Process for producing ceramic materials using silicon carbide

Abstract

Process for producing bodies from ceramic materials using silicon carbide, comprising the steps: configuration of fiber-reinforced porous bodies (1, 5) that consist of carbon on a base (2) that is inert relative to liquid silicon, the bodies having cavities (3) that are accessible from the exterior or surface recesses (3′), and the cavities (3) being closed at the bottom in the porous bodies or the surface recesses (3′) together with the base (2) forming a reservoir that is sealed at the bottom; heating the configuration by introduction of energy to melt the silicon (6) that is present in the reservoir; and infiltrating the melted silicon in the bodies (1, 5) and reaction of the silicon with the carbon to form silicon carbide; and use of the thus produced bodies as brake disks and as clutch driving disks.

Description

The process will be explained by the accompanying drawings, of which

FIG. 1 shows a cross-section through a cylindrical porous carbon body 1, which, in contact with a base 2, which is provided with a layer 4 that consists of boron nitride, forms a reservoir 3, in which an amount of silicon in the form of particles 6 that is sufficient for reaction or a compact body is contained, and

FIG. 2 shows a cross-section through a porous initial body 5 that consists of carbon for a carbon-ceramic brake disk with a molded-on pot body 5′ on a base 2 as shown in FIG. 1, and Si particles 6 are also contained in the reservoir 3 that is formed from the pot body.

In the illustrated embodiments, silicon is received over the entire interior jacket surface of the cylinder ring (FIG. 1) or over the interior surface of the basin-shaped reservoir that is shown in FIG. 2.

Heating of the configuration shown in FIG. 1 is preferably effected by introduction of energy into the base 2 or especially preferably into the porous carbon body 1 itself; this may be accomplished by, for example, induction of turbulence or by radiation.

In the process, in the bed of the particles 6, the silicon melts into the reservoir 3 that is formed from the cavity in contact with the base 2 and penetrates into the porous carbon body 1 through the inside jacket surface of the cylinder ring. The carbon in the body 1 reacts with the penetrated silicon with the formation of silicon carbide. The coating of the base 2 with a layer 4 that consists of boron nitride in this case brings about that after the cooling of the body that is glazed through reaction to form silicon carbide, it can be dissolved easily from the base 2.

In the same way, the configuration that is shown in FIG. 2 is heated, and here, a more porous body that consists of carbon 5 is used, which in the center has a molded-on pot in the form of a jacket surface 7 and the cover surface 8 of a truncated cone. In the center of the cover surface 8, there is a recess 9 with a circular cross-section that forms a hollow cylinder. The silicon that is present in the reservoir 3 that is formed in the form of a recess that is open at the top may penetrate the body 5 in this embodiment after melting over a surface that is larger in comparison to FIG. 1. The part 1′ of the body, corresponding to the friction in the brake disk area exposed during braking, may not come into contact here with the boron nitride of layer 4; avoiding contamination with boron nitride is desired for the friction layer of a brake disk.

The effect is illustrated through the following examples:

EXAMPLE 1

Molded Bodies with Threefold Fiber Protection

A prepreg (impregnated fabric) was produced from a fabric of carbon multifilaments (3 K rovings, i.e., 3000 individual carbon filaments with a surface area-related mass of about 240 g/m²) by impregnation by an aqeous resol. Excess phenol resin was removed by pressing. The fabric was cut into laminar structures of about 500 mm in diameter, and the latter were stiffened with intermediate layers of siliconized paper at about 140° C. in a press under a pressure of about 5 MPa for three hours.

The pressed and stiffened stacks of impregnated fabrics were then carbonized in a furnace under nitrogen as a cover gas at a temperature of up to 900° C. In the process it was heated at a rate of about 4 K/h from 300° C. up to 600° C. to achieve uniform carbonization. After cooling, also under cover gas, the carbonized fabric plates were impregnated again with a phenol resin (Novolak, Bakelite IT 491®), dried and in turn carbonized under cover gas for about 8 hours at 950° C. After cooling to room temperature, it was impregnated again, this time with tar pitch with a softening temperature of about 60° C. according to DIN [German Industrial Standard] 52025. The impregnated fabric plates were carbonized again at about 950° C. for about eight hours. Then, the plates were heated under cover gas to 2200° C., left at this temperature for twenty minutes, and ground in a fly cutter mill with a 5 mm sieve insert after cooling.

The ground material (2,750 g) was then mixed with a mixture that consists of 1,500 g of a phenol resin (resol, Norsophen 1203®, Bakelite Company) and 450 g of a ground (maximum particle size 20 μm) of coal-tar pitch with a softening temperature of 230° C. according to DIN 52025 at room temperature (23° C.) in a Z-arm kneader. The homogenized mixture was completely hardened in a mold in a heatable press at 1.5 MPa (15 bar) and a temperature of 150° C. for two hours. The hardened molded body was removed and carbonized as above at 900° C.

EXAMPLE 2

Molded Bodies with Simple Fiber Protection

A prepreg (impregnated fabric) was produced from a fabric of carbon multifilaments (3 K rovings, i.e., 3000 individual carbon filaments with a surface-area-related mass of about 240 g/m²) produced by impregnation with an aqueous resol. Excess phenol resin was removed by pressing. The fabric was cut into laminar structures of about 500 mm in diameter, and the latter were hardened with intermediate layers of siliconized paper at about 140° C. in a press under a pressure of about 5 MPa for three hours. The hardened material was ground in a fly cutter mill with a 5 mm sieve insert.

The ground material (2,750 g) was then mixed with a mixture of 1,500 g of a phenol resin (resol, Norsophen 1203®, Bakelite Company) and 450 g of a ground (maximum particle size of 20 μm) coal-tar pitch with a softening temperature of 230° C. according to DIN 52025 at room temperature (23° C.) in a Z-arm kneader. The homogenized mixture was completely hardened in a mold in a heatable press at 1.5 MPa (15 bar) and a temperature of 150° C. for two hours. The hardened molded body was removed and carbonized as above at 900° C.

EXAMPLE 3

Siliconization of the Molded Bodies

In each case, 3 molded bodies in the form of cylindrical disks at a height of 36 mm, an inside diameter of 155 mm and an outside diameter of 380 mm, which had been produced according to Examples 1 and 2,

• • a) were applied according to the conventional way (siliconization by attaching the molded body to the wicks that consist of porous carbon material, which are in contact with a bath that consists of liquid silicon, heating rate of 10 K/minute, holding time of 30 minutes, temperature about 1600° C., vacuum), and
  • b) according to the invention, by the cylindrical ring disks being placed on quadratic graphite plates with an edge length of 450 mm and a boron nitride coating with a thickness of about 0.1 mm, the empty space in the center of the cylindrical ring was filled with silicon granulate (diameter range about 0.5 mm to 4 mm), and this configuration was heated in an evacuated induction furnace to 1600° C. during a period of about 4.2 minutes; the temperature was held for another two minutes.

The differently treated molded bodies were cooled; they were completely siliconized according to the selected time, i.e., the remaining percentage by mass of matrix-carbon in the sample was less than 7%.

In these molded bodies, the proportion of carbon fibers that were not attacked in the infiltration with silicon was then determined. In this case, the following was produced as a mean value via the molded bodies examined:

		b) According to the
	a) Wicking process	invention
Molded bodies according to	95.1%	96.4%
Example 1
Molded bodies according to	52.0%	95.3%
Example 2

LIST OF REFERENCE NUMERALS

• 1 Cylindrical porous carbon bodies
• 1′ Cylindrical part of the porous carbon bodies 5
• 2 Base
• 3 Cavity as reservoir
• 3′ Recess open at the top as a reservoir
• 4 Boron nitride layer
• 5 Porous body that consists of carbon
• 6 Silicon
• 7 Jacket surface
• 8 Cover surface
• 9 Recess with circular cross-section

Claims

1. Process for producing bodies comprising ceramic materials using silicon carbide, the process comprising the steps of: configuring fiber-reinforced porous bodies, the bodies comprising:carbon on a base, which base is inert relative to liquid silicon, andcavities, which cavities are accessible from exterior or surface recesses of the bodies, wherein the cavities are closed at a bottom in the porous bodies the surface recesses together with the base forming a reservoir that is sealed at the bottom,heating the bodies by introduction of energy to melt silicon that is present in the reservoir, andinfiltrating the melted silicon in the bodies and reacting of the silicon with the carbon to form silicon carbide.

2. The process according to claim 1, wherein the bodies are heated through inductive heating.

3. The process according to claim 1, wherein the configuration is heated by radiant heating.

4. The process according to claim 1, wherein the base comprises at least one selected from the group consisting of graphite and a graphite sheet.

5. The process according to claim 1, further comprising applying a layer boron nitride on the base.

6. The process according to claim 1, wherein the porous body comprising carbon has a form of a sheath layer of a truncated cone with a cylindrical disk that is mounted on the exterior of the base and a cover disk with a central recess in the form of a hollow cylinder.

7-9. (canceled)

10. A body produced in accordance with claim 1, wherein the body is a friction disk.

11. A body produced in accordance with claim 1, wherein the body is a brake disk.

12. A body produced in accordance with claim 1, wherein the body is a clutch driving disk.

13. A ceramic material produced by a process comprising: configuring fiber-reinforced porous bodies, the bodies comprising: carbon on a base, which base is inert relative to liquid silicon, andcavities, which cavities are accessible from exterior or surface recesses of the bodies, wherein the cavities are closed at a bottom in the porous bodies or the surface recesses together with the base forming a reservoir that is sealed at the bottom,heating the bodies by introduction of energy to melt silicon that is present in the reservoir, andinfiltrating the melted silicon in the bodies and reacting of the silicon with the carbon to form silicon carbide.