The internal oxidation of a two-phase at.% Se alloy in pure oxygen was studied at 750, 800 and 830 • C. The alloy is composed of a dilute solid solution of selenium in silver) and Ag 2 Se intermetallic particles. The internal oxidation of this alloy proceeds through gradual in-situ oxidation of the Ag 2 Se particles as well as through diffusive internal oxidation of selenium from solid solution. Gradual in-situ internal oxidation of Ag 2 Se particles reflects itself in the appearance of two internal-oxidation fronts, inner and outer, marking the beginning and end of the in-situ oxidation of Ag 2 Se particles. The oxide phase formed during in-situ oxidation is the molten double oxide, Ag 2 SeO 3 . A theoretical treatment of the phase relationships in a hypothetical Ag-Ag 2 Se-Ag 2 SeO 3 ternary phase diagram is presented to assist the explanation of the mechanism of in-situ oxidation. The kinetics of oxidation are presented in Part II.KEY WORDS: silver-selenium alloy; Ag 2 Se in-situ oxidation; Ag 2 SeO 3 ; internal oxidation of two-phase alloys.
AbstractAmelogenesis imperfecta (AI) is an inherited tooth disorder with widely varying phenotypes. The aim of this study was to determine the microhardness and microstructure characteristics of the enamel in AI teeth. The AI phenotypes examined were hypoplastic (pitted and smooth form), hypomaturated, and hypocalcified. Six AI patients were diagnosed according to clinical characteristics. The microhardness of the enamel was measured on axial cuts of AI teeth acquired from the patients. The measurements were done on several sites from the enamel surface towards the dentine-enamel junction using the Vickers scale. Values of microhardness were compared to corresponding control teeth. The microstructure of AI enamel types was evaluated using scanning electron microscopy. The values of microhardness in pitted hypoplastic AI samples were, on average, lower compared to the control enamel and dropped markedly towards the dentine-enamel junction. The smooth hypoplastic enamel was not only extremely thin but also much softer than control enamel. The values for hypomaturated AI fluctuated, but the palatal sites were markedly softer than in the control tooth. Hypocalcified enamel was the softest, with values resembling those of dentin. Microstructural changes varied from altered orientation of enamel prisms in pitted hypoplastic AI to lack of normal prismatic structure and severe porosity in hypocalcified AI. The present results suggest different microhardness profiles and microstructures in each phenotype. Variations among phenotypes are expected with larger case selection in this genetically heterogeneous disease.
A soft magnetic composite material was prepared from a commercial, iron-based, soft magnetic powder. Its morphology and composition were examined using SEM, EDS and AES. The flat surface of the sample was found to be of a homogeneous composition, corresponding to the basic soft magnetic powder, whereas phosphorous and zinc were found in the subsurface layers of the sample. These were accessed and probed through the pores in the sample surface. AES and XPS analyses was also performed on non-compressed soft magnetic powder particles, yielding phosphorous compounds.
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