On the nucleation, growth and impingement of plate-like α-Zn2SiO4 spherulites in glaze layer: a confocal and electron microscopic study

Confocal and electron microscopic observations of willemite (α-Zn2SiO4) crystalline ware glaze, fired to 1270 °C and then aged at 1080 °C for 5 h, indicated the glaze decomposed as (Zn, Ti, Ca)-rich and (Si, Al, K, Na)-rich regions, from which willemite crystallites and amorphous droplets were formed, respectively. Under the constraint of the glaze thickness, the willemite crystallites further developed into plate-like spherulites, which consists of lath-like crystals growing at the order of [0 0 0 1]⪢〈1 0 1̄ 0〉>〈2 1̄ 1̄ 0〉 and viable for coalescence over {2 1̄ 1̄ 0} habit plane. The impinged plate-like spherulites formed a flat interface at the early stage of crystallization, but irregular interface in late stage due to weaving, truncation and lateral coalescence of the crystals. The {2 1̄ 1̄ 0}-specific coalescence can be rationalized by Brownian-type motion/rotation of the crystals until parallel epitaxy is reached.