Figure 7 shows the schematic diagram of the formation of product particle P from reactants A and B. The relative dissolution rate determines the dominant formation mechanism. When the dissolution rates of A and B are comparable (Fig. 7(a)), both reactants dissolve in the molten salt and the product particles precipitate under a high degree of supersaturation (solution-precipitation process: mechanism 1). In this case, particles have a growth form, which is often different from the equilibrium form. Typical examples are Bi2WO6 obtained from Bi2O3 and WO3 using Li2SO4-Na2SO4 (Kimura & Yamaguchi, 1982) and TiZrO4 from TiO2 and ZrO2 using KCl (Kimura et al., 1992). The Bi2WO6 and TiZrO4 particles have rectangular and irregularly rounded shapes, whereas the equilibrium forms are an oblate an oblate sphere and needle, respectively.