Laser treatment of plasma-sprayed ZrSiO4 coatings

Self-supported zircon (ZrSiO4) coatings have been deposited by means of atmospheric pressure plasma spraying, a high rate deposition method. Zircon is one of the technologically important oxide ceramic material known for its refractoriness, its low thermal expansion and low thermal conductivity. However, it is well known that ZrSiO4 dissociates into ZrO2 and SiO2 in the high temperature plasma torch during plasma spraying, the rapid quenching preventing reverse combination of both components into ZrSiO4. Usually, high temperature annealing (about 1500 °C) is applied in order to combine SiO2 and ZrO2 into ZrSiO4. In this contribution, we investigate an attractive technological alternative to recombine SiO2 and ZrO2 into ZrSiO4 by laser treatment with a scanning continuous wave CO2 laser. We also investigate the addition of SiO2 rich glassy particles to the plasma spray powders in order to facilitate the recombination of ZrO2 and SiO2 into ZrSiO4 during laser treatment. By carefully adjusting the CO2 laser treatment parameters (laser power density, scanning speed) we show that the SiO2 and ZrO2 phases indeed recombine into ZrSiO4. It appears in this contribution that the addition of low melting point SiO2 rich particles strongly benefits the reaction of zirconia and silica into zircon.