A new non-silicate refractory of low thermal expansion

Preliminary experiments were conducted aimed at developing refractory ceramics of low thermal expansion based on calcium dialuminate CaAl4O7. This compound was synthesized by a specific cycle of calcination, regrinding and firing (finally at 1450 degrees C), the emerging phases having been identified by X-ray diffraction. The obtained product was combined in various proportions with the highly refractory calcium zirconate CaZrO3; also, CaAl4O7 specimens were impregnated with SiC using the chemical vapour deposition (CVD) technique. Thermal expansion up to 900 degrees C and porosity data were established for a number of compositions. The obtained microstructures were shown as scanning electron microscope pictures. From among the potential applications, the continuous casting of steel is indicated, the composites containing CaZrO3 and vapour deposited SiC being regarded as promising materials for submerged nozzles. (C) 1998 Elsevier Science Limited and Techna S.r.l.