Synthesis and atmospheric instability of well crystallized rod-shaped V_2O_4・2H_2O powders prepared in an aqueous solution(<Feature>Global Innovation in Advanced Ceramics)

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Synthesis of well crystallized rod-shaped V_2O_4・2H_2O powders of 100 nm in width in an aqueous solution containing NH_4VO_3 and N_2H_4・H_2O under atmospheric pressure had been investigated. The optimal conditions for atmospherically hot-water treatment at 95℃ were found to be as follows: pH 2.5-3.5 and an appropriate amount of N_2H_4・H_2O. How the solution conditions affect the crystal structures and morphologies of the products is discussed. At pH<2.5, no precipitates formed. At pH 4.0-4.5, V_<10>O_<24>・12H_2O would generally be obtained if N_2H_4・H_2O was excessive. It was independent of reduction of NH_4VO_3 solution to tetravalent solids on the dosage of reducing agent N_2H_4・H_2O. The morphologies of the V_2O_4・2H_2O had no obvious relationship with the pH and the dosage of N_2H_4・H_2O. It seems that before treated at 95℃ the products were sheet-shaped, and then cleaved along specific crystalline directions after treated, forming rod bunches. The stability of V_2O_4 2H_2O in acid solution and in air was also investigated. The results showed that V_2O_4-2H_2O was unstable in air and could undergo oxidization to be a quasiamorphous rod-shaped V_<10>O_<24>・12H_2O, especially at high pH, with excessive N_2H_4・H_2O, drying at 150℃ in flowing air, and/or being exposed to air for several days.
社団法人日本セラミックス協会の論文
2008-03-01