Structure of Liquid Antimony by Neutron Diffraction

Neutron diffraction patterns from liquid antimony have been obtained at 660 and 800℃. The structure factors are nearly independent of temperature. Comparing the results with the structure of liquid bismuth and the hard sphere model the existence of two structure types in liquid antimony previously indicated seems to be ambiguous. The electrical resistivity was calculated using Ziman\u27s theory and compared with experimental data. From this in the case of liquid antimony the invalidity of the Born approximation in Ziman\u27s theory was found

Potentiometric determination of the gibbs energies of formation of SrZrO and BaZrO

The Gibbs free energies of formation of strontium and barium zirconates have been determined in the temperature range 960 to 1210 K using electrochemical cells incorporating the respective alkaline-earth fluoride single crystals as solid electrolytes. Pure strontium and barium monoxides were used in the reference electrodes. During measurements on barium zirconate, the oxygen partial pressure in the gas phase over the electrodes was maintained at a low value of 18.7 Pa to minimize the solubility of barium peroxide in the monoxide phase. Strontium zirconate was found to undergo a phase transition from orthorhombic perovskite (o) with space group Cmcm; D172h to tetragonal perovskite (t) having the space group 14/mcm;D 184h at 1123 (±10) K. Barium zirconate does not appear to undergo a phase transition in the temperature range of measurement. It has the cubic perovskite (c) structure. The standard free energies of formation of the zirconates from their component binary oxides AO (A = Sr, Ba) with rock salt (rs) and ZrO2 with monoclinic (m) structures can be expressed by the following relations: SrO (rs) + ZrO2 (m) → SrZrO3 (o) ΔG± = -74,880 - 14.2T (±1200) J mol-1 SrO (rs) + ZrO2 (m) → SrZrO3 (t) ΔG±= -73,645 - 15.37T (±200) J mol-1 BaO (rs) + ZrO2 (m) → BaZrO4 (c) ΔG± = -127,760-1.79T (±1250) J mol-1 The results of this study are in reasonable agreement with calorimetric measurements reported in the literature. Systematic trends in the stability of alkaline-earth zirconates having the stoichiometry AZrO3 are discussed

Partial Structure Factors of Liquid Na-K and Al-Mg Alloys(Physics)

Three partial structure factors S_(Q) have been evaluated from the scattered X-ray intensities of liquid Na-K and Al-Mg alloys assuming that the S_(Q) are independent of the relative abundance of the respective elements in the alloys. The functions S_(Q) and S_(Q) and the reduced radial distribution functions G_(r) and G_(r) obtained in this work are very similar to those observed in the respective pure liquid metals. In both cases, S_(Q) and G_(r) have maxima which lie in between those of the pure elements. From these results, liquid Na-K and Al-Mg alloys are interpreted as random mixing fluids. A comparison between the partial structure factors obtained in this work and those calculated from the hard sphere model was made. Adequate agreement was obtained on the low angle side of the first peak, but agreement on the whole pattern is not necessarily found. The electrical resistivity was calculated using Faber-Ziman\u27s theory and compared with experimental data

Sulphur potential measurements with a two-phase sulphideoxide electrolyte

The open circuit potentials of the galvanic cell,Pt (or Au)|(Ar + H2S + H2)'||CaS + ZrO2(CaO)|| (Ar + H2S+ H2)"|Pt (or Au) has been measured in the temperature range 1000 to 1660 K and PH2S:PH 2 ratios from 1.73×10-5 to 2.65×10-1. The solid electrolyte consists of a dispersion of calcium sulphide in a matrix of calcia-stabilized zirconia. The surface of the electrolyte is coated with a thin layer of calcium sulphide to prevent the formation of water vapour by reaction of hydrogen sulphide with calcium oxide or zirconia present in the electrolyte. The use of a point electrode with a catalytically active tip was necessary to obtain steady emfs. At low temperatures and high sulphur potentials the emfs agreed with the Nernst equation. Deviations were observed at high temperatures and low sulphur potentials, probably due to the onset of significant electronic conduction in the oxide matrix of the electrolyte. The values of oxygen and sulphur potentials at which the electronic conductivity is equal to ionic conductivity in the two-phase electrolyte have been evaluated from the emf response of the cell. The sulphide-oxide electrolyte is unsuitable for sulphur potential measurements in atmospheres with high oxygen potentials, where oxidation of calcium sulphide may be expected

Thermodynamic properties and phase equilibria for Pt-Rh alloys

The activity of rhodium in solid Pt-Rh alloys is measured in the temperature range from 900 to 1300 K using the solid-state cell Pt-Rh, Rh + Rh2O3/(Y2O3)ZrO2/Pt1-xRhx + Rh2O3, Pt-Rh The activity of platinum and the free energy, enthalpy, and entropy of mixing are derived. Activities exhibit moderate negative deviation from Raoult's law. The mixing properties can be represented by a pseudosubregular solution model in which excess entropy has the same type of functional dependence on composition as the enthalpy of mixing, ΔH = XRh (1 - XRh)[-10,970 + 45XRh] J/mol ΔSE = XRh (1- XRh)[-3.80 + 1.55 × 10-2 XRh] J/mol·K The negative enthalpy of mixing obtained in this study is in qualitative agreement with predictions of semiempirical models of Miedema and co-workers and Colinet et al. The results of this study do not support the solid-state miscibility gap suggested in the literature, but are consistent with liquidus data within experimental uncertainty limits

Improved modelling of liquid GeSe2_2: the impact of the exchange-correlation functional

The structural properties of liquid GeSe$_2$ are studied by using first-principles molecular dynamics in conjuncton with the Becke, Lee, Yang and Parr (BLYP) generalized gradient approximation for the exchange and correlation energy. The results on partial pair correlation functions, coordination numbers, bond angle distributions and partial structure factors are compared with available experimental data and with previous first-principle molecular dynamics results obtained within the Perdew and Wang (PW) generalized gradient approximation for the exchange and correlation energy. We found that the BLYP approach substantially improves upon the PW one in the case of the short-range properties. In particular, the Ge$-$Ge pair correlation function takes a more structured profile that includes a marked first peak due to homopolar bonds, a first maximum exhibiting a clear shoulder and a deep minimum, all these features being absent in the previous PW results. Overall, the amount of tetrahedral order is significantly increased, in spite of a larger number of Ge$-$Ge homopolar connections. Due to the smaller number of miscoordinations, diffusion coefficients obtained by the present BLYP calculation are smaller by at least one order of magnitude than in the PW case.Comment: 6 figure

Atomic Distribution and Magnetic Moment in Liquid Iron by Neutron Diffraction

The structure of iron in the liquid state has been studied by neutron diffraction at 1620℃. After calculation of the interference function (Fourier analysis), the atomic radial distribution function was evaluated from which interatomic distance and coordination number were obtained. The value of the magnetic moment of iron in the liquid state which was derived from the correction for the paramagnetic neutron scattering was 1.2 μB

System Cu-Rh-O: Phase diagram and thermodynamic properties of ternary oxides CuRhO₂ and CuRh₂O₄

An isothermal section of the phase diagram for the system Cu-Rh-O at 1273 K has been established by equilibration of samples representing eighteen different compositions, and phase identification after quenching by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive analysis of X-rays (EDX). In addition to the binary oxides Cu2O, CuO, and Rh2O3, two ternary oxides CuRhO2 and CuRh2O4 were identified. Both the ternary oxides were in equilibrium with metallic Rh. There was no evidence of the oxide Cu2Rh2O5 reported in the literature. Solid alloys were found to be in equilibrium with Cu2O. Based on the phase relations, two solid-state cells were designed to measure the Gibbs energies of formation of the two ternary oxides. Yttria-stabilized zirconia was used as the solid electrolyte, and an equimolar mixture of Rh+Rh2O3 as the reference electrode. The reference electrode was selected to generate a small electromotive force (emf), and thus minimize polarization of the three-phase electrode. When the driving force for oxygen transport through the solid electrolyte is small, electrochemical flux of oxygen from the high oxygen potential electrode to the low potential electrode is negligible. The measurements were conducted in the temperature range from 900 to 1300 K. The thermodynamic data can be represented by the following equations: 1/2Cu20+Rh203→CuRhO2 Af(ox)G°/J mol-1 = - 18,040 + 0.975 T/K (+ 40) CuO + Rh203 →CuRh204 Af(ox)G°/J mol-1 = - 23,760 + 1-92 TIK (+ 325), where Δf(ox) Go is the standard Gibbs energy of formation of the interoxide compounds from their component binary oxides. Based on the thermodynamic information, chemical potential diagrams for the system Cu-Rh-O were developed

Thermodynamic evidence for phase transition in MoO<SUB>2-&#948;</SUB>

The standard Gibbs free energy of formation of MoO2-&#948;, &#916;fG(MoO2-&#948;), has been measured over a wide temperature range (925 to 1925) K using an advanced version of bi-electrolyte solid-state electrochemical cell incorporating a buffer electrode: Pt|Mo + MoO2-&#948;||(Y2O3)ThO2||(CaO)ZrO2||O2(0.1MPa)|Pt The Gibbs free energy of formation of MoO2-&#948;, which is directly related to the measured cell e.m.f., can be represented by two linear segments: &#916;fG&#176;(MoO2-&#948;)&#177;570(Jmol-1)=-579,821+170.003(T/K) in the temperature range(925 to 1533)K, and &#916;fG&#176;(MoO2-&#948;)&#177;510(Jmol-1)=-564,634+160.096(T/K) in the temperature range (1533 to 1925) K. The change in slope at T = 1533 K is probably related to the phase transition of MoO2 from monoclinic structure with space group P21/c to tetragonal structure characteristic of rutile with space group P42/mnm. The enthalpy and entropy change for the phase transition are: &#916;Htr = (15.19 &#177; 2.1) kJ &#183; mol-1; &#916;Str = (9.91 &#177; 1.27) J &#183; mol-1&#183; K-1. The standard enthalpy of formation of MoO2-&#948; at T = 298.15 K assessed by the third-law method is: &#948;fH(M&#177;O2-&#948;) = (-592.28 &#177; 0.33) kJ&#183; mol-1. The new measurements refine thermodynamic data for MoO2

Contactless electrochemical reduction of titanium (II) chloride by aluminum

Because of the strong affinity between aluminum and titanium, it has not been possible to produce pure titanium by direct aluminothermic reduction of titanium chlorides. Described in this article is a new process for contactless reduction of titanium dichloride by aluminum in which titanium dichloride and the reductant (aluminum or aluminum alloy) were physically separated, but electrochemically connected through molten NaCl and an external circuit. Titanium dichloride was spontaneously reduced to metal by a cathodic reaction with the simultaneous discharge of chlorine ions into the melt. At the anode, metal aluminum was oxidized to form aluminum chloride dissolved in the molten salt. The electrons were transferred between the electrodes through the external circuit. The concentration of aluminum in titanium produced at 1223 and 1273 K varied from values below the detection limit of the X-ray fluorescence analysis (0.01 mass pct) to 4.5 mass pct. The average contamination was 0.76 mass pct Al. When an aluminum-nickel alloy was used as the reductant, nickel was not detected in the titanium obtained by reduction. This observation suggests that aluminum scrap may be used as a cheap reductant in this contactless electrochemical process