PREPARATION OF HIGH THERMAL EXPANSION COEFFICIENT PORCELAINS FUSED TO METALS

Usually the thermal expansion coefficients (TEC) of metals are higher than that of porcelains. In order to match the TECs in the case of coating porcelains on metals, high TEC porcelains are needed. In this research, the high TEC phase leucite(KAlSi2 O6) in the high TEC porcelain was prepared by sol-gel method. The crystal size of leucite made by sol-gel is about 77nm through controlling the process parameters. The process from xerogel to leucite was investigated by means of DSC (differential scanning calorimetry), TG (thermogravimetry), XRD ( X-ray diffraction) and IR(infrared absorption spectrum). Leucite had been detected after the gel was treated at 900°C, this formation temperature is about 250°C lower than that of melting method.The porcelain made from 50% of the leucite powder and 50%o of low fused temperature frit has an average TEC of 19.2× 10-6/° C from room temperature to 450°C, which is much higher than the common porcelains.