KR20020051045A - Liquid phase sintered silicon carbide by slip casting and a method for manufacturing the same - Google Patents

Abstract

PURPOSE: Provided is a liquid sintered silicon carbide with high density and good mechanical properties ranging from room to high temperature by slip casting silicon carbide doped with alumina and yttria as sintering aids. CONSTITUTION: The preparation method of liquid sintered silicon carbide is as follows: preparing a slip by mixing 55-65wt.% of silicon carbide doped with alumina and yttria as sintering aids with 35-45wt.% of water; adding 0.3-0.7wt.%(based on 100pts.wt. of the slip of dispersant such as polyammonium methacrylate); adjusting pH of the slip to be 8.3-9.5; slip casting and drying; sintering at 1800-1850deg.C in inert atmosphere.

Description

Liquid-sintered silicon carbide sintered body by injection molding and its manufacturing method {LIQUID PHASE SINTERED SILICON CARBIDE BY SLIP CASTING AND A METHOD FOR MANUFACTURING THE SAME}

The present invention relates to a method for producing a liquid phase sintered silicon carbide sintered body by injection molding. More specifically, as a sintering aid to improve the dispersibility of the silicon carbide mixed powder to which alumina (Al ₂ O ₃ ) and yttria (Y ₂ O ₃ ) are added to prepare a slip, and then injection molding into the prepared slip By manufacturing a molded article by the sintering method, the liquid sintered silicon carbide sintered body can be used for flame guides and nozzle parts of various burners, having high relative density and excellent mechanical properties after sintering, and maintaining strength characteristics from room temperature to high temperature. It is about.

Conventional pressure sintered silicon carbide prepared by adding carbon and boron compounds as a sintering aid is one of the most commonly used structural ceramics due to its strength, Young's modulus, excellent corrosion and erosion resistance. However, it must be sintered at a high temperature of 2100 ° C. or higher, and has a disadvantage in that low toughness and strength cannot be maintained at high temperatures of 1200 ° C. or higher.

On the other hand, recently, reports have been made on liquid sintered silicon carbide capable of producing a compact sintered body at a temperature of 2000 ° C. or lower and excellent in strength and toughness.

Liquid sintered silicon carbide was first reported by M. Omori et al. (“Composite Silicon Carbide Sintered Shapes and Its Manufacture,” U. S. patent 4502983, Mar. 5, 1985) by adding various rare earth compounds to silicon carbide as a sintering aid.

Subsequently, alumina was added to silicon carbide as a sintering aid ("Pressureless Sintering of Silicon Carbide with Addition of Aluminum Oxide," Reports Res. Lab. Asahi Glass Co., Ltd., 36 (1), (1986) 25 -36) showed that the bending strength measured at room temperature and 1400 ° C of the silicon carbide sintered body sintered at 2000 ° C. for 5 hours was 700 MPa and 470 MPa, respectively, and the toughness was 6 MPa · m ^{1/2, which} is twice that of boron and carbon Reported a degree value.

Density of Silicon Carbide Sintered Sintered at 2150 ° C with Alumina-Yttria ("Preparation of Pressureless-Sintered SiC-Al ₂ O ₃ -Y ₂ O ₃ ," J. Mat. Sci., 23 (1988) 3744- 49) showed 3.11 g / cm ³ and 470 MPa strength.

According to Japanese patent ("silicon carbide ceramics and its manufacturing method," Japanese Patent Application Laid-open No. Hei 9-67165, 1987, 3), one of Al-Si-O, Zr-Si-O and Ln-Si-O compounds in silicon carbide and It was reported that any one of carbon fiber, silicon carbide fiber, silicon carbide whisker, silicon carbide short fiber, silicon nitride whisker and silicon nitride short fiber was added to prepare a sintered body having a room temperature strength of 1000 MPa and fracture toughness of 15 MPa · m ^1/2 or more. The high strength and toughness of such sintered compacts is due to the addition of fibers or whiskers.

In addition, there have been a number of reports in which silicon carbide sintered bodies have been produced by adding MgAl ₂ O ₄ or yttria (“Method for manufacturing silicon carbide sintered bodies,” Japanese Patent Laid-Open No. Hei 9-227233, 1997, 9).

As described above, there are many documents and patents related to the production of sintered compacts and measurement of physical properties mainly by sintering aids and general forming methods in the production of liquid phase sintered silicon carbide, but liquid phases having high density, excellent physical properties and strength from room temperature to high temperature There is no report on the manufacturing method of the sintered silicon carbide sintered body.

Therefore, there is a need for a method for producing a liquid phase sintered silicon carbide sintered body having high density, excellent physical properties and strength from room temperature to high temperature.

The present invention has been made to solve the above problems, the present inventors added the water and dispersant as a dispersion medium to the silicon carbide mixed powder to which the sintering aid is added to prepare a slip by adjusting the pH and then molded by injection molding into the slip It has been found that the above object can be achieved by preparing and sintering, thus completing the present invention.

Accordingly, an object of the present invention is to provide a method for producing a liquid phase sintered silicon carbide sintered body having high density, excellent physical properties and strength from room temperature to high temperature by injection molding.

In order to achieve the above object, the present invention

a) as a sintering aid to prepare a slip by adding 35 to 45% by weight of water as a dispersion medium to a silicon carbide mixed powder containing alumina and yttria to 55 to 65% by weight, and to 100 parts by weight of the powder and water slip. Adding 0.3 to 0.7 parts by weight of a dispersant and adjusting the pH of the slip to 8.3 to 9.5;

b) manufacturing a molded body by injection molding with the slip; And

c) sintering the molded body at a temperature of 1800 to 1850 ° C;

It provides a method for producing a liquid phase sintered silicon carbide sintered body having high density and excellent physical properties, including the strength from room temperature to high temperature.

Hereinafter, the present invention will be described in more detail.

In the step a), first, 55 to 65% by weight of silicon carbide powder to which alumina and yttria are added as a sintering aid is mixed with 35 to 45% by weight of water as a dispersion medium.

If the amount of water added to the dispersion medium exceeds 45% by weight, the dispersibility of the slip is excellent, but the molded product formed by pouring the slip into the gypsum mold contains a lot of water, which makes handling of the product difficult and the molded product easily deforms during drying. have. When the amount of water to the powder is less than 35% by weight, the powder hardly mixes with the water, and the viscosity of the slip obtained by adding the dispersant and adjusting the pH of the slip is very high, which is not suitable for injection molding.

Next, a dispersant is added to the slip of the powder and water. A polyammonium methacrylate type is used as the dispersant, and it is preferable to add 0.3 to 0.7 parts by weight of the dispersant based on 100 parts by weight of the slip of the silicon carbide powder and water.

If the dispersant of less than 0.3 parts by weight is added to the slip made of silicon carbide powder and water, the viscosity of the slip is high, which is not suitable for injection molding.If the dispersant of more than 0.7 parts by weight is added, the particles which are well dispersed in water cause slippage. There is a tendency to increase the viscosity of, so the addition of more dispersants is not suitable.

Next, the pH of the slip is adjusted to 8.3 to 9.5.

If the pH of the slip is less than 8.3, the zeta potential of the particles does not show a complete dispersion, resulting in insufficient slip stability over time. If the pH is above 9.5, the gypsum surface is damaged and it is difficult to be demolded. not.

In step b), the molded body is manufactured by injection molding with the slip prepared in step a), and then, in step c), the molded body is dried and sintered under an inert atmosphere at 1800 to 1850 ° C. To prepare a silicon carbide sintered body.

In addition, the present invention provides a liquid phase sintered silicon carbide sintered body manufactured according to the above-described manufacturing method.

The liquid phase sintered silicon carbide sintered body of the present invention has a high density and excellent physical properties, and has the property that the strength is maintained from room temperature to high temperature.

Hereinafter, the present invention will be described in more detail based on the following Examples and Comparative Examples. However, these examples are only for illustrating the present invention, but the present invention is not limited thereto.

[Examples 1 to 4 and Comparative Examples 1 to 2]

Two kinds of 93% by weight of silicon carbide powder added with 5.6% by weight of alumina and 1.4% by weight of yttria (hereinafter referred to as A9Y1) and 4.55% by weight of alumina and 1.4% by weight of yttria (hereinafter referred to as A8Y2) as sintering aids In the composition, 0.2 wt% of polyvinyl alcohol (PVB) and ethanol were added as a dispersing medium as a molding aid (binder) and ball milled for 24 hours to prepare slip.

The powder thus obtained was dried and pulverized, and the pulverized powder was sieved through a 50 mesh sieve to prepare granules. The granulated powder was first press-molded in a steel mold having a width of 30 and a length of 50 mm, followed by a pressure of 2 tons. The specimens of Comparative Examples 1 and 2 were prepared by cold isostatic pressing with powder molding.

In addition, in the same A9Y1 and A8Y2 composition used for powder molding, in the 55, 60 and 65% by weight of the mixed powder, 30 to 45% by weight of water as a dispersion medium, 0.5 and 0.7 parts by weight of polyammonium methacrylate as a dispersant and a binder Slip was prepared by adding 0.01 and 0.05 parts by weight of polyvinyl alcohol and ball milling for 24 hours. The slip obtained was obtained by adjusting the spindle number of the pH and Brookfield viscometer. The viscosity was measured at 100 rpm using 2. Thus prepared slips were poured into gypsum molds having a width of 45, a length of 60, and a height of 40 mm to prepare molded articles of Examples 1 to 4 by injection molding.

The specimens of Examples and Comparative Examples prepared by the powder molding and injection molding were sintered at 1800 and 1850 ° C. for 1 hour in an argon gas atmosphere at atmospheric pressure in a furnace in which the heating element was graphite.

The density of the sintered specimens was measured using the Archimedes principle, and the obtained sintered body was finally polished with a diamond grindstone of # 1000, processed into specimens having a width of 4, a thickness of 3, and a length of 40 mm, inner span 10, and outer span. (outer span) 4 point bending strength was measured at room temperature under the condition of 30mm and crosshead speed 0.5mm / min.

The characteristics of the slips produced by powder molding and injection molding and the physical properties of the silicon carbide sintered compact are shown in Table 1.

Composition / molding method Weight of powder (% by weight) Dispersant / Binder (wt%) PH / viscosity of slip (cP) Sintering Temperature / Retention Time Density (g / cm ³ ) Strength (MPa) Comparative Example 1 A9Y1 / powder molding - -/ 0.2 -/- 1800 ℃ / 1 hour 3.170 386.0 Comparative Example 2 A8Y2 / powder molding - -/ 0.2 -/- 1800 ℃ / 1 hour 3.200 506.7 Example 1 A9Y1 / Injection Molding 55 0.7 / 0.05 9.10 / 19.4 1800 ℃ / 1 hour 3.180 541.2 Example 2 A8Y2 / Injection Molding 55 0.7 / 0.05 9.35 / 20.2 1800 ℃ / 1 hour 3.225 559.8 Example 3 A8Y2 / Injection Molding 60 0.5 / 0.01 8.80 / 66.3 1800 ℃ / 1 hour 3.203 656.7 Example 4 A8Y2 / Injection Molding 65 0.5 / 0.01 8.88 / 134.7 1850 ℃ / 1 hour 3.210 577.6

As shown in Table 1, the silicon carbide sintered body by injection molding showed higher density and bending strength values than the specimens prepared by powder molding regardless of 55 to 65% by weight of the powder.

As described above, it was confirmed that the molded article produced by the uniformly dispersed slip by the addition of the dispersant and the pH adjustment had a great influence on the densification and physical properties of silicon carbide.

[Examples 5 to 8 and Comparative Examples 3 to 4]

By powder molding of Comparative Example 1, the A9Y1 composition was sintered at 1750 ° C. and the A8Y2 composition was 1800 ° C. for 1 hour to prepare specimens of Comparative Examples 3 to 4. In addition, 30 to 45% by weight of water, 0.3, 0.5 and 0.7% by weight of dispersant, and 0.01 and 0.05% by weight of binder were added to 55, 60 and 65% by weight of the mixed powder of A9Y1 and A8Y2 composition, and the ball was slipped for 24 hours. Was prepared. The molded product of Examples 5 to 8 was prepared by injection molding in the same manner as in Example 1.

In the same manner as in Example 1, the specimens prepared by the powder molding and the injection molding were sintered at 1750, 1800 and 1850 ° C. in an argon gas atmosphere at atmospheric pressure in a furnace in which the heating element was graphite.

The density and strength of the sintered specimens were measured in the same manner as in Example 1, and the high temperature bending strength of the sintered compact was 4 mm wide, 3 mm thick and 40 mm long, with an outer span of 30 mm and a crosshead speed of 0.5 mm / min. Conditions were measured at temperatures of 1000 and 1200 ° C. and the results are shown in Table 2.

As shown in Table 2, the bending strength of the silicon carbide sintered body produced by injection molding showed a higher strength value than that produced by powder molding, and the bending strength values measured at 1000 and 1200 ° C were measured at room temperature. Since it has a value similar to that of the silicon carbide sintered body produced by the injection molding it can be seen that it can be used in flame guides and nozzle parts of various burners used at high temperatures of more than 1200 ℃.

Composition / molding method / powder quantity Dispersant / Binder (wt%) PH / viscosity of slip (cP) Sintering Temperature / Retention Time Density (g / cm ³ ) Room temperature strength (MPa) High Temperature (1000 ℃) Strength (MPa) High temperature (1200 ℃) Strength (MPa) Comparative Example 3 A9Y1 / powder molding /- -/ 0.2 -/- 1750 ℃ / 1 hour 3.130 403.0 405.0 341.0 Comparative Example 4 A8Y2 / powder molding /- -/ 0.2 -/- 1800 ℃ / 1 hour 3.200 506.7 419.7 382.4 Example 5 A9Y1 / injection molding / 55% by weight 0.3 /- 9.31 / 13.8 1800 ℃ / 1 hour 3.156 492.7 449.2 457.5 Example 6 A9Y1 / injection molding / 55% by weight 0.7 / 0.01 9.07 / 13.0 1800 ℃ / 1 hour 3.201 573.7 561.6 565.1 Example 7 A8Y2 / injection molding / 55% by weight 0.3 /- 9.30 / 12.2 1800 ℃ / 1 hour 3.183 508.3 550.6 490.5 Example 8 A8Y2 / injection molding / 65% by weight 0.5 / 0.01 8.88 / 134.7 1850 ℃ / 1 hour 3.210 577.6 528.7 599.6

[Examples 9 to 11 and Comparative Examples 5 to 7]

The specimens of Comparative Examples 5 to 7 were prepared by powder molding with the composition of A8Y2 of Example 1. In addition, to the 60 and 65% by weight of the A8Y2 mixed powder, 40 and 35% by weight of water, 0.5% of a dispersant, and 0.01% by weight of a binder were added and ball milled for 24 hours to prepare a slip, and the slip thus prepared was subjected to the slip example 1 The molded product was prepared by the same injection molding.

In the same manner as in Example 1, the specimens prepared by the powder molding and the injection molding were sintered at 1750, 1850, and 1900 ° C. in an argon gas atmosphere at atmospheric pressure in a furnace in which the heating element was graphite.

The density and strength of the sintered specimens were measured in the same manner as in Example 1, and the results are shown in Table 3.

Composition and amount of powder Dispersant / Binder (wt%) PH / viscosity of slip (cP) Sintering Temperature / Retention Time Density (g / cm ³ ) Room temperature strength (MPa) Comparative Example 5 A8Y2 / 60 wt% 0.5 / 0.01 8.80 / 66.3 1900 ℃ / 1 hour 3.179 518.8 Comparative Example 6 A8Y2 / 65 wt% 0.5 / 0.01 8.88 / 134.7 1750 ℃ / 1 hour 3.199 490.5 Comparative Example 7 A8Y2 / 65 wt% 0.5 / 0.01 8.80 / 66.3 1900 ℃ / 1 hour 3.196 441.0 Example 9 A8Y2 / 60 wt% 0.5 / 0.01 8.80 / 66.3 1800 ℃ / 1 hour 3.203 656.7 Example 10 A8Y2 / 60 wt% 0.5 / 0.01 8.88 / 134.7 1850 ℃ / 1 hour 3.208 636.6 Example 11 A8Y2 / 65 wt% 0.5 / 0.01 8.88 / 134.7 1850 ℃ / 1 hour 3.210 577.6

Sintering the molded product produced by injection molding at the sintering temperature below 1750 ℃ shows higher density and strength value than the specimen produced by powder molding. Concentration occurred and was not suitable. In addition, since sintering at 1900 ° C. or higher causes a decrease in density and strength, it can be seen that a molded product prepared by injection molding can be obtained by sintering at a temperature of 1800 ° C. to 1850 ° C. to obtain a sintered body having an optimal density and strength value. Can be.

As described above, according to the present invention, water is added as a dispersion medium to a predetermined weight percent silicon carbide powder in which alumina and yttria are mixed, and an appropriate amount of a dispersing agent of polyammonium methacrylate is added and the pH of the slip is adjusted. By manufacturing the slip by adjusting, and manufacturing the molded body by injection molding with the manufactured slip, and manufacturing the sintered body, it is possible to obtain a liquid-sintered silicon carbide sintered body having high density, excellent physical properties and strength maintained from room temperature to high temperature have.

Claims (3)

a) as a sintering aid to prepare a slip by mixing a mixture of alumina and yttria with silicon carbide mixed with 55 to 65% by weight of water as a dispersion medium and 35 to 45% by weight of water, and 100 parts by weight of the powder and water slip Adding 0.3 to 0.7 parts by weight of a dispersant and adjusting the pH of the slip to 8.3 to 9.5; b) manufacturing a molded body by injection molding with the slip; And c) sintering the molded body at a temperature of 1800 to 1850 ° C Method for producing a liquid phase sintered silicon carbide sintered body having high density and excellent physical properties, including the strength is maintained from room temperature to high temperature. The method of claim 1, wherein in step a), the dispersant is a polyammonium methacrylate system. Liquid sintered silicon carbide sintered body having high density and excellent physical properties prepared according to the method of claim 1 and maintaining strength from room temperature to high temperature.