New Ways of Revealing the Microstructures of SiC Materials

Abstract

In order to understand the relationships which exist between the microstructures and mechanical properties of ceramic materials and to clarify their respective mechanisms of corrosion, a detailed picture of their microstructures is of particular importance. The examination of such structures using field emission scanning electron microscopy in combination with EDX analysis as well as the FIB technique are demonstrated on polished and electrochemically corroded LPS (liquid phase sintered SiC) and SSiC materials. The possibilities for revealing the diffusion zones in semi-conducting SiC grains are presented. These methods also help to explain the core-shell structures caused by electrochemical corrosion.

Electrochemical corrosion of silicon-infiltrated silicon carbide ceramics in aqueous solutions

“…The contrast visible in the in-lens images indicates that the conductivity of the rim was typically higher than that of the core. The interpretation of the in-lens images of different SiC materials is given in detail in [14]. A few small SiC inclusions were also observed in the remaining silicon.…”

“…For SiO 2 layers with relatively low electron densities the lowest thickness that could be detected is approximately 2-3 nm. Details are described elsewhere [14].…”

“…The thickness of the formed corrosion layers was determined using the Oxford Instruments thin film measurement tool [14,16] allowing layers between 1 nm and 1 mm in thickness to be measured. For SiO 2 layers with relatively low electron densities the lowest thickness that could be detected is approximately 2-3 nm.…”

“…Dissolution of the grains was found in alkaline solutions due to the formation of soluble silicates [12][13][14][15]. In contrast, formation of a SiO 2 layer was observed in acids.…”

“…However, the corrosion rates of ceramics are generally very low compared with those of metals. Over the last few years the electrochemical corrosion behaviour of solid phase-sintered SiC ceramics and liquid phasesintered SiC ceramics (LPS-SiC) has been investigated [8][9][10][11][12][13][14]. The investigations of the SSiC materials showed an inverse relationship between the corrosion rate and the resistivity of the material.…”