Thermochemistry of GaBO3 and phase equilibria in the Ga2O3–B2O3 system

Employing a Tian-Calvet-type calorimeter operating in the scanning mode at temperatures from 1120 to 1220 K, the enthalpy change, Δ_dH, associated with the decomposition of GaBO₃ (=1/2β-Ga₂O₃+1/2B₂O₃(liq.)) and the corresponding decomposition temperature, T_d, were determined: Δ_dH=30.34±0.6 kJ/mol, T_d=1190±5 K. Using the transposed-temperature-drop method the thermal enthalpy, H(T)−H(295 K), of GaBO₃ was measured as a function of temperature, T, in the region from 760 to 1610 K; the results obtained are

[H(T)−H(295 K)]/(J/mol)=104.8·(T/K)−31 300 (760 K<T<1190 K),

[H(T)−H(295 K)]/(J/mol)=138.8·(T/K)−41 480 (1190 K<T<1590 K).

On the basis of the experimental results, the enthalpy and entropy of formation, Δ_fH and Δ_fS, respectively, of GaBO₃ from the component oxides were derived:

Δ_fH=−30.34 kJ/mol,Δ_fS=−25.50 J/(K·mol) at 1190 K,

Δ_fH=−10.55 kJ/mol,Δ_fS=−5.48 J/(K·mol) at 298 K.

The enthalpy versus temperature curve shows, apart from a step associated with the decomposition of GaBO₃, a further step at 1593 K which is attributed to a monotectic equilibrium.     

Calorimetric investigation on the Pb---Sm and Sn---Sm alloys

The integral enthalpy of formation of the Sm---Pb and Sm---Sn melts at 1203 K, h^f, was determined by direct reaction calorimetry (drop method) in the Pb and Sn rich sides with the help of a high-temperature Tian-Calvet calorimeter. The results can be fitted respectively with reference to the mole fraction of samarium, x, as follows:

h^f/kJ mol⁻¹=x(1−x)(−109.8−372.0.7x) with0> X_Sm >0.27

and

h^f/kJ mol⁻¹=x(1−x)(−277.0−105.4.x) with0> X_Sm >0.27

for the Sm---Pb and Sm---Sn melts respectively. They yield the following partial enthalpies of samarium at infinite dilution: −109.8 and −277.0 kJ mol⁻¹ respectively.

Such negative values suggest the existence of a strong short-range order in the liquid state. The stoichiometry and the thermal stability of these associations needs additional thermodynamic determinations concerning mainly the free enthalpy of formation. It will be determined by Knudsen-effusion combined with mass spetrometry in a further work.     

Determination of constitutive parameters by forming-limit tests

Goya and Ito have developed a constitutive expression of plastic materials introducing two essential parameters μ() and β() which denote the magnitude and directional angle of the plastic strain increment, respectively, where denotes the directional angle of the stress increment in the deviatoric stress space.

In this report, the authors investigate specific forms of μ() and β(), and determine the values of material constants through the application of the linear-comparison solid theory to the localized necking problem of a rigid-plastic plate subjected to biaxial stretching.

The specified forms of the transition parameters are described as follows:

,

μ()={cos(−)}^1+0.9φ

,

, where γ and K₀ are new material constants, and denotes the deviation of the current stress state from the uniaxial stress state.     

On the vapourization thermodynamics of cobalt trifluoride

The sublimation of CoF₃(s) was studied. The temperature dependence of the total vapour pressures as measured by the torsion method in the temperature range 700–830 K fit on the equation:

log(p/kPa)=(11.60±0.20)−10630±400)/(T/K)

Both the sublimation reactions:

Cof₃(s)= Cof₃(g) (1)

2Cof₃(s)=2Cof₂(s)+F₂(g) (2)

occur during the vapourization of CoF₃(s) where the molar fraction of the reaction (1) was found equal to 0.60±0.05, practically constant in the covered experimental temperature range. The standard enthalpies Δ_subH°(298)=216±4 and 204±3 kJ mol⁻¹ for reactions (1) and (2) respectively were derived from second- and third-law treatment of the data. New values for the enthalpy of formation of CoF₃(s) and CoF₃(g) equal to −773±5 and −557±10 kJ mol⁻¹, respectively, were derived.     

Gibbs free energy of formation of the ternary oxide Nd3RuO7

The Gibbs free energy of formation of Nd₃RuO₇(s) has been determined using solid-state electrochemical cell employing oxide ion conducting electrolyte. The electromotive force (e.m.f.) of the following solid-state electrochemical cell has been measured, in the temperature range from 929.3 to 1228.6 K.

Cell: (−)Pt/{Nd₃RuO₇(s) + Nd₂O₃(s) + Ru(s)}//CSZ//O₂(p(O₂) = 21.21 kPa)/Pt(+)

The Gibbs free energy of formation of Nd₃RuO₇(s) from elements in their standard state, calculated by the least squares regression analysis of the data obtained in the present study, can be given by:

{Δ_fG°(Nd₃RuO₇, s)/(kJ mol⁻¹) ± 1.6} = −3074.3 + 0.6097(T/K); (929.3 ≤ T/K ≤ 1228.6).

The uncertainty estimate for Δ_fG°(T) includes the standard deviation in e.m.f. and the uncertainty in the data taken from the literature. The intercept and the slope of the above equation correspond to the enthalpy of formation and entropy, respectively, at the average experimental temperature of T_av. = 1079 K.     

Synthesis, crystal structure and thermal decomposition mechanism of the complex [Sm(p-BrBA)3bipy·H2O]2·H2O

Thermodynamic activities of aluminum in the iron–aluminum system were determined between about 720 and 850 K for the composition range between 23 and 33 at.% Al which includes the D0₃-ordered nonstoichiometric intermetallic compound Fe₃Al. For this purpose an electromotive force method with a single-crystal CaF₂ electrolyte was used, and the following cell arrangement was employed:

(−)Pt|Ir|Al_0.85Sn_0.15, Na₃AlF₆|CaF₂|Al_1±xFe_3±x, Na₃AlF₆|Ir|Pt (+).

Activities of iron were obtained by means of a Gibbs-Duhem integration for the same composition range. The results of the activity measurements were interpreted in terms of a statistical–thermodynamic model for nonstoichiometric phases with the D0₃-superstructure based on defect formation energies from the literature. It was found that non-stoichiometry in Fe₃Al is caused by anti-structure atoms on two of the three possible sublattices.     

On the contiguity of carbide phase in WC–Co hardmetals

In this paper the analysis of dependence of carbide phase contiguity in WC–Co hardmetals on the variation coefficient of WC grain size distribution is carried out. The relationship proposed is

C=1−V_Co^0.644exp(0.391V)

Here C is the contiguity, V_Co is the volume fraction of binder and V is the coefficient of variation. This relation is obtained on the basis of experimental data available in the literature. The basic meaning of this model is that with its help one more microstructural parameter V is introduced explicitly. This parameter essentially affects the mechanical behaviour of WC–Co hardmetals.     

The limiting molar partial enthalpies of mixing of iron, cobalt, nickel, palladium and platinum in liquid gallium and indium

Gallium and indium have been used as solvents for the determination of the molar partial enthalpy of mixing Δ_mixh_m^o(TM, Ga or In) (denoting liquid transition metal (TM) in infinite liquid gallium or indium) of the pure liquid transition metals Fe, Co, Ni, Pd and Pt by direct reaction calorimetry between 1000 K and 1500 K with the exception of Δ_mixh_m^o(Fe, In) (because of the shape of its equilibrium phase diagram). All the limiting enthalpies listed below refer to the liquid state. With pure gallium as solvent, they correspond to the reaction

TM(liq) − nGa(liq) → TM₁Ga_n(liq)

at the experimental temperature T_e, with n 1.

1. (i) Δ_mixh_m^o in gallium is found for Fe, Co, Ni, Pd and Pt to be −2, −44, −82, −144 and −155 kJ mol⁻¹.

2. (ii) Δ_mixh_m^o in indium is found for Co, Ni, Pd and Pt to be +28, −25, −127 and −114 kJ mol⁻¹.

In both solvents, these limiting enthalpies vary with a similar trend. This observation makes it possible to predict the limiting molar partial enthalpy Δ_mixh_m^o(Fe, In) of mixing of iron in indium as +70 kJ mol⁻¹. The results have been compared with the data proposed by Miedema and co-workers.     

Subsolidus phase relation and crystal structure of the PrBa2−xSrxCu3O7±δ system

The PrBa_2−xSr_xCu₃O_7±δ solid solution was investigated by means of X-ray powder diffraction in combination with Rietveld analysis. The Sr-doped Pr123 single phase could be synthesized at 950 °C in air. The solubility of PrBa_2−xSr_xCu₃O_7±δ solid solution is 0.2≤x≤0.6. The structure of PrBa_2−xSr_xCu₃O_7±δ is orthorhombic for x=0.2. The structure transforms into tetragonal for 0.3≤x≤0.6. In the PrBa_2−xSr_xCu₃O_7±δ structure, Sr ions can replace Ba ions, the highest value is x=0.6 under our experimental condition. But Sr ions could not replace Pr ions. Furthermore Pr ions could not occupy the sites of Ba ions in the PrBa_2−xSr_xCu₃O_7±δ system. Both ionic radii and chemical properties play an important role in the mutual substitution of Pr, Ba and Sr ions in the Pr123 structure of the PrBa_2−xSr_xCu₃O_7±δ system.     

Melt processed YBa2Cu3O7−x superconductors

The superconducting YBa₂Cu₃O_7−x samples were prepared by an Arc-Cast-Annealing (ACA) and Arc-Quench-Powder-Growth (AQPG) processes as modifications of QMG and MPMG techniques. Pe'lets of YBa₇Cu₃O_7−x were quenched by arc-casting in a water cooled copper mould and then the solidified rods were annealed at different temperatures and times to store the superconductivity. Annealed at an appropriate temperature the cast rods showed rising superconducting properties with increasing the annealing time. Some of the rods after solidification were crushed to give powder which was compacted and then subjected to a melt growth process. As a result of this processing, large grained textured YBCO superconductors with dispersed 211 inclusions in the superconducting grains were produced. The microstructure and physical properties of these ACA and AQPG samples were investigated when subject to various temperature cycles. It was found that the volume fraction and size distribution of the second phase inclusions were dependent upon the maximum temperature during the melt growth process. The critical current density (J_c) for ACA and AQPG samples was estimated from magnetization loops using Bean's critical state model. It was found that the value of J_c of AQPG sample was much higher than that of ACA sample.     

Differential calorimetric analysis of the binary system Sb–Zn

The experimental study of the system Sb–Zn by differential calorimetry made it possible to plot the whole phase diagram. We found the stability domains of existence of the stoichiometric compound SbZn and the solid solutions which extend on both sides from the compositions corresponding to Sb₃Zn₄ (forms γ and β) and Sb₂Zn₃ (forms η and ζ). Sb₃Zn₄ and Sb₂Zn₃ are both congruent melting compounds at 566 and 568 °C respectively with an eutectic transformation at 563 °C:

liquid(43% Zn) ↔ Sb₃Zn₄(γ) + Sb₂Zn₃(η).

Sb₂Zn₃(ζ) is formed at 407 °C starting from Sb₃Zn₄(β) and zinc. The decomposition, by cooling, occurs around 360 °C.     

Ba4In2−x(CO3)1+xO6−2.5x and Ba4In0.8Cu1.6(CO3)0.6O6.2—new indium oxycarbonates closely related to n=3 Ruddlesden–Popper phases

Investigations of phase relations in the Ba-rich part of the In₂O₃–BaO(CO₂)–CuO pseudo-ternary system at 900 °C have revealed the existence of new indium–copper oxycarbonate – Ba₄In_0.8Cu_1.6(CO₃)_0.6O_6.2. Rietveld refinement of the X-ray powder diffraction data combined with infrared studies gives evidence that this phase is a oxycarbonate crystallising in the tetragonal structure (space group I4/mmm) with unit cell parameters: a=4.0349(1) Å and c=29.8408(15) Å. In the binary part of the In₂O₃–BaO(CO₂) system we have identified the occurrence of Ba₄In_2−x(CO₃)_1+xO_6−2.5x oxycarbonate solid solution showing a crystal structure also described by I4/mmm space group, but with the unit cell parameters: a=4.1669(1) Å and c=29.3841(11) Å for x=1. The existence range of this phase, −0.153<x<0.4, includes chemical compositions of earlier found phases: Ba₅In_2+xO_8+0.5x with 0≤x≤0.45 (known as the -solid solution), as well as the binary Ba₄In₂O₇ phase. The crystal structures of both new oxycarbonates are isomorphic and related to n=3 member of the Ruddlesden–Popper family.     

Comparative magnetic studies of (Sm, Nd) trichloroacetates and their heteronuclear CuLn2(CCl3COO)8·6H2O systems: structure and spectroscopy of a new type of Eu trichloroacetate

Two series of compounds: heteronuclear CuLn₂(CCl₃COO)₈·6H₂O (Ln = Nd and Sm) and their simple analogues Ln(CCl₃COO)₃·2H₂O (Ln = Eu, Nd, Sm) were synthesized. New Eu(III) trichloroacetate; Eu(CCl₃COO)₃·3H₂O·CH₃OH was obtained, its molecular structure was determined by X-ray diffraction and compared with the data of respective systems reported earlier. Magnetization was measured and the susceptibility was derived in the limit of low field. Magnetic susceptibilities were calculated and discussed for series of homo- and hetero-nuclear chloroacetates.

Untypical hysteresis was found (two loops) in samarium trichloroacetate. This phenomenon is most probably the effect of flops of spins in magnetic fields of 30,000 Oe and very weak (if any) interaction intermediated by weak hydrogen bonding between the chains. A similar magnetic behavior was observed in neodymium carboxylate where the magnetic ordering was observed as a result of Nd–Nd interaction at low temperature (1.6 K). For this system, the magnetic moment depends on magnitude of the magnetic field and ferromagnetic ordering appears at low temperatures. The strongest interactions of coupled ions and antiferromagnetic ordering with T_N=6.5 K were found in CuSm₂(CCl₃COO)₈·6H₂O single crystals.

Heisenberg model was applied in the calculations for three interacting ions located linearly. The following relation was derived:

and applied in calculations of the exchange integrals. Mechanism of the exchange interaction was discussed on the basis of the obtained results.     

Synthesis, crystal structure, oxygen stoichiometry, and electrical conductivity of La1−aCaaCr0.8Ti0.2O3−δ solid solutions

Series of perovskite-type compounds La_1−aCa_aCr_0.8Ti_0.2O_3−δ (a=0–1.0) were synthesized by the ceramic technique in air (final heating 1350 °C). The crystal structure of the compounds after cooling in air to room temperature was characterized as orthorhombic in space group Pbnm. Analysis of the lattice constants shows a noticeable decrease with increasing Ca content. All compounds prepared were stable in air and in a stream of Ar/1 Pa O₂ at 20–1400 °C, as also in Ar/5% H₂ (pH₂O/pH₂=0.01) at 850–1000 °C. Oxygen stoichiometry and electrical conductivity of the solid solutions with a=0.0–1.0 are investigated. Increasing Ca contents decrease the stability of the oxides in respect to the thermal dissociation of oxygen. All compounds are p-type semiconductors in the temperature range 20–1000 °C at oxygen partial pressures of 10⁻¹⁵ to 0.21×10⁵ Pa. A maximum conductivity of about 30 S/cm in air at 1000 °C is observed for the composition with a=0.6 corresponding to a ratio of Cr³⁺/Cr⁴⁺=1 at an oxygen stoichiometry near 3.0, and oxidation states of La, Ca, Ti, and O ions of 3+, 2+, 4+, and 2−, respectively.     

Zur Kenntnis von RbBa3Ca4Cu3V7O28

Single crystals of RbBa₃Ca₄Cu₃V₇O₂₈ were prepared above the melting point of the reaction mixture. It crystallizes with hexagonal symmetry, space group C_6V⁴-P6₃mc, a 11.1751, c 12.434 Å, Z = 2. RbBa₃Ca₄Cu₃V₇O₂₈ is the second member of a new structure type of the copper-oxovanadates. Ba²⁺ shows an unusual 12-fold coordination. The two calcium positions are coordinated by trigonal prisms and octahedra respectively. The copper coordination is characterized by a stretched square pyramid. The Cu²⁺ ions are outside the centre nearly in plane of the pyramids.

Zusammenfassung

Einkristalle von RbBa₃Ca₄Cu₃V₇O₂₈ wurden oberhalb des Schmelzpunktes der Reaktionsmischung erhalten. Die Verbindung kristallisiert hexagonal, Raumgruppe C_6V⁴-P6₃mc, a 11.1751, c 12.434 Å, Z = 2. RbBa₃Ca₄Cu₃V₇O₂₈ ist das zweite Beispiel für einen neuen Strukturtyp der Kupfer-Oxovanadate, mit 12-fach koordinierten Ba²⁺ -Ionen. Die zwei Calciumpositionen sind trigonal prismatisch bzw. oktaedrisch koordiniert. Die Koordination der Cu²⁺-Ionen ist durch eine gestreckte Pyramide charakterisiert. Cu²⁺ ist auβerhalb des Polyederzentrums nahezu in der quadratischen Fläche der Pyramide angeordnet.     

Evolution of magnetic hardness in the HfFe6Ge6-type RMn6Sn6−xGax and RMn6Sn6−xInx compounds (R=Tb, Dy; 0.2≤x≤1.4)

The HfFe₆Ge₆-type RMn₆Sn_6−xX_x′ solid solutions (R=Tb, Dy, X′=Ga, In; x≤1.4) have been studied by powder magnetization measurements. All the series are characterized by ferrimagnetic ordering and by a decrease in Curie temperatures with the substitution (ΔT_c/Δx≈−39 K for X′=Ga and ΔT_c/Δx≈−75 K for X′=In). The RMn₆Sn_6−xGa_x systems are characterized by a strong decrease in the spin reorientation temperature with substitution (ΔT_t/Δx≈−191 K and −78 K for R=Tb and Dy, respectively) while this transition almost does not change in systems containing indium. The coercive fields drastically decrease with the substitution in the TbMn₆Sn_6−xGa_x system while the substitution of In for Sn has a weaker effect. The coercive fields of the Dy compounds do not vary greatly with the substitution in both series. The behaviour of the TbMn₆Sn_6−xGa_x is compared with the evolutions observed in the TmMn₆Sn_6−xGa_x series. This comparison strongly suggests that the replacement of Sn by Ga changes the sign of the A₀² crystal field parameter.     

Study of extraction of the ndcl3-smcl3-hcl-h2o-di-(2-ethylhexyl)-phosphoric-acid-kerosine system

The extraction equilibrium relations of neodymium and samarium were studied in the system HCl (1.0 mol dm⁻³)-di-(2-ethylhexyl) phosphorie acid (HDEHP), for a wide range of neodymium and samarium concentration (0.02-1.20 mol dm⁻³), mole fraction (X_i=0.005-0.995) and acidity (C_H+=0.27-1.06 mol dm⁻³). A relatively simple, high precision model for the distribution ratio D_i was established by correlating the experimental data with a progressive regression program D_i=exp(a₁+a₂I+a₃C_H++a₄X_i)I^a5X_i^{a6 In C_H+ + a7 In(1-X_i})

The extraction behaviour of the neodymium-samarium binary system was studied using the above model. The study of acid equilibrium shows that the extraction proceeds according to the cation exchange reaction within this range of experimental parameters. The neodymium and samarium concentrations in the organic phase increase rapidly and reach a maximum, and then decrease as the aqueous concentration increases; the maximum concentration appears at about 0.3-0.4 mol dm⁻³ of aqueous neodymium and samarium concentration. The variation of separation factors, β_Sm/Nd, was also studied with the change in aqueous acidity, rare earth concentration and mole fraction, β_Sm/Nd vary between 6.5 and 10.2 and the average value is 8.77.     

Preparation and structural characterization of perovskite-type LaxLn1−x″CoO3 by the thermal decomposition of heteronuclear complexes, LaxLn1−x″| Co(CN)6| · nH2O (Ln″ = Sm and Ho)

Perovskite-type La_xLn_1−x″CoO₃ oxides are prepared by the thermal decomposition of La_xLn_1−x″ [Co(CN)₆] · nH₂O hetero-nuclear complexes. Except for LaCoO₃ (hexagonal), the structures observed for La_xSm_1−xCoO₃ are othorhombic. While the perovskite-type oxide HoCoO₃ is not formed by decomposition at 1000°C of the corresponding hexacyano complex, the partial replacing of Ho with La is effective in forming the pervoskite-type oxide having an orthorhombic structure containing Ho even at 800°C. A monotonous correlation (quasi-linear relationship) was found between the b- and c-lattice constants of the orthorhombic structures of the perovskite-type oxides and the effective radii of Ln ions, defined as r_eff = xr_1.a + (1 − x)r_1.0″. The distortion parameter for the orthorhombie cell (3″a/b−1) increaseswith decrease in r_eff and is expected to be 0.270 for perovskite-type HoCoO₃. The crystal structure of the La_xLn_1−x″, CoO₃ oxides is mainly controlled by the effective radii of Ln ions.     

On the extrusion of silver-sheathed superconducting billets fabricated by explosive compaction of YBa2Cu3O7 powder

Explosive compaction of YBa₂Cu₃O₇ superconducting powder and forward extrusion of the produced “green” billet were employed to fabricate high critical temperature, T_c, superconducting composite rods consisting of a superconducting YBa₂Cu₃O₇ core and a silver metallic sheath. Experimental observations regarding the “soundness” of the fabricated component with respect to the compacting and processing conditions used as well as to the properties of the superconducting powder are reported. Microstructural and stochiometric changes and defects occuring in the “green” compacted billet and the extruded rod are indicated and discussed.     

The diffusion and trapping of hydrogen in high purity aluminum

The diffusion and trapping of hydrogen in high purity (99.999 wt%), polycrystalline aluminum was investigated using both isothermal and constant heating rate desorption techniques. Constant heating rate desorption was used to elucidate the effects of microstructural trap states on the apparent diffusivity of hydrogen in aluminum. Isothermal desorption of hydrogen from annealed, uniformly charged, cylindrical specimens was bulk diffusion controlled. Diffusion data exhibited simple Arrhenius behavior between 30 and 600°C and is described with 95% confidence by

Constant heating rate desorption spectra revealed three distinct trapping states with desorption energies 15.3±4.8, 43.5±17.5, and 84.8±32.2 kJ/mol. These trapping states are associated with interstitial lattice sites, dislocations, and vacancies, respectively. Identification, quantification, and understanding the role of these trap states in permeation and desorption experiments helps explain the large scatter in reported values of the diffusivity of hydrogen in aluminum.