Abstract
The phase diagram and specific electrical conductivity of fused salt systems ZnCl2-SnCl2, ZnCl2-NH4 Cl and ZnCl2-SnCl2⋅2H2O, which are used generally as flux in soldering, were measured to clear a relation between the structures of these mixed salts and the spread area of Pb-Sn eutectic solder on copper base plate.The results obtained were as follows:1) The diagram of ZnCl2-SnCl⋅2 system is a simple eutectic with no solid solution, and ZnCl2-NH4Cl system forms a intermediate compound formation with two simple eutectics. It seems the diagram of ZnCl2-SnCl2⋅2H2O system is a intermediate compound formation type.2) The dissociation of ZnCl2-SnCl2 system was presumed as follows from the basis of J.D. Mackenzie theory on single zinc-chloride;3ZnCl2→ZnCl64-+2Zn, 2+, SnCl2→Sn22++2Cl-3) Isotherms of specific conductivity of ZnCl2-SnCl2 system deviate negatively from additivity when plotted against composition, and three partial negative deviations were found near the compositions of two eutectics and a intermediate compound in ZnCl2-NH4Cl system at just above liquidus temperature for each.4) The transition temperature obtained from temperature.dependence of activation energy for electrical conductivity of ZnCl2-SnCl2 or ZnCl2-NH4Cl systems coincided with the temperature required for good spreading of the solder on copper plate, using these systems as flux. This result showed that an effective action temperature range of flux is from the liquidus to the transition temperature of itself and, therefore, a recommendable soldering temperature is limitted by these temperatures of flux to be used generally.5) Th flux action of ZnCl2-SnCl2⋅S2H2O system could be explained as follows;SnC-l2⋅2H2O→SnCl2+2H2OZnCl2+H2O→Zn(OH)Cl+HClCuO+2HCl→CuCl2+H2OAlthough two equations of the latter were presented by H.H.Manko, the H2O produced by the dissociation of SnCl2⋅2H2O during heating reacts with ZnCl2 and forms HC1. The HO and SnCl2 act as flux in soldering of the range 180-350°C, and no SnCl2⋅2H2O acts as flux in the form of itself.
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