CN113248258B - Silicon carbide-based composite ceramic material with high spectral selectivity and preparation method and application thereof - Google Patents

Abstract

The invention relates to a silicon carbide-based composite ceramic material with high spectral selectivity and a preparation method and application thereof; the silicon carbide-based composite ceramic material has a main phase of SiC and a second phase of TiB ₂ And/or ZrB ₂ (ii) a Preferably, the main phase content is 50vol% to 100vol% in the main phase and the second phase; the second phase content is 0vol% to 50 vol%.

Description

A kind of silicon carbide-based composite ceramic material with high spectral selectivity and its preparation method and application

technical field

The invention relates to a silicon carbide-based composite ceramic material with high spectral selectivity, a preparation method and application thereof, and belongs to the technical field of solar thermal power generation.

Background technique

Energy depletion and environmental pollution in the process of energy utilization are urgent problems for human beings today. As a new type of clean energy, solar energy is inexhaustible and plays a pivotal role in solving the energy crisis.

Solar thermal power generation technology can effectively convert solar energy into electrical energy that can be used by human beings. In this, the heat absorber is the key component of the solar thermal power generation system, which transfers the energy of solar radiation into the heat transfer fluid, which will be used for the thermodynamic cycle to generate electricity. However, due to the serious heat loss in the actual heat transfer process (mainly heat radiation, but also heat conduction and convection), the solar energy received by the absorber is not completely transferred to the heat transfer fluid. Therefore, the development of absorber materials with high solar absorption coefficient α (0.3-2.5 μm) and low thermal emissivity ε (2.5-16 μm) is one of the important problems to be solved in solar thermal power generation technology.

Silicon carbide ceramics have high solar absorption coefficient, high thermal conductivity, good high temperature oxidation resistance, excellent high temperature mechanical properties and other excellent properties, which make them suitable for solar heat absorption materials. However, the high thermal radiation properties of silicon carbide ceramics will absorb energy and dissipate in the form of thermal radiation, which greatly reduces its actual efficiency during use. Therefore, it is of great significance to improve the spectral selectivity α/ε of silicon carbide ceramics.

SUMMARY OF THE INVENTION

In view of the problem that the spectral selectivity of the silicon carbide ceramics mentioned above is too low when applied to solar heat absorbing materials, the present invention provides a silicon carbide composite ceramic material with high spectral selectivity and a preparation method and application thereof.

In a first aspect, the present invention provides a silicon carbide composite ceramic material with high spectral selectivity, wherein the main phase of the silicon carbide-based composite ceramic material is SiC, and the second phase is TiB ₂ and/or ZrB ₂ ; Preferably, in the main phase and the second phase, the content of the main phase is 50vol%-100vol%; the content of the second phase is 0vol%-50vol%.

TiB ₂ and ZrB ₂ were chosen as the second phase materials to tune the spectral selectivity of SiC ceramics because of their extremely low infrared emissivity. When SiC is compounded with it, the advantages of high solar absorptivity, high thermal conductivity, and excellent anti-oxidation properties of SiC and the low infrared emissivity of the second phase can be combined to prepare a high-spectrum selective solar heat absorber with excellent comprehensive properties. Material.

Preferably, the silicon carbide-based multiphase ceramic material further includes a B-C system sintering aid; the content of the main phase and the second phase is 90-96 wt %; the mass ratio of the B-C system sintering aid to the total raw materials is: 4-10wt%, the sum of each component is 100%.

The spectral selectivity of pure solid-phase silicon carbide ceramics is 1.424. When 0<the content of the second phase≤5vol%, because in the 11-13μm band, the emissivity of SiC is extremely low, while the emissivity of TiB ₂ /ZrB ₂ is relatively high, which makes a small amount (0-5vol%) of the first phase After the two-phase recombination, the emissivity of the composite material increases, resulting in a decrease in selectivity. When 5vol% TiB ₂ was incorporated, the spectral selectivity of the multiphase ceramics was 1.403; when 5vol% ZrB ₂ was incorporated, the spectral selectivity of the multiphase ceramics was 1.398, both of which were lower than those of pure solid-phase silicon carbide ceramics. . When 5vol%<the content of the second phase≤50vol%, the spectral selectivity of the multiphase ceramics showed an upward trend. Specifically, when the second phase is TiB ₂ , its spectral selectivity increases from 1.403 to 1.632 with the increase of the dosage; when the second phase is ZrB ₂ , its spectral selectivity increases from 1.398 to 1.549 with the increase of dosage .

Preferably, the spectral selectivity α/ε of the prepared SiC-TiB ₂ multiphase ceramic material is: 1.403-1.632; the spectral selectivity α/ε of the prepared SiC-ZrB ₂ multiphase ceramic material is: 1.398-1.549.

In a second aspect, the present invention provides a method for preparing the above-mentioned silicon carbide composite ceramic material with high spectral selectivity, comprising: adding raw SiC powder, TiB ₂ and/or ZrB ₂ powder, and BC system sintering aid to no Add binder to water ethanol and ball mill to obtain slurry; dry, crush and granulate the obtained slurry to obtain mixed powder; dry the mixed powder to form, and then go through cold isostatic pressing and negative pressure Dewaxing and atmospheric sintering to obtain composite ceramic blocks.

Preferably, the particle size of the SiC powder is 0.5-1 μm; the particle size of the TiB ₂ powder is 1-3 μm; the particle size of the ZrB ₂ powder is 1-3 μm. The finer the particle size of the powder, the more conducive to sintering and densification, which can reduce the content of pores and improve the mechanical properties and thermal conductivity of the sample.

Preferably, in the BC system sintering aid, the B source is at least one of B ₄ C, B powder, and boric acid; the C source is at least one of phenolic resin, fructose, amorphous carbon, and carbon black. kind.

Preferably, the binder is at least one of phenolic resin, PVA and PVB.

Preferably, the ball mill is a planetary ball mill, and the time is 18-24 hours, so that the powder is as uniform and refined as possible, which can promote sintering.

Preferably, the dry pressing pressure is 10-20 MPa, and the pressure holding time is 5-15 seconds.

Preferably, the cold isostatic pressing pressure is 150-250 MPa, and the pressure holding time is 1-3 minutes.

Preferably, the negative pressure dewaxing temperature is 900-1100° C., and the holding time is 0.5-2 hours.

Preferably, the normal pressure sintering temperature is 2000-2200°C, preferably 2100-2200°C; the holding time at the highest temperature point is 0.5-2 hours; the normal pressure sintering atmosphere is an argon atmosphere.

In a third aspect, the present invention provides the application of the above-mentioned silicon carbide composite ceramic material with high spectral selectivity in a solar heat absorber material.

With the increase of the second phase content (>5vol%), the spectral selectivity of the samples showed an upward trend; when the second phase content was the same, the spectral selectivity improvement brought by TiB ₂ was greater than that of ZrB ₂ .

The silicon carbide-based composite ceramic provided by the invention has high solar energy spectral selectivity, and can have the advantages of high thermal conductivity and excellent oxidation resistance inherent in silicon carbide ceramics, and can be used as a solar heat absorber in a solar thermal power generation system. Material use, which goes beyond its inherent scope of use, as structural ceramics. The sintering method adopted in the present invention is a solid-phase atmospheric pressure sintering method, which can realize mass production of products and provide a basis for its practical large-scale application.

Description of drawings

Figure ₁ shows the spectral selectivity of SiC-based composite ceramics with different dosages of TiB and _ZrB .

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

The present invention selects TiB ₂ and ZrB ₂ with low infrared emissivity as the second phase, and adjusts the spectral selectivity of silicon carbide ceramics through solid-phase sintering. And with silicon carbide as the main phase, it can be combined with its inherent excellent properties, such as high thermal conductivity, excellent anti-oxidation properties, etc., so as to prepare a hyperspectral selective solar heat absorber material with excellent comprehensive properties. And the sintering method of atmospheric pressure sintering provides the basis for the mass production of products.

The following exemplifies the method for preparing the silicon carbide-based composite ceramic with high solar energy spectral selectivity provided by the present invention:

Prepare raw materials, mix materials, and ball mill to obtain mixed slurry. According to the formula of hyperspectral selective silicon carbide ceramics, SiC powder, TiB ₂ and/or ZrB ₂ powder are weighed as the main raw material powder, and the BC system raw material is added as a sintering aid. After the above raw materials are weighed, they are mixed into absolute ethanol, a binder is added, and silicon carbide balls are added as a ball milling medium, and the mixed slurry is obtained by ball milling on a planetary ball mill for a period of time. The particle size of the SiC powder may be 0.5-1 μm; the particle size of the TiB ₂ powder may be 1-3 μm; the particle size of the ZrB ₂ powder may be 1-3 μm. The above-mentioned SiC and TiB ₂ /ZrB ₂ main raw material powders can account for 90-96 wt % of the total raw material mass. In this part, the proportion of SiC can be 50 vol % to 100 vol %; the proportion of TiB ₂ /ZrB ₂ can be 0vol%-50vol%. The B source in the sintering aid can be one or more of B ₄ C, B powder and boric acid, and the C source can be one or more of phenolic resin, fructose, amorphous carbon and carbon black. The mass ratio of the above-mentioned BC system sintering aid to the total raw material may be 4-10 wt %. The binder is one or more of phenolic resin, PVA and PVB. The binder is additionally added, and the amount thereof is about 2wt%-10wt% of the mass of the raw material. The mixing time can be 12-24 hours, preferably 18-24 hours, in order to obtain as uniform and refined powder as possible and to promote the sintering process.

The green body samples are obtained through the processes of drying, crushing, granulation, dry pressing and cold isostatic pressing. Wherein, the drying conditions may be drying at 60-100° C. for 12-36 hours. The crushing method can be manual grinding or mechanical crushing. The granulation method can be spray granulation or nylon sieve; the dry pressing pressure can be 10-20MPa, and the pressure holding time can be 5-15 seconds; the cold isostatic pressing pressure can be 150-250MPa, and the pressure holding time can be 1 -3 minutes.

After negative pressure dewaxing and atmospheric pressure sintering, ceramic samples with high solar energy spectrum selectivity were obtained. Among them, the negative pressure dewaxing temperature can be 900-1100 ℃, the maximum temperature holding time can be 0.5-2 hours; the normal pressure sintering temperature can be 2000-2200 ℃, preferably 2100-2200 ℃, the holding time can be 0.5-2 Hour.

The above ceramic sample was processed into a disc with a diameter of 35mm and a thickness of 3mm, and its two sides were ground to be tested for solar absorptivity (α) and thermal emissivity (ε), and the spectral selectivity (α/ε) was calculated. ε).

The test results are: the spectral selectivity of pure solid-phase silicon carbide ceramics is 1.424. When 0<content of the second phase≤5vol%, the spectral selectivity tends to decrease. Because in the 11-13μm band, the emissivity of SiC is extremely low, while the emissivity of TiB ₂ /ZrB ₂ is relatively high, which makes the emissivity of the composite material increase after a small amount (0-5vol%) of the second phase is recombined, thus increasing the emissivity of the composite material. resulting in a decrease in selectivity. When 5vol% TiB ₂ was incorporated, the spectral selectivity of the multiphase ceramics was 1.403; when 5vol% ZrB ₂ was incorporated, the spectral selectivity of the multiphase ceramics was 1.398, both of which were lower than those of pure solid-phase silicon carbide ceramics. . When 5vol%<the content of the second phase≤50vol%, the spectral selectivity of the multiphase ceramics showed an upward trend. Specifically, when the second phase is TiB ₂ , its spectral selectivity increases from 1.403 to 1.632 with the increase of the dosage; when the second phase is ZrB ₂ , its spectral selectivity increases from 1.398 to 1.549 with the increase of dosage .

The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the foregoing content of the present invention belong to the present invention. protected range.

Example 1

Preparation of pure solid-phase sintered silicon carbide ceramics. Weigh 188g SiC powder as raw material, 2g B ₄ C powder as boron source, 4g carbon black as one of carbon sources, and add 20g phenolic resin solution as binder and carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample is 1.424.

Example 2

A silicon carbide-based multiphase ceramic with a second phase of 5 vol% TiB ₂ was prepared. Weigh 150g of SiC powder and 11.1g of TiB ₂ as the main raw material, that is, SiC accounts for 95 vol% and TiB ₂ accounts for 5 vol%. In addition, 1.17g of B ₄ C powder was added as a boron source, 3.43g of carbon black was used as one of the carbon sources, and 17.14g of phenolic resin solution was added as a binder and a carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample is 1.403.

Example 3

The silicon carbide-based composite ceramics with the _second phase of 5vol% ZrB2 were prepared. Weigh 150g of SiC powder and 15.05g of ZrB ₂ as the main raw material, that is, the ratio of SiC to the two is 95vol%, and the proportion of ZrB ₂ is 5vol%. In addition, 1.76g of B ₄ C powder was added as a boron source, 3.51g of carbon black was used as one of the carbon sources, and 17.56g of phenolic resin solution was added as a binder and a carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample was 1.398.

Example 4

A silicon carbide-based multiphase ceramic with a second phase of 15 vol% TiB ₂ was prepared. 135g of SiC powder was weighed, and 33.5g of TiB ₂ was used as the main raw material, that is, SiC accounted for 85 vol% and TiB ₂ accounted for 15 vol%. In addition, 1.79 g of B ₄ C powder was added as a boron source, 3.59 g of carbon black was used as one of the carbon sources, and 17.93 g of phenolic resin solution was added as a binder and a carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample was 1.43.

Example 5

A silicon carbide-based multiphase ceramic with a _second phase of 15 vol% ZrB2 was prepared. Weigh 135g of SiC powder and 45.41g of ZrB ₂ as the main raw material, that is, the ratio of SiC to the two is 85vol%, and that of ZrB ₂ is 15vol%. In addition, 1.92g of B ₄ C powder was added as a boron source, 3.84g of carbon black was used as one of the carbon sources, and 19.19g of phenolic resin solution was added as a binder and a carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample was 1.43.

Example 6

A silicon carbide-based multiphase ceramic with a second phase of 25 vol% TiB ₂ was prepared. Weigh 120g of SiC powder and 56.25g of TiB ₂ as the main raw material, that is, the ratio of SiC to the two is 75vol%, and the proportion of TiB ₂ is 25vol%. In addition, 1.88g of B ₄ C powder was added as a boron source, 3.75g of carbon black was used as one of the carbon sources, and 18.75g of phenolic resin solution was added as a binder and a carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample was 1.499.

Example 7

A silicon carbide-based multiphase ceramic with a second phase of 25 vol% ZrB ₂ was prepared. Weigh 120g of SiC powder and 76.25g of ZrB ₂ as the main raw material, that is, the ratio of SiC to the two is 75vol%, and the proportion of ZrB ₂ is 25vol%. In addition, 2.09 g of B ₄ C powder was added as a boron source, 4.18 g of carbon black was used as one of the carbon sources, and 20.88 g of phenolic resin solution was added as a binder and a carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample is 1.464.

Example 8

A silicon carbide-based multiphase ceramic with a second phase of 35 vol% TiB ₂ was prepared. Weigh 100g of SiC powder and 75.72g of TiB ₂ as the main raw material, that is, the ratio of SiC to the two is 65vol%, and the proportion of TiB ₂ is 35vol%. In addition, 1.87g of B ₄ C powder was added as a boron source, 3.74g of carbon black was used as one of the carbon sources, and 18.69g of phenolic resin solution was added as a binder and a carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample is 1.525.

Example 9

A silicon carbide-based composite ceramic with a second phase of 35 vol% ZrB ₂ was prepared. Weigh 100g of SiC powder, and 102.64g of ZrB ₂ is the main raw material, that is, the ratio of SiC to the two is 65vol%, and the proportion of ZrB ₂ is 35vol%. In addition, 2.16g of B ₄ C powder was added as a boron source, 4.31g of carbon black was used as one of the carbon sources, and 21.56g of phenolic resin solution was added as a binder and a carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample is 1.476.

Example 10

A silicon carbide-based composite ceramic with 50 vol% TiB2 as the _second phase was prepared. 85g of SiC powder was weighed, and 119.53g of TiB ₂ was used as the main raw material, that is, the ratio of SiC to the two was 50vol%, and the proportion of TiB ₂ was 50vol%. In addition, 2.18g of B ₄ C powder was added as a boron source, 4.35g of carbon black was used as one of the carbon sources, and 21.76g of phenolic resin solution was added as a binder and a carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample was 1.632.

Example 11

A silicon carbide-based composite ceramic with a _second phase of 50 vol% ZrB2 was prepared. Weigh 85g of SiC powder and 162.03g of ZrB ₂ as the main raw material, that is, SiC accounts for 50vol% of the two, and ZrB ₂ accounts for 50vol%. In addition, 2.63g of B ₄ C powder was added as a boron source, 5.26g of carbon black was used as one of the carbon sources, and 26.28g of phenolic resin solution was added as a binder and a carbon source to form all the raw materials. All raw materials were added to an appropriate amount of anhydrous ethanol, and ball milled on a planetary ball mill for 24 hours to obtain a mixed slurry. The mixed powder is obtained after drying, crushing, sieving and granulation. The mixed powder was dry-pressed at a pressure of 15 MPa with a holding time of 15 seconds, and then cold isostatically pressed at a pressure of 200 MPa for a holding time of 3 minutes to obtain a green sample. The green sample was kept at 900°C for 0.5 hours for negative pressure dewaxing, and then kept at 2200°C for 1 hour for normal pressure sintering to obtain a ceramic sample. After testing, the calculated spectral selectivity of this sample is 1.549.

Claims (10)

_1. The application of TiB or _ZrB in improving the spectral selectivity of silicon carbide-based composite ceramic materials, wherein the main phase of the silicon carbide-based composite ceramic material is SiC, and the second phase is TiB or _{ZrB 2} ; in the main phase and the second phase, the main phase content is 50vol%-85vol%; the second phase content is 15vol%-50vol%; The spectral selectivity α/ε of the prepared SiC-TiB ₂ multiphase ceramic material is: 1.43-1.632; the spectral selectivity α/ε of the prepared SiC-ZrB ₂ multiphase ceramic material is: 1.43-1.549. 2 . The application of TiB ₂ or ZrB ₂ according to claim 1 in improving the spectral selectivity of silicon carbide-based composite ceramic materials, wherein the silicon carbide-based composite ceramic materials further comprise BC system sintering aids ; The content of the main phase and the second phase is 90-96 wt %; the mass ratio of the BC system sintering aid to the total raw material is 4-10 wt %, and the sum of the contents of each component is 100%. 3. The application of TiB ₂ or ZrB ₂ in improving the spectral selectivity of silicon carbide-based composite ceramic materials according to claim 1, wherein the preparation method of the silicon carbide-based composite ceramic materials comprises: mixing raw materials SiC powder, TiB ₂ or ZrB ₂ powder, and BC system sintering aid are added to anhydrous ethanol, then a binder is added, and the slurry is obtained by ball milling; the obtained slurry is dried, crushed and granulated to obtain a mixed powder ; The mixed powder is formed by dry pressing, and then a composite ceramic block is obtained by cold isostatic pressing, negative pressure dewaxing and normal pressure sintering. 4. The application of TiB ₂ or ZrB ₂ in improving the spectral selectivity of silicon carbide-based composite ceramic materials according to claim 3, wherein the particle size of the SiC powder is 0.5-1 μm; the TiB ₂ The particle size of the powder is 1-3 μm; the particle size of the ZrB ₂ powder is 1-3 μm. 5. The application of TiB ₂ or ZrB ₂ according to claim 3 in improving the spectral selectivity of silicon carbide-based composite ceramic materials, wherein, in the BC system sintering aid, the B source is B ₄ C, At least one of B powder and boric acid; C source is at least one of phenolic resin, fructose, amorphous carbon and carbon black. 6. The application of TiB or _ZrB according to claim ₃ in improving the spectral selectivity of silicon carbide-based composite ceramic materials, wherein the binder is at least one of phenolic resin, PVA, and PVB. kind. 7. The application of TiB ₂ or ZrB ₂ according to claim 3 in improving the spectral selectivity of silicon carbide-based multiphase ceramic materials, wherein the dry pressing pressure is 10-20MPa, and the dwell time is 5 -15 seconds; the cold isostatic pressing pressure is 150-250 MPa, and the holding time is 1-3 minutes. 8 . The application of TiB ₂ or ZrB ₂ according to claim 3 in improving the spectral selectivity of silicon carbide-based multiphase ceramic materials, wherein the negative pressure dewaxing temperature is 900-1100° C., and the holding time is 0.5-2 hours; the normal-pressure sintering temperature is 2000-2200° C.; the holding time at the highest temperature point is 0.5-2 hours; the normal-pressure sintering atmosphere is an argon atmosphere. 9 . The application of TiB ₂ or ZrB ₂ in improving the spectral selectivity of silicon carbide-based multiphase ceramic materials according to claim 8 , wherein the normal pressure sintering temperature is 2100-2200° C. 10 . 10. The application of TiB ₂ or ZrB ₂ in improving the spectral selectivity of silicon carbide-based composite ceramic materials according to claim 1, wherein the silicon carbide-based composite ceramic materials are used in solar heat absorber materials .

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