Surface Oxide Composition Research Articles

On the nature of oxides on InP surfaces

The chemical composition of surface oxides grown on InP is investigated using x-ray photoelectron spectroscopy. Native oxides prepared by various chemical treatments, anodic oxides, and thermal oxides are examined. Core level energies and intensities and valence band spectra are compared with data for standard compounds. In a first step we show that, depending on the preparation procedure, oxides can be classified into three groups which have properties similar to crystalline In(OH)3, InPO4, and In(PO3)3, respectively. The large variations observed in atomic compositions and the shape of valence band spectra suggest that the oxides could be amorphous nonstoichiometric phases. A description based on a mixture of well defined compounds (e.g., In2O3+P2O5 or In2O3+InPO4) seems to be inadequate. Chemical and anodic phosphorus-rich oxides are identified as Inx(PO3)y polyphosphates.

Characterization of surface oxides by Raman spectroscopy

Raman spectroscopy is shown to provide direct information on the composition and structure of surface oxides formed on alloys. Previously, identification of specific compounds present in these oxides only could be inferred from conventional surface analysis methods. In our studies, backscattering spectra were obtained from thick oxide films (⪞10 μm) present on high purity and commercial stainless steels after exposure to air and coal gasifier environments at 980 °C. With as-grown oxides, data were obtained from the outer oxide regions. Spectra from inner regions also were measured using grazing-angle sectioning techniques. The presence of impurities and minor alloying constituents in the substrates are shown to have profound effect on results; for example, the addition of a few percent of titanium and manganese resulted in the formation of a duplex scale with a thin, complex, outer layer and a relatively thick α–Cr2O3 inner scale.

The oxidation of type 316 stainless steel in low pressure oxygen at temperatures between 873 and 1223 K

AbstractThe oxidation of type 316 stainless steel in low pressure oxygen (1.8 × 10−2 to 1.3 × 10−5 N/m2) in the temperature range 873 to 1223K has been studied. The kinetics are determined from weight gain measurements and the surface oxide composition determined by a number of experimental techniques. In the as‐received condition a thin Cr2O3 layer forms with some incorporation of manganese, at rates governed by lattice diffusion in the alloy. After a vacuum anneal for 24 hours at 1273K two types of behaviour are found. In the first a chromium rich M2O3 layer forms, with in certain cases initial formation of Fe2O3, the kinetics of which indicate that grain boundary diffusion in the alloy is rate determining. In the second a more rapid growth of an Fe2O4 oxide is found, subsequently followed by slower kinetics as a Cr2O3 layer again forms. No discernable relationship between oxidation rates and either pressure or temperature is found.

The influence of surface oxide composition and structure on carburization in carburization in carbon monoxide – carbon dioxide

AbstractThe oxidation and carburization of two 20 Cr 30 Ni alloys with nominally 0 and 0.5 wt % Si have been investigated by cyclic exposure to carbon monoxide and carbon dioxide at 1000°C.In carbon monoxide a chromium oxide film is formed which inhibits further carbon deposition. In carbon dioxide an iron chromium oxide of the spinel type is formed which during subsequent exposure to carbon monoxide acts as a catalyst for carbon deposition. In some areas a breakthrough of the initially formed chromium oxide layer occurs during carbon dioxide treatment. Extensive carbon penetration takes place in these breakthrough areas.The spinel formation and the breakthrough is retarded in the silicon‐containing steel owing to the formation of a thin continuous silica layer at the metal‐chromium oxide interface. This has a beneficial effect on the carburization resistance.The results also imply that it is possible to lower the catalytic effect of the tube material on carbon deposition or even on coke formation by controlling the surface oxide composition and structure.

Investigation of composition of surface oxides of molybdenum by the method of secondary ion-ion emission.: V Ya Kolot et al,Izv AN SSSR S

Investigation of composition of surface oxides of molybdenum by the method of secondary ion-ion emission.: V Ya Kolot et al,Izv AN SSSR S