Institute of Metal
Physim of the Academy of Sciences of the Ukrainian SSR, Kiev The Effect of Impurities on the P + a Transformation Process in Tin 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. B HacTomueik pa6ol.e npencTasneHH AaHHMe o BJIHHHHU npuMeceB Ha fl --* a npeBpaweme onoBa BbIcoKoB ~U C T O T H (99,99950/): TeMnepaTypy a z B nepexona-To, a a p o m n e ~~~e EI POCT HpHcTannoB a-Sn.
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.
The data on the impurity effect on the process of the pa 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.