Systems Fe-O and Cu-O: Thermodynamic data for the equilibria Fe-"FeO," Fe-Fe3O4, "feO"-Fe3O4, Fe3O4-Fe2O3, Cu-Cu2O, and Cu2O-CuO from emf measurements

Research output: Contribution to journalArticleResearchpeer-review

83 Citations (Scopus)

Abstract

The chemical potential of oxygen (μO2) defined by the reactions And 1.5Fe + O2 ⇌ 0.5Fe3O4, 2Fe + O2 ⇌2"FeO," 6"FeO" + O2 ⇌ 2Fe3O4, 4Fe3O4 + O2 ⇌6Fe2O3, 4Cu + O2 ⇌2Cu2O, 2Cu2O + O2 ⇌4CuO has been determined using an electrochemical method with calcia-stabilized zirconia solid electrolytes. The Fe + Fe3O4, Fe + "FeO," and Cu + Cu2O equilibria were measured using air as the reference, and these results are thus absolute determinations of μO2 Cu + Cu2O and Fe + "FeO" were then used as reference electrodes for other measurements reported both here and elsewhere. The results for the nO2 values are [in J mol-1, 7 in kelvins, with a reference pressure for O2 of 1 bar (105 Pa)] for Cu + Cu2O (±62), -347705 + 246.0967- 12.905371n 7 (750 < 7< 1330), forFe + "FeO" (±100), -605 812 + 1366.7187 - 182.795571n 7 + 0.1O35972 (833 < T < 1O42), -519357 + 59.4277+ 8.92767m 7 (1O42 < 7< 1184), -551 159 + 269.4O47- 16.948471n 7 (1184 < 7< 1450), for "FeO" + Fe3O4 (±306), -581 927 - 65.6187 + 38.741071n 7 (833 < 7 < 1270), forFe + Fe3O4(±107), -607 673 + 1060.9947- 132.390971n 7+ 0.0665772 (750 < 7< 833), and for Cu2O + CuO (±117), -292 245 + 377.0127 - 23.197671n 7 (800 < 7 < 1300). The standard enthalpy of formation of Fe3O4 is -1115.4 ± 0.2 kjmol-1, in excellent agreement with that deduced from the quartz-fayalite-iron and quartz-fayalite-magnetite equilibria at higher temperatures. The results for the Fe3O4 + Fe2O3 equilibrium are less certain and have therefore not been presented in the form of a simple equation. For the other equilibria, the results represent a significant improvement in accuracy over existing measurements.

Original languageEnglish
Pages (from-to)470-486
Number of pages17
JournalAmerican Mineralogist
Volume73
Publication statusPublished - 1988
Externally publishedYes

Cite this