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.     

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.     

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.     

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.     

Thermodynamic Properties of Matrine in Ethanol

In this paper, the enthalpies of dissolution of matrine in ethanol (EtOH) were measured using a RD496-2000 Calvet microcalorimeter at 309.65 K under atmospheric pressure. The differential enthalpy (Δ_dif H _m) and molar enthalpy (Δ_sol H _m) of dissolution of matrine in ethanol were determined. And the relationship between heat and the amount of solute was also established. Based on the thermodynamic and kinetic knowledge, the corresponding kinetic equation that described the dissolution process was determined to be \fracdadt=2.36×10^-4(1-a)^1.09{\frac{{\rm d}\alpha}{{\rm d}t}=2.36\times 10^{-4}(1-\alpha )^{1.09}} . Moreover, the half-life, t _1/2 = 48.89 min, Δ_sol H _m = −12.40 kJ · mol⁻¹, Δ_sol S _m = −354.7 J · mol⁻¹ · K⁻¹, and Δ _sol G _m =  97.43  kJ · mol⁻¹ of the dissolution process were also obtained. The results show that this work not only provides a simple method for the determination of the half-life for a drug but also offers a theoretical reference for the clinical application of matrine.     

Preparation of volatile oxygen-containing americium compounds separated by gas thermochromatography

Gas thermochromatographic experiments aimed to prepare volatile oxygen-containing americium compounds were performed. Under the experimental conditions, Am formed three volatile compounds: AmO₂, previously unknown trioxide AmO₃, and, presumably, acid of the composition H₂AmO₄, with centers of the adsorption zones at ∼475, ∼315, and ∼140°C. The calculated enthalpies of adsorption −ΔH _a⁰ of these compounds on the quartz surface (kJ mol⁻¹) are 180 ± 10, 144 ± 7, and 109 ± 8, respectively. Americium di- and trioxide are less volatile than the respective oxides of U, Np, and Pu. The same trend was observed with the presumed acids.     

Sintering studies on submicrometre-sized Y-Ba-Cu-oxide powder

The isothermal sintering behaviour of submicrometre-sized (<50 nm) powders of single-phase YBa₂Cu₃O _x (123) and unreacted stoichiometric mixture of submicrometre-sized (<50 nm) powders of BaCO₃, Y₂O₃ and CuO (which on calcination at 1173 K gives YBa₂Cu₃O _x ) was investigated through dilatometry under different sintering atmospheres. The sintering rate of the powder compacts was impeded by the presence of oxygen. The activation energies,Q, of sintering were determined to be 1218 kJ mol^–1 in argon, 1593 kJ mor^–1 in air and 2142 kJ mol^–1 in oxygen. A decrease in the apparent sintered density with increasing oxygen partial pressure was also observed. X-ray diffraction and thermal analyses (thermogravimetry and differential thermal analysis) showed no reaction during sintering of the single-phase product. Pellets fabricated from uncalcined powder exhibit two stages of sintering, one between 1073 and 1173 K having an activation energyQ=627kJ mol^–1, and a second one above 1173 K withQ=383.7 kJ mol^–1. A.c. susceptibility, resistivity and critical current density were determined as a function of the temperature of the sintered samples.     

Oxidation of carbohydrazide with nitric acid

The kinetics of carbohydrazide oxidation with nitric acid in aqueous solutions was studied. In the range [HNO₃] = 3–7 M, the reaction rate is described by the equation −d[(NH₂NH)₂CO]/dt = k[(NH₂NH)₂CO][HNO₃] ⁿ , where n = 3.6 and 2.9 at 70 and 90°C, respectively. The constant k = (6.65 ± 0.23) × 10⁻⁴ l^2.9 mol^−2.9 h⁻¹ at 90°C, and the activation energy of the reaction in 7 M HNO₃ is 124 kJ mol⁻¹. The Fe(III) and especially Tc(VII) ions considerably accelerate the reaction, whereas the uranyl ions accelerate it insignificantly. The reaction mechanism in which the reactive species oxidizing carbohydrazide is nitronium ion NO₂⁺ was suggested.     

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.     

Rheological properties of Y-Si-Al-O-N glasses — elastic moduli,viscosity and creep

Three oxynitride glasses from the Y-Si-Al-O-N system and differing in their N/O ratio were studied in the 800–1000 °C temperature range. Their viscosities were measured using a threepoint bending test through the glass transition domain. For a given temperature, 4.8 wt % N₂ enhances the viscosity by three orders of magnitude in comparison with the corresponding oxide glass. Nitrogen also improves creep resistance. The activation enthalpy for creep, aboveT _g, is of the same order as those measured for silicon nitride ceramic (∼900 kJ mol⁻¹). The elastic moduli were determined by ultrasonic techniques, from room temperature up to 1200 °C, which allowed calculation of the free activation enthalpy for viscous flow. Owing to the sharp decrease of shear modulus in the glass transition domain, the free activation enthalpy (∼500 kJ mol⁻¹) greatly differs from the activation enthalpy usually measured in creep studies.     

Formation of volatile neptunium trioxide NpO<Subscript>3</Subscript> and two other products of neptunium oxidation

Thermochromatographic (TC) experiments aimed to obtain volatile products of thermal oxidation of trace amounts of ²³⁷Np were performed. The oxidation products were separated on quartz TC columns. The carrier gas was He, and the reagent, O₂ in a concentration of 50 or 1 vol %. The gaseous mixture was dried to a residual water vapor concentration of 10⁻⁴%. Three volatile species depositing at 425 ± 25, 245 ± 25, and 60 ± 30°C were formed under the experimental conditions. The product depositing in the first adsorption zone is NpO₂; that depositing in the second zone, neptunium trioxide NpO₃; and that depositing in the third zone is tentatively identified as the acid HNpO₄. The calculated enthalpies of adsorption −ΔH _a⁰ (kJ mol⁻¹) of the deposited products on quartz are as follows: 167 ± 6 (NpO₂), 124 ± 6 (NpO₃), and 81 ± 7 (presumably HNpO₄).     

An investigation of the effect of Ti, Pd and Zr on the dehydriding kinetics of MgH2

The effect of additives Ti, Pd and Zr on the rate of hydrogen desorption from MgH₂ is investigated using high-pressure differential scanning calorimetry. Van’t Hoff analysis as well as X-ray powder diffraction measurements confirm that no new intermetallic phases are formed in these systems but enhanced dehydriding kinetics are obtained in the presence of Pd and Zr. For the Mg–Zr composite, Zr precipitates are formed throughout the material on heating to 500 °C but these do not grow with further thermal cycling. The desorption rate for all the composites was found to increase with temperature as well as pressure difference between experimental and equilibrium pressures. A value of 114 ± 4 kJ mol⁻¹ was obtained for the activation energy for dehydriding of the Mg–Ti–Pd composite.     

Crystal growth of tetragonal ZrO2 in the glass system ZrO2-SiO2 prepared by the sol-gel process from metal alkoxides

Glasses in the system ZrO₂-SiO₂ containing 40 to 60 mol % ZrO₂ were prepared by the sol-gel process from metal alkoxides. Tetragonal ZrO₂ was precipitated by heat treatment at 800 and 1200° C, and its crystal growth was measured by differential thermal and X-ray diffraction analyses. At 800 to 900° C, tetragonal ZrO₂ crystals grew three-dimensionally and the activation energy for growth was calculated as about 680 kJ mol⁻¹. On the other hand, the secondary growth of tetragonal ZrO₂ at 1000 to 1200° C followed the cube-root-of-time law. The activation energy for secondary growth was about 380 kJ mol⁻¹. It is suggested that the diffusion of Zr⁴⁺ ions is the rate-limiting process for the secondary crystal growth of tetragonal ZrO₂.     

Reduction of Np(V) with Fe(II) in weakly acidic solutions containing H<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>

The kinetics of the reaction of Np(V) with Fe(II) in dilute perchloric and nitric acid solutions containing H₂C₂O₄ was studied by spectrophotometry. In the range pH 1–2, the reaction rate is described by the equation d[Np(V)]/dt = k[Np(V)][Fe(II)][H₂C₂O₄]²[H⁺]^−1.6, k = 182 mol^−1.4 l^1.4 s⁻¹. The activation energy in the range 25–45°C is 26 kJ mol⁻¹. The reaction mechanism involves formation of Fe(II) and Np(V) oxalate complexes, followed by their reaction with the participation of the H⁺ ion.     

Investigation on Phase Transitions and Thermodynamic Properties of 1-Dodecylamine Hydrochloride (C<Subscript>12</Subscript>H<Subscript>25</Subscript>NH<Subscript>3</Subscript>Cl)(s) by an Improved Adiabatic Calorimeter

1-Dodecylamine hydrochloride was synthesized by the solvent-thermal method. The structure and composition of the compound were characterized by chemical and elemental analyses, the X-ray powder diffraction technique, and X-ray crystallography. The main structure and performance of an improved automated adiabatic calorimeter are described. Low-temperature heat capacities of the title compound are measured by the new adiabatic calorimeter over the temperature range from 78 K to 397 K. Two solid-to-solid phase transitions have been observed at the peak temperatures of (330.78 ± 0.43) K and (345.09 ± 0.16) K. The molar enthalpies of the two phase transitions of the substance were determined to be (25.718 ± 0.082) kJ · mol⁻¹ and (5.049 ± 0.055) kJ · mol⁻¹, and their corresponding molar entropies were calculated as (77.752 ± 0.250) J · mol⁻¹ · K⁻¹ and (14.632 ± 0.159) J · mol⁻¹ · K⁻¹, respectively, based on the analysis of heat–capacity curves. Experimental values of heat capacities for the title compound have been fitted to two polynomial equations. In addition, two solid-to-solid phase transitions and a melting process of C₁₂H₂₅NH₃Cl(s) have been verified by differential scanning calorimetry.     

Synthesis and nonlinear optical properties of novel Y-type polyurethanes with high thermal stability of dipole alignment

2,3-Di-(2′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3′-dimethoxy-4,4′-biphenylenediisocyanate to yield novel Y-type polyurethanes 4–5 containing 2,3-dioxy benzylidenemalononitrile group as a nonlinear optical (NLO)-chromophore, which constituted parts of the polymer backbones. Polyurethanes 4–5 were soluble in common organic solvents such as acetone and N,N-dimethylformamide. They showed a thermal stability up to 270 °C in thermogravimetric analysis thermograms and the glass-transition temperatures (T _g) obtained from differential scanning calorimetry thermograms were around 116–135 °C. The second harmonic generation (SHG) coefficients (d ₃₃) of poled polymer films at 106.4 mm⁻¹ fundamental wavelength were around 9.07 × 10⁻¹⁹ C (2.72 × 10⁻⁹ esu). The dipole alignment exhibited high thermal stability up to 10 °C higher than T _g, and there was no SHG decay below 145 °C due to the partial main-chain character of the polymer structure, which was acceptable for nonlinear optical device applications.     

Non-isothermal crystallization and isothermal transformation kinetics of the Ni68.5Cr14.5P17 metallic glass

Non-isothermal crystallization of the Ni_68.5Cr_14.5P₁₇ alloy is characterized by differential scanning calorimetry (DSC) and X-ray techniques. Transformation occurs in two stages at peak temperatures 622±1 and 692±1 K (at 20 K min^–1), with H ₁=1.50+0.1 kJ mol^–1 and H ₂=3.0±0.1 kJ mol^–1. Precipitation of a nickel phase occurs in the first stage and a (NiCr)₃ P phase is formed during the second stage. An approach to the isothermal kinetics of the two crystallization events is derived within the frame work of the Johnson-Mehl-Avrami theory.     

Interaction of intermetallic compounds of rare-earth metals, nickel, and aluminum with hydrogen

AtT=293 K andp _H2≤10 MPa. we synthesized hydridesR _3Ni8Al-H_7.2–15.2 (R=Nd. Sm. Gd. Tb. Dy, Ho, Er, Tm, and Lu). The X-ray analysis revealed an isotropic deformation of the original crystal lattice due to hydrogen penetration. For the hydrides obtained, the lattice constanta exceeds that of the original intermetallide by 3.9–6.0% and the constantc and the cell volumeV are increased by 6.0–12.6% and 15.6–26.4%, respectively. The volume expansion per absorbed hydrogen atom is (2.4–3.6)·10⁻³ nm⁻³. By construction of the isotherms of hydrogen desorption for the systemsR _3Ni>8Al-H, we established the existence of the α-solid hydrogen solution and the region of its coexistence with β-hydride, the region of coexistence of β- and γ-hydrides, and the β- and γ-hydride phases. Heats of the phase transitions were determined as follows: ΔH=31.4±0.8 kJ/(mole H₂) in the system Gd₃Ni₈Al-H for the transition γ→β, ΔH=39.8±1.1 kJ/(mole H₂) in the system Tb₃Ni₈Al−H for the transition β→α. and ΔH=37.1±5.1 kJ/(mole H₂) in the system Tm₃Ni₈Al−H for the transition γ→β. Among the products of hydrogenation, intermetallic compounds Lu₃Ni8Al and Tm₃Ni₈Al. we revealed the β′- and γ-phases. We also found that, atp _H2≤10 MPa andT=400–430 K, the phases of Sm₃Ni₈Al and Gd₃Ni₈Al decay into two hydridesRH_2–3 andR(Ni.Al)₅H _x . Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36, No. 1, pp. 76–82, January–February, 2000.     

Spill-over process of hydrogen sorption on palladized alumina,yttria and zeolite 4A

Doping of alumina, yttria and zeolite 4A with small quantities of palladium (down to 0.025%) was done. It was shown that these oxides, which do not normally absorb hydrogen, after the doping acquire a considerable capacity for hydrogen absorption. The sorption of hydrogen is occurring by the spill-over effect from metallic palladium to the oxide. The process is exothermal, taking place in two stages between 60 and 350 °C. Activation energies of the first stage range from 120 to 167 kJ mol^–1 and for the second one from 20 to 30 kJ mol^–1. After cooling to room temperature in hydrogen flow, the samples are able to absorb considerable quantities of oxygen which reacts exothermally with the previously formed hydride. On next exposition to hydrogen, a vigorous reaction of it with the adsorbed oxygen is taking place already at room temperature. Enthalpies of hydrogen absorption, — H, are of the order of 10 kJ g^–1, showing a tendency of increase after repeated exposures to hydrogen.     

Dissolution of UO<Subscript>2</Subscript> in the N<Subscript>2</Subscript>O<Subscript>4</Subscript>-H<Subscript>2</Subscript>O system

The kinetics of the UO₂ dissolution in the N₂O₄-H₂O system was studied. At 25°C, the process is kinetically controlled, whereas at 55°C the process occurs initially under kinetic control (3 min) and then under diffusion-kinetic control. At 80°C, the process occurs exclusively under diffusion-kinetic control. The apparent activation energy was estimated at ∼39 kJ mol⁻¹.