Influence of oxidation on the wetting behavior of liquid silicon on Si3N4-coated substrates

Silicon nitride coating on a silica substrate has been fired in atmospheres of air, argon and nitrogen, at temperatures of 900 and 1100 °C, with holding times of 30 min, two and four hours. The oxygen concentration after oxidation, measured by LECO analyses, increased with increase in oxidation temperature, time and partial pressure of oxygen. The increase in mass of the coating together with the increase in oxygen concentration corresponded to the formation of a Si2N2O layer.Sessile drop wetting experiments with holding temperatures of approximately 50, 100 and 150 °C above the melting point of silicon has been performed. It was found that a high oxygen content in the coating led to enhanced non-wettability properties. Wetting angles around 100° were achieved with oxygen concentrations higher than 14 wt%. In contrast, oxygen levels around 2 wt% resulted in angles around 60°. During the experiments, deoxidation and infiltration of the coating occurred. At high temperatures the reaction rate increased significantly leading to penetration of the coating.