Oxidation of Minor Elements from an Iron–Nickel–Chromium–Cobalt–Phosphorus Alloy in 17.3% CO2–H2 Gas Mixtures at 700–1000 °C
- 137 Downloads
Fe–Ni–Cr–Co–P alloys were exposed to 17.3% CO2–H2 gas mixtures to investigate the oxidation of minor elements in metallic alloys in the early solar system. Reaction temperatures varied between 700 and 1000 °C. Gas-phase equilibrium was attained at 800, 900, and 1000 °C, yielding H2–H2O–CO–CO2 gas mixtures. Experiments at 700 and 750 °C did not achieve gas-phase equilibrium and were performed in H2–CO2 gas mixtures. Reaction timescales varied from 1 to 742 h. The experimental samples were characterized using optical microscopy, electron microprobe analysis, wavelength-dispersive-spectroscopy X-ray elemental mapping, and X-ray diffraction. In all experiments Cr experiences internal oxidation to produce inclusions of chromite (FeCr2O4) and eskolaite (Cr2O3) and surface layers of Cr-bearing magnetite [(Fe,Cr)3O4]. At 900 and 1000 °C, P is lost from the alloy via diffusion and sublimation from the metal surface. Analysis of P zoning profiles in the remnant metal cores allows for the determination of the P diffusion coefficient in the bulk metal, which is constant, and the internally oxidized layer, which is shown to vary linearly with distance from the metal surface. At 800 and 900 °C, P oxidizes to form a surface layer of graftonite [Fe3(PO4)2] while at 700 and 750 °C P forms inclusions of the phosphide-mineral schreibersite [(Fe,Ni)3P].
KeywordsOxidation Fe–Ni–Cr–Co–P alloy Eskolaite (Cr2O3) Chromite (FeCr2O4) Magnetite (Fe3O4) Schreibersite ([Fe,Ni]3P) Graftonite (Fe3[PO4]2) Diffusion
- 11.J. Crank, The Mathematics of Diffusion (Oxford University Press, New York, 1975).Google Scholar
- 12.A. D. Le Claire and G. Neumann, in Numerical Data and Functional Relationship in Science and Technology. Landolt-Bornstein, New Series, Group III, ed. H. Mehrer, Vol. 26 (Springer Verlag, Berlin, 1990).Google Scholar