Silicon carbide foam ceramic and preparation method and application thereof

Abstract

The application discloses a silicon carbide foam ceramic and a preparation method and application thereof, and the preparation raw material of the silicon carbide foam ceramic is calculated according to 100% in mass percentage, and the preparation raw material comprises 15-85wt% of liquid ceramic precursor of a structural unit shown in formula (I), 2ppm-2.0wt% of a curing initiator, and 14-85wt% of a filler; and the preparation raw material further comprises a microsphere foaming agent, and the content of the microsphere foaming agent is 9-45wt% of the total amount of the liquid ceramic precursor, the curing initiator and the filler. The silicon carbide foam ceramic has a closed pore structure, low relative density, high porosity, good thermal stability, high compressive strength, can be sintered at a low temperature, good oxidation resistance, and still has high compressive strength after being oxidized at 1400 DEG C for 10h.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a silicon carbide foam ceramic, its preparation method, and its application. Background Technology

[0002] Foam ceramics, due to their high specific surface area, low relative density, high wear resistance, and thermal shock resistance, have been widely used in aerospace, energy, chemical, environmental protection, and biological fields. Among them, silicon carbide foam ceramics, with their excellent high-temperature resistance, corrosion resistance, and oxidation resistance, have attracted researchers' attention and development efforts in many fields, especially in high-temperature thermal protection systems.

[0003] Slurry processing, as a conventional method for preparing silicon carbide ceramics, is characterized by simple processing conditions and the ability to fabricate complex-shaped components. Based on the composition of the silicon carbide slurry, slurries can be divided into three main categories: non-polymer slurries, ordinary organic polymer slurries, and ceramic precursor slurries. Non-polymer slurries and ordinary organic polymer slurries generally use deionized water or organic solvents as dispersion media and high-molecular-weight polymers (such as polyethylene glycol) or cross-linking polymers (such as acrylamide and methylene acrylamide) as binders. The slurry is shaped by drying or initiating polymer cross-linking to obtain ceramic preforms. Although the preparation of silicon carbide ceramics using these two types of slurries is a fairly mature process, it still faces challenges such as low ceramic yield and cumbersome post-processing procedures (requiring deesterification).

[0004] Against this backdrop, organic polymer ceramic precursor slurries, as a newly developed type of slurry, have gained increasing favor among researchers. Ordinary organic polymer slurries almost completely degrade (deesterify) after pyrolysis, thus primarily serving only a binding and shaping function. In contrast, the organic polymer precursors in ceramic precursor slurries, besides acting as binders and shapers, can be transformed into matrix ceramic materials with high yield during pyrolysis, undergoing a transformation from organic polymers to inorganic materials and from amorphous structures to crystalline ceramics. Therefore, using precursors to prepare slurries not only simplifies production steps and increases overall ceramic yield but also lowers sintering temperatures, reducing or eliminating the need for sintering aids, thereby lowering overall costs and improving the overall performance of ceramic components. Furthermore, adding inert or active fillers to the precursors can reduce the likelihood of cracking in the ceramic green body during pyrolysis and decrease shrinkage. Therefore, precursor slurries have become a good choice for preparing ceramic components. However, common silicon carbide precursor slurries are prepared using solid polycarbosilane solutions. Solid polycarbosilanes require a large amount of solvent for dissolution during use, which limits the ceramic yield; the pyrolysis products are also carbon-rich, affecting material properties. In recent years, novel high-performance liquid silicon carbide ceramic precursors with low viscosity, high ceramic yield, and a moderately adjustable carbon-silicon ratio have overcome the above-mentioned shortcomings of solid silicon carbide precursors. These novel liquid precursors and their slurry systems have been increasingly widely used in silicon carbide-based composite materials, ceramic coatings, and high-temperature adhesives. However, their application research and development in porous foam ceramics is still in its early stages, and their potential remains to be explored and utilized.

[0005] In the preparation of porous ceramics, using a properly proportioned slurry can not only improve the ceramic yield but also effectively reduce shrinkage and defects generated during pyrolysis, resulting in uniform components with crack-free surfaces. The slurry method for preparing porous ceramics is often combined with molding methods such as the replication template method, direct foaming method, and sacrificial template method to obtain foam ceramics with different pore shapes, porosities, and relative densities. Samples prepared using the replication template method, especially using polyurethane foam as a template, have low density and good connectivity; however, the pore supports will form cavities or cracks during pyrolysis due to the decomposition of polyurethane, affecting mechanical strength. While the conventional direct foaming method using slurries is simple and convenient, it cannot precisely control pore size distribution, porosity, and pore shape, affecting the regularity of the foam ceramic structure and adversely impacting mechanical strength. The pore distribution of samples prepared using the sacrificial template method is related to the dispersion of the pore-forming agent in the slurry; therefore, the selection of the amount and type of sacrificial template is crucial to the quality of the finished product. Currently, research on the preparation of foam ceramics using precursor slurries is limited, and the technology still needs further development.

[0006] According to the Gibson-Ashby equation, foam ceramic samples with low relative density and high porosity exhibit relatively poor compressive strength, and silicon carbide foam ceramics require certain oxidation resistance and mechanical strength to be used as thermal protection layers. Therefore, the technology for preparing a foam ceramic with high porosity, low relative density, high compressive strength, and high oxidation resistance using liquid ceramic precursor slurry remains to be developed. Summary of the Invention

[0007] In order to improve the above-mentioned technical problems, the present invention aims to provide a silicon carbide foam ceramic, its preparation method and application. The silicon carbide foam ceramic of the present invention has the characteristics of relatively simple preparation process, high porosity and high compressive strength, and can still maintain high compressive strength after high temperature oxidation.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A silicon carbide foam ceramic, wherein the raw materials for preparing the silicon carbide foam ceramic, by weight percentage (100%), comprise:

[0010] The liquid ceramic precursor of the structural unit shown in Formula (I) is 15-85 wt%, the curing initiator is 2 ppm-2.0 wt%, and the filler is 14-85 wt%.

[0011]

[0012] Wherein, X is -CH=CH2, -C≡CH, or -CH2-CH=CH2; x = 0 to 0.3, preferably 0.1 to 0.2;

[0013] R1 and R2 may be the same or different, and are independently selected from H, C1-C 10 One of alkyl groups or -C6H5, y = 0 to 0.9, preferably 0.3 to 0.9; and x and y are not both 0;

[0014] The raw materials also include a microsphere foaming agent, the content of which is 9 to 45 wt% of the total amount of the liquid ceramic precursor, curing initiator and filler.

[0015] For example, y can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9.

[0016] According to embodiments of the present invention, the content of the microsphere foaming agent is exemplary to be 9 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, or 45 wt%.

[0017] According to an embodiment of the present invention, the viscosity of the liquid ceramic precursor is less than 200 mPa·s, preferably 20-80 mPa·s. The ceramic yield of the liquid ceramic precursor is higher than 72%, preferably higher than 80%. Preferably, the liquid ceramic precursor is a polymer silicon carbide ceramic precursor.

[0018] According to an embodiment of the present invention, R1 and R2 may be the same or different, and are independently selected from H and C. 1-4 Alkyl or -C6H5, R1 and R2 are further preferably H or Me.

[0019] According to an embodiment of the present invention, the filler comprises silicon carbide micro powder, and further comprises at least one selected from silicon micro powder, zirconium silicide micro powder, zirconium dioxide micro powder, zirconium boride, alumina micro powder, hafnium silicide micro powder, zirconium micro powder, aluminum micro powder, and boron micro powder.

[0020] According to an embodiment of the present invention, the filler may include 14-68 wt% silicon carbide micro powder, 0-10 wt% silicon micro powder, 0-50 wt% zirconium silicide micro powder, 0-50 wt% zirconium dioxide micro powder, 0-50 wt% zirconium boride, 0-50 wt% alumina micro powder, 0-50 wt% hafnium silicide micro powder, 0-10 wt% zirconium micro powder, 0-5 wt% aluminum micro powder, and 0-5 wt% boron micro powder.

[0021] According to an embodiment of the present invention, the silicon carbide micro powder is β-SiC micro powder with a median particle size of 0.5–50 μm, preferably 0.5–10 μm, and more preferably 0.5–5 μm. For example, the content of the silicon carbide micro powder is 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, or 68 wt%.

[0022] According to an embodiment of the present invention, the median particle size of the silicon micropowder is 0.5–50 μm, preferably 0.5–10 μm, and more preferably 0.5–5 μm. For example, the content of the silicon micropowder is 0, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%.

[0023] According to an embodiment of the present invention, the median particle size of the boron micropowder is 0.5–20 μm, preferably 0.5–10 μm, and more preferably 0.5–5 μm. For example, the content of the boron micropowder is 0, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0024] According to an embodiment of the present invention, the median particle size of the zirconium dioxide micropowder is 0.2–20 μm, preferably 0.2–10 μm, and more preferably 0.2–5 μm. For example, the content of the zirconium dioxide micropowder is 0, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%.

[0025] According to an embodiment of the present invention, the median particle size of the hafnium silicide micropowder is 0.2–20 μm, preferably 0.2–10 μm, and more preferably 0.2–5 μm. For example, the content of the hafnium silicide micropowder is 0, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%.

[0026] According to an embodiment of the present invention, the median particle size of the alumina micro powder is 0.2–50 μm, preferably 0.2–10 μm, and more preferably 0.5–5 μm. For example, the content of the alumina micro powder is 0, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%.

[0027] According to an embodiment of the present invention, the median particle size of the zirconium silicide micropowder is 0.2–50 μm, preferably 0.2–10 μm, and more preferably 0.5–5 μm. For example, the content of the zirconium silicide micropowder is 0, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%.

[0028] According to an embodiment of the present invention, the median particle size of the zirconium boride micropowder is 0.5–20 μm, preferably 0.5–10 μm, and more preferably 0.5–5 μm. For example, the content of the zirconium boride micropowder is 0, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, or 50 wt%.

[0029] According to an embodiment of the present invention, the median particle size of the zirconium micropowder is 0.5–50 μm, preferably 0.5–10 μm, and more preferably 0.5–5 μm. For example, the content of the zirconium micropowder is 0, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%.

[0030] According to an embodiment of the present invention, the median particle size of the aluminum micropowder is 0.5–50 μm, preferably 0.5–10 μm, and more preferably 0.5–5 μm. For example, the content of the aluminum micropowder is 0, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0031] According to an embodiment of the present invention, the raw materials for preparing the silicon carbide foam ceramic include: 15-85 wt% liquid ceramic precursor, 14-68 wt% silicon carbide micro powder, 0-10 wt% silicon micro powder, 0-5 wt% boron micro powder, 0-50 wt% zirconium silicide micro powder, 0-50 wt% zirconium dioxide micro powder, 0-50 wt% zirconium boride micro powder, 0-50 wt% alumina micro powder, 0-50 wt% hafnium silicide micro powder, 0-10 wt% zirconium micro powder, 0-5 wt% aluminum micro powder, and 2 ppm-2.0 wt% curing initiator.

[0032] More preferably, the raw materials for preparing the silicon carbide foam ceramic include: 34.5-50 wt% of liquid ceramic precursor of the structural unit shown in formula (I), 20-65 wt% of silicon carbide micro powder, 1-10 wt% of silicon micro powder, 1-5 wt% of boron micro powder, 0-40 wt% of zirconium silicide micro powder, 0-40 wt% of zirconium dioxide micro powder, 0-40 wt% of zirconium boride micro powder, 0-40 wt% of alumina micro powder, 0-40 wt% of hafnium silicide micro powder, 0-5 wt% of zirconium micro powder, 0-3 wt% of aluminum micro powder, and 20 ppm-0.5 wt% of curing initiator;

[0033] The raw materials also include a microsphere foaming agent, the content of which is 9 to 43.5 wt% of the total amount of the liquid ceramic precursor, curing initiator and filler.

[0034] According to an embodiment of the present invention, the expansion start temperature of the microsphere foaming agent is higher than 100°C and the end temperature is lower than 200°C; preferably, it is the DU series of Nouryon Expansion microsphere foaming agent (expanding agent). It should be noted that microsphere foaming agents produced by other manufacturers with similar principles should also be included in the protection. More preferably, at least one of 053DU40, 051DU40, 043DU80, 920DU20, 920DU40, and 909DU80 is preferred, and particularly preferably 920DU40 and 909DU80.

[0035] According to an embodiment of the present invention, the curing initiator may be selected from, but is not limited to, at least one of a platinum catalyst (including a caster catalyst), dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, and azobisisobutyronitrile.

[0036] According to an embodiment of the present invention, the porosity of the silicon carbide foam ceramic is 80-95%, for example, 80%, 82%, 85%, 88%, 90%, 92%, 94%, or 95%.

[0037] According to an embodiment of the present invention, the relative density of the silicon carbide foam ceramic is 0.05 to 0.20.

[0038] According to an embodiment of the present invention, the compressive strength of the silicon carbide foam ceramic is 1.9 to 4.5 MPa.

[0039] According to an embodiment of the present invention, the compressive strength retention rate of the silicon carbide foam ceramic after oxidation at 1200-1500℃ is 40% to 80%, for example, 40%, 50%, 60%, 70%, or 80%.

[0040] The present invention also provides a method for preparing the above-mentioned silicon carbide foam ceramic, the method comprising the following steps:

[0041] (1) Preparation of slurry: The liquid ceramic precursor, curing initiator, filler and microsphere foaming agent of the structural unit shown in formula (I) are mixed to prepare slurry;

[0042] (2) The slurry in step (1) is foamed and thermally cured to obtain a ceramic preform;

[0043] (3) The ceramic preform obtained in step (2) is pyrolyzed under an inert atmosphere to obtain silicon carbide foam ceramic.

[0044] According to an embodiment of the present invention, in step (1), the viscosity of the slurry is 0.2 to 4.5 Pa·s, preferably 0.6 to 3.7 Pa·s.

[0045] According to an embodiment of the present invention, in step (1), the mixing method can be any one of magnetic stirring, mechanical stirring, vibration, or ball milling.

[0046] According to an embodiment of the present invention, in step (1), the prepared slurry may also be aged; the aging method of the slurry is standing and / or heating treatment, wherein the standing time is preferably 1 to 10 days, more preferably 3 to 7 days; the heating temperature is 40 to 110°C, preferably 50 to 90°C, and the heating time is 0.5 to 24 hours, preferably 3 to 10 hours.

[0047] According to an embodiment of the present invention, step (2) specifically involves heating and foaming the aged slurry and then solidifying it to obtain a ceramic preform.

[0048] According to an embodiment of the present invention, in step (2), the atmosphere during thermosetting can be any one of air, nitrogen, or argon.

[0049] According to an embodiment of the present invention, in step (2), the curing process adopts a single-stage or segmented heating mode. As one implementation method, the specific process is as follows: (i) Single-stage heating mode: heating from room temperature to 120-190°C at a heating rate of 0.5-10°C / min, and holding for 0.5-12 hours. (ii) Segmented heating mode: First stage: heating from room temperature to 105-165°C at a heating rate of 2-10°C / min, and holding for 0.1-6 hours; Second stage: heating to 120-190°C at a heating rate of 0.5-5°C / min, and holding for 0.5-12 hours. Preferably, the temperature of the second stage is higher than that of the first stage.

[0050] According to an embodiment of the present invention, step (2) further includes a post-processing step: naturally cooling the prepared ceramic preform to room temperature.

[0051] According to an embodiment of the present invention, in step (3), the inert atmosphere is either an argon atmosphere or a nitrogen atmosphere, and the gas flow rate is preferably 50 to 300 ml / min.

[0052] Preferably, in step (3), the pyrolysis process employs a gradient heating mode, for example, divided into 1 to 7 heating stages; and preferably, the temperatures of the temperature zones are not the same. Alternatively, pyrolysis can be carried out at a gradient increasing temperature.

[0053] Preferably, the pyrolysis can have the same or different heating rates in different temperature regions, or the same or different heating rates in one temperature region, for example, the heating rate of each temperature region is 0.1℃ / min to 10℃ / min, and the same or different holding times, for example, the holding time of each temperature region is 10min-10h, preferably 10min-3h.

[0054] Preferably, the pyrolysis has the same or different heating rates within a temperature range, for example, the pyrolysis temperature is 160 to 1600°C, and there are different heating rates within this temperature range, with the temperature gradient increasing.

[0055] For example, the pyrolysis process is as follows: heating from room temperature to 190°C at a heating rate of 4°C / min, heating from 190°C to 265°C at a heating rate of 1°C / min, heating from 265°C to 295°C at a heating rate of 0.5°C / min, heating from 295°C to 350°C at a heating rate of 0.3°C / min, heating from 350°C to 1150°C at a heating rate of 3°C / min, and holding at that temperature for 1 hour.

[0056] Preferably, when pyrolysis is carried out sequentially in 2 to 7 temperature zones, pyrolysis is first performed in the first stage temperature zone, and then the next stage temperature zone is entered sequentially, such as the second stage temperature zone, the third stage temperature zone, and so on.

[0057] For example, the temperature of the first stage can be 160-190℃, such as 180-190℃; the temperature of the second stage can be 190-600℃, such as 240-600℃; the temperature of the third stage can be 270-1600℃, such as 285-1600℃; and the pyrolysis can be carried out at a gradually increasing temperature.

[0058] Preferably, when pyrolysis is carried out sequentially in four or more temperature zones, for example, the temperature of the fourth stage can be 285–1150°C, or for example, 300–1150°C. Another example is that the temperature of the fifth stage can be 400–1600°C, or for example, 450–1600°C. Yet another example is that the temperature of the sixth stage can be 550–1200°C, or for example, 600–1100°C. And yet another example is that the temperature of the seventh stage can be 1000–1200°C, or for example, 1120–1160°C.

[0059] One implementation method involves the following steps: First stage: heating from room temperature to 190℃ at a rate of 4℃ / min; Second stage: heating from 190℃ to 245℃ at a rate of 2℃ / min; Third stage: heating from 245℃ to 285℃ at a rate of 1℃ / min; Fourth stage: heating from 285℃ to 300℃ at a rate of 0.15℃ / min; Fifth stage: heating from 300℃ to 450℃ at a rate of 1℃ / min; Sixth stage: heating from 450℃ to 600℃ at a rate of 2℃ / min; Seventh stage: heating from 600℃ to 1150℃ at a rate of 3℃ / min, holding at this temperature for 1 hour, and then cooling to room temperature in the furnace to obtain silicon carbide foam ceramic. Multiple stages can be combined into a single stage.

[0060] According to an embodiment of the present invention, step (3) further includes a post-processing step: cooling the prepared product to room temperature in the furnace.

[0061] The present invention also provides applications of the above-mentioned silicon carbide foam ceramics in aerospace, energy and transportation fields, preferably as lightweight high-temperature structural materials, high-temperature thermal protection materials, and high-temperature gas filtration.

[0062] The beneficial effects of this invention are:

[0063] (1) The silicon carbide foam ceramic of the present invention has a closed-cell structure, low relative density, high porosity, good thermal stability, high compressive strength, can be sintered at a low temperature, has good oxidation resistance, and still has high compressive strength after oxidation at 1400℃ for 10h.

[0064] (2) The slurry of the present invention can be freely foamed and thermo-cured-pyrolytic ceramicized under relatively mild conditions. The size and shape of the ceramic components can be freely adjusted according to the mold. The preparation method is simple and has good processability. The liquid ceramic precursor used is commercially available, and the other raw materials are also easy to obtain, which is conducive to the low-cost large-scale production of silicon carbide foam ceramics.

[0065] (3) The viscosity of the liquid ceramic precursor shown in formula (I) used in this invention is less than 200 mPa·s, which can effectively reduce the sintering temperature and achieve good encapsulation and bonding of filler particles during pyrolysis, suppressing and eliminating defects such as cracks and non-uniform deformation during the preparation of foam ceramics. No solvent is used in the preparation of slurry using the liquid ceramic precursor, which is beneficial to environmental protection; the liquid ceramic precursor has a high ceramic yield and low viscosity, which can prepare slurry containing a high content of filler, further reducing costs and increasing ceramic yield.

[0066] (4) The present invention uses microsphere foaming agent as template. The microsphere foaming agent is a hollow microsphere. It expands during the thermal curing process of the slurry to fix the pore structure. It is basically decomposed during the pyrolysis process. The residual rate in the prepared foam ceramic is low, and the pore structure is controllable and uniform. The porosity and relative density of the foam ceramic can be freely adjusted by adjusting its dosage.

[0067] Terminology Definitions and Explanations

[0068] “C 1- C 10 "Alkyl" refers to straight-chain and branched alkyl groups having 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 carbon atoms. 1- "C6 alkyl" means a straight-chain or branched alkyl group having 1, 2, 3, 4, 5, or 6 carbon atoms. The alkyl group is, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, 2-methylbutyl, 1-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, neopentyl, 1,1-dimethylpropyl, 4-methylpentyl, 3-methylpentyl, 2-methylpentyl, 1-methylpentyl, 2-ethylbutyl, 1-ethylbutyl, 3,3-dimethylbutyl, 2,2-dimethylbutyl, 1,1-dimethylbutyl, 2,3-dimethylbutyl, 1,3-dimethylbutyl, or 1,2-dimethylbutyl, or their isomers. Attached Figure Description

[0069] Figure 1 The TG-DTG curves of liquid polycarbosilane KH-VHPCS-1 and KH-VHPCS-2 in Examples 1-2 of this invention are shown.

[0070] Figure 2 This is a microscopic morphology diagram of the silicon carbide foam ceramic of Example 1 of the present invention.

[0071] Figure 3 The image shows the TG curve of the silicon carbide foam ceramic of Example 1 of the present invention.

[0072] Figure 4 This is a microscopic morphology image of the silicon carbide foam ceramic of Example 1 of the present invention after oxidation at 1400℃ for 10 hours.

[0073] Figure 5 The image shows the pore size distribution curve of the silicon carbide foam ceramic of Example 1 of the present invention.

[0074] Figure 6 This is a microscopic morphology diagram of the silicon carbide foam ceramic of Embodiment 2 of the present invention.

[0075] Figure 7 This is a microscopic morphology diagram of the silicon carbide foam ceramic of Example 3 of the present invention.

[0076] Figure 8 This is a microscopic morphology diagram of the silicon carbide foam ceramic of Example 4 of the present invention.

[0077] Figure 9 This is a microscopic morphology diagram of the silicon carbide foam ceramic of Example 5 of the present invention. Detailed Implementation

[0078] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0079] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0080] In the following embodiments, the density of the foam ceramic samples was tested using the Archimedes displacement method; the porosity and pore size distribution of the foam ceramic samples were tested using a Poremaster 60 mercury porosimeter from the American company Quanta Computer; and the compressive strength of the foam ceramic samples was tested using an Instron 5567 universal testing machine from the American company Instron.

[0081] Example 1

[0082] (1) Weigh out 0.5μm silicon carbide micro powder, 0.5μm silicon micro powder, 0.5μm boron micro powder, dicumyl peroxide, and vinyl polycarbosilane precursor (KH-VHPCS-1, structural formula (CH2SiH2)) at mass fractions of 61wt%, 3wt%, 1wt%, 0.3wt%, and 34.7wt%, respectively. 0.9 (CH2SiHCH=CH2) 0.1 The raw materials (with a viscosity of 30 mPa·s and a ceramic yield of 86% at 1100℃) were mixed with 20.4 wt% Expansel 920DU40 microsphere foaming agent based on the total amount of the precursor, filler, and initiator. The mixture was then mechanically stirred in a flask for 2 hours to obtain a uniformly mixed ceramic slurry with a room temperature viscosity of 2.73 Pa·s. The slurry was allowed to stand for 3 days and then mechanically stirred again before use to ensure uniform mixing.

[0083] (2) Transfer the slurry to a sealed mold and place it in an oven for foaming and thermal curing in air using a segmented heating method. First stage: Temperature rises from room temperature to 165℃ at a rate of 4℃ / min, held for 20min; Second stage: Temperature rises from 165℃ to 175℃ at a rate of 0.5℃ / min, held for 30min, allowing the slurry to fully thermally cure and foam. After the heating process is complete, allow it to cool naturally to room temperature to obtain a uniform silicon carbide foam ceramic preform with no surface cracks.

[0084] (3) Place the cured foam ceramic preform in a tube furnace, use argon atmosphere as protective gas, set the gas flow rate to 100 ml / min, and use segmented heating mode to ceramicize the cured preform. Stage 1: Heating from room temperature to 190℃ at a rate of 4℃ / min, holding for 10 min; Stage 2: Heating from 190℃ to 245℃ at a rate of 2℃ / min, holding for 20 min; Stage 3: Heating from 245℃ to 285℃ at a rate of 1℃ / min, holding for 20 min; Stage 4: Heating from 285℃ to 300℃ at a rate of 0.15℃ / min, holding for 20 min; Stage 5: Heating from 300℃ to 450℃ at a rate of 1℃ / min, holding for 30 min; Stage 6: Heating from 450℃ to 600℃ at a rate of 2℃ / min, holding for 30 min; Stage 7: Heating from 600℃ to 1150℃ at a rate of 3℃ / min, holding for 1 h, then cooling to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0085] The density of the pyrolyzed silicon carbide foam ceramic is 0.26 g / cm³. 3 It has a relative density of 0.09, a porosity of 90.31%, and a compressive strength of 3.87 MPa. The TG-DTG curve of its precursor KH-VHPCS-1 is shown below. Figure 1 As shown, the microstructure of silicon carbide foam ceramics is as follows: Figure 2 As shown, the TG curve of the foam ceramic is as follows: Figure 3 As shown in the figure, the ceramized foam ceramic has a uniform internal structure, with pore sizes mainly distributed between 50 nm and 8.7 μm. Its pore size distribution curve is shown in the figure. Figure 5 As shown, the SiC micropowder exhibits good adhesion, with dense pore walls and no obvious defects, which is beneficial for improving the mechanical properties and antioxidant properties of the sample.

[0086] The foam ceramic samples pyrolyzed at 1150℃ were placed in alumina crucibles and then placed in a tube furnace with an inert atmosphere at a target temperature of 1600℃ and a high-temperature muffle furnace at a target temperature of 1400℃, respectively. Their high-temperature resistance and high-temperature oxidation resistance were evaluated by testing their compressive strength. After heat treatment at 1600℃ for 2 hours, the compressive strength of the samples was 3.57 MPa; after oxidation at 1400℃ for 10 hours, the residual compressive strength was 2.92 MPa. The microstructure after oxidation is shown below. Figure 4 As shown above, the silicon carbide foam ceramic of the present invention has good high-temperature resistance and high-temperature oxidation resistance, as well as high compressive strength, and can be used as a thermal protection material.

[0087] Example 2

[0088] (1) Weigh out 0.5μm silicon carbide micro powder, 1μm silicon micro powder, 0.5μm boron micro powder, benzoyl peroxide and vinyl-containing polycarbosilane precursor (KH-VHPCS-2, structural formula (CH2SiH2)) in the following proportions: 61wt%, 3wt%, 1wt%, 0.5wt% and 34.5wt%. 0.775 (CH2SiHCH=CH2) 0.225 The mixture (with a viscosity of 40 mPa·s and a ceramic yield of 89% at 1100℃) was then mixed with 12.9 wt% Expansel 920DU40 microsphere foaming agent based on the total amount of the aforementioned precursor, filler, and initiator. The raw materials were placed in a tetrafluoroethylene tank and shaken for 2 hours to obtain a uniformly mixed ceramic slurry with a room temperature viscosity of 2.85 Pa·s. The slurry was allowed to stand for 3 days and then mechanically stirred again before use to ensure uniform mixing.

[0089] (2) Transfer the slurry to a sealed mold, place it in an oven, and heat it to 180°C at a rate of 3°C / min under air atmosphere. Then, foam and heat-cur it at 180°C for 60 minutes. After the heating process is completed, allow it to cool naturally to room temperature to obtain a uniform silicon carbide foam ceramic preform with no surface cracks.

[0090] (3) The cured foam ceramic preform was placed in a tube furnace, and argon atmosphere was used as the protective gas. The gas flow rate was set to 150 ml / min. The cured preform was ceramicized using a segmented heating mode. First stage: heating from room temperature to 190℃ at a heating rate of 4℃ / min and holding for 10 min; Second stage: heating from 190℃ to 285℃ at a heating rate of 2℃ / min and holding for 20 min; Third stage: heating from 285℃ to 300℃ at a heating rate of 0.2℃ / min and holding for 30 min; Fourth stage: heating from 300℃ to 600℃ at a heating rate of 2℃ / min and holding for 30 min; Fifth stage: heating from 600℃ to 1150℃ at a heating rate of 3℃ / min and holding for 30 min. The preform was then cooled to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0091] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0092] The TG-DTG curve of its precursor KH-VHPCS-2 is as follows: Figure 1 As shown.

[0093] The density of the silicon carbide foam ceramic is 0.36 g / cm³. 3 It has a relative density of 0.13, a porosity of 88.1%, and a compressive strength of 3.80 MPa. Its microstructure is as follows: Figure 6 As shown, the residual compressive strength after oxidation at 1400℃ for 10 hours is 2.15 MPa.

[0094] Example 3

[0095] (1) Weigh out 5μm silicon carbide micro powder, 1μm silicon micro powder, 1μm boron micro powder, cassiterite catalyst and vinyl polycarbosilane precursor (KH-VHPCS-1, structural formula (CH2SiH2)) in the following proportions: 57wt%, 5wt%, 3wt%, 20ppm and 35wt%. 0.9 (CH2SiHCH=CH2) 0.1 The raw materials (with a viscosity of 30 mPa·s and a ceramic yield of 86% at 1100℃) were mixed with 9.1 wt% Expansel 909DU80 microsphere foaming agent based on the total amount of the precursor, filler, and initiator. The mixture was then mechanically stirred in a flask for 10 hours to obtain a uniformly mixed ceramic slurry with a room temperature viscosity of 2.52 Pa·s.

[0096] (2) Transfer the slurry to a sealed mold and place it in an oven. Heat the mold to 190°C at a rate of 5°C / min in air. Foam and heat-cur at 190°C for 2 hours. After the heating process is completed, allow it to cool naturally to room temperature to obtain a uniform silicon carbide foam ceramic preform with no surface cracks.

[0097] (3) The cured foam ceramic preform is placed in a tube furnace, and argon atmosphere is used as the protective gas. The gas flow rate is set to 100 ml / min. The cured preform is ceramicized using a segmented heating mode. First stage: heating from room temperature to 190℃ at a heating rate of 4℃ / min and holding for 20 min; Second stage: heating from 190℃ to 600℃ at a heating rate of 1℃ / min and holding for 1 h; Third stage: heating from 600℃ to 1150℃ at a heating rate of 3℃ / min and holding for 2 h. The preform is then cooled to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0098] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0099] The density of the silicon carbide foam ceramic is 0.43 g / cm³. 3 It has a relative density of 0.16, a porosity of 82.3%, and a compressive strength of 2.77 MPa. Its microstructure is as follows: Figure 7 As shown, the residual compressive strength after oxidation at 1400℃ for 10 hours is 1.25 MPa.

[0100] Example 4

[0101] (1) Weigh out 1μm silicon carbide micro powder, 5μm silicon micro powder, 1μm boron micro powder, azobisisobutyronitrile and methyl vinyl polycarbosilane precursor (structural formula (CH2SiH2)) in the following proportions: 55wt%, 5wt%, 5wt%, 0.2wt% and 34.8wt%. 0.9 (CH2SiCH3CH=CH2) 0.1 The mixture (with a viscosity of 40 mPa·s and a ceramic yield of 82% at 1100℃) was then mixed with 28.2 wt% Expansel 909DU80 microsphere foaming agent based on the total amount of the aforementioned precursor, filler, and initiator. The raw materials were then placed in a two-necked flask, heated in an oil bath at 85℃ for 5 hours, and mechanically stirred to obtain a homogeneous slurry with a room temperature viscosity of 2.63 Pa·s.

[0102] (2) Transfer the slurry to a sealed mold, place it in an oven, and heat it to 170°C at a heating rate of 2°C / min under air atmosphere to foam and heat-cur it for 2 hours. After the heating process is completed, allow it to cool naturally to room temperature to obtain a uniform silicon carbide foam ceramic preform with no surface cracks.

[0103] (3) The cured foam ceramic preform was placed in a tube furnace, using argon atmosphere as the protective gas at a flow rate of 100 ml / min. A segmented heating mode was used to ceramicize the cured preform. The first stage was: heating from room temperature to 190℃ at a rate of 4℃ / min, holding for 10 min; the second stage was: heating from 190℃ to 270℃ at a rate of 2℃ / min, holding for 20 min; the third stage was: heating from 270℃ to 350℃ at a rate of 0.5℃ / min, holding for 20 min; the fourth stage was: heating from 350℃ to 600℃ at a rate of 5℃ / min, holding for 30 min; the fifth stage was: heating from 600℃ to 1150℃ at a rate of 10℃ / min, holding for 30 min. The preform was then cooled to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0104] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0105] The density of the silicon carbide foam ceramic is 0.22 g / cm³. 3 It has a relative density of 0.08, a porosity of 92.7%, and a compressive strength of 2.63 MPa. Its microstructure is as follows: Figure 8 As shown, the residual compressive strength after oxidation at 1400℃ for 10 hours is 1.17 MPa.

[0106] Example 5

[0107] (1) Weigh out 5μm silicon carbide micro powder, dicumyl peroxide and allyl polycarbosilane precursor (KH-AHPCS-1, structural formula (CH2SiH2)) at mass fractions of 65wt%, 0.3wt% and 34.7wt%. 0.9 (CH2SiHCH2-CH=CH2) 0.1 The mixture (with a viscosity of 20 mPa·s and a ceramic yield of 73% at 1100℃) was then mixed with 43.3 wt% Expansel 909DU80 microsphere foaming agent based on the total amount of the aforementioned precursor, filler, and initiator. The raw materials were placed in a two-necked flask, heated in an oil bath at 85℃ for 5 hours, and mechanically stirred to obtain a homogeneous slurry with a room temperature viscosity of 3.53 Pa·s.

[0108] (2) Transfer the slurry to a sealed mold, place it in an oven, and heat it to 170°C at 5°C / min in an air atmosphere to foam and heat-cur it for 2 hours. After the heating process is completed, allow it to cool naturally to room temperature to obtain a uniform silicon carbide foam ceramic preform with no surface cracks.

[0109] (3) The cured foam ceramic preform was placed in a tube furnace, using argon atmosphere as the protective gas at a flow rate of 200 ml / min. A segmented heating mode was used to ceramicize the cured preform. The first stage involved heating from room temperature to 190°C at a rate of 4°C / min, holding for 10 min. The second stage involved heating from 190°C to 350°C at a rate of 1°C / min, holding for 1 h. The third stage involved heating from 600°C to 1150°C at a rate of 3°C / min, holding for 1 h. The preform was then cooled to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0110] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0111] The density of the silicon carbide foam ceramic is 0.18 g / cm³. 3 It has a relative density of 0.06, a porosity of 92.7%, and a compressive strength of 1.97 MPa. Its microstructure is as follows: Figure 9 As shown, the residual compressive strength of the sample after oxidation at 1400℃ for 10 hours was 0.82 MPa.

[0112] Example 6

[0113] (1) Weigh out 0.5μm silicon carbide micro powder, 1μm silicon micro powder, 5μm boron micro powder, di-tert-butyl peroxide and methyl-containing polycarbosilane precursor (structural formula (CH2SiH2)) in the following proportions: 49wt%, 10wt%, 1wt%, 0.2wt% and 39.8wt%. 0.9 (CH2SiHMe) 0.1 The raw materials (with a viscosity of 30 mPa·s and a ceramic yield of 75% at 1100℃) were mixed with 22.4 wt% Expansionl051DU40 microsphere foaming agent based on the total amount of the precursor, filler, and initiator. The raw materials were then placed in a ball mill jar and ball-milled for 2 hours in a planetary ball mill to obtain a uniformly mixed slurry with a room temperature viscosity of 1.14 Pa·s. The slurry was allowed to stand for 3 days, and then mechanically stirred to ensure uniform mixing before use.

[0114] (2) The slurry was transferred to a sealed mold and placed in an oven for curing in an air atmosphere using a segmented heating mode. The first stage involved heating from room temperature to 130°C at a rate of 3°C / min, followed by a holding time of 0.5 hours. The second stage involved heating from 130°C to 160°C for foaming and thermal curing for 4 hours at a rate of 1°C / min. After the heating process, the material was allowed to cool naturally to room temperature, resulting in a uniform silicon carbide foam ceramic preform with no surface cracks.

[0115] (3) The cured foam ceramic preform was placed in a tube furnace, using nitrogen atmosphere as the protective gas at a flow rate of 150 ml / min. A single-stage heating and gradient temperature rise mode was used to ceramicize the preform. The temperature was increased from room temperature to 190°C at a rate of 4°C / min, then to 265°C at a rate of 1°C / min, then to 295°C at a rate of 0.5°C / min, then to 350°C at a rate of 0.3°C / min, and finally to 1150°C at a rate of 3°C / min, and held at these temperatures for 1 hour. The furnace was then cooled to room temperature to obtain silicon carbide foam ceramic.

[0116] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0117] The density of the silicon carbide foam ceramic is 0.23 g / cm³. 3 The relative density is 0.08, the porosity is 90.3%, and the compressive strength is 4.31 MPa. After oxidation at 1400℃ for 10 h, the residual compressive strength of the sample is 2.01 MPa.

[0118] Example 7

[0119] (1) Weigh out 0.5 μm silicon carbide micro powder, 5 μm silicon micro powder, 1 μm boron micro powder, platinum catalyst and vinyl polycarbosilane precursor (KH-VHPCS-2, structural formula (CH2SiH2)) in the following proportions: 51 wt%, 3 wt%, 1 wt%, 50 ppm and 45 wt%. 0.775 (CH2SiHCH=CH2) 0.225 The mixture (with a viscosity of 40 mPa·s and a ceramic yield of 89% at 1100℃) was then mixed with 25.3 wt% Expansel 053DU40 microsphere expander, based on the total amount of the aforementioned precursor, filler, and initiator. The raw materials were placed in a two-necked flask and heated in a 60℃ oil bath for 2 hours, then mechanically stirred to obtain a slurry with a room temperature viscosity of 1.62 Pa·s. After aging for 2 days, the slurry was mechanically stirred again to ensure uniform mixing before use.

[0120] (2) The slurry was transferred to a sealed mold and placed in an oven for curing under a nitrogen atmosphere using a segmented heating mode. The first stage involved heating from room temperature to 120°C at a rate of 3°C / min, followed by holding at that temperature for 0.5 hours. The second stage involved heating from 130°C to 150°C for foaming and thermal curing for 1 hour at a rate of 0.5°C / min. After the heating process, the material was allowed to cool naturally to room temperature, resulting in a uniform silicon carbide foam ceramic preform with no surface cracks.

[0121] (3) The cured foam ceramic preform was placed in a tube furnace, using argon atmosphere as the protective gas, with a gas flow rate set to 150 ml / min. A segmented heating mode was used to ceramicize the cured preform. The first stage: heating from room temperature to 190℃ at a rate of 4℃ / min, holding for 10 min; the second stage: heating from 190℃ to 270℃ at a rate of 2℃ / min, holding for 10 min; the third stage: heating from 270℃ to 350℃ at a rate of 0.5℃ / min, holding for 20 min; the fourth stage: heating from 350℃ to 600℃ at a rate of 5℃ / min, holding for 1 h; the fifth stage: heating from 600℃ to 1150℃ at a rate of 10℃ / min, holding for 3 h. The preform was then cooled to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0122] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0123] The density of the silicon carbide foam ceramic is 0.25 g / cm³. 3 The relative density is 0.09, the porosity is 89.7%, and the compressive strength is 3.97 MPa. After oxidation at 1400℃ for 10 h, the residual compressive strength of the sample is 1.92 MPa.

[0124] Example 8

[0125] (1) Weigh out 0.5μm silicon carbide micro powder, 1μm silicon micro powder, 5μm boron micro powder, dicumyl peroxide and vinyl polycarbosilane precursor (KH-VHPCS-1, structural formula (CH2SiH2)) in mass fractions of 42wt%, 5wt%, 3wt%, 1wt% and 50wt%. 0.9 (CH2SiHCH=CH2) 0.1 The mixture (with a viscosity of 30 mPa·s and a ceramic yield of 86% at 1100℃) was then mixed with 25.3 wt% Expansel 043DU80 microsphere foaming agent based on the total amount of the aforementioned precursor, filler, and initiator. The raw materials were placed in a two-necked flask and heated in a 60℃ oil bath for 2 hours, then mechanically stirred to obtain a slurry with a room temperature viscosity of 654 mPa·s. The mixed slurry was transferred to a sample bottle and allowed to stand for 2 days. Before use, the slurry was mechanically stirred again to ensure uniform mixing.

[0126] (2) The slurry was transferred to a sealed mold and placed in an oven for curing under an argon atmosphere using a segmented heating mode. The first stage involved heating from room temperature to 120°C at a rate of 3°C / min, holding for 0.4 hours. The second stage involved heating from 130°C to 170°C for foaming and thermal curing for 0.5 hours at a rate of 5°C / min. After the heating process, the material was allowed to cool naturally to room temperature, resulting in a uniform silicon carbide foam ceramic preform with no surface cracks.

[0127] (3) The cured foam ceramic preform was placed in a tube furnace, and argon atmosphere was used as the protective gas. The gas flow rate was set to 150 ml / min. The cured preform was ceramicized using a segmented heating mode. First stage: heating from room temperature to 190℃ at a heating rate of 4℃ / min and holding for 30 min; Second stage: heating from 190℃ to 270℃ at a heating rate of 2℃ / min and holding for 10 min; Third stage: heating from 270℃ to 350℃ at a heating rate of 0.5℃ / min and holding for 1.5 h; Fourth stage: heating from 350℃ to 600℃ at a heating rate of 5℃ / min and holding for 10 min; Fifth stage: heating from 600℃ to 1600℃ at a heating rate of 3℃ / min and holding for 1 h. The preform was then cooled to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0128] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0129] The density of the silicon carbide foam ceramic is 0.24 g / cm³. 3 The relative density is 0.09, the porosity is 90.2%, the compressive strength is 3.72 MPa, and the residual compressive strength of the sample after oxidation at 1400℃ for 10 h is 1.96 MPa.

[0130] Example 9

[0131] (1) Weigh out 1μm silicon carbide micro powder, 0.5μm zirconium oxide micro powder, 1μm silicon micro powder, dicumyl peroxide and methyl vinyl polycarbosilane precursor (structural formula (CH2SiH2)) in the following proportions: 30wt%, 20wt%, 3wt%, 1wt% and 46wt%. 0.9 (CH2SiMeCH=CH2) 0.1The raw materials (with a viscosity of 40 mPa·s and a ceramic yield of 76% at 1100℃) were mixed with 26.7 wt% Expansel 920DU20 microsphere foaming agent based on the total amount of the precursor, filler, and initiator. The raw materials and milling beads were then placed in a ball mill jar and shaken for 2 hours to obtain a slurry with a room temperature viscosity of 972 mPa·s. The mixed slurry was transferred to a sample bottle and allowed to stand for 4 days. Before use, the slurry was shaken again to ensure uniform mixing.

[0132] (2) Transfer the slurry to a sealed mold, place it in an oven, and heat it to 180°C at 3°C / min under an argon atmosphere to foam and heat-cur it for 1 hour. After the heating process is completed, allow it to cool naturally to room temperature to obtain a uniform silicon carbide foam ceramic preform with no surface cracks.

[0133] (3) The cured foam ceramic preform is placed in a tube furnace, and argon atmosphere is used as the protective gas. The gas flow rate is set to 150 ml / min. The cured preform is ceramicized using a segmented heating mode. First stage: heating from room temperature to 190℃ at a heating rate of 5℃ / min and holding for 30 min; Second stage: heating from 190℃ to 600℃ at a heating rate of 1℃ / min and holding for 2 h; Third stage: heating from 600℃ to 1600℃ at a heating rate of 3℃ / min and holding for 1 h. The preform is then cooled to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0134] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0135] The density of the silicon carbide foam ceramic is 0.26 g / cm³. 3 The relative density is 0.08, the porosity is 89.7%, the compressive strength is 3.31 MPa, and the residual compressive strength of the sample after oxidation at 1400℃ for 10 h is 1.87 MPa.

[0136] Example 10

[0137] (1) Weigh out 2μm silicon carbide micro powder, 1μm alumina micro powder, 1μm aluminum micro powder, benzoyl peroxide and vinyl polycarbosilane precursor (KH-VHPCS-1, structural formula (CH2SiH2)) in mass fractions of 20wt%, 30wt%, 2wt%, 1wt% and 47wt%. 0.9 (CH2SiHCH=CH2) 0.1The mixture (with a viscosity of 30 mPa·s and a ceramic yield of 86% at 1100℃) was then mixed with 34.6 wt% Expansel 920DU40 microsphere foaming agent based on the total amount of the aforementioned precursor, filler, and initiator. The raw materials and milling beads were placed in a ball mill jar and milled for 1 hour in a planetary ball mill to obtain a slurry with a room temperature viscosity of 883 mPa·s. The mixed slurry was transferred to sample vials and allowed to stand for 3 days. Before use, the slurry was mixed again using a ball mill to ensure uniformity.

[0138] (2) Transfer the slurry to a sealed mold, place it in an oven, and heat it to 175°C at 3°C / min under a nitrogen atmosphere to foam and heat-cur it for 1 hour. After the heating process is completed, allow it to cool naturally to room temperature to obtain a uniform silicon carbide foam ceramic preform with no surface cracks.

[0139] (3) The cured foam ceramic preform was placed in a tube furnace, and argon atmosphere was used as the protective gas. The gas flow rate was set to 200 ml / min. The cured preform was ceramicized using a segmented heating mode. First stage: heating from room temperature to 190℃ at a heating rate of 3℃ / min and holding for 1 h; Second stage: heating from 190℃ to 295℃ at a heating rate of 0.8℃ / min and holding for 40 min; Third stage: heating from 295℃ to 600℃ at a heating rate of 2℃ / min and holding for 3 h; Fourth stage: heating from 600℃ to 1150℃ at a heating rate of 3℃ / min and holding at 1150℃ for 1 h. The preform was then cooled to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0140] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0141] The density of the silicon carbide foam ceramic is 0.21 g / cm³. 3 The relative density is 0.07, the porosity is 90.4%, the compressive strength is 3.92 MPa, and the residual compressive strength of the sample after oxidation at 1400℃ for 10 h is 2.02 MPa.

[0142] Example 11

[0143] (1) Weigh out 1μm silicon carbide micro powder, 1μm hafnium silicide micro powder, 5μm silicon micro powder, 0.5μm boron micro powder, and cassiterite catalyst and methylallyl polycarbosilane precursor (structural formula (CH2SiH2)) in the following proportions: 30wt%, 30wt%, 2wt%, 2wt%, 20ppm and 36wt%. 0.9 (CH2SiMeCH2-CH=CH2) 0.1The mixture (with a viscosity of 50 mPa·s and a ceramic yield of 78% at 1100℃) was then added, along with 29.5 wt% Expansionl 920DU40 microsphere foaming agent based on the total amount of the aforementioned precursor, filler, and initiator. The raw materials were added to a two-necked flask and mechanically stirred under nitrogen protection to obtain a slurry with a room temperature viscosity of 3.18 Pa·s. The mixed slurry was transferred to a sample bottle and allowed to stand for 3 days. Before use, the slurry was mechanically stirred again to ensure uniform mixing.

[0144] (2) Transfer the slurry to a sealed mold, place it in an oven, and heat it to 175°C at 3°C / min under a nitrogen atmosphere to foam and heat-cur it for 1 hour. After the heating process is completed, allow it to cool naturally to room temperature to obtain a uniform silicon carbide foam ceramic preform with no surface cracks.

[0145] (3) The cured foam ceramic preform was placed in a tube furnace, and argon atmosphere was used as the protective gas. The gas flow rate was set to 200 ml / min. The cured preform was ceramicized using a segmented heating mode. First stage: heating from room temperature to 190℃ at a heating rate of 3℃ / min and holding for 10 min; Second stage: heating from 190℃ to 295℃ at a heating rate of 0.8℃ / min and holding for 1 h; Third stage: heating from 295℃ to 450℃ at a heating rate of 1℃ / min and holding for 1.5 h; Fourth stage: heating from 450℃ to 600℃ at a heating rate of 2℃ / min and holding for 20 min; Fifth stage: heating from 600℃ to 1150℃ at a heating rate of 3℃ / min and holding at 1150℃ for 1 h. The preform was then cooled to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0146] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0147] The density of the silicon carbide foam ceramic is 0.26 g / cm³. 3 The relative density is 0.06, the porosity is 90.1%, the compressive strength is 3.83 MPa, and the residual compressive strength of the sample after oxidation at 1400℃ for 10 h is 1.98 MPa.

[0148] Example 12

[0149] (1) Weigh out 0.5 μm silicon carbide micro powder, 1 μm zirconium silicide micro powder, 1 μm zirconium micro powder, 0.5 μm boron micro powder, cassiterite catalyst and vinyl polycarbosilane precursor (KH-VHPCS-1, structural formula (CH2SiH2)) in the following proportions: 40 wt%, 10 wt%, 10 wt%, 3 wt%, 40 ppm and 37 wt%. 0.9(CH2SiHCH=CH2) 0.1 The mixture (with a viscosity of 30 mPa·s and a ceramic yield of 86% at 1100℃) was then mixed with 24.4 wt% Expansel 920DU40 microsphere foaming agent based on the total amount of the aforementioned precursor, filler, and initiator. The raw materials were added to a two-necked flask and mechanically stirred under nitrogen protection to obtain a slurry with a room temperature viscosity of 3.09 Pa·s. The mixed slurry was transferred to a sample bottle and allowed to stand for 3 days. Before use, the slurry was mechanically stirred again to ensure uniform mixing.

[0150] (2) Transfer the slurry to a sealed mold, place it in an oven, and heat it to 180°C at 2°C / min under a nitrogen atmosphere to foam and heat-cur it for 0.5h. After the heating process is completed, allow it to cool naturally to room temperature to obtain a uniform silicon carbide foam ceramic preform with no surface cracks.

[0151] (3) Place the cured foam ceramic preform in a tube furnace, use nitrogen atmosphere as protective gas, set the gas flow rate to 100 ml / min, and use segmented heating mode to ceramicize the cured preform. Stage 1: Heating from room temperature to 190℃ at a rate of 3℃ / min, holding for 10min; Stage 2: Heating from 190℃ to 245℃ at a rate of 1℃ / min, holding for 10min; Stage 3: Heating from 245℃ to 295℃ at a rate of 0.3℃ / min, holding for 40min; Stage 4: Heating from 295℃ to 450℃ at a rate of 1℃ / min, holding for 10min; Stage 5: Heating from 450℃ to 600℃ at a rate of 2℃ / min, holding for 20min; Stage 6: Heating from 600℃ to 1150℃ at a rate of 2℃ / min, holding at 1150℃ for 1h, then cooling to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0152] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0153] The density of the silicon carbide foam ceramic is 0.26 g / cm³. 3 The relative density is 0.08, the porosity is 89.7%, the compressive strength is 3.62 MPa, and the residual compressive strength of the sample after oxidation at 1400℃ for 10 h is 1.73 MPa.

[0154] Example 13

[0155] (1) Weigh out 2μm silicon carbide micro powder, 1μm zirconium boride micro powder, 0.5μm zirconium micro powder, cassiterite catalyst and vinyl polycarbosilane precursor (KH-VHPCS-1, structural formula (CH2SiH2)) at mass fractions of 20wt%, 40wt%, 5wt%, 40ppm and 35wt%. 0.9 (CH2SiHCH=CH2) 0.1 The mixture (with a viscosity of 30 mPa·s and a ceramic yield of 86% at 1100℃) was then added, along with 26.3 wt% Expansel 920DU40 microsphere foaming agent based on the total amount of the aforementioned precursor, filler, and initiator. The raw materials were added to a two-necked flask and mechanically stirred under nitrogen protection to obtain a slurry with a room temperature viscosity of 2.77 Pa·s. The mixed slurry was transferred to a sample bottle and allowed to stand for 3 days. Before use, the slurry was mechanically stirred again to ensure uniform mixing.

[0156] (2) The slurry was transferred to a sealed mold and placed in an oven for thermal curing under a nitrogen atmosphere using a segmented heating mode. First stage: the temperature was increased from room temperature to 150℃ at a rate of 5℃ / min and held for 0.5h; Second stage: the temperature was increased from 150℃ to 180℃ at a rate of 3℃ / min, foaming and thermally curing for 1h. After the heating process was completed, the material was allowed to cool naturally to room temperature to obtain a uniform silicon carbide foam ceramic preform with no surface cracks.

[0157] (3) The cured foam ceramic preform was placed in a tube furnace, using nitrogen atmosphere as the protective gas at a flow rate of 100 ml / min. A segmented heating mode was used to ceramicize the cured preform. The first stage was: heating from room temperature to 190℃ at a rate of 3℃ / min, holding for 30 min; the second stage was: heating from 190℃ to 295℃ at a rate of 0.5℃ / min, holding for 1 h; the third stage was: heating from 295℃ to 450℃ at a rate of 1℃ / min, holding for 20 min; the fourth stage was: heating from 450℃ to 1150℃ at a rate of 2℃ / min, holding for 1 h at 1150℃; the fifth stage was: heating from 1150℃ to 1400℃ at a rate of 1.5℃ / min, holding for 2 h at 1400℃. After the heating process was completed, the preform was cooled to room temperature in the furnace to obtain silicon carbide foam ceramic.

[0158] (4) Place the pyrolyzed silicon carbide foam ceramic into an alumina crucible, set the temperature of the muffle furnace to 1400℃, and after the set temperature is reached, place the crucible and the sample into the muffle furnace for oxidation for 10h.

[0159] The density of the silicon carbide foam ceramic is 0.29 g / cm³. 3The relative density is 0.07, the porosity is 88.9%, the compressive strength is 3.17 MPa, and the residual compressive strength of the sample after oxidation at 1400℃ for 10 h is 1.73 MPa.

[0160] The embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A silicon carbide foam ceramic, characterized in that, The raw materials for preparing the silicon carbide foam ceramic, by weight percentage (100%), include: The structural unit shown in formula (I) contains 15-85 wt% liquid ceramic precursor, 2 ppm-2.0 wt% curing initiator, and 14-85 wt% filler. Equation (I) Wherein, X is -CH=CH2, -C≡CH, or -CH2-CH=CH2; R1 and R2 may be the same or different, and are independently selected from H, C1-C 10 One of the alkyl groups or -C6H5; x = 0~0.3; y = 0~0.9; and x and y are not both 0 at the same time; The raw materials also include a microsphere foaming agent, the content of which is 9-35 wt% of the total amount of the liquid ceramic precursor, curing initiator, and filler. The filler comprises 14-68 wt% silicon carbide micro powder, 0-10 wt% silicon micro powder, 0-15 wt% zirconium silicide micro powder, 0-25 wt% zirconium dioxide micro powder, 0-40 wt% zirconium boride, 0-20 wt% alumina micro powder, 0-30 wt% hafnium silicide micro powder, 0-5 wt% zirconium micro powder, 0-3 wt% aluminum micro powder, and 0-5 wt% boron micro powder; and the contents of silicon micro powder, zirconium silicide micro powder, zirconium dioxide micro powder, zirconium boride, alumina micro powder, hafnium silicide micro powder, zirconium micro powder, aluminum micro powder, and boron micro powder are not all 0; The viscosity of the liquid ceramic precursor is 20-80 mPa·s.

2. The silicon carbide foam ceramic according to claim 1, characterized in that, The raw materials for preparing the silicon carbide foam ceramic include: 34.5~50wt% of liquid ceramic precursor of the structural unit shown in formula (I), 20~65wt% of silicon carbide micro powder, 1~10wt% of silicon micro powder, 1~5wt% of boron micro powder, 0~15wt% of zirconium silicide micro powder, 0~25wt% of zirconium dioxide micro powder, 0~40wt% of zirconium boride micro powder, 0~20wt% of alumina micro powder, 0~30wt% of hafnium silicide micro powder, 0~5wt% of zirconium micro powder, 0~3wt% of aluminum micro powder, and 20ppm~0.5wt% of curing initiator; The raw materials also include a microsphere foaming agent, the content of which is 9 to 35 wt% of the total amount of the liquid ceramic precursor, curing initiator and filler.

3. The silicon carbide foam ceramic according to claim 1, characterized in that, The expansion start temperature of the microsphere foaming agent is higher than 100°C, and the end temperature is lower than 200°C.

4. The silicon carbide foam ceramic according to claim 1, characterized in that, The microsphere foaming agent is at least one of 053DU40, 051DU40, 043DU80, 920DU20, 920DU40, and 909DU80.

5. The silicon carbide foam ceramic according to claim 1, characterized in that, The curing initiator is selected from at least one of platinum catalyst, dicumyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, and azobisisobutyronitrile.

6. The silicon carbide foam ceramic according to claim 1, characterized in that, The porosity of the silicon carbide foam ceramic is 80-95%.

7. The silicon carbide foam ceramic according to claim 1, characterized in that, The relative density of the silicon carbide foam ceramic is 0.05~0.

20.

8. The silicon carbide foam ceramic according to claim 1, characterized in that, The compressive strength of the silicon carbide foam ceramic is 1.9~4.5 MPa.

9. The silicon carbide foam ceramic according to claim 1, characterized in that, The compressive strength retention rate of the silicon carbide foam ceramic after oxidation at 1200-1500℃ is 40%~80%.

10. The method for preparing silicon carbide foam ceramic according to any one of claims 1-9, characterized in that, The method includes the following steps: (1) Preparation of slurry: The liquid ceramic precursor, curing initiator, filler and microsphere foaming agent of the structural unit shown in formula (I) are mixed to prepare slurry; (2) The slurry in step (1) is foamed and thermally cured to obtain a ceramic preform; (3) The ceramic preform obtained in step (2) is pyrolyzed under an inert atmosphere to obtain silicon carbide foam ceramic.

11. The method according to claim 10, characterized in that, In step (1), the viscosity of the slurry is 0.2~4.5 Pa·s.

12. The method according to claim 10, characterized in that, In step (1), the prepared slurry is also aged; the aging method of the slurry is standing and / or heating treatment, wherein the standing time is 1 to 10 days; the heating temperature is 40 to 110℃ and the heating time is 0.5 to 24h.

13. The method according to claim 10, characterized in that, In step (2), the curing process adopts a single-stage or segmented heating mode; the single-stage heating mode is: from room temperature to 120~190℃, the heating rate is 0.5~10℃ / min, and the temperature is held for 0.5~12h; or the segmented heating mode is: the first stage: from room temperature to 105~165℃, the heating rate is 2~10℃ / min, and the temperature is held for 0.1~6h; the second stage: the temperature is raised to 120~190℃, the heating rate is 0.5~5℃ / min, and the temperature is held for 0.5~12h.

14. The method according to claim 10, characterized in that, In step (3), the pyrolysis process adopts a gradient heating mode, which is divided into 1 to 7 heating stages; or, the pyrolysis is carried out at a temperature gradient.

15. The method according to claim 14, characterized in that, The pyrolysis has the same or different heating rates in different temperature regions, or the same or different heating rates in one temperature region, with the heating rate of each temperature region being 0.1℃ / min to 10℃ / min, and the same or different holding times, with the holding time of each temperature region being 10min to 10h.

16. The method according to claim 15, characterized in that, The pyrolysis has the same or different heating rates within a temperature range, with the pyrolysis temperature being 160~1600℃, or it has different heating rates within the temperature range, and the temperature gradient increases.

17. The method according to claim 15, characterized in that, When pyrolysis is carried out sequentially in 2 to 7 temperature zones, it first pyrolyzes in the first stage temperature zone, and then sequentially enters the next stage temperature zone, that is, sequentially enters the second stage temperature zone pyrolysis, the third stage temperature zone pyrolysis, and so on.

18. The method according to claim 17, characterized in that, The temperature in the first stage is 160~190℃; the temperature in the second stage is 190~600℃; the temperature in the third stage is 270~1600℃; and the pyrolysis can be carried out at a gradually increasing temperature.

19. The method according to claim 17, characterized in that, When pyrolysis occurs sequentially in four or more temperature zones, the temperature of the fourth stage is 285~1150℃.

20. The method according to claim 19, characterized in that, The temperature in the fifth stage is 400~1600℃.

21. The method according to claim 20, characterized in that, The temperature in the sixth stage is 550~1200℃.

22. The method according to claim 21, characterized in that, The temperature in the seventh stage is 1000~1200℃.

23. The application of silicon carbide foam ceramics according to any one of claims 1-9 in the fields of aerospace, energy and transportation.

24. The application according to claim 23, characterized in that, It is used in the fields of lightweight high-temperature structural materials, high-temperature thermal protection materials, and high-temperature gas filtration.

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