Toshiyuki Sata

Valence stability of molybdenum in alkaline earth molybdates

Abstract Presence of oxygen stability range in ternary oxides was experimentally verified for molybdenum(IV) perovskites, and the widths of stability range were determined of BaMoO 3 , SrMoO 3 and CaMoO 3 . Moreover, the tetravalent state of molybdenum was found to be more strongly stabilized in these compounds than in its binary oxide. A concept of lattice self-potential was examined in order to explain this phenomenon. Contribution of A-cation to the retention of high valence state of B-cation in the perovskite ABO 3 was also discussed.

Phase Relations in the System Ca3(PO4)2-Mg2SiO4 and Formation of 1-1 Compound Ca3Mg2(PO4)2

Phase relations in the system C3P-M2S (abbreviations: C=CaO, M=MgO, P=P2O5 and S=SiO2) were investigated by means of the quenching method at temperatures up to 1600°C. Primary crystals are tricalcium phosphate and forsterite, and an intermediate compound sc appeared coexisting with the above compounds and liquid. Two minima of liquidus are located at 1440°C between C3P and sc, and at 1410°C between sc and M2S. Liquid disappears below 1365°C. The original composition of sc is C3M2PS (50-50mol% of C3P-M2S) or (C0.6M0.4)5PS (60-40mol% of C5PS-M5PS), and has a solid solution range in both sides of this composition. This sc compound decomposes to both β-C3P and forsterite below 1365°C.

Phase relations in the system Ca3(PO4)2-MgO-SiO2

Phase relations in the system tricalcium phosphate (3CaO⋅P2O5=C3P)-enstatite (MgO⋅SiO2=MS) have been investigated in the temperature range 1100 to 1600°C by means of the quenching method. C3P takes β-type (whitrockite) in a wide region by dissolution of MgO, and diopside (d) appeared in the composition range more than 40mass% C3P by a reach in between MgSiO3 and liberated CaO. The enstatite transfers to iron-free pigeonite (pi) by taking CaO in an MS-rich region, where pi coexists with protoenstatite, MgSiO3 (pr). Primary crystals which appeared in a wide region are β-C3P and pi, and primary diopside appears in a narrow region at a minimum temperature (1265-1305°C). In the subsolidus region below 1245°C, β-C3P coexists with d, pi or pi-pr mixture. The system is not binary and it should be discussed from the ternary system C3P-M-S and the quaternary system C3P-CMS2-MS-S.

Reactions between Bi2Sr2CaCu2Oy Superconducting Oxide and Metallic Copper and Their Preventions

Powders of a superconductor oxide, Bi2Sr2CaCu2Oy (BSCC, 2212), were packed in a copper tube and hotpressed in the temperature range from 500°to 800°C for 1h under 200kg/cm2 aiming at fabrication of superconducting wire using copper sheath. The reactions between the copper and the BSCC were investigated. The reaction began above 600°C, and a red-brown reaction layer of 70μm was observed at 800°C. Powder mixtures of the oxide and copper were hot-pressed. Results of EPMA and XRD of the reaction layer showed that the 2212 phase decomposed to a 2201 phase and CuO and then to Cu2O accompanied by the oxidation of the copper tube. For prevention of such reactions, electroplating of gold or silver was applied to the inner face of the copper tube. The reactions were suppressed by electroplating 20μm of gold or 40μm of silver. But a semiconductive temperature change of the electrical resistivity was seen for 60μm of Ag. Finally, in the results of hot-pressing at 700°C for 1h flowing oxygen into the tube at 1.5kg/cm2 using 20μm Au or 40μm Ag on copper, zero resistance was not shown for Au-electroplating, but it was obtained at 22K for the Ag-plating. Thus, a possibility of fabrication of copper sheath wire with silver-plating holding oxygen pressure in the copper tube during an extrusion or a hot-pressing process was confirmed.