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The structural and thermodynamic properties of pure water and sodium chloride solutions at high temperatures and pressures are studied by using molecular dynamics simulations and quantum molecular simulations. Properties are calculated as functions of temperature and pressure. The results show that the structure of pure water becomes looser as temperature increases from 298 to 400 K, with the collapse of the traditional tetrahedral structure. For sodium chloride solutions, the same collapse is also found with the increased concentration. Moreover, a critical point for the diffusion coefficient ofandis evident when the temperature increases linearly under 100 atm. At the critical points, the ions are abnormally clustered, due to the weakly hydrogen-bonded water molecules. The cluster size of the ions is synchronous with the corresponding diffusion coefficients. [ABSTRACT FROM AUTHOR]

Crystalline hexagonal B(N 1- x C x ) and cubic B-C-N compounds have been synthesized from a precursor produced from melamine and boric acid by application of high temperature and high pressure. The synthesized products were characterized by X-ray diffraction. The lattice parameters for the hexagonal crystal are a=2.506 Å, c=6.657 Å, and that for the cubic crystal is a=3.596 Å. The X-ray photoelectron spectra of the B-C-N compound indicate the presence of B-N, C-N, C-C, and B-C bonds, which suggests that boron, carbon, and nitrogen atoms all bond with one another and that the B-C-N crystal is a compound in which the three kinds of atoms are mixed atomically. The composition of the B-C-N compound is B 0.47 C 0.23 N 0.30 . A strong absorption band at 1000∼1120 cm -1 attributable to the cubic B-C-N phase is observed in the infrared spectrum. The photoluminescence spectrum of hexagonal B-C-N powder measured at room temperature features a broad peak centered at 374 nm, corresponding to the band-edge emission of h-B-C-N, and is similar to that of w-GaN. [ABSTRACT FROM AUTHOR]