Melting curves of lithium, sodium, potassium, and rubidium to 80 kilobars

The melting curves of lithium, sodium, potassium, and rubidium have been determined to pressures of 80 kb. The experiments were carried out in modified single-stage piston-cylinder apparatus, and the precision of the data is ±2°. Rather sharp changes in the slopes of the melting curves are shown for lithium, potassium, and rubidium at pressures of approximately 60 kb, and little change in melting temperature for those substances takes place between 60 and 80 kb. This abrupt flattening of the melting curve may represent maxima in the fusion curves analogous to that previously discovered for cesium. The curve for sodium is regular and increases to the highest pressure obtained. Within the precision of available experimental data on compression of the alkali metals, melting temperatures of all these alkalis are linear, with the volume of the melting solid up to breaks in slopes of the curves at approximately 60 kb, for lithium, potassium, and rubidium. The melting curve of sodium is linear with the volume of the melting solid to 80 kb. The breaks in slopes of the fusion curve probably associated with maxima in potassium, rubidium, and cesium take place when the solids have undergone a total compression of approximately 35%, whereas the break in slope of the lithium curve takes place at a total compression of approximately 22%.