Use of Sucrose in the Charge for Reaction Sintering of SiC-Based Ceramics

Abstract

Sucrose (sugar) is proposed as a replacement for conventional phenol formaldehyde resins in charges for the production of reaction-sintered silicon carbide. The main disadvantage of phenol formaldehyde resins is their high toxicity. In addition, the storage life of such resins is limited and requires refrigerated conditions. The shelf life of charges prepared with phenol formaldehyde resins is only several days. The shelf life of charges containing sucrose extends up to two months (at an ambient temperature of 25–30°C). Thus, the use of sugar syrup as a plasticizer significantly improves the environmental conditions of production, reduces harmful releases into the environment, extends the shelf life of the charges, and lowers production costs. The starting charge (dry) contained approximately 19 wt.% primary carbon (carbon black) and 81 wt.% silicon carbide. A plasticizer (60% sugar syrup) was introduced in the charge in an amount of 15 wt.%, which added approximately 2 wt.% secondary carbon to the final composition of the compacts. As a result, the compacts contained 79 wt.% silicon carbide and 21 wt.% carbon. The optimal compaction pressure was 8 MPa. The coke (secondary carbon) that formed after pyrolysis of sucrose exhibited 25% greater porosity than the coke produced by pyrolysis of phenol formaldehyde resins. This facilitated the transport of silicon vapors inside the compacts during reaction sintering, allowing the production of sintered articles with a specific density of 3.08–3.10 g/cm³. The hardness of the plates produced in this way increased from 23 to 25 GPa. X-ray examination and chemical analysis of the samples were performed, and their microstructure and mechanical properties were studied. These results were used to establish the optimal mean particle size for the starting silicon carbide powder and the required sucrose addition for producing dense ceramic composites with high mechanical properties.