The effect of impurities on the β → α transformation process in tin

Abstract

This article presents data on the impurities influencing the , ! ? 4 a transformation of high purity tin (99.9995%): temperature of the a ~, 9 transition-To, nucleation and acrystal growth. A detailed discussion of the problem of the nucleation and a-crystal growth of highpurity tin (99.9995% Sn) was given in a previous review (LARIKOV, BRICE). This article deals with the question of impurities influencing some parameters of the j3 -+ OL transforniation of high-purity tin. B HacTomueik pa6ol.e npencTasneHHThe data on the impurity effect on the process of the p -a transformation of tin obtained for up to -60 "C are put together in the reviews by BUSCH, KERN, BY-KHOVSKY. Supplementary information concerning this problem may be found also in the work of LOHBERG, PRESCHE ; MACINTOSCH. On the whole, the data on the effect of impurities on the p + a transformation of tin may be divided into three groups: those concerning the effect of impurities on the p a transition temperature, on the formation of the a-Sn nuclei and on the growth rate of the a-Sn crystals. polymorphic transformation To, there are essential disagreements in literature. Thus, COHEN and EIJK give the values of 20" and 18 "C; COHEN, DECKER give 12" to 14.3 "C (see reviews by BUSCH and BYKHOVSKY). Further, RAYNOLD, SMITH established for 99.997% pure tin with lead as the main impurity (0.003~0 Pb) that To = 13.2 "C; if the main impurity is iron then To = 10.4 "C. As it was noted already, the last determination of To = + 1.5 "C was made for 99.9995% purity tin (BYKHOVSKY, LARIKOV, FALCHENEO). The given result implies that the presence of small amounts of impurities leads, as a rule, to To increase.The question about the effect of impurities on the rate of the a-Sn centre nucleation under the j3 -+ a transformation of tin was considered in many works.It should be noted, first of all, that similarly t o deformation (CEERTOCK; LOHBERO, PRESCHE) of semiconducting compounds such as InSb, CdTe isomorphic t o tin, lead to the essential shortening of the incubation period preceding the appearance of the a-Sn nuclei, that is, bring to the acceleration of the j3 --t a transformation of tin (GORYUNOVA). There are also data which show that the particles of the second phase, crystallized from the supersaturated solid solution a t low temperature, accelerate the nucleation and , ! l -+ OL transition on the whole (ROGERS, FYDELL).The effect of soluble impurities on the nucleation and growth of the centres of a new phase is determined by the character of their distribution, that is, the effect As to the temperature of the oc 10