Thermodynamics of the URuC system

Thermodynamic measurements by the electromotive force method were made on the binary intermetallic phases URu₃ and U₃Ru₅ and on the ternary carbides URu₃C_0.7 and U₂RuC₂ of the URu and the URuC systems between 950 and 1200 K using galvanic cells with CaF₂ single crystal electrolytes: U, UF₃¦CaF₂¦UF₃, URu₃, Ru; U, UF₃¦CaF₂¦UF₃, U₃Ru₅, URu₃; Ru, URu₃, UF₃¦CaF₂¦UF₃, URu₃C_0.7, Ru, C; U, UF₃¦CaF₂¦UF₃, URu₃C_0.7, U₂RuC₂, C. The Gibbs energies of formation of URu₃, U₃Ru₅, URu₃C_0.7 and U₂RuC₂ were evaluated from the measured electromotive force which give ^fΔG^o〈URu₃〉 = −199 100 + 35.9 T J mol^−1fΔG^o〈U₃Ru₅〉 = −398 600 + 43.6 T J mol^−1fΔG^o〈URu₃C_0.7〉 = −192 600 + 2.5 T J mol^−1fΔG^o〈U₂RuC₂〉 = −380 200 + 52.5 T J mol⁻¹ The implications of these thermodynamic data for the behaviour of the fission product ruthenium in irradiated carbide fuels are discussed.     

Comparison of the magnetic properties of MmFeband NdFeB compounds

NdFeB and corresponding MmFeB compounds were studied, the high field magnetization at 4.2 K, the a.c. susceptibility (4.2 < T < 300 K) and the anisotropy field were measured using the singular point detection technique (77 < T < 570 K). At room temperature the anisotropy field of the MmFeB is about 3T, whereas that of NdFeB compounds is about 7T. The MmFeB compounds showed effects due to the cerium (lowering the Curie temperature) as well as due to the neodymium (spin reorientation at low temperatures).     

Phase equilibrium diagram of the system MnCrO

A hypothetical oxygen pressure-composition phase diagram and a projection of the oxygen pressure-temperature-composition diagram on the composition triangle were constructed from phase equilibria in the system MnCrO on the basis of the data available in literature. The temperature-composition phase equilibrium diagram of this same system in air was specified. Isomorphism of solid solutions with spinel and hausmannite structure and their intertransformation was studied. Two chemical compounds, MnCr₂O₄ and Cr₄Mn₂₈O₄₈, are supposed to exist in the system.     

Bubble-point pressures of the H2COCO2 system

Bubble-point pressures of the H₂COCO₂ system were measured at temperatures from 253.15 to 303.15 K and pressures up to 9 MPa. Multiple bubble-points were observed within certain limits of hydrogen compositions. The data have been compared with the calculated results by the Redlich-Kwong and the Peng-Robinson equations of state.     

Investigation of the CeFe binary system

The CeFe binary system was investigated and an FeCe binary phase diagram was proposed. This system consists of

• 1.(i) two peritectic reactions, γ-Fe + L → Ce₂Fe₁₇ and Ce₂Fe₁₇ + L → CeFe₂, occurring isothermally at 1063°C and 925°C respectively;
• 2.(ii) a eutectic reaction, L → CeFe₂ + Ce, occurring isothermally at 592°C with eutectic containing 83.3 at.% Ce (92.6 wt.% Ce);
• 3.(iii) a peritectoid reaction, γ-Fe + Ce₂Fe₁₇ → α-Fe(Ce), occurring isothermally at 922 °C.

The solid solubility of cerium in iron in the temperature range 850–900 °C was found to be less than 0.04 at.% (0.1 wt.%). The Curie temperature of α-Fe(Ce) was slightly lowered with increasing cerium content in solid solution.     

Phase investigations of the AlIr system

The phase behavior of the AlIr system has been studied using differential thermal analysis, electron microprobe analysis, X-ray diffraction, chemical analysis and X-ray fluorescence. Our work confirms the existence of four compounds: Al₉Ir₂, Al₃Ir, Al_2.7Ir and AlIr. We also observed an additional intermetallic phase, with a stoichiometry corresponding to Al₁₃Ir₄; however, this compound exhibits a complex X-ray pattern and currently no structure has been determined.Peritectic temperatures were determined for Al₉Ir₂ (900 °C), Al₁₃Ir₄ (1015 °C) and Al₃Ir (1450 °C). The Al_2.7Ir phase is stable to above 1450 °C, and the congruent melting temperature of AlIr is 2120 ± 20 °C. The solubility of aluminum in iridium was measured between 1085 and 1850 °C, and the maximum solid solubility was extrapolated to 18 at.% at 2058 °C. The maximum solid solubility of iridium in aluminum was measured to be less than 0.1 at.%. A phase diagram for the AlIr system is presented.     

Determination of the copper activity of liquid CuLa alloys

The thermodynamic activities of liquid CuLa alloys were obtained at 1549 K by Knudsen effusion experiments. The experimentally known concentration and temperature dependences of thermodynamic properties of liquid CuLa alloys are explained on the basis of an association model. These results are discussed in comparison with the enthalpy of crystallization and the crystallization temperature as well as the enthalpy of melting and the melting temperature of lanthanum-rich glassy and crystalline alloys respectively.     

An investigation of the polythermal diagram of the H2ONa2HPO4Na2SO4 system

The polythermal diagram of the ternary system H₂ONa₂HPO₄Na₂SO₄ has been established, setting up nine isotherms obtained between 0 and 25°C by conductimetric analysis. The solubility domains of the various solid phases have been determined. One eutectic, three stable and one metastable transitional transformations have been observed. Temperature and composition of the eutectic point have been obtained by thermal analysis at constant flow.     

An investigation of the low oxidation state chemistry of rhenium in the BaOReRe2O7 phase diagram

The first systematic survey of the BaOReRe₂O₇ phase diagram is reported, with emphasis on the reduced ternary oxides. At 800°C, the previously reported compounds Ba₃Re₂O₉, Ba₂ReO₅, and Ba₃ReO₆ were observed, all of which contain Re(VI) in ReO₆ octahedra. The stability of these phases is apparently due to ReO π-bonding in and between the octahedra. The previously unknown structure of Ba₂ReO₅ was determined by powder neutron diffraction and found to be isotypic with that of K₂VO₂F₃ (space group Pnma), with a = 7.3233(2), b = 5.7745(1), and c = 11.4124(2), Å. ReO₆ octahedra share adjacent corners to produce cis chains which are held together by 10 coordinated Ba atoms.     

First principles search of hard materials within the SiCN ternary system

Starting from C₃N₄ and Si₃N₄ stoichiometries and from the pseudocubic model structure of the former, intermediate phases SiC₂N₄ and Si₂CN₄ are proposed and geometry optimised within density functional built pseudopotential method using both local density (LDA) and generalised gradient approximations (GGA). The ternary compounds are found to be less stable than the two binary systems but the trends in the calculated magnitudes of the bulk moduli B₀ from the fit of the E(V) curves with Birch equation of state: B₀ (SiC₂N₄)=334.5 GPa and B₀ (Si₂CN₄)=270.3 GPa can be interpolated from those of the two extreme compounds: B₀ (C₃N₄)=424.1 GPa and B₀ (Si₃N₄)=219.8 GPa. This translates the chemical role of the substituting element on one hand and allows validating Cohen's semiempirical law relating B₀ to the inverse powers of the average interatomic distances on the other hand. From a mismatch of the chemical bonding in Si(C)NC(Si) chain observed by the electron localisation function (ELF) plot we propose an interpretation for the instability of the intermediate ternary phases. The electronic structure (density of states and band structures) obtained from augmented spherical wave (ASW) calculations of the relaxed structures point to semiconducting behaviour with smaller band gaps for the intermediate phases (∼2 eV, compared with the ∼4 eV gap of binaries).     

Calorimetric studies of CeCu AND CeMgCu alloys

Using different calorimeters, the following measurements have been carried out.

• 1.(i) The integral enthalpies of mixing of CeCu binary and some CeMgCu ternary liquid alloys,
• 2.(ii) The enthalpy of formation and the enthalpy of melting of the intermetallic compound CeCu₂.
• 3.(iii) The heat content of solid and liquid CeCu₂.

The observed concentration and temperature dependence of the measured values of the enthalpies of mixing as well as the glass-forming abilities of these alloys are explained on the basis of an association model.     

High-Tc superconductivity in the ErBaCuO and related systems

ErBa₂Cu₃O₇ and Er_0.5Y_0.5Ba₂Cu₃O₇ are both high-T_c superconductors attaining zero resistance above 80 K. Preliminary studies indicate that Yb_1−xY_xBa₂Cu₃O₇ also exhibits zero resistance above 77 K.     

The excess enthalpies of liquid GaGeTe and GaSnTe alloys

The excess enthalpies of the liquid alloys GaGeTe and GaSnTe were measured in a heat-flow calorimeter at 1203 K. The enthalpy surface in the ternary space in both systems is characterized by a valley stretching from the exothermic minimum in the GaTe system to the minima of the GeTe and SnTe systems. The minima in the ternary systems were found in this valley, i.e. on the sections Ga₂Te₃-GeTe and Ga₂Te₃-SnTe. A comparison of the experimental data with those calculated from the excess enthalpies of the constituent binaries with the aid of the Bonnier model, reveals only small deviations. A preliminary investigation was made into the ternary phase diagram of GaSnTe. This system contains the two quasibinary sections Ga₂Te₃-SnTe, GaTe-SnTe and the ternary compound Ga₆SnTe₁₀. The previously reported compounds Ga₂SnTe₃ and GaSnTe₂ do not exist.     

Phase diagram for the system Bi2O3CaOSrOCuO in the SrO-rich region

It has been found experimentally that phase diagram for the system Bi₂O₃CaOSrOCuO in SrO-rich region at 850°C in the open air includes three elementary tetrahedra: CaOSrOSr₆Bi₂O₁₁Sr₂CuO₃, CaOSr₂CuO₃Sr₆Bi₂O₁₁Sr_3,5Ca_0,5Bi₂O₇ and Sr₃Bi₂O₆Sr₆Bi₂O₁₁Sr_3,5Ca_0,5Bi₂O₇ Sr₂CuO₃. In the considered interval of corresponding oxide concentrations quaternary oxides are not formed under the above conditions.     

Ab initio quantum chemical studies of the electronic properties of the hydrogen bonded N2HF,N2HCl, (HCN)2 and NH3HCN complexes

The results of ab initio self-consistent field (SCF) and configuration interaction (CI) calculations on the hydrogen bonded N₂HF, N₂HCl, (HCN)₂ and NH₃HCN complexes, using basis sets that range from double-zeta plus polarization to triple-zeta plus double polarization, are reported. The primary objective of this work has been to calculate the changes in the dipole moments and the electric field gradients (EFGs) at the quadrupolar ¹⁴N, ²H and ³⁵Cl nuclei that are induced by H-bonding. Since the interpretation of the H-bond induced shifts requires a knowledge of the molecular dynamics in weakly H-bonded molecular complexes such as those studied in the present work, we have taken into account the effects of vibrational averaging on both the EFGs and dipole moments utilizing harmonic intermolecular force fields that were generated using ab initio SCF methods. The results of these calculations are compared with the corresponding experimental quantities that are obtained from the microwave spectra of these complexes.     

Solid state phase equilibria in the PtGaAs system

The PtGaAs solid state equilibrium phase diagram was determined at 600 °C with the use of X-ray powder diffraction, electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). No ternary PtGaAs phases were found and limited solid solubility was measured in the constituent binary PtGa and PtAs compounds. GaAs, PtGa and PtAs₂ form a region of three-phase equilibrium which dominates the GaAs side of the phase diagram. The phase diagram is in agreement with previous observations that PtGa and PtAs₂ are the stable phases when platinum thin films are reacted to completion on GaAs.