CN109384459B - A kind of fiber reinforced silica thermal insulation ceramic material and its preparation method and application - Google Patents

Abstract

The invention relates to a fiber-reinforced silicon dioxide heat-insulating ceramic material and a preparation method and application thereof. The preparation method comprises the following steps: (1) preparing a prefabricated body; (2) multiple sol-gel treatments: dipping the prefabricated body into silica sol, and then gelling to finish primary sol-gelling treatment; repeating sol-gelation treatment for multiple times, and sequentially reducing the density of silica sol used for impregnation to form gradient impregnation; (3) drying the material treated in the step (2) to obtain a green body; (4) and sintering the green body to obtain the fiber reinforced silicon dioxide heat-insulating ceramic material. The preparation method can prepare the heat-insulating ceramic material with high compressive strength and low heat conductivity, and can be applied to an aircraft heat-insulating system.

Description

A kind of fiber reinforced silica thermal insulation ceramic material and its preparation method and application

technical field

The present invention relates to the technical field of thermal insulation ceramic materials, in particular to a fiber reinforced silica thermal insulation ceramic material and a preparation method and application thereof.

Background technique

Fiber (such as quartz fiber) reinforced silica composite material is a multi-functional composite material developed in recent years that can meet the functions of heat insulation, wave transmission and load bearing at the same time. It has good heat insulation performance and compressive strength. High, low thermal expansion coefficient, low density and other advantages, are widely used in the aerospace field. At present, fiber-reinforced silica composites mainly focus on their application in the field of load bearing or wave transmission, and less research on their application in the field of heat insulation. Due to the rigidity of fiber-reinforced silica composites, compared with thermal insulation materials such as aerogels and cotton felts, fiber-reinforced silica composites can withstand a certain pressure while maintaining heat insulation. more suitable use.

At present, the methods for preparing fiber-reinforced silica composites mainly include gel impregnation and pull-up impregnation. The pull-up dipping method has the advantages of fast speed and short cycle time without gelation in the dipping process, but this method has poor control over the size and uniformity of pores. The gel impregnation method is a sol-gel reaction initiated by regulating the temperature. The gel and the preform are cross-linked and gradually integrated, the internal pores are relatively small and uniform, and the material properties are more stable. Compared with the pulling method, the gel method has better control over the size and uniformity of the pores, so it is favored by many researchers.

However, the direction of the currently prepared fiber-reinforced silica composite materials is high-density and high-strength materials. Through continuous densification, higher compressive strength is achieved to meet the load-bearing requirements, but the porosity of the composite material is reduced. , the thermal insulation effect becomes poor, and the thermal insulation performance of the material is sacrificed to a certain extent. Studies have shown that among the same type of ceramic materials, materials with lower density generally have better thermal insulation effect and lower compressive strength. In addition, too dense materials have a larger weight under the same volume, which is not suitable for the weight reduction requirements of aircraft in the aerospace field.

Therefore, while retaining a certain compressive strength, improving the thermal insulation effect of the material and reducing the thermal conductivity of the material is of great significance for the development of fiber-reinforced silica composite materials.

In view of this, the present invention is proposed.

SUMMARY OF THE INVENTION

One of the objectives of the present invention is to provide a preparation method of a fiber-reinforced silica thermal insulating ceramic material. The preparation method adopts a gradient impregnation method to complete densification in the preparation process, and can obtain a dense surface structure, gelatin The cross-linking with the preform is sufficient, the interface bonding is good, the porosity of the ceramic can be higher, the pores are more uniform, and the thermal insulation effect is better.

(2) Technical solutions

In order to solve the above-mentioned technical problems, the present invention provides the following technical solutions:

1. A preparation method of a fiber-reinforced silica heat-insulating ceramic material, the preparation method comprising:

(1) prepare a preform;

(2) Multiple sol-gelation treatments: impregnate the preform with silica sol and then perform gelation to complete one sol-gelation treatment; repeat the sol-gelation treatment multiple times, and impregnate the used silica sol The density decreases successively, forming a gradient impregnation;

(3) drying the processed material in step (2) to obtain a green body;

(4) Sintering the green body to obtain the fiber-reinforced silica heat insulating ceramic material.

2. According to the preparation method described in technical solution 1, in step (2), the total number of sol-gelation treatments is 2 to 4 times, and the density of the silica sol used in the previous dipping is higher than that used in the subsequent dipping. The density of silica sol is 2-10% higher;

Preferably, the density of the silica sol used in step (2) is in the range of 1.1˜1.4 g/cm ³ .

3. According to the preparation method described in technical solution 2, ultrafiltration or vacuum distillation is performed on the silica sol with lower density to obtain the silica sol with the density required in step (2).

4. According to the preparation method described in technical solution 2, during the sol-gelation treatment, if the density of the silica sol is lower than 1.2 g/cm ³ , an alkaline gelling aid is added during the gelation process; preferably , the alkaline gelling assistant is hexamethylenetetramine or carbamide; more preferably, the concentration of the alkaline gelling assistant is 1-10 wt.%.

5. The preparation method according to any one of technical solutions 1 to 4, in step (1), the preform is a preform with a fiber volume content of 20-40%;

Preferably, the fibers are processed into a preform blank by weaving or needling, and then pretreated with an organic solvent to obtain the preform.

6. According to the preparation method described in any one of technical solutions 1 to 4, the sol-gel reaction is triggered by regulating the temperature to complete the gelation of the sol;

Preferably, the temperature is adjusted to 60-100°C to initiate the sol-gel reaction;

More preferably, the gelation temperature of the high-density silica sol is lower than the gelation temperature of the low-density silica sol.

7. According to the preparation method described in technical solution 1, drying is carried out under the conditions of humidity of 60-90% and temperature of 20-50°C;

Preferably, after drying is completed, before sintering, the green body is dried at 100-200°C.

8. According to the preparation method described in technical solution 1, the sintering is performed at 500-800° C., and the sintering time is 1-3 hours;

Preferably, the sintering is carried out as follows:

The first temperature is sintered for 0.5-1 hour, and then the second temperature is sintered for 1-2 hours; wherein, the first temperature is lower than the second temperature, and a blasting operation is performed in the sintering device during the sintering.

9. A fiber-reinforced silica heat-insulating ceramic material, prepared by the preparation method described in any one of technical solutions 1 to 8.

10. Application of the fiber-reinforced silica heat-insulating ceramic material according to technical solution 9 in an aircraft heat-insulating system.

(3) Beneficial effects

The above-mentioned technical scheme of the present invention has the following advantages:

(1) The preparation method provided by the present invention can produce a dense surface structure, sufficient cross-linking between the gel and the preform, good interface bonding, higher porosity of ceramics, and more uniform pores. Thermal insulation ceramic material with better thermal insulation effect.

(2) In the present invention, the crosslinking reaction time between the matrix and the fiber is greatly shortened by using a variety of gelling auxiliary agents, and the reaction product of the auxiliary agent is discharged by using the air sintering system of blasting, without adding other components, so as to obtain uniform and stable insulation material.

(3) The present invention prepares a thermal insulation ceramic with a compressive strength of 40-80 MPa at room temperature and a thermal conductivity of 0.1-0.6 W/(m·k). The ceramic still has good thermal insulation performance at 300°C, and the thermal conductivity is lower than 0.3W/(m·k).

Description of drawings

FIG. 1 is a schematic flow chart of the preparation method of the fiber-reinforced silica heat-insulating ceramic material provided by the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

The present invention provides a preparation method of a fiber-reinforced silica heat-insulating ceramic material, as shown in FIG. 1 , the preparation method includes:

(1) Preparation of preforms

Preforms (ie fiber preforms) can be obtained by processing fibers (such as fiber yarns) by weaving or needle punching. In order to ensure the impregnation effect, the processed preform can also be pretreated to remove the wetting agent, so as to obtain the impregnated preform with good surface wettability. The pretreatment can be accomplished by using an organic solvent, and the organic solvent can adopt existing products, such as acetone, ethanol, chloroform, etc., which are not listed here in the present invention.

The present invention preferably uses a preform with a fiber volume content of 20-40%, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30% , 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%. For the preform, the higher the fiber content is, the higher the compressive strength of the final material is, but the density and thermal conductivity of the material are sacrificed greatly. Therefore, the present invention controls the fiber content in the preform to 20-40% , taking into account compressive strength, thermal conductivity and density.

(2) Multiple sol-gelation treatments

The preform is impregnated with silica sol and then gelled to complete a sol-gelation treatment; the sol-gelation treatment is repeated for several times, and the density of the silica sol used for impregnation is successively reduced to form gradient impregnation.

In this step, the impregnation method can be a vacuum/pressure impregnation method, and the multiple impregnations are carried out according to the gradient impregnation method, and the density of the silica sol used for the impregnation is successively reduced to achieve the purpose of densification.

The inventors also carried out the following optimization in this step, so that the crosslinking between the gel and the preform is more sufficient, the interface bonding is good, the porosity of the ceramic can be higher, the pores are more uniform, and the thermal insulation effect is better. Good: The total number of sol-gelation treatments is 2 to 4 times, and the density of the silica sol used in the previous impregnation is 2 to 10% higher than that of the silica sol used in the subsequent impregnation (for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%).

For better results, the density of the used silica sol is in the range of 1.1-1.4 g/cm ³ (inclusive, two endpoints), for example, 1.1 g/cm ³ , 1.15 g/cm ³ , 1.2 g/cm 3 . cm ³ , 1.25 g/cm ³ , 1.3 g/cm ³ , 1.35 g/cm ³ , 1.4 g/cm ³ . The density of the silica sol used is relatively small, and the silica sol of this density can control the porosity of the green body to be larger, and the pores can be controlled to be fine and uniform, and can achieve weight reduction and improve thermal insulation. purpose of the effect.

The silica sol used can be a commercially available product. For gradient impregnation, a silica sol with a lower density can be concentrated by ultrafiltration or vacuum distillation to obtain a silica sol with a required density. For silica sol with a density lower than 1.2g/ ^cm3 , because the normal gelation time is too long (not less than 120h), it is not suitable for promotion, and the gelation can be accelerated by adding an alkaline auxiliary; Sexual additives can be hexamethylenetetramine, carbamide, etc., with a concentration of 1 to 10wt.%, for example, can be 1wt.%, 2wt.%, 3wt.%, 4wt.%, 5wt.%, 6 wt. %, 7 wt. %, 8 wt. %, 9 wt. %, 10 wt. %. Depending on the amount added, the gel time can be shortened to 12h to 36h.

There are various methods for promoting the conversion of sol to gel, and the present invention preferably adopts the method of regulating temperature to achieve this conversion. In combination with the density of the above-mentioned silica sol and the times of gradient dipping, the present invention preferably adjusts the temperature to 60-100° C. to initiate the sol-gel reaction. The higher the density of the silica sol, the lower the temperature or the shorter the time to be provided. Therefore, when performing multiple sol-gelation treatments, the gelation temperature of the silica sol with high density is lower than that of the silica sol with low density. gelation temperature.

(3) Drying

The material treated in step (2) is dried to obtain a green body.

The green body after gelation is preferably dried by slow treatment at low temperature and high humidity for a long time to protect the green body. After completion, it can be further dried at 100-200°C.

Preferably, when drying, the humidity can be controlled at 60%-90% (for example, it can be 60%, 65%, 70%, 75%, 80%, 85%, 90%), and the temperature is at 20-50°C (For example, it may be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C).

(4) Sintering

The green body is sintered to obtain the fiber-reinforced silica heat-insulating ceramic material.

Preferably, the sintering is performed at 500˜800° C., and the sintering time is 1˜3 hours. Preferably, the sintering is performed according to the following method: sintering at the first temperature for 0.5-1 hour, and then sintering at the second temperature for 1-2 hours; wherein, the first temperature is lower than the second temperature, and during the sintering process The blasting operation is carried out in the sintering device.

For the green body with the addition of gel additives, the sintering device is blasted during the sintering process to ensure that the sintering device is well ventilated, thereby reducing the residue of the reaction product of the additive in the green body. The addition of the additive will have a certain effect on the green body. However, the present invention controls the addition amount to be 1-10 wt.%, so that the pores are still in the mesoporous range, and there is no obvious damage to the material properties.

The present invention also provides a fiber-reinforced silica heat-insulating ceramic material, which is prepared by the above-mentioned preparation method. It has the advantages of high compressive strength, low thermal conductivity and low density. The compressive strength at room temperature reaches 40-80MPa, and the thermal conductivity at room temperature reaches 0.1-0.6W/(m·k). The material still has a Good thermal insulation performance, thermal conductivity lower than 0.3W/(m·k), good thermal insulation effect, can be used in aircraft thermal insulation system.

The following are examples of the present invention.

Preparation materials:

Silica sol gel: the density is 1.16g/cm ³ ;

The above silica sol gel is distilled under reduced pressure (of course, ultrafiltration can also be used in other embodiments) to prepare silica sol with densities of 1.28 g/cm ³ and 1.36 g/cm ³ for use.

Example 1

The quartz fiber is processed into a preform with a fiber volume content of 20% by mechanical needling, and the sizing agent is removed by an organic solvent (acetone is used in this example) to obtain a preform for impregnation with good surface wettability, which is used for Subsequent impregnation step.

The preform was impregnated by a vacuum/pressure impregnation method with silica sol with a density of 1.28 g/ ^cm3 , the preform was filled with fillers and densified, and then a sol-gel reaction was carried out to cross-link the gel and the preform. Gradually integrated, the temperature of the first sol-gel reaction was controlled to be 70 °C, the time was 36 h, and no gelling agent was added; silica sol with a density of 1.16 g/cm ³ was used to impregnate the preform by vacuum/pressure impregnation method , and then carry out a sol-gel reaction. The temperature of the second sol-gel reaction is controlled to be 90° C., the time is 36h, and a concentration of 1wt.% hexamethylenetetramine is added as a gelling aid.

The material obtained after the sol-gelation treatment was dried under the conditions of a humidity of 90% and a temperature of 20° C. to obtain a green body.

Finally, the green body was sintered at 600 °C for 1 h, and then sintered at 800 °C for 1 h. During the sintering process, the sintering device was blasted to obtain a compressive strength of 56 MPa and a thermal conductivity of 0.12 w/(m k). Insulation ceramic material with a density of 1.12g/ ^cm3 .

Example 2

The quartz fiber is processed into a preform with a fiber volume content of 20% by mechanical needling, and the sizing agent is removed by an organic solvent (acetone is used in this example) to obtain a preform for impregnation with good surface wettability, which is used for Subsequent impregnation step.

The preform was impregnated by a vacuum/pressure impregnation method with silica sol with a density of 1.28 g/ ^cm3 , the preform was filled with fillers and densified, and then a sol-gel reaction was carried out to cross-link the gel and the preform. Gradually integrated, the temperature of the first sol-gel reaction was controlled to be 70 °C, the time was 36 h, and no gelling agent was added; silica sol with a density of 1.16 g/cm ³ was used to impregnate the preform by vacuum/pressure impregnation method , and then carry out a sol-gel reaction, controlling the temperature of the second sol-gel reaction to be 90° C. and the time of 36h, and 2 wt.% carbodiamide as a gelling aid.

The material obtained after the sol-gelation treatment was dried under the conditions of a humidity of 90% and a temperature of 20° C. to obtain a green body.

Finally, the green body was sintered at 600 °C for 1 h, and then sintered at 800 °C for 1 h. During the sintering process, the sintering device was blasted to obtain a compressive strength of 50 MPa and a thermal conductivity of 0.14 w/(m·k). Insulation ceramic material with a density of 1.14g/ ^cm3 .

Example 3

The quartz fiber is processed into a preform with a fiber volume content of 20% by mechanical needling, and the sizing agent is removed by an organic solvent (acetone is used in this example) to obtain a preform for impregnation with good surface wettability, which is used for Subsequent impregnation step.

The preform was impregnated by a vacuum/pressure impregnation method with silica sol with a density of 1.28 g/ ^cm3 , the preform was filled with fillers and densified, and then a sol-gel reaction was carried out to cross-link the gel and the preform. Gradually integrated, the temperature of the first sol-gel reaction was controlled to be 70 °C, the time was 36 h, and no gelling agent was added; silica sol with a density of 1.16 g/cm ³ was used to impregnate the preform by vacuum/pressure impregnation method , and then the sol-gel reaction was carried out, and the temperature of the second sol-gel reaction was controlled to be 100 °C and the time was 120 h, and no gelling auxiliary was added.

The material obtained after the sol-gelation treatment was dried under the conditions of a humidity of 90% and a temperature of 20° C. to obtain a green body.

Finally, the green body was sintered at 600 °C for 1 h, and then sintered at 800 °C for 1 h. During the sintering process, the sintering device was blasted to obtain a compressive strength of 60 MPa and a thermal conductivity of 0.12 w/(m·k). Insulation ceramic material with a density of 1.10g/ ^cm3 .

Example 4

The quartz fiber is processed into a preform with a fiber volume content of 30% by mechanical needle punching, and the sizing agent is removed by an organic solvent (acetone is used in this example) to obtain a preform for impregnation with good surface wettability, which is used for Subsequent impregnation step.

The preform was impregnated by a vacuum/pressure impregnation method with silica sol with a density of 1.28 g/ ^cm3 , the preform was filled with fillers and densified, and then a sol-gel reaction was carried out to cross-link the gel and the preform. Gradually integrated, the temperature of the first sol-gel reaction was controlled to be 70 °C, the time was 36 h, and no gelling agent was added; silica sol with a density of 1.16 g/cm ³ was used to impregnate the preform by vacuum/pressure impregnation method , and then carry out a sol-gel reaction. The temperature of the second sol-gel reaction is controlled to be 90° C., the time is 36h, and a concentration of 1wt.% hexamethylenetetramine is added as a gelling aid.

The material obtained after the sol-gelation treatment was dried under the conditions of a humidity of 90% and a temperature of 20° C. to obtain a green body.

Finally, the green body was sintered at 600 °C for 1 h, and then sintered at 800 °C for 1 h. During the sintering process, the sintering device was blasted to obtain a compressive strength of 59 MPa and a thermal conductivity of 0.18 w/(m k). Insulation ceramic material with a density of 1.32g/ ^cm3 .

Example 5

The quartz fiber is processed into a preform with a fiber volume content of 30% by mechanical needle punching, and the sizing agent is removed by an organic solvent (acetone is used in this example) to obtain a preform for impregnation with good surface wettability, which is used for Subsequent impregnation step.

The preform was impregnated with silica sol with a density of 1.36 g/cm ³ by vacuum/pressure impregnation method, the preform was filled with fillers and densified, and then a sol-gel reaction was carried out to cross-link the gel and the preform. Gradually integrated, the temperature of the first sol-gel reaction was controlled to be 60 °C, the time was 36 h, and no gelling agent was added; silica sol with a density of 1.28 g/cm ³ was used to impregnate the preform by vacuum/pressure impregnation method , and then carry out the sol-gel reaction, controlling the temperature of the second sol ^- gel reaction to be 70 °C, the time of Methods The preform was impregnated, followed by a sol-gel reaction. The temperature of the third sol-gel reaction was controlled to be 90° C. and the time was 36 hours. The concentration of hexamethylenetetramine was 1 wt.

The material obtained after the sol-gelation treatment was dried under the conditions of a humidity of 90% and a temperature of 20° C. to obtain a green body.

Finally, the green body was sintered at 600 °C for 1 h, and then sintered at 800 °C for 1 h. During the sintering process, the sintering device was blasted to obtain a compressive strength of 68MPa and a thermal conductivity of 0.36w/(m·k). Insulation ceramic material with a density of 1.47g/ ^cm3 .

Example 6

The quartz fiber is processed into a preform with a fiber volume content of 40% by mechanical needling, and the sizing agent is removed by an organic solvent (acetone is used in this example) to obtain a preform for impregnation with good surface wettability, which is used for Subsequent impregnation step.

The preform was impregnated with silica sol with a density of 1.36 g/cm ³ by vacuum/pressure impregnation method, the preform was filled with fillers and densified, and then a sol-gel reaction was carried out to cross-link the gel and the preform. Gradually integrated, the temperature of the first sol-gel reaction was controlled to be 60 °C, the time was 36 h, and no gelling agent was added; silica sol with a density of 1.28 g/cm ³ was used to impregnate the preform by vacuum/pressure impregnation method , and then carry out the sol-gel reaction, controlling the temperature of the second sol ^- gel reaction to be 70 °C, the time of Methods The preform was impregnated, followed by a sol-gel reaction. The temperature of the third sol-gel reaction was controlled to be 90° C. and the time was 36 hours. The concentration of hexamethylenetetramine was 1 wt.

The material obtained after the sol-gelation treatment was dried under the conditions of a humidity of 90% and a temperature of 20° C. to obtain a green body.

Finally, the green body was sintered at 600 °C for 1 h, and then sintered at 800 °C for 1 h. During the sintering process, the sintering device was blasted to obtain a compressive strength of 77 MPa and a thermal conductivity of 0.45 w/(m·k). Insulation ceramic material with a density of 1.56g/ ^cm3 .

Example 7

The quartz fiber is processed into a preform with a fiber volume content of 20% by mechanical needling, and the sizing agent is removed by an organic solvent (acetone is used in this example) to obtain a preform for impregnation with good surface wettability, which is used for Subsequent impregnation step.

The preform was impregnated by a vacuum/pressure impregnation method with silica sol with a density of 1.28 g/ ^cm3 , the preform was filled with fillers and densified, and then a sol-gel reaction was carried out to cross-link the gel and the preform. Gradually integrated, the temperature of the first sol-gel reaction was controlled to be 70 °C, the time was 36 h, and no gelling agent was added; silica sol with a density of 1.16 g/cm ³ was used to impregnate the preform by vacuum/pressure impregnation method , and then carry out a sol-gel reaction. The temperature of the second sol-gel reaction is controlled to be 90° C., the time is 36h, and a concentration of 1wt.% hexamethylenetetramine is added as a gelling aid.

The material obtained after the sol-gelation treatment was dried under the conditions of a humidity of 90% and a temperature of 20° C. to obtain a green body.

Finally, the green body was sintered at 600 °C for 2 h to obtain a thermal insulating ceramic material with a compressive strength of 56 MPa, a thermal conductivity of 0.14 w/(m·k) and a density of 1.14 g/cm ³ .

Example 8

The quartz fiber is processed into a preform with a fiber volume content of 20% by mechanical needling, and the sizing agent is removed by an organic solvent (acetone is used in this example) to obtain a preform for impregnation with good surface wettability, which is used for Subsequent impregnation step.

The preform was impregnated by a vacuum/pressure impregnation method with silica sol with a density of 1.28 g/ ^cm3 , the preform was filled with fillers and densified, and then a sol-gel reaction was carried out to cross-link the gel and the preform. Gradually integrated, the temperature of the first sol-gel reaction was controlled to be 70 °C, the time was 36 h, and no gelling agent was added; silica sol with a density of 1.16 g/cm ³ was used to impregnate the preform by vacuum/pressure impregnation method , and then carry out a sol-gel reaction. The temperature of the second sol-gel reaction is controlled to be 90° C., the time is 36h, and a concentration of 1wt.% hexamethylenetetramine is added as a gelling aid.

The material obtained after the sol-gelation treatment was dried under the conditions of a humidity of 90% and a temperature of 20° C. to obtain a green body.

Finally, the green body was sintered at 800 °C for 2 h to obtain a thermal insulating ceramic material with a compressive strength of 50 MPa, a thermal conductivity of 0.12 w/(m·k), and a density of 1.12 g/cm ³ .

The compressive strength (at normal temperature), thermal conductivity (at normal temperature) and density of the insulating ceramic materials prepared in the above-mentioned respective examples are recorded, and the results are shown in Table 1.

The raw materials and molding process for preparing ceramics used in Examples 1 to 3 are exactly the same, and the dipping times, preform content and silica sol density are the same, but different gelling additives or no additives are used. The gelling aids and silica sols used in Examples 4 to 6 have the same density, but different dipping times and preform contents are selected respectively. The dipping times, the preform content, the gelling aid and the density of the silica sol used in Examples 7 to 8 are all the same, but different sintering systems are selected respectively. It can be seen from the results in Table 1 that the thermally insulating ceramic materials prepared in the above examples have lower thermal conductivity and higher compressive strength.

By observing the data results in Table 1, it can be seen that the use of hexamethylenetetramine as a gelling aid can effectively improve the gelation rate, and the thermal conductivity of the prepared ceramic material is kept at a low level. By increasing the number of impregnations or increasing the fiber volume content of the preform, the compressive strength of the material can be effectively improved, but its thermal conductivity is also significantly increased. Different sintering temperatures have a slight effect on the strength and thermal conductivity of the material. It may be that the incomplete volatilization of the auxiliary reaction products at lower temperatures leads to a slight increase in thermal conductivity, while higher temperatures have a certain effect on the fiber strength of the preform. Damage causes a slight decrease in strength. The ceramic material prepared by the invention has higher compressive strength, lower density and obvious advantage of porosity while having lower thermal conductivity.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (18)

1. A preparation method of a fiber reinforced silicon dioxide heat insulation ceramic material is characterized by comprising the following steps: the preparation method comprises the following steps:

(1) preparing a prefabricated body;

(2) multiple sol-gel treatments: dipping the prefabricated body into silica sol, and then gelling to finish primary sol-gelling treatment; repeating sol-gelation treatment for multiple times, and sequentially reducing the density of silica sol used for impregnation to form gradient impregnation;

(3) drying the material treated in the step (2) to obtain a green body;

(4) and sintering the green body to obtain the fiber reinforced silicon dioxide heat-insulating ceramic material.

2. The method of claim 1, wherein: in the step (2), the total number of sol-gel treatments is 2 to 4, and the density of the silica sol used in the previous impregnation is 2 to 10% higher than that of the silica sol used in the subsequent impregnation.

3. The method of claim 2, wherein:

the density of the silica sol used in the step (2) is 1.1-1.4 g/cm³Within the range of (1).

4. The method of claim 2, wherein: and (3) carrying out ultrafiltration or reduced pressure distillation on the silica sol with lower density to obtain the silica sol with the density meeting the requirement of the step (2).

5. The method of claim 2, wherein: when the sol-gel treatment is carried out, the density of the silica sol is less than 1.2g/cm³Then adding an alkaline gelling aid during gelling.

6. The method of claim 5, wherein: the alkaline gel auxiliary agent is hexamethylenetetramine or carbamide.

7. The method of claim 6, wherein: the concentration of the alkaline gel auxiliary agent is 1-10 wt.%.

8. The production method according to any one of claims 1 to 7, characterized in that: in the step (1), the preform is a preform with a fiber volume content of 20-40%.

9. The method of claim 8, wherein: processing the fiber into a preform blank in a weaving or needling mode, and then carrying out pretreatment by using an organic solvent to obtain the preform.

10. The production method according to any one of claims 1 to 7, characterized in that: the sol-gel reaction is initiated by regulating and controlling the temperature to complete the gelation of the sol.

11. The method of manufacturing according to claim 10, wherein: regulating the temperature to 60-100 ℃ to initiate sol-gel reaction.

12. The method of claim 11, wherein: the gelation temperature of the high-density silica sol is lower than that of the low-density silica sol.

13. The method of claim 1, wherein: drying the mixture under the conditions that the humidity is 60-90% and the temperature is 20-50 ℃.

14. The method of manufacturing according to claim 13, wherein:

and after drying, drying the green body at 100-200 ℃ before sintering.

15. The method of claim 1, wherein: and sintering at 500-800 ℃ for 1-3 hours.

16. The method of claim 15, wherein: the sintering is carried out according to the following method:

sintering for 0.5-1 hour at the first temperature and then sintering for 1-2 hours at the second temperature; wherein the first temperature is lower than the second temperature, and the air blowing operation is performed into the sintering device during the sintering process.

17. A fiber reinforced silica thermal insulation ceramic material is characterized in that: prepared by the preparation method of any one of claims 1 to 16.

18. Use of the fiber reinforced silica insulating ceramic material of claim 17 in an aircraft insulation system.

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