A new investigation of the system Ni–P

The binary system Ni–P is one of the constituents of the ternary system Ni–P–Sn which provides the basic knowledge for understanding the interactions between Sn-based solders and common Ni(P) metallization. In this study a new version of the Ni–P phase diagram was established based on XRD, EPMA and DTA measurements. The present diagram differs in some important details from the literature version. For the phases Ni5P2 high temperature (HT) and Ni12P5 HT the existence of a considerable homogeneity range is proposed. In Ni5P2 the transformation between HT and low temperature (LT) modification comprises a peritectic and a eutectoid reaction, whereas for the transition in Ni12P5 two eutectoids are proposed. Unfortunately, the high temperature phases cannot be stabilized by quenching, so that all data have to rely on the results of thermal analyses. Furthermore, Ni5P4 was found to be formed by a peritectic reaction, and a eutectic was observed between Ni5P4 and NiP. The phase NiP1.22 that had been reported in the literature could not be found at all. Although the experimental work was complicated by the high vapor pressure of phosphorus at P concentrations higher than 40 at.% (which caused the explosion of quartz tubes and prevented the preparation of equilibrium samples at higher temperatures), it could still be shown that the phase NiP3 is probably stable down to room temperature in contrast to the literature reports.