Ultra-high temperature ceramic hollow microspheres and their preparation method

Abstract

The present invention discloses a method for preparing ultra-high temperature ceramic hollow microspheres, which comprises the following steps: performing solvothermal treatment on a precursor solution containing zirconium silicate solution and phenolic resin to obtain precursor microspheres; and calcining the precursor microspheres in segments to obtain ultra-high temperature ceramic hollow microspheres. The ultra-high temperature ceramic hollow microspheres prepared by the present invention, during high-temperature service, near the phase transition temperature of zirconia, the phase transition of zirconia ceramics occurs, and the microspheres are prone to rupture in a high-temperature thermal shock environment. And the silica softened near this phase transition temperature becomes a buffer medium for volume shrinkage and expansion during the temperature change process, ensuring the integrity of the hollow microspheres. Moreover, the zirconia-silica composite ultra-high temperature ceramic hollow microspheres of the present invention have excellent heat resistance. The components zirconia / silica contained in the coating are common high-temperature oxide systems, and the melting point of zirconia is as high as 2700 °C.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature ceramic materials, and particularly relates to an ultra-high temperature ceramic hollow microsphere and a preparation method thereof. Background Art

[0002] In order to protect the interior of hot-end components from the harm of high-temperature environments and extend their service life, in recent years, the research and development of various high-temperature materials have received increasing attention, especially in the fields of aerospace and aviation aircraft, where the demand for super high-temperature thermal insulation materials is becoming more and more urgent. In recent years, people have continuously developed new low-thermal-conductivity materials.

[0003] Hollow microspheres are a kind of lightweight particulate powder material with a spherical hollow structure, having characteristics such as heat insulation, sound insulation, high strength, corrosion resistance, chemical stability, and excellent dispersibility. Currently, hollow glass microspheres have been widely used in these fields. They are mainly composed of a silicate glass system in terms of chemical composition, and usually, a composition system of alkali metal or alkaline earth metal borosilicate containing several oxide additives is preferably adopted. Therefore, the temperature resistance grade of such hollow glass microspheres is relatively low, and the application range is limited.

[0004] To solve the above problems, researchers have tried to make high-melting-point ceramics into a hollow structure. Chinese Patent Application CN102923771A uses butyl zirconate as the zirconium source, glacial acetic acid as the complexing agent, and ethanol as the solvent, and prepares zirconia hollow microspheres with a particle size of 4 - 6 μm by a solvothermal method. However, the high-temperature phase transformation of zirconia ceramics near 1163 °C is likely to cause the cracking of hollow microspheres, thereby affecting the heat insulation performance in high-temperature environments. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, provide a preparation method of an ultra-high temperature ceramic hollow microsphere, and also correspondingly provide the ultra-high temperature ceramic hollow microsphere prepared by this preparation method, which has excellent heat insulation performance in high-temperature environments.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A preparation method of an ultra-high temperature ceramic hollow microsphere, comprising the following steps:

[0008] Performing solvothermal treatment on a precursor solution containing a zirconium-silicon solution and phenolic resin to obtain precursor microspheres; subjecting the precursor microspheres to staged calcination to obtain ultra-high temperature ceramic hollow microspheres.

[0009] Preferably, the zirconium-silicon solution is a mixture of a metal inorganic salt and an alcohol solution, and the metal inorganic salt includes an inorganic salt containing Zr 4+ and an inorganic salt containing Si 4+Inorganic salts. Considering the high-temperature phase transition of zirconia, an appropriate amount of low-melting-point silica material is added in the present invention to avoid cracking of the microspheres. However, excessive silica will cause a decrease in the temperature resistance of the material. Among the metal inorganic salts, Zr 4+ and Si 4+ The molar ratio is 1:1 to 4.

[0010] Preferably, in the precursor solution, the sum of the moles of Zr 4+ and Si 4+ The molar ratio to phenolic resin is 2 to 6:1. Since phenolic resin can be converted into the load-bearing core of hollow microspheres at high temperature, phenolic resin is introduced here, and the content should not be too high to avoid damaging the microsphere morphology due to violent carbonization reaction.

[0011] Preferably, the temperature of the solvothermal treatment is 150°C to 250°C, and the time of the solvothermal treatment is 5 h to 24 h.

[0012] Preferably, the specific process of the staged calcination is as follows: heating at a heating rate of 1°C / min to 5°C / min to 600°C to 800°C, holding for 1 h to 5 h in a vacuum or inert atmosphere, and then cooling with the furnace; then heating at a heating rate of 10°C / min to 20°C / min to 1000°C to 1500°C, holding for 1 h to 5 h in an air atmosphere, and finally cooling with the furnace. A composite material of spherical oxide-coated carbon spheres is obtained by low-temperature vacuum or inert atmosphere calcination. High-temperature air calcination promotes the sintering of the oxide shell while removing the carbon sphere core.

[0013] Preferably, the inorganic salt containing Zr 4+ is ZrCl 4 , ZrOCl 2 ·8H 2 O or Zr(NO 3 ) 4 ·5H 2 O, and the inorganic salt containing Si 4+ is SiCl 4 .

[0014] Preferably, the alcohol solution is a mixed solution of a chelating agent and an alcohol.

[0015] Preferably, the chelating agent is acetylacetone or a polyhydroxy compound, and the alcohol is one or more of methanol, ethanol, and propanol.

[0016] Preferably, the molar ratio of the metal inorganic salt, the chelating agent and the alcohol is 1∶2-3∶16-36. The hydrolysis-polycondensation process of metal ions in the solution environment must be controlled to obtain a stable solution system. In the present invention, controlling the ratio of the chelating agent to the metal inorganic salt to be 1:2-3 can promote the nucleophilic substitution reaction between the hydroxyl group in the chelating agent and the metal salt, forming a stable coordination intermediate.

[0017] As a general inventive concept, the present invention also provides an ultra-high temperature ceramic hollow microsphere prepared by the above preparation method.

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] 1. For the ultra-high temperature ceramic hollow microspheres prepared by the present invention, it is found during the high-temperature service process that near the phase transition temperature of zirconia, the phase transition of zirconia ceramics occurs, and the microspheres are prone to rupture under high-temperature thermal shock conditions. However, silica that softens near this phase transition temperature becomes a buffer medium for volume shrinkage and expansion during the temperature change process, ensuring the integrity of the hollow microspheres.

[0020] 2. The zirconia-silica composite ultra-high temperature ceramic hollow microspheres of the present invention have excellent heat resistance. The components zirconia / silica contained in the coating are common high-temperature oxide systems, and the melting point of zirconia is as high as 2700 °C.

[0021] 3. The present invention can obtain a series of zirconia-silica composite ultra-high temperature ceramic hollow microspheres with adjustable compositions and structures by adjusting the components and changing the process. The preparation method is simple and the process has obvious advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 SEM image of the zirconia-silica composite ultra-high temperature ceramic hollow microspheres prepared in Example 1;

[0023] Figure 2 XRD pattern of the zirconia-silica composite ultra-high temperature ceramic hollow microspheres prepared in Example 1;

[0024] Figure 3 SEM image of the zirconia-silica composite ultra-high temperature ceramic hollow microspheres prepared in Example 2;

[0025] Figure 4 SEM image of the zirconia-silica composite ultra-high temperature ceramic hollow microspheres prepared in Example 2 after high-temperature assessment. DETAILED DESCRIPTION OF THE INVENTION

[0026] The following further describes the present invention with reference to specific preferred embodiments, but does not limit the protection scope of the present invention thereby.

[0027] Example 1:

[0028] First, add 1 part of ZrCl 4 and 1 part of SiCl 4 to 4 parts of acetylacetone solution, and then add 40 parts of ethanol and stir well to obtain a zirconium-silicon solution; then dissolve 0.5 part of phenolic resin in 10 parts of ethanol; next, mix the zirconium-silicon solution and the phenolic resin solution, perform solvothermal treatment at 150 °C for 24 h, and then dry the product at 80 °C for 6 h to obtain precursor microspheres; calcine the precursor microspheres in stages, first heat up to 800 °C at a heating rate of 5 °C / min, keep the temperature for 5 h in a vacuum or inert atmosphere, and then cool down with the furnace to obtain an intermediate product; then heat up to 1500 °C at a heating rate of 20 °C / min, keep the temperature for 1 h in an air atmosphere, and finally cool down with the furnace to obtain zirconia-silica composite ultra-high temperature ceramic hollow microspheres.

[0029] The zirconia-silica composite ultra-high temperature ceramic hollow microspheres obtained in this example have a density of 0.46 g / cm 3 , and their microscopic morphology is as shown in Figure 1 . The surface is smooth and dense, and the XRD analysis pattern is as shown in Figure 2 , showing the diffraction peaks of the phases zirconia and silica.

[0030] Example 2:

[0031] First, add 4 parts of ZrCl 4 and 1 part of SiCl 4 to 15 parts of acetylacetone solution, and then add 80 parts of ethanol and stir well to obtain a zirconium-silicon solution; then dissolve 1 part of phenolic resin in 10 parts of ethanol; next, mix the zirconium-silicon solution and the phenolic resin solution, perform solvothermal treatment at 250 °C for 5 h, and then dry the product at 80 °C for 10 h to obtain precursor microspheres; calcine the precursor microspheres in stages, first heat up to 600 °C at a heating rate of 1 °C / min, keep the temperature for 2 h in a vacuum or inert atmosphere, and then cool down with the furnace to obtain an intermediate product; then heat up to 1000 °C at a heating rate of 10 °C / min, keep the temperature for 5 h in an air atmosphere, and finally cool down with the furnace to obtain zirconia-silica composite ultra-high temperature ceramic hollow microspheres, as shown in Figure 3 , and their density is 0.72 g / cm 3 . After 1 min of high-temperature static assessment at 2000 °C, the surface is smooth and there is no cracking phenomenon, as shown in Figure 4 .

[0032] The above are only the preferred embodiments of the present application and do not impose any form of limitation on the present application. Although the present application is disclosed as above with the preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the scope of the technical solution of the present application, makes some changes or modifications using the technical content disclosed above, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A preparation method of ultra-high temperature ceramic hollow microspheres, characterized in that, it comprises the following steps: Performing solvothermal treatment on a precursor solution containing zirconium silicate solution and phenolic resin to obtain precursor microspheres; Calcining the precursor microspheres in stages to obtain ultra-high temperature ceramic hollow microspheres; The zirconium silicate solution is a mixture of a metal inorganic salt and an alcohol solution. The metal inorganic salt includes an inorganic salt containing Zr 4+ and an inorganic salt containing Si 4+ . In the metal inorganic salt, the molar ratio of Zr 4+ to Si 4+ is 1:1 or 4:1; In the precursor solution, Zr 4+ and Si 4+ The molar sum of and phenolic resin is in a molar ratio of 2 to 6:1; The specific process of the staged calcination is as follows: The temperature is raised to 600 °C to 800 °C at a heating rate of 1 °C / min to 5 °C / min, and kept warm for 1 h to 5 h under vacuum or inert atmosphere, and then cooled with the furnace; Then the temperature is raised to 1000 °C to 1500 °C at a heating rate of 10 °C / min to 20 °C / min, and kept warm for 1 h to 5 h in an air atmosphere, and finally cooled with the furnace; The Zr-containing 4+ inorganic salt is ZrCl 4 , ZrOCl 2 ∙8H 2 O or Zr(NO 3 ) 4 ∙5H 2 O, and the Si-containing 4+ inorganic salt is SiCl 4 ; The alcohol solution is a mixed solution of a chelating agent and an alcohol.

2. The preparation method of ultra-high temperature ceramic hollow microspheres according to claim 1, characterized in that, the temperature of the solvothermal treatment is 150°C to 250°C, and the time of the solvothermal treatment is 5h to 24h.

3. The preparation method of ultra-high temperature ceramic hollow microspheres according to claim 1, characterized in that, the chelating agent is acetylacetone or a polyhydroxy compound, and the alcohol is one or more of methanol, ethanol and propanol.

4. The preparation method of ultra-high temperature ceramic hollow microspheres according to claim 3, characterized in that, the molar ratio of the metal inorganic salt, the chelating agent and the alcohol is 1∶2-3∶16-36.

5. Ultra-high temperature ceramic hollow microspheres prepared by the preparation method according to any one of claims 1-4.

Images