Enthalpy of mixing of liquid Ni-Zr and Cu-Ni-Zr alloys

The partial (Δ and the integral (ΔH) enthalpies of mixing of liquid Ni-Zr and Cu-Ni-Zr alloys have been determined by high-temperature isoperibolic calorimetry at 1565 ± 5 K. The heat capacity (C _p) of liquid Ni₂₆Zr₇₄ has been measured by adiabatic calorimetry (C _p=53.5±2.2 J mol⁻¹ K⁻¹ at 1261±15 K). The integral enthalpy of mixing changes with composition from a small positive (Cu-Ni, ΔH (x _Ni=0.50, T=1473 to 1750 K)=2.9 kJ mol⁻¹) to a moderate negative (Cu-Zr; ΔH(x _Zr=0.46, T=1485 K)=−16.2 kJ mol⁻¹) and a high negative value (Ni-Zr; ΔH(x _Zr=0.37, T=1565 K)=−45.8 kJ mol⁻¹). Regression analysis of new data, together with the literature data for liquid Ni-Zr alloys, results in the following relationships in kJ mol⁻¹ (standard states: Cu (1), Ni (1), and Zr (1)):for Ni-Zr (1281≤T≤2270 K),

Thermodynamics of Ca-Ga alloys

The enthalpies of formation of the intermetallic compounds CaGa₄, Ca₃Ga₈, and CaGa₂, at 298.15 K, were determined by high-temperature liquid gallium solution calorimetric measurements to be −24.9 ± 4.9 kJ·g at.⁻¹, −25.4 ± 2.4 kJ·g at.⁻¹, and −38.8 ± 4.8 kJ·g at.⁻¹, respectively. The enthalpies of formation of CaGa₄ at 988 K and that of Ca₃Ga₈ at 1070 K were determined, using precipitation calorimetry, to be −28.2 ± 1.7 kJ·g at.⁻¹ and −22.5 ± 1.4 kJ·g at.⁻¹, respectively. The integral enthalpy of mixing of the (Ca-Ga) liquid alloys (ΔH ⁰) measured at 1309 K are described by the following Redlich-Kister equation:

Interdiffusion in Co-Mn alloys

Interdiffusion coefficient in cobalt-manganese alloys has been determined by Matano's method in the temperature range between 1133 and 1423 K on (pure Co)-(Co-30.28 at. pct Mn alloy) and (pure Co)-(Co-51.76 at. pct Mn alloy) couples. This, ∼D, has been found to increase with the increase of manganese content. However, the activation energy (∼Q) and frequency factor ( ₀) show a maximum at about 10 at. pct Mn. The concentration dependence of and has been discussed taking into account the thermodynamic properties of the alloy. The difference in between the ferro- and paramagnetic phases in Co-5 at. pct Mn alloy has been found to be 24 kJ/mol, which is larger, than that for the diffusion of Mn⁵⁴ in this alloy. Further it has been found that the Kirkendall marker moves toward manganese-rich side, showing that manganese atoms diffuse faster than cobalt atoms. From the marker shift, the intrinsic diffusion coefficients,D _Co andD _Mn, at 33 at. pct Mn have been determined as follows:D _Co=0.22×10⁻⁴ exp(−263 kJ mol⁻¹/RT) m²/s, andD _Mn=0.98×10⁻⁴ exp(−229 kJ mol⁻¹/RT) m²/s.     

Intrinsic kinetics of the reaction between zinc sulfide and water vapor

The reaction between zinc sulfide and water vapor is a component reaction in a new reaction scheme recently developed to transform zinc sulfide to zinc oxide through the use of lime and water vapor. The intrinsic kinetics of this reaction for ultrafinely ground (<1 μm) ZnS particles was determined by carrying out measurements in the absence of heat- and mass-transfer effects. The reaction products were identified to be ZnO and H₂S. The kinetics of the reaction can be represented by and 3.94<C _H2_O <9.84 mol/m³ withn=1.28 andk ₁=45.3 exp(−14600/T) m³·mol⁻¹·s⁻¹, whereX _B is the fractional conversion. DAESOO KIM, formerly Granduate Student at the University of Utah     

Kinetics of gold(III) chloride complex reduction using sulfur(IV)

In this article, the effect of different kinetic parameters such as pH, temperature, gold, and reductant concentrations on the rate of Au reduction from aqueous chloride solutions by NaHSO₃ is investigated. On the basis of available experimental data, the possible mechanism of [AuCl₄]⁻ reduction by sulfur(IV) is also assumed. The suggested mechanism yields the rate equation for reduction of [AuCl₄]⁻, which is given in the form

Activities of oxygen in liquid Bi,Sn, and Ge from electrochemical measurements

Modified coulometric titrations on the galvanic cell: O in liquid Bi, Sn or Ge/ZrO₂( + CaO)/Air, Pt, were performed to determine the oxygen activities in liquid bismuth and tin at 973, 1073 and 1173 and in liquid germanium at 1233 and 1373 K. The standard Gibbs energy of solution of oxygen in liquid bismuth, tin and germanium for 1/2 O₂ (1 atm) →O (1 at. pct) were determined respectively to be ΔG° (in Bi) = −24450 + 3.42T (±200), cal· g-atom⁻¹ = − 102310 + 14.29T (±900), J·g-atom⁻¹, ΔG° (in Sn) = −42140 + 4.90T (±350), cal· g-aton⁻¹ = −176300 + 20.52T (± 1500), J-g-atom⁻¹, ΔG° (inGe) = −42310 + 5.31 7 (±300), cal·g-atom⁻¹ = −177020 + 22.21T(± 1300), J· g-atom⁻¹, where the reference state for dissolved oxygen was an infinitely dilute solution. It was reconfirmed that the modified coulometric titration method proposed previously by two of the present authors produced far more reliable results than those reported by other investigators. TOYOKAZU SANO, formerly a Graduate Student, Osaka University     

Grain refinement induced by electromagnetic stirring: A dendrite fragmentation criterion

The influence of electromagnetic stirring (EMS) on grain refinement has been studied for two copper-base alloys (Cu-1 wt pct Ni-1 wt pct Pb-0.2 wt pct P and Cu-4 wt pct Zn-4 wt pct Sn-4 wt pct Pb) solidified in a Bridgman furnace. Metallographic inspection of the specimens, temperature measurements during solidification, and numerical simulations performed with CALCOSOFT revealed that the efficiency of EMS is strongly dependent upon the penetration of the liquid in the mushy zone and therefore upon the position of the convection vortices with respect to the liquidus front. In particular, the low-concentration alloy could be grain refined only at high power and when the coil was moved close to the liquidus front. These results were analyzed on the basis of a dendrite fragmentation criterion similar to Flemings’ criterion for local remelting of the mushy zone. Considering that the component of the fluid flow velocity along the thermal gradient, , must be larger than the casting speed, V _c , dendrite fragmentation occurs if

Occlusion and ion exchange in the molten (lithium chloride-potassium chloride-alkali metal chloride) salt + zeolite 4A system with alkali metal chlorides of sodium, rubidium, and cesium

Interaction between molten salts of the type LiCl-KCl-MeCl (Me = Na, Rb, Cs, x _MeCl = 0 to 0.5, x _KCl/x _LiCl = 0.69) and zeolite 4A have been studied at 823 K. The main interactions between these salts and zeolite are molten salt occlusion to form salt-loaded zeolite and ion exchange between the molten salt and salt-loaded zeolite. No chemical reaction has been observed. The extent of occlusion is a function of the concentration of MeCl in the zeolite and is equal to 11±1 Cl⁻ per zeolite unit cell, (AlSiO₄)₁₂, at infinite MeCl dilution. The ion-exchange mole fraction equilibrium constants (separation factors) with respect to Li are decreasing functions of concentration of MeCl in the zeolite. At infinite MeCl dilution, they are equal to 0.84, 0.87, and 2.31 for NaCl, RbCl, and CsCl, respectively, and increase in the order Na<Rb<Cs at identical MeCl concentrations. The standard ion-exchange chemical potentials are equal to −(0.0±0.5) kJ·mol⁻¹, −(0.4±0.3) kJ·mol⁻¹, and −(6.5±0.5) kJ·mol⁻¹ for Na⁻, Rb⁻¹, and Cs⁺, respectively.     

Free energy of formation of Mo2C and the thermodynamic properties of carbon in solid molybdenum

The activity of C in the two-phase region Mo+Mo₂C has been obtained from the C content of iron rods equilibrated with metal+carbide powder mixtures. From this activity data the free energy of formation of α-Mo₂C has been determined as ΔG _f ^o (α-Mo₂C) (1270 to 1573 K)=−47,530−9.46T±920 J/mol. This is in good agreement with the expression obtained from gas-equilibration studies by Gleiser and Chipman, ΔG _f ^o (α-Mo₂C) (1200 to 1340 K)=−48,770−7.57 J/mol, but both our and Gleiser and Chipman's values are about 10 pct lower than those of Pankratz, Weller and King calculated from ΔH _f,298 ^o andC _p vs T data. With the aid of available data for the solid solubility of C in Mo, the thermodynamic properties of C in the terminal solid solution have been calculated as J/mol, J/mol and , the excess entropy ofC in the solid solution assumingC is in the octahedral interstices =43.4±8.2 J/deg.-mol.     

Shear ligament phenomena in Fe3Al intermetallics and micromechanics of shear ligament toughening

The environment-assisted cracking behavior of a Fe₃Al intermetallic in an air moisture environment was studied. At room temperature, tensile ductility was found to be increased with strain rate, from 10.1 pct at 1×10⁻⁶ s⁻¹ to 14.3 pct at 2 × 10⁻³ s⁻¹. When tensile tests were done in heat-treated mineral oil on specimens that have been heated in the oil for 4 hours at 200°C, ductility was found to be recovered. These results suggest the existence of hydrogen embrittlement. Shear ligaments, which are ligament-like structures connected between microcracks, were observed on the tensile specimens. They undergo ductile fracture by shearing and enhance fracture toughness. This toughness enhancement (represented byJ _l ) was estimated by a micromechanical model. The values of the unknown parameters, which are the average ligament length , the area fractionV _l , and the work-to-fractureτ ₁ γ ₁, were obtained from scanning electron microscopy (SEM) observation. The total fracture toughnessK _c andJ _l were reduced toward a slower strain rate. The experimental fracture toughness,K _Q , was found to be increased with strain rate, from 35 MPa at 2.54×10⁻⁵ mm·s⁻¹ to 47 MPa at 2.54×10⁻² mm·s⁻¹. The fact that strain rate has a similar effect onK _Q andK _c verifies the importance of shear ligament in determining fracture toughness of the alloy. With the presence of hydrogen, length and work-to-fracture of the shear ligament were reduced. The toughening effect caused by shear ligament was reduced, and the alloy would behave in a brittle manner.     

Henrian activity coefficient of Pb in Cu-Fe mattes and white metal

A transpiration method was used to evaluate the Henrian activity coefficient of Pb (γ°_Pb) in Cu-Fe mattes and white metal. Values for the activity coefficient of Pb (γ _Pb) have been evaluated as a function of the Cu/Fe molar ratio from 1 to ∞, as a function of the sulfur deficiency (defined as SD=X _S−1/2X _Cu−X _Fe, where X ₁ is the mole fraction of the ith species) from −0.02 to +0.02, and at temperatures between 1493 and 1573 K. Analysis of γ _Pb as a function of the trace element concentration reveals that the activity coefficient is independent of Pb content at weight percents less than 0.2. Dependence of γ _Pb on temperature was found to be slight, and as such, comparison of data obtained by other investigators at 1473 K was possible. Agreement in the data is excellent, and all the data have been used to generate the empirical equation

Kinetics of reduction of gold(III) complexes using H2O2

In this article, the effect of different kinetic parameters, namely, temperature, pH, and reductant concentration, on the rate of Au(III) reduction from aqueous chloride solutions by H₂O₂ was investigated. The possible mechanism of complex [Au(OH)₄]⁻ ion reduction by hydrogen dioxide is also discussed and the model mechanism based on experimental data is postulated. On the basis of the suggested mechanism, the rate equation for Au precipitation is given in the form , in which respective rate constants k ₁, k ₃, and k ₅ were determined experimentally and are given in the text.     

Kinetics of chlorination of zirconia in mixture with petroleum coke by chlorine gas

Studies on the kinetics of carbothermic chlorination of zirconium dioxide in gaseous chlorine were carried out with petroleum coke fines in powder form. The amounts of ZrO₂ chlorinated were found to be directly proportional to the time of chlorination in the temperature range studied (973 to 1273 K). The activation energy values for chlorination of ZrO₂, in mixture with petroleum coke, was found to be 18.3 kJ/mole. The influence of particle size of petroleum coke on the chlorination of ZrO₂ (−38 + 25 μm) was studied, and it was found that the rate of chlorination increased up to the size range of −75 to +53 μm, and the size finer than this produced negligible increase. The amount of petroleum coke in the mixture above 17.41 pct in excess of the stoichiometry resulted in very little increase in the rate. The effect of the partial pressure of chlorine (pCl₂) on the rate of chlorination was found to obey the following relationship, derived from the Langmuir adsorption isotherm:

A general method for estimation of fracture surface roughness: Part I. Theoretical aspects

An assumption-free general method is developed for quantitative estimation of fracture surface roughness from the measurements performed on the fracture profiles generated by sectioning planes which are normal to the average topographic plane of the fracture surface. The input data are the profile roughness parameter,R _L, and angular orientation distribution of line elements on the fracture profile,f(α). It is shown that

Interdiffusion in the carbides of the Nb-C system

Interdiffusion coefficients in Nb₂C and NbC_1−x were measured using bulk diffusion couples in the temperature range from 1400 °C to 1700 °C. Marker experiments were used to show that carbon is the only component undergoing significant diffusion in both carbides. Carbon concentrations were measured by difference using electron probe microanalysis, and interdiffusion coefficients were taken from Boltzmann-Matano analyses of the resulting concentration profiles. This analysis clearly showed that, in NbC_1−x, interdiffusion coefficient varies with carbon concentration, and is expressed by

Interaction behavior of nitrogen in liquid niobium

The kinetics and mechanism of absorption/desorption of nitrogen in liquid Nb were investigated in the temperature range of 2470 °C to 2670 °C in samples levitated in a N₂/Ar stream with various nitrogen partial pressures. The nitrogen solution reaction in liquid Nb was found to be exothermic, with the standard enthalpy and entropy of solution of −236.4 ± 23.3 kJ/mol and −-5.3 ± 8.3 J/K · mol, respectively. Above the threshold flow rate of the N₂/Ar stream, the absorption process was determined to be second order with respect to nitrogen concentration, indicating that the rate-controlling step is either the adsorption of nitrogen molecules on the liquid surface or dissociation of adsorbed nitrogen molecules into surface-adsorbed atoms. The desorption process was found to be second order as well. At lower flow rates, however, the absorption rate was found to depend on the gas-phase mass transfer rate. The rate equation for nitrogen absorption in the range of 2470 °C to 2670 °C is given by with the value ofQ calculated to be −327.2 ± 20.6 kJ/mol, while nitrogen desorption at 2670 °C follows the relation      

An electrochemical investigation of the thermodynamic properties of the NaCl-AlCl3 system at subliquidus temperatures

The phase relations in the NaCl-AlCl₃ system ( ) have been determined in the temperature range from 373 to 623 K by isothermal equilibration, electrical conductivity, and electromotive force measurements. Only one ternary compound, NaAlCl₄, was found to be stable, with a melting point of 426 K. The standard Gibbs energy of formation of NaCl and NaAlCl₄ has been measured in the temperature range from 423 to 623 K by a novel galvanic cell technique involving in-situ electrogenerated chlorine electrode in the Na/β″-alumina/NaCl, NaAlCl₄/Cl₂,C and Al/NaCl, NaAlCl₄/Cl₂,C cells along with the Na/β″-alumina/NaCl,NaAlCl₄/Al cell. The Δ _f G _NaCl(s ^)/o and values have been calculated as −412.4+0.095 T (±1) kJ mol⁻¹ and −1117.5+0.2460 T (±2) kJ mol⁻¹, respectively. The standard entropy of NaAlCl₄ (s) at 298 K, computed from the results of the study and the auxiliary information from the literature (184 J K⁻¹ mol⁻¹), show good agreement with the estimated JANAF value (188.28 J K⁻¹ mol⁻¹). The enthalpy of formation of NaAlCl₄ (l) from NaCl (s) and AlCl₃ (s) at 550 K obtained in the present study (−1850 J mol⁻¹) is in agreement with that computed from the heat-capacity measurements (−1910 J mol⁻¹). The present measurements are unique, as a new electrochemical technique is employed in a cell with low-melting sodium chloroaluminate electrolyte to obtain the thermodynamic properties of NaCl and NaAlCl₄ at significantly low temperatures. The Gibbs energy of formation of NaCl (s) is, thus, measured at temperatures as low as 423 K by an electrochemical technique for the first time, in this work.     

Thermodynamics of the system NaF-AlF3: Part VII. Non-stoichiometric solid cryolite

Earlier data are recalculated to give the boundaries of the homogeneous field of solid cryolite. The equilibrium constant

The rate of formation of intermetallic layers between aluminum and steel below 660°C

The rate of formation of intermetallic compounds between aluminum and three ferritic steels, one austenitic steel, and Inconel has been determined by an electrolytic method. The steel was held at zero potential with respect to aluminum in a NaCl-AlCl₃ melt, and the current measured. Comparison of measured thicknesses of intermetallic layers with those calculated from the integrated current gives an average deposition efficiency of 95 pct. For the Type 304 austenitic steel thickness (min), andk is given by logk= −6400/T(⁰K) +4.469. The ferritic steels show a linear rate of growth of Al₅Fe₂, with an initial higher rate such that extrapolation of the linear curve back to zero time gives an intercept of 16±7 μm. The rate constants (mm min⁻¹) may be represented by log (rate)=α/T+β, and the values of α and β are respectively −2650 and−0.788 for a plain carbon steel,−6580 and + 3.469 for a 1.3 pct Cr, 0.4 pct Mo steel, and−5950 and +2.466 for a 2.2 pct Cr, 0.9 pct Mo steel. The more highly alloyed steels are thus attacked, more slowly. Results for Inconel could not be fitted to any simple equation. With the ferritic steels growth is by aluminum diffusing inwards; with Inconel it is by nickel diffusing outward.