Phase Equilibria in the V₂O₅NaVO₃Ca(VO₃)₂Mn₂V₂O₇
System and Interactions of Phases
with H₂SO₄ and NaOH Solutions

T. I. Krasnenko^a, T. P. Sirina^b, and M. V. Rotermel’^a

^a Institute of Solid State Chemistry, Ural Division, Russian Academy of Sciences,
Pervomaiskaya ul. 91, Yekaterinburg, 620219 Russia

^b ChNVTs Metallurgiya, Chelyabinsk, Russia

Received June 1, 2007

Abstract—Phase composition of the V₂O₅NaVO₃Ca(VO₃)₂Mn₂V₂O₇ system was studied, and a subsolidus
phase diagram constructed. The tetrahedration of the diagram is determined by the fact that the end-member of
Ca_{1 x}Mn_x(VO₃)₂ solid solution is in equilibrium with all compounds of the system (V₂O₅, NaVO₃, Ca(VO₃)₂),
vanadium -bronzes Na_xV₂O₅ (0.22 x 0.40) and -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 metavan-
adates. At 20C, the degree of vanadium dissolution 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 in aqueous NaOH to 20%. For
Na₂Mn₃(V₂O₇)₂, decreases from 92 to 80% as pH changes from 0.5 to 2.5; at pH above 4, = 30%.

DOI: 10.1134/S0036023608090234

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