Funct. Mater. 2023; 30 (4): 519-525.

doi:https://doi.org/10.15407/fm30.04.519

The behavior of Co3-xMІІx(PO4)2·8H2O (MІІ = Mg, Mn, Zn) solid solutions at elevated temperatures

N.M.Antraptseva, O.D.Kochkodan, N.V.Solod, O.O.Kravchenko

National University of Life and Environmental Sciences of Ukraine,Heroiv Oborony Str., 17, 03041, Kyiv, Ukraine

Abstract: 

It has been determined that heating of solid solutions of hydrated medium phosphates of the composition Со3-xМxII(PO4)2·8Н2O (МII = Mg, Mn, Zn) is accompanied by dehydration processes with the formation of lower hydration phosphates with the composition Со3-xМxII(PO4)2·nН2O, where 1.0≤n≤7.0. Further dehydration leads to the realization of the processes of amorphization and condensation of the phosphate anion. It has been shown that the content of condensed phosphates, depending on the cationic composition of the solid solution, is 7.2–9.6 rel. % P2O5 gen. The anionic composition of the heating products is simplified with the beginning of crystallization of the solid phase. Anhydrous crystalline phosphate identified as Со3-xМxII(PO4)2 (МII = Mg, Mn, Zn) is thermally stable when heated to 900ºC. It has been determined that the cation nature affects not only the change of thermal stability of octahydrates, but also the temperature intervals of realization of all stages of the process of their dehydration. The most sensitive to the cationic composition of solid solutions was the depth of implementation of anionic condensation processes, which, judging by the number of condensed phosphates, occurs more fully in the heat treatment products of manganese-containing phosphates – Со3-xМnx(PO4)2·8Н2O. It has been shown that an increase in the heating rate of Со3-xМxII(PO4)2 8Н2O (МII = Mg, Mn, Zn) from 1.3 deg/min to 10.0 deg/min leads to a shift of temperatures of realization of dehydration, amorphization, anion condensation and crystallization of anhydrous phosphates towards higher temperatures.

Keywords: 
solid solutions, hydrated phosphates, condensation, cation nature, thermal properties

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