Phase equilibria in the V2O5-NaVO3-Ca(VO3)2-Mn2V2O7 system and interactions of phases with H2SO4 and NaOH solutions |
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| Authors: | T I Krasnenko T P Sirina M V Rotermel’ |
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| Institution: | (1) Institute of Solid State Chemistry, Ural Division, Russian Academy of Sciences, Pervomaiskaya ul. 91, Yekaterinburg, 620219, Russia;(2) ChNVTs Metallurgiya, Chelyabinsk, Russia |
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| Abstract: | Phase composition of the V2O5-NaVO3-Ca(VO3)2-Mn2V2O7 system was studied, and a subsolidus phase diagram constructed. The tetrahedration of the diagram is determined by the fact that the end-member of Ca1–x Mn x (VO3)2 solid solution is in equilibrium with all compounds of the system (V2O5, NaVO3, Ca(VO3)2), vanadium β-bronzes Na x V2O5 (0.22 ≤ x ≤ 0.40) and κ-bronzes (0.25 ≤ x ≤ 0.45, 0 ≤ y ≤ 0.16), Mn2V2O7, and Na2Mn3(V2O7)2 and with the end-members of reciprocal solid solutions based on calcium and sodium metavanadates. At 20°C, the degree of vanadium dissolution α for Na2Ca(VO3)4 is 100% for 0.5 ≤ pH ≤ 10; for the other phases of the system, vanadium dissolution ranges from 100 to 10% for pH below 3.5; in the alkaline pH range, ≤ 10%. Sodium for calcium substitution in Ca(VO3)2 increases α in aqueous NaOH to 20%. For Na2Mn3(V2O7)2, α decreases from 92 to 80% as pH changes from 0.5 to 2.5; at pH above 4, α = 30%. |
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