KR20180025719A - Method For Preparing Fused Silica Sintered Material Using Gel-Casting Process - Google Patents

Abstract

The present invention relates to a method of manufacturing a fused silica sintered material by using a gel-casting method. The present invention includes: a step of making a mixed solution by dissolving acrylamide, which is a monomer, and N,N′-Methylenebis (acrylamide), which is a polymer, in a predetermined solvent; a step of making slurry by adding fused silica powder to the mixed solution and milling the mixture for 20-30 hours; a step of making a molded body by mixing a catalyst and an initiator with the slurry and injecting the mixture into a predetermined mold; a step of soaking the molded body in a predetermined organic solvent to substitute moisture of the body with the organic solvent; and a step of separating the molded body from the mold, and sintering the molded body.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method for producing a fused silicate sintered body using a gel casting method,

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 method for facilitating demoulding of a gelled body in a mold.

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.

However, it is difficult to demold the molded article from the mold, and cracks are likely to occur during the drying process and organic matter removal process. The drying time is long and the drying condition is difficult to prevent cracking or deformation. And the molding density is low, and it is necessary to pay attention to the toxicity of organic substances to be added (Non-Patent Document 0001).

There is a method of applying a resin that does not contain silicon as a release agent to the surface of a mold before the slurry is put into a mold by a conventional demolding method (Non-Patent Document 0006), a method of applying carbon tetrachloride (CCl4) (Patent Document 0004).

When a resin decarboxylator is used, there is a problem that the resin is not effectively demoulded due to the adhesive force, and the surface of the molded article is scratched. When carbon tetrachloride demolding agent is applied, carbon tetrachloride can be easily demoulded, but carbon tetrachloride used as a demolding agent is a toxic substance that is fatal to the human body. It is known as a substance that damages health through respiratory and skin contact.

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 KR 10-1999-016261 A

 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 Journal of American Ceramic Society, Vol. 74, No. 3, 612-618, 1991

An object of the present invention is to provide a manufacturing method for manufacturing a sintered body by preventing the molded body from being damaged and demolding the molded body in a manner harmless to the human body.

The present invention provides a method for producing a sintered body using a gel-casting method, which comprises the steps of adding to a predetermined solvent an acrylamide monomer and an acrylonitrile monomer such as N, N'-Methylenebis (acrylamide ) To prepare a mixed solution, adding a fused silica powder to the mixed solution and ball milling for 20 to 30 hours to prepare a slurry, mixing a catalyst and an initiator into the slurry, A step of immersing the molded body in a predetermined organic solvent to replace the water inside the molded body with the organic solvent, and demolding the molded body from the mold, and sintering the molded body.

In one embodiment, the organic solvent may be any one of acetone and ethanol.

In one embodiment, the method may further include the step of demolding the molded body from the mold, and then drying the molded body at a normal temperature and a normal humidity for a predetermined period of time.

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

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.

INDUSTRIAL APPLICABILITY According to the present invention, a gelled molded article can be easily demoulded from a mold without a demolding agent, whereby no defects are formed on the surface of the molded article.

Further, according to the present invention, since a mold-breaking agent harmful to the human body is not used, the effect of the molded body on the human body is weak.

1 is a flowchart showing a method of manufacturing a sintered body according to an embodiment of the present invention.
2 to 7 are conceptual diagrams showing a method of replacing water of a molded article according to the present invention.

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 is added to the mixed solution and ball milled for 20 to 30 hours to prepare a slurry.

Here, the fused silicate powder may be mixed with the mixed solution at 40 to 75 vol%. In addition, in order to increase the strength of the sintered body, the silicon nitride may be added to the mixed solution in an amount of 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.

There is a high possibility that the surface of the molded body is cracked or broken when the molded body is demolded from the mold. Conventional demolding agents lowered the wettability of distilled water and lowered the reactivity with the polymer, thereby preventing defects in the molded body and facilitating demoulding.

However, when the molded body is demolded by the conventional method, when the size of the molded body is increased, the molded body containing water has a lower end deformation of the molded body due to its own weight.

In particular, resin or carbon tetrachloride has been used as a conventional demolding agent. When resin is used, the problem of wettability is unsatisfactory, and the method of applying carbon tetrachloride is difficult to use as a harmful substance to human body.

On the other hand, if the drying speed is increased during the drying process of the molded body, cracks are generated in the molded body due to high surface tension and shrinkage of water. For this reason, conventionally, the molded article must be dried for a long time under a low temperature and high humidity atmosphere.

The present invention uses an organic solvent having a low surface tension and good volatility, instead of a demolding agent harmful to human body.

Specifically, as shown in FIGS. 1 to 6, by replacing moisture contained in the molded body with an organic solvent having a good volatility as a concentration gradient principle before releasing the molded body 220 from the mold 210, And the strength of the formed body can be increased.

Further, since the surface tension of the organic solvent is low and volatility is good, the molded article can be dried quickly without cracking even in a room temperature and normal atmosphere.

Here, the organic solvent may be acetone or alcohol. The gelled molded body and the mold are immersed in a water tank containing the organic solvent to remove moisture inside the molded body, thereby facilitating the demoulding and drying process, causing surface scratches and deformation Do not.

As described above, the demoulding method according to the present invention enhances the strength of a molded body and enables easy demoulding. In addition, the demoulding method according to the present invention makes it possible to quickly dry a molded article under a normal-temperature and normal-humidity atmosphere.

Meanwhile, the mold and the water tank used in the demoulding method according to the present invention may be all materials having stability to the organic solvent.

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.

When the organic additives added to the slurry, that is, the monomer, the dimer, the catalyst, the initiator, and the dispersant are not completely removed, the sintering does not proceed and the mechanical strength can be very low.

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.

In order to remove the organic additive described above, the step of sintering the formed body may include a step of raising the temperature to 600 to 900 ° C at a rate of 1 ° C / min at room temperature under an air atmosphere, And then heat-treated at a rate of 5 ° C / min in an air atmosphere to each 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 1]

To 45 ml of distilled water, 4.1 wt% of acrylamide monomer and 0.1 wt% of methylene bisacrylamide were added to prepare a mixed solution. 120 g (55 ml) of fused silicate ceramic powder as a main ingredient of the radome was mixed to obtain 55 vol% To prepare a fused silicate slurry.

0.4% by weight of ammonium polycarboxylate, an anionic dispersant, was added to the slurry prepared as described above, mixed by ball milling for 24 hours, and vacuum degassed at room temperature until no bubbles were observed.

Then, 0.005 mol% of tetramethylethylenediamine and 0.01 mol% of initiator ammonium persulfate were added to the catalyst, and the mixture was injected into a mold made of Teflon and gelled.

The gelling reaction takes about 5 to 10 minutes. When the gelling is completed, the gelated molded body and the mold are immersed in a substitution solvent (acetone, ethanol) water bath, the solvent is continuously stirred, and the solvent is repeated twice. At this time, the volume ratio of the solvent to the molded body was 100: 1.

As shown in Table 1, the gelled molded body was demolded and the surface of the molded body was observed and the results are shown.

Comparative Example Honor Decolorizer unused Resin
(resin) Carbon tetrachloride (CCl ₄ ) unused unused Water substitution
Solvent none none none Acetone ethanol Demolding
Ease Very bad Bad Very good Very good Good Surface condition damage Surface defect Good Good Good Applicable size small type small type small type large large Mold material various various Corrosion resistance
Material (metal) Chemical resistance
material various anatomy
Hazard none none Fatal effect weak Drying conditions Hardness Hardness Hardness ease ease

As shown in Table 1, in the comparative example, not only the demoulding was extremely bad, but also the molded body was broken. Also, in the case of the comparative example using the resin decarburant, the adhesion between the mold and the molded article remained, resulting in surface scratches.

In addition, when the carbon tetrachloride demolding agent is applied, the demoulding state and the defect of the molded body are extremely good, but it is harmful to the respiratory system and the skin system of the human body and is limited to the corrosion resistant material in the selection of the mold.

In addition, since a molded article containing a large amount of water is infinitesimal, a large deformation causes a deformation at the lower end due to its own weight after demoulding.

On the other hand, according to the present invention, both acetone and ethanol can be easily demoulded without cracking and breakage by lowering the concentration of water and giving a certain strength. In addition, the hazard is weak compared to carbon tetrachloride. Particularly, in the case of acetone solvent substitution, it is necessary to use a mold made of an chemical resistant material, and it has a characteristic that the demoulding is very good although it affects to.

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 (6)

In a method of manufacturing 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 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;
Immersing the molded body in a predetermined organic solvent to replace water inside the molded body with the organic solvent; And
Removing the molded body from the mold, and sintering the molded body. The method according to claim 1,
Wherein the organic solvent is any one of acetone and ethanol. 3. The method of claim 2,
Further comprising the step of removing the molded body from the mold and drying the molded body at a normal temperature and a normal humidity for a predetermined period of time. 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 of claim 4,
Further comprising the step of vacuum degassing at room temperature to remove the bubbles of the slurry. 6. The method according to claim 5,
Characterized in that distilled water is mixed with 4 to 5 wt% of acrylamide and 0.1 to 0.2 wt% of methylene bisacrylamide.

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