 13 (a). These results showed that the FeGe ₂ phase was coarsened and localized to the eutectic mixture by cycle testing. In the mapping of the Ge element, the region of the Ge main phase appeared to be coarsened, but the Ge element was uniformly distributed in the eutectic mixture. The Ge intensity (maximum value of 5991 cps) in the region of the Ge main phase was larger than the intensity observed in FIG. 13 (a).

In FIG. 13 (c), in the BEI micrograph, the dark gray region of the eutectic mixture was separated into a dense region and a dilute region. The dense region (maximum value 1933 cps) corresponded to the Fe high content region, and the dilute region corresponded to the Fe low content region of the Fe element mapping.

Further, during the cycle test at high temperature, the phase diagram showing the periodic composition modulation showing that the Fe high content region is surrounded by the Fe low content region and Fe and Ge are present in the eutectic mixture is shown in FIG. It was distributed in two regions based on. The periodic composition-modulated metallographic structure is known as the lamella microstructure and represents a thermodynamically stable phase structure of the eutectic mixture. The morphology of the metallographic structure depends on the eutectic system, cooling conditions, and the vessel by the nucleation growth process, as the metallic structure is formed by short-range atomic diffusion during solidification (radiation).

<Evaluation result of reactivity with PCM container>
The effect of using a carbon-based material, specifically a crucible made of graphite, as the PCM container was investigated.

FIG. 14 is a BEI micrograph and a carbon mapping image of the cross section of the heat storage material of Example 2 after the heat storage heat dissipation cycle. FIG. 14 (a) is a reflected electron image (BEI) micrograph and a carbon mapping image of a cross section of the heat storage material of Example 2 after a cycle test in vacuum, and FIG. 13 (b) is a carbon mapping image. FIG. 3 is a reflected electron image (BEI) micrograph and a carbon mapping image of a cross section of the heat storage material of Example 2 _{after a cycle test under N 2 flow as an inert gas.}

BEI from photomicrographs, (a) in a vacuum, in any of the post-cycle test in (b) N ₂ flow, it can be seen that carbon scarcely included.
That is, the heat storage material of Example 2 was hardly react with the graphite crucible during the cycle test in a vacuum and under a stream of N _2. In addition, the amount of carbon by point analysis of EPMA was below the detection limit.

Therefore, it was found that a container of the heat storage material of the Fe-Ge alloy in a non-oxidizing atmosphere, for example, a carbon-based material such as graphite can be preferably used as the encapsulation material.

Further, it was confirmed that in all of the heat storage materials of the present invention, the volume change due to melting was less than 2%, and the volume change was sufficiently suppressed.

Since the heat storage material of the present invention contains a Ge alloy, it can be used at a high temperature and has excellent heat storage and heat dissipation characteristics.
Therefore, the heat storage material of the present invention has industrial applicability.

1 ... Heat storage capsule 2 ... Heat storage material 3 ... Capsule 3a ... First half body 3b ... Second half body 4a ... Male screw 4b ... Female screw 10 ... Heat storage body 11 ... Accommodator 11a ... Outer cylinder 11b ... Thin tube 11c ... Plate material 12 ... Heat storage Material 100 ... Solar heat storage device 20 ... Mirror 30 ... Generator 110 ... Heat receiving part 120 ... Heat storage device 121 ... Housing 123 ... Heat storage material 124 ... Transfer device 125 ... Pump 126 ... Reserve tank 127 ... Piping 128 ... Control device 130 ... Flow Road piping 130a ... Sub piping 130b ... Sub piping 130c ... Sub piping 200 ... Solar thermal power generation device E ... Energy conversion unit (heat exchanger)
S ... Sun S1 ... Temperature sensor

Claims (15)

A heat storage material characterized in that the Ge phase and the second phase exist in equilibrium in a solidified state, and the Ge phase and the second phase contain an alloy forming a eutectic. The heat storage material according to claim 1, wherein the second phase is an intermetallic compound containing Ge. The intermetallic compound containing Ge that is in equilibrium with the Ge phase is one of K, Sc, Ti, Cr, Mn, Fe, Co, Ni, Mg, Sr, Rh, Pd, Hf, Pt, or a rare earth element. The heat storage material according to claim 2, wherein at least one is contained as a constituent element. The third aspect of claim 3 is that the alloy has a eutectic composition between the Ge phase and the intermetallic compound containing Ge that is in equilibrium with the Ge phase, or a composition containing an excess of Ge with respect to the eutectic composition. The heat storage material described. The heat storage material according to any one of claims 1 to 4, wherein the eutectic temperature of the eutectic formed by the Ge phase and the second phase is 650 ° C. or higher. The heat storage material according to any one of claims 1 to 5, wherein the content of the Ge element in the alloy is 40 atomic% or more. A heat storage material characterized by containing a Ge alloy. The heat storage material according to claim 7, wherein the Ge alloy is a Fe-Ge alloy. The heat storage material according to claim 7 or 8, wherein the Ge alloy contains a eutectic alloy. The heat storage material according to claim 9, wherein the Ge alloy is a hypereutectic Ge alloy containing an excess of Ge in addition to the eutectic alloy. The heat storage material according to any one of claims 7 to 10, wherein the proportion of Ge in the Ge alloy is 70 atomic% or more and 99 atomic% or less. The heat storage material according to any one of claims 7 to 11, wherein the latent heat storage capacity of the Ge alloy is 1.28 GJ / m ^{3 or more.} The heat storage material according to any one of claims 7 to 12, which is used in a temperature range of 650 ° C. or higher. A heat storage power generation device comprising the heat storage material according to any one of claims 7 to 13. The heat storage power generation device according to claim 14, wherein the heat obtained by condensing sunlight is stored.

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