Journal of Applied Physics · 1981 · 10 citations · 2 references
Natural SciencesChemistryMaterials ScienceMagnetic MaterialsSurface ChemistrySurface ScienceFerromagnetic MaterialsIron OxidesMineral Surface ChemistryPowder ProcessingSurface AdsorptionSurface OxidationCeramic PowdersFerrous AlloysImpuritiesIron StabilityOxygen Content AnalysisPowder CharacterizationSurface AreaSurface Area Characterization
Iron powders with Hc between 350 Oe and 1000 Oe were prepared by borohydride reduction of ferrous sulfate. The powders were stabilized by a chromating procedure. This paper discusses the effect of the chromating as observed by: TEM, changes in surface area, O2 content, ESCA/Auger and adsorption. Chromating coats the surface of the particles with a layer of FeCr2O4. Oxygen content in chromated powders is generally ∼8% while in the unchromated powders, it varies between 11 and ≳16%. This increase in O2 can be correlated with a decrease in σs. Sheet-like impurities are observed in unchromated powders which have been identified as FeOOH. Chromating results in a reduction in surface area of the particles as measured by N2 adsorption. The stability of the powders is greatly improved with chromating. Powders subjected to 80% R.H. for 112 days showed that the unchromated powder lost 25% of its original magnetization, while the chromated powder lost only 3%. Simultaneously, a band of FeO and Fe2O3 formed around the particles. Adsorption studies of reference polymers have shown that chromating reduces the acidic surface sites of the powders.
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