A simplified model for evaluation of hot-pressed silicon nitride (HPSN) has been derived which accounts for the amount and type of grain boundary phase and for the composition at the Si3N4/oxide reaction interface. The model proved suitable for explaining the oxidation behaviour of a wide range of materials including MgO, CeO2, (CeO2 + SiO2), (Y2O3 + SiO2), (MgO + Y2O3) additives. Some deductions are also possible on how to improve the oxidation resistance of HPSN.
Working on the basis of a theoretical equation for the surface tension of liquids recently deduced by Mon and Stroud, a semi-empirical relationship was obtained between this quantity and the isothermal compressibility which, through the performance of several approximations, will embrace some widely published relationships as special cases. The results agree satisfactorily with experimental data for the most characteristic simple liquids.
Change in the corrosion resistance of amorphous alloys FeNiBP due to the improve in chromium content (0 to 14 atome %) has been investigated in 0.1 N H2SO4: the higher the chromium content, the lower the corrosion current density and the higher the corrosion potential.
The alloy containing 10 at % chromium shows spontaneous passivation.
In the temperature range 20–83°C, the activation energies of the active and passive currents have been estimated from the slope of the Arrhénius plots.
CdGa2O4, CoGa2O4 and six mixed spinels CdxCo1−xGa2O4 (x = 0.1, 0.15, 0.25, 0.50, 0.75 and 0.85) were synthesized, in polycrystalline form, by solid state reaction at 1273 K between CdO and Ga2O3 impregnated with cobalt nitrate in the desired proportions. By means of X-ray diffraction analysis, the lattice parameter, a0, oxygen parameter, u, and cation distribution for each spinel were determined. a0 was found to increase continuously from 832.8 pm for x = 0 up to 860.1 pm for x = 1. The u-parameter also increases, along the same composition range, from 0.386 up to 0.392. Cation distribution in the mixed spinels was found to be dependent on composition. In particular, it is seen that the presence of Cd2+ enhances the relative octahedral preference of Co2+, and the tetrahedral preference of Ga3+.
The occurrence of lead on copper underpotential effects is dependent on concentration of ethylenediamine and acetate ions in the solution and also on solution pH. The cause of variations in intensity of occurrence of underpotential effects is the change in the state of chemical stability of the system Cu(111)/Pb+2 + CH3 COO− + ethylenediamine + H+.
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