Densification and Crystallization Kinetics of Cordierite Glass-Ceramic Coatings on Rigid Substrates

We report our findings on the sintering kinetics of slip-cast glass-ceramic coatings on rigid substrates at temperatures between 900°C and 1000°C; the glass-ceramic crystallizes into cordierite at sintering temperatures above 900°C. Changes in coating thickness during sintering were monitored in situ using an optical setup, and the crystallization of the coatings was determined by x-ray diffraction. The coatings went through a rapid shrinkage due to initial densification, followed by an expansion stage caused by the transformation of the glass into a crystalline phase with a lower density. The rate and extent of the expansion were more noticeable at sintering temperatures above 900°C. We also found that wetting between the glass-ceramic and the substrate was important to the sintering kinetics and sintered microstructure of the coatings. For coatings formed on silicon substrate, growth of large pores was observed at the glass-ceramic/silicon interface. Using wafer-curvature measurement technique, we found a significant tensile stress build-up in the coatings during the initial stage of sintering. We believe that the combination of poor wetting and the tensile stress build-up led to the observed desintering phenomenon at the glass-ceramic/silicon interface.