Phase equilibria in the system CoO-MnO-TiO2-Co

The phase diagram of the oxide system TiO2-MnO-CoO in equilibrium with meta llic cobalt at variable temperature and oxygen pressure has been constructe d using the static method of investigation of heterogeneous equilibria and X-ray diffraction analysis. Three continuous solid-solution series: ConMn1- nO, ConMn1-nTiO3 and ComMn2-mTiO4 with the structures of NaCl, ilmenite and spinel, respectively, have been found. The concentration dependencies of e quilibrium partial oxygen pressure on the low-oxygen boundaries of homogene ity regions of solid solutions ConMn1-nTiO3 and ComMn2-mTiO4 have been meas ured at 1073, 1173 and 1273 K. The equilibrium compositions of coexisting p hases have been defined in each equilibrium study. These complex data permi t us to present P-T-X diagrams of the system CoO-MnO-TiO2-Co either as thre e isothermal sections (1073, 1173 and 1273 K) or as series of isobar-isothe rmal sections. Using an example of the solid solution ConMn1-nTiO3, we showed, that our da ta can be used for the calculation of concentration dependencies for compon ent activities of solid solutions at various temperatures. We have applied the method based on solving the Gibbs-Duhem equations for each solid phase, that participates in equilibrium, and equations of laws of mass action for all possible independent chemical reactions between system components at e quilibrium conditions. (C) 1999 Elsevier Science Ltd. All rights reserved.