Pure ZnS and CdS were synthesized under hydrothermal conditions. The reactions of Zn or ZnO with S at 240°C yielded pure ZnS. Similar reactions at lower temperatures gave plate crystals of an unknown phase along with ZnS and ZnO. Pure CdS was obtained by the reaction between CdO and S at 240°C while the reaction of metal Cd and S gave a mixture. The as-prepared CdS crystals had rod shapes.

Iron group metal sulfides were synthesized from the elements under hydrothermal condition. For nickel sulfides, two kinds of nickel metal powder, coarse powder passed through 63 mm mesh and fine powder passed through 3 mm mesh, were used as the starting materials. The reaction with the coarse Ni powder gave NiS with appreciable amount of Ni, Ni 3 S 2 , and Ni 9 S 8 . Pure NiS was obtained by the reaction with the fine Ni powder at 240? C for 10 h. The lowest nickel sulfide Ni 3 S 2 was obtained as a single phase product of the reaction if the coarse Ni powder was used. From these results, the fine and coarse powders were found to be suitable for the syntheses of NiS and Ni 3 S 2 , respectively. The lowest cobalt sulfide Co 9 S 8 was obtained almost as a single phase though the XRD pattern of the product showed some unidentified peaks. Pure Co 9 S 8 was obtained by washing the reaction product with HNO 3 . In the Fe-S system, FeS was obtained with a small amount of Fe 3 O 4 .

Pure copper (11) sulfide, CuS, was successfully prepared by a simple reaction of copper and sulfur powder in water at low temperatures (2: 60 °C), though the solid state reaction of the elements requires higher temperatures to complete the reaction. Pure Copper (I) sulfide (Cu 2 S) and silver (I) sulfide (Ag 2 S) were also prepared by similar reactions between the elements above 150 °C and 90 °C, respectively. Two phases (chalcocite-Q and chalcocite-low) were observed in the yielded Cu 2 S. Observation with the scanning electron microscope revealed that the CuS was composed of the particles of polyhedral frameworks with dimensions of 2 -3 flm. Whereas the particle sizes of the as-prepared Cu 2 S were similar to those of CuS, the particles had indefinite frameworks. For Ag 2 S, the as-prepared particles at 90 oc were like sharp thin blades and became duller with the increasing reaction temperature.