The heat of formation of the single-phase NiSn electrodeposit

Abstract

The heat of formation of tin-nickel electrodeposit was measured by solution calorimetry. A single phase obtained between 47·5 and 60·3 at.% Ni had a heat of formation (at 298 K) best represented as a linear function of composition. The constant partial molar enthalpies were, for nickel, −11·6 kJ/g atom, and for tin, −47·4 kJ/g atom; the estimated error is 5% or more. The alloy, not a phase appearing in the accepted phase diagram, decomposes slowly above 575 K with a small positive enthalpy change for the reaction considered at 298 K. It can be argued that the alloy is in fact a phase stable at its usual temperature of formation 340 K. The volume change on formation of the alloy is constant within the single-phase composition range and is numerically quite large (−1·3±0·1 cm3/g atom at 298 K). It is believed that this is the first study made of an alloy intermetallic compound which can only be prepared at relatively low temperatures.