A Thermodynamic Study of the Wuestite Phase.

Ackermann, R.J.; Sandford, R. W.

doi:10.2172/4455676

Cited by 7 publications

(5 citation statements)

References 6 publications

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“…[8]. The standard enthalpy and entropy for reaction [5] were evaluated from the temperature dependence, --27,295 _ 20 log Po2 -----~-6.6115 • 0.0218 These results agree well with the data of other workers (i0, [12][13][14][15][16]19) and should be more accurate since the use of air as a reference electrode eliminates one of the principal sources of error, namely, the thermodynamic properties of gaseous phases or other twophase coexistence mixtures which are used to establish the partial pressure of oxygen at the reference electrode. The results of this study for the standard free energy of formation of iron-rich wiistite are com- pared with previous data in Table I.…”

Section: Resultssupporting

confidence: 80%

“…Transformation temperature for decomposition of wi2stite to magnetite.--The temperature corresponding to the decomposition of wfistite into magnetite has been reported to be between 565 ~ and 620~ (16,19,42). This temperature can be uniquely determined by the triple point where iron, magnetite, and a particular composition of wfistite are in equilibrium.…”

Section: Iron-rich Boundary Of Wismentioning

confidence: 99%

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

Rizzo

Gordon²,

Cutler³

1969

J. Electrochem. Soc.

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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 ~ 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.

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Section: Resultssupporting

confidence: 80%

Section: Iron-rich Boundary Of Wismentioning

confidence: 99%

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

Rizzo

Gordon²,

Cutler³

1969

J. Electrochem. Soc.

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“…10. [15,36,37,41,42,45,[52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] and calculated lines. The calculated oxygen isobars are shown by the dashed lines.…”

Section: Phase Diagramsmentioning

confidence: 99%

“…Equilibrium oxygen partial pressures over the wüstite stability field: experimental points[35][36][37][38][39][40][41][42][43][44][45][46] and calculated lines.…”

mentioning

confidence: 99%

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Thermodynamic reevaluation of the Fe–O system

Hidayat

Shishin

Jak

et al. 2015

Calphad

115

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Development of a reduction process and test results of the reduction equilibria of wustite as a function of oxygen content and temperature

1992

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A new measurement technique allows the continuous measurement of the oxygen contents of the wustite as a function of temperature without having to pass through the disintegration of the wustite to iron and magnetite and have the accompanying problems during the chemical analysis by cooling the sample. Measurements are carried out in form of isothermal oxygen reduction tests, starting with pure Fe2O3 in a thermogravimetric balance with an upstream gas mixer which, operating with CO2/CO gas mixtures, ensures a graduation of the input reduction potential CO'2 in steps of 1%. Simultaneous weighing of the test material sample permits, by means of the measured weight loss and relation to the charged amount of Fe2O3, a very accurate measurement of the oxygen concentration within the test material at any point in time during testing. Testing was carried out along these lines in the range between 700 and 1300°C. The results show that, at constant temperatures, the wustite oxygen contents decrease linearly from the right‐ to the left‐hand boundary of the wustite field, with the oxygen pressure of the gas phase (log pCO2/pCO or log pO2). When comparing these results with the findings of Darken and Gurry, a difference becomes apparent in the curves of the log pO2 values as a function of the temperature. While our own curves are substantiated by very many measured values, the curves of Darken and Gurry are based on only twenty‐three values at four different temperatures. Based on this result, systems of equations are developed which describe the homogeneous field of the wustite in the Fe‐O‐C reduction system without any gaps. An equivalent system of equations can also be developed from the values of a literature evaluation carried out by Giddings and Gordon. The curves resulting from the two equations do not differ very greatly. But the differences are large enough for corresponding variances to be expected when establishing the wustite boundaries and, thus, the position of the wustite field in the phase diagram.

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A Thermodynamic Study of the Wuestite Phase.

Cited by 7 publications

References 6 publications

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

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

Thermodynamic reevaluation of the Fe–O system

Development of a reduction process and test results of the reduction equilibria of wustite as a function of oxygen content and temperature

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