Abstract
When the metals do not make a solid solution all over the range of compositions, the nature of diffusion is very much complex. The following phenomena observed seem, therefore, to be somewhat noticeable.
1) Diffusion phenomena between pure Cu and Zn: The foils composed of many layers of the two metals were made by alternate electroplating. The change of the electric resistance caused by heating these specimens in a vacuum furnace presented a maximum and minimum values at a certain point (Fig. 1, 2 and 3), which was understood as follows; at the beginning of diffusion, there were produced α and β-phases together, and then developed β-phase only, after that β-phase changed gradually to α-phase, and finally becomes chiefly α-phase. The processes were ascertained by the X-ray photographs taken by the back reflection method (Fig. 4).
2) Evaporation of Zn from Zn-Cu alloys: A piece of alloys was heated in vacuum at a certain temperature, and the change of its weight was measured as a function of time. The fact denoted by Dunn that the amount of Zn evaporated varies as the square root of the time, is recognised during a comparatively short time. The X-ray examination of the surface showed that the β-phase loses at first Zn, then α-phase and finally the surface becomes a pure Cu layer as seen in Fig. 6.
3) Diffusion phenomena between Cu and Zn-Cu alloys: A thin Cu plate was pressed against the surface of a block of Zn-Cu alloy, and heated at various temperatures. The each surface of contact was examined with X-ray method; for the Cu surface, there was produced the α-phase which increased step by step (Fig. 8 A), and for the alloy surface there appeared unexpectedly β-phase which vanishes gradually and changed into entirely of α-phase (Fig. 8 B).
