High-temperature-resistant heat-insulating light foamed ceramic and preparation method thereof

Abstract

According to the method, chitosan and ceramic particles are added into a liquid ceramic organic precursor for physical stirring and foaming, so that on one hand, the viscosity of the liquid ceramic organic precursor can be increased due to the addition of the chitosan and the ceramic particles, and on the other hand, the viscosity of the liquid ceramic organic precursor can be increased; on the one hand, chitosan and ceramic particles can diffuse and gather towards a gas-liquid foam interface to form a foam protection layer, chitosan is a natural polymer with positive charges, and the protection layer formed by accumulation of particles on the surface of foam can repel each other, so that the gas-liquid composite foam is formed. The foam ceramic with high percentage of close area can be obtained after the foam ceramic is cured and fired, and the foam ceramic can be applied to production and preparation of non-ablative thermal protection materials in the fields of aerospace and the like.

Description

Technical Field

[0001] The invention discloses a high temperature resistant heat insulating lightweight foam ceramic and a preparation method thereof, which can be applied to the production and preparation of non-ablative thermal protection materials in the fields of aerospace and the like. Background Art

[0002] Foam ceramics, as the third type of porous ceramics developed after porous ceramics and honeycomb porous ceramics, have the properties of light weight, high temperature resistance, wave absorption and heat insulation, and are widely used in metallurgy, environmental protection and energy saving, aerospace and other fields. According to the different pore arrangement methods, foam ceramics can be divided into open-cell foam ceramics with interconnected pores and closed-cell foam ceramics with independent pores. Open-cell foam ceramics are good catalyst carriers, filtration separation, biomedical materials, etc., and closed-cell foam ceramics are good thermal insulation, wave absorption and damping materials. At present, open-cell foam ceramics can be prepared by organic foam impregnation, sol-gel, freeze-drying and other processes, and the process is relatively simple, while the preparation of closed-cell foam ceramics can only rely on direct foaming to a large extent, which is more difficult to prepare. Closed-cell foam ceramics have the properties of high temperature resistance, oxidation resistance, high efficiency and heat insulation, and have irreplaceable and huge application prospects in the fields of aerospace thermal protection. Therefore, designing and optimizing the preparation technology of closed-cell ceramic foam is an important part of promoting the development of the foam ceramic field.

[0003] Manabu et al. mixed solid polycarbosilane and foaming agent azodicarbonamide by ball milling and pressed them, then heat treated them at 250℃ in a nitrogen environment, the solid polycarbosilane melted, the foaming agent decomposed and foamed, and then the foamed sample was transferred to air for curing at 200℃ to obtain a cured foam ceramic green body. Finally, after firing at 1000℃, silicon carbide foam ceramic with a porosity of 59% to 85% was obtained, of which the closed-cell content was about 5% (Journal of theEuropean Ceramic Society.2012,32,503–510). Fei Li et al. mixed zirconium oxide sol, phenolic resin, emulsifier, foaming agent and curing agent, foamed and cured at 75℃ to obtain a foam ceramic green body, and then fired at 1600℃ to obtain a closed-cell zirconium carbide foam ceramic with a porosity of 83% to 90% (Journal of the European Ceramic Society.2014,34,3513–3520). Patent application CN117736012A discloses a silicon carbide foam ceramic and its preparation method and application. The slurry is prepared by mixing a liquid ceramic precursor, a curing initiator, a filler and a microsphere foaming agent, and then heated to foam and cure to obtain a foam ceramic green body. Finally, the slurry is fired to obtain a silicon carbide foam ceramic with a closed-cell structure. The silicon carbide foam ceramic has good antioxidant properties and still has a high compressive strength after oxidation at 1400°C for 10 hours.

[0004] The reported method has the following defects:

[0005] (1) The closed-cell content in the foam ceramics prepared by the reported method is low.

[0006] (2) In order to ensure the effective carbon thermal reduction reaction during the ceramic transformation process, the reported method requires the ceramic to be fired at a higher temperature.

[0007] (3) The reported method requires the use of a large amount of microsphere foaming agent, which will destroy the foam wall during the firing process and reduce the closed cell ratio. Summary of the invention

[0008] In order to improve the above-mentioned foam ceramic problems, the present invention provides a high-temperature resistant, heat-insulating, lightweight foam ceramic and a preparation method thereof. The method uses a physical direct foaming process and does not require the use of an additional foaming agent. It is applicable to a variety of foam ceramic systems and can be used to prepare closed-cell, high-temperature resistant, heat-insulating, lightweight foam ceramics.

[0009] To achieve the above object, the specific technical solution of the present invention is a method for preparing high temperature resistant heat insulating lightweight foam ceramics, comprising the following steps:

[0010] (1) adding a catalyst to a liquid ceramic organic precursor and stirring to dissolve the catalyst;

[0011] (2) adding chitosan and ceramic particles to the liquid ceramic organic precursor after adding the catalyst in (1), stirring and dispersing the mixture evenly to obtain a dispersion;

[0012] (3) subjecting the dispersion in (2) to high-speed mechanical stirring for foaming to obtain wet foam;

[0013] (4) placing the wet foam in (3) into a mold and placing it in an oven for curing to obtain a foam ceramic green body;

[0014] (5) pyrolyzing and firing the foam ceramic green body in (4) in an inert atmosphere to obtain foam ceramic;

[0015] Furthermore, the liquid ceramic organic precursor may be one or more of liquid polycarbosilane, liquid polysiloxane, liquid polyborosilazane and the like.

[0016] Furthermore, the particle size of the ceramic particles is 50nm to 500nm.

[0017] Furthermore, the ceramic particles may be one or more of alumina, silicon carbide, zirconium oxide, silicon boride and the like.

[0018] Furthermore, the firing temperature of the foam ceramic green body ranges from 900°C to 1200°C.

[0019] Furthermore, the deacetylation degree of the chitosan is not less than 80%.

[0020] Furthermore, the mass of the chitosan is 10% to 30% of the mass of the liquid ceramic organic precursor.

[0021] Furthermore, the catalyst is dibenzoyl peroxide or diisopropylbenzene peroxide.

[0022] The invention also provides a high temperature resistant heat insulating lightweight foam ceramic prepared by the method.

[0023] In the above technical solution, in order to make the chitosan and ceramic particles disperse evenly, appropriate ultrasonic treatment can be performed;

[0024] In the above technical solution, high-speed stirring can continuously bring air into the dispersion to achieve a foaming effect.

[0025] The principle of the present invention is that under high-speed stirring, air will be continuously introduced into the dispersion to form bubbles. At this time, the dispersion will stabilize the bubbles from two aspects. On the one hand, the addition of chitosan and ceramic particles will increase the viscosity of the liquid ceramic organic precursor and reduce the escape of air bubbles, thereby maintaining a certain amount of bubbles. On the other hand, chitosan and ceramic particles will diffuse and gather at the gas-liquid foam interface to form a foam protective layer. Since chitosan is a naturally positively charged polymer, the protective layer formed by the accumulation of particles on the foam surface will repel each other, which can effectively reduce or prevent bubble rupture, growth, and annexation. In addition, the addition of ceramic particles can improve the strength of the foam ceramic green body and prevent the decomposition of the ceramic organic precursor during the firing process from causing large-area material cracking.

[0026] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0027] 1. The present invention does not involve the use of a foaming agent, which reduces the damage to the foam wall. Chitosan will decompose during the firing process and almost no residue will remain.

[0028] 2. The present invention can adjust the foaming amount by controlling the addition amount of chitosan and ceramic particles and the stirring conditions, and the operation is simple.

[0029] 3. The present invention uses ceramic organic precursors to carry out ceramic firing, and the firing temperature is relatively low.

[0030] 4. The present invention can be applied to the production and preparation of non-ablative thermal protection materials in the fields of aerospace and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the silicon carbide foam ceramic green body in Example 1. DETAILED DESCRIPTION

[0032] The following is combined with Figure 1 The present invention is further described with examples:

[0033] Embodiment 1:

[0034] A high temperature resistant heat insulating lightweight foam ceramic and a preparation method thereof, comprising the following steps:

[0035] (1) Add 0.5 g of diisopropylbenzene peroxide catalyst to 100 g of liquid polycarbosilane and stir to dissolve.

[0036] (2) Add 10 g of chitosan and 10 g of alumina ceramic particles to (1) and stir to disperse evenly.

[0037] (3) The dispersion in (2) was stirred mechanically at a high speed of 700 rpm to foam to obtain wet foam.

[0038] (4) The wet foam prepared in (3) is placed in a mold and placed in an oven for curing at 120° C. for 2 h, 180° C. for 2 h, and 220° C. for 6 h to obtain a silicon carbide foam ceramic green body.

[0039] (5) The silicon carbide foam ceramic green body prepared in (4) was pyrolyzed and fired at 1000° C. in a nitrogen atmosphere at a heating rate of 1° C. / min and kept at this temperature for 2 h to obtain silicon carbide foam ceramic.

[0040] The final prepared silicon carbide foam ceramic has a density of 0.34g / cm 3 The porosity is 68%, the closed porosity is 85%, and the shrinkage rate is less than 3% after treatment at 1600℃ for 2h.

[0041] Figure 1 This is a physical picture of the silicon carbide foam ceramic green body in the above method.

[0042] Embodiment 2:

[0043] A high temperature resistant heat insulating lightweight foam ceramic and a preparation method thereof, comprising the following steps:

[0044] (1) Add 0.5 g of dibenzoyl peroxide catalyst to 50 g of liquid polycarbosilane and stir to dissolve.

[0045] (2) Add 10 g of chitosan and 10 g of alumina ceramic particles to (1) and stir to disperse evenly.

[0046] (3) The dispersion in (2) was stirred mechanically at a high speed of 600 rpm to foam to obtain wet foam.

[0047] (4) The wet foam prepared in (3) is placed in a mold and placed in an oven for curing at 120° C. for 2 h, 180° C. for 2 h, and 220° C. for 6 h to obtain a silicon carbide foam ceramic green body.

[0048] (5) The silicon carbide foam ceramic green body prepared in (4) was pyrolyzed and fired at 1000° C. in a nitrogen atmosphere at a heating rate of 1° C. / min and kept at this temperature for 2 h to obtain silicon carbide foam ceramic.

[0049] The final prepared silicon carbide foam ceramic has a density of 0.13g / cm 3 The porosity is 76%, the closed porosity is 78%, and the shrinkage rate is less than 5% after treatment at 1600℃ for 2h.

[0050] Embodiment 3:

[0051] A high temperature resistant heat insulating lightweight foam ceramic and a preparation method thereof, comprising the following steps:

[0052] (1) Add 0.1 g of diisopropylbenzene peroxide catalyst to 100 g of liquid polyborosilazane and stir to dissolve.

[0053] (2) Add 15 g of chitosan and 10 g of silicon carbide ceramic particles to (1) and stir to disperse evenly.

[0054] (3) The dispersion in (2) was stirred mechanically at a high speed of 800 rpm to foam to obtain wet foam.

[0055] (4) The wet foam prepared in (3) is loaded into a mold and placed in an oven for curing. The mold is kept at 150° C. for 2 h, 200° C. for 2 h, and 240° C. for 6 h to obtain a silicon-boron-carbon-nitrogen foam ceramic green body.

[0056] (5) The silicon boron carbon nitride foam ceramic green body prepared in (4) is pyrolyzed and fired at 1200° C. in a nitrogen atmosphere at a heating rate of 1° C. / min and kept at this temperature for 2 h to obtain silicon boron carbon nitride foam ceramic.

[0057] The final prepared silicon carbide foam ceramic has a density of 0.38g / cm 3 The porosity is 82%, the closed porosity is 90%, and the shrinkage rate is less than 5% after treatment at 1600℃ for 2h.

[0058] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and implement it accordingly. It can be understood by those skilled in the art that various replacements, changes and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the contents disclosed in the embodiments of this specification, and the scope of protection of the present invention shall be subject to the scope defined in the claims.

Claims

1. A method for preparing a high temperature resistant, heat insulating, lightweight foam ceramic, characterized in that: The following steps are involved: Add the catalyst to the liquid ceramic organic precursor and stir to dissolve. Adding chitosan and ceramic particles to the liquid ceramic organic precursor after adding the catalyst, and stirring and dispersing them uniformly to obtain a dispersion; The dispersion is subjected to high-speed mechanical stirring for foaming to obtain wet foam; The wet foam is loaded into a mold and placed in an oven for curing to obtain a foam ceramic green body; The foam ceramic green body is pyrolyzed and fired in an inert atmosphere to obtain the foam ceramic.

2. The preparation method according to claim 1, characterized in that: The liquid ceramic organic precursor is one or more of liquid polycarbosilane, liquid polysiloxane, and liquid polyborosilazane.

3. The preparation method according to claim 1, characterized in that: The particle size of the ceramic particles is 50nm to 500nm.

4. The preparation method according to claim 1, characterized in that: The ceramic particles are one or more of aluminum oxide, silicon carbide, zirconium oxide, and silicon boride particles.

5. The preparation method according to claim 1, characterized in that: The firing temperature of the foam ceramic green body ranges from 900°C to 1200°C.

6. The preparation method according to claim 1, characterized in that: The deacetylation degree of the chitosan is not less than 80%.

7. The preparation method according to claim 1, characterized in that: The mass of the chitosan is 10% to 30% of the mass of the liquid ceramic organic precursor.

8. The preparation method according to claim 1, characterized in that: The catalyst is dibenzoyl peroxide or dicumyl peroxide.

9. A high temperature resistant, heat insulating, lightweight foam ceramic prepared according to the method of any one of claims 1 to 8.

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