WO2017038715A1 - Alloy material - Google Patents

Abstract

The purpose of the present invention is to easily provide a p-type thermoelectric material that is light with high thermoelectric characteristics. Provided is an alloy having magnesium, calcium and silicon as constituent elements, characterized in that the atomic ratio of the elements constituting the alloy are, when the magnesium, calcium and silicon content are each set as Mg, Ca, and Si, 0 atm%≦Mg/(Mg+Ca+Si)<50 atm% 10 atm% ≦Ca/(Mg+Ca+Si)≦70 atm% 20 atm%≦Si/(Mg+Ca+Si)≦60 atm%, and the oxygen content in the alloy is 10 atm% or less.

Description

Alloy material

The present invention relates to an alloy material and a manufacturing method thereof. More specifically, the present invention relates to an alloy material containing calcium, magnesium and silicon and a thermoelectric conversion element using the same.

Thermoelectric conversion elements are known as elements capable of mutual conversion between thermal energy and electrical energy. This thermoelectric conversion element is composed of two types of p-type and n-type thermoelectric conversion materials (thermoelectric materials), and these two types of thermoelectric materials are electrically connected in series, and are thermally parallel. The configuration is arranged. In this thermoelectric conversion element, when a voltage is applied between both terminals, movement of holes and movement of electrons occur, and a temperature difference occurs between both surfaces (Peltier effect). Moreover, if this thermoelectric conversion element gives a temperature difference between both surfaces, a hole movement and an electron movement will also occur, and an electromotive force will be generated between both terminals (Seebeck effect). For this reason, as a device for cooling a personal computer CPU, refrigerator, car air conditioner, etc. using the Peltier effect, as an element for a power generation device using waste heat generated from a waste incinerator using the Seebeck effect, etc. Consideration is ongoing. In particular, since the amount of waste heat of an automobile engine is so large that it cannot be ignored, it is considered to generate power using the waste heat of the engine, and the temperature range is said to be several hundred degrees.

Conventionally, Bi ₂ Te ₃ has been mainly put to practical use as a thermoelectric material constituting a thermoelectric conversion element, and Se is generally added when forming an n-type thermoelectric material with a Bi—Te-based material. However, since the elements Bi, Te and Se constituting these thermoelectric materials are highly toxic, there is a risk of environmental pollution. Therefore, a thermoelectric material having a low environmental load, that is, having no toxicity is desired. Bi-Te materials are mainly used at about 100 ° C. and are not suitable for use in automobile exhaust heat. Furthermore, lightweight and resource-rich materials are desired for use in automotive waste heat recovery.

Mg ₂ Si is known as a non-toxic and high-performance n-type medium temperature thermoelectric material (see, for example, Patent Document 1). Although a mixture of Mg ₂ Si and CaMgSi has been proposed as a p-type thermoelectric material using a homologous element (see, for example, Patent Document 2), the Seebeck coefficient at 400 ° C. is as small as 60 μV / K or less and can be used practically. Thermoelectric properties are not obtained. Further, Mg and Ca are volatile at low temperatures, and it is difficult to easily obtain a material having a Ca—Mg—Si composition with a specified composition. Furthermore, it has not been clarified which crystal phase is present to improve the thermoelectric characteristics.

Japanese Unexamined Patent Publication No. 2002-368291 Japanese Unexamined Patent Publication No. 2008-147261

An object of the present invention is to easily provide a p-type thermoelectric material that is lightweight and has high thermoelectric properties.

In view of such a background, the present inventors made extensive studies. As a result, it has been found that a thermoelectric material having a high Seebeck coefficient can be produced by optimizing the composition of Mg—Ca—Si, and the present invention has been completed.

That is, the present invention resides in the following [1] to [12].
[1] An alloy having magnesium, calcium and silicon as constituent elements, and the atomic ratio of the elements constituting the alloy is 0 atm% when the contents of magnesium, calcium and silicon are Mg, Ca and Si, respectively. ≦ Mg / (Mg + Ca + Si) <50 atm%
10 atm% ≦ Ca / (Mg + Ca + Si) ≦ 70 atm%
20 atm% ≦ Si / (Mg + Ca + Si) ≦ 60 atm%
And an oxygen content in the alloy is 10 atm% or less.
[2] The alloy according to [1], including at least one crystal phase of the group consisting of a CaMgSi phase, a CaMg ₂ phase, a Ca ₂ Si phase, and a Ca ₅ Si ₃ phase.
[3] The alloy according to [1] or [2], including a CaMgSi phase and at least one of a CaMg ₂ phase or a Ca ₅ Si ₃ phase.
[4] The alloy according to any one of [1] to [3], including a CaMgSi phase and a Ca ₅ Si ₃ phase.
[5] The above [1] to [4], in which the CaMgSi phase is included as a main phase, and the diffraction angle of the diffraction peak caused by the CaMgSi phase (211) plane is shifted to the low angle side by 0.05 ° or more. The described alloy.
[6] The alloy according to any one of [1] to [5], wherein the bulk density is 1.2 g / cm ³ or more and 2.1 g / cm ³ or less.
[7] The alloy according to any one of [1] to [6], wherein the semiconductor property is p-type.
[8] The method for producing an alloy according to any one of the above [1] to [7], comprising a step of synthesizing an alloy from magnesium, calcium and silicon and a step of hot pressing the alloy at 600 ° C to 1100 ° C. .
[9] The manufacturing method according to [8], wherein an alloy including at least a Ca ₅ Si ₃ phase is hot pressed in the hot pressing step.
[10] The production method according to [8] or [9] above, wherein in the hot pressing step, an alloy containing a CaMgSi phase and a CaMg ₂ phase is hot pressed.
[11] A thermoelectric conversion element having a structure in which the alloy according to [7] is bonded to an n-type semiconductor.
[12] The thermoelectric conversion element according to the above [11], wherein the main phase of the n-type semiconductor is Mg ₂ Si.

Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments.

The present invention is an alloy having magnesium, calcium and silicon as constituent elements, and the atomic ratio of the elements constituting the alloy is 0 atm when the contents of magnesium, calcium and silicon are Mg, Ca and Si, respectively. % ≦ Mg / (Mg + Ca + Si) <50 atm%
10 atm% ≦ Ca / (Mg + Ca + Si) ≦ 70 atm%
20 atm% ≦ Si / (Mg + Ca + Si) ≦ 60 atm%
And the oxygen content in the alloy is 10 atm% or less.

The alloy here may be any shape such as a bulk shape represented by a melt, a molded body, a sintered body, a powder shape, and a film shape. In the production method described later, an alloy obtained by sintering an alloy obtained by arc melting by a method such as a melt or hot pressing can be read as a sintered body. In particular, a sintered body obtained by hot pressing is preferable because the composition and crystal phase in the bulk body become more uniform and exhibit stable performance.

The present invention relates to an alloy having magnesium, calcium and silicon as constituent elements, and when the atomic ratio of the elements constituting the alloy is Mg, Ca and Si, respectively. 0 atm% ≦ Mg / (Mg + Ca + Si) <50 atm%
10 atm% ≦ Ca / (Mg + Ca + Si) ≦ 70 atm%
20 atm% ≦ Si / (Mg + Ca + Si) ≦ 60 atm%
It is characterized by
10 atm% ≦ Mg / (Mg + Ca + Si) <50 atm%
10 atm% ≦ Ca / (Mg + Ca + Si) ≦ 50 atm%
20 atm% ≦ Si / (Mg + Ca + Si) ≦ 50 atm%
It is preferable that

More preferably, 20 atm% ≦ Mg / (Mg + Ca + Si) <50 atm%
30 atm% ≦ Ca / (Mg + Ca + Si) ≦ 50 atm%
16 atm% ≦ Si / (Mg + Ca + Si) ≦ 33 atm%
More preferably, 20 atm% ≦ Mg / (Mg + Ca + Si) <50 atm%
30 atm% ≦ Ca / (Mg + Ca + Si) ≦ 50 atm%
20 atm% ≦ Si / (Mg + Ca + Si) ≦ 30 atm%
It is.

When the magnesium content is 50 atm% or more, it is difficult to produce a dense material because the alloy composition is not stable. By containing a certain amount of magnesium, it is possible to improve the thermoelectric characteristics by partially generating a MgCaSi phase with good thermoelectric characteristics, so the magnesium content is preferably 10 atm% or more, More preferably, it is 20 atm% or more.

In addition, when calcium is present in an amount of more than 70 atm%, calcium is easily isolated and oxidized, which adversely affects the formation of a bulk. On the other hand, the calcium content is preferably 30 atm% or more. Thus, the ratio of crystal phases of disilicide calcium containing alloy (CaSi ₂₎ or calcium silicide (CaSi) is reduced, an alloy of the present invention exhibit more significantly semiconductor characteristics.

The Ca / Si atomic weight ratio of the alloy of the present invention is preferably larger than 1. As a result, the ratio of the Ca ₇ Mg _7.25 Si ₁₄ crystal phase contained in the alloy decreases, and the alloy of the present invention exhibits a higher Seebeck coefficient.

Further, when the silicon content is less than 20 atm%, magnesium or calcium is easily isolated, oxidized, and oxygen is more easily contained, so that bulk properties cannot be maintained. Further, when the silicon content is more than 60 atm%, calcium disilicide (CaSi ₂ ) or calcium silicide (CaSi) in the material increases, so that the semiconductor is changed to the conductor and the thermoelectric characteristics are lost. More preferably, it is 30 atm% or less. It is possible to suppress the formation of _Ca 7 _Mg 7.25 _{Si 14} in doing so.

The amount of metals other than magnesium, calcium and silicon is preferably small from the viewpoint of ease of synthesis, preferably less than 10 atm%, more preferably less than 5 atm%, more preferably 1 atm based on the total amount of magnesium, calcium and silicon. More preferably, it is less than%.

Further, the present invention is characterized in that the oxygen content in the alloy is 10 atm% or less. When the oxygen content in the alloy is more than 10 atm%, the oxidation of the material tends to proceed. In particular, calcium easily reacts with moisture, becomes calcium hydroxide, and the volume expands, so that even if a bulk is produced, cracking occurs. Further, it becomes difficult to form a Ca—Mg—Si phase or the like having excellent thermoelectric characteristics, and the thermoelectric characteristics are also deteriorated. The oxygen content in the alloy is more preferably 7 atm% or less, and still more preferably 5 atm% or less. The oxygen content in the alloy refers to the ratio of oxygen in the total amount of metal elements and oxygen in the alloy.

The property of the present invention is preferably a bulk body. The thermoelectric conversion method generates electricity when a temperature difference occurs at both ends of the element, but the element needs to have a certain thickness in order for the temperature difference to appear more conspicuously. Therefore, a bulk body is preferable to a powder or film.

Here, the bulk body is a structure having a thickness of 0.100 mm or more. Here, the thickness in the structure means the length of the thinnest part in the structure. Examples of the structure include a lump, a melt, and a sintered body.

The bulk body is preferably as dense as possible depending on the application. By densifying the bulk body, it is possible to reduce open pores in the bulk body, suppress deterioration of the element due to oxidation or the like, and improve mechanical strength. However, a lower density may be preferable.

The density of the alloy of the present invention is preferably 2.1 g / cm ³ or less, more preferably 2.0 g / cm ³ or less, more preferably 1.6 g / cm ³ or less. As a result, the weight can be reduced and it can be used more effectively in automobile applications. Usually, the density of the alloy of the present invention is 1.2 g / cm ³ or more.

The alloy of the present invention preferably contains at least one crystal phase of the group consisting of a CaMgSi phase, a CaMg ₂ phase, a Ca ₂ Si phase, and a Ca ₅ Si ₃ phase. Thereby, the alloy of this invention shows a higher thermoelectric conversion characteristic.

The alloy of the present invention further preferably includes a CaMgSi phase and at least one of a CaMg ₂ phase or a Ca ₅ Si ₃ phase, and more preferably includes a CaMgSi phase and a Ca ₅ Si ₃ phase. Thereby, the alloy of the present invention exhibits a higher Seebeck coefficient.

The CaMgSi phase exhibits semiconductor characteristics, and an alloy containing this phase further improves the thermoelectric characteristics of the Seebeck coefficient portion.

It can be confirmed by X-ray diffraction measurement that the alloy of the present invention has at least one of the above crystal phases. For example, a diffraction peak detected in an X-ray diffraction measurement (hereinafter referred to as “XRD”) using Cu as a radiation source is represented by JCPDS (Joint Committe for Powder Standards) card data corresponding to each crystal phase. It can be confirmed by referring. When there are multiple crystal phases, there are crystal phases that do not have overlapping peaks, or crystal orientations are identified at three or more locations in the scanning range of diffraction angle 2θ = 20 ° to 80 ° The crystal phase was judged to be present.

When the alloy of the present invention includes a CaMgSi phase, the CaMgSi phase is preferably the main phase. Thereby, the alloy of the present invention exhibits a higher Seebeck coefficient. Here, the CaMgSi phase is the main phase. In the XRD pattern of the alloy, a diffraction peak due to the CaMgSi phase can be confirmed, and the diffraction peak indicating the maximum intensity in the diffraction peak group is a peak due to the CaMgSi phase. Indicates that there is. For example, when identifying a crystal phase using a JCPDS card in XRD measurement, the card no. The diffraction peak at the (211) plane and the diffraction angle 2θ = 33.218 ° in CaMgSi: 01-089-1917 is a diffraction peak indicating the maximum intensity of CaMgSi.

In the CaMgSi phase contained in the alloy of the present invention, the diffraction angle of the diffraction peak due to the (211) plane is preferably shifted to the low angle side. The shift amount is preferably shifted to the low angle side by 0.05 ° or more, more preferably 0.1 ° or more, further preferably 0.2 ° or more, and further preferably 0.3 ° or more. Thus, causing a peak shift by other phases to CaMgSi phase, especially CaMg ₂ forms a solid solution, the lattice is (211) that extends in a direction perpendicular to the surface, to generate a distortion, improve the Seebeck coefficient It is presumed that

On the other hand, the Ca ₇ Mg _7.25 Si ₁₄ phase exhibits conductive properties, and an alloy containing this in a low content exhibits a higher Seebeck coefficient. The fact that the alloy of the present invention contains the Ca ₇ Mg _7.25 Si ₁₄ phase at a low content is the ratio of the maximum diffraction peak intensity of the Ca ₇ Mg _7.25 Si ₁₄ phase to the maximum peak intensity in the XRD pattern of the alloy. Can be expressed as Specifically, the alloy of the present invention has a (221) phase (Card No.) of Ca ₇ Mg _7.25 Si ₁₄ with respect to the maximum peak intensity when scanning 2θ = 20 ° to 80 ° with an X-ray diffractometer. .01-088-1551) is preferably 50% or less, more preferably 10% or less, and even more preferably less than 3%.

Further, the Mg ₂ Si phase exhibits n-type semiconductor characteristics, and an alloy containing this at a low content exhibits p-type semiconductor characteristics and higher thermoelectric characteristics. Include low-content alloy the Mg 2 _Si phase of the present invention, in the XRD pattern of the alloy, can be expressed relative to the maximum peak intensity, the ratio of the maximum diffraction peak intensity of Mg 2 _Si phase. Specifically, the alloy of the present invention has a (111) phase of Mg ₂ Si (card No. 01-071-9591) with respect to the maximum peak intensity when scanning 2θ = 20 ° to 80 ° with an X-ray diffractometer. The peak intensity is preferably 10% or less, more preferably 1% or less, and still more preferably no (111) phase peak is detected.

Here, as a method for determining the presence of the Mg ₂ Si phase, first, when a diffraction peak identified by Mg ₂ Si alone cannot be confirmed, it is determined that the Mg ₂ Si phase does not exist in the alloy.

Further, since the peak position (2θ = 2.257 °) of the Mg ₂ Si (111) plane is close to the peak position (2θ = 24.533 °) of the CaMgSi (102) plane, the diffraction peak attributed to either phase It may not be possible to judge. In this case, the intensity at the diffraction peak of 2θ = 24.25 ° ± 0.3 ° in the alloy is converted as the respective contributions of the Mg ₂ Si (111) surface and the CaMgSi (102) surface, and Mg ₂ Si Judgment was made by regarding the diffraction peak intensity contribution of the (111) plane as the diffraction peak intensity of the Mg ₂ Si (111) plane. Specifically, based on the ratio (0.037) of the diffraction peak intensity of the (211) plane of the CaMgSi phase described in the JCPDS card and the diffraction peak intensity of the (102) plane of CaMgSi, the Mg ₂ Si phase (I (Mg ₂ Si)) was calculated by the following calculation: I (Mg ₂ Si) (%) = (maximum peak intensity of alloy (24.25 ° ± 0.3 °) −CaMgSi (211) ) Area peak intensity
× 0.037) / CaMgSi (211) plane peak strength The alloy of the present invention preferably has a resistance value at 400 ° C. of 0.1 Ωcm or less, more preferably 0.05 Ωcm or less.

Further, the alloy of the present invention exhibits p-type semiconductor characteristics and exhibits physical properties such as a thermal expansion coefficient close to that of Mg ₂ Si.

Furthermore, when a material having Mg ₂ Si as a main phase is used for the n-type semiconductor and the material of the present invention is used for the p-type semiconductor, a thermoelectric conversion element that is stably driven can be manufactured. Bonding method may be joined to the bulk of the Mg 2 _Si and the present invention directly, in order to reduce the stress generated, but may also comprise a metal layer, that joins the close physical properties materials, simple In addition, direct bonding is also preferable in that a pn junction is possible.

The present invention can be used as a sputtering target by producing a bulk body. In particular, since it has high thermoelectric properties, it has a certain conductivity and allows DC sputtering as well as RF sputtering. By using such a sputtering target, a Ca—Mg—Si thin film having a specified composition can be produced.

Next, the manufacturing method of the present invention will be described. Although an example of the manufacturing method is shown here, it is not always necessary to use that method.

The production method of the present invention includes a step of synthesizing an alloy from magnesium, calcium and silicon, a step of pulverizing the alloy according to circumstances to obtain an alloy powder having an oxygen content of 10 atm% or less, And a hot press treatment at a temperature of 1 ° C. to 1100 ° C.

First, magnesium, calcium and silicon, when the atomic ratio of elements is magnesium, calcium and silicon, respectively, Mg, Ca and Si, depending on the melting method, for example, when using the arc melting method, 0atm% ≦ Mg / (Mg + Ca + Si) <70atm%, taking into account that magnesium and calcium volatilize
10 atm% ≦ Ca / (Mg + Ca + Si) ≦ 70 atm%
9 atm% ≦ Si / (Mg + Ca + Si) ≦ 60 atm%
Need to be mixed so that
10 atm% ≦ Mg / (Mg + Ca + Si) <70 atm%
10 atm% ≦ Ca / (Mg + Ca + Si) ≦ 50 atm%
9 atm% ≦ Si / (Mg + Ca + Si) ≦ 50 atm%
It is preferable to mix so that
0 atm% ≦ Mg / (Mg + Ca + Si) <50 atm%
10 atm% ≦ Ca / (Mg + Ca + Si) ≦ 70 atm%
20 atm% ≦ Si / (Mg + Ca + Si) ≦ 60 atm%
It is more preferable to mix so that
10 atm% ≦ Mg / (Mg + Ca + Si) <50 atm%
10 atm% ≦ Ca / (Mg + Ca + Si) ≦ 50 atm%
20 atm% ≦ Si / (Mg + Ca + Si) ≦ 50 atm%
It is more preferable to mix so that
50 atm% ≦ Mg / (Mg + Ca + Si) <70 atm%
20 atm% ≦ Ca / (Mg + Ca + Si) ≦ 40 atm%
9 atm% ≦ Si / (Mg + Ca + Si) ≦ 30 atm%
It is still more preferable to mix so that it may become.

Although raw materials may be added so as to have the above-described composition after synthesis, it is preferable to synthesize after including all the raw materials having the above-described composition. It is desirable that the amount of oxygen contained in the raw material is as small as possible. Specifically, it is preferably 10 atm% or less, and more preferably 5 atm% or less.

In addition, the synthesis method is not particularly limited, but a synthesis method in which oxygen is not contained as much as possible is preferable. For this purpose, an arc melting method, which is an apparatus that uses as little oxygen-containing equipment as possible in a container or the like, is preferable. In particular, the vapor pressures at the melting points of calcium (melting point: about 800 ° C.) and magnesium (melting point: about 650 ° C.) are as high as 0.87 Torr and 2.2 Torr, respectively. It is difficult to make. On the other hand, since the arc melting method can raise the temperature to the melting temperature in a few seconds, volatilization of each additive component during the treatment can be suppressed. Further, as a melting condition, it is preferable to perform the treatment at a high power for a short time rather than melting at a low discharge power for a long time. The amount of current depends on the input amount of raw material, and the current value is preferably 15 A or more per gram, more preferably 20 A or more. Also, if the raw material contains more calcium than silicon, an alloy or oxide film is formed on the surface during arc melting, so the current amount is insufficient at a current value of 10 A or less per gram of raw material, and the film melts. As a result, it is difficult to obtain a homogeneous alloy. In particular, calcium precipitates without being alloyed, and calcium is oxidized after synthesis, so that it becomes easy to contain a large amount of oxygen. The upper limit is preferably 100 A or less per gram. When a current exceeding 100 A is applied, magnesium and calcium are instantly volatilized, making it difficult to produce a specified alloy. The raw materials are preferably mixed uniformly during arc melting. By doing so, the synthesized alloy becomes more uniform. Furthermore, a specified element may be added for fine adjustment to the specified composition. The calcium silicide-based material synthesized in this way has a composition within the scope of the present invention, and the oxygen content is 10 atm% or less.

Next, the obtained alloy material is pulverized into powder form if necessary. In order that the oxygen content in the alloy is 10 atm% or less, the pulverization operation is preferably performed in an inert gas atmosphere so as not to increase the oxygen content after the synthesis of the alloy. By doing so, oxidation of the powder surface can be prevented and the amount of oxygen contained can be kept low. When the alloy powder is used for firing, it is preferable to remove certain coarse particles. By doing so, it becomes possible to prevent cracking of the sintered body due to coarse grains. The particle size to be removed is preferably 300 μm or more, more preferably 150 μm or more.

Next, the alloy powder is hot pressed at 600 to 1100 ° C., preferably 600 to 900 ° C. The hot press method is a device that advances sintering by applying temperature while pressing powder. By uniaxial pressing during heating, it assists diffusion during firing, and when the diffusion coefficient is low or the particle size of metals, etc. This is a firing method that makes it possible to sinter materials that are difficult to sinter, such as when there is a large sinter. Depending on the composition, baking is performed by a hot press method, but the density is improved as compared with the prior art, and a bulk body of 1.3 g / cm ³ or more, further 1.8 g / cm ³ or more can be obtained.

The firing temperature in the hot press treatment is 600 ° C. or higher and 1100 ° C. or lower, preferably 600 ° C. or higher and 900 ° C. or lower, more preferably 700 ° C. or higher and 1000 ° C. or lower, and still more preferably 700 ° C. or higher and 800 ° C. or lower. At temperatures lower than 600 ° C., sintering does not proceed and the density is improved only to the same extent as the density of the molded body. Further, if firing is performed at a temperature higher than 1100 ° C., the melting point is close, so the alloy may be melted.

The pressure during firing is preferably 10 MPa or more and 100 MPa or less. This is because the density of the bulk body is improved, and even a generally used carbon mold can be used. The sintering atmosphere is preferably performed in an inert gas atmosphere such as nitrogen or argon containing no oxygen or in a vacuum.

The alloy subjected to hot pressing in the firing step in the production method of the present invention, that is, the alloy obtained in the synthesis step preferably includes at least a Ca ₅ Si ₃ phase, and may include a CaMgSi phase and a Ca ₅ Si ₃ phase. Further preferred. Thereby, the alloy finally obtained contains a CaMgSi phase as a main phase.

The alloy subjected to hot pressing in the firing step in the production method of the present invention, that is, the alloy obtained in the synthesis step preferably contains at least a CaMgSi phase, and more preferably contains a CaMgSi phase and a CaMg ₂ phase. As a result, the finally obtained alloy (sintered body) contains the CaMgSi phase as the main phase, and further, since there are few phases containing Si, the generation of the Ca ₇ Mg _7.25 Si ₁₄ phase and the CaSi ₂ phase is suppressed. It becomes possible. Furthermore, since CaMg ₂ tends to dissolve, it tends to generate lattice distortion of the CaMgSi phase.

The alloy subjected to hot pressing in the firing step in the production method of the present invention, that is, the alloy obtained in the synthesis step preferably includes at least one of a CaMgSi phase and a CaMg ₂ phase or a Ca ₅ Si ₃ phase, and more preferably Includes a CaMgSi phase and a Ca ₅ Si ₃ phase, more preferably a CaMgSi phase, a CaMg ₂ phase, and a Ca ₅ Si ₃ phase. Thereby, the alloy finally obtained has a suitable performance as a thermoelectric conversion element.

Moreover, it is preferable that the alloy subjected to the hot press treatment in the firing step in the production method of the present invention does not contain an Mg phase.

The bulk body of the present invention may be processed into a predetermined dimension. The processing method is not particularly limited, and a surface grinding method, a rotary grinding method, a cylindrical grinding method, or the like can be used. Since it reacts with water, care must be taken when handling water or grinding fluid during processing.

The bulk body of the present invention can also be used as a sputtering target. In that case, it may be fixed (bonded) to a flat or cylindrical support with an adhesive such as a solder material, if necessary. The material of the support is not particularly limited as long as it has a high thermal conductivity and can support the molded product, but a metal such as Cu, SUS or Ti is preferable because of its high thermal conductivity and high strength. As the shape of the support, a flat plate-shaped support is used for a flat plate-shaped molded product, and a cylindrical support is used for a cylindrical molded product. The adhesive (bonding material) for adhering the molded product and the support is not particularly limited as long as it has sufficient adhesive strength to support, but a conductive resin, a tin solder material or an indium solder material is used. I can do it. Indium solder is preferable because it has high conductivity and thermal conductivity, and is soft and easily deformed. The reason is that the heat of the target surface can be efficiently cooled, the stress between the polycrystalline body and the support generated by thermal expansion can be absorbed, and the bulk body can be prevented from cracking.

The sputtering target of the present invention can produce a thin film having a predetermined ratio of magnesium, calcium and silicon by sputtering.

It is a plot of Seebeck coefficient-measurement temperature of Example 6.

Examples will be described below, but the present invention is not limited thereto.
(Composition, purity)
Quantification was performed using an ICP-MS (inductively coupled plasma mass spectrometry) apparatus. The composition ratio was calculated as the ratio of each element to the total amount of calcium, magnesium and silicon. The purity was defined as the ratio (atm%) of the total amount of calcium, magnesium and silicon in all the detected metal elements.
(Oxygen content)
The measurement object is pyrolyzed, the oxygen content is measured by a thermal conductivity method using an oxygen / nitrogen / hydrogen analyzer (manufactured by Leco), and the ratio to the total amount of calcium, magnesium and silicon in the alloy (atm%) ).
(Bulk density)
The bulk density of the bulk body was calculated by measuring dimensions and weight.
(Seebeck coefficient)
The measured object was processed into a required shape, and the Seebeck coefficient was measured from room temperature to 600 ° C. according to JIS R 1650-1 using a thermoelectric property evaluation apparatus (manufactured by ULVAC: ZEM-3). The measurement atmosphere was carried out under reduced pressure He.
(X-ray diffraction measurement)
A normal powder X-ray diffractometer (device name: Ultimate III, manufactured by Rigaku Corporation) was used for normal measurement. The conditions for XRD measurement are as follows.
Radiation source: CuKα ray (λ = 0.15418 nm)
Measurement mode: 2θ / θ scan Measurement interval: 0.01 °
Divergence slit: 0.5 deg
Scattering slit: 0.5 deg
Receiving slit: 0.3mm
Measurement time: 1.0 seconds Measurement range: 2θ = 20 ° -80 °
The crystal phase to be identified was identified using the following JCPDS card.
CaMgSi: 01-089-1917
Ca ₇ Mg _7.25 Si ₁₄ : 01-088-1551
CaMg ₂ : 01-072-5708
Mg ₂ Si: 01-071-9591
Ca ₅ Si ₃ : 01-070-7854, 01-082-1714
Ca ₂ Si: 01-089-4856
CaSi ₂ : 01-071-4840
CaSi: 01-087-0894
Mg: 01-089-4856
Ga ₁₄ Si ₁₉ : 01-087-0861
(Resistivity)
The measured object was processed into a necessary shape, and the resistivity from room temperature to 600 ° C. was measured using a thermoelectric property evaluation apparatus (manufactured by ULVAC: ZEM-3). The measurement atmosphere was carried out under reduced pressure He.

[Examples 1 to 5, Comparative Examples 1 to 3]
Magnesium powder (purity: 99.9%, manufactured by Furuuchi Chemical), calcium (particle size: 3-5 mm, purity 99% manufactured by Furuuchi Chemical), silicon (particle size: 2-5 mm, purity: 5N, manufactured by Kojundo Chemical Laboratory) After mixing to a total of 10 g, argon arc melting was performed for 3 minutes at a current of 200 A (comparative example 1 only 100 A). The resulting material was pulverized in a mortar in a nitrogen atmosphere to obtain a powder under a sieve having an opening of 150 μm. When the composition ratio and the oxygen content were confirmed, the results shown in Table 1 were obtained.

Hot press treatment was performed using the prepared powder under the following conditions.
Hot press temperature: 800 ° C
Atmosphere: Vacuum (50 Pa) Holding time 1 hour Pressure: 50 MPa
Mold material: Carbon (Material: IG-11) Mold sintered body Size: 40 mm x 12 mm
The measured Seebeck coefficient in Example 1 was 85 μV / K.

Table 2 shows the oxygen content and bulk density of the obtained bulk material. In Comparative Examples 1 and 3, cracks occurred and a bulk body could not be obtained.

When the bulk Seebeck coefficient of Comparative Example 2 was measured, the value was as low as 3 μV / K, and it was confirmed that the material was difficult to use as a thermoelectric element.

Table 2 shows the oxygen content and bulk density of the alloys of Examples 1 to 5 and Comparative Examples 1 to 3, Table 3 shows the Seebeck coefficient at 400 ° C., and Table 4 shows the crystal phase contained in the alloy (melt). Table 5 shows the crystal phases contained in the alloy (sintered body).

[Examples 6 to 11]
Alloys were produced in the same manner as in Examples 1 to 5 except that the composition of the alloy powder was the composition ratio shown in Table 1 and the hot press was set to 800 ° C.

The composition ratio and oxygen content of the alloy powders of Examples 6 to 11 are shown in Table 1, the oxygen content and bulk density of the alloy in Table 2, the Seebeck coefficient at 400 ° C. in Table 3, and the alloy (melt) content. Table 4 shows the crystal phase to be processed, Table 5 shows the crystal phase contained in the alloy (sintered body), Table 6 shows the resistance value, and Table 7 shows the analysis result of the XRD pattern.

In Tables 4 and 5, for example, when ◎ is described in CaMgSi, a diffraction peak due to the CaMgSi phase can be confirmed in the XRD pattern of the alloy, and the diffraction peak indicating the maximum intensity in the diffraction peak group is CaMgSi. Indicates a phase. Similarly, ◯ indicates that, for example, when ◯ is described in CaMgSi, a diffraction peak due to the CaMgSi phase can be confirmed in the XRD pattern of the alloy.

In Table 4, there are examples where two ◎ are attached in the same example, but this is because the maximum peak intensities of CaMgSi and Ca ₅ Si ₃ exist at the same diffraction angle, and the intensity ratio cannot be clearly divided. It is written. From the peaks other than the maximum peak intensity, it was confirmed that the above two phases were present.

In Table 4, Ca ₇ Mg _7.25 Si ₁₄ is not marked with a _circle, but the peak intensity ratio in Table 7 shows a value larger than 1. This cannot be confirmed, but is mechanically calculated from the XRD intensity at the corresponding diffraction angle.

Also, the plot of Seebeck coefficient and measurement temperature of Example 6 is posted.

(Comparative Example 4)
Arc melting was performed under the same conditions as in Example 3 except that the arc melting current was set to 50 A, but the raw materials did not melt, and the peaks of magnesium, calcium, and silicon as raw materials were mainly obtained, and the alloy was obtained. There wasn't.

(Comparative Example 5)
When arc melting was performed under the same conditions as in Example 3 except that the arc melting current was 500 A and the total weight was 3 g, the raw material was volatilized and could not be recovered.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

It should be noted that the entire contents of the specification, claims, drawings and abstract of Japanese Patent Application No. 2015-169147 filed on August 28, 2015 are cited here as disclosure of the specification of the present invention. Incorporate.

Claims (12)

1. An alloy having magnesium, calcium and silicon as constituent elements, and the atomic ratio of the elements constituting the alloy is 0 atm% ≦ Mg / when the contents of magnesium, calcium and silicon are Mg, Ca and Si, respectively. (Mg + Ca + Si) <50 atm%
   10 atm% ≦ Ca / (Mg + Ca + Si) ≦ 70 atm%
   20 atm% ≦ Si / (Mg + Ca + Si) ≦ 60 atm%
   And an oxygen content in the alloy is 10 atm% or less.
2. The alloy according to claim 1, comprising at least one crystal phase of the group consisting of a CaMgSi phase, a CaMg ₂ phase, a Ca ₂ Si phase, and a Ca ₅ Si ₃ phase.
3. The alloy according to claim 1, comprising a CaMgSi phase and at least one of a CaMg ₂ phase or a Ca ₅ Si ₃ phase.
4. Alloy according to any one of claims 1 to 3 comprising a CaMgSi phase and _Ca 5 Si ₃ phases.
5. The alloy according to any one of claims 1 to 4, which includes a CaMgSi phase as a main phase, and a diffraction angle of a diffraction peak caused by the CaMgSi phase (211) plane is shifted by 0.05 ° or more to the low angle side.
6. The alloy according to any one of claims 1 to 5, wherein a bulk density is 1.2 g / cm ³ or more and 2.1 g / cm ³ or less.
7. The alloy according to any one of claims 1 to 6, wherein the alloy exhibits p-type semiconductor characteristics.
8. The method for producing an alloy according to any one of claims 1 to 7, comprising a step of synthesizing an alloy from magnesium, calcium and silicon and a step of hot pressing the alloy at 600 ° C to 1100 ° C.
9. In the hot pressing process, the production method according to claim 8, hot pressing an alloy containing at least Ca ₅ Si ₃ phases.
10. In the hot pressing process, the production method according to claim 8 or 9, hot pressing the alloy containing CaMgSi phase and CaMg ₂ phases.
11. A thermoelectric conversion element having a structure for joining the alloy according to claim 7 and an n-type semiconductor.
12. The thermoelectric conversion element according to claim 11, wherein the main phase of the n-type semiconductor is Mg ₂ Si.

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