Investigation of solders surface tension in temperature range from melting point up to 673К
Résumé
Solders are fusible metal alloys, used in industry to create permanent bond between metal surfaces. In order to achieve this, solders need to be heated above their melting point and used in liquid phase. Low melting temperature is essential from technological point of view, as well as for soldered components safety. Typical solders have Lead (Pb) аs а base component, having melting temperature of 600.6 K. Adding up to 60% of Tin (Sn) to the alloy, reduces melting temperature down to 456-461 K in average. Since 2006, RoHS regulation enforce industrial use of Lead-Free solders, typically having much higher melting temperature. However, Pb:Sn solders with up to 40% Sn still have their industrial applications, usually used for soldering Cu and Zn coated pipes while the 60% Sn containing solders are used for soldering of electrical cables. The achieving of these goals requires knowledge of liquid phase surface tension. Because of the difficulties, related to such measurement, the available data in literature are limited. The current report presents an equipment for measurement of the surface tension, based on the Wilhelmy plate method as well as the applied measurement procedure. The Wilhelmy method has relatively good stability. The contact angle also can be considered zero for the examined samples therefore correction coefficients are not required for the measurement. The results from measurement of Pb:Sn in ratio 40:60 and also in ratio 60:40 show that the oxidation in excess of Pb lowers the surface tension while for the case with excess of Sn, the oxidation lead to increase of the surface tension if compare with the surface tension obtained for the same solders but under non-oxidizing conditions. This could be attributed to formation in excess of PbO and SnO on the liquid surface of the corresponding solder.