J.B. Clark

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...

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.

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.

High-pressure synthesis of YScO3, HoScO3, ErScO3, and TmScO3, and a reevaluation of the lattice constants of the rare earth scandates

The rare earth scandates AScO/sub 3/, where A = Y, La, Nd, Sm, Gd, Dy, Ho, Er, and Tm, were prepared, and their unit cell constants were determined. The single-phase compounds YScO/sub 3/, HoScO/sub 3/, ErScO/sub 3/, and TmScO/sub 3/ were prepared for the first time by use of high pressures. 1 figure, 4 tables.

Binary alloy systems at high pressure

Abstract The composition-temperature-pressure phase relations of binary alloy systems are discussed. Topics include the effect of pressure on liquidi and eutectic points, the effect of pressure on solid solubility, polymorphism of intermetallic compounds, the formation and dissociation of intermetallic compounds, the similarity of phase diagrams of related systems and the coupling of composition-temperature-pressure phase diagrams with thermochemical data. The systems HgTl, AlSi, AlGe, ZnAs and CdPb are presented as examples.

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.

The infrared spectra, phase transition, and structural properties of tetraethylammonium hexafluoroantimonate (C2H5)4NSbF6

Abstract (C2H5)4NSbF6 (TEAHFA) is face-centered cubic with a = 11.487 A at ambient temperature and undergoes a first-order phase transition at 246 K on cooling and at 272 K on heating. The infrared spectra of TEAHFA confirm the cubic structure of the room temperature phase I in which no evidence could be found for the existence of hydrogen bonds between the cations and anions.

The aluminium-germanium eutectic temperature to 40 kilobars

Abstract The AlGe eutectic temperature was studied to 40 kbar, and can be described by t (°C)=415.5 + 0.746 P −0.0268 P 2 . The curve rises initially with pressure, passes through a maximum at 13.9 kbar, 420.7°C, and then falls with further pressure increase. The volume change upon melting is 0.32 cm 3 /g-at. at atmospheric pressure, and disappears at 13.9 kbar. At higher pressures the volume of the solid is higher than that of the liquid.

High-Pressure Phase Boundaries of Tl2CO3 and Rb2CO3

The high-pressure phase diagrams of RbzCOz and TI2.CO3 were studied by means of differential thermal analysis. The P62C03 II/I transition line rises linearly with pressure from 300.5 °C to a triple point near 9 kilobars, 402 °C where a new phase P&2CO3 III appears. The resulting RbzCOt II/III and III/I transition lines were followed to 30 kilobars. TI2CO3 at atmospheric pressure has phase transitions at 212.5°C (III/II) and at 260.5°C (II/I). The III/II phase boundary rises with pressure, and meets the falling II/I boundary at