A method for preparing mullite slurry for fiber-reinforced oxide-based composite materials

Abstract

The present invention relates to a method for preparing mullite slurry for fiber-reinforced oxide-based composite materials, comprising the following steps: preparing Al2O3 sol, mixing aluminum source, deionized water, catalyst and additives in proportion, stirring and heating to obtain a stable sol; preparing SiO2 sol, mixing silicon source, anhydrous ethanol, deionized water and additives in proportion, adjusting pH value by catalyst, stirring and heating to obtain a stable sol; preparing mullite powder, mixing Al2O3 sol and SiO2 sol in proportion, stirring, heating and sintering to obtain a mullite block, and grinding the block to obtain mullite powder; preparing mullite slurry, mixing Al2O3 sol, SiO2 sol, mullite powder, dispersant and additives in proportion, and ball milling to obtain mullite slurry. The present invention has good rheological properties and can meet the requirements of preparing oxide-based composite material components by dipping or brushing.

Description

Technical Field

[0001] The invention relates to the technical field of oxide ceramic-based composite material preparation, and in particular to a method for preparing mullite slurry for fiber-reinforced oxide-based composite material. Background Art

[0002] Continuous oxide fiber reinforced oxide ceramic matrix composites have excellent properties such as low density, high specific strength, thermal shock resistance, and oxidation resistance. They are emerging candidate materials with great potential for hot end components in the aerospace field. Mullite (3Al2O3·2SiO2 or 2Al2O3·SiO2) has a high melting point, low density, small linear expansion coefficient, stable physical and chemical properties at high temperatures, and excellent creep resistance and thermal shock resistance. It is currently the most studied and most promising matrix material for oxide ceramic matrix composites.

[0003] At present, the commonly used processes for preparing continuous oxide fiber reinforced oxide ceramic matrix composites are slurry-infiltration and sol-gel. The sol-gel process is to use oxide sol to impregnate fiber preforms, prepare the matrix through drying, sintering and other processes, and then perform multiple impregnation-drying-sintering to finally obtain a composite material. The sol cost of this process is relatively low, the purity is high, the designability is strong, the preparation temperature is low, the thermal damage to the fiber is small, and the matrix component is highly uniform. However, the preparation cycle of this process is long, the volume shrinkage during the preparation process is obvious, the product density is low, and the mechanical properties are low. The slurry-infiltration process is to use slurry to impregnate or brush the fiber preform or fiber cloth, and obtain a dense composite material by high-temperature sintering without pressure or hot pressing. The preparation method of this process is simple and the preparation cycle is short, but the preparation temperature of this process is usually greater than 1200°C, which causes great damage to the fiber. In addition, the poor uniformity of the matrix component causes large differences in the performance of various parts of the material.

[0004] In CN 110526728 B "A fiber-reinforced mullite ceramic-based composite material and its preparation method", alumina powder, silica sol and dispersant are mixed, and an impregnation precursor is prepared by ball milling. In this method, the alumina powder is prone to uneven dispersion, resulting in uneven distribution of the mullite phase. In CN 10658982 B "A method for preparing a porous mullite ceramic / epoxy resin composite material", the prepared silica sol and the prepared alumina slurry are mixed, and ammonia water is added to obtain 3Al2O3·2SiO2 gel, which is then heated in an oven to obtain silicon aluminum powder. The above method has problems such as poor purity of the mullite phase and uneven distribution. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing mullite slurry for fiber-reinforced oxide-based composite materials; the specific technical scheme is as follows:

[0006] A method for preparing mullite slurry for fiber-reinforced oxide-based composite materials comprises the following steps:

[0007] Step 1: preparing alumina sol: mixing aluminum source, deionized water, catalyst and additives in proportion, stirring and heating to obtain stable alumina sol;

[0008] Step 2: preparing silica sol: mixing silicon source, anhydrous ethanol, deionized water and additives according to proportion, adding catalyst to adjust pH value, stirring and heating to obtain stable silica sol;

[0009] Step 3: preparing mullite powder: mixing alumina sol and silica sol in proportion, stirring, heating and sintering to obtain a mullite block, and then grinding the block to obtain mullite powder;

[0010] Step 4: preparing mullite slurry: mixing alumina sol, silica sol, mullite powder, dispersant and additives in proportion, and obtaining a stable mullite slurry through ball milling.

[0011] The method for preparing a mullite slurry for a fiber-reinforced oxide-based composite material, the preferred embodiment of which is that in step 1, the aluminum source is aluminum isopropoxide; the catalyst is one of nitric acid or hydrochloric acid; the additive is one or more of oxalic acid, formamide or citric acid, and the additive is used to prolong the gel time and enhance the stability of the sol;

[0012] Aluminum isopropoxide 10 wt% to 30 wt%, deionized water 60 wt% to 90 wt%, catalyst 0.3 wt% to 2.0 wt%, additive 0.5 wt% to 2.0 wt% are mixed;

[0013] The mixing is to first mix the aluminum source with deionized water, wait for the hydrolysis to be complete, wash the generated boehmite precipitate with deionized water, and then drop the catalyst;

[0014] Heating is carried out throughout the hydrolysis process, and the heating temperature is 80℃~90℃;

[0015] The solid content of the alumina sol is 20 wt% to 40 wt%, the average particle size of the alumina sol is 5 nm to 30 nm, and the viscosity ranges from 60 mPa·s to 100 mPa·s.

[0016] The method for preparing a mullite slurry for a fiber-reinforced oxide-based composite material, the preferred embodiment of which is that in step 2, the silicon source is tetraethyl orthosilicate; the catalyst is one of nitric acid or hydrochloric acid;

[0017] The additive is oxalic acid or N, N is one or more of dimethylformamide or citric acid, and the function of the additive is to prolong the gel time and enhance the stability of the sol;

[0018] Mix 30wt%~70wt% of ethyl orthosilicate, 10wt%~30wt% of anhydrous ethanol, 10wt%~40wt% of deionized water, and 2~10wt% of additives;

[0019] The mixing is to dissolve the silicon source and anhydrous ethanol under stirring, then add the catalyst solution, and finally add the additive, the pH value of which is 1;

[0020] Heating is carried out during the process of adding the catalyst dropwise, and the heating temperature is 30°C~60°C.

[0021] The solid content of the silica sol is 20 wt% to 60 wt%, the average particle size of the sol is 1 nm to 20 nm, and the viscosity is 30 mPa·s to 110 mPa·s.

[0022] The method for preparing a mullite slurry for a fiber-reinforced oxide-based composite material, wherein a preferred embodiment is as follows: in step three, the alumina sol obtained in step one and the silica sol obtained in step two are stirred and mixed in a molar ratio of (2.5-4.5): (1.5-2.5), and subjected to a heating treatment at 60°C-90°C to obtain a silica-alumina gel; and then subjected to sintering at 1000°C-1300°C and grinding to obtain a mullite powder with an average particle size of 20nm-100nm.

[0023] The method for preparing a mullite slurry for a fiber-reinforced oxide-based composite material, the preferred embodiment of which is that in step 4, the dispersant is one or both of polyethylene glycol and polyvinyl alcohol, the molecular weight of polyethylene glycol is 2000-10000, and the molecular weight of polyvinyl alcohol is 16000-20000;

[0024] The additive is one or more of yttrium oxide powder, magnesium oxide powder, boron oxide powder, and lanthanum oxide powder;

[0025] Mixing in a ratio of 30wt% to 60wt% of alumina sol, 10wt% to 25wt% of silica sol, 30wt% to 50wt% of mullite powder, 1wt% to 10wt% of dispersant, and 0wt% to 10wt% of additives;

[0026] The ball milling is carried out using a planetary ball mill, the ball milling speed is 100 r / min~200 r / min, and the ball milling time is 2 h~12 h;

[0027] The mullite slurry has a solid content of 30 wt% to 80 wt% and a viscosity of 20 mPa·s to 120 mPa·s.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] (1) The mullite slurry prepared by the present invention has controllable and adjustable bonding properties and can be used to prepare fiber-reinforced oxide ceramic-based composite materials by dipping or brushing;

[0030] (2) The mullite slurry prepared by the present invention can be designed with strong components, and can modify the matrix of the oxide ceramic-based composite material by adding other oxide powders, thereby achieving the effect of changing the performance of the composite material;

[0031] (3) The mullite slurry prepared by the present invention has high mullite phase purity, small mullite powder particle size, large specific surface area, high sintering activity, and low sintering temperature required for preparing oxide ceramic-based composite materials, which can reduce thermal damage to fibers. DETAILED DESCRIPTION Example

[0032] First, 10% aluminum isopropoxide is ground and dissolved in 88% deionized water at 85°C. After stirring for 1 hour, the mixture is filtered or centrifuged. An appropriate amount of deionized water is taken to wash the boehmite precipitate. After adding deionized water, 0.5% nitric acid and 1.5% oxalic acid are added dropwise under stirring conditions. The mass concentration of nitric acid is 1 mol / L. The mixture is stirred for 30 min to 60 min to obtain an alumina sol.

[0033] Then, 50% of ethyl orthosilicate was dissolved in 10% of anhydrous ethanol and 30% of deionized water in portions, and 10% of dimethylformamide was added at 40°C with stirring. At the same time, 1 mol / L of nitric acid was added dropwise to adjust the pH to 1, and the mixture was stirred for 30 min to 60 min to obtain silica sol. 70% of alumina sol and 30% of silica sol were mixed uniformly by stirring, heated at 60°C for 2 h to 12 h, and then transferred to a sintering furnace and sintered at 1200°C for 30 min to 120 min to obtain mullite powder.

[0034] Finally, 36% alumina sol, 14% silica sol, 40% mullite powder, 5% polyethylene glycol and 5% yttrium oxide powder were put into a ball mill with a ball-to-material mass ratio of 10:1, a rotation speed of 200 r / min, and ball milling for 12 h to obtain a mullite slurry with a solid content of 60% and a viscosity of 80 mPa·s. Example

[0035] First, 10% aluminum isopropoxide is ground and dissolved in 88% deionized water at 85°C. After stirring for 1 hour, the mixture is filtered or centrifuged. An appropriate amount of deionized water is taken to wash the boehmite precipitate. After adding deionized water, 0.5% nitric acid and 1.5% oxalic acid are added dropwise under stirring conditions. The mass concentration of nitric acid is 1 mol / L. The mixture is stirred for 30 min to 60 min to obtain an alumina sol.

[0036] Then, 50% of ethyl orthosilicate was dissolved in 10% of anhydrous ethanol and 30% of deionized water in portions, and 10% of dimethylformamide was added at 40°C with stirring. At the same time, 1 mol / L of nitric acid was added dropwise to adjust the pH to 1, and the mixture was stirred for 30 min to 60 min to obtain silica sol. 70% of alumina sol and 30% of silica sol were mixed uniformly by stirring, heated at 60°C for 2 h to 12 h, and then transferred to a sintering furnace and sintered at 1200°C for 30 min to 120 min to obtain mullite powder.

[0037] Finally, 36% alumina sol, 14% silica sol, 45% mullite powder and 5% polyethylene glycol were put into a ball mill with a ball-to-material mass ratio of 10:1, a rotation speed of 200 r / min, and ball milling for 12 h to obtain a mullite slurry with a solid content of 55% and a viscosity of 60 mPa·s. Example

[0038] First, 10% aluminum isopropoxide is ground and dissolved in 88% deionized water at 85°C. After stirring for 1 hour, the mixture is filtered or centrifuged. An appropriate amount of deionized water is taken to wash the boehmite precipitate. After adding deionized water, 0.5% nitric acid and 1.5% oxalic acid are added dropwise under stirring conditions. The mass concentration of nitric acid is 1 mol / L. The mixture is stirred for 30 min to 60 min to obtain an alumina sol.

[0039] Then, 50% of ethyl orthosilicate was dissolved in 10% of anhydrous ethanol and 30% of deionized water in portions, and 10% of dimethylformamide was added at 40°C with stirring. At the same time, 1 mol / L of nitric acid was added dropwise to adjust the pH to 1, and the mixture was stirred for 30 min to 60 min to obtain silica sol. 70% of alumina sol and 30% of silica sol were mixed uniformly by stirring, heated at 60°C for 2 h to 12 h, and then transferred to a sintering furnace and sintered at 1200°C for 30 min to 120 min to obtain mullite powder.

[0040] Finally, 60% alumina sol, 23.6% silica sol, 15% mullite powder, 0.4% polyethylene glycol and 1% yttrium oxide powder were put into a ball mill with a ball-to-material mass ratio of 6:1 and a rotation speed of 100 rpm for 12 h to obtain a mullite slurry with a solid content of 40% and a viscosity of 30 mPa·s.

[0041] The above specific embodiments are only used to illustrate the technical solution of the present invention, rather than to limit it. Any person familiar with this technology can make various changes, modifications and substitutions without departing from the technology and scope of the present invention. The protection scope of the present invention shall be subject to the scope defined in the claims.

Claims

1. A method for preparing a mullite slurry for a fiber-reinforced oxide-based composite material, characterized in that: The steps include: Step 1: preparing alumina sol: mixing aluminum source, deionized water, catalyst and additives in proportion, stirring and heating to obtain stable alumina sol; Step 2: preparing silica sol: mixing silicon source, anhydrous ethanol, deionized water and additives according to proportion, adding catalyst to adjust pH value, stirring and heating to obtain stable silica sol; Step 3: preparing mullite powder: mixing alumina sol and silica sol in proportion, stirring, heating and sintering to obtain a mullite block, and then grinding the block to obtain mullite powder; Step 4: preparing mullite slurry: mixing alumina sol, silica sol, mullite powder, dispersant and additives in proportion, and ball milling to obtain a stable mullite slurry; In step 1, the aluminum source is aluminum isopropoxide; the catalyst is one of nitric acid or hydrochloric acid; the additive is one or more of oxalic acid, formamide or citric acid, and the additive is used to extend the gel time and enhance the stability of the sol; Mixing in a ratio of 10wt% to 30wt% of aluminum isopropoxide, 60wt% to 90wt% of deionized water, 0.3wt% to 2.0wt% of a catalyst, and 0.5wt% to 2.0wt% of an additive; The mixing is to first mix the aluminum source with deionized water, wait for the hydrolysis to be complete, wash the generated boehmite precipitate with deionized water, and then drop the catalyst; Heating is carried out during the entire hydrolysis process, and the heating temperature is 80℃~90℃; The alumina sol has a solid content of 20 wt% to 40 wt%, an average particle size of 5 nm to 30 nm, and a viscosity range of 60 mPa·s to 100 mPa·s; In step 2, the silicon source is tetraethyl orthosilicate; the catalyst is one of nitric acid or hydrochloric acid; The additive is one or more of oxalic acid, N,N-dimethylformamide or citric acid, and the additive is used to prolong the gel time and enhance the stability of the sol; Mix 30 wt%~70wt% of ethyl orthosilicate, 10 wt%~30wt% of anhydrous ethanol, 10 wt%~40wt% of deionized water, and 2~10wt% of additives; The mixing is to dissolve the silicon source and anhydrous ethanol under stirring, then add the catalyst solution, and finally add the additive, the pH value of which is 1; Heating is done during the process of adding the catalyst, and the heating temperature is 30℃~60℃; The solid content of the silica sol is 20 wt% to 60 wt%, the average particle size of the sol is 1 nm to 20 nm, and the viscosity is 30 mPa·s to 110 mPa·s; In step 3, the alumina sol obtained in step 1 and the silica sol obtained in step 2 are stirred and mixed in a molar ratio of (2.5-4.5): (1.5-2.5), and heated at 60°C-90°C to obtain a silica-alumina gel; and then sintered at 1000°C-1300°C, and ground to obtain a mullite powder with an average particle size of 20nm-100nm; In step 4, the dispersant is one or both of polyethylene glycol and polyvinyl alcohol, the molecular weight of polyethylene glycol is 2000-10000, and the molecular weight of polyvinyl alcohol is 16000-20000; The additive is one or more of yttrium oxide powder, magnesium oxide powder, boron oxide powder, and lanthanum oxide powder; Mixing the alumina sol in a ratio of 30 wt% to 60 wt%, the silica sol in a ratio of 10 wt% to 25 wt%, the mullite powder in a ratio of 30 wt% to 50 wt%, the dispersant in a ratio of 1 wt% to 10 wt%, and the additive in a ratio of 1 wt% to 10 wt%; The ball milling is carried out using a planetary ball mill, the ball milling speed is 100 r / min~200 r / min, and the ball milling time is 2 h~12 h; The mullite slurry has a solid content of 30 wt% to 80 wt% and a viscosity of 20 mPa·s to 120 mPa·s.