Mechanism of lustre formation in scheelite-based glazes
Résumé
This work elucidates the mechanism responsible for the lustre effect of scheelite-based glazes for single-firing wall tiles. The surface decoration is obtained with a thin film composed of a Si-Ca-Zn-Al-K-B fit and 10 wt% WO3 on zircon-engobed substrates for single-firing wall tiles (maximum temperature of 1130 degrees C for 50 min). The observed lustre effect is sub-adamantine and pearlescent. It is sub-adamantine because scheelite nanocrystals at the surface, with a relatively high refractive index (n=1.93), cause considerable reflection of light. The lustre is also wealdy pearlescent because the nano-crystals oriented with the (004) plane parallel to the surface give interference with the underlying glassy layer (n approximate to 1.5), where randomly dispersed scheelite crystals occur. This model apparently applies to the glazes decorated with ceria, although the latter exhibits iridescence due to the high refractive index of ceria (n=2.05) which yields stronger interference effect with the underlying glassy substrate. (C) 2013 Elsevier Ltd. All rights reserved.