CN114790117B - Preparation method of oxide fiber-based porous ceramic with hierarchical structure - Google Patents

Abstract

The invention provides a method for preparing oxide fiber-based porous ceramics with a hierarchical structure. The method is mainly divided into three stages: first, sieve the agglomerated mullite loose cotton with a sieve to obtain dispersed chopped fibers , using it as a matrix for hierarchical structure growth; thereafter, adding aluminum source and mullite fiber to a selected organic solvent and complexing agent to obtain a mixed slurry, and dispersing the boron source and catalyst to the mixed slurry through a pH regulator In the slurry, a porous ceramic green body is prepared in combination with a sol-gel-injection molding method; finally, the prepared green body is subjected to heat treatment to obtain a composite material with a hierarchical structure. The beneficial effects of the invention are: the obtained composite material has excellent properties such as low density, high porosity, low thermal conductivity and the like.

Description

A method for preparing oxide fiber-based porous ceramics with hierarchical structure

Technical Field

The invention belongs to the field of ceramics, and in particular relates to a method for preparing oxide fiber-based porous ceramics with a hierarchical structure.

Background Art

Mullite (chemical composition: 3Al ₂ O ₃ ·2SiO ₂ ) is a stable compound in the binary system of aluminosilicate. Mullite fiber exhibits excellent thermal shock resistance, high temperature creep resistance, thermal stability, mechanical properties and dielectric properties due to its stable crystal structure. Mullite fiber-based porous ceramics present a typical three-dimensional network structure, with the advantages of high chemical stability, low thermal conductivity and good creep performance. However, the pore diameter inside traditional fiber-based porous ceramics can reach tens of microns, and the thermal insulation effect in high temperature environment needs to be improved. Therefore, it is urgent to develop a new type of oxide fiber-based porous ceramic with good high temperature thermal insulation performance.

Summary of the invention

In view of this, the present invention aims to provide a method for preparing oxide fiber-based porous ceramics with a hierarchical structure.

To achieve the above object, the technical solution created by the present invention is implemented as follows:

A method for preparing oxide fiber-based porous ceramics with a hierarchical structure comprises the following preparation steps:

S1: Add 0.06 mol isopropanol (C ₃ H ₈ O) and 0.01 mol ethyl acetoacetate (C ₆ H ₁₀ O ₃ ) into a beaker, stir magnetically for 10 min to make it uniform, add 0.01 mol aluminum sec-butoxide (C ₁₂ H ₂₇ AlO ₃ ) dropwise therein, and continue stirring magnetically to obtain a uniform mixed slurry;

S2: Add 0.005 mol of sieved and ground mullite chopped fibers to the mixed slurry prepared in S1, and stir mechanically until the fibers are evenly dispersed in the slurry. Then, add 0.00045 mol of manganese dioxide (MnO ₂ ) and 0.002 mol of boron oxide (B ₂ O ₃ ) powder in sequence, and stir sufficiently to evenly disperse the manganese dioxide and boron oxide powders in the mullite fiber slurry. During the process, adjust the pH value by adding distilled water, and obtain a sol containing mullite fibers through a hydrolysis reaction;

S3: injecting the sol obtained in S2 into a mold, and obtaining a gel block containing mullite fibers through polycondensation reaction and pre-pressing;

S4: placing the gel block obtained in S3 in an oven for drying, demolding to obtain a mullite fiber porous ceramic body, and finally sintering in a high-temperature furnace to obtain a mullite fiber-based porous ceramic with a hierarchical structure.

Furthermore, the compression molding in S3 produces a cylindrical block.

Furthermore, the mullite fibers added to S2 are uniformly dispersed chopped fibers.

Furthermore, the added amount of manganese dioxide was 0.04 g.

Furthermore, in step S4, the specific system of high temperature heat treatment is: heating to 1200°C at a heating rate of 5°C/min, keeping the temperature for 3 hours and cooling with the furnace.

Furthermore, the optimal addition amount of boron oxide is 0.15 g.

The oxide fiber-based porous ceramics prepared by the method have good thermal insulation performance.

Furthermore, the oxide fiber-based porous ceramics can be used as aerospace thermal protection materials and industrial furnace thermal insulation materials.

The advantages and positive effects of the invention are:

In order to further improve the high-temperature thermal insulation performance of oxide fiber-based porous ceramics, the present invention proposes a method for preparing oxide fiber-based porous ceramics with a hierarchical structure. A sol-gel combined with a closed sintering method is used to introduce secondary structures such as aluminum borate whiskers and alumina wafers into the mullite fiber skeleton. The obtained aluminum borate whisker/alumina wafer/mullite fiber composite structure can divide the original large pores (tens of microns) inside the porous ceramic into micron pores or even nano pores, significantly extending the heat conduction path and weakening thermal radiation, thereby reducing the thermal conductivity of the porous ceramic and improving the thermal insulation effect.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1a is a scanning electron microscope image of the oxide fiber-based porous ceramic prepared in Example 1 in the preparation method of the present invention;

FIG1b is a scanning electron microscope image of the oxide fiber-based porous ceramic prepared in Example 2 in the preparation method of the present invention;

FIG1c is a scanning electron microscope image of the oxide fiber-based porous ceramic prepared in Example 3 in the preparation method of the present invention;

FIG1d is a scanning electron microscope image of the oxide fiber-based porous ceramic prepared in Example 4 in the preparation method of the present invention;

FIG. 1e is a scanning electron microscope image of the oxide fiber-based porous ceramic prepared in Example 5 in the preparation method of the present invention.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the invention to clearly and completely describe the technical solutions in the embodiments of the invention. Obviously, the described embodiments are only part of the embodiments of the invention, not all of them. Based on the embodiments in the invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the invention. In the absence of conflict, the embodiments in the invention and the features in the embodiments can be combined with each other.

In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

A method for preparing oxide fiber-based porous ceramics with a hierarchical structure, the steps of which are as follows:

(1) Solution preparation

1) According to the required molar ratio of organic solvent to complexing agent, 3.7 g of isopropanol (C ₃ H ₈ O) and 1.3 g of ethyl acetoacetate (C ₆ H ₁₀ O ₃ ) are pipetted and added dropwise into a beaker, and stirred on a magnetic stirrer for 10 to 15 minutes to obtain a uniformly mixed organic solution.

2) Add an aluminum source, ie, 2.46 g of aluminum sec-butoxide (C ₁₂ H ₂₇ AlO ₃ ), dropwise into the above organic solution using a dropper, and continue stirring with a magnetic stirrer for 25 to 30 minutes to allow the aluminum sec-butoxide to be uniformly dissolved in the mixed solution.

(2) Preparation of active sol

1) Add 2.0 g of sieved and ground mullite chopped fibers to the prepared mixed solution, and mechanically stir until the fibers are evenly dispersed in the mixed solution to obtain mullite fiber slurry.

2) Weigh 0.04 g of manganese dioxide (MnO ₂ ) powder and add it to the slurry. Stir thoroughly to make the manganese dioxide evenly dispersed in the mullite fiber slurry.

3) Weigh 0.15 g of boron oxide (B ₂ O ₃ ) powder and add it to the slurry. Stir thoroughly to make the boron oxide evenly dispersed in the mullite fiber slurry.

4) 2 g of distilled water is taken up by a dropper and uniformly added to the mullite fiber slurry at a rate of 0.033 g/s. The pH value is adjusted by adding distilled water, and a sol containing mullite fibers is obtained by hydrolysis reaction.

(3) Gel casting

1) The obtained sol is injected into a mold, and a gel block containing mullite fibers is obtained through polycondensation reaction and pre-pressing.

(4) Heat treatment

1) The gel block is placed in an oven for drying at 70°C for 180 minutes. During the drying process, part of the organic matter in the gel is volatilized. After demolding, a mullite fiber porous ceramic body is obtained.

2) The mullite fiber porous ceramic body is placed in a high temperature furnace for high temperature sintering. The heat treatment system is set as follows: the heating rate is 5°C/min, the temperature is raised to 1200°C, the holding time is 3h, and the furnace is cooled. Finally, an oxide fiber-based porous ceramic with a hierarchical structure is obtained.

Example 1

3.7 g of isopropyl alcohol, 1.3 g of ethyl acetate, 2.46 g of aluminum sec-butoxide, 2.0 g of mullite fiber, 2.0 g of distilled water, 0.15 g of boron oxide, and 0.04 g of manganese dioxide.

The organic solvent is isopropanol; the complexing agent is ethyl acetate; the aluminum source is aluminum sec-butoxide; the porous ceramic matrix is mullite fiber; the gelling agent is distilled water; the boron source is boron oxide; the catalyst is manganese dioxide. The heat treatment temperature is 1200°C.

Example 2

The difference from Example 1 is that the amount of boron oxide added is 0.1 g.

Example 3

The difference from Example 1 is that the amount of boron oxide added is 0.2 g.

Example 4

The difference from Example 1 is that the amount of manganese dioxide added is 0.02 g.

Example 5

The difference from Example 1 is that the added amount of manganese dioxide is 0.06 g.

The density, porosity and thermal conductivity of the oxide fiber-based porous ceramics obtained in Examples 1-5 are shown in

Table 1.

The above data show that the oxide fiber-based porous ceramics prepared by this method have good thermal insulation properties.

The present invention adopts mullite fiber with excellent thermal stability and heat insulation performance as a matrix, and prepares a mullite fiber-based porous ceramic with a hierarchical structure by in-situ growing secondary structures such as aluminum borate whiskers and aluminum oxide wafers on the surface of the mullite fiber. The sliding nodes formed by the cross-interlocking of the internal secondary structures (aluminum borate whiskers and aluminum oxide wafers) can improve the deformability of the porous ceramic; and the multi-level pore structure formed by the overlap of the mullite fibers and the cross-intersection of the secondary structures can effectively improve the high-temperature heat insulation performance of the porous ceramic.

In the application process of mullite fiber porous ceramics, the two important parameters of density and thermal conductivity are inversely proportional. Therefore, in the process of entering the secondary structure into the mullite fiber-based porous ceramics, it should be ensured that the density of the porous ceramics is not significantly increased while effectively regulating the pore size and pore size distribution of the porous ceramics. The multi-level pores formed by the overlap of fibers and the intersection of the secondary structure can effectively reduce the thermal conduction and thermal radiation of the porous ceramics, thereby improving its high-temperature thermal insulation performance.

The embodiments of the present invention are described in detail above, but the contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made according to the application scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims (9)

1. A preparation method of oxide fiber-based porous ceramic with hierarchical structure is characterized in that: the preparation method comprises the following preparation steps:

s1: weighing 6 parts of isopropanol, adding 1 part of ethyl acetoacetate into the isopropanol, stirring to obtain a mixed solution, adding 1 part of aluminum sec-butoxide into the mixed solution, and continuously stirring to ensure that the aluminum sec-butoxide is completely dissolved in the mixed solution to obtain uniform mixed slurry;

s2: adding 0.5 part of mullite chopped fiber into the mixed slurry prepared in the step S1, continuously stirring to obtain mullite fiber slurry, sequentially adding 0.045 part of manganese dioxide and 0.2 part of boron oxide powder, fully stirring to uniformly disperse the manganese dioxide and the boron oxide powder in the mullite fiber slurry, dripping water into the slurry, and carrying out hydrolysis reaction to obtain sol containing mullite fibers;

s3, injecting the sol obtained in the step S2 into a mold, and obtaining a gel block containing mullite fibers through condensation polymerization and prepressing of a pressure head;

and S4, placing the gel block obtained in the step S3 in a baking oven for drying, demolding to obtain a porous ceramic blank, and sintering the porous ceramic blank in a high-temperature furnace to finally obtain the oxide fiber-based porous ceramic with the hierarchical structure.

2. The method of manufacturing according to claim 1, characterized in that: and S2, adding the mullite fiber which is a chopped fiber with uniform dispersion, wherein the mol ratio of the mullite fiber to the ethyl acetoacetate is 1:2.

3. The method of manufacturing according to claim 1, characterized in that: the molar ratio of manganese dioxide to ethyl acetoacetate added in S2 is 1:22.

4. The method of manufacturing according to claim 1, characterized in that: and the molar ratio of the boron oxide to the acetoacetic acid ethyl ester added in the S2 is 1:5.

5. The method of manufacturing according to claim 1, characterized in that: and S3, performing compression molding to obtain a cylindrical block.

6. The method of manufacturing according to claim 1, characterized in that: in the step S4, the high-temperature furnace heat treatment system: heating to 1200 ℃ at a heating rate of 5 ℃/min, preserving heat for 3 hours, and cooling in a furnace.

7. An oxide fiber-based porous ceramic prepared by the method of claim 1.

8. The method of manufacturing according to claim 1, characterized in that: the oxide fiber-based porous ceramic has good heat insulation performance.

9. The method of manufacturing according to claim 1, characterized in that: the prepared oxide fiber-based porous ceramic is applied to an aerospace plane heat protection system and an insulating layer of an industrial furnace.

Images