Cyanides tend to form linear chains of molecules in solid, which are tightly bonded by strong intermolecular interactions due to highly polar cyano group; they are hydrogen bonding and dipole-dipole interactions. Hydrogen cyanide and acetonitrile are prototypes of cyanides, showing chracteristic structural phase transitions under pressure with rearrangement of linearly aligned molecules. Vibrational spectral study of the phase transition and chemical reaction in cyanides are reviewed.
High-pressure Raman spectroscopy of solid oxygen has been carried out at room temperature up to 110 GPa in order to study the recently observed structural phase transition at 96 GPa. The vibron and lattice phonons of ε-phase corresponding to the transition became undetectable although the vibron wavenumber in ε-phase has shown a line pressure dependence with a coefficient of 2. 33 cm-1/GPa and reached 1753cm-1 at 94 GPa. This result provided evidence that the structural transition is accompanied by a insulator-metal transition. The results have been discussed with a view to molecular dissociation comparing with those of the other Vlb elemental materials.
Experimental aspects of pressure-induced metallization and structural change of rare gas solids are reviewed. The metallization process of xenon, which has been extensively investigated through optical measurements, is described in more detail as an example.
This article reviews our recent x-ray studies on solid halogens under high pressure. We found an empirical scaling rule including atomic coordinates for iodine and bromine. By applying the Herzfeld criterion, we also found a scaling rule for the metallization process prior to molecular dissociation. The Maximum Entropy Method was employed to analyze the powder diffraction data and obtain the electron density map in solid iodine at pressures up to 20 GPa. The electron density between adjacent iodine molecules is shown to form a two-dimensional network around 16 GPa in association with metallization.
The pressure-induced dissociation and metallization of molecular crystals are reviewed from theoretical point of view with particular references to ice and solid hydrogen. The problem on the presence of the symmetric hydrogen-bond phase of ice (ice X) is discussed and the reason why the theoretical metallization pressure of ice is very high in comparison with other molecular solids is predicated. The present theoretical aspect on the assumed molecular metallic phase of hydrogen is also discussed briefly.
The rice grains ( Oryaa sativa L. Japonica, cultivar Koshihikari) harvested in Niigata prefecture in 1994 was soaked in water, and subjected to high pressure treatment at 400MPa for 10min. The rice thus high-pressure-treated was then boiled for cooking. The physical properties of the cooked rice were compared with those of a control rice with respect to the hardness, stickiness and conductivity immediately after cooking, and also with respect to those with time during the storage. The highpressure-treated rice exhibited higher stickiness than the control rice immediately after cooking, but it became harder than the control rice the next day. Furthermore, the high-pressure-treated rice exhibited higher conductivity immediately after cooking than the control rice, and the conductivity increased with time during the storage. Scanning electron micrographs (SEM) indicated that the grains of the highpressure-treated rice were swollen by the high pressure treatment, with water effectively penetrating into the peripheral portion of each starch granule, and when such rice was cooked, deep vacant holes and thick walls of starch gel were formed in each grain. It has been confirmed that the rice subjected to such high pressure treatment, when cooked, is tasty even after becoming hard with time during storage.
Various mini-autoclaves for hydrothermal reactions are introduced. Accessary processes such as electrode, gas-pressuring, ball milling, phase seperation and others under hydrothermal conditions are shown for originarity for hydrothermal research.