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Updated: Jul 7, 2026

Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials
Published on: May 15, 2015
High-pressure melting curve of nitrogen and the liquid-liquid phase transition
Goutam Dev Mukherjee1, Reinhard Boehler
1Max-Planck-Institut für Chemie, Hochdruckmineralphysik, Postfach 3060, D-55020 Mainz, Germany. gdm@mpch-mainz.mpg.de
Abstract:
The melting curve of nitrogen was measured up to 71 GPa, a fourfold increase in pressure over previous measurements. The measurements were made using the laser-heated diamond anvil cell and melting was detected in situ by the laser speckle method. The melting temperature rises linearly up to a maximum at 50 GPa and 1920 K, and with increasing pressure suddenly decreases linearly to 1400 K at 71 GPa. This sharp drop in the melting slope (dT/dP) above 50 GPa indicates the appearance of a liquid denser than the solid and of a liquid-liquid phase transition. The sharpness of the changes suggests that the transition is first order and is a liquid-liquid polymer transition. This conclusion is consistent with earlier theoretical studies and experimental evidence that pressure transforms molecular nitrogen into a chainlike polymeric form.
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