Low Pressure Injection Molding Reaction Sintered Silicon Carbide Process

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Because of its high temperature resistance, wear resistance, high strength, corrosion resistance and other properties, SiC ceramics are widely used in aerospace, petroleum industry, chemical industry and military protection and other fields. Reaction sintering is a preparation method for the preparation of high-performance SiC ceramic materials at near-scale, and has been widely used in SiC kiln furniture, desulfurization nozzles, corrosion-resistant pump impellers and bulletproof plates.

However, reaction sintered SiC ceramics are mainly formed by plaster casting or dry pressing. On the one hand, a large number of discarded gypsum molds produced by gypsum grouting can easily cause environmental pollution; on the other hand, the gypsum grouting process is complex, difficult to automate, and product quality is poor. Although dry pressing is low in cost and easy to automate, it is not easy to form products with complex shapes.

In recent years, in order to achieve low-cost and automated molding of high-tech ceramics with complex shapes, injection molding of high-tech ceramics has become more and more popular, especially in the field of ceramic preparation such as alumina and zirconia. Forming technologies such as dewaxing and degreasing have been greatly developed.

SIMUWU is committed to providing related equipment and technology for the silicon carbide sintering industry. In the following, we will provide a process method for low pressure injection molding reaction sintering silicon carbide.

Process flow:

α-SiC powder is used as the main raw material, the SiC content is more than 98%, and the particle size is F1200 and F150; the carbon black of N330 is used; the dispersants selected are oleic acid (OA), stearic acid (SA), silane Coupling agent (KH550), polyvinylpyrrolidone (PVP) and hexadecylamine; using paraffin wax (PW) as a binder.

The SiC powder of two specifications, F1200 and F150, is particle-graded according to the mass ratio of 3:7, and the homogeneously mixed SiC powder is added to the paraffin at 80 ° C, and a certain amount of dispersant is added. Stir at a stirring rate of 300 r/min for 30 min. After that, the low pressure injection reaction sintered SiC green body samples were prepared by using a hot press injection machine.

The size of the low-pressure injection blank is 3mm×4mm×30mm. The low-pressure injection process is: the temperature is 80°C, and the injection pressure is 0.8MPa. The formed green body is subjected to low-temperature dewaxing in a tube furnace. The low-temperature dewaxing process is as follows: first, the temperature is raised to 100 °C for 2 hours, and then kept for 1 hour; secondly, the temperature is heated to 200 °C for 2 hours and kept for 1 hour; then from 200 °C at the same heating rate Continue to rise to 300°C and keep for 2h; finally, cool to room temperature naturally. The degummed sample was put into a graphite crucible, and the silicon powder was weighed according to the mass ratio of the green body to silicon of 1:1, and the silicon powder was evenly distributed around the green body.

The process of reaction sintering is as follows: first, the temperature is raised to 1000°C for 1 hour at room temperature; after that, the temperature is raised to 1200°C for 3 hours and then kept for 1h; then, the temperature is raised to 1450°C for 1 hour and then kept for 0.5h, and finally the furnace is heated to 1450°C for 0.5h Cool, keep the vacuum degree in the furnace less than 10Pa during the whole sintering process.

After reaction sintering, the residual Si on the surface is removed by grinding and polishing.

Process points:

The order of the effect of dispersant on the viscosity of reactive sintered SiC slurry is PVP < silane < OA < SA < hexadecylamine. When 1 wt.% hexadecylamine was added to a slurry with a solids content of 70 wt.%, the viscosity of the slurry was a minimum of 300 mPa s.
When the carbon content is 7 wt.%, the performance of the reaction sintered SiC ceramic material is the best, and its bulk density, open porosity, flexural strength, Vickers hardness and fracture toughness reach 2.89 g/cm3, 0.06 %, 259 MPa, 2950 and 4.35 MPa m1/2.
If the carbon content is too low, the residual Si of the brittle phase in the silicon carbide ceramic material will increase, and the density and strength will decrease; if the carbon content is too high, the uniformity of the slurry will be deteriorated, and hole defects will be easily formed in the silicon carbide ceramic material.

Vacuum furnace equipment selection:

The following are SIMUWU RVS-S series silicon carbide sintering furnace products. The sintering furnace can be reliably used for pressureless silicon carbide sintering and silicon carbide reaction sintering, as well as various related processes.