Abstract
Stoichiometric cordierite (2MgO-2Al2O3-5SiO2) with additions of titania have been investigated for use as coatings on low thermal expansion refractory concretes. These concretes have coefficients of thermal expansion on the order of 2 ppm/°C. Titania additions of up to 8 mole percent were investigated and the effect of titania in the crystallization of cordierite was examined. Cordierite coatings were air plasma sprayed and both glass and crystalline coatings were produced. The crystalline structure of the coating was found to be dependent upon the preheat temperature of the substrate. Preheats greater than 700 °C produced a mixture of a quartz solid solution and indialite whereas glass coatings were produced at preheats less than 700 °C. Coefficients of thermal expansion for the cordierite materials were dependent upon titania addition and generally increased with addition of titania. In the glass state, the thermal expansion was modestly increased (4.6 to 4.9 ppm/°C) with titania additions, but the quartz and indialite forms of the cordierite increased from 1.2 to 4.7 ppm/°C as the titania addition increased from 0 to 8 mole percent.
