A method for preparing a low-density zirconium diboride-silicon carbide foam ceramic material

Abstract

The application relates to a preparation method of a low-density zirconium diboride-silicon carbide foam ceramic material and belongs to the technical field of foam ceramic preparation. The application aims at solving the problems of forming difficulty and sintering shrinkage of the zirconium diboride-silicon carbide foam ceramic. The preparation method is simple. The silicon carbide template prepared by impregnating a ceramic impregnation solution under vacuum conditions is dried and sintered in subsequent steps, and finally, the low-density zirconium diboride-silicon carbide foam ceramic is obtained. The low-density zirconium diboride-silicon carbide foam ceramic material prepared by the application has the characteristics of uniform structure, nanometer-level grains and excellent mechanical properties, and has a good application prospect in the high-temperature heat insulation field.

Description

Technical Field

[0001] This invention belongs to the field of foam ceramic preparation technology, specifically relating to a method for preparing low-density zirconium diboride-silicon carbide foam ceramic material. Background Technology

[0002] Compared to conventional aircraft, hypersonic vehicles fly at much higher speeds (greater than Mach 5) and have a wider flight range (20–100 km). With continuous advancements in science and technology, hypersonic vehicles are evolving towards longer endurance, longer range, and higher Mach numbers. During flight, due to the increasing flight time and speed, hypersonic vehicles face high-temperature environments of 1600°C, and even up to 3000°C. The thermal impact at high speeds causes ablation and deformation of the vehicle's exterior, and can even damage internal electronic components, severely impacting safe operation. The ever-increasing Mach numbers of hypersonic vehicles place higher demands on their thermal protection systems, requiring them to be lighter, more heat-resistant, more thermally insulated, more stable, lower in cost, and have shorter manufacturing cycles.

[0003] Materials meeting service temperatures above 2500℃ include zirconium diboride-silicon carbide ultra-high temperature ceramics, refractory metals, and C / C composites. Refractory metals possess high melting points, high hardness, and ease of processing; however, their high density and susceptibility to oxidation make them unsuitable for hypersonic vehicle thermal protection systems. C / C composites typically have lower density and good mechanical properties, and are currently widely used in thermal protection systems. However, C / C composites generally have complex manufacturing processes, and under high-temperature aerodynamic loads, oxidation and ablation occur, leading to performance degradation and affecting reusability. Zirconium diboride-silicon carbide ultra-high temperature ceramics, with their extremely high melting points (above 3000℃) and good high-temperature stability, are considered highly promising thermal protection materials for hypersonic vehicles.

[0004] However, low-density zirconium diboride-silicon carbide foam ceramics currently face challenges in molding and sintering shrinkage, posing a challenge to the synthesis of zirconium diboride-silicon carbide foam ceramics with high porosity and excellent properties. Wang et al. achieved a minimum density of 0.82 g / cm³ for zirconium diboride-silicon carbide foam ceramics prepared using a partial sintering method. 3 The lowest density of the zirconium diboride-silicon carbide foam ceramic prepared by Chen et al. using the in-situ boron-carbothermic reduction reaction was 1.38 g / cm³. 3 Zhang et al. prepared zirconium diboride-silicon carbide foam ceramics using a foaming method, achieving a minimum density of 0.54 g / cm³. 3Currently prepared zirconium diboride-silicon carbide foam ceramic materials still suffer from high density, failing to meet the demand for lightweight thermal protection materials. Therefore, a novel preparation method is designed to produce low-density, high-phase-purity zirconium diboride-silicon carbide foam ceramics with a three-dimensional network structure, meeting the needs of high-temperature thermal protection applications. Summary of the Invention

[0005] This invention provides a method for preparing low-density zirconium diboride-silicon carbide foam ceramic material to solve the problems of molding difficulties and sintering shrinkage faced by zirconium diboride-silicon carbide foam ceramics. The invention first utilizes tetraethyl orthosilicate and linear phenolic resin to form a hybrid gel, which is then carbonized into a porous silicon carbide material. A zirconium-containing ceramic impregnation solution is then impregnated into a porous silicon carbide template, and the low-density zirconium diboride-silicon carbide foam ceramic is obtained through drying and sintering steps.

[0006] The present invention discloses a method for preparing a low-density zirconium diboride-silicon carbide foam ceramic material, the method comprising the following steps:

[0007] Step 1: At room temperature, add linear phenolic resin, hexamethylenetetramine and tetraethyl orthosilicate to ethanol and dissolve them completely by magnetic stirring; form a gel in a water bath and dry it at room temperature until the mass does not change, to obtain a dry gel; carbonize the dry gel and then take it out to obtain a porous silicon carbide template material.

[0008] Step 2: Dissolve ZrOCl2·8H2O, H3BO3, and sucrose in a solvent composed of ethylene glycol and H2O to obtain an impregnation solution; wherein the molar ratio of ZrOCl2·8H2O, H3BO3, and sucrose is 1:3~5:4~6; after aging the impregnation solution, immerse the porous silicon carbide template material obtained in Step 1 in the impregnation solution, evacuate it, depressurize and remove it, impregnate it, and dry it thoroughly until the quality no longer changes.

[0009] Step 3: Place the dried sample from Step 2 into a tube furnace for sintering, and cool it to room temperature with the furnace to obtain zirconium diboride-silicon carbide foam ceramic material.

[0010] Furthermore, the concentration of linear phenolic resin added in step one is 0.1 g / mL to 2 g / mL, the concentration of hexamethylenetetramine is 0.01 g / mL to 0.2 g / mL, and the concentration range of tetraethyl orthosilicate is 0.2 g / mL to 4 g / mL.

[0011] Furthermore, the gelation temperature in step one is 60℃~80℃, and the carbonization conditions are: heating to 1300~1500℃ at a heating rate of 1~10℃ / min and holding at that temperature for 2h.

[0012] Furthermore, the ratio of ethylene glycol to H2O in step two is 1:1 to 1:5.

[0013] Furthermore, in step two, a vacuum is drawn to 10000 Pa and maintained for 30 minutes. After depressurization, the sample is removed and impregnated twice. Then, it is dried at 80°C.

[0014] Furthermore, the drying temperature described in step two is 80°C.

[0015] Furthermore, the molar ratio of ZrOCl2·8H2O, H3BO3, and sucrose in step two is 1:4:5.

[0016] Furthermore, the concentration of ZrOCl2·8H2O added in step two is 0.3 g / mL to 1.5 g / mL.

[0017] Furthermore, the sintering conditions described in step three are as follows: heating from room temperature to 800–1200°C at a heating rate of 1–10°C / min and holding at that temperature for 0.5–1 h; heating to 1300–1700°C at a heating rate of 1–5°C / min and holding at that temperature for 2–4 h.

[0018] Furthermore, the low-density zirconium diboride-silicon carbide foam ceramic material has a mesh pore size of 1–5 μm and a density of 0.3–0.5 g / cm³. 3 .

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0020] (1) This invention utilizes tetraethyl orthosilicate and linear phenolic resin to form a hybrid gel, which is then carbonized to form a silicon carbide template. Subsequently, zirconium diboride material is generated in situ on the template through impregnation, drying, and sintering, ultimately forming a zirconium diboride-silicon carbide foam ceramic material. The linear phenolic resin, as a reaction raw material for the template, forms a gel with tetraethyl orthosilicate, which can meet the requirements for preparing low-density Si gel under normal pressure drying conditions.

[0021] (2) The zirconium diboride-silicon carbide foam ceramic material described in this invention has a micron-level pore structure and a nano-level grain size. The uniform network structure is beneficial to the mechanical properties of the foam ceramic material, enabling it to meet the load-bearing capacity of high-temperature thermal protection materials and has good application prospects for high-temperature thermal protection. Attached Figure Description

[0022] Figure 1 The image shows the XRD pattern of the silicon carbide template in Example 1.

[0023] Figure 2 Here is a SEM image of the silicon carbide template in Example 1;

[0024] Figure 3EDS image of the silicon carbide template in Example 1;

[0025] Figure 4 The image shows the XRD pattern of the zirconium diboride-silicon carbide foam ceramic in Example 1.

[0026] Figure 5 The image shows a SEM image of the zirconium diboride-silicon carbide foam ceramic in Example 1. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the spirit of the contents disclosed in the present invention will be described in detail below. After understanding the embodiments of the present invention, any person skilled in the art can make changes and modifications based on the technology taught in the present invention without departing from the spirit and scope of the present invention.

[0028] The illustrative embodiments and descriptions of the present invention are used to explain the present invention, but are not intended to limit the present invention.

[0029] Example 1: A method for preparing a low-density zirconium diboride-silicon carbide foam ceramic material, the specific operation is as follows:

[0030] At room temperature, 1 g of linear phenolic resin, 0.01 g of hexamethylenetetramine, and 0.2 g of tetraethyl orthosilicate were added to 10 mL of ethanol solvent. The mixture was thoroughly dissolved by magnetic stirring and transferred to a sealed bottle. A gel was formed in the sealed bottle under an 80°C water bath. After 48 hours of gelation, the gel was dried at room temperature until it no longer changed in mass, forming a dry gel. The dry gel was then carbonized in a tube furnace, heated to 1400°C at a rate of 4°C / min, and held at this temperature for 2 hours to obtain a porous silicon carbide template material.

[0031] Dissolve 3g of ZrOCl2·8H2O, 2.3g of H3BO3, and 1.3g of sucrose in a solvent consisting of 5mL of ethylene glycol and 5mL of H2O. Stir magnetically until fully dissolved to form a ceramic impregnation solution. Immerse the silicon carbide template in the impregnation solution, evacuate to 10000MPa, and maintain this pressure for 30 minutes. Release the pressure and remove the template. Repeat the impregnation process twice. Then, dry the template at 80℃ until its quality no longer changes.

[0032] The dried sample was placed in a tube furnace for sintering. The sintering process was as follows: the temperature was increased from room temperature to 1000℃ at 5℃ / min and held for 0.5h; then the temperature was increased to 1500℃ at 2℃ / min and held for 2h. After that, the sample was cooled to room temperature in the furnace to obtain zirconium diboride-silicon carbide foam ceramic material.

[0033] The XRD image of the prepared silicon carbide template is as follows Figure 1As shown in the image, the phase after carbonization of the dry gel is silicon carbide.

[0034] SEM images of the prepared silicon carbide template are as follows: Figure 2 As shown in the image, the silicon carbide template is composed of nanoscale silicon carbide grains, exhibiting a uniform porous structure with pores distributed below 5 μm.

[0035] EDS image of the prepared silicon carbide template as follows Figure 3 As shown in the image, the carbonization process was quite thorough, and the raw materials underwent a carbothermal reduction reaction to produce silicon carbide with high purity.

[0036] The XRD image of the prepared zirconium diboride-silicon carbide foam ceramic is as follows: Figure 4 As shown in the image, the sintered phase is zirconium diboride-silicon carbide, with no impurity phases present.

[0037] SEM images of the prepared zirconium diboride-silicon carbide foam ceramics are as follows: Figure 5 As shown in the image, the prepared zirconium diboride-silicon carbide foam ceramic exhibits a uniform network structure with pore sizes ranging from 1 to 5 μm. The density of the generated zirconium diboride-silicon carbide foam ceramic is measured to be only 0.35 g / cm³. 3 .

[0038] Example 2: A method for preparing a low-density zirconium diboride-silicon carbide foam ceramic material, the specific operation is as follows:

[0039] At room temperature, 2 g of linear phenolic resin, 0.02 g of hexamethylenetetramine, and 2 g of tetraethyl orthosilicate were added to 10 mL of ethanol solvent. The mixture was thoroughly dissolved by magnetic stirring and transferred to a sealed bottle. A gel was formed in the sealed bottle under an 80°C water bath. After 48 hours of gelation, the gel was dried at room temperature until it no longer changed in mass, forming a dry gel. The dry gel was then carbonized in a tube furnace, heated to 1400°C at a rate of 4°C / min, and held at this temperature for 2 hours to obtain a porous silicon carbide template material.

[0040] Dissolve 6g of ZrOCl2·8H2O, 4.6g of H3BO3, and 2.6g of sucrose in a solvent consisting of 5mL of ethylene glycol and 5mL of H2O. Stir magnetically until fully dissolved to form a ceramic impregnation solution. Immerse the silicon carbide template in the impregnation solution, evacuate to 10000Pa, and maintain this vacuum for 30 minutes. Release the pressure and remove the template. Repeat the impregnation process twice. Then, dry the template at 80℃ until its quality no longer changes.

[0041] The dried sample was placed in a tube furnace for sintering. The sintering regime was as follows: the temperature was increased from room temperature to 1000℃ at a rate of 5℃ / min and held for 0.5 h; then the temperature was increased to 1500℃ at a rate of 2℃ / min and held for 3 h. After sintering, the sample was cooled to room temperature in the furnace to obtain zirconium diboride-silicon carbide foam ceramic material with a density of 0.5 g / cm³. 3 The pore size is below 2 μm.

Claims

1. A method for preparing a low-density zirconium diboride-silicon carbide foam ceramic material, characterized in that... The method includes the following steps: Step 1: At room temperature, add linear phenolic resin, hexamethylenetetramine, and tetraethyl orthosilicate to ethanol and stir magnetically until fully dissolved; form a gel in a water bath and dry at room temperature until the mass does not change, to obtain a dry gel. The dried gel was carbonized and then removed to obtain a porous silicon carbide template material. The concentration of the added linear phenolic resin was 0.1 g / mL to 2 g / mL, the concentration of hexamethylenetetramine was 0.01 g / mL to 0.2 g / mL, and the concentration of tetraethyl orthosilicate was 0.2 g / mL to 4 g / mL. The gelation temperature was 60℃ to 80℃, and the carbonization conditions were: heating to 1300 to 1500℃ at a heating rate of 1 to 10℃ / min and holding at that temperature for 2 hours. Step 2: Dissolve ZrOCl2·8H2O, H3BO3, and sucrose in a solvent composed of ethylene glycol and H2O to obtain an impregnation solution; wherein the molar ratio of ZrOCl2·8H2O, H3BO3, and sucrose is 1:3~5:4~6; after aging the impregnation solution, immerse the porous silicon carbide template material obtained in Step 1 in the impregnation solution, evacuate it, depressurize and remove it, impregnate it, and dry it thoroughly until the quality no longer changes. Step 3: Place the dried sample from Step 2 into a tube furnace for sintering, and cool it to room temperature with the furnace to obtain zirconium diboride-silicon carbide foam ceramic material. The sintering conditions are as follows: heating from room temperature to 800-1200℃ at a heating rate of 1-10℃ / min, holding at that temperature for 0.5-1 h; and heating to 1300-1700℃ at a heating rate of 1-5℃ / min, holding at that temperature for 2-4 h. The low-density zirconium diboride-silicon carbide foam ceramic material has a mesh pore size of 1-5 μm and a density of 0.3-0.5 g / cm³. 3 .

2. The method for preparing a low-density zirconium diboride-silicon carbide foam ceramic material according to claim 1, characterized in that... The ratio of ethylene glycol to H2O in step two is 1:1 to 1:

5.

3. The method for preparing a low-density zirconium diboride-silicon carbide foam ceramic material according to claim 1, characterized in that... In step two, a vacuum of 10,000 Pa is drawn and maintained for 30 minutes. After depressurization, the sample is removed and impregnated twice. Then, it is dried at 80°C.

4. The method for preparing a low-density zirconium diboride-silicon carbide foam ceramic material according to claim 1, characterized in that... The drying temperature described in step two is 80°C.

5. The method for preparing a low-density zirconium diboride-silicon carbide foam ceramic material according to claim 1, characterized in that... The molar ratio of ZrOCl2·8H2O, H3BO3 and sucrose in step two is 1:4:

5.

6. A method for preparing a low-density zirconium diboride-silicon carbide foam ceramic material according to claim 1 or 5, characterized in that... The concentration of ZrOCl2·8H2O added in step two is 0.3 g / mL to 1.5 g / mL.

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