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.     

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.     

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.     

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.     

A study on the phase diagram of AlF3CsF system

Phase relations of the AlF₃CsF system have been investigated by the methods of DTA and XRD with quenching technique. Four compounds were identified: Cs₃AlF₆, CsAlF₄, CsF·2AlF₃ and CsF·3AlF₃. Cs₃AlF₆ melts congruently at 790°C. The first eutectic, E₁, between Cs₃AlF₆ and CsF is located in 10.0 mol% AlF₃ at 654°C. CsF·2AlF₃ and CsF·3AlF₃ melt incongruently at 508° and 653°C, respectively. The second eutectic, E₂, was observed in 42.0 mol% AlF₃ at 471°C. The compound CsAlF₄ formed in the solid eutectic when cooled below 443°C. CsAlF₄ has α and β forms, transformation of which takes place reversibly at 422°C. All phase structures in the system were confirmed by X-ray powder diffraction analysis.     

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.     

Calorimetric investigations and thermodynamic calculation of Zn–Al–Ga system

The results of calorimetric investigations and thermodynamic calculation of Zn–Al–Ga system are presented in this article. The research was carried out experimentally, using Oelsen calorimetry in temperature interval 800–1,000 K, and by thermodynamic calculation, applying general solution model in temperature interval 800–1,600 K. The enthalpy space diagram, the enthalpy isotherm diagram, as well as the values for zinc activities, partial and integral molar Gibbs excess energies have been determined. Comparison of experimentally obtained results and the results calculated by general solution model was done at the temperatures 800, 900, and 1000 K, which indicated a good mutual agreement.     

The thermal transformation of Na LiA zeolites. A new polymorph in the system Li2OAl2O3SiO2

High-temperature phase transformations of A zeolite with various degrees of exchange of Na⁺ with Li⁺ ions were investigated. An increase in the number of Li⁺ ions per unit cell accelerates the thermal transformation of the zeolite framework to the amorphous state. Above 730°C, four phases (carnegieite, nepheline, β-eucryptite, and a new phase—γ-eucryptite) were identified. Only γ- and β-eucryptite phases were obtained from pure LiA zeolite. γ-eucryptite is a new metastable polymorph in the system Li₂OAl₂O₃SiO₂. γ-eucryptite a₀ = 7.231(3)Å, b₀ = 10.270(6) Å, c₀ = 12.054(7) Å) is transformed to β-eucryptite (a₀ = 10.533(5) Å, c₀ = 11.148(5) Å) above 840°C.     

A preparatory and X-ray diffraction study of the SrCl2NdCl3 system

The SrCl₂NdCl₃ system was examined over the full composition range by the Guinier powder X-ray diffraction technique. A solid solution, Sr_(1−x)Nd_xCl_(2+x), was found for the composition region 0 < x < 0.18. Beyond the solid solution region two intermediate chloride phases were identified: Sr_0.80Nd_0.20Cl_2.20 (Sr₄NdCl₁₁) and Sr_0.643Nd_0.357Cl_2.357 (Sr₉Nd₅Cl₃₃). Orthorhombic Sr₄NdCl₁₁ is isostructural with vernier-type Sr₄DyCl₁₁; lattice parameters are a = 7.230(5); b = 35.292(18), and c = 6.826(4)Å. The phase Sr₉Nd₅Cl₃₃ exhibits hexagonal symmetry with lattice parameters a = 12.908(6) and c = 24.823(10), Å and is isostructural with Nd₁₄Cl₃₃.     

New oxyborates in the MgMnBO system

Two new oxyborate compounds were synthesized during a study of the phase relationships between the pinakiolite-ludwigite series of compounds. The structural topologies of these previously unreported materials have been determined experimentally by comparing calculated with observed electron microscope images. Both of these structures are very similar to each other, and also closely related to pinakiolite which consists of flat walls of edge-sharing octahedra connected to zigzag chains of octahedra by triangular BO₃ groups. The two new structures contain similar infinite walls which are separated by slabs of octahedra that are wider than the zigzag chains found in pinakiolite. A new series of structurally related oxyborate compounds can be envisaged and are described.     

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).     

The oxygen potentials corresponding to the YBa2Cu3O6+x phase in the YBaCuO system

Phase relations in the vicinity of the YBa₂Cu₃O_6+x in the CuO-rich part of the YBaCuO system were studied by the equilibration and quenching technique. At 950°C, the system is characterized by the large number of solid four-phase combinations. The oxygen potential as a function of temperature for two four-phase combinations, i.e., YBa₂Cu₃O_6+x + BaCuO₂ + BaCu₂O₂ + Y₂BaCuO₅ and YBa₂Cu₃O_6+x + BaCu₂O₂ + Y₂BaCuO₅ + Cu₂O, were studied by means of solid state EMF measurements. At higher oxygen potentials the pair of YBa₂Cu₃O_6+x and Y₂BaCuO₅ is stable in contact with BaCuO₂. At lower oxygen pressures this pair coexists in equilibrium with BaCu₂O₂ or Cu₂O.