Melting line of calcium characterized by in situ LH-DAC XRD and first-principles calculations

In this work, the melting line of calcium has been characterized both experimentally, using synchrotron X-ray diffraction in laser-heated diamond-anvil cells, and theoretically, using first-principles calculations. In the investigated pressure and temperature range (pressure between 10 and 40 GPa and temperature between 300 and 3000 K) it was possible to observe the face-centred phase of calcium and to confirm (and characterize for the first time at these conditions) the presence of the body-centred cubic and the simple cubic phase of calcium. The melting points obtained with the two techniques are in excellent agreement. Furthermore, the present results agree with the only existing melting line of calcium obtained in laser-heated diamond anvil cells, using the speckle method as melting detection technique. They also confirm a flat slope of the melting line in the pressure range between 10 and 30 GPa. The flat melting curve is associated with the presence of the solid high-temperature body-centered cubic phase of calcium and to a small volume change between this phase and the liquid at melting. Reasons for the stabilization of the body-centered face at high-temperature conditions will be discussed.

Phase equilibria and salting out of butyric acid in the ternary system potassium nitrate + water + 2-(2-butoxyethoxy)ethanol

Visual polythermal method in the bynary system of water-2-(2-butoxyethoxy) ethanol in the range of –25÷0° C the ice melting line is determined and the phase equilibria in the ternary system potassium nitrate–water–2-(2-butoxyethoxy) ethanol are studied in the range of 10.0–90.0° C. The ice melting line in the water–2-(2-butoxyethoxy) ethanol binary system is a flat, smooth line. This form of the melting line shows a hidden separation in liquid mixtures. It has been found that potassium nitrate salts out 2-(2-butoxyethoxy)ethanol from water-organic mixtures, and at 31.7° C in the ternary system of potassium nitrate–water–2-(2-butoxyethoxy)ethanol, separation begins. The compositions of the solutions corresponding to the critical solubility points at several temperatures have been determined. The isothermal phase diagrams of the ternary system at 10.0, 25.0, 30.0, 31.7, 35.0, 50.0, 90.0° С have been plotted. The distribution coefficients of 2-(2-butoxyethoxy) ethanol between the liquid phases of monotectic state have been calculated. It is shown that the effect of salting-out 2-(2-butoxyethoxy) ethanol from aqueous solutions with potassium nitrate increases with increasing temperature. The concentration of 2-(2-butoxyethoxy) ethanol in the organic phase of monotectics at 90.0° C is 90 wt.% with a distribution coefficient of 897.

Thermodynamics, dynamics, and structure of supercritical water at extreme conditions

Molecular dynamics (MD) simulations to understand the thermodynamic, dynamic, and structural changes in supercritical water across the Frenkel line and the melting line have been performed.

In situ characterization of the high pressure – high temperature melting curve of platinum

In this work, the melting line of platinum has been characterized both experimentally, using synchrotron X-ray diffraction in laser-heated diamond-anvil cells, and theoretically, using ab initio simulations. In the investigated pressure and temperature range (pressure between 10 GPa and 110 GPa and temperature between 300 K and 4800 K), only the face-centered cubic phase of platinum has been observed. The melting points obtained with the two techniques are in good agreement. Furthermore, the obtained results agree and considerably extend the melting line previously obtained in large-volume devices and in one laser-heated diamond-anvil cells experiment, in which the speckle method was used as melting detection technique. The divergence between previous laser-heating experiments is resolved in favor of those experiments reporting the higher melting slope.