Crystal growth and some physicochemical studies on an organic intermolecular compound of anthranilic acid and N,N-dimethylamino benzaldehyde

The phase diagram of anthranilic acid and N,N-dimethylaminobenzaldehyde system gives two eutectics (E1 and E2) and a 1:1 intermolecular compound with congruent melting point. The mole fractions of anthranilic acid at E1 and E2 are 0.10 and 0.95, respectively. The negative values of heat of mixing of eutectics suggest that there is clustering of molecules in their eutectic liquid melt. The positive values of excess free energy for eutectics indicate that the interactions between the like molecules are stronger than those of unlike molecules. It can be inferred from single crystal X-ray analysis of the intermolecular compound that it crystallized in monoclinic unit cell with C2/c space group and a reasonably large sized intermolecular compound crystal was grown by slow evaporation technique at room temperature. The optical studies on the intermolecular compound give two strong emission bands with two lmax values one at 380 nm and second at 450 nm with total quantum efficiency 0.49.

Aqueous nonelectrolyte solutions — Part XX: Formula of structure I methane hydrate, congruent dissociation melting point, and formula of the metastable hydrate

Sixteen new measurements of high precision for structure I methane hydrate with water between 31.93 and 47.39 °C are shown to be metastable and exhibit higher methane pressures than found by earlier workers. Comparison of earlier measurements between 26.7 and 47.2 °C permit positive identification of the structure II and the structure I hydrates. Forty-nine equilibrium constants Kp(h1[Formula: see text]l1g) for dissociation of structure I methane hydrate into water and methane, 32 between –0.29 and 26.7 °C for the stable hydrate and 17 between 31.93 and 47.39 °C for the metastable hydrate, are best represented by a three-parameter thermodynamic equation, which indicates a standard error (SE) of 0.63% on a single Kp(h1[Formula: see text]l1g) determination. The congruent dissociation melting point C(h1l1gxm) of metastable structure I methane hydrate is at 47.41 °C with SE 0.02 °C and at pressure 505 MPa. The congruent equilibrium constant Kp(h1[Formula: see text]l1g) is 102.3 MPa with SE 0.2 MPa. ΔH°t(h1[Formula: see text]l1g) is 62 281 J mol–1 with SE 184 J mol–1, and the congruent formula is CH4·5.750H2O with SE 0.059H2O. At the congruent point, ΔV(h1[Formula: see text]l1g) is zero within experimental precision, and its estimate is 1.3 with SE 1.6 cm3 mol–1. The stability range of structure I methane hydrate with water extends from quadruple point Q(s1h1l1g) at –0.29 °C up to quadruple point Q(h1h2l1g) at 26.7 °C, and its metastability range with water extends from 26.7 °C up to the congruent dissociation melting point C(h1l1gxm) at 47.41 °C. Key words: methane hydrate, clathrate structure I, metastability range, dissociation equilibrium constant, formula, congruent melting point, metastability of structure I hydrate.

Aqueous nonelectrolyte solutions. Part XIX. Congruent dissociation melting point and the formula of structure II methane hydrate

Twenty-four equilibrium pressures, P(h2l1g), of structure II methane hydrate h2 with water l1 between 27.0 and 46.9°C are well represented by a four-parameter equation, which indicates a standard error (SE) of 1.95% on a single pressure measurement. Forty equilibrium constants Kp(h2[Formula: see text]l1g) for dissociation of structure II methane hydrate into water and methane between 27.0 and 47.7°C and at pressures up to 784 MPa at 45.0°C are best represented by a three-parameter thermodynamic equation, which indicates an SE 1.25% on a single Kp(h2[Formula: see text]l1g) determination. The congruent dissociation melting point C(h2l1gxm) of structure II methane hydrate is at 47.71°C with SE 0.03°C and at pressure 533 MPa with SE 5 MPa. The congruent Kp(h2[Formula: see text]l1g) is 102.9 with SE 0.3 MPa, ΔH°t(h2[Formula: see text]l1g) is 61 531 with SE 244 J mol–1, and the congruent formula is CH4·5.670H2O with SE 0.061H2O. At congruent point ΔV(h2[Formula: see text]l1g) = 0 and its estimate is 1.0 with SE 1.6 cm3 mol–1. Stability range of structure II methane hydrate with water extends from quadruple point Q(h1h2l1g) at 26.7°C and 55.5 MPa up to quadruple point Q(h2h3l1g) at 47.3°C and 620 MPa. The metastability range of structure I methane hydrate with water is discussed.Key words: methane hydrate, clathrate structure II, stability range, dissociation equilibrium constant, formula, congruent melting point, metastability of structure I hydrate.

Phase transition, growth, and optical properties of NdxLa1−xSc3(BO3)4 crystals

The low-temperature phase, trigonal phase, of space group R32 was discovered in the compound LaSc3(BO3)4 (LSB) doped with arbitrary concentration of Nd3+ ions (NLSB). For LSB, the lattice constants are a = 9.820 ± 0.003 Å, c = 7.975 ± 0.003 Å. The decomposition of NLSB phase was observed in two regions of temperature below and above the congruent melting point by differential thermal analysis and x-ray powder diffraction methods. The single crystals of 2 × 2 × 3mm3 of dominant trigonal phase for x = 0.5 were grown by the flux method (LiBO2). Second harmonic generation effect was observed in NLSB for x = 0 to 1. The concentration dependence of fluorescence lifetime was measured and derived from Dexter's theory of resonant energy transfer.

Melt Growth of ZnGeP2: Homogeneity Range and Thermochemical Properties

ABSTRACTZnGeP2 crystallized from the melt via horizontal gradient freezing shows the tendency to decompose into Ge and GeP when the equilibrium vapor pressure is not exactly controlled during the entire crystallization process. Using differential thermal analysis (DTA) it was found that ZnGeP2 has a truly congruent melting point of 1311 K. Adding small amounts of the elements and binaries in the ternary system Zn-Ge-P to stoichiometric ZnGeP2 a significant deflection of the liquidus curve was observed at the melting point of ZnGeP2- From DTA, X-ray diffractometry (XRD), photoluminescence (PL), transmission and conductivity measurements it was concluded that the melt grown material was highly compensated. The presence of a broad acceptor and donor band in the band gap could be associated with phosphorous and zinc point defects in the crystal lattice. It is assumed that the defect concentrations are of the order 1019 cm−3.

Measurements of to Temperatures of Supersaturated Si-As Alloys

The congruent melting point, or To curve, of crystalline Si-As alloys has been measured in the range of 1.6 to 18.1 at. % arsenic by line source electron beam annealing. Alloys were created by ion implantation of As into 0.1mm Si-on-sapphire and crystallized by pulsed laser melting. To temperatures decrease from 1673±10K at 2.0 at.% As to 1516±30K at 18.1 at.% As. The results of these measurements are significantly higher than the previous results of studies using pulsed laser melting techniques. Advantages of the e-beam technique over previous techniques are discussed. Chemical free energy functions of the solid and liquid phases were calculated from existing thermodynamic data. The calculated To curve agrees with the measured values only in low concentration region (less than 8 at.%).