KR20010077623A - Fabrication of the Green Body Consisting of Silicon Carbide Mixed with Carbon Powders Using Gel-casting Method - Google Patents

Abstract

PURPOSE: Provided is a preparation method of SiC/C mold by gel casting which is characterized by adding five kinds of additives to SiC/C powder step by step. The resultant SiC/C mold has high forming density and forming strength so that it shows large and complicate shapes. CONSTITUTION: The preparation method for SiC/C mold is as follows: preparing a SiC/C slurry by adding 0.5-1.0wt.% of naphthalene sulfonic formaldehyde condensate(T-N) as a dispersant and water to SiC/C powder composed of 70-90wt.% of SiC and 10-30wt.% of C, and ball-mixing for 1hr.; adding a binder, 12-18wt.% of acrylamide (AM, C2H3CONH2), and cross-linker, 0.5-0.8wt.% of N,N-methylene bisacrylamide (MBAM, (C2H3CONH)2CH2), and ball-mixing for 24hrs.; adding a catalyst, 1.0-6.0mL/L of tertramethylethylenediamine(TEMED), and ball-mixing for 30min.; adding a reaction initiator, 0.2g/L of ammonium persulfate(APS, (NH4)2S2O8), and mixing for 5min.; removing foams; molding and polymerizing; drying.

Description

Fabrication of Silicon Carbide Mixed Carbon Forms Using Gel-Casting Method {Cabrication of the Green Body Consisting of Silicon Carbide Mixed with Carbon Powders Using Gel-casting Method}

The present invention relates to a method of molding ceramics, and more particularly, to prepare a slurry by mixing and dispersing an additive in a mixture of coarse silicon carbide powder and fine carbon powder in several stages, and then injecting into a mold and polymerizing the gel. The present invention relates to a method for producing a SiC / C molded article which shows high molding strength and molding density by a gel casting method and is capable of being processed raw.

In the conventional case, the ceramic molding is a hydrostatic molding in which a dry powder is charged into an elastic mold and then subjected to hydrostatic pressure, and a slurry prepared by mixing and dispersing the ceramic powder in a solution with a dispersant is injected into a porous mold such as a plaster mold. Injection molding drying by capillary force, press injection molding to increase the osmotic pressure by increasing pressure to increase the molding rate in injection molding method, and adding about 30 wt% binder by weight ratio of ceramic powder Plastic injection fluid with high viscosity is injected into the mold under pressure, and then molded and then degreased with the binder. Polymerization by injecting a slurry into a mold of desired shape It was prepared by a method such as gel-casting.

Hydrostatic pressure molding method is not possible to continuous process, there is a problem in mass production process application, and expensive equipment must be used. The injection molding method changes the characteristics of the molded body sensitively depending on the conditions of the slurry and the drying environment, so that the yield of the molded body is low and the processing time is long. In addition, the molding mold has to be replaced frequently, the density gradient occurs in the molded body, and the molding strength is low. In manufacturing large parts, there are problems such as cracking and collapse. The press injection molding method can obtain a denser compacted body in a relatively short time than the injection molding method, but it does not solve the problems such as density gradient and low molding strength in the molded body, which is a fundamental problem of injection molding. Injection molding uses a large amount of organic binder, which requires a long time in the degreasing process, and in the case of thick moldings, the disadvantage of being destroyed during degreasing and the difficulty of completely removing the pores left after degreasing in the subsequent sintering process, in addition to pressing metals There is a disadvantage in that a large cost is required to manufacture the mold.

Gel casting molding is a technology that applies injection molding, which is a ceramic molding technology, and polymerization, which is a manufacturing process for polymers. It can be formed regardless of mold materials such as metal, glass, and plastic, and it is possible to manufacture molded articles having relatively high molding strength. Is relatively easy to remove, and has many advantages over other molding methods when forming a large member of complex shape. Gel casting molding was developed in the United States in the early 1990s and has been reported for the manufacture of molded articles of ceramics such as alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ) and silicon nitride (Si ₃ N ₄ ).

However, in the production of silicon carbide / carbon (SiC / C) molded bodies in which coarse silicon carbide powder and fine carbon powder are mixed by gel casting method, the size of carbon powder is generally smaller than that of silicon carbide, so that silicon carbide and carbon powder In addition to the difficulty of uniformly dispersing, due to the problem that fine carbon particles are adsorbed to the organic binder to form agglomerates, there have been no examples of success in producing SiC / C molded bodies by gel casting.

The present invention has been made to solve the above problems, an object thereof is to provide a method for producing a SiC / C molded article having a high molding density and molding strength by a gel casting method using five process additives.

The new molding method to be developed requires that silicon carbide (SiC) and carbon (C) powder be uniformly dispersed in the slurry without forming aggregates even when carbon particles are adsorbed to the additive, and form a uniform molded body after polymerization.

That is, an object of the present invention is to prepare a slurry in which silicon carbide and carbon are uniformly dispersed by mixing and dispersing five kinds of additives in SiC / C powder step by step and injecting into a mold to polymerize high molding density and It is to provide a method for producing a bio-processable SiC / C molded body having a molding strength.

Figure 1 is a silicon carbide / carbon molded article manufacturing process flow chart according to the present invention

Figure 2 is a photo of silicon carbide / carbon molded article according to the present invention

In order to realize the above object, in the present invention, SiC / C powder, a dispersant, a binder, a catalyst, and a reaction initiator are mixed and dispersed stepwise in distilled water to prepare a slurry to remove bubbles. The slurry from which bubbles were removed was injected into a mold, polymerized using a microwave oven, and then demolded and dried to prepare a SiC / C molded body having high molding density and molding strength.

1 is a process flowchart showing a process for producing a SiC / C molded body according to the present invention. The present invention will be described in detail with reference to FIG. 1 as follows. First, 50-55 vol% distilled water in 70-90 wt% silicon carbide (SiC) and 10-30 wt% carbon (C) composition SiC / C powder and 0.5-1.0 wt% dispersant naphthalenesulfonic acid formaldehyde condensate (TN) The SiC / C slurry was prepared by adding 1 hour of mixing. 12 to 18 wt% of acrylamide (AM, C ₂ H ₃ CONH ₂ ) as a main monomer and N, N'-methylene bisacrylamide (cross-linker) as a binder in the prepared slurry MBAM, (C ₂ H ₃ CONH) ₂ CH ₂ ) 0.5-0.8 wt% are added and again mixed for 24 hours. Thereafter, 1.0 to 6.0 ml / l of tetramethylethylenediamine (TEMED), which is a catalyst, was added and mixed for 30 minutes, and 0.1 to 0.8 g / l of ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) was used as a reaction initiator. After the addition and mixing for 5 minutes, the bubble is removed. The bubble-free slurry is injected into a mold and polymerized using a microwave oven, and then demolded and dried in a temperature and humidity atmosphere of various stages to prepare a SiC / C molded body showing high molding density and molding strength.

EXAMPLE

In order to prepare SiC / C molded body, 80 wt% SiC, 20 wt% C SiC / C powder, 1 wt% dispersant TN and distilled water were added to a polyethylene vessel, and SiC balls were charged together for 1 hour mixing. After the addition, 16 wt% of AM and 0.7 wt% of MBAM were added as a binder, followed by ball mixing for 24 hours. To the slurry prepared, 3.8 ml / l of tetramethylethylenediamine (N, N, N ', N'-tetramethylethylenediamine) was added to the slurry, followed by ball mixing for 30 minutes, and ammonium persulfate (NH ₄ ) ₂ S as a reaction initiator. ₂ O ₈ ) was added again 0.2 g / l and mixed again for 5 minutes, and then bubbles were removed and injected into a plastic mold. After the polymerization and demolding using a microwave oven for fast and uniform heating, SiC / C molded body was prepared by drying while lowering the relative humidity from 85% to 55% at 45 ℃.

2 is a photograph of a disk-shaped SiC / C molded body prepared. No cracking occurred on the surface. Shrinkage and molding density were calculated by measuring dimensions and weight, and molding strength was measured by three-point bending method.

As a result of calculating the change of molding density according to the solid content in the SiC / C slurry, it was shown in Table 1, and the shrinkage of the molded product was 6.3% and 7.1% in the thickness direction and the diameter direction, respectively, when the solid content was 50 vol%.

In the case of using SiC / C slurry prepared by adding 18 wt% of acrylamide binder to 48.2 vol% of solid content, the mold density and the molding strength of the completely dried molded body were 1.85 g / cm 3 and 30 MPa, respectively. It was possible.

As described above, the present invention is a method of manufacturing SiC / C molded body by using the gel casting method, and a large complex shape capable of bioprocessing with high molding strength and molding density using only five process additives without any special equipment. It is easy to manufacture a SiC / C molded body.

Reaction bonded silicon carbide, which is made of SiC by infiltrating molten silicon (Si) in a SiC / C molded body in vacuum and then silicizing carbon, has excellent chemical resistance, abrasion resistance, and thermal conductivity. It can be applied to mechanical seals, fixtures for chemical plants, and pump parts. The optimum density of SiC / C shaped bodies for reacting with molten silicon is known to be 1.85 g / cm 3.

The gel casting SiC / C molding method capable of producing a molded article having a molding density of 1.85 g / cm 3 by controlling a solid content as well as a large complex shape can be applied to the production of reaction-bonded silicon carbide whose application field is expanding.

Claims (4)

In the production of silicon carbide mixed carbon (SiC / C) molded body, SiC / C powder, dispersant, binder, catalyst and reaction initiator are mixed and dispersed step by step in distilled water to prepare slurry to remove bubbles and inject into mold Polymerizing using a stove, followed by demolding and drying to produce a SiC / C molded body. The method of claim 1, wherein 0.5 to 1.0 wt% of naphthalenesulfonic acid formaldehyde condensate (TN) is first used as a dispersant in SiC / C powders of 70 to 90 wt% silicon carbide (SiC) and 10 to 30 wt% carbon (C). ) And mixing with distilled water for 1 hour to prepare a SiC / C pre-slurry in which silicon carbide and carbon are uniformly dispersed. The method of claim 1, wherein 12 to 18 wt% of acrylamide (C ₂ H ₃ CONH ₂ ), which is a main monomer, as a binder, and N, N'- which is a cross-linker, in a SiC / C preliminary slurry. 0.5 to 0.8 wt% of methylenebisacrylamide ((C ₂ H ₃ CONH) ₂ CH ₂ ) was added and mixed for 24 hours, followed by addition of 1.0 to 6.0 ml / l of tetramethylethylenediamine (TEMED) as a catalyst. Mixing and dispersing for 5 minutes by adding 0.1 to 0.8 g / l of ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) which is a reaction initiator. The method of claim 1, wherein the demolded molded body is dried at a temperature of 40 to 50 ° C. for 2 to 3 days at a relative humidity of 90 to 80%, 1 to 2 days at 70 to 60%, and 1 to 2 days at 60 to 50%. step.