Study of interactions between silicon and coated graphite for application to photovoltaic silicon processing

The crystallization of silicon for photovoltaic applications is currently performed by directional solidification in amorphous silica crucibles. In order to avoid sticking, silica crucibles are coated with a layer of silicon nitride which acts as an interface releasing agent between the silicon and the crucible. Due to silica softening and subsequent transformations during the melting-solidification cycle, Si₃N₄-coated silica crucibles can be used only one time. A more interesting solution would be to have a graphite crucible which could be used several times in view of its high mechanical performances at elevated temperatures. The goal of this study is to determine in which way the Si₃N₄ coating can also be used for graphite crucibles. The study is conducted by means of the sessile drop technique and microstructure characterizations carried out by optical microscopy. For comparison purposes, experiments are also performed for the standard configuration of Si₃N₄-coated silica.