MOTION OF MARKERS AND BUBBLES IN SOLIDS BY SELF-DIFFUSION IN A TEMPERATURE GRADIENT

In a pure substance a temperature gradient gives rise to a current of atoms relative to the lattice planes. This current is compensated by the motion of lattice planes in the end face system. It is shown that markers or bubbles are not fixed to the lattice planes in the case of a free surface boundary condition. Thus such markers do not indicate the motion of lattice planes as was formerly supposed. Another mechanism for the motion of such markers is therefore proposed: the disturbance of the temperature gradient in the vicinity of the marker generates an uncompensated current of atoms, which causes the marker migration. The velocity of elliptical markers can be calculated analytically. The calculation is carried out for spherical bubbles in metals and ionic crystals. Spheres are found to be an equilibrium form of moving bubbles. Copyright © 1968 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim