Effect of Na2O addition on crystallization behavior and properties of 25 wt%Al2O3–SiO2–CaO non-metallic inclusion-type oxides

Abstract

The 25 wt%Al2O3–SiO2–CaO inclusion with high basicity has the characteristics of high melting point and strong crystallization tendency. The effect of Na2O addition on the crystallization behavior and properties of 25 wt%Al2O3–SiO2–CaO non-metallic inclusion-type oxides was systematically investigated in the current study. The time-temperature-transformation (TTT) diagrams and continuous-cooling-transformation (CCT) diagrams were constructed introducing the single hot thermocouple technology (SHTT). The crystallization temperature decreased from 1640.15 K to 1514.15 K with the Na2O content increased from 0 to 6.92 wt%, then rose to 1564.15 K when the content of Na2O was equal to 11.81 wt%. Above 1473.15 K, the incubation time was first prolonged and then shortened with the increase of Na2O content. The crystallization tendency was first inhibited and then promoted with increasing the Na2O addition. The XRD result showed that the precipitated crystals of the oxide system transformed from Ca2Al(AlSiO7) to NaCaAlSi2O7 when the content of Na2O exceeded 6.92 wt%. The FESEM micrograph showed that the morphology of crystals from all samples demonstrated spherical or rod-like. The calculated melting point decreased from 1840.81 to 1680.29 K then rose to 1755.56 K with the increase of Na2O content. The crystallization tendency or ability of the oxide system could be predicted by the initial crystallization potential, the viscosity at the melting point, the rate of change of viscosity with temperature as well as the activation energy of crystallization.