抄録
As reported in previous papers (J. Phys. Soc. Japan, 9 (1954) 702; ibid. 10 (1955) 794), single crystals of solid solutions NaCl-CaCl2 contain two kinds of plate-zones extending parallel to {111} and {310} planes of the matrix. The present study concerns with the change of these plate-zones by heat treatments at various temperatures. Single crystals of solid solutions NaCl-CaCl2 containing 10 mole per cent CaCl2, which have been made uniform solid solutions by pre-heating at 400°C (being slightly above the solid-solubility limit of the phase diagram of NaCl-CaCl2 system), were aged at room temperature or heated at higher temperatures. It is found that the {310} plate-zone is stable only at low temperatures, while the {111} plate-zone is more stable at higher temperatures. As the heating temperature is raised, the {111} plate-zone gradually tends from a coherent structure to an incoherent structure. Rotating-crystal X-ray photographs for the crystal heat-treated at 300°C (being slightly below the solid-solubility limit of the phase diagram) reveal that the final products of the precipitation have the crystal structure of CaCl2, with an orientation favouring the structure model of the {111} plate-zones proposed in Part II.
