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.     

Developing high strain rate superplasticity inAlMgScZr alloys using equal-channel angular pressing

The processing of metallic alloys through the procedure of equal-channel angular pressing (ECAP) provides an opportunity for achieving superplastic ductilities at very high strain rates. This paper reports experimental data from an investigation of a series of AlMgScZr alloys processed by ECAP. The results show the occurrence of high tensile ductilities at testing strain rates above 10⁻² s⁻¹.     

Plasticité de transformation d'un acier à mémoire de forme Fe18Mn8Cr5Ni5Si

Transformation plasticity of a Fe18Mn8Cr5Ni5Si shape memory steel. This paper presents an experimental study of the transformation plasticity related to the γ→ε martensitic transformation in a Fe-18Mn-8Cr-5Ni-5Si shape memory steel. Under a weak bending stress the as-quenched austenitic samples showed a transformation plasticity by cooling at 170K with a plasticity coefficient h≈2. During heating, this transformation plasticity, related to the memory effect, is reversible, partially or completely, depending on whether the initial stress was maintained or removed at 295K during heating.     

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.     

Oxidation resistance of LnSiON powders (Ln=Y,Gd and La)

For application of LnSiON (Ln=Y, Gd and La) oxynitride materials, e.g. as host-lattices for lamp phosphors, oxidation resistance up to about 600 °C in air is a prerequisite. In this study we prepared LnSiON (Ln=Y, Gd and La) powders by solid state reaction and observed via TGA/DTA-experiments that most compounds are oxidation resistant up to 600 °C in air. The stability in air at high temperatures increases going from Ln₅(SiO₄)₃N, Ln₄Si₂O₇N₂, LnSiO₂N, Ln₂Si₃O₃N₄ to Ln₃Si₈O₄N₁₁. This is explained by an increasing cross-linking between the siliconoxygennitrogen tetrahedra in this sequence. For the lattices with less cross-linking between the siliconoxygennitrogen tetrahedra we observed that the oxidation resistance decreases slightly going from Y and Gd to La. For these lattices, also, an additional weight gain was observed during the oxidation reaction, which was higher than expected for complete oxidation. The additional weight gain was ascribed to an intermediate phase in which nitrogen retention takes place.     

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.     

Hydrolysis of POAl bonds in AlPO4 and SAPO molecular sieves

It is shown for three AlPO₄ and SAPO molecular sieves (structures SAPO-5, AlPO₄-17, SAPO-17, and SAPO-44) that the framework is attacked by water in the temperature range between ca. 323 and 473 K. The structural damage is more severe in the presence of ions such as NH⁺₄ or Na⁺, probably due to a shift in POAl hydrolysis equilibrium.     

Stereoselective synthesis of C15C24 and C25C30 fragments of dolabelides

The stereocontrolled synthesis of a C15C24 fragment of dolabelides is reported. The C19 and C21 hydroxyl-bearing stereocenters were installed using ruthenium-mediated asymmetric hydrogenations of cyclic hemiketal 4 and β-keto ester 7. The C25C30 portion of dolabelides was prepared as well by ring opening of chiral epoxy alcohol 12 to set up the C27 stereogenic center.     

Synthese und charakterisierung eines stabilen heterobimetallischen TitanCobalt komplexes mit unverbrückter TiCo-bindung

Unusually stable [(^tC₄H₉O)₃Ti-Co(CO)₄] has been prepared by treating the appropriate carbonylmetallate anion with chloro titanium t-butoxide as well as by protolysis of CH₃Ti(O^tC₄H₉)₃ with HCo(CO)₄. Spectroscopic data indicate that the alkoxide and carbonyl ligands are nonbridging, establishing C_3v-symmetry at the cobalt atom.     

Phase equilibria in the ternary system: MgONa2OP2O5: Partial system: Mg3(PO4)2Mg4Na(PO4)3Na4P2O7Mg2P2O7

The partial system Mg₃(PO₄)₂Mg₄Na(PO₄)₃Na₄P₂O₇Mg₂P₂O₇ in the ternary system MgONa₂OP₂O₅ was investigated using thermal and X-ray diffraction analyses and microscopy, and its phase diagram has been determined. In this range of composition, two binary phosphates occur: Mg₄Na(PO₄)₃ and Mg₆Na₈(P₂O₇)₅. The former melts incongruently (at 1155°C) and the latter does congruently (at 808°C). In the partial system of interest, the two sections Mg₄Na(PO₄)₃Mg₂P₂O₇ and Mg₄Na(PO₄)₃Mg₆Na₈(P₂O₇)₅ are studied, and their phase diagrams are established. The partial system is divided into three partial ternary systems in which two ternary eutectics and one ternary peritectic occur.     

Paramagnetic GdIIIFeIII heterobimetallic complexes of DTPA-bis-salicylamide

The reaction between DTPA (diethylenetriaminepenta-acetic acid)-anhydride and p-aminosalicylic acid (PAS) affords a novel ligand, [DTPA(PAS)₂], able to form stable heterobimetallic complexes with Gd³⁺ and Fe³⁺ ions. The lanthanide ion occupies an internal coordination cage formed by three nitrogen atoms, two carboxylate and two carboxoamido groups of the ligand, whereas the outer salicylic moieties form stable chelate rings with Fe^III ions. The stoichiometry of the resulting heterobimetallic complexes, established by measurements of water proton relaxation enhancement, is [(H₂O)-Gd-DTPA(PAS)₂]₂-Fe(H₂O)₂ or [(H₂O)-Gd-DTPA(PAS)₂]₃-Fe depending on the pH of the aqueous solution. The individual contributions to the observed relaxation enhancement from Gd³⁺ and Fe³⁺ paramagnetic ions have been clearly distinguished and analysed.     

The system YPO4Ca3(PO4)2Ca2P2O7

The ternary system YPO₄Ca₃(PO₄)₂Ca₂P₂O₇ has been investigated by differential thermal analysis, powder X-ray diffraction, and microscopy in reflected light. Its phase diagram and isothermal section at room temperature have been determined. The system contains only one double phosphate which is formed at the 1:1 molar ratio YPO₄:Ca₃(PO₄)₂, i.e., Ca₃Y(PO₄)₃.     

Viscosities of dimethyl carbonate with alcohols at several temperatures: UNIFAC-VISCO interaction parameters (OCOO/alcohol)

Viscosities have been determined for the binary mixtures dimethyl carbonate (DMC) + methanol, + ethanol, + 1-propanol, + 2-propanol, + 1-butanol, + 2-butanol, and + 1-pentanol at 293.15, 298.15, 303.15 and 313.15 K and atmospheric pressure. Viscosity deviations for the binary systems were fitted to the Redlich–Kister equation. From the experimental data (DMC or diethyl carbonate with above mentioned alcohols at the same temperatures) the interaction parameters (CH₃OHOCOO) and (OHOCOO) have been determined for their application in the UNIFAC-VISCO method, based on contribution groups, to predict the dynamic viscosities of the binary mixtures. Root-mean-square deviations are also gathered. The group contribution thermodynamic viscosity model GC-UNIMOD has been used to predict the dynamic viscosity of the binary mixtures at 298.15 K and their deviations have been shown.     

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.     

C(sp)H?O and C(sp)H?O hydrogen bonds in acyclic- and cyclic-organotellurium carboxylates

The reactions between R₂TeI₂ (R₂=(CH₃)₂, C₄H₈, C₅H₁₀) and AgOCOR′ (R′=C₆H₅, 4-NO₂C₆H₄, CHCHC₆H₅) (molar ratio 1:2) yield diorganotellurium dicarboxylates: (CH₃)₂Te(OCOC₆H₅)₂ (1), C₅H₁₀ Te(OCOC₆H₅)₂ (2), C₄H₈Te(OCO4-NO₂C₆H₄)₂ (3) and C₄H₈Te(OCOCHCHC₆H₅)₂ (4). They are characterized by IR, (¹H, ¹³C, ¹²⁵Te) solution NMR; (¹³C, ¹²⁵Te) solid state NMR spectroscopy. The X-ray structures of 1-4 (the immediate environment about tellurium is that of distorted trigonal bipyramidal geometry with a stereochemically active electron lone pair) are described in the context of their ability to generate intermolecular CH?O hydrogen bonds, which lead to the formation of supramolecular assemblies.     

Improved chemoselectivity in intramolecular alkylidene carbene CH insertion

The alkylidene carbene generated by chloromethylenation / α-elimination of 1 proceeds with a high degree of selectivity for methoxy CH insertion over methine insertion, to give 2. The carbene generated with trimethylsilydiazomethane results in an approximately 1:1 mixture of 2 and 3.     

Multicomponent CoMgONaZSM-5 catalyst for hydrocarbon synthesis from CO + H2 mixtures containing CO2 and/or N2

The catalyst under study was prepared by kneading a physical mixture of precipitated cobalt hydroxycarbonate, magnesia and NaZSM-5 with water as a binder. This mixture was pretreated by drying at 120 °C or by calcination at 450 °C. Adsorption measurements revealed that NaZSM-5 was not affected by the solid state reaction with cobalt component and magnesia. When the catalyst was reduced, the metallic phase originated from different precursors depending on the thermal pretreatment. The composition of the unreduced part of the oxidic cobalt was also affected; after reduction, the surface of the dried sample contained both Co(II) and Co(III) in the ratio of 1.8 to 1.0, while that of the calcined sample consisted mostly of Co(III). Carbon monoxide was adsorbed in several forms, but only the most weakly bonded form desorbed without decomposition. Pretreatment by calcination caused a shift in the optimum synthesis temperature and a very marked decrease in the C₅⁺ fraction yield compared with the dried sample. The addition of nitrogen to the syngas caused an increase in the liquid hydrocarbon selectivity, while carbon dioxide, especially at higher concentrations, decreased the hydrocarbon yield substantially. The effect of reaction pressure depended on the feed gas composition.