Eliezer Rapoport

Model for Melting‐Curve Maxima at High Pressure

A two‐species model for the liquid proposed by Klement in order to account for the existence of high‐pressure melting‐curve maxima is further examined from the point of view of the theory of regular solutions. Equations for the concentration of the two species as a function of pressure and temperature are derived. A survey of structural data on liquids provides positive evidence for the existence of two species in the melts of some pure substances.

Phase Diagrams of H2O and D2O at High Pressures

The VIII/VII phase boundaries of solid H2O and D2O were studied by means of differential thermal analysis. The thermal hysteresis of the transition decreases with increasing pressure, but the presumed equilibrium temperatures are independent of pressure to 40 kbar. The transition is of the first order, and the average transition temperature is −3°C in both cases. The ice VI/VII transition pressure at 25°C is 21.39 ± 0.05 kbar, in good agreement with other recent studies, but considerably lower than Bridgmans value. The heavy ice VI/VII and VI/VIII transition lines are located ∼1.4 kbar below the ice VI/VII and VI/VIII transition lines. The heavy ice VI/VII transition at 25°C occurs at 19.90 ± 0.07 kbar. Bridgmans melting curves of ice VI and ice VII are shown to be correct. The melting curve of heavy ice VI is ∼2°C above that of ice VI, but the heavy‐ice VI/VII/liquid triple point is located at 78°C, 20.6 kbar as compared with 81.6°C, 21.97 kbar for H2O. The melting curve of heavy ice VII appears to hav...

Phase Diagrams of Sodium Nitrite and Potassium Nitrite to 40 kbar

The phase diagrams of NaNO2 and KNO2 were determined to 40 kbar. The NaNO2 phase diagram consists of five solid phases and the liquid. The ferroelectric Curie point (the III—II phase transition) and the Neel point (the I—II transition) were detected by differential thermal analysis (DTA) and determined to 40 kbar. The results are in good agreement with the work of Gesi and his co‐workers to 10 kbar. Points on the III—IV boundary were determined by the volume‐discontinuity method. The transition manifests itself as a break in the slope of the compression curve of NaNO2 and seems to be a second‐order transition. The transition pressures are lower than those estimated previously. The melting curve increases with pressure. A new high‐pressure solid‐phase, NaNO2 V, wad discovered. The I—V phase boundary branches off the melting curve at the liquid—I—V triple point at 9.8 kbar and 343°C.The KNO2 phase diagram consists of six solid phases and the liquid. The I—II and IV—V phase boundaries, determined by DTA, ris...

Melting‐Curve Maxima at High Pressure. II. Liquid Cesium. Resistivity, Hall Effect, and Composition of Molten Tellurium

Hall effect and electric‐conductivity data for liquid tellurium are analyzed by means of the two‐species model. Liquid tellurium is proposed to consist of two species, the normal form and another, metallic, form similar to one of the high‐pressure phases of tellurium. The analysis yields a value for the interaction energy w which explains the irregularity in the high‐pressure melting curve reported by Stishov, Tikhomirova, and Tonkov. Isoconcentration lines in the p‐T plane are constructed for liquid tellurium and also for liquid cesium.

High-pressure phase relations of RbH2PO4, CsH2PO4, and KD2PO4

Abstract The phase diagrams of RbH2PO4 (RDP), CsH2PO4 (CDP), and KD2PO4 (DKDP) have been determined to ∼40 kbar. Attempts are made to correlate the present phase diagrams with that of KH2PO4 and determine which phases are isostructural. The large isotope effect found for KD2PO4 is in agreement with the isotope effects in H2O, D2O.

Phase Transformations and Melting in KH2PO4 to 40 kbar

The phase diagram of KH2PO4 was determined to 40 kbar by differential thermal analysis. New phase transitions were found, and the diagram consists of six solid phases and the liquid. Dehydration of KH2PO4 above 200°C is suppressed by pressure, and the melting curve was successfully determined to the highest pressure.

Unsymmetrical Friction and Pressure Calibration in Internally‐Heated Piston‐Cylinder Type High‐Pressure Devices

It is shown that the procedure of evaluating pressure losses in internally‐heated piston‐cylinder devices by assuming symmetrical friction is in error below ∼500°C. Previous results may be in error by as much as ∼5 kilobars at 40 kilobars and 25°C. A method of calibration is described which evaluates such unsymmetrical pressure losses.

Melting and Polymorphism of Potassium Cyanide and Thiocyanate to 44 kbar

The phase diagrams of KCN and KSCN were studied by means of differential thermal analysis. Bridgmans KCN II appears to be metastable. The transition line between cubic KCN I and orthorhombic KCN V runs from −60°C at 1 bar to the I/IV/V triple point at 20.0 kbar, 41°C. The KCN III/IV transition line lies at slightly higher temperatures than found by Bridgman. The melting curve of KCN is similar to that of KCl, with the III/I/liquid triple point at 22.2 kbar, 823°C. The phase behavior and the probable structures of the high‐pressure phases of KCN and also of KNO2 can be simply explained as a combination of coordinational polymorphism and disordering. Three new solid phases of KSCN were found, and the melting curves and transition lines were followed to 44 kbar. There was no evidence of premelting in KSCN.

Effect of pressure on solid-solid transitions in some silver and cuprous chalcogenides

Abstract Phase transitions in Ag 2 S, Ag 2 Se, Ag 2 Te, Cu 2 S and Cu 2 Se were studied by differential thermal analysis (DTA) to 40 kbar. The transition temperature lines increase with pressure with initial slopes of 1.57, 6, 11.48, and 0.5°C/kbar, respectively, for the first four and −0.6°Ckbar for (probably copper-deficient) Cu 2 Se.

Polymorphism of potassium sulphate, selenate and chromate to 40 kbar

Abstract Phase transitions of K 2 SO 4 K 2 SeO 4 and K 2 CrO 4 have been studied to 30–40 kbar by means of differential thermal analysis. The first-order transition temperatures increase with pressure from room-pressure values of 584°, 476° and 688.5°C with initial slopes of 18.3, 22.7 and 22.1 deg kbar , respectively. The transition lines of K 2 SO 4 and K 2 CrO 4 appear to have triple points at 22.6 kbar, 996° and 16.6 kbar, 994°, respectively, with the appearance of new high-temperature phases. The analysis of earlier high-temperature X-ray results on the thermal expansion of K 2 CrO 4 suggests strongly that the inversion at 668.5°C is preceded by second-order changes in the range 300–550° as in the case of K 2 SO 4 .