CN115043672A - A kind of realization method of re-strengthening of alumina ceramics - Google Patents

Abstract

The invention discloses a method for realizing the re-strengthening of alumina ceramics, belonging to the technical field of ceramic material preparation. The method comprises the following steps: preparing coating sol: mixing the alumina sol and the silica sol, adjusting the pH value to 2-3, stirring for 1 hour at normal temperature to uniformly mix, adding a fluxing agent, and stirring for more than 1 hour to obtain a mullite precursor sol; preparation and sintering of a prestressed coating: and (2) immersing the alumina ceramic into the mullite precursor sol for a certain time, slowly lifting and pulling at a constant speed to obtain a uniform sol film layer, repeatedly lifting and pulling for several times, and then sintering at the low temperature of 900-1300 ℃ for 1 h. The invention prepares the mullite coating with low expansion coefficient on the surface of the densified alumina ceramic at low temperature, and residual compressive stress can be formed in the coating, thereby realizing the purpose of alumina reinforcment.

Description

A kind of realization method of re-strengthening of alumina ceramics

technical field

The invention relates to the technical field of ceramic material synthesis, in particular to a method for realizing re-strengthening of alumina ceramics.

Background technique

Alumina ceramics are structural ceramics with α-Al ₂ O ₃ as the main crystal phase. Because of their high strength, high hardness, high temperature resistance, good electrical insulation properties, especially excellent chemical stability and oxidation resistance, And raw materials are widely sourced and cheap, and have been widely used in engineering fields such as electronics, aviation, machinery, chemical industry, and construction.

However, alumina ceramic materials have problems such as high thermal expansion coefficient, thermal shock resistance, and thermal conductivity that are not as good as those of non-oxides, and as a typical brittle material, it is compressive but not tensile, and the fracture strain is small when it is damaged. Brittle fracture. Therefore, the simple realization of the enhancement and toughening of alumina and the improvement of its reliability are the decisive factors to realize the re-development of alumina.

At present, the methods for improving the strength of alumina ceramics include improving the sintering process, introducing particle reinforcing phases (particles, fibers), bionic layered structures, surface treatment, etc., but these methods are mainly used in important fields such as military industry and aerospace, and are also affected by cost. and shape size limitations. And for the alumina that has been sintered and densified, there is no research on effectively realizing its re-strengthening.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the prior art, the present invention provides a method for realizing re-strengthening of alumina ceramics. The invention prepares a mullite coating whose thermal expansion coefficient is lower than that of alumina at a low temperature (900-1400° C.) on the surface of the sintered alumina. The strength of alumina ceramics has been improved again.

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

The invention provides a method for realizing re-strengthening of alumina ceramics, comprising:

(1) Preparation of coating sol: Mix the raw material alumina sol and silica sol for synthesizing the mullite sample, adjust the pH to 2-3, stir at room temperature for 1 hour to make it evenly mixed, and then add flux, and then stirring for more than 1 hour to obtain the mullite precursor sol;

(2) Preparation and sintering of prestressed coating: The alumina ceramic is immersed in the mullite precursor sol for about 10s-40s, and then slowly pulled at a constant speed to obtain a uniform sol film layer, and the pulling is repeated 2-10 times, and then 900 ~ 1300 ℃ low temperature sintering for 1h.

Preferably, in the step (1), the solid content of the alumina sol is 10-50 wt %, the pH value is less than 5, and the particle size of the alumina is 20-100 nm. The solid content of the silica sol is 10-50 wt %, the pH value is less than 5, and the particle size of the silica is 20-100 nm.

Further, the alumina sol and the silica sol are

比例混合。

Proportional mix.

Preferably, the pH-adjusting substance is an organic acid (20% citric acid solution) or ammonia water.

Further, the co-solvent is one or more of B ₂ O ₃ , MgO and K ₂ O.

Further, in the step (2), the time of immersion in the mullite precursor sol is 10s-40s; the number of times is 2-10 times. The coating thickness can be increased by increasing the number of pulls.

The present invention also provides a prestressed alumina ceramic material, which is prepared by the above method.

As a relatively stable compound in the Al ₂ O ₃ -SiO ₂ binary system, mullite has low thermal conductivity, high high temperature strength, good thermal shock resistance, low thermal expansion coefficient, oxidation resistance, chemical corrosion resistance, and at the same time. Has good high temperature stability and thermal shock resistance. Therefore, by preparing a mullite coating on the surface of alumina, it can not only form prestress enhancement, but also impart better high temperature stability and thermal shock resistance to alumina.

Compared with the prior art, the present invention has the following beneficial effects:

The invention prepares the mullite coating with low expansion coefficient on the surface of densified alumina ceramics at low temperature. During the cooling process, the substrate shrinks greatly and the coating shrinks less, and the two pull each other through the strong interface, so the coating will form Residual compressive stress (similar to tempered glass), as shown in Figure 1, to achieve the purpose of re-strengthening of alumina.

Description of drawings

Fig. 1 is the structural schematic diagram of the material prepared by the method of Example 1 of the present invention and the stress schematic diagram of its cross-section;

FIG. 2 is a SEM picture of the material prepared by the method of Example 1 of the present invention.

Detailed ways

In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, the following will be described in detail with reference to the accompanying drawings and specific embodiments.

The reagents and materials used in the examples and comparative examples can be obtained through commercial channels unless otherwise specified.

The present invention provides a method for realizing re-strengthening of alumina ceramics, and the specific embodiments are as follows.

Example 1

A method for realizing re-strengthening of alumina ceramics, comprising:

(1) Preparation of coating sol: 20% SiO ₂ sol (pH2-4) with solid content was slowly added dropwise to 20% solid content Al ₂ O ₃ sol (pH 3.6-4.1), (Al ₂ O ₃ sol × 20%): (SiO ₂ sol × 20%) = 7:3, adjust the pH to 2-3 with ammonia water, stir at room temperature for 1 h to make it evenly mixed, then add flux B ₂ O ₃ and stir for 1 h to obtain molybdenum. comestone precursor sol;

(2) Preparation and sintering of prestressed coating: Immerse the sintered and densified alumina ceramics in the mullite precursor sol for about 40s, and then slowly pull up at a constant speed to obtain a uniform sol film layer, which can be dried at 60 °C. Continue to pull, repeat 5 times, and then sinter at a high temperature of 1100 ° C and a low temperature for 1 hour.

It can be seen from FIG. 2 that the mullite coating prepared by the present invention is uniformly attached to the alumina base ceramic.

Example 2

In this example, (Al ₂ O ₃ sol×20%): (SiO ₂ sol×20%)=8:3, and other conditions are the same as those in Example 1.

Example 3

In this example, (Al ₂ O ₃ sol×20%): (SiO ₂ sol×20%)=12:3, and other conditions are the same as those in Example 1.

In order to highlight the beneficial effects of the materials prepared by the method of the present invention, the inventors designed a comparative example as follows.

Comparative Example 1

In this comparative example (Al ₂ O ₃ sol×20%): (SiO ₂ sol×20%)=1:1, and other conditions are the same as those in Example 1.

The flexural strength performance test was carried out on the materials prepared by the methods of Examples 1-3 and Comparative Example 1 above.

Table 1 Flexural strength of alumina and prestressed alumina ceramics

It can be seen from Table 1 that the flexural strength of the prestressed alumina ceramic composite material prepared by the method of the present invention is 30% higher than that of the alumina ceramic matrix.

Within a limited range, by adjusting the process parameters of each step in the present invention, the properties of the prepared composite material are consistent with the foregoing embodiments, and will not be repeated here.

To sum up, the present invention prepares a mullite coating with a low expansion coefficient on the surface of densified alumina ceramics at a low temperature. During the cooling process, the substrate shrinks greatly, and the coating shrinks less, and residual compressive stress will be formed in the coating, thereby realizing The purpose of alumina re-strengthening.

The above are the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be regarded as the present invention. the scope of protection of the invention.

Claims (7)

1. A method for realizing the re-strengthening of alumina ceramics is characterized by comprising the following steps:

(1) preparing coating sol: mixing the alumina sol and the silica sol, adjusting the pH to 2-3, stirring at normal temperature for 1h to mix uniformly, adding a fluxing agent, and stirring for more than 1h to obtain a mullite precursor sol;

(2) preparation and sintering of a prestressed coating: and (3) immersing the alumina ceramic into the mullite precursor sol for about 10-40 s, slowly lifting at a constant speed to obtain a uniform sol film layer, repeatedly lifting for 2-10 times, and then sintering at the low temperature of 900-1300 ℃ for 1 h.

2. The method for realizing the reinforcementation of the alumina ceramic according to claim 1, wherein in the step (1), the solid content of the alumina sol is 10-50 wt%, the pH value is less than 5, and the particle size of the alumina is 20-100 nm.

3. The method for realizing the reinforcment of the alumina ceramic according to claim 2, wherein the solid content of the silica sol is 10 to 50 wt%, the pH value is less than 5, and the particle size of the silica is 20 to 100 nm.

4. The method for realizing the reinforcementation of alumina ceramics according to claim 3, wherein the alumina sol and the silica sol are mixed with each other

And (4) mixing the components in proportion.

5. The method for realizing the reinforcementation of the alumina ceramic according to claim 4, wherein the pH adjusting substance is a 20% citric acid solution or ammonia water.

6. The method for realizing the reinforcementation of the alumina ceramic according to claim 5, wherein the cosolvent is B ₂ O ₃ 、MgO、K ₂ One or more of O.

7. A pre-stressed alumina ceramic material, characterized in that it is obtained by a process according to any one of claims 1 to 6.

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