Growth of zinc platelets on zinc single crystals under diffusion conditions

Abstract

The surface morphology of zinc platelets on zinc single crystals in the presence of hydrogen or argon is investigated. Platelets appear only on the pyramidal and prismatic faces and not upon the basal face of the zinc single crystals. It is shown that the smooth basal faces of the platelets change their shape in skeletal. The results are discussed and are in conformance with Chernov's theory for the disturbance of the morphological stability of crystal forms. The kinetics of growth of platelets on the pyramidal {1 0 1¯ 1} and prismatic {1 0 1¯ 0} faces of zinc single crystals and the alteration with time t the edge length a of the {0 0 0 1} basal face of the same crystals in the presence of argon were studied. The results of measurement of the edge a with time show that at the moment when the critical size a k is reached, the transition from kinetic to diffusion regimes starts. The comparison between the time when the visible platelets appear on the zinc crystals and the a 2 vs. t curves revealed that the first platelets grow exactly at the transition between the two regimes. It has been established that during the initial stage, when the size L is small, the platelets grow at a constant rate. During further growth, as the size L increases and reaches the critical dimension L k , a change in the L 2 vs. t curves appear: the linear curve is transformed into parabolic one. In conformance with the morphological theory of Chernov in the isotropic case, it is concluded that the platelets grow in a kinetic and a diffusion regime. During the growth of the platelets, part of them after reaching a certain thickness terminate their growth. The termination of the frontal growth is probably related to the transformation of their atomically rough surfaces into flat faces. The kinetic investigations led to the conclusion that part of the platelets do not grow following a screw dislocation mechanism. The observed transformation of triangular platelets into trapezoidal suggests that their frontal faces are atomically rough. The growth of the trapezoidal platelets is discussed and explained by a normal mechanism, while the growth of triangular platelets is attributed to a screw dislocation growth pattern.