Characterization of metal precipitates in magnesium oxide

A method, based on subtractive coloration or high-temperature reduction, has been developed to produce metal precipitates or colloids in oxides. The structure, symmetry, morphology and composition of precipitates were analysed by analytical electron microscopy and neutron scattering techniques. In the MgO: Ni system, the colloids were coherent nickel precipitates having a f.c.c. structure (ao = 3·52 Å), and occasionally a b.c.c. structure (ao = 2·88Å). The coherent precipitates were found to have either ⟨100⟩m‖⟨111⟩p or ⟨100⟩m‖⟨100⟩p matrix-precipitate relationship, depending on the high-temperature reduction treatment. From the neutron-magnetic-scattering measurements, the ratio of magnetic to nuclear scattering amplitudes for the (111) precipitate reflection was determined to be 17% below the value for pure nickel, indicating the presence of a magnetically ‘dead’ layer around the precipitates, a small amount of impurities incorporated into the precipitates, or a small fraction of another phase of nickel.