Kichizo Niwa

STUDIES ON DIFFUSION IN MOLTEN METALS

Diffusion coefficients in molten metals were measured for Sn-Pb, Bi-Pb, Sb-Pb, Cd-Pb, Sn-Bi, and Sb-Sn from 450° to 600°C. Since the observed activation energies of these metals in the liquid state were found to be of the same order as those for nonmetallic solutions, the diffusing substance may be small particles such as metal ions. For Pb-Sn, Pb-Bi, and Sn-Bi, the concentration dependences of diffusion coefficients were determined at about 500°C. The results show that the relations between diffusion coefficients and atomic fractions obey the thermodynamic formulas of irreversible processes. For a ternary system, Pb-Sn-Bi, the diffusion coefficient of tin decreases as bismuth is added. This effect has been explained in thermodynamic terms.

Electron diffraction study of flake graphite extracted from molten pig iron

Single graphite flakes segregated from molten carbon or silicon-rich iron at 1200° to 1500°C were subjected to electron diffraction experiments. The results indicated that the well developed thick flakes are composed of one single crystal, while the thin almost colorless flakes consist of two or three single crystals oriented with the basal plane parallel to the flake surface and rotated at an angle of 15°, 18°, 22°, 25° or 28° about the C-axis. The stacking of the atomic layers in each single crystal indicates that they are α and β-type, or a more disordered structure, at each instant. Double diffraction evidence and additional electron microdiffraction observations showed that the thin single flake has an aggregate structure with two close-packed single crystals.