EFFECT OF MASS TRANSFER OF SYSTEMS Mn(Fe,Co)Mo(W)O4–Na2CO3 AND ENVIRONMENT AND NEED FOR HIS ACCOUNT WHEN IDENTIFYING MOLYBDATES AND TUNGSTATES OF MULTIVALENT d-ELEMENTS, Mn, Fe, Co, ON BASIS OF THERMOGRAVIMETRIC DATA

Abstract

The paper presents the experimental and calculated data for study of exchange reactions in the systems Mn(Fe,Co)Mo(W)O4–Na2CO3 with methods of thermodynamics, thermogravimetry, kinetics topochemically reactions and stoichiometry, analysis and synthesis which led to the identification of the effect of mass transfer between the system and the environment – a phenomenon characteristic of molybdates (tungstates) polyvalent d-elements (Mn,Fe,Co) in contrast to similar derivatives of d-elements (Ni, Zn, Cd, Ag) with constant valency. It identified the genesis and the mechanism of manifestation of this phenomenon, which, as shown by theoretical analysis and experimental data, due to polivalentes Mn (Fe,Co) and hence the possibility of occurrence in the systems Mn(Fe,Co)Mo(W)O4–Na2CO3 exchange reactions of Mn(Fe, Co)Mo(W)O4+Na2CO3→ →Mn(Fe,Co)CO3+Na2Mo(W)O4, dissociation of Mn(Fe,Co)CO3=Mn(Fe,Co)O+CO2 and redox Mn(Fe,Co)O+1/2О2→Mnx(Feх,Cox)Oy where y=x+1/2О2, leading to the loss of CO2 and the conversion of Mn(Fe,Co)O – degradation products of Mn(Fe,Co)CO3 at the expense of the oxygen of environment to the oxide type-Mnx(Feх,Cox)Oy, the composition of which is determined by the process temperature. It is established that the above reactions form the basis of the unique phenomenon in solid state chemistry of molibdates (wolframates) of polyvalent d-elements discovered for the first time, in the opinion of the authors. This phenomenon is associated with the proceeding of Mn(Fe,Co)Mo(W)O4–Na2CO3 processes in their heat treatment. It is shown that successive thermal dissociation reactions of Mn(Fe,Co)CO3 lead to their loss of CO2 (mass reduction) and oxidation of the formed Mn(Fe,Co)O by air oxygen to Mnх(Feх,Coх)Oу=x+1/2О2 (mass growth): CO2 donor systems and O2 acceptors, and the medium (air) – O2 donor and CO2 acceptor. The proposed methodology is a reasonable choice of the reaction from the expected, the occurrence of which is absolutely reliable in given physicochemical conditions.