CN105000917B - Preparation method of mullite oxidation resistant coating - Google Patents

Abstract

The invention relates to a method for preparing a mullite anti-oxidation coating, in particular to a method for preparing a mullite/SiC double-layer structure anti-oxidation coating on the surface of a carbon/carbon composite material. In the present invention, the pre-calcined mullite powder A and the mullite precursor powder B are prepared according to a mass ratio of 4 to 6:1, and the pre-calcined mullite powder A and the mullite precursor powder B are prepared, and then a certain amount of Proportionally mix the film-forming aids and drying inhibitors and mix them evenly to obtain a slurry, immerse the substrate in the slurry, and apply the slurry coating by dipping and pulling technology; after coating, calcining at 1480-1515°C to obtain Mullite anti-oxidation coating. The invention has simple process, cheap and easy-to-obtain raw materials, and is convenient for industrialized production. The obtained coating has the advantages of uniform and compact, excellent bonding performance, strong high-temperature oxidation resistance, and the like.

Description

A kind of preparation method of mullite anti-oxidation coating

technical field

The invention relates to a method for preparing a mullite anti-oxidation coating, in particular to a method for preparing a mullite/SiC double-layer structure anti-oxidation coating on the surface of a carbon/carbon composite material.

Background technique

Due to its low thermal expansion coefficient, low density, high thermal and electrical conductivity, high strength and high modulus at high temperature, and a series of excellent characteristics such as ablation resistance, corrosion resistance, and stable friction coefficient, carbon/carbon composite materials have become a material with great development potential. It is a high-temperature structural material with broad application prospects, and has been widely used in aviation, aerospace, energy and petrochemical industries. However, since the oxidation initiation temperature of carbon/carbon composites is only 450°C, the oxidation failure in high-temperature oxidizing atmosphere has become one of the main reasons restricting the application and development of carbon/carbon composites. Improving the oxidation resistance of carbon/carbon composites is the key to expanding the application range of carbon/carbon composites.

Anti-oxidation coating technology is the most effective technical approach to solve the problem of high-temperature oxidation resistance of carbon/carbon composites that has been proven by practice. Since the anti-oxidation coating with a single-layer structure is difficult to meet the application requirements, the development of a double-layer or multi-layer structure coating system has become an inevitable trend in the development of anti-oxidation coating technology. Because mullite ceramics has a series of advantages such as good high-temperature phase stability, excellent mechanical properties, strong thermal shock/thermal cycle resistance, and corrosion resistance, it becomes an ideal anti-oxidation coating material system. In addition, since the coefficient of thermal expansion of mullite ceramics is very similar to that of SiC ceramics, combining the two can give full play to their respective advantages to achieve an ideal protective effect. Therefore, the anti-oxidation coating structure of carbon/carbon composite materials with SiC ceramics as the bottom layer and mullite ceramics as the outer coating has attracted extensive attention of researchers in recent years.

At present, the main preparation technologies of mullite coating include plasma spraying method, electron beam physical vapor deposition (EB-PVD), chemical vapor deposition (CVD) and so on. Compared with the traditional coating preparation method, the sol-gel method has the following advantages: first, the process equipment is simple and the equipment cost is low; second, the coating preparation speed is fast, and the production capacity advantage is obvious; third, it can achieve more The low preparation temperature avoids thermal damage to the substrate material during the coating preparation process; fourth, it has a strong ability to design and control the microstructure of the material; fifth, it has low requirements on the shape of the substrate, making it easier to prepare coatings on substrates with complex shapes. Floor. However, there are still many shortcomings in the traditional sol-gel coating preparation process, which restricts its development and application. The main defects are: 1) the coating is loose and porous, and the density is low; 2) the bonding between the coating and the substrate is poor, and the coating is easy to crack and peel off during drying or sintering; 3) the upper limit of the coating thickness is low, and it is difficult to Meet the thickness requirements of the anti-oxidation coating; 4) The preparation process needs to go through multiple coating-drying-sintering processes, and it is difficult to prepare a uniform and dense coating with an ideal thickness through a single coating.

Contents of the invention

The purpose of the present invention is to overcome the defects of the above-mentioned prior art, by combining the dipping-lifting technology and the sol-gel process, it provides a coating preparation that can be completed at one time without multiple cycles and post-heat treatment, and has low preparation cost , short cycle, simple operation and so on.

A kind of preparation method of mullite anti-oxidation coating of the present invention comprises the following steps:

step one

With soluble aluminum salt and silicate as raw materials, in molar ratio, Al:Si:organic solvent:catalyst=(2～3):(1～1.5):(4～9):(0.3～0.5), prepared The raw material, the organic solvent and the catalyst are refluxed to obtain a gel; the obtained gel is dried and calcined at 1200-1350°C in an oxygen-containing atmosphere to obtain pre-calcined mullite powder A;

step two

With soluble aluminum salt and silicate as raw materials, in molar ratio, Al:Si:organic solvent:catalyst=(2～3):(1～1.5):(4～9):(0.3～0.5), prepared Raw materials, organic solvents and catalysts are refluxed at 60-85°C, and then deionized water is added dropwise; and the temperature is raised to 80-85°C for at least 8 hours, then cooled and aged; after aging, at 80-120°C Dry to obtain mullite precursor powder B;

step three

According to the mass ratio, pre-calcined mullite powder A:mullite precursor powder B=4～6:1, pre-calcined mullite powder A, mullite precursor powder B, and then prepared Membrane aids, drying inhibitors, solvents; mix the prepared pre-calcined mullite powder A, mullite precursor powder B, film-forming aids, drying inhibitors, and solvents to obtain a slurry, and the matrix Immerse in the slurry, and apply the slurry by dipping and pulling technology; after coating, calcining at 1480-1515°C to obtain the mullite anti-oxidation coating.

A kind of preparation method of mullite anti-oxidation coating of the present invention; In step 1,

The soluble aluminum salt is selected from one of nonahydrate aluminum nitrate, hexahydrate and aluminum chloride; the water needed for the reaction in step 1 is provided by the crystal water in the aluminum salt;

The silicate is selected from at least one of ethyl orthosilicate, methyl orthosilicate, and propyl orthosilicate;

The organic solvent is selected from at least one of dehydrated ethanol and dehydrated methanol;

The catalyst is at least one selected from glacial acetic acid and hydrofluoric acid.

A method for preparing a mullite anti-oxidation coating of the present invention; in step 1, the reflux reaction is: reflux reaction for 3-5h under heating in a water bath at 45-75°C, and then heat up to 80-100°C for 10-14h , to obtain a gel.

A method for preparing a mullite anti-oxidation coating of the present invention; in step 1, after the gel is obtained, dry at 80-120°C for 8-72 hours; after drying, ball mill at 150-350rpm for 1-4 hours, Carry out calcination at 1200-1350° C. for 2-3 hours, and cool down to room temperature with the furnace to obtain pre-calcined mullite powder A.

A kind of preparation method of mullite anti-oxidation coating of the present invention; In step 2;

The soluble aluminum salt is selected from at least one of aluminum acetate, Al(NO ₃ ) ₃ 9H2O, and anhydrous aluminum chloride;

The silicate is selected from at least one of ethyl orthosilicate, methyl orthosilicate, and propyl orthosilicate;

The organic solvent is selected from at least one of dehydrated ethanol and dehydrated methanol;

The catalyst is selected from at least one of glacial acetic acid and hydrofluoric acid;

The molar ratio of the dropped deionized water to the aluminum element in the system is 3-7:6.

A kind of preparation method of mullite anti-oxidation coating of the present invention; In step 2

A kind of preparation method of mullite anti-oxidation coating of the present invention; In step 2;

Carry out reflux reaction at 60-85°C for 4-6 hours, then drop deionized water; and heat up to 80-85°C for at least 8 hours, then cool and age; when aging, the control time is 1-2 months, The temperature is 40-65° C.; after aging, dry at 100-120° C. for 10-14 hours and ball mill at 150-350 rpm for 1-4 hours to obtain the mullite precursor powder B.

A method for preparing a mullite anti-oxidation coating of the present invention; in step 3, pre-calcined mullite powder A: mullite precursor powder B=4～6:1 according to the mass ratio, and pre-calcined Mullite powder A, mullite precursor powder B, and the total mass of pre-calcined mullite powder A and mullite precursor powder B is 10-10% of the total mass of the solvent used. 25wt%; according to the 0.3-1.5% of the total mass of pre-calcined mullite powder A and mullite precursor powder B, the film-forming aid is prepared; the film-forming aid is selected from polyvinylpyrrolidone, polyvinylpyrrolidone, At least one of vinyl butyral; according to 5 ~ 8wt% of the total mass of the solvent, a drying inhibitor is formulated; the drying inhibitor is selected from at least one of oxalic acid and glycerol; the solvent is selected from At least one of absolute ethanol, absolute methanol, and acetone.

A kind of preparation method of mullite anti-oxidation coating of the present invention; Its optimal technical scheme comprises the following steps:

Step A

According to the molar ratio, the molar ratio of Al(NO ₃ ) ₃ 9H2O, tetraethyl orthosilicate, absolute ethanol and glacial acetic acid is 3:1:5～8:0.3～0.5, with Al(NO ₃ ) ₃ · Mix 9H ₂ O, tetraethyl orthosilicate, absolute ethanol and glacial acetic acid evenly, then reflux for 3-5 hours under heating in a water bath at 45-75°C, then raise the temperature to 80-100°C for 10-14 hours to obtain a gel The resulting gel is dried at 80-120°C for 8-72 hours; after drying, it is ball milled at 150-350rpm for 1-4 hours, then calcined at 1200-1350°C for 2-3 hours, and cooled to room temperature with the furnace to obtain pre-calcined Mullite powder A;

Step B

In molar ratio, aluminum acetate: Al(NO ₃ ) ₃ 9H ₂ O: anhydrous aluminum chloride: ethyl orthosilicate = 1.8:0.4:0.8:1; with aluminum acetate, Al(NO ₃ ) ₃ · 9H ₂ O, anhydrous aluminum chloride, ethyl orthosilicate;

Then, according to the molar ratio, glacial acetic acid: tetraethyl orthosilicate = 1 ~ 2:5 to prepare glacial acetic acid,

Dissolve the prepared aluminum acetate, Al(NO ₃ ) ₃ 9H ₂ O, anhydrous aluminum chloride, tetraethyl orthosilicate, and glacial acetic acid in absolute ethanol. After reflux reaction for 3-5 hours under heating in a water bath at 70°C, add deionized water dropwise. The molar ratio of the added deionized water to the aluminum element in the system is 3-7:6, and then heat up to 80-85°C to react for 8 -12h; After the reaction, age the gel obtained by the reaction at 40-65°C for 1-2 months, then dry it at 100-120°C for 10-14h, and then ball mill it at 200-300rpm for 1-4h to obtain mullite Stone precursor powder B; the molar ratio of aluminum acetate, Al(NO ₃ ) ₃ 9H ₂ O, aluminum element in anhydrous aluminum chloride to absolute ethanol used is 3:5-8;

Step C

According to the mass ratio, pre-calcined mullite powder A:mullite precursor powder B=4～6:1, preferably 4.8-5.5:1, pre-calcined mullite powder A, mullite precursor Powder B, and then prepare film-forming aids, drying inhibitors, and solvents; mix the prepared pre-calcined mullite powder A, mullite precursor powder B, film-forming aids, drying inhibitors, and solvents The slurry is obtained after uniformity, the substrate is immersed in the slurry, and the slurry is coated by dipping and pulling technology; after coating, it is calcined at 1480-1515°C to obtain a mullite anti-oxidation coating; the film-forming aid The agent is selected from at least one of polyvinylpyrrolidone polyvinyl butyral, and the quality of the film-forming aid used is 0.8-1.2% of the total mass of the pre-calcined mullite powder A and the mullite precursor powder B; The solvent is composed of absolute ethanol and acetone in a volume ratio of 7:3 to 5, and the total mass of the pre-calcined mullite powder A and the mullite precursor powder B is the total mass of the solvent used. 10-25 wt% of the mass; the desiccant is oxalic acid, and the amount of oxalic acid is 5-8 wt% of the total mass of the solvent.

The invention discloses a method for preparing a mullite anti-oxidation coating; when slurry coating is carried out by dipping and pulling technology, the pulling rate is controlled to be 05-3mm/min, and the temperature is 40-50°C.

The invention relates to a method for preparing a mullite anti-oxidation coating; when slurry coating is carried out by dipping and pulling technology, the nitrogen flow rate in the pulling kettle is controlled to be 1.0-2L/min, preferably 1.5L/min.

A kind of preparation method of mullite anti-oxidation coating of the present invention; Described matrix is prepared by following scheme:

Step I

First, 60-65wt.% Si, 10-30wt.% SiC, 5-10wt.% carbon powder, 1-5wt.% Al ₂ O ₃ are placed in a ball mill jar and wet milled at a speed of 200-250r/min. Take it out after -4h, put it in a drying oven at 80-120°C and dry it for 48-72h, and sieve to obtain -60 mesh embedding powder;

Step II

Put the embedding powder into a graphite jar and embed the C/C composite material sample in the embedding powder, heat it to 1750°C-1800°C in argon atmosphere in a vacuum sintering furnace, and keep it warm for 2-2.5 h, cooled to room temperature, took out the sample, cleaned the sample with absolute ethanol ultrasonically and dried it at 80-120°C for 2-4h to obtain a SiC coating-coated C/C composite material sample (that is, the matrix material ).

The invention discloses a method for preparing a mullite anti-oxidation coating; the molar ratio of aluminum to silicon in the obtained mullite outer coating can be adjusted according to requirements.

The invention discloses a method for preparing a mullite anti-oxidation coating; the molar ratio of aluminum to silicon in the obtained mullite outer coating is preferably 3:1.

Principles and advantages

The invention realizes the single-cycle molding of the coating, and overcomes the disadvantages of low single coating thickness, easy peeling off of the coating prepared by the sol-gel method, and the need to repeat the coating-sintering cycle process for many times.

The present invention adopts a reasonable multi-component coating slurry formula design, which contains pre-calcined mullite powder, mullite precursor powder, film-forming aids, drying inhibitors and mixed solvents according to reasonable ingredients. A new type of coating slurry was prepared after mixing. The coating slurry can greatly improve the ceramic pyrolysis yield and limit coating thickness of the coating slurry, eliminate the coating cracking phenomenon in the sintering process, and obtain a dense and crack-free thick coating through a single coating.

The present invention controls the synthesis of the mullite precursor to be carried out under the incomplete hydrolysis sol-gel route by using a non-aqueous solvent and strictly isolating the environmental moisture, thereby improving the sintering activity of the mullite and controlling the mullite The uniformity of particle shape improves the coating density.

The invention achieves sufficient impregnation of the surface of the substrate by coating the slurry, thereby greatly improving the bonding interface between the mullite outer coating and the SiC bottom layer, thereby avoiding the peeling phenomenon of the coating. At the same time, by precisely controlling the process parameters such as the pulling rate, ambient temperature and gas flow rate, the purpose of improving the coating uniformity and controlling the drying rate is achieved, which improves the uniformity of the coating and avoids cracking during the drying process.

In a word, the present invention uses the synergistic effect of pre-calcined mullite powder, mullite precursor powder, film-forming aids, and drying inhibitors through ingenious component design, especially pre-calcined mullite powder, mullite The interaction between the stone precursor powders has achieved unexpected results. After one-time pulling coating, the finished product has the advantages of uniform and dense coating, excellent bonding performance, and strong high-temperature oxidation resistance.

Description of drawings

Accompanying drawing 1 is the SEM photo of the surface of the mullite outer coating prepared by the embodiment of the present invention 1;

Accompanying drawing 2 is the SEM photo of the mullite/SiC double coating section prepared by the embodiment of the present invention 1;

Accompanying drawing 3 is the mullite outer coating surface XRD pattern that the embodiment of the present invention 1 prepares;

Figure 4 is the oxidation weight loss curve of the mullite/SiC double-layer coating coated C/C substrate prepared in Example 1 of the present invention under air oxidation at 1500°C.

It can be seen from Fig. 1 that the surface of the mullite outer coating prepared by the process of Example 1 is dense and free of cracks.

It can be seen from FIG. 2 that the thickness of the mullite outer coating prepared by the process of Example 1 reaches about 180 μm, and it is well combined with the SiC bottom layer.

It can be seen from FIG. 3 that the mullite outer coating prepared by the process of Example 1 is mainly composed of 3/2 mullite and cristobalite phases.

It can be seen from Figure 4 that the mullite/SiC coated C/C composite material prepared by the process of Example 1 has excellent oxidation resistance under the air oxidation condition of 1500°C.

detailed description

Example 1:

Preparation of SiC coating by embedding method: First, put 180g of Si powder, 90g of SiC powder, 15g of carbon powder, and 15g of Al ₂ O ₃ into a ball mill jar for wet grinding at a speed of 200r/min for 24h, then take it out and put it in a drying oven Dry at 90°C for 12 hours, and then sieve through a 60-mesh sieve to obtain the embedding powder.

Put the embedding powder into a graphite jar and embed the C/C matrix sample in the embedding powder, heat it to 1750°C in an argon atmosphere in a vacuum sintering furnace, keep it warm for 2 hours, and then cool it slowly to room temperature Take out the sample. The sample was ultrasonically cleaned with absolute ethanol and dried at 90°C for 2 hours to obtain a SiC coating-coated C/C composite sample.

Preparation of mullite outer coating by sol-gel method:

1) Dissolve 10.4165g tetraethyl orthosilicate and 56.247g Al(NO ₃ ) ₃ 9H ₂ O in 14mL ethanol, add 1.800g glacial acetic acid, reflux for 4 hours in a water bath at 60°C and then heat up to 80°C React for 12 hours, then dry the gel obtained from the reaction and ball mill it at 250rpm for 2 hours, then put it into a muffle furnace with a heating rate of 5°C/min, keep it at 1200°C for 2 hours, and then cool to room temperature with the furnace to prepare pre-calcined mullite powder Material A;

2) After dissolving 6.1233g of aluminum acetate, 0.1500g of Al(NO ₃ ) ₃ 9H ₂ O, 12.4000g of anhydrous aluminum chloride and 10.4165g of ethyl orthosilicate in 50mL of absolute ethanol, add 1.2g of glacial acetic acid as After the catalyst was stirred, after the solid reagent was completely dissolved in absolute ethanol, it was refluxed and reacted in a water bath at 60°C for 4 hours in a water-isolated environment, and then slowly added 0.042g of deionized water dropwise, and then the temperature was raised to 80°C for 12 hours. After the reaction, the gel obtained by the reaction was aged for 2 months, dried at 120°C for 12 hours, and ball milled at 250 rpm for 2 hours to obtain the mullite precursor powder B;

3) After mixing 35mL of absolute ethanol and 15mL of acetone evenly, add 0.19g of polyvinylpyrrolidone (PVP) and stir until completely dissolved, then add 15g of pre-calcined mullite powder A and 3.75g of mullite precursor powder B and 2.5mL of oxalic acid were ball milled at 250rpm for 4h to obtain a coating slurry; 4) The sample of SiC-coated C/C composite material was immersed in the slurry obtained in step 3), and then coated by a pull After sintering in a tube furnace at 1500°C for 2 hours, a C/C composite sample coated with a mullite/SiC double-layer structure anti-oxidation coating was obtained. During pulling coating, the pulling rate is controlled to be 1mm/min, the pulling ambient temperature is 45°C, and the nitrogen flow rate in the pulling kettle is 1.5L/min. The weight loss rate of the obtained coating sample was only 0.38% after being oxidized at 1500°C for 100 hours in the air environment. Its high temperature oxidation resistance is far superior to similar products.

Example 2:

Preparation of SiC coating by embedding method: First, put 260g Si powder, 96g SiC powder, 40g carbon powder, 4g Al ₂ O ₃ in a ball mill jar and wet grind for 24 hours at a speed of 200r/min, then take it out and put it in a drying oven Dry at 90°C for 12 hours, and then sieve through a 60-mesh sieve to obtain the embedding powder.

Put the embedding powder into a graphite jar and embed the C/C matrix sample in the embedding powder, heat it to 1800°C in an argon atmosphere in a vacuum sintering furnace, keep it warm for 2 hours, and then cool it slowly to room temperature Take out the sample. The sample was ultrasonically cleaned with absolute ethanol and dried at 90°C for 2 hours to obtain a SiC coating-coated C/C composite sample.

Preparation of mullite outer coating by sol-gel method:

1) Dissolve 41.666g of tetraethyl orthosilicate and 224.988g of Al(NO ₃ ) ₃ 9H ₂ O in 200mL of ethanol, add 30g of glacial acetic acid, reflux for 4 hours under heating in a water bath at 60°C, and then heat up to 80°C for reaction After 12 hours, the gel obtained by the reaction was dried and ball milled at 250rpm for 2 hours, then put into the muffle furnace at a heating rate of 5°C/min, kept at 1200°C for 2 hours, and then cooled to room temperature with the furnace to obtain pre-calcined mullite powder A;

2) After dissolving 60.6930g of aluminum acetate, 3.7498g of Al(NO ₃ ) ₃ 9H ₂ O, 12.0000g of anhydrous aluminum chloride and 52.0852g of ethyl orthosilicate in 200mL of absolute ethanol, add 20g of glacial acetic acid as a catalyst After stirring, after the solid reagent was completely dissolved in absolute ethanol, reflux and react in a water bath at 60°C for 4 hours in a water-isolated environment, then slowly add 0.21 g of deionized water dropwise, and then raise the temperature to 80°C for 12 hours. After the reaction, the gel obtained by the reaction was aged for 2 months, dried at 120°C for 12 hours, and ball milled at 250 rpm for 2 hours to obtain the mullite precursor powder B;

3) After mixing 35mL of absolute ethanol and 15mL of acetone evenly, add 0.5g of polyvinylpyrrolidone (PVP) and stir until completely dissolved, then add 17g of pre-calcined mullite powder A and 4.25g of mullite precursor powder B and 2.5mL of oxalic acid were ball-milled at 250rpm for 4h to obtain a coating slurry; 4) The sample with SiC-coated C/C composite material was immersed in the slurry obtained in step 3), and pulled once After coating, it was sintered at 1500°C for 2 hours in a tube furnace to obtain a C/C composite sample coated with mullite/SiC double-layer structure anti-oxidation coating. During pulling coating, the pulling rate is controlled to be 1mm/min, the pulling ambient temperature is 45°C, and the nitrogen flow rate in the pulling kettle is 1.5L/min. After the coating was completed, it was sintered in a tube furnace at 1500°C for 2 hours to obtain a C/C composite sample coated with a mullite/SiC double-layer structure anti-oxidation coating. The weight loss rate of the obtained coating sample was only 0.45% after being oxidized at 1500°C for 100 hours in the air environment. Its high temperature oxidation resistance is far superior to similar products.

Claims (2)

1. a kind of preparation method of mullite ORC, it is characterised in that comprise the following steps：

Step A

In molar ratio, Al (NO₃)₃·9H₂The mol ratio of O, tetraethyl orthosilicate, dehydrated alcohol and glacial acetic acid is 3：1：5～8：0.3 ～0.5, with taking Al (NO₃)₃·9H₂O, tetraethyl orthosilicate, dehydrated alcohol and glacial acetic acid, mix homogeneously, then in 45-75 DEG C of water 80-100 DEG C of reaction 10-14h is warming up to again after lower back flow reaction 3-5h of bath heating, obtains gel；Gained gel is at 80-120 DEG C It is dried 8-72 hours；With 150-350rpm after drying, after ball milling 1-4 hours, in atmosphere, calcined in 1200-1350 DEG C 2-3 hours, cool to room temperature with the furnace, obtain precalcining porzite powder A；

Step B

In molar ratio, aluminum acetate：Al(NO₃)₃·9H₂O：Anhydrous Aluminum chloride：Tetraethyl orthosilicate=1.8:0.4:0.8:1；With taking vinegar Sour aluminum, Al (NO₃)₃·9H₂O, anhydrous Aluminum chloride, tetraethyl orthosilicate；

Then, in molar ratio, glacial acetic acid：Tetraethyl orthosilicate=1～2:5 with taking glacial acetic acid,

By with aluminum acetate, the Al (NO for taking₃)₃·9H₂O, anhydrous Aluminum chloride, tetraethyl orthosilicate, glacial acetic acid are dissolved in dehydrated alcohol, In the environment of isolation moisture, after back flow reaction 3-5h under 60-70 DEG C of heating in water bath, then Deca deionized water, institute's Deca Deionized water is 3～7 with the mol ratio of aluminium element in system:6, then raise temperature to 80-85 DEG C of reaction 8-12h；After reaction terminates The gel that reaction is obtained is aged 1～2 month at 40-65 DEG C, with 200-300rpm after being then dried 10-14h at 100-120 DEG C Rotating speed ball milling 1-4h after obtain mullite precursor powder material B；Aluminum acetate used, Al (NO₃)₃·9H₂In O, anhydrous Aluminum chloride Aluminium element is 3 with the mol ratio of dehydrated alcohol used：5～8；

Step C

In mass ratio, precalcining porzite powder A：Mullite precursor powder material B=4～6:1, with taking precalcining porzite powder A, mullite precursor powder material B, then with taking coalescents, drying retarder, solvent；By with the precalcining porzite powder for taking Slurry is obtained after A, mullite precursor powder material B, coalescents, drying retarder, solvent mix homogeneously, matrix is immersed into slurry In, carry out slurry coating using Best-Effort request technology；After having coated, in 1480～1515 DEG C of calcinings, mullite antioxidation is obtained Coating；At least one of the coalescents in Polyvinylprrilone butyral, used film forming auxiliary agent Quality is the 0.8-1.2% of precalcining porzite powder A and mullite precursor powder material B gross mass；The solvent is by anhydrous second Alcohol and acetone by volume 7:3～5 compositions, and match somebody with somebody two kinds of the precalcining porzite powder A for taking and mullite precursor powder material B Powder gross mass is 10～25wt% of solvent for use gross mass；The desiccant is oxalic acid, and consumption of oxalic acid is the total matter of solvent 5～8wt% of amount.

2. the preparation method of a kind of mullite ORC according to claim 1；It is characterized in that：Carried using dipping When pull technology carries out slurry coating, it is 05-3mm/min to control the rate of pulling, and temperature is 40-50 DEG C.