JP5725658B2 - Method for producing wavelength selective thermal radiation or heat absorbing material - Google Patents

Description

  The present invention relates to a method for producing a wavelength-selective heat radiation material or heat absorption material used in the solar energy utilization industry field that generates power and hot water using solar heat, and in the space industry field that develops heat utilization equipment in a space environment. About.

  In order to effectively use solar thermal energy, thermal radiation or heat absorption materials having various wavelength selectivity have been studied and developed.

  The present inventor first obtained a mask made of an alumina film having a large number of regularly arranged holes by anodizing a metal aluminum sheet and further treating the anodized sheet using a predetermined etching method. The alumina film mask is placed on a heat-resistant substrate, and a dry etching method using a predetermined etching gas is applied to provide excellent thermal stability and high durability that can withstand long-term use at high temperatures. A method for producing wavelength-selective thermal radiation or heat-absorbing material was proposed and patented (Patent Document 1).

  According to the present invention, the emissivity can be increased in an arbitrary wavelength region by changing the size of the periodic fine structure (fine concavo-convex structure) on the surface, which is very effective as a heat radiation or heat absorption material. Things can be made.

Japanese Patent No. 3472838 JP 2005-271097

However, on the other hand, the dry etching method still has a problem that it is very difficult to produce a large area of heat radiation or heat absorption material. For example, it takes about 6 hours to produce a material of mm ² level.

  In order to solve the above problems, the present inventor has paid attention to a technique for forming a periodic fine structure by treating a Ni-base superalloy decomposed by spinodal with an etching solution (see, for example, Patent Document 2).

  This patent document 2 applies a mesoscale square regular unevenness formed by treating a Ni-base superalloy with an etching solution, and applies this to cooling fins for electronic devices or ICs. Is intended. However, in such applications, strict accuracy is not required for the regular uneven dimensions.

  In contrast, wavelength-selective thermal radiation or heat-absorbing materials require strict accuracy for regular irregular dimensions. That is, the periodic microstructure obtained by treating the spinodal-decomposed Ni-base superalloy with the etching solution has a cavity size of about 500 nm, but in order to effectively apply to the use of the present invention, A surface smoothness of about 50 nm (about 500 atoms), which is about 1/10 of that, is required. However, such surface smoothness cannot be realized even if precise polishing is performed.

  Therefore, the present inventor does not form a cavity (unevenness) by directly using the phase structure (γ phase + γ ′ phase) of the outermost surface of the substrate on which regular unevenness is formed. This can be achieved by chemically or electrochemically dissolving and / or physically deleting and forming cavities (unevenness) using the inner phase structure (γ phase + γ ′ phase) exposed thereby. The inventors have found that the problem can be solved and completed the present invention.

That is, the present invention provides a process for preparing an alloy base material capable of two-phase separation by spinodal decomposition when supersaturated solid solution is aged in a two-phase coexistence region;
Aging the alloy base material in a two-phase coexistence region to cause spinodal decomposition, and forming a regularly arranged first phase and a second phase arranged between the first phases; The step of selectively dissolving and removing the second phase to a predetermined depth to lift the first phase, and the first phase that has been lifted by dissolving and removing the second phase physically And removing the first phase physically by ultrasonic waves, and then selectively dissolving and removing the first phase on the surface. A method for producing thermal radiation or heat absorbing material.

  Here, the wavelength-selective heat radiation material and the wavelength-selective heat absorption material are the same. This material has the characteristic that when this material is heated by a heat source such as a heater, it emits heat only in a specific wavelength region. When used in an application (purpose) using such a characteristic, the wavelength selective heat It becomes a radiation material. On the other hand, when it receives heat radiation from the outside, such as the sun, it has the characteristic of absorbing only a specific wavelength region, but when used in applications (purposes) that use such characteristics, wavelength selective heat absorption Become a material.

  The present invention removes both the first phase and the second phase on the outermost surface of the alloy base material in which the first phase and the second phase are regularly arranged by spinodal decomposition. Since the cavities are formed using the first phase and the second phase on the inner side, macroscopic unevenness on the outermost surface of the alloy substrate (for example, generated by cutting or machining) Structure of the outermost surface due to residual unevenness on the surface, difference in the outermost surface crystal phase due to surface “step difference”, and “displacement” (error) that occurs when cutting a predetermined crystal plane (crystal axis) from the bulk material By eliminating the adverse effects of spatial non-uniformity) and obtaining a microscopically uniform surface structure (smoothness of about 50 nm), effective accuracy as a wavelength selective thermal radiation or heat absorption material A cavity with high dimensional accuracy can be formed.

  Moreover, by etching the alloy substrate in which the alloy base material is subjected to aging treatment in the two-phase coexistence region and subjected to spinodal decomposition, a large-area heat radiation or heat absorption material can be easily produced in a short time.

  Also, an alloy base material that undergoes spinodal decomposition, such as a Ni-based alloy, has low electrical conductivity, and therefore low reflection in the infrared region. In order to prevent this, reflection in the infrared region can be improved by coating a metal or alloy having a higher electrical conductivity than the alloy base material. Further, by setting the metal or alloy to be coated to a melting point higher than that of the alloy substrate, it can be used stably even at high temperatures.

(1)-(4) is explanatory drawing which shows the outline | summary of this invention method in order. The result of having observed the surface fine structure obtained in the Example with the scanning electron microscope is shown, (a) is the photograph seen from the front, (b) is the photograph seen from the diagonal. The result of having observed the surface fine structure obtained by the comparative example with the scanning electron microscope is shown, (a) is the photograph seen from the front, (b) is the photograph seen from the diagonal. The figure which showed the experimental result which compared the wavelength selection performance of an example and a comparative example with the calculation result of an ideal structure (A)-(c) is a photograph showing the result of observation of the surface microstructure of a sample prepared by changing the heat treatment conditions with a scanning electron microscope.

  Hereinafter, embodiments of the present invention will be described in detail.

  First, when a supersaturated solid solution is subjected to an aging treatment in a two-phase coexistence region, an alloy base material capable of two-phase separation by spinodal decomposition is prepared. An alloy base material that can be separated into two phases by spinodal decomposition refers to an alloy having a free energy curve inflection in a free energy versus concentration diagram of the alloy.

  Spinodal decomposition is a phase decomposition that does not involve nucleation, and the tissue generated by spinodal decomposition exhibits a periodic modulation structure. A typical alloy is a Ni-based alloy (see Patent Document 1). Other than Ni-based alloys, alloy base materials that can be separated into two phases by spinodal decomposition are widely known to those skilled in the art. See, for example, Fundamentals of Metal Physics-Material Science, Eiichi Fujita, published by Agne Technology Center, p157-166. Therefore, the alloy base material of the present invention is not limited to the Ni-based alloy.

  The alloy base material is desirably a single crystal, but even a polycrystal having a crystal orientation that is substantially the same (for example, a polycrystal cast in the same crystal growth direction) is suitable for use according to the present invention. It can be applied effectively.

  In addition, the crystal orientation of the alloy substrate surface applied in the present invention is not particularly specified. For example, the present invention can be applied to the (001) plane and the (110) plane.

  Next, the alloy base material is subjected to aging treatment in a two-phase coexistence region to cause spinodal decomposition, thereby forming a regularly arranged first phase and a second phase arranged between the first phases. .

  In order to apply to the use of the present invention, it is necessary to set the dimensions of the regularly arranged first phase and second phase with high accuracy. For this purpose, it is necessary to appropriately set the alloy composition (type of additive element, blending amount), aging treatment conditions, and the like (see, for example, Patent Document 1). Various techniques for making a regular arrangement of desired dimensions are known. For example, it is well known to those skilled in the art that when the aging temperature is increased, the structure of the γ ′ phase becomes coarse.

  For the relationship between the aging temperature and the structure of the γ 'phase in Ni-base superalloys, see AM Ges, O. Fornaro, HA Palacio, Coarsening behavior of a Ni-base superalloy under different heat treatment conditions, Materials Science and Engineering A, 458 (2007), pp.96-100. Therefore, this invention can set the desired dimension of the 1st phase and the 2nd phase which are regularly arranged based on these known knowledge.

  Then, the first surface on the outermost surface of the alloy base material (see FIG. 1 (1)) in which the first phase regularly arranged and the second phase arranged between the first phases are formed. The two phases (γ phase) are selectively dissolved and removed to a predetermined depth, and the first phase (γ ′ phase) on the outermost surface is lifted (see FIG. 1 (2)). This is a chemical or electrochemical etching process that acts only on the second phase (γ phase) on the outermost surface, leaving the first phase (γ ′ phase) on the outermost surface. It is processing. Control of the etching process (control of the etching depth with respect to the base material) is performed by adjusting the composition, concentration, temperature, time and the like of the processing liquid. Such techniques themselves are widely known to those skilled in the art.

For example, for etching the γ phase, etching is performed electrochemically using an etching treatment solution of HClO ₄ : 2-butoxyethanol: glycerin = 10: 48: 6 [volume ratio]. The control of the depth of the etching process varies depending on the concentration of the processing liquid, the temperature of the processing liquid, the current density, etc., but generally the desired depth (the first phase on the outermost surface ( Etching can be performed to such a depth that a part of the γ ′ phase is lifted.

  Thereafter, the first phase (γ ′ phase) on the outermost surface that has been lifted by dissolving and removing the second phase (γ phase) is removed. For example, the first phase (γ ′ phase) remaining on the outermost surface is removed by a physical method such as ultrasonic cleaning. For ultrasonic cleaning, a general apparatus widely known to those skilled in the art can be used.

  As a result, both the first phase (γ ′ phase) and the second phase (γ phase) that were on the outermost surface of the base material were removed from the surface of the alloy base material, and the first phase that was inside The phase (γ ′ phase) and the second phase (γ phase) appear on the surface of the alloy substrate (see FIG. 1 (3)).

  In such a state, the exposed first phase (γ ′ phase) is selectively dissolved and removed (see FIG. 1 (4)).

  In the γ ′ phase etching, for example, a treatment solution of HCl (37%): HNO 3 (60%): pure water = 42: 8: 33 [volume ratio] is used. In this etching, when the temperature of the etching processing liquid rises, the etching rate increases, but the etching depth varies. Further, if the etching solution concentration is too low, the wall surface of the microstructure of the alloy base material tends to be roughened. If the etching solution concentration is too high, the etching rate is too high and it becomes difficult to control the etching depth.

  Therefore, for example, the etching treatment liquid temperature is 40 ° C. or less, and the content of water contained in the etching treatment liquid is 20 to 40%.

  Thus, the substrate surface can form a cavity with high dimensional accuracy that is effective as a wavelength-selective thermal radiation or heat absorption material that is not affected by the unevenness of the outermost surface.

  In this etching process, a part of the surface region of the γ phase is also etched (see FIG. 1 (4)).

  Next, the surface of the exposed second phase (γ phase) has a melting point higher than that of the second phase (γ phase) of the alloy base material and electric conductivity than that of the second phase (γ phase). High metal or alloy, preferably a precious metal such as platinum, a metal selected from W, Ta and Mo or an alloy thereof. Platinum is excellent in wavelength selection characteristics and is preferable.

  The coating thickness must be at least the skin depth of the electromagnetic wave. Also, it is not good to make it too thick in order to avoid peeling at high temperatures. Therefore, although it depends on the type of coating metal, 70 nm to 150 nm is preferable.

  A Ni-based superalloy base material (single crystal) was prepared, in which a supersaturated solid solution was subjected to an aging treatment in a two-phase coexistence region and two-phase separation into a γ phase and a γ ′ phase by spinodal decomposition.

  The composition of this Ni-base superalloy substrate is as follows.

In mass%, Cr: 6.4%, Al: 5.6%, Ti: 1.0%, Mo: 0.6%, W: 6.4%, Co: 9.7%, Re: 3. 0%, Hf: 0.1%, balance Ni and inevitable impurities This Ni-base superalloy substrate was heat-treated. The heat treatment conditions are as follows.

Solution heat treatment (7 steps)
Heated to 1276 ° C in 3 hours, held at 1276 ° C / 4 hours, held at 1286 ° C for 10 minutes, held at 1286 ° C / 2 hours, held at 1296 ° C for 10 minutes, held at 1296 ° C for 3 hours, held at 1303 ° C for 10 minutes After 1303 ° C / 3 hours hold 1312 ° C 10 minutes warm up 1312 ° C / 2 hours hold 1315 ° C 10 minutes warm up 1315 ° C / 2 hours hold 1317 ° C 5 minutes warm up 1317 ° C / 1 hour hold Rapid cooling (cooling at 300 ° C / min from around 1300 ° C)
Primary aging heat treatment (1 step)
After solution heat treatment, cooled to 400 ° C or lower, held at 1140 ° C for 6 hours, then rapidly cooled secondary aging heat treatment (1 step)
After the primary aging heat treatment, after cooling to 400 ° C. or lower, holding at 870 ° C./20 hours and then rapidly cooling, the obtained base material is cut into a predetermined size so that the (110) surface becomes the surface, and then machined and polished did.

  Next, the outermost γ phase was etched. Etching conditions are as follows.

・ Etch temperature 25 ℃
Treatment solution concentration HClO ₄ (60%): 2-butoxyethanol (99%): glycerin = 10: 48: 6
-A constant voltage power supply is used with a constant 30V, and the current value is 1-1.
A desired etching depth could be obtained in an etching process time of about 1 minute.

  Next, ultrasonic cleaning treatment was performed. The processing conditions are as follows.

・ UA-100 manufactured by Kokusai Denki Alpha Co., Ltd.
・ Output 100W (average 65W), frequency 36kHz
Next, an etching process for the γ ′ phase was performed. Etching conditions are as follows.

・ Treatment solution concentration HC1 (37%): HNO ₃ (60%): Pure water = 42, 8, 33 (volume ratio)
・ Etch temperature is constant at 25 ℃
・ Processing solution concentration is constant at 42: 8: 33
Etching for about 13 minutes gave a fine structure (concavo-convex structure having a cavity) with an aspect ratio of about 1.

  Furthermore, the obtained surface was coated with a concavo-convex structure by plating.

・ Coating component Platinum ・ Coating thickness 100nm
By this method, an area of the square meter class could be manufactured in units of 1 hour.

  The result of having copied the obtained fine structure with the scanning electron microscope is shown to Fig.2 (a) and (b). (A) is a photograph viewed from directly above, and (b) is a photograph viewed from an oblique direction.

Comparative Example A Ni-based alloy substrate similar to that in Example 1 was prepared, and this Ni-based alloy substrate was heat-treated under the same heat treatment conditions as in Example 1. In the same manner as in Example 1, the obtained base material was cut into a predetermined size so that the (110) plane was the outermost surface, and was machined and polished. Next, the outermost γ ′ phase was etched to remove the γ ′ phase. The etching conditions for the γ ′ phase are the same as in the example.

The obtained fine structure (uneven structure having cavities) was coated by plating. The coating conditions are the same as in the examples. The result of having copied the obtained fine structure with the scanning electron microscope is shown to Fig.3 (a), (b). (A) is a photograph viewed from directly above, and (b) is a photograph viewed from an oblique direction.

  The dimensional accuracy of the wavelength selective thermal radiation or heat absorbing material of the obtained examples and comparative examples was measured. When counting the number of rectangles (squares) each having a side of 200 nm to 1000 nm within the same area, the wavelength selective thermal radiation or heat absorbing material of the example is 1.65 times that of the comparative example, It was confirmed that the dimensional accuracy of the concavo-convex structure was improved by the manufacturing method of the present invention.

  Moreover, the experimental result which compared the wavelength selection performance of an Example and a comparative example is shown in FIG. 4 with the calculation result of an ideal structure. From this figure, it can be seen that the wavelength selectivity is improved in the example compared to the comparative example. For example, when the difference in average reflectance between the visible light region (0.38-0.77 μm) and the infrared region (2-5 μm) is compared, it is 0.33 in the comparative example and 0.52 in the embodiment.

(Experimental example)
In the above examples, samples were prepared by changing the aging treatment conditions as follows.

(1) Aged at 1140 ° C. for 6 hours after solution treatment (2) Aged at 1175 ° C. for 6 hours after solution treatment (3) Aged at 1135 ° C. for 6 hours after solution treatment 5A to 5C show the results of observing the surface fine structure of each sample with a scanning electron microscope, and the measurement results of the average dimensions of the recesses of each sample (1) to (3) are shown below. Shown in

(1) 337nm
(2) 350nm
(3) 480nm
From the above experimental results, it was confirmed that the dimensions of the regularly arranged first phase and second phase can be accurately set by changing the aging treatment conditions.

  In the example described above, the wavelength-selective solar-absorbing material has been mainly described. However, wavelength selectivity such as a wavelength-selective emitter that promotes thermal radiation at a specific wavelength and suppresses thermal radiation at other wavelengths is required. It can be applied to any use.

Claims (4)

A step of preparing an alloy base material capable of two-phase separation by spinodal decomposition when supersaturated solid solution is aged in a two-phase coexistence region;
Aging the alloy base material in a two-phase coexistence region to cause spinodal decomposition, and forming a regularly arranged first phase and a second phase arranged between the first phases; ,
Selectively dissolving and removing the second phase to a predetermined depth to raise the first phase;
A step of physically removing the first phase floating by dissolution and removal of the second phase with ultrasonic waves;
Removing the first phase physically by ultrasonic wave, and then selectively dissolving and removing the first phase on the surface;
A method for producing a wavelength-selective thermal radiation or heat-absorbing material, comprising: After selectively dissolving and removing the first phase on the surface, the surface of the second phase on the surface layer has a melting point higher than that of the second phase of the alloy base material, and is higher than that of the second phase. The method for producing a wavelength-selective thermal radiation or heat absorption material according to claim 1, further comprising a step of coating a metal or alloy having high electrical conductivity, or a noble metal. The metal or alloy having a melting point higher than that of the second phase and higher electrical conductivity than that of the second phase is a metal selected from W, Ta, and Mo or an alloy thereof. The method for producing a wavelength-selective thermal radiation or heat absorption material according to claim 2.   The alloy base material is a nickel-based alloy single crystal that can be separated into two phases of a γ phase (first phase) and a γ 'phase (second phase) by spinodal decomposition. A method for producing a wavelength-selective thermal radiation or heat-absorbing material described in 1.

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