Two-step reduction process and spark plasma sintering for the synthesis of ultra fine SiC and ZrB2 powder mixtures

Abstract

A novel two-step reduction process is proposed for the synthesis of homogeneously intermixed nano-SiC/ZrB2 powder using ZrSiO4, B4C and C. During the conventional carbo-borothermal reduction process, B4C reacted with ZrSiO4 to form borosilicate glass or B2O3. The reactions for the formation of B2O3 had lower Gibbs free energy than those to synthesize ZrB2 and SiC. The borosilicate glass also promoted the strong grain growth of ZrB2 and inhibited the formation of SiC. In order to solve the problem, the synthesis process was divided into the carbothermal reduction of ZrSiO4, and subsequent conversion of the resultant ZrC into ZrB2. By the two-step reduction process, the formation of SiC was achieved and the grain growth of ZrB2 could be effectively suppressed. Spark plasma sintering process also helped to minimize the grain growth of the synthesized powder by the fast heating/cooling rate of 100°C/min. The synthesized ZrB2–SiC powders were 10–40nm in size and were homogeneously inter-mixed.