CN1686945A - Silica sol solidification method for forming ceramic component - Google Patents

Abstract

The invention relates to a method for forming ceramic parts by solidifying silica sol, and belongs to the technical field of material preparation. The method is to mix ethyl orthosilicate and sodium hydroxide solution, hydrolyze the ethyl orthosilicate to form silica sol through mechanical stirring, then add engineering ceramic powder into this silica sol solution, stir and mix to obtain ceramic slurry The ceramic slurry is injected into a non-porous mold, solidified at a temperature of 25-10°C, and a ceramic green body of a desired shape is formed. By adopting this process, the non-viscous barren engineering ceramic slurry can be directly solidified to form a desired shape, and a ceramic green body with a certain strength can be obtained. The invention is suitable for molding preparation of ceramic products of different types and shapes, the dry strength of the molded green body is high, and the ceramic green body is not easily damaged; the molding process is simple, and the preparation of the silica sol solution is convenient and convenient for production.

Description

Method for solidifying and molding ceramic parts with silica sol

technical field

The present invention relates to a new method of forming ceramic parts. By adopting this process, the non-viscous barren engineering ceramic slurry can be directly solidified to form a desired shape, and a ceramic green body with a certain strength can be obtained. It belongs to the technical field of material preparation.

Background technique

Engineering ceramic materials, such as alumina, zirconia, silicon nitride, silicon carbide, etc., have a series of excellent mechanical properties and chemical stability such as high strength, high hardness, high temperature resistance, wear resistance and corrosion resistance, so in There are more and more applications in modern science and technology and industrial fields (such as aerospace, chemical industry, machinery, information, electronics, life science, etc.). These materials are mostly used as a structural component, have various shapes, and require precise dimensions to achieve near-net size molding. Traditional molding and manufacturing processes such as dry pressing and cold isostatic pressing are difficult to prepare ceramic parts with complex shapes, while ordinary slip casting is limited to thin-walled ceramic parts. There is a density gradient inside the thick-walled ceramic molding, and when sintering Prone to defects and cracks.

In recent years, some new ceramic slurry direct solidification molding processes have been developed internationally. For example, the Oak Ridge National Laboratory in the United States proposed a method called gel injection molding. This process is formed by the polymerization of organic monomers. The three-dimensional gel network, so that the ceramic suspension is injected into the mold and solidified into a ceramic body in situ. This method can form engineering ceramic parts of different types and shapes, but most of the organic monomers have certain toxicity; in addition, single When the body is polymerized, the surface will have cracks and other defects after the part in contact with the air dries. Therefore, the application of this process is limited.

Contents of the invention

The invention proposes a new method for in-situ solidification of ceramic slurry to form ceramic components. The principle is to mix ethyl orthosilicate and sodium hydroxide solution at room temperature, hydrolyze the ethyl orthosilicate to form silica sol by mechanical stirring, then add engineering ceramic powder to this silica sol solution, stir and mix The ceramic slurry is obtained, and the ceramic slurry is injected into a non-porous mold, and can be solidified quickly at a temperature of 25-10° C., and a ceramic green body of a desired shape is molded. By adopting this method, various complex shapes of ceramic parts can be molded without any defects such as cracks.

The method for coagulating silica sol to form ceramic parts proposed by the present invention is characterized in that: the method is to mix ethyl orthosilicate and sodium hydroxide solution, stir the ethyl orthosilicate to hydrolyze to generate silica sol by mechanical stirring, and then Add engineering ceramic powder into this silica sol solution, stir and mix to obtain a ceramic slurry, inject the ceramic slurry into a non-porous mold, solidify at a temperature of 25-10°C, and form a ceramic body of the desired shape. The method includes the following steps in turn:

(1) First prepare the silica sol liquid, mix ethyl orthosilicate and sodium hydroxide solution, the volume ratio of the two is 6:4～8:2, stir at room temperature, then place to obtain the silica sol;

(2) Add ceramic powders, such as alumina, zirconia, silicon nitride, and silicon carbide, into the above-mentioned silica sol solution, stir well to obtain a uniformly dispersed ceramic slurry, and the volume ratio of ceramic powder to silica sol liquid is 40～ 60: 60~40;

(3) Pouring the uniformly dispersed ceramic slurry into a non-porous mold made of metal, plastic or glass material, pouring the slurry into the mold and placing it to solidify at 10-25°C, and demoulding.

In the method for the above-mentioned colloidal silica sol solidification forming ceramic parts, the dispersant of the step (2) is polyacrylate solution, tetramethylammonium hydroxide solution, polyacrylic acid solution, ammonium citrate, added in sodium polyacrylate solution Any one, the added amount of the dispersant is within 2wt% of the weight of the ceramic powder.

In the above method for coagulating silica sol to shape ceramic parts, the pH value of the sodium hydroxide solution in the step (1) is 10.0-13.0.

In the above-mentioned method for coagulating silica sol to form a ceramic part, in the step (3), the solidified and formed ceramic body is demoulded, and then dried at 60-100°C.

The present invention has the following advantages:

1) It is suitable for the molding and preparation of ceramic products of different types and shapes;

2) The formed ceramic body has a smooth surface without any defects;

3) The dry strength of the molded green body is high, and the ceramic green body is not easily damaged;

4) The molding process is simple, the silica sol solution is convenient to prepare, and is convenient for production.

Detailed ways

Below in conjunction with embodiment technical scheme of the present invention is described further:

1) First prepare the silica sol liquid, mix ethyl orthosilicate and sodium hydroxide solution, the volume ratio of the two is 6:4-8:2. Stir at room temperature for 1 to 4 hours, and then stand for 3 to 6 days to obtain silica sol.

2) Add engineering ceramic powder, such as alumina, zirconia, silicon nitride, silicon carbide, etc., into the above-mentioned silica sol solution, stir well, and the volume ratio of ceramic powder to silica sol liquid is 40-60:60-40.

3) The uniformly dispersed ceramic slurry is poured into a non-porous mold made of metal, plastic or glass material, and the slurry is poured into the mold and placed at 10-25° C. for 20-60 minutes. The silica sol molecules gradually produce a gel reaction to form a network structure, so that the ceramic slurry is solidified into a ceramic body of the desired shape.

4) The solidified and formed ceramic body has a certain strength and can be demolded directly, and then dried at 60-100° C., and the bending strength of the ceramic body after drying can reach 5 MPa. It is much stronger than the green body of traditional grouting.

Embodiment 1: Forming of alumina ceramic ring

Dissolve 140 ml of sodium hydroxide with a pH value of 11.9 and 60 ml of tetraethyl orthosilicate at room temperature, stir mechanically for 2 hours, and then leave for 5 days to obtain a silica sol solution. Then 700 grams of ceramic powder was added to the solution, and 7 milliliters of dispersant polyacrylate solution was added at the same time. Use a stirrer to stir for 1 hour to make it completely and evenly dispersed to obtain a stable ceramic slurry. Then inject the above ceramic slurry into the metal mold, place it at 15°C for curing, and the slurry solidifies in about 30 minutes to form a ceramic ring body with a certain strength, which can be demolded.

Example 2: Silicon carbide ceramic tube forming

Mix 100 ml of sodium hydroxide solution with a pH value of 12.3 and 35 ml of tetraethyl orthosilicate at room temperature, stir mechanically for 1.5 hours, and place it for 4 days to obtain a silica sol solution; then add 480 grams of silicon carbide ceramic powder to the above silica sol At the same time, 2 ml of tetramethylammonium hydroxide solution was added to the solution, and mechanically stirred for 1 hour to achieve complete dispersion, suspension and stable silicon carbide ceramic slurry. Immediately, the silicon carbide slurry was injected into a plastic mold, and the slurry was solidified after being placed at 10° C. for 25 minutes to obtain a silicon carbide ceramic tube body. After demoulding, the shape is intact, no cracks, no deformation.

Embodiment 3: Forming of silicon nitride ceramic green body

Mix 120 ml of sodium hydroxide solution with a pH value of 12.8 and 43 ml of tetraethyl orthosilicate at room temperature, stir for about 1 hour, and stand for 3 days to obtain a silica sol solution. Add 570 grams of silicon nitride ceramic powder into the silica sol solution to disperse and stir, and at the same time add 1.5 ml of polyacrylic acid solution as a dispersant, and mechanically stir for 1.5 hours to obtain a uniformly dispersed silicon nitride slurry, and then inject the slurry into the glass In the mold, the gel reacts and solidifies at 15°C. After about 40 minutes, the slurry solidifies to form a green body, which can be demoulded directly without damage.

Embodiment 4: Forming of zirconia ceramics

100 ml of sodium hydroxide solution with a pH value of 12.5 was mixed with 36 ml of tetraethyl orthosilicate at room temperature. Stir for 1.5 hours, place at room temperature for 4 days to obtain a stable silica sol solution, then add 510 grams of zirconia ceramic powder to the above solution, and add ammonium citrate as a dispersant at the same time, the dosage is 5 grams, and mechanically stir for 2 hours to make it Completely dissolve and disperse to obtain a stable ceramic slurry, then inject it into the metal mold, and carry out gel reaction solidification at 18°C. After about 0.5 hours, the slurry solidifies to form a relatively hard zirconia ceramic body, which can be demolded . After demoulding, it is dried in a drying oven at 60-100°C, and the strength of the ceramic green body is further improved after drying.

Embodiment 5: the forming of quartz ceramic rod

Quartz powder is used as fused silica ceramic powder with a particle size of about 2 microns. First, silica sol is prepared by mixing 150 ml of sodium hydroxide solution with a pH value of 12.5 and 55 ml of tetraethyl orthosilicate at room temperature and stirring mechanically. 1 hour, after standing for 3 days to obtain a uniform silica sol solution, then add 700 grams of quartz ceramic powder to the silica sol solution, and at the same time add sodium polyacrylate solution as a dispersant, the dosage is 6 ml, and then stir for 1 hour to obtain a suspension The good ceramic slurry is then injected into the metal mold and placed at 16°C for about 30 minutes. The slurry is solidified to obtain a quartz ceramic rod. After demoulding, the molded body is intact without deformation and defects.

Claims (4)

1. The method for coagulating silica sol to form ceramic parts is characterized in that: the method is to mix ethyl orthosilicate and sodium hydroxide solution, stir the ethyl orthosilicate to hydrolyze to generate silica sol, and then mix the engineering Add ceramic powder into this silica sol solution, stir and mix to obtain ceramic slurry, inject the ceramic slurry into a non-porous mold, solidify at a temperature of 25-10°C, and form a ceramic green body of the desired shape. Contains the following steps in turn: (1) First prepare the silica sol liquid, mix ethyl orthosilicate and sodium hydroxide solution, the volume ratio of the two is 6:4～8:2, stir at room temperature, then place to obtain the silica sol; (2) Add ceramic powder, such as alumina, zirconia, silicon nitride, and silicon carbide, to the above-mentioned silica sol solution, then add a dispersant, and fully stir to obtain a uniformly dispersed ceramic slurry. The mixture of ceramic powder and silica sol liquid The volume ratio is 40～60:60～40; (3) Pouring the uniformly dispersed ceramic slurry into a non-porous mold made of metal, plastic or glass material, pouring the slurry into the mold, placing it to solidify, and demoulding. 2. The method for forming ceramic parts by coagulating silica sol according to claim 1, characterized in that the pH value of the sodium hydroxide solution in the step (1) is 10.0-13.0. 3. The method for solidifying and forming ceramic parts from silica sol according to claim 1, characterized in that: the dispersant in the step (2) is polyacrylate solution, tetramethylammonium hydroxide solution, polyacrylic acid solution, lemon Ammonium acid, adding any one of the sodium polyacrylate solution, the added amount of the dispersant is within 2wt% of the ceramic powder weight. 4. The method for forming ceramic parts by coagulation of silica sol according to claim 1, characterized in that in the step (3), the solidified and formed ceramic body is demoulded, and then dried at 60-100°C.