1990 Fiscal Year Final Research Report Summary
Synthesis of Mixed Valenced Oxide Minerals
| Project/Area Number |
01470055
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | Hokkaido University |
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Principal Investigator |
KIKUCHI Takeshi Hokkaido University, Faculty of Science, Assistant Professor, 理学部, 助教授 (60211190)
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| Co-Investigator(Kenkyū-buntansha) |
ISHII Kuninobu Hokkaido University, Faculty of Engineering, Professor, 工学部, 教授 (00001214)
MIURA Hiroyuki Hokkaido University, Faculty of Science, Lecturer, 理学部, 講師 (70157436)
HARIYA Yu Hokkaido University, Faculty of Science, Professor, 理学部, 教授 (50000815)
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| Project Period (FY) |
1989 – 1990
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| Keywords | Solid solution / Mineral synthesis / Hausmannite / Spinel / Mixed valency / Jacobsite / Cryptomelane / Fluorite structure |
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| Research Abstract |
(1) Making of Phase Equilibrium Diagram of the System Jacobsite (MnFe_2O_4) -Hausmannite (Mn_3O_4)
Phase diagram of the system jacobsite-hausmannite was made by solid state reactions under hematite-magnetite oxygen buffers. Compositions of the two phase region where a cubic phase and a tetragonal phase coexisted were determined by electron microprobe analysis. A thermodynamical approach revealed that the equilibrium concentration relations among chemical constituents such as Mn^<2+>, Fe^<2+>, Mn^<3+>, Fe^<3+> and vacancy of metal in the cubic phase.
(2) Observation of Thermal Decompostion Behavior of Pyrolusite by Means of Hihg Temperature Powder X-ray Diffractometer
Two kinds of thermally different pyrolusite (S) and (D) are known ; (S) shows one endothermic peak about 650^ﾟC and (D) has two endothermic peaks about the same temperature. High temperature X-ray measurements for these showed that (S) decomposed at about 650^ﾟC and transformed to bixbyite (alpha-Mn_2O^3) exclusively, whereas (D) converted to gamma-Mn_2O_3 and Mn_5O_8 in addition to bixybite. Thermal behavior of (D) was explicable from the oxygen deficiency in (D).
(3) Thermal Transformation of Cryptomelane (A_xMn_8O_<16>. nH_2O, A=K, Na)
Tetragonal cryptomelane was converted to a monoclinic cryptomelane and bixybite by heating at about 700^ﾟC in air. Alkali ions in the part were concentrated in the tunnel and caused the transformation to monoclinic phase accompanying with simulutaneous formation of bixbyite. Structural study in dicated that the Mn^<3+> ions were ordered in the monoclinic cryptomelane.
(4) Valence State of Tellurium in Bismuthtellurates
Valence state of tellurium in the compounds appeared in the pseudo-ternary system Bi_2O_3-Sro-TeO_2 and Bi_2O_3-Pbo-TeO_2 in air was mostly in the state of Te^<4+>. In a superstructure of fluorite, Bi_2SrTeO_7, tellurium ion existed as Te^<6+>.
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