Synthesis, Characterization, and Thermochemical Study on a Ternary Complex [Sm(m-MOBA)3phen]2

A new ternary solid complex of samarium chloride hexahydrate with m-methoxybenzoic acid and 1,10-phenanthroline, [Sm(m-MOBA)₃phen]₂ (m-MOBA: m-methoxybenzoic; phen: 1,10-phenanthroline), was synthesized and characterized by elemental analysis, IR spectra, UV spectra, molar conductance, and thermogravimetric analysis. The dissolution enthalpies of SmCl₃·6H₂O (s), m-HMOBA(s), phen·H₂O (s), and [Sm(m-MOBA)₃phen]₂(s) in the calorimetric solvent (V_DMF:V_CYC:V_HCl = 2:1:2) were determined by an advanced solution-reaction isoperibol calorimeter at 298.15 K, respectively. The standard molar enthalpy of reaction was determined to be D_r H_m^q = (233.97 ±1.15) kJ · mol^-1{\Delta_{\rm r} H_{\rm m}^\theta =(233.97 \pm 1.15)\,{\rm kJ}\,{\cdot}\,{\rm mol}^{-1}}. In accordance with Hess’ law, the standard molar enthalpy of formation of the title complex [Sm(m-MOBA)₃phen]₂(s) was estimated to be −(5054.6 ± 9.5) kJ · mol⁻¹.     

Thermal Diffusivity and Heat of Formation of Harzburgite and Its Major Constituent Minerals

The thermal diffusivity, D, and its temperature dependence of Oman harzburgite rock and its major mineral olivine have been evaluated from the basic properties such as seismic velocities, density, and Debye temperature. The Arrhenius-type temperature dependence of the diffusivity was utilized to evaluate the heat of formation, ΔH _D. The diffusivity values, 1.80mm² · s⁻¹ and 2.1mm² · s⁻¹ obtained at room temperature for harzburgite and olivine, respectively, are consistent with available data. The diffusivity values for Oman harzburgite are overestimated by an amount of 0.27mm² · s⁻¹ relative to those of PNG harzburgite. The ΔH _D value (−2.40 kJ · mol⁻¹) for harzburgite rock of the Oman ophiolite suite is comparable with that (−2.90 kJ · mol⁻¹) of the harzburgite rock of Papua New Guinea. The disagreements in the thermal diffusivity and heat of formation values may be partly due to ignoring the effect of pyroxene in Oman harzburgite.     

Measurement of Gibbs energies of formation of CoF2 and MnF2 using a new composite dispersed solid electrolyte

Gibbs energies of formation of CoF₂ and MnF₂ have been measured in the temperature range from 700 to 1100 K using Al₂O₃-dispersed CaF₂ solid electrolyte and Ni+NiF₂ as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF₂ thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al₂O₃ in the solid electrolyte and NiF₂ (or CoF₂) at the electrode, the dispersed solid electrolyte was coated with pure CaF₂, thus creating a composite structure. The free energies of formation of CoF₂ and MnF₂ are (± 1700) J mol⁻¹; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF₂ as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol⁻¹, which compares with a value of −671·5 (± 4) kJ mol⁻¹ given in Janaf tables. For solid MnF₂, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol⁻¹, which is significantly different from a value of −803·3 kJ mol⁻¹ given in the compilation by Barinet al.     

Thermophysical Property Measurements of Liquid Gadolinium by Containerless Methods

Thermophysical properties of liquid gadolinium were measured using non-contact diagnostic techniques with an electrostatic levitator. Over the 1585 K to 1920 K temperature range, the density can be expressed as ρ(T) = 7.41 × 10³ − 0.46 (T − T _m) (kg · m⁻³) where T _m = 1585 K, yielding a volume expansion coefficient of 6.2 × 10⁻⁵ K⁻¹. In addition, the surface tension data can be fitted as γ(T) = 8.22 × 10² − 0.097(T − T _m)(10⁻³ N · m⁻¹) over the 1613 K to 1803 K span and the viscosity as η(T) = 1.7exp[1.4 × 10⁴/(RT)](10⁻³ Pa · s) over the same temperature range.     

Effect of aluminum doping on electrical and dielectric aging behavior against current impulse of ZPCCY-based varistors

The electrical and dielectric aging behavior against current impulse (5–1,200 A) in the Zn-Pr-Co-Cr-Y-based varistors was investigated with aluminum doping level (0–0.01 mol%). The varistors doped with 0–0.001 mol% Al were destroyed at higher current impulse beyond 900 A and the varistors doped with 0.005–0.01 mol% Al exhibited high stability against current impulse. The clamp ratio (K) at given current impulse ranges decreased with increasing Al doping level. The varistor doped with 0.01 mol% Al exhibited the lowest K value, with 1.65 at a current impulse of 10 A and 2.38 at a current impulse of 1,200 A. The best electrical and dielectric stability against current impulse of 1,200 A was obtained at 0.01 mol% Al, where %\Updelta E_{1  \textmA/cm²} = -3.4%\%\Updelta E_{1\;\text{mA/cm}^2} = -3.4\%, %Δα = 0%, %ΔJ _L = −26.3%, %Δε′_APP = +3.4%, and %Δtanδ = −7.7%. Conclusively, Al doping level was optimized at 0.01 mol% in terms of the surge withstand capability (SWC).     

On the α-relaxation in bulk polyoxymethylene

Values quoted forΔH _α, the activation energy of the high temperatureα-relaxation in polyoxymethylene (POM), range from 20 to 92 kcal mol⁻¹. This paper seeks to rationalize the discrepancy by remeasuringΔH _α using time-temperature superposition of torsional creep and dynamic compliances for a POM specimen annealed at 160° C. Superposition of loss compliance curvesJ″ (ω, T) is possible over the range 20 to 120° C but creep compliance curvesJ(t, T) fail to superpose above about 70° C. The creep anomaly is explained in terms of the McCrum-Morris reduction equations in which the unrelaxed complianceJ _U ^T increases with temperature more rapidly than the relaxed complianceJ _R ^T . The activation energyΔH _α has a constant value of 21±1 kcal mol⁻¹ below about 70° C. Above about 70° C,ΔH _α increases steadily up to 33±2 kcal mol⁻¹ at 120° C.     

Diffusivity and solubility of oxygen in solid palladium

The solid solubility c _O of oxygen in palladium in equilibrium with gaseous oxygen has been determined from absorption-desorption experiments for temperatures T of 1123 and 1173 K and oxygen partial pressures between 2.7 × 10³ and 4.0 × 10⁴ Pa. The relationship between c _O, and T is given by , where R = 8.314 JK⁻¹ mol⁻¹ is the universal gas constant, ΔH _s = −13.55 kJ/mol denotes the heat of solution of oxygen in palladium and the constant a amounts to or . The diffusion coefficient D _O of oxygen in solid palladium has been determined by incomplete isothermal internal oxidation of Pd–Fe alloys using the data on the oxygen solubility in palladium. The temperature dependence of D _O obeys the Arrhenius equation D _O = D ⁰ exp(−E _d/RT) with pre-exponential factor D ⁰ = 2.33 × 10⁻⁷ m²/s and activation energy of diffusion of oxygen in palladium, E _d = 102.76 kJ/mol     

Benzene-methanol association. The excess molar enthalpy and second virial cross coefficients of (benzene+methanol)(g) and (cyclohexane+methanol)(g)

New measurements of the excess molar enthalpyH _m ¹ of (yCH₃OH+(1−y)C₆H₆)(g) and (yCH₃OH+(1−y)C₆H₁₂)(g) measured at standard atmospheric pressure over the temperature range 363.2 to 433.2 K are reported. these measurements supplement earlier measurements made over the range 454.2 to 523.0 K at pressures up to 4.0 MPa. The nonideality of the methanol vapor is described using a quasi chemical model model in which only dimer and tetramer association equilibria are considered. The values ofH _m ¹ for the (methanol+cyclohexane)(g) mixture were found to agree well with values calculated using the association model. For (methanol+benzene)(g) the experimental values ofH _m ¹ were found to be approximately 20% smaller than values calculated from the model and this was attributed to weak association between the unlike molecules. A quasi-chemical model used to describe the association between the unlike molecules yielded a value of the equilibrium constantK ₁₂(298.15 K)=0.22 MPa⁻¹, and a value for the enthalpy of the methanol-benzene association of ΔH ₁₂=−13 kJ·mol⁻¹. Second virial crosscoefficientsB ₁₂ for methanol-cyclohexane and methanol-benzene have been derived from theH _m ¹ measurements.     

Phase and morphology evolution of calcium carbonate precipitated by carbonation of hydrated lime

Phase and morphology evolution of CaCO₃ precipitated during carbonation of lime pastes via the reaction Ca(OH)₂ + CO₂ → CaCO₃ + H₂O has been investigated under different conditions (pCO₂ ≈ 10^−3.5 atm at 60 % RH and 93 % RH; pCO₂ = 1 atm at 93 % RH) using XRD, FTIR, TGA, and SEM. Simulations of the pore solution chemistry for different stages and conditions of carbonation were performed using the PHREEQC code to investigate the evolution of the chemistry of the system. Results indicate initial precipitation of amorphous calcium carbonate (ACC) which in turn transforms into scalenohedral calcite under excess Ca²⁺ ions. Because of their polar character, { 21[`3]4 } \left\{ {21\bar{3}4} \right\} scalenohedral faces (type S) interact more strongly with excess Ca<sup>2+</sup> than non-polar { 10[`1]4 } \left\{ {10\bar{1}4} \right\} rhombohedral faces (type F), an effect that ultimately favors the stabilization of { 21[`3]4 } \left\{ {21\bar{3}4} \right\} faces. Following the full consumption of Ca<sup>2+</sup> ions and further dissolution of CO<sub>2</sub> leading to a pH drop of the pore solution, { 21[`3]4 } \left\{ {21\bar{3}4} \right\} scalenohedra are subjected to dissolution. This eventually results in re-precipitation of { 10[`1]4 } \left\{ {10\bar{1}4} \right\} rhombohedra at close-to-neutral pH. This crystallization sequence progresses through the carbonated depth with a strong dependence on the degree of exposure to CO₂, which is controlled by the carbonated pore structure governing the diffusion of CO₂. Both the carbonation process and the scalenohedral-to-rhombohedral transformation are kinetically favored under high RH and high pCO₂. Supersaturation plays a critical role on the nucleation density and size of CaCO₃ crystals. These results have important implications in understanding the behavior of ancient and modern lime mortars for applications in architectural heritage conservation.     

Heating Characteristics of Transformer Oil-Based Magnetic Fluids of Different Magnetic Particle Concentrations

The heating ability of mineral oil-based magnetic fluids with different magnetic particle concentrations is studied. The calorimetric measurements were carried out in an alternating magnetic field of 500 A · m⁻¹ to 2500 A · m⁻¹ amplitude and of 1500 kHz frequency. The revealed H ⁿ law-type dependence of the temperature increase rate, (dT/dt) _t=0, on the amplitude of the magnetic field indicates the presence of superparamagnetic and partially ferromagnetic particles in the tested samples since n > 2. The specific absorption rate (SAR) defined as the rate of energy absorption per unit mass increases with a decrease of the volume fraction of the dispersed phase. This can be explained by the formation of aggregates in the samples with a higher concentration of magnetic particles.     

Experimental Study of the Critical Behavior of the Isochoric Heat Capacity of Aqueous Ammonia Mixture

The isochoric heat capacity of a NH₃ + H₂O (0.2607 mole fraction of ammonia) mixture has been measured in the near- and supercritical regions. Measurements were made in the single- and two-phase regions including the coexistence curve using a high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter. Measurements were made along 38 liquid and vapor isochores in the range from 120.03 kg · m⁻³ to 671.23 kg · m⁻³ and at temperatures from 478 K to 634 K and at pressures up to 28 MPa. Temperatures at the liquid–gas phase transition curve, T _S(ρ), for each measured density (isochore) and the critical parameters (T _C and ρ _C) for the 0.2607 NH₃ + 0.7393  H₂O mixture were obtained using the quasi-static thermograms technique. The expanded uncertainty of the heat-capacity measurements at the 95 % confidence level with a coverage factor of k = 2 is estimated to be 2 % to 3 % in the near-critical and supercritical regions, 1.0 % to 1.5 % in the liquid phase, and 3 % to 4 % in the vapor phase. Uncertainties of the density, temperature, and concentration measurements are estimated to be 0.06 %, 15mK, and 5×10⁻⁵ mole fraction, respectively. An unusual behavior of the isochoric heat capacity of the mixture was found near the maxcondetherm point (in the retrograde region). The value of the Krichevskii parameter was calculated using the critical properties data for the mixture and vapor-pressure data for the pure solvent (H₂O). The derived value of the Krichevskii parameter was used to analyze the critical behavior of the strong (C _P , K _T ) and weakly (C _V ) singular properties in terms of the principle of isomorphism of critical phenomena in binary mixtures. The values of the characteristic parameters (K ₁, K ₂), temperatures (τ ₁, τ ₂), and the characteristic density differences (Δρ ₁, Δρ ₂) were calculated for the NH₃ + H₂O mixture by using the critical-curve data.     

Critical and Gaussian Conductivity Fluctuations in Granular Ho1?xPrxBa2Cu3O7?δ Superconductor

Fluctuations in the electrical conductivity of polycrystalline Ho_1−x Pr _x Ba₂Cu₃O_7−δ superconductors were investigated with Ho contents from x=0.01 up to 0.10. Samples were prepared by the standard solid-state reaction technique. The method of analysis is based on the determination of the quantity c_s^-1=-\fracddTlnDs\chi_{\sigma}^{-1}=-\frac{d}{dT}\ln\Delta\sigma, where Δσ=σ−σ _R is the fluctuation conductivity. The results show that the resistive transition proceeds in two stages as seen by the temperature derivative of the resistivity near T _C . In the normal phase, Gaussian and critical fluctuation conductivity regimes were identified. The pairing transition splitting, associated with Pr doping and related to the occurrence of a phase separation, as observed in studies with other rare earth elements, was not clearly observed. On approaching the zero-resistance state, our results show a power-law behavior that corresponds to a phase transition from a paracoherent to a coherent state of the granular array. This behavior was not affected by Pr doping.     

A Study of Specific Heat Capacity Functions of Polyvinyl Alcohol–<Emphasis Type="Italic">Cassava</Emphasis> Starch Blends

The specific heat capacity (C _sp) of polyvinyl alcohol (PVOH) blends with cassava starch (CSS) was studied by the differential scanning calorimetry method. Specimens of PVOH–CSS blends: PPV37 (70 mass% CSS) and PPV46 (60 mass% CSS) were prepared by a melt blending method with glycerol added as a plasticizer. The results showed that the specific heat capacity of PPV37 and PPV46 at temperatures from 330 K to 530 K increased from (2.963 to 14.995)  J· g⁻¹ · K⁻¹ and (2.517 to 14.727)  J · g⁻¹· K⁻¹, respectively. The specific heat capacity of PVOH–CSS depends on the amount of starch. The specific heat capacity of the specimens can be approximated by polynomial equations with a curve fitting regression > 0.992. For instance, the specific heat capacity (in J · g⁻¹ · K⁻¹) of PPV37 can be expressed by C _sp = −17.824 + 0.063T and PPV46 by C _sp = −18.047 + 0.061T, where T is the temperature (in K).     

Phosphonium iodine as nickel corrosion inhibitor in 1 M sulfuric acid medium

The inhibiting action of alkyltriphenylphosphonium iodine salt ((C₈H₁₇)Ph₃P⁺,I⁻) towards the corrosion behaviour of nickel in 1 M H₂SO₄ solution has been studied. This compound was found to retard both anodic and cathodic reactions of nickel corrosion. At constant temperature, the corrosion rate decreases with increasing inhibitor concentration. On the other hand, the increase in temperature leads to an increase in the corrosion rate. The activation energy, ΔE _a, were calculated. They were found 19.3 kJ mol⁻¹ and 71.1 kJ mol⁻¹, respectively for the uninhibited solution and in the presence of 10⁻³ M of phosphonium salt. The inhibitor adsorption was identified to occur according to Langmuir isotherm. The equilibrium constant, k, as well as the free energy of adsorption, Δ_ads G°, for inhibitor process were then calculated. Phosphonium iodine exhibited a singular behaviour for T ≥ 318 K where inhibitor desorption increases.     

Spillover effect in the hydrogen absorption by the polycrystalline powder alloy FeNi1.75Cu1.5Mo0.5 and electric conductivity of the pressed powder

The process of hydrogen absorption by the FeNi_1.75Cu_1.5Mo_0.5 alloy in the polycrystalline form was investigated for both the pure and palladized forms (0.008 76% Pd) at temperatures from ambient to 600 °C in a hydrogen flow. Using differential scanning calorimetry, (DSC) thermogravimetry (TG) and X-ray diffraction, the influence of palladization on the hydrogen absorption was demonstrated. Kinetic analysis of the DSC thermograms, the kinetic and thermic parameters of hydrogen absorption were determined. The TG thermograms showed that on hydrogen absorption a weight change took place due to water formation and reduction of the oxide film at the surface of the powder particles. The activation energies of hydrogen absorption were 170 kJ mol⁻¹ for the original powder and 32 kJ mol⁻¹ for the palladized one. The enthalpies of the absorption ranged from ΔH = −5 to ΔH = −380 J g⁻¹ for the original and palladized powder, respectively. The rate constants of the absorption depended on the palladization and were found to be 0.03 and 1.20 s⁻¹, respectively, at 162 °C. The electric conductivity of the pressed powder (9 kbar) increases on heating in both air and a hydrogen atmosphere up to 600 °C, tending to a constant value. The changes of the parameters characteristic of the palladized form are ascribed to the mechanism of a hydrogen spillover effect due to the presence of palladium.     

Thermophysical and Magnetic Properties of Carbon Beads Containing Cobalt Nanocrystallites

Magnetic Co-beads were fabricated in the course of a three-step procedure comprising preparation of a metal–acrylamide complex, followed by frontal polymerization and finally pyrolysis of the polymer. The composites obtained were composed of cobalt nanocrystallites stabilized in a carbon matrix built of disordered graphite. The crystallite size, material morphology, fraction of the magnetic component, and thus the magnetic properties can be tailored by a proper choice of the processing variables. The samples were subjected to an alternating magnetic field of different strengths (H = 0 to 5 kA · m⁻¹) at a frequency of f = 500 kHz. From the calorimetric measurements, we concluded that the relaxation processes dominate in the heat generation mechanism for the beads pyrolyzed at 773 K. For the beads pyrolyzed at 1073 K, significant values of magnetic properties, such as the coercive force and remanence give substantial contribution to the energy losses for hysteresis. The specific absorption coefficient (SAR) related to the cobalt mass unit for the 1073 K pyrolyzed beads (SAR = 1340   W ·g^-1 _cobalt){({\it SAR} = 1340 \, \, {\rm W} \cdot {\rm g}^{-1 }_{\rm cobalt})} is in very good conformity with the results obtained by other authors. The effective density power loss, caused by eddy currents, can be neglected for heating processes applied in magnetic hyperthermia. The Co-beads can potentially be applied for hyperthermia treatment.     

Testing the hypothesis of a general linear model using nonparametric regression estimation

Summary Given the modelY _i =m(χ _i )+ɛi,whereE(ɛ _i) =0,X _i ≠Ci=1, ...,n, andC is ap-dimensional compact set, we have designed a new method for testing the hypothesis that the regression function follows a general linear model,m(·) ∈ {m _θ(·) =A ^t (·)θ}_{θ∈Θ⊂ℛq} , withA a function fromℜ ^p toℜ ^q. The statistic, denoted ΔASE, used fortesting the given hypothesis is defined to be the difference between the average squared errors (ASE) associated with the non-parametric estimator ofm and the minimum distance parametric estimator ofm. The asymptotic normality of both ΔASE and the minimum distance estimators is proved under general conditions. Alternative bootstrap versions of ΔASE are also considered.     

Combustion synthesis of TiNi intermetallic compounds

The synthesis of the TiNi intermetallic compound using the thermal explosion mode of the combustion synthesis technique has been used to determine the heat of fusion, ΔH _m (7.77 kcal mol⁻¹), of the TiNi intermetallic and the heat capacity,C _p1 (17.96 cal mol⁻¹ K⁻¹), of the liquid-phase TiNi. The effect of heating rate and degree of dilution of the Ti + Ni powder compact reactants with previously synthesized TiNi on the ignition,T _ig, and combustion,T _c, temperatures in an argon atmosphere have been determined. It was found thatT _c was dependent on heating rate and dilution with TiNi, whereasT _ig remained unchanged with respect to these two process variables.     

Low-Temperature Heat Capacities and Standard Molar Enthalpy of Formation of Potassium Benzoate C<Subscript>7</Subscript>H<Subscript>5</Subscript>O<Subscript>2</Subscript>K(s)

Potassium benzoate C₇H₅O₂K (CAS Registry No. 582-25-2) was synthesized by the method of liquid phase reaction. Chemical and elemental analyses, FTIR, and X-ray powder diffraction (XRD) techniques were applied to characterize the composition and structure of the compound. Low-temperature heat capacities of the compound were measured by a precision automated adiabatic calorimeter over the temperature range from 78 K to 398 K. A polynomial equation of the heat capacities as a function of temperature was fitted by the least-squares method. Smoothed heat capacities and thermodynamic functions of the compound were calculated based on the fitted polynomial. In accordance with Hess’s law, a reasonable thermochemical cycle was designed, and 100 mL of 1 mol · dm⁻³ NaOH solution was chosen as the calorimetric solvent. The standard molar enthalpies of dissolution for the reactants and products of the supposed reaction in the selected solvent were measured by an isoperibol solution-reaction calorimeter. Finally, the standard molar enthalpy of formation of the title compound C₇H₅O₂K (s) was derived to be -(610.94 ± 0.77) kJ · mol⁻¹.     

Scaling of the Temperature Dependent Resistivity and Hall Effect in Ba(Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)As<Subscript>2</Subscript>

We show that the temperature-dependent resistivity ρ(T), Hall number n _H(T) and the cotangent of the Hall angle cot θ _H(T) of Ba(Fe_1−x Co _x )As₂ (x=0.0–0.2) can be scaled using a recently proposed model-independent scaling method (Luo et al. in Phys. Rev. B 77:014529, 2008). The zero field normal-state resistivity above T _c can be reproduced by the expresion r(T) = r₀ +cTexp(- \frac2\varDelta T )\rho(T) = \rho_{0} +cT\exp(- \frac{2\varDelta }{T} ) and scaled using the energy scale Δ, c and the residual resistivity ρ ₀ as scaling parameters. The scaling parameters have been calculated and the compositional variation of 2Δ and ρ ₀ has been determined. The 2Δ(x) dependence show almost linear decreasing in underdoped regime, minimum corresponding to the T _c maximum and increasing in overdoped regime. The latter is different from that reported for cuprates. The existence of a universal metallic ρ(T) curve which, however, is restricted for the underdoped compounds to temperatures above a structural and antiferromagnetic transition is interpreted as an indication of a single mechanism which dominates the scattering of the charge carriers in Ba(Fe_1−x Co _x )As₂ (x=0.0–0.2).