Thermodynamic stability of barium thorate, BaThO3, from a Knudsen effusion study

The Gibbs energy of formation of barium thorate was determined using the Knudsen effusion forward collection technique. The evaporation process could be represented by the equation

BaThO₃(s)=ThO₂(s)+BaO(g)

The vapour pressure of BaO(g) over the two-phase mixture of BaThO₃(s) and ThO₂(s) was obtained from the rate of effusion of BaO(g) and could be represented as

ln(p/Pa) (±0.39)=−50526.5/T/K+26.95 (1770≤T/K≤2136)

The Gibbs energy of formation of BaThO₃(s) could be derived from this data and represented as

Δ_fG°(BaThO₃(s))/kJ mol⁻¹±8.0=−1801.75+0.276T/K

     

Thermal properties of cerium and thorium tellurates

Enthalpy increment measurements on CeTe₂O₆ (s) and ThTe₂O₆ (s) were carried out using a Calvet micro-calorimeter. The enthalpy increment values were least squares analyzed, with the constraint that H⁰(T)−H⁰ (298.15 K) at 298.15 equals 0 and C_p⁰ (298.15 K) is equal to the value estimated by Kellog’s method.The dependence of the enthalpy increment with temperature can be given as:

H⁰(T)−H⁰ (298.15 K)(J mol⁻¹)=189.95 T (K)+15.226×10⁻³ T² (K) +15.414×10⁵/T (K)−63157 (CeTe₂O₆ (s), 391.5–848.0 K)

H⁰(T)−H⁰ (298.15 K)(J mol⁻¹)=191.34 T (K)+14.993×10⁻³ T² (K) +14.668×10⁵/T (K)−63300 (ThTe₂O₆ (s), 391.5–909.3 K)

Molar heat capacity C_p⁰(T), S(T) and Gibb’s free energy functions were evaluated.     

Thermodynamic properties of the ternary system InSb–NiSb–Sb in the temperature range 640–860 K

The ternary InSb–NiSb–Sb system has been studied by X-ray diffraction and by potentiometry. The electromotive forces (EMF) have been measured in the temperature range 640<T/K<860 by using the following galvanic cell:

with x (0.075<x<0.498) and y (0<y<0.359). The investigated samples are located on the following lines of the Gibbs triangle: InSb–Ni_0.33Sb_0.66, InSb–Ni_0.48Sb_0.52, InSb–NiSb, Sb–(InSb)_0.75(NiSb)_0.25, Sb–(InSb)_{0. 5}(NiSb)_0.5, Sb–(InSb)_0.25(NiSb)_0.75. From these measurements, the values of the partial molar thermodynamic functions (Δμ°_m,In, ΔH°_m,In, ΔS°_m,In) (data at reference pressure p⁰=10⁵ Pa), for the liquid InSb alloy, for the three solid heterogeneous regions InSb–NiSb₂–Sb, InSb–NiSb_1±δ?–NiSb₂, InSb–NiSb_1±δ, for six ternary liquid–solid alloys, have been calculated.     

Low-temperature thermoelectric properties of α- and β-Zn4Sb3 bulk crystals prepared by a gradient freeze method and a spark plasma sintering method

The low temperature thermoelectric properties of Zn₄Sb₃ samples prepared by the gradient freeze (GF) method and sintering have been characterized. With decreasing temperature a dramatic rise in the thermal expansion is observed associated with the structural transition from β- to α-phase; Δl/l=2.8×10⁻⁴ at T_s^GF=257.4 K for GF and Δl/l=1.6×10⁻⁴ at T_s^S=236.5 K for sintered samples. Enhancement is observed in electrical conductivity and p-type thermopower at T_s^GF and T_s^S, while a reduction is observed in the magnetic susceptibility. The GF sample exhibits higher thermoelectric performance than the sintered sample. The power factor of the α-phase in the GF sample is twice as large as that of the β-phase; it exceeds 20 μW/cm·K² between 120 and 240 K, indicating that the α-phase Zn₄Sb₃ is one of the prime candidates for thermoelectric materials for cryogenic use.     

Pressure–composition isotherms in the Mg2Ni–H2 system

A relatively pure Mg₂Ni intermetallic compound was prepared by partial melting and sintering. Absorption and desorption pressure–composition isotherms for the Mg₂Ni–H₂ system were obtained. The relationships between the equilibrium plateau pressure (P_eq) and the temperature were

and

The procedure to obtain the pressure–composition isotherms was explained and a method to calculate the composition for pressure–composition isotherms (“the summation method”) was also suggested.     

Adsorption of platinum(IV) onto D301R resin

Pt(IV) was quantitatively adsorbed by D301R resin in the medium of pH = 3.47. The statically saturated adsorption capacity is 410 mg/g. Pt(IV) adsorbed on D301R resin can be eluted by 1.0-2.0 mol/L NaOH. The rate constant is k₂₉₈ = 5.43 × 10⁻⁵S⁻¹. The adsorption of Pt(IV) on D301R resin obeys the Freundlich isotherm. The adsorption parameters of thermodynamics are as follows: enthalpy change ΔH = 4.37 kJ/mol, Gibbs free energy change ΔG = −5.39 kJ/mol, and entropy change ΔS = 32.76 J/(mol·K). The apparent activation energy is E_a = 22.5 kJ/mol. The coordination molar ratio of the functional group of D301R resin to Pt(IV) is 2:1.     

Sorption behavior of iminodiacetic acid resin for indium

In（Ⅲ） was quantitatively adsorbed by iminodiacetic acid resin （IDAAR） in the medium of pH = 4.52. The statically saturated sorption capacity of IDAAR is 235.5 mg·g^-1. 1.0 mol·L^-1 HCl can be used as an eluant. The elution efficiency is 97.9%. The resin can be regenerated and reused without apparent decrease of sorption capacity. The sorption rate constant is k298 = 1.94 × 10-5 s^-1. The apparent sorption activation energy of IDAAR for In（Ⅲ） is 20.1 kJ·mol^-1. The sorption behavior of IDAAR for In（HI） obeys the Freundlich isotherm. The enthalpy change is AH= 17.2 kJ·mol^-1.     

Conductivity of a new pyrophosphate Sn0.9Sc0.1(P2O7)1−δ prepared by an aqueous solution method

New pyrophosphate Sn_0.9Sc_0.1(P₂O₇)_1−δ was prepared by an aqueous solution method. The structure and conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ have been investigated. XRD analysis indicates that Sn_0.9Sc_0.1(P₂O₇)_1−δ exhibits a 3 × 3 × 3 super structure. It was found that Sn_0.9Sc_0.1(P₂O₇)_1−δ prepared by an aqueous method is not conductive. The total conductivity of Sn_0.9Sc_0.1(P₂O₇)_1−δ in open air is 2.35 × 10⁻⁶ and 2.82 × 10⁻⁹ S/cm at 900 and 400 °C respectively. In wet air, the total conductivity is about two orders of magnitude higher (8.1 × 10⁻⁷ S/cm at 400 °C) than in open air indicating some proton conduction. SnP₂O₇ and Sn_0.92In_0.08(P₂O₇)_1−δ prepared by an acidic method were reported fairly conductive but prepared by similar solution methods are not conductive. Therefore, the conductivity of SnP₂O₇-based materials might be related to the synthetic history. The possible conduction mechanism of SnP₂O₇-based materials has been discussed in detail.     

Synthesis and characterization of a series of bis(dimethyl-n-octylsilyl)oligothiophenes for organic thin film transistor applications

A series of bis-dimethyl-n-octylsilyl end-capped oligothiophenes consisting of two to six thiophene units has been synthesized and characterized to develop novel organic semiconductor materials. The UV–vis spectral data indicate that these silyl end-capped oligothiophenes have longer conjugation lengths as evidenced by the higher λ_max values than the corresponding unsubstituted thiophene oligomers. The thermal analyses indicate that the bis-silylated oligothiophenes show lower melting point (DSi-4T = 80 °C; DSi-5T = 115 °C; DSi-6T = 182 °C) than the corresponding dialkylated thiophene oligomers by 100 °C and hexamer DSi-6T exhibits a liquid crystalline mesophase at 143 °C. The α,ω-bis(dimethyl-n-octylsilyl)oligothiophenes (DSi-6T) have a remarkably high solubility in chloroform which are comparable to the corresponding α,ω-dihexyloligothiophenes. The remarkably increased solubility by these silyl end groups leads bis-silylated oligothiophenes to be applicable to solution processable devices for thin film transisitor (TFT) by utilizing a spin-coating technique. α,ω-Bis(dimethyl-n-octylsilyl)sexithiophene can be deposited as active semiconducting layer in thin film transistors, either by vacuum evaporation or by spin-coating. A high charge-carrier mobility has been obtained for both deposition techniques, μ = 4.6 × 10⁻² and 1.4 × 10⁻² cm² V⁻¹ s⁻¹, respectively.     

Elastic properties of amorphous and crystalline B1−xCx and boron at low temperatures

We present measurements of the internal friction (Q⁻¹) and speed of sound variation (δ

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₀) of amorphous boron (a-B) and amorphous B₉C (a-B₉C). The elastic properties of these materials, which can only be produced as thin films, are consistent with those of other amorphous solids measured to date and exhibit good agreement with the tunneling model (TM) of amorphous solids. The TM parameter

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γ_t²/ρ

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_t² extracted from the elastic data has the same order of magnitude as that observed for all amorphous solids studied to date; a review will be presented. Using the results from the elastic measurements, we calculate the T² thermal conductivity Λ expected in the TM regime (T≤1 K) for a-B. The predicted thermal conductivity falls within the expected range for amorphous solids and agrees with the thermal conductivity of the crystalline icosahedral boride MB_68-δ (M=Y, Gd), which has been previously shown to exhibit glass-like excitations. We have also measured the internal friction and speed of sound variation of bulk polycrystalline c-B_1−xC_x at low temperatures (0.07 K<T<10 K). The elastic properties evolve towards the behavior characteristics of amorphous solids for increasingly carbon-deficient (x<0.20) specimens. The magnitude of the internal friction for the most carbon-deficient crystalline c-B_1−xC_x sample (x=0.1, c-B₉C) is comparable to that for a-B and a-B₉C, thereby confirming the inherent glass-like vibrational properties of carbon-deficient c-B_1−xC_x. Such behavior supports the glass-like character of carbon-deficient c-B_1−xC_x high temperature (T>50 K) thermal transport reported previously and provides the first experimental evidence for the presence of two-level systems (TLS) in these crystalline solids. However, discrepancies with the tunneling model are present; the data for c-B_1−xC_x bear some similarity to those for amorphous metals in which electronic relaxation channels are active, although details are still unclear. Previous studies have shown that the TM quantity C=Pγ_t²/ρ

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_t² (“tunneling strength”) is essentially independent of the material's shear modulus G=ρ

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_t² over a factor of 17. The elastic data presented in this work now extend the observed independence of the tunneling strength, C, over a factor of 70 in shear modulus.     

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.     

Interfacial interaction of solid nickel with liquid Pb-free Sn–Bi–In–Zn–Sb soldering alloys

The dissolution process of nickel in liquid Pb-free 87.5% Sn–7.5% Bi–3% In–1% Zn–1% Sb and 80% Sn–15% Bi–3% In–1% Zn–1% Sb soldering alloys has been investigated by the rotating disc technique at 250–450 °C. The temperature dependence of the nickel solubility in soldering alloys obeys a relation of the Arrhenius type c_s = 4.94 × 10² exp(−39500/RT)% for the former alloy and c_s = 4.19 × 10² exp(−40200/RT)% for the latter, where R is in J mol⁻¹ K⁻¹ (8.314 J mol⁻¹ K⁻¹) and T is in K. Whereas the solubility values differ considerably, the dissolution rate constants are rather close for these alloys and fall in the range (1–9) × 10⁻⁵ m s⁻¹ at disc rotational speeds of 6.45–82.4 rad s⁻¹. Appropriate diffusion coefficients vary from 0.16 × 10⁻⁹ to 2.02 × 10⁻⁹ m² s⁻¹. With both alloys, the Ni₃Sn₄ intermetallic layer is formed at the interface of nickel and the saturated or undersaturated melt at dipping times of 300–2400 s. The other Ni–Sn intermetallic compounds are found to be missing. A simple mathematical equation is proposed to evaluate the Ni₃Sn₄ layer thickness in the case of undersaturated melts. The tensile strength of the nickel-to-alloy joints is 94–102 MPa, with the relative elongation being 2.0–2.5%.     

Role of thermal stability and vapor pressure of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)magnesium(II) and its triamine adduct in producing magnesium oxide thin film using a plasma-assisted LICVD process

Thin films of magnesia were deposited on various substrates using plasma-assisted liquid injection chemical vapor deposition with volatile Mg(tmhd)₂·2H₂O (1) (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione). The precursor complexes, Mg₂(tmhd)₄·(2), and Mg(tmhd)₂·pmdien (3) (pmdien; N,N,N′,N″,N″-pentamethyldiethylenetriamine) were prepared from Mg(tmhd)₂·2H₂O (1). The temperature dependence equilibrium vapor pressure (p_e)_T data yielded a straight line when log p_e was plotted against reciprocal temperature in the range of 360–475 K, leading to standard enthalpy of vaporization (Δ_vapH°) values of 59 ± 1 and 67 ± 2 kJ mol^− 1 for (2) and (3) respectively. Thin films of magnesium oxide were grown at 773 K using complex (1) on various substrate materials. These films were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray for their composition and morphology.     

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.     

The preparation and thermodynamic properties of Fe(II)---Fe(III) hydroxide-carbonate (green rust 1); Pourbaix diagram of iron in carbonate-containing aqueous media

Carbonate-containing green rust 1, GR1(CO₃²⁻), is prepared by oxidation of Fe(OH)₂ in aqueous solution. Ferrous hydroxide is precipitated from NaOH and FeSO₄·7H₂O solutions and carbonate ions are added as a Na₂CO₃ solution. For sufficiently large concentrations of sodium carbonate, SO₄²⁻ ions do not play any role during the oxidation process and, at the end of the first stage of reaction, Fe(OH)₂ oxidizes into GR1(CO₃²⁻). In the second stage of reaction, GR1(CO₃²⁻) oxidizes into α-FeOOH goethite except when the transformation of ferrous hydroxide is partial, which leads to the formation of magnetite. From the X-ray diffraction analysis of GR1(CO₃²⁻), lattice parameters of its hexagonal cell are found to be a = 3.160 ± 0.005 Å and C = 22.45 ± 0.05 Å. From the Mössbauer analysis of the stoichiometric GR1(CO₃²⁻), which leads to a Fe²⁺:Fe³⁺ ratio of 2:1, the chemical formula is established to be: [Fe₄^(II)Fe₂^(III)(OH)₁₂][CO₃·2H₂O]. The 78 K Mössbauer spectrum of the compound can be fitted with three quadrupole doublets, two Fe²⁺ doublets d₁ and D₂ corresponding to isomer shifts (IS) of 1.27 and 1.28 mm s⁻¹ and quadrupole splittings (QS) of 2.93 and 2.67 mm s⁻¹, respectively, and one Fe³⁺ doublet D₃ with an IS of 0.47 mm s⁻¹ and QS of 0.43 mm s⁻¹. These three doublets were already used to fit the Mössbauer spectrum of chloride-containing GR1(Cl⁻) [see J.M.R. Génin et al., Mat. Sci. Forum8, 477 (1986) and J.M.R. Génin et al., Hyp. Int. 29, 1355 (1986)]and therefore are characteristic of GR1 compounds. From the recording of electrode potential E and the pH of the suspension versus time during the oxidation, the standard free enthalpy of formation of stoichiometric GR1(CO₃²⁻) is estimated to be ΔG °_f = − 966.250 cal mol⁻¹. Knowing the chemical formula and ΔG °_f of GR1(CO₃²⁻) the Pourbaix diagram of iron in carbonate-containing aqueous solutions is drawn.     

Structural properties of Li–borate glasses doped with Sm and Eu ions

A Li–borate glass system doped with samarium and europium has been prepared by a conventional melt quenching technique. Europium content was kept constant at 0.01 mol%. The general formula was

xSm₂O₃ + (100 − x) [0.84B₂O₃ + 0.15Li₂O + 0.01Eu₂O₃]

where x = 0.1, 0.2, 0.5, 0.6 and 0.7 mol%. The density was measured and the corresponding molar volume was evaluated .The former was found to increase by increasing Sm while the later exhibits opposite trend. The average optical basicity, Λ_th, electron negativity χ_2av and electron polarizability α²⁻ were calculated for the prepared compositions. Infrared spectra were obtained at room temperature for the prepared glasses before and after γ irradiation. The results showed that the three main appeared bands are most likely due to the bending and/or stretching vibration of both tetrahedral BO₄ and triagonal BO₃ borate units. ESR spectra were recorded at room temperature before and after γ-irradiation. It was found that the oxygen atoms of BO₃ units are responsible for the formation of the hole paramagnetic centers after irradiation in the glass matrix.     

The anodic behaviour of copper in static and flowing hydrochloric acid solutions

The dissolution of copper in 0·36 to 3·6 HCl was studied both in static and in flowing solutions using flow rates between 0·098 and 1·14 ms⁻¹, all in the region of laminar flow.Steady state anode potential current curves, potentiodynamic sweep and potentiostatic pulse techniques and impedance measurements, in the range of 0·02–7 kHz, were used. In both static and flowing solutions dissolution of copper occurs to a monovalent state, as chloro-complexes CuCl⁻₂ and CuCl²⁻ with exchange currents for the two reactions of 1·9 × 10⁻⁵ A mm⁻² and 8 × 10⁻⁷ Amm⁻² respectively in 1·44 MHCl. The cuprous chloride layer first forms a monolayer and subsequently grows to considerable thicknesses. The double layer capacity is constant at 0·17 ± 0·03 μFmm⁻² at potentials below multilayer formation and this is interpreted as implying that there is no specific adsorption of chloride ions prior to formation of the cuprous chloride layer. As the flow rate increases the film becomes thinner so delaying the formation of the film of critical thickness required for passivation.     

Magnetite stability in aqueous solutions as a function of temperature

Magnetite solubility, as a function of temperature and partial hydrogen pressure, with reference to the typical conditions of the operating fluid of a steam generator of a thermal power plant, has been studied by rigorously solving the problem of equilibria and adopting the scheme proposed by Sweeton and Baes [J. Chem. Thermodynamics2, 479 (1970)]. Stoichiometric calculations have proved that magnetite solubility attains its maximum value, which depends on the characteristics of the electrolytic solution, when the temperature is about 100°C, independently of the type of environment. A rigorous pH calculation was carried out using the method of the characteristic function, which can be applied also to complex systems, and assuming that the effect of the ionic strength may be neglected. The main aim of this study, besides helping power plant chemists to select a proper feedwater conditioning, was to calculate the pH, on a molal basis, of a solution through the best-fit of its exact values, as a function of ammonia concentration inside the inverval 1.0 × 10⁻⁸ to 9.0 × 10⁻³ m with a third-degree logarithmic polynomial. The results, which were obtained in the case of a solution containing NH₄OH and H₂CO₃, demonstrate the validity of this technique which allows the pH of a fairly complex system to be computed accurately. It also allows the correct amount of magnetite dissolution products to be evaluated without considering in detail its chemical equilibria when the solution temperature is above 200°C. This remark was derived from the pH calculations of an ammonia containing solution, which showed its independence of partial hydrogen pressure in the high temperature region, at least as far as the interval 0–1 atm was concerned. The determination of the pH, on a molar basis, of a solution at temperatures of 200, 250, 300 and 350°C, contaminated with sea water so that its acid conductivity was 300μΩ⁻¹cm⁻¹, has been performed. These results have shown that the buffering effectiveness of ammonia is negligible when its concentration falls within the interval 1.0 × 10⁻⁶ to 2.0 × 10⁻⁵ M, whereas in the range 6.0 × 10⁻⁵ to 3.0 × 10⁻⁴ M, its effect is quite pronounced.     

High temperature oxidation of Nb-10 at. % W alloy

By means of the “interruption kinetic technique”, as applied to oxidation of tungsten under 0.048 bar O₂, the oxygen diffusion coefficient in growing WO_8−x has been determined for the temperature range of 568–908°C and may be expressed as: D = 6.83 × 10⁻² exp (−29,890/RT), with the activation energy given in cal/mole. Calculations are made to show the influence of temperature on the concentration of oxygen vacancies in WO_3−x, on their free energy of formation and on the ionic conductivity in WO_3−x. From the kinetic data of W oxidation at 800°C, prior to interruption-annealing, values of oxygen diffusion coefficients due to oxygen transport via lattice and short-circuit paths have been calculated as functions of time for growing WO_3−x. A simplified oxidation model is used for evaluation of the oxidation rate constant of W at 800°C.