Lattice Parameter and Redox Equilibria in CaO-containing Wustite.

Abstract

Equilibrium relation among oxygen potential in atmosphere, composition and lattice parameter in CaO-containing wustite have been studied at 1 273 K. Wustite plates with the molar cation fraction M Ca /(M Fe +M Ca ) (=M Ca-Fe ) ranging from 0.0058 to 0.079 were equilibrated with CO-CO 2 gas mixtures. Composition of the wustite specimens was determined by chemical analysis and thermo-gravimetric method. Lattice parameter of the CaO-containing wustite was measured by X-ray diffraction method. The relation between the lattice parameter a and the gas ratio Ks (= P CO2 /P CO ) in the gas mixture was expressed by a=(4.2975+0.560.M Ca-Fe )-1.470×10 -2 .In(Ks) (A). The variation of a with M Ca-Fe and molar ratio M Fe /M O in the CaO-containing wustite was given by a=1.916+0.565.(M Ca-Fe )+4.719.(M Fe /M O )-2.316.(M Fe /M O ) 2 (A). Then the lattice parameter may be used as the index of the composition in CaO- containing wustite. The 'iso-lattice-parameter' line was drawn within the wustite field in the isothermal section of the system FeO-Fe 2 O 3 -CaO. The molar ratio M Fe2O3 /M FeO of the CaO-containing wustite on the Fe 2 O 3 -rich side slightly increases with an increase in CaO content but the ratio on the FeO-rich side does not change. The solubility of CaO in the wustite equilibrated with both metallic iron and 2CaO.Fe 2 O 3 was estimated to be ∼9 mol% CaO.