Sakae Takeuchi, Kazuo Furukawa and Kôki Gunji
It is known that Mn-Wüstite (Fe,Mn)O takes the form of solid solution over all the proportions of Fe-and Mn-atoms,and its oxygen content varies with oxygen pressure in the thermal equilibrium and with temperature. So we examined the quantitative relation between the solid and gas phases in the above mentioned system. Taking into consideration the previous papers in which Wüstite and Magnetite solid solutions were discussed, a configurational model for the Mn-Wüstite is assumed as follows: (1) O– – and metal ions are arranged on the lattice of NaCl-type, (2) in the negative ion lattice-sites O– – ions are perfectly packed, (3) in the positive ion sites Fe+ +, Mn+ + and vacancies are randomly distributed, and (4) the electron-defects are trapped on some of Fe+ + ions producing Fe+ + + so that the total electrical charge of the crystal is neutralized. Considering such a model the partition function of Mn-Wüstite was formulated on the base of statistical thermodynamics, and the equilibrium relation between the solid composition and oxygen pressure in the gas phase was calculated. The calculated result is in agreement with the experimental values by Matoba and Gunji (1954) and our reexamination data obtained by the measurement of weight change using a spring balance.
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