Formation of composite SiC-C coatings on graphite via annealing Si-melt in CO

Abstract

A method for the synthesis of silicon carbide–graphite composite coatings is proposed and described. The method is based on the two simultaneous chemical reactions involving graphite. One of these reactions consists of the chemical interaction of a silicon molten mass with carbon monoxide on the surface of the graphite at a temperature slightly exceeding the melting point of silicon. It transforms Si into gaseous silicon monoxide (SiO) and SiC. Simultaneously, a second reaction involves the SiO in the transformation of the graphite itself into SiC. A coating with a thickness exceeding 1 mm is formed during the synthesis. The resulting coating has high mechanical strength and hardness. Samples of the composite coating were investigated via scanning electron microscopy, energy-dispersive spectroscopy , Raman spectroscopy , XRD, and nanoindentation . The coating has a complicated structure. It consists of a dense overlayer of SiC and has a branched structure consisting of dendrite-like SiC crystals extending into the depth of the graphite. The dendrites are interspersed with large (up to 20 μm) single-crystalline SiC grains consisting of predominantly cubic polytypes. The coating leads to significant hardening of the material: the composite has a hardness of 28 GPa, which is ~254 times higher than the hardness of the original graphite surface. • A method is proposed for the formation of protective SiC coatings on graphite. • The method consists of annealing of graphite with Si melt in presence of CO. • Thick, up to 1 mm coatings are being formed in 20 min at low T (1450C).