The Determination of Phase Boundaries and Thermodynamic Functions in the Iron-Oxygen System by EMF Measurements

H. F. Rizzo, R. S. Gordon, I. B. Cutler
1969 Journal of the Electrochemical Society  
Coulometric titration in a high-temperature cell employing a stabilized zirconia electrolyte was used successfully in the determination of phase boundaries and related thermodynamic data in the iron-oxygen system. The standard free energy of formation of oxygen-deficient wiistite was determined between 540 ~ and 1200~ Values agree to within 500 cal of the most critically reviewed data. The free energy of reaction for the formation of magnetite from wiistite and oxygen was determined between 900
more » ... ermined between 900 ~ and 1200~ The composition of the iron-rich boundary of wiistite was found to decrease very slightly in oxygen content with increasing temperature. For all practical purposes, however, the composition of the boundary can be considered constant at FeOi.05. The compositions of oxygen-rich wiistite agreed fairly well with existing data. Evidence was presented, however, for the existence of additional phases in the region of the Fe-O diagram between the presently reported oxygen-rich wfistite and magnetite. The temperature for the Fe, FexO, Fe304 three-phase equilibrium was found experimentally to be 610 ~ • 10~ Extrapolation of low temperature (T < 900~ FezO-Fe304 equilibrium data resulted in lower transformation temperatures. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 207.241.231.82 Downloaded on 2018-07-20 to IP Vol. 116, No. 2 PHASE BOUNDARIES & THERMODYNAMIC FUNCTIONS 267 /~ ~Spring Loaded Muilite Tube Zirconio Electrolyte Gas Inlet Gas Outtet fat Gas ~t m"-~ Shield ~ ~ Alumina Disc ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 207.241.231.82 Downloaded on 2018-07-20 to IP
doi:10.1149/1.2411812 fatcat:bcmatyip7zbk5il2qn62vwhlpu