KR20180025717A - Method For Preparing Fused Silica Sintered Material Containing Silicon Nitride Using Gel-Casting Process - Google Patents

Abstract

The present invention relates to a method for preparing a fused silica sintered body using a gel-casting method. The present invention provides a method for preparing a sintered body using a gel-casting method, which comprises the steps of: dissolving acrylamide as a monomer and N,N′-methylenebis(acrylamide) as a dimer in a certain solvent to prepare a mixed solution; adding fused silica powder and silicon nitride to the mixed solution to subject the mixed solution to ball milling processing for 20 to 30 hours, thereby preparing slurry; mixing a catalyst and an initiator with the slurry to inject the mixture into a certain mold to prepare a molded body; removing the molded body from the mold to sinter the molded body, wherein 40 to 75 vol% of the fused silica powder and 0.25 to 5 wt% of the silicon nitride are added to the mixed solution. The molded body prepared by the method of the present invention has excellent thermal and shock resistance against air resistance, high mechanical strength, and excellent radio permeability, thereby making the molded body able to be utilized as a protective material of a microwave explorer.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a fused silica crucible containing silicon nitride by gel casting,

The present invention relates to a method for producing a fused silica crucible by using a gel-casting method. More specifically, the present invention relates to a manufacturing method for producing a fused silica crucible by adding nitride-based silicon nitride to improve mechanical strength.

Known complex shaping techniques to date include techniques such as injection molding, slip casting, and processing. Injection molding involves a problem that the molded body is broken or cracked when the binder is removed because the binder contains 20 wt% or more of binder.

In addition, slip casting has a disadvantage in that a density gradient occurs in the inside of the formed body, which causes distortion during sintering and the strength of the formed body is low. The production of a molded body by machining is not economical (Non-Patent Document 0001).

The gel casting method developed to overcome the disadvantages of the conventional complicated shape producing technique is disclosed in Patent Documents 0001 to 0003 and Non-Patent Documents 0002 to 0005. This method is a combination of a ceramic process and a polymer manufacturing technique. A ceramic powder is mixed with a solution of an organic monomer and a dimer, which is a network forming agent, to prepare a slurry. And the monomers through the gelling reaction are polymerized to form a ceramic compact structure and sintered.

U.S.A. Patent No. 4894194, Jan 16, 1990 U.S.A. Patent No. 5028362, Jul 2, 1991 U.S.A. Patent No. 5145908, Sep 8, 1992

 Journal of American Ceramic Society, Vol. 81, No. 3, 581-591, 1998  Journal of the American Ceramic Society  Ceramic Bulletin, Vol. 70, No. 10, 1641-1649, 1991  Journal of the American Ceramic Society, Vol. 74, No. 3, 612-618, 1991  Journal of the European Ceramics Society, Vol. 17, No.2-3, 407-413, 1997

It is an object of the present invention to provide a method for producing a fused silica crucible having excellent thermal, mechanical and chemical durability.

The present invention provides a method for producing a sintered body using a gel-casting method, which comprises the steps of adding a monomer, acrylamide, and an equivalent amount of methylene bisacrylamide (N, N'-Methylenebis ) To prepare a mixed solution, adding a fused silica powder and silicon nitride to the mixed solution and ball milling for 20 to 30 hours to prepare a slurry, mixing the catalyst and the initiator into the slurry, And a step of sintering the molded body, wherein the fused silicate powder is contained in an amount of 40 to 75 vol% and the silicon nitride is contained in an amount of 0.25 to 5 wt% In a solution.

In one embodiment, the step of preparing the mixed solution may further include a step of adjusting the pH to 10 to 11 by adding a base to the mixed solution.

In one embodiment, the slurry may further comprise 0.1 to 0.8 wt% of ammonium polycarboxylate.

In one embodiment, the catalyst is N, N, N'N'-Tetramethylethylenediamine and the initiator may be Ammonium Persulfate.

In one embodiment, the step of sintering the shaped body may include heating the formed body in an oxygen atmosphere at a temperature of 600 to 900 ° C. for 1 to 2 hours to remove the organic substances contained in the formed body, And heating the shaped body at 1150 to 1400 캜 in a nitrogen atmosphere.

In one embodiment, the step of preparing the slurry may further include a step of vacuum defoaming at room temperature to remove the bubbles of the slurry.

In one embodiment, the mixed solution may be prepared by mixing 4 to 5 wt% of acrylamide and 0.1 to 0.2 wt% of methylene bisacrylamide in distilled water.

The fused silicate sintered body manufactured by the method according to the present invention can be utilized as a protection material for a microwave searcher because it has excellent thermal shock resistance by air resistance (aerodynamic heating), high mechanical strength, and excellent radio wave permeability.

1 is a flowchart showing a method of manufacturing a sintered body according to an embodiment of the present invention.
FIGS. 2A and 2B are graphs showing changes in shear stress with respect to shear rate change of the slurry according to the present invention. FIG.
FIG. 3 is a graph showing a viscosity change according to the addition amount of silicon nitride in the slurry according to the present invention.
4 is a graph showing the result of analyzing the bonding structure of the sintered body by infrared spectroscopy (FT-IR).
5 is a graph showing changes in the bending strength of the sintered body with changes in sintering temperature.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein like reference numerals are used to designate identical or similar elements, and redundant description thereof will be omitted. In the following description of the embodiments of the present invention, a detailed description of related arts will be omitted when it is determined that the gist of the embodiments disclosed herein may be obscured. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. , ≪ / RTI > equivalents, and alternatives.

Hereinafter, a method for producing a sintered body according to the present invention will be described.

1 is a flowchart showing a method of manufacturing a sintered body according to an embodiment of the present invention. Hereinafter, a method for manufacturing a sintered body according to the present invention will be described with reference to FIG.

First, in the production process according to the present invention, a step of preparing a mixed solution by dissolving acrylamide, which is a monomer, and N, N'-methylenebis (acrylamide), which is a monomer, in a predetermined solvent is performed.

Here, the mixed solution may be prepared by mixing 4 to 5 wt% of acrylamide and 0.1 to 0.2 wt% of methylene bisacrylamide in distilled water.

Next, fused silica powder and silicon nitride are added to the mixed solution, followed by ball milling for 20 to 30 hours to prepare a slurry.

Here, the fused silicate glass powder may be mixed in the mixed solution at 40 to 75 vol% and the silicon nitride may be mixed at 0.25 to 5 wt%.

At this time, in order to secure the fluidity of the slurry and to ensure that the fused silica powder in the slurry is well dispersed, the ball milling can be performed after 0.1 to 0.8 wt% of ammonium polycarboxylate, which is an anionic dispersant, is added.

On the other hand, it is confirmed that the slurry for gel casting has a newtonian flow behavior in which the change of shear stress with respect to shear rate change linearly changes, so that the ceramic powders in the slurry are uniformly dispersed . However, a slurry having a viscosity of 100 cps or more is not completely removed from the bubbles during the defoaming process and is present as a defect after molding, causing stress due to friction with the mold surface during casting, causing cracking in the drying process.

It is possible to control the behavior of the slurry using a dispersant in the process of manufacturing the slurry using only the fused silica powder. However, when the slurry is prepared by adding silicon nitride for improving the mechanical strength, the fused silicate And silicon nitride powders, the slurry is not uniformly dispersed.

In order to solve the above-described problems, the present invention can control the addition amount of silicon nitride to 0.25 to 5.0 wt% and adjust the pH of the slurry to 10 to 11 using a base so that the slurry can be uniformly dispersed .

Here, the base may be sodium hydroxide.

Next, the slurry is mixed with a catalyst and an initiator, and the mixture is injected into a predetermined mold to produce a molded body.

Here, the catalyst may be N, N, N'N'-Tetramethylethylenediamine, and the initiator may be Ammonium Persulfate. Each of the catalyst and the initiator may be added in an amount of 0.001 to 0.2 mol% of the monomer.

Finally, the step of demolding the molded body from the mold and sintering the molded body is proceeded.

Here, after the mold is demolded from the mold, the inside of the mold can be removed through the thermostat. Thereafter, the sintered body in an amorphous state can be manufactured by sintering at a temperature range of 1150 to 1400 ° C.

In order to prevent oxidation in the sintering step, heat treatment is performed so as not to generate a crystal in a nitrogen atmosphere, so that Si-N bond is formed in a part of the Si-O bond to increase the mechanical strength.

On the other hand, the organic additives added to the slurry, that is, monomers, dimers, catalysts, initiators and dispersants, can not be completely removed in a nitrogen atmosphere, so that sintering does not proceed and very low mechanical strength can be exhibited.

On the other hand, in the general air atmosphere, silicon nitride is oxidized and converted into stable silica during sintering. In order to prevent this, atmosphere control in sintering is indispensable.

The step of sintering the molded body to generate Si-N bonds in the sintered body and to remove the organic additive described above includes heating the molded body in an oxygen atmosphere to remove the organic substances contained in the molded body, And heating the shaped body in a nitrogen atmosphere.

Specifically, the sintering step is a step of raising the temperature at a temperature of 600 to 900 ° C. at a temperature of 600 to 900 ° C. under an oxygen atmosphere, maintaining the temperature at a rate of 1 ° C./min and keeping it for 1 hour to completely remove the organic matter, Heat treating the sintered body to a sintering temperature.

Here, it was confirmed that the organic materials used for gel casting were completely oxidized at 720 ° C by pulverizing the dried molded body and performing thermogravimetric / differential thermal analysis (TG / DTA). Thus, the heating temperature in an oxygen atmosphere is preferably 800 ° C.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples. However, the scope and contents of the present invention are not construed to be limited or limited by the following Examples and Experimental Examples.

[Example]

To 45 ml of distilled water, 4.1 wt% of acrylamide monomer and 0.1 wt% of methylene bisacrylamide were completely dissolved to prepare a mixed solution, and the solution was adjusted to pH 10.5 with sodium hydroxide.

119.048 g (54.291 ml) of fused silica powder as a main ingredient of radome and 2.438 g (0.709 ml) of silicon nitride powder as an additive were mixed and fused silica slurry (100 ml) of 55 vol% added with 2 wt% .

0.4 wt% of ammonium polycarboxylate, which is an anionic dispersant, was added to the slurry prepared as described above and mixed by ball milling for 24 hours.

The mixed slurry was vacuum degassed at room temperature until no bubbles were visible using a rotary pump and a deaerator. The catalyst was added with 0.005 mol% tetramethylethylenediamine and 0.01 mol% initiator ammonium persulfate, mixed with Teflon Lt; / RTI > mold and gelled.

The gelation reaction takes about 5 to 10 minutes. When the gelling is completed, the gelled molded body and the mold are immersed in a substitution solvent (acetone, ethanol) water bath and the solvent is continuously stirred to replace the water inside the molded body with acetone having low surface tension, And dried using a hygrostat.

The dried molded body was heated at a temperature raising rate of 1 占 폚 / min from room temperature to 600 to 900 占 폚 using an atmosphere furnace, and then the heated temperature was maintained for 1 to 2 hours. At this time, the atmosphere was oxygen atmosphere and the flow rate of oxygen gas was 0.1 to 1.0 L / min.

After the organic matter was completely removed from the molded body, nitrogen gas was introduced at a rate of 0.1 to 1.0 L / min instead of oxygen gas to make the atmosphere in the furnace nitrogen atmosphere and heat treatment to a sintering temperature (1150 to 1400 ° C) .

Although the fused silicate powder is used as the ceramic powder in the embodiment of the present invention, the present invention is not limited thereto.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.

In addition, the above detailed description should not be construed in all aspects as limiting and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.

Claims (7)

In a method for producing a sintered body using a gel-casting method,
Preparing a mixed solution by dissolving acrylamide and N, N'-methylenebis (acrylamide), which are monomers, in a predetermined solvent;
Adding a fused silica powder and silicon nitride to the mixed solution and ball milling for 20 to 30 hours to prepare a slurry;
Mixing the slurry with a catalyst and an initiator, and injecting the slurry into a predetermined mold to produce a molded body; And
Demolding the molded body from the mold, and sintering the molded body,
Wherein the fused silicate crucible powder is mixed with the mixed solution in an amount of 40 to 75 vol% and the silicon nitride is mixed in the mixed solution in an amount of 0.25 to 5 wt%. The method according to claim 1, wherein the step of preparing the mixed solution comprises:
Further comprising adding a base to the mixed solution to adjust the pH to 10 to 11. 3. The method of claim 2,
Wherein the slurry further comprises 0.1 to 0.8 wt% of ammonium polycarboxylate. The method of claim 3,
The catalyst is tetramethylethylenediamine (N, N'N'-Tetramethylethylenediamine)
Wherein the initiator is ammonium persulfate. ≪ RTI ID = 0.0 > 21. < / RTI > 5. The method according to claim 4,
Heating the formed body in an oxygen atmosphere at a temperature of 600 to 900 DEG C for 1 to 2 hours to remove organic matter contained in the formed body; And
And heating the shaped body from which the organic material has been removed in a nitrogen atmosphere at a temperature of 1150 to 1400 占 폚. 6. The method of claim 5,
Further comprising the step of vacuum degassing at room temperature to remove the bubbles of the slurry. 7. The method according to claim 6,
Characterized in that distilled water is mixed with 4 to 5 wt% of acrylamide and 0.1 to 0.2 wt% of methylene bisacrylamide.

Images