The Pressure-Temperature Phase Diagram of Na-K Alloys and the Effect of Pressure on the Resistance of the Liquid Phase

Abstract

By determining the pressures at which discontinuities occur in resistance isotherms of mixtures sodium and potassium in various proportions, it has been possible to map out the phase diagram of the binary system Na-K as a function of pressure, temperature and composition. The pressure range is 10,000 kg/${\mathrm{cm}}^2$, and the temperature range from 0° to 150°. The results are presented in two diagrams. The composition of the eutectic in the subsystem (solid Na-solid ${\mathrm{Na}}_2$K-liquid) is almost independent of pressure over the range, whereas the composition of the eutectic (solid K-solid ${\mathrm{Na}}_2$K-liquid) moves from about 67 atomic percent K at atmospheric pressure to 59 percent at 10,000 kg/${\mathrm{cm}}^2$. The rise of melting temperature with pressure is markedly less for the alloys than for the pure metals: the rise of melting temperature for the first eutectic mentioned above produced by 10,000 kg/${\mathrm{cm}}^2$ is 42°, against 68° for pure sodium. The corresponding figures for the second eutectic are 42° against 105° for pure potassium. In addition to the phase data, some results are given for the relative resistance of the liquid alloys as a function of pressure.