CN106966744A - A kind of fibre reinforced alumina ceramic composite material and preparation method thereof - Google Patents

Abstract

The present invention relates to a kind of fibre reinforced alumina ceramic composite material and preparation method thereof.Wherein, the preparation method comprises the following steps：S101：Using Alumina gel as precursor, vacuum impregnation is carried out to carbon felt, then densification will be carried out with the impregnated carbon felt of Alumina gel, to prepare the aluminium oxide ceramics of fibre reinforced；S102：Vacuum impregnation is carried out to the aluminium oxide ceramics of fibre reinforced using sol-gal process, then dries, sinters, and is cooled to room temperature, to prepare Si Al C coatings.According to a kind of preparation method of fibre reinforced alumina ceramic composite material of the present invention, its short preparation period and cost is low；According to a kind of fibre reinforced alumina ceramic composite material of the present invention, its mechanical property, resistance to elevated temperatures are excellent.

Description

A kind of carbon fiber reinforced alumina ceramic composite material and preparation method thereof

technical field

The invention relates to the field of materials, in particular to a carbon fiber reinforced alumina ceramic composite material and a preparation method thereof.

Background technique

Alumina ceramics have the advantages of high melting point, good high temperature chemical stability, high modulus and strength, etc., and can be used for a long time in high temperature oxidizing environment. However, bulk alumina ceramics generally have low toughness and are prone to catastrophic failure, which limits its application in engineering structures. In order to improve the mechanical properties of alumina ceramics, various toughening mechanisms have been widely used, mainly including particle reinforcement, whisker reinforcement and fiber reinforcement, among which particle and whisker toughening can significantly improve the strength of alumina ceramics, but for The increase in toughness is low, and the particle and whisker toughened alumina ceramics are mostly hot-pressed, which makes it difficult to form large and complex structures. At present, the use of high-modulus, high-strength fibers to toughen ceramics is considered to be a promising way to improve the toughness of ceramics. According to the theory of composite materials, when the crack extends to the fiber, the energy is absorbed by the detachment of the fiber from the matrix section, and the stress concentration is eased. When some fibers are broken and pulled out of the matrix under the action of tensile stress, a large amount of energy will also be consumed. These All are beneficial to enhance the toughness of ceramic materials.

There are many methods for preparing alumina ceramics, among which the sol-gel method is a common method for preparing alumina ceramics, which is to hydrolyze and polycondense aluminum alkoxide or aluminum salt at slightly higher than room temperature to obtain sol and A method for obtaining alumina ceramics by thermally cracking the gel and then thermally cracking it. The outstanding features of this method in material preparation are: (1) Since the size of the particles is at the nanometer level during the gelation process, the sintering temperature can be greatly reduced; (2) The chemical composition can be very uniform in a single-phase matrix (3) Before cracking, it passes through two states of sol and gel, so it is easy to impregnate and shape the fiber and its braid, so it is convenient to prepare fiber-reinforced composite materials.

According to the different alumina raw materials prepared by the sol-gel method, the preparation of alumina sol can be divided into organic salt raw material method, inorganic salt raw material method, and powder method. The organic salt method uses aluminum isopropoxide as the raw material. In a device with stirring, reflux and feeding functions, the organic raw material is added dropwise to water, stirred vigorously at 80°C, most of the alcohol is evaporated, and then refluxed for several hours. In the inorganic salt method, the metal salt is digested in hydrochloric acid or aluminum chloride or the analytically pure aluminum nitrate is dissolved in water, and the pH of the solution is adjusted with ammonia water. The powder method uses SB powder (boehmite) or alumina powder to disperse the powder to obtain a sol.

Carbon fiber is a good reinforcement material because of its high specific strength, specific modulus and fatigue strength. However, carbon fiber is very prone to oxidation above 400°C, resulting in a catastrophic decline in material performance. Silicon carbide fiber is also a good reinforcement material, and its heat resistance and oxidation resistance are better than carbon fiber, but silicon carbide fiber is very expensive, which limits its scope of use. Therefore, on the basis of solving the oxidation resistance of carbon fiber, it is of great significance to reduce the cost as much as possible to expand its application range.

Contents of the invention

The present invention aims to solve one of the technical problems in the related art at least to a certain extent.

Therefore, an object of the present invention is to propose a method for preparing a carbon fiber reinforced alumina ceramic composite material with excellent mechanical properties and high temperature resistance, short preparation period and low cost.

A method for preparing a carbon fiber reinforced alumina ceramic composite material according to an embodiment of the present invention includes the following steps: S101: Using aluminum sol as a precursor, vacuum impregnate carbon felt, and then vacuum impregnate the carbon felt impregnated with aluminum sol Densification treatment to prepare carbon fiber-reinforced alumina ceramics; S102: Vacuum impregnation of carbon fiber-reinforced alumina ceramics by sol-gel method, then drying, sintering, and cooling to room temperature to prepare Si-Al-C coated Floor.

According to a carbon fiber reinforced alumina ceramic composite material according to an embodiment of the present invention, carbon fiber is used as a reinforcement of alumina ceramics, which has high specific strength and specific modulus, no creep, good fatigue resistance, small thermal expansion coefficient, and corrosion resistance. , and the cross-section wettability of alumina sol and carbon fiber is relatively good, and the interfacial bonding force is moderate. The carbon fiber in the form of carbon felt ensures the uniform distribution of the reinforcement phase, avoiding the problem of uneven distribution of particle reinforcement and whisker reinforcement. The carbon fiber reinforced alumina ceramic composite material is densified by vacuum impregnation, which greatly increases the mechanical strength of the material. Compared with the preparation of alumina ceramics by the powder sintering method, the preparation of alumina ceramics by the sol-gel method can reduce the sintering temperature from 1800 ° C to 1300 ° C, greatly reducing equipment requirements and energy consumption. The Si-Al-C anti-oxidation coating adopted in the invention is very dense, well combined with the alumina substrate, and can effectively enhance the oxidation resistance of the material.

In addition, the method for preparing a carbon fiber-reinforced alumina ceramic composite material according to the above-mentioned embodiments of the present invention may also have the following additional technical features:

Further, in step S102, the vacuum impregnation process of the carbon fiber reinforced alumina ceramics uses a mixed solution composed of tetraethyl orthosilicate-based silica sol, aluminum nitrate-based alumina sol and egg white solution.

Further, in step S102, the preparation of the mixed solution includes the following steps: taking 30mL-40mL of tetraethyl orthosilicate, 15g-25g of aluminum nitrate and a certain amount of hexamethylenetetramine, adding 55mL-65mL of water and Ethanol mixed solution to prepare ethyl orthosilicate-based silica sol and aluminum nitrate-based alumina sol; add 100mL to 130mL of egg white to the said ethyl orthosilicate-based silica sol and aluminum nitrate-based alumina sol solution.

Further, in step S101, the densification treatment step is specifically: after drying the carbon felt impregnated with aluminum sol, the temperature is raised to 1200-1400°C at a heating rate of 4°C/min-6°C/min, vacuum Sinter for 1h to 3h, then cool to room temperature.

Further, in step S101 , the precursor is aluminum nitrate sol, wherein the concentration of aluminum ions is 3 mol/L˜4 mol/L, and the viscosity of aluminum sol is 4 mPa·S˜6 mPa·S.

Further, in step S102, the sintering temperature is 1200°C-1400°C.

Further, the preparation method of aluminum nitrate sol includes the following steps: adding excess aluminum nitrate to water to prepare aluminum nitrate solution; heating the aluminum nitrate solution to 85°C-90°C, and adding 10%- 15% ammonia water until the pH value of the liquid is 3.5-5.0, then evaporate water to make the concentration of aluminum ions reach 5mol/L-6mol/L, filter, and take the filtrate to obtain aluminum nitrate sol.

Another object of the present invention is to propose a carbon fiber reinforced alumina ceramic composite material.

A carbon fiber reinforced alumina ceramic composite material according to the present invention comprises: a reinforcing body, the reinforcing body is carbon felt; a matrix, the matrix is impregnated in the void of the reinforcing body by a vacuum impregnation method, and is prepared into a composite material with the reinforcing body; An oxidation coating, the anti-oxidation coating is a Si-Al-C coating, and the anti-oxidation coating wraps the composite material.

Further, the density of the carbon fiber reinforced alumina ceramic composite material is greater than or equal to 2.5 g/cm ³ .

Further, the carbon felt is polyacrylonitrile-based carbon felt.

Additional aspects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Description of drawings

Fig. 1 is a flowchart of a method for preparing a carbon fiber reinforced alumina ceramic composite material according to an embodiment of the present invention.

detailed description

A method for preparing a carbon fiber reinforced alumina ceramic composite material of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in Figure 1, a method for preparing a carbon fiber reinforced alumina ceramic composite material according to an embodiment of the present invention includes the following steps:

S101: Using aluminum sol as a precursor, vacuum impregnate carbon felt, and then densify the carbon felt impregnated with aluminum sol to prepare carbon fiber-reinforced alumina ceramics. Specifically, first use aluminum nitrate sol as a precursor to vacuum impregnate the carbon felt after ultrasonic cleaning, and then dry it. After drying, put it into a high-temperature furnace for vacuum sintering, keep vacuum cooling to room temperature, and complete a densification process. Then repeat the above steps 10 to 12 times until the weight of the sample no longer increases, so as to obtain carbon fiber reinforced alumina composite ceramics. As the reinforcement of alumina ceramics, carbon fiber has high specific strength and specific modulus, no creep, good fatigue resistance, small thermal expansion coefficient, corrosion resistance, and the cross-sectional wettability of alumina sol and carbon fiber is relatively good. Moderate force. The carbon fiber in the form of carbon felt ensures the uniform distribution of the reinforcement phase, avoiding the problem of uneven distribution of particle reinforcement and whisker reinforcement.

S102: Vacuum impregnating carbon fiber reinforced alumina ceramics by using a sol-gel method, then drying, sintering, and cooling to room temperature to prepare a Si-Al-C coating. Specifically, a certain amount of egg white is first dissolved in a small amount of deionized water, and stirred to a clear liquid, that is, liquid A; the precursor for preparing a certain amount of tetraethyl orthosilicate-based silica sol and aluminum nitrate-based alumina sol Mix liquid B, add A dropwise into B to obtain C, and stir evenly, place carbon fiber reinforced alumina ceramics in liquid C for vacuum impregnation, and then dry; after drying, dry carbon fiber reinforced alumina ceramics The alumina ceramics are sintered in a vacuum sintering furnace. After the sintering is completed, the vacuum is maintained and the furnace is cooled to room temperature to obtain a carbon fiber reinforced alumina ceramic composite material with an anti-oxidation coating. Compared with the preparation of alumina ceramics by the powder sintering method, the preparation of alumina ceramics by the sol-gel method can reduce the sintering temperature from 1800 ° C to 1300 ° C, greatly reducing equipment requirements and energy consumption. The Si-Al-C anti-oxidation coating adopted in the invention is very dense, well combined with the alumina substrate, and can effectively enhance the oxidation resistance of the material.

A carbon fiber reinforced alumina ceramic composite material according to the present invention includes: a reinforcement body, a matrix and an anti-oxidation coating. Wherein, the reinforcing body is carbon felt. As the reinforcement of alumina ceramics, carbon fiber has high specific strength and specific modulus, no creep, good fatigue resistance, small thermal expansion coefficient, corrosion resistance, and the cross-sectional wettability of alumina sol and carbon fiber is relatively good. The force is moderate; the carbon fiber in the form of carbon felt ensures the uniform distribution of the reinforcement phase, avoiding the problem of uneven distribution of particle reinforcement and whisker reinforcement. The matrix is impregnated in the void of the reinforcement by vacuum impregnation, and a composite material is prepared with the reinforcement. Compared with the preparation of alumina ceramics by the powder sintering method, the preparation of alumina ceramics by the sol-gel method can reduce the sintering temperature from 1800 ° C to 1300 ° C, greatly reducing equipment requirements and energy consumption. The anti-oxidation coating is a Si-Al-C coating, and the anti-oxidation coating wraps the composite material. The Si-Al-C anti-oxidation coating is very dense and well combined with the alumina matrix, which can effectively enhance the oxidation resistance of the material.

The present invention will be described in detail below in conjunction with specific embodiments.

Example 1

Embodiment 1 is a specific preparation process of a carbon fiber reinforced alumina ceramic composite material, which uses alumina as a matrix, polyacrylonitrile-based carbon felt as a reinforcement, and a Si-Al-C oxidation-resistant coating on the surface, including The following specific steps:

Take 100g of aluminum nitrate, add deionized water, heat and stir in a water bath, wherein the temperature of the water bath is set at 85°C, and continue to stir in the water bath for 30-40 minutes to hydrolyze the aluminum nitrate as much as possible. Then add 12.5% ammonia water in batches until the pH of the liquid is 3.5-5. While further promoting hydrolysis, the properties of the sol are stabilized and the size of the colloidal particles is adjusted. Then evaporate the liquid, so that the concentration of aluminum ions is 6mol/L, and the viscosity is about 6mPa·S. This concentration and viscosity can increase the impregnation efficiency as much as possible while ensuring the impregnation effect. Then filter to obtain a translucent aluminum sol.

Primary densification: put the ultrasonically cleaned carbon felt (the geometric size of the carbon felt is about 4.5mm╳5.5mm╳82mm) into the aluminum sol for vacuum impregnation for 2 hours, and after the impregnation is complete, dry it at 50°C for 2 hours to make the sol become gel, then becomes a xerogel with no cracking on the surface. After drying, put it into a high-temperature furnace for vacuum sintering, the heating rate is 4°C-6°C, and the predetermined temperature is 1300°C to ensure that the xerogel is transformed into α-alumina. After reaching the predetermined temperature, keep it warm for 2 hours to make the sintering complete. Then keep vacuum cooling to room temperature to complete a densification process.

Repeated densification: take one densification step as a cycle, repeat 12 times, and complete the densification process of the composite material after 12 densification cycles, and obtain a carbon fiber reinforced alumina ceramic composite material with a density of 2.8g/cm ³ .

Preparation of Si-Al-C anti-oxidation coating: dissolve 100mL of egg white in a little deionized water, and stir until a clear liquid, that is, liquid A; take 40mL of tetraethyl orthosilicate, 20g of aluminum nitrate and 4g of six Methylenetetramine was slowly and uniformly mixed and dissolved in a mixture of 60mL deionized water and 10mL ethanol, and stirred to prepare a precursor mixture of tetraethylorthosilicate-based silica sol and aluminum nitrate-based alumina sol , that is, liquid B; add the liquid in liquid A dropwise to liquid B and stir evenly to obtain liquid C; put the carbon fiber reinforced alumina ceramic composite material in liquid C and vacuum impregnate it for 1 hour, then dry it at 40°C; Under the following conditions, the dried carbon fiber reinforced alumina ceramic composite material was sintered at 1400°C for 30 minutes. Egg white is rich in macromolecular protein, and it will be carbonized above 700°C, providing a large amount of activated carbon source. The reaction principle of coating preparation is:

_2Si2O (s) _{+ 2Al2O3} (s)+7C(s)→4SiAlC(s)+2CO(g)+ _CO2 (g)

After the sintering is completed, the furnace is closed for cooling and vacuumized to room temperature to obtain a carbon fiber reinforced alumina composite material with an anti-oxidation coating.

Example 2

Embodiment 2 is a specific preparation process of a carbon fiber reinforced alumina ceramic composite material, which uses alumina as a matrix, polyacrylonitrile-based carbon felt as a reinforcement, and a Si-Al-C oxidation-resistant coating on the surface, including The following specific steps:

Take 100g of aluminum nitrate, add deionized water, heat and stir in a water bath, wherein the temperature of the water bath is set at 90°C, and continue to stir in the water bath for 30-40 minutes to hydrolyze the aluminum nitrate as much as possible. Then add 15% ammonia water in batches until the pH of the liquid is 3.5-5, further promote the hydrolysis, stabilize the properties of the sol, and adjust the size of the colloidal particles. Then evaporate the liquid so that the concentration of aluminum ions is 5mol/L and the viscosity is about 6mPa·S. This concentration and viscosity can increase the impregnation efficiency as much as possible while ensuring the impregnation effect. Then filter to obtain a translucent aluminum sol.

Primary densification: put the ultrasonically cleaned carbon felt (the geometric size of the carbon felt is about 4.5mm╳5.5mm╳82mm) into the aluminum sol for vacuum impregnation for 2 hours, and after the impregnation is complete, dry it at 50°C for 2 hours to make the sol become gel, then becomes a xerogel with no cracking on the surface. After drying, put it into a high-temperature furnace for vacuum sintering, the heating rate is 4-6°C, and the predetermined temperature is 1400°C to ensure that the xerogel is transformed into α-alumina. After reaching the predetermined temperature, keep it warm for 2 hours to make the sintering complete. Then keep vacuum cooling to room temperature to complete a densification process.

Repeated densification: take one densification step as a cycle, repeat 12 times, and complete the densification process of the composite material after 12 densification cycles, and obtain a carbon fiber reinforced alumina ceramic composite material with a density of 2.6g/cm ³ .

Preparation of Si-Al-C anti-oxidation coating: dissolve 100mL of egg white in a little deionized water, and stir until a clear liquid, that is, liquid A; take 30mL of tetraethyl orthosilicate, 18g of aluminum nitrate and 4g of six Methylenetetramine was slowly and uniformly mixed and dissolved in a mixture of 65mL deionized water and 15mL ethanol, and stirred to prepare a precursor mixture of tetraethylorthosilicate-based silica sol and aluminum nitrate-based alumina sol , that is, liquid B; add the liquid in liquid A dropwise to liquid B and stir evenly to obtain liquid C; put the carbon fiber reinforced alumina ceramic composite material in liquid C and vacuum impregnate it for 1 hour and then dry it at 35°C; Under the following conditions, the dried carbon fiber reinforced alumina ceramic composite material is sintered at 1200°C for 30 minutes. Egg white is rich in macromolecular protein, and it will be carbonized above 700°C, providing a large amount of activated carbon source. The reaction principle of coating preparation is:

_2Si2O (s) _{+ 2Al2O3} (s)+7C(s)→4SiAlC(s)+2CO(g)+ _CO2 (g)

After the sintering is completed, the furnace is closed for cooling and vacuumized to room temperature to obtain a carbon fiber reinforced alumina composite material with an anti-oxidation coating.

According to a carbon fiber reinforced alumina ceramic composite material of the present invention, carbon fiber is used as a reinforcement of alumina ceramics, which has high specific strength and specific modulus, no creep, good fatigue resistance, small thermal expansion coefficient, corrosion resistance, and The cross-section wettability of alumina sol and carbon fiber is relatively good, and the interfacial bonding force is moderate. The carbon fiber in the form of carbon felt ensures the uniform distribution of the reinforcement phase, avoiding the problem of uneven distribution of particle reinforcement and whisker reinforcement. The density of the carbon fiber reinforced alumina ceramic composite material is controlled to be greater than or equal to 2.5g/cm ³ through the vacuum impregnation method, which greatly increases the mechanical strength of the material. Compared with the preparation of alumina ceramics by the powder sintering method, the preparation of alumina ceramics by the sol-gel method can reduce the sintering temperature from 1800 ° C to 1300 ° C, greatly reducing equipment requirements and energy consumption. The Si-Al-C anti-oxidation coating adopted in the invention is very dense, well combined with the alumina substrate, and can effectively enhance the oxidation resistance of the material.

In the description of this specification, descriptions with reference to the terms "one embodiment", "some embodiments", "example", "specific examples", or "some examples" mean that specific features described in connection with the embodiment or example , structure, material or characteristic is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples and features of different embodiments or examples described in this specification without conflicting with each other.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention, those skilled in the art can make the above-mentioned The embodiments are subject to changes, modifications, substitutions and variations.

Claims (10)

1. a kind of preparation method of fibre reinforced alumina ceramic composite material, it is characterised in that comprise the following steps：

S101：Using Alumina gel as precursor, vacuum impregnation is carried out to carbon felt, then will be caused with the impregnated carbon felt of Alumina gel Densification process, to prepare the aluminium oxide ceramics of fibre reinforced；

S102：Vacuum impregnation is carried out to the aluminium oxide ceramics of fibre reinforced using sol-gal process, then dries, sinters, and Room temperature is cooled to, to prepare Si-Al-C coatings.

2. a kind of preparation method of fibre reinforced alumina ceramic composite material according to claim 1, its feature exists In in step s 102, the aluminium oxide ceramics progress vacuum impregnation process to fibre reinforced is aoxidized using tetraethyl orthosilicate base The mixed liquor of Ludox, nitric acid aluminium base alumina sol and egg solution composition.

3. a kind of preparation method of fibre reinforced alumina ceramic composite material according to claim 2, its feature exists In in step s 102, the preparation of the mixed liquor comprises the following steps：

Take 30mL~40mL tetraethyl orthosilicate, 15g~25g aluminum nitrate and a certain amount of hexamethylenetetramine add 55mL~ To prepare tetraethyl orthosilicate base silica sol and nitric acid aluminium base alumina sol in 65mL water and alcohol mixeding liquid；

100mL~130mL egg is added into the tetraethyl orthosilicate base silica sol and nitric acid aluminium base alumina sol Clear solution.

4. a kind of preparation method of fibre reinforced alumina ceramic composite material according to claim 1, its feature exists In in step S101, densif iotacation processing step is specially：After the impregnated carbon felt drying of the use Alumina gel, according to 4 DEG C/min~6 DEG C/min heating rate is warming up to 1200 DEG C~1400 DEG C, vacuum-sintering 1h~3h is subsequently cooled to room temperature.

5. a kind of preparation method of fibre reinforced alumina ceramic composite material according to claim 1 or 4, its feature It is, in step S101, the precursor is nitric acid Alumina gel, wherein, aluminum ions concentration is 3mol/L~4mol/L, aluminium The viscosity of colloidal sol is 4mPaS~6mPaS.

6. a kind of preparation method of fibre reinforced alumina ceramic composite material according to claim 1, its feature exists In in step s 102, sintering temperature is 1200 DEG C~1400 DEG C.

7. a kind of preparation method of fibre reinforced alumina ceramic composite material according to claim 6, its feature exists In the preparation method of the nitric acid Alumina gel comprises the following steps：

Excessive aluminum nitrate is added to the water, to prepare aluminum nitrate solution；

The aluminum nitrate solution is heated to 85 DEG C~90 DEG C, after aluminum nitrate is completely dissolved, 10%~15% ammoniacal liquor is added PH value to liquid is 3.5~5.0, and then evaporating moisture makes aluminum ions concentration reach after 5mol/L~6mol/L, filters, takes Filtrate, that is, obtain aluminum nitrate colloidal sol.

8. a kind of fibre reinforced alumina ceramic composite material, it is characterised in that including：

Reinforcement, the reinforcement is carbon felt；

Matrix, described matrix is submerged in by vacuum impregnation technology in the space of the reinforcement, is prepared into the reinforcement Composite；

Antioxidant coating, the antioxidant coating is Si-Al-C coatings, and the antioxidant coating wraps up the composite.

9. a kind of fibre reinforced alumina ceramic composite material as claimed in claim 8, it is characterised in that the carbon fiber The density for strengthening alumina ceramic composite material is more than or equal to 2.5g/cm³。

10. a kind of fibre reinforced alumina ceramic composite material as claimed in claim 8, it is characterised in that the carbon felt For PAN based carbon felt.