The relative dissolution rate determines the dominant formation mechanism. Thus, the , , and faces have almost the same growth rate under a high degree of supersaturation reaction stage , resulting in the rectangular shape.
Figure The increase in the formation rate is a consequence of 1 an increase in the contact area of the reactant particles and 2 an increase in the mobility of the reactant species in the molten salt Arendt et al.
Powder characteristics 2. An example is needlelike BaTiO3 Hayashi et al.
In contrast, in molten salt synthesis, molten salt covers the surfaces of all particles present and prevents the formation of necks between the product particles. Figure 7 shows the schematic diagram of the formation of product particle P from reactants A and B. The Wulff plot is a polar diagram of the specific surface free energy, which is determined by the combination of solid and liquid materials.
A sharp cusp implies that a certain face has much lower free energy than other faces and the crystal will be facetted. A similar procedure is employed to prepare needlelike and platelike KNbO3 particles Li et al. The growth under a low degree of supersaturation is similar to that in the single-crystal growth from solution. In this case, the single-crystalline Na0. In this case, platelike Fe2O3 particles are single crystals but the obtained MFe2O4 particles are poly-crystalline, and the topotactic relationship is preserved in each grain, i. The degree of supersaturation is high when the product particles are formed by the solution-precipitation process mechanism 1 and, consequently, aggregates often form.
The solubility values are 2. In this case, platelike Fe2O3 particles are single crystals but the obtained MFe2O4 particles are poly-crystalline, and the topotactic relationship is preserved in each grain, i. The particle shape is shown in Fig.
This is fairly larger than the mobility in the solid state reaction. A large diffusion coefficient and solubility enhance the material transport in the molten salt. The platelike Bi4Ti3O12 particles are easily obtained by molten salt synthesis using KCl and their size can be easily controlled by selecting the heating temperature and duration. The rate of Ostwald ripening depends on the diffusion coefficient, the solubility, and the atomic structure of the particle surfaces Rahaman, The molten salt decreases the temperature range of the reaction.