The structures of glassy and molten states in the PbO–SiO2 system were investigated by X-ray diffraction analysis. In the glass, the Pb–O bond has the ionic charactor in the SiO2-rich region and has more of the covalent charactor with increasing PbO concentration. The atomic distance of Pb–Pb pair, 0.375 nm, is not changed with changing PbO concentration, and Pb atoms are considered to be arranged with local order in the glass. The Pb–Pb peaks in the SiO2-rich region correspond roughly to multiples of 0.374 nm, and Pb atoms seem to be arranged in a simple and straight chain. However, the arrangement probably tends to consist of twisted and zigzag PbO4 chains with increasing PbO concentration. In the molten state, a part of the three-dimensional network structure of covalent Pb–O bond seems to be destroyed and, the concentration of Pb2+ ion which is free in the melt increases. Then Pb–Pb pairs with the distance around 0.50 nm increase due to increase in straight chains such as ionic Pb2+–O2−–Pb2+ which hardly exist in the glass.
The interdiffusion coefficients in the α-phase of Cu–Al–Zn alloys \ ildeDZnZnCu, \ ildeDZnAlCu, \ ildeDAlAlCu and \ ildeDAlZnCu have been determined by an extended Boltzmann-Matano method in a temperature range from 1043 to 1203 K. All of the four interdiffusion coefficients are positive, and they are very sensitive to the solute concentration. The activation energies for the interdiffusion of the ternary alloys are similar to those for the tracer diffusion of Cu–Al and Cu–Zn binary alloys. Large positive interaction parameters εZn(Al) and εAl(Zn) indicate that Al and Zn atoms in the Cu–Al–Zn alloys have repulsive force between each other.
In order to check conventional results obtained by the traditional experimental methods, the concentration and temperature ranges of the miscibility gap are closely examined by Mössbauer spectroscopy. The present result does not support the earlier Williams’ result that the upper limiting temperature of the miscibility gap is about 830 K, but proposes that it is about 950 K. The proposed miscibility gap is well expressed by the regular solution treatment on the whole, and lies over the concentration range from 10 to 86 at%Cr at low temperatures around 750 K.
The concentration and temperature dependences of the incubation time, the analysis of the transformation rate based on the Johnson-Mehl equation, and the time evolution of the Mössbauer spectrum suggest that the nucleation and growth process plays a dominant role in the phase decomposition of Fe–Cr alloys around 748 K in the concentration range from 21 to 36.3%Cr. The spinodal decomposition becomes predominant in the concentration range from 42 to about 60%Cr. The decomposition mode shows a gradual transition from the nucleation and growth to the spinodal decomposition with increasing Cr content.
The kinetics of the oxidation reaction of As(III) with dissolved molecular oxygen in alkaline solutions was investigated. The oxidation rate of As(III) obeys the equation, R=k2′·CAs(III)·pO2·aMOH, in aqueous NaOH and KOH solutions. The principal rate determining step in this oxidation reaction appears to be a chemical reaction process. Support of this analysis lies in an apparent activation energy of 73.2 kJ·mol−1 and reaction rates independent of the agitation speed. The oxidation rates of As(III) increased in various alkaline solutions according to the sequence of KOH<NaOH<LiOH. This sequence coincides with the amount of free water available in the solutions. Also, the accumulation of As(V) tends to suppress the reaction slightly.
The kinetics of the oxidation of As(III) with oxygen in alkaline solutions in the presence of Cu(II) was studied. The oxidation reaction of As(III) proceeds via two different pathways, one dependent on and the other independent of pO2. The former pathway is influenced by the concentration of alkali, showing a suppressed tendency with the increase in alkali concentration. On the other hand, the latter is independent of the concentration of alkali. The dependences of the two pathways on the concentration of Cu(II) appear to be different from each other. The experimental rate equation was found to be (Remark: Graphics omitted.) The apparent activation energy is 105.3 kJ·mol−1 for the former pathway and 21.3 kJ·mol−1 for the latter. The reaction rate is affected by the presence of alkali in the solution, exhibiting an accelerating tendency according to the sequence of LiOH<NaOH<KOH.
The diffusion problems in the desorption process of an element through both grain boundary and bulk of a thin plate was solved on the basis of finite thickness model. A grain boundary was assumed to be a high-diffusivity plane perpendicular to the plate. Concentration profiles in the plate as a function of desorption time were calculated for the cases in which the diffusing element was distributed uniformly in the plate and was concentrated in a grain boundary as an initial condition. The grain boundary segregation of the latter case was also considered. Further the application of the calculation model to the oxygen desorption of molybdenum was examined. The oxygen diffusion through the grain boundary of molybdenum was successfully explained by the segregation model.
An investigation was carried out on the grain refinement of Al–Cu alloys containing 4, 10 and 24 mass%Cu by the vacuum superstircasting with high rotation speeds of a stirrer up to 23 rev/s applied during solidification under continuous furnace cooling. The size of primary solid particles in these alloys consistently decreases, the grain structure becomes fine and the crystal morphology changes from rosette type to spherical type with the increase in rotation speed from 13 to 23 rev/s. The minimum size of primary solid particles at 23 rev/s is 133±32 μm in Al-4%Cu, 124±44 μm in Al-10%Cu and 120±51 μm in Al-24%Cu alloy. It is thus expected that the mechanical grain refinement during solidification of the alloy can be established by high rotation of a stirrer inserted in the solid-liquid coexisting zone of the alloy, since the dendrites formed are destroyed into non-dendritic primary solid particles by shearing operation with the rotation of the stirrer. The coarsening of primary solid particles (grain growth) under fluid flow is theoretically evaluated on the basis of the experimental results to determine the mixing diffusivity.