CO2 laser-induced structure changes on a zircon refractory

A zircon (ZrSiO4) refractory was treated by CO2 laser surface melting in order to improve its surface density and to modify the corresponding microstructure in present study. The laser-induced microstructure and phase structure changes have been investigated by scanning transmission microscopy incorporating energy dispersive X-ray (EDX) technique and X-ray diffraction analysis. Laser surface melting treatment was readily achieved over a wide range of scanning velocities from 4 to 16 mm s 1 although the melting temperature of the zircon is very high, and the molten depth was almost linearly decreased with increasing scanning velocity. Cracks and pores could be eliminated at the lowest scanning velocity of 4 mm s 1 whereas some pores in the laser-molten zone and cracks only in the overlapped zone were produced at the higher scanning velocities of 8, 12 and 16 mm s 1. The microstructure of the laser-molten zone was characterized by a dendrite structure with interdendritic segregation to some extent. Laser-melting treatment led to the decomposition of ZrSiO4 into ZrO2 and SiO2 and thus the selected evaporation of SiO2 during heating process. The consequent rapid solidification resulted in the formation of the phase m-ZrO2 instead of the phase ZrSiO4 under equilibrium conditions. # 2003 Elsevier B.V. All rights reserved.