Activity Measurements of Mg in the Ternary Cu-Mg-Si System Using Thermogravimetric Knudsen Effusion Method

The high vapor pressure of Mg in comparison with Cu and Si enables the use of thermogravimetric Knudsen effusion method (KEM) to determine the thermodynamic properties of binary Cu-Mg, Mg-Si, and ternary Cu-Mg-Si alloys. In the current study, the weight loss of solid Mg with time has been determined at different constant temperatures between 705 K and 788 K (432 °C and 515 °C) by using KEM, and from these diagrams, the sublimation rate of Mg was calculated. By introducing the sublimation rates into the equation derived from the kinetic gas theory, the enthalpy change of sublimation reaction of Mg at the experimental temperatures was calculated to be 147.5 ± 6.5 kJ mol^?1, which is close to the 143.8 ± 0.5 kJ mol^?1 calculated using the thermodynamic data available in the literature. Similar procedure was also applied to the binary Cu-Mg, Mg-Si, and ternary Cu-Mg-Si alloys where the activities of Mg with respect to the Mg wt pct with W _Cu:W _Si = 20:80 were calculated. The diversion points in the activity–composition diagrams gave the phase boundary compositions in the phase diagrams. The phase boundary compositions of Mg in the alloys determined using KEM were in good agreement with the known binary and the constructed ternary phase diagram using FactSage thermochemical software and databases.     

ASSESSMENT OF REDUCTION BEHAVIOR OF HEMATITE IRON ORE PELLETS IN COAL FINES FOR APPLICATION IN SPONGE IRONMAKING

Studies on isothermal reduction kinetics (with F grade coal) in fired pellets of hematite iron ores, procured from four different mines of Orissa, were carried out in the temperature range of 850–1000°C to provide information for the Indian sponge iron plants. The rate of reduction in all the fired iron ore pellets increased markedly with a rise of temperature up to 950°C, and thereafter it decreased at 1000°C. The rate was more intense in the first 30 minutes. All iron ores exhibited almost complete reduction in their pellets at temperatures of 900 and 950°C in < 2 hours' heating time duration, and the final product morphologies consisted of prominent cracks. The kinetic model equation 1 ? (1 ? α)^1/3 = kt was found to fit best to the experimental data, and the values of apparent activation energy were evaluated. Reductions of D. R. Pattnaik and M. G. Mohanty iron ore pellets were characterized by higher activation energies (183 and 150 kJ mol^?1), indicating carbon gasification reaction to be the rate-controlling step. The results established lower values of activation energy (83 and 84 kJ mol^?1) for the reduction of G. M. OMC Ltd. and Sakaruddin iron ore pellets, proposing their overall rates to be controlled by indirect reduction reactions.     

Effect of TiO2 on Sintering and Grain Growth Kinetics of MgO from MgCl2·6H2O

The effect of TiO₂ on the grain growth kinetics of MgO prepared from MgCl₂·6H₂O was studied by the tradition phenomenological rate equation. The results showed that the addition of TiO₂ decreased the activation energy of MgO grain growth, accelerated the growth rate of MgO grain, and markedly promoted the sintering of MgO. Without TiO₂ addition, the MgO grain growth exponent $ n $ was 3, the grain growth activation energy $ Q $ was 556.9 kJ·mol^?1, and the process was considered as volume diffusion controlled. With 0.2 wt pct TiO₂ addition, the MgO grain growth exponent $ n $ was 2, the grain growth activation energy $ Q $ was 272.8 kJ·mol^?1, and the process was considered as interface diffusion controlled. The apparent and closed porosities of MgO-0.2 wt pct TiO₂ sample were decreased significantly, and the bulk density increased to 3.49 g·cm^?3 (relative density is 97.5 pct). The main mechanism of TiO₂ promoting the sintering of MgO was that TiO₂ solubilized in MgO to form unequivalence substitutional solid solutions and cation vacancies that were favorable to cation diffusion.     

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.     

Calorimetry Investigation of Phase Stability and Thermal Property in Ti-5 % Ta Alloy

An accurate measurement of enthalpy increment H _T–H _298.15 has been made for Ti-5 % Ta alloy in the temperature range of 463–1,257 K using drop calorimetry. This temperature interval covers the low temperature α + β two phase and also the α(hcp) → β(bcc) transformation domain (1,083 K ≤ T ≤ 1,183 K), in which the enthalpy versus temperature variation exhibited a clearly delineated inflection. The drop calorimetry data has been phenomenologically modelled to obtain the transformation enthalpy, Δ°H _tr ^α→β as 66 J g^?1. Further, in the α → β diffusive transformation zone the transformation kinetics has been quantitatively modelled in terms of Kolmogorov–Johnson–Mehl–Avrami model of diffusion limited phase transformation, to obtain the effective activation energy as 284 ± 10 kJ mol^?1.     

Luminescence modification of Eu3+-activated molybdate phosphor prepared via co-precipitation

Eu-activated CaMoO4 phosphors were co-precipitated in an aqueous solution, and NH3·H2O, NH4HCO3 and (NH2)2CO as pre-cipitating aid agents were compared based on the morphology and particle size distribution of the phosphor samples. Sm3+ as sensitizer ion was investigated on the luminescence of CaMoO4:Eu, and it could strengthen the 406 nm absorption of this phosphor. At last, the scheelite CaMoO4:Eu and wolframite ZnMoO4:Eu were selected to compare their host absorption. The result showed that the scheelite molybdate host exhibited stronger UV absorption than wolframite one.     

Investigation of the kinetics of reduction of nickel tungstate by hydrogen

In the present work, the kinetics of reduction of nickel tungstate, NiWO₄, by hydrogen was investigated by a thermogravimetric method in the temperature range 891 to 1141 K. The experiments were conducted under both isothermal and nonisothermal conditions. The products were examined by X-ray diffraction analysis. The results indicate that the reduction reaction proceeds in two steps; first, reduction of NiWO₄ to nickel as well as WO₂ and then WO₂ to tungsten. From the isothermal experiments, the activation energies of the two reaction steps were calculated to be 95.3 ± 4.9 and 80.8 ± 6.4 kJ · mol⁻¹, respectively. The activation energy value obtained from nonisothermal experiments for the first step is in agreement with the isothermal experiments. The values are compared with the activation energies reported in other literature for the individual oxides. Formerly with Royal Institute of Technology, Stockholm, Sweden     

Effect of Ball Burnishing Treatment on the Fatigue Behavior of 316L Stainless Steel Operating Under Anodic and Cathodic Polarization Potentials

Corrosion fatigue (CF) behavior of AISI 316L was investigated in a 3 pct NaCl aqueous solution at an R = ? 1 stress ratio and a frequency of 60?Hz at room temperature. The test scale specimen was 7 cm². The passive (0 mV_Ref), pitting (120?mV_Ref), and cathodic (? 1400?mV_Ref) polarization potentials were statically applied and recorded during CF tests until the samples were broken. The shaft material surface was treated with a ball burnishing (BB) process. By the results, the fatigue behavior of AISI 316L was affected by polarization potential and surface treatment. Under 0?mV potential charged tests for 5?×?10⁵ cycles, BB treatment raised the CF strength of the shaft material from about 448 to 702?MPa with a percent 57 increase. Fractographic observations revealed that corrosion pits occurred during the experiments where anodic potential was applied and that transgranular surface fractures occurred in all cases.     

Pyrite oxidation with ozone: stoichiometry and kinetics

One of the most frequent causes of refractoriness in precious metals leaching is their occlusion or fine dissemination into a pyritic matrix. This study experimentally explores the acid leaching of pyrite with ozone, suggests the stoichiometry of the reaction, estimates its activation energy and defines the effect of the main variables on the leaching kinetics. The results of stoichiometry tests allow establishing that one mole of pyrite requires 7.7 moles of ozone to produce one mole of ferric ion and 2 moles of HSO₄? ions. A decrease in the particle size, solution pH and solids’ concentration of the leaching system increases pyrite dissolution. The type of acid (nitric, sulphuric and hydrochloric) does not affect pyrite dissolution rate. Up to 60% of pyrite is dissolved when the optimal experimental conditions are employed (1?g pyrite (?25?µm), 800?mL of 0.18?M of H₂SO₄, 800?rev?min^?1, 1.2?L?min^?1 gas stream O₂/O₃ with 0.079?g O₃?L^?1 and 25°C). The apparent activation energy of the pyrite-ozone reaction is 14.92?kJ?mol^?1, and the absence of a passive layer on the pyrite surface and the linearity of the dissolution profiles suggest that the dissolution kinetics is controlled by the chemical reaction.     

Structural,morphological and optical properties of new Eu-doped and vacancied lead molybdato-tungstates

A new tetragonal,scheelite-type Pb_(1-3 x)■_xEU_(2 x)(MoO_4)_(1-3 x)(WO_4)_(3 x)(0 x ≤0.1970 and ■ denotes A-site vacancies) solid solution was synthesized via solid state reaction method. The X-ray diffraction(XRD) and scanning electron microscopy(SEM) results confirm the formation of single, tetragonal scheelite-type phases(space group I4_1/a) with the average crystallite size in the range of ～20-100 μm. Substitution of Pb~(2+) with Eu~(3+) is relatively easy despite the large difference in ionic radii, and the formation of vacancies is necessary to compensate the excess positive charge in PbMoO_4 framework. A change in lattice parameters(both a and c as well as lattice parameter ratio c/a) and progressive deformation of MoO_4 and WO_4 tetrahedra with increasing Eu concentration are observed. Thermal stability of Eu-doped materials strongly depends on the concentration of Eu3+ ions. The Pb_(1-3 x)■_xEu_(2 x)(MoO_4)_(1-3 x)(WO_4)_(3 x) solid solution for x=0.0098 shows the highest melting point(1057 ℃) which is slightly higher than that of pure PbMoO_4(1040 ℃). The UV-vis diffuse reflectance spectroscopy(DRS) and the Tauc plots were used to extrapolate the optical indirect band gap(E_g) of doped materials. Eu-doped ceramics are insulators(E_g 3 eV) and their band gap nonlinearly decreases with increasing dopant concentration.     

Investigation of Structural and Diffuse Phase Transition of New Nano Lead-Free System xBAO – yBZT − (1 − x − y) BCT

We present in this article the latest development of single-phase nanocrystalline ceramics, x(BiAlO₃) ? y(BaZr_0.2Ti_0.8O₃) ? (1 ? x ? y) (Ba_0.7Ca_0.3TiO₃), abbreviated as xBAO ? yBZT ? (1 ? x ? y) BCT with (x, y) = (0, 0.50), (0.01, 0.49), (0.03, 0.47), and (0.1, 0.4), which were prepared using a high-energy ball milling technique. In the current study, BZT ? xBCT has been selected as a host system to be incorporated into BiAlO₃. Their properties of structure, relative dielectric permittivity (ε), diffuse phase transition (γ), peak broadening (δ _γ ), and deviation from Curie–Weiss law (ΔT _C) were systematically investigated. However, the decreasing trend of Curie temperature (T _c) in the system does not obey the Vegard’s law. Analysis of X-ray diffraction patterns shows the solid solubility of (Bi³⁺, Ca²⁺) into A-site and that of (Zr⁴⁺, Al³⁺) into B-site of pure BaTiO₃ lattice of tetragonal symmetry with space group P4mm. The values of γ (1.75 to 1.63) confirmed that the ceramic has intermediate behavior between the relaxor and normal ferroelectric, which is evaluated by modified Curie–Weiss law. The high value of quality factor (115), when x = 0.01, y = 0.49 at 1-kHz frequency and temperature 323 K (50  °C), decreases with the increasing frequency.     

Kinetics of Ammonia Leaching of Multimetal Sulphides

This paper briefly describes the studies carried out on oxidative ammonia leaching of Cu-Zn-Pb multimetal sulphides. Kinetics of zinc and copper dissolution were studied with ? 200 + 300 mesh BSS fraction and 1% solids in the slurry. It is observed that the dissolution of sphalerite proceeds by a phase boundary reaction model and that of copper via diffusion through product layer in the temperature range of 70-100°C. The rate equations for zinc and copper dissolution are given by:

1 ? (1 ? α)^1/3 = k _Zn[NH₃][pO₂]^1/2

1 ? 2/3α ? (1 2/3α )^2/3 = k^Cu[NH₃]²[pO₂]^1/2

where the symbols have the usual meanings.

Activation energies for zinc and copper dissolution reactions are estimated to be 66.5 and 55.4 kJ/mole, respectively. Activation energy values thus obtained are also comparable to those obtained using a differential approach.

The leaching results obtained with 10% solids using a wide range of particle size (? 140 + 500 mesh) indicate that copper dissolution is chemically controlled in ammonia as well as ammonia-ammonium sulphate medium in the temperature range of 115-135°C. However, at lower temperature (?55°C). the leaching reaction follows a diffusion model. Zinc dissolution data show deviations from the shrinking core model due to high extractions in the initial stages.     

Enthalpies of formation of borides of iron,cobalt, and nickel by solution calorimetry in liquid copper

The enthalpies of formation at 1385 ±2 K of the following crystalline borides have been determined by high temperature solution calorimetry using liquid copper as the calorimetric solvent. Fe₂B-67.87 ±8.05 kJ mol⁻¹, Co₂B -58.1 ±7.0 kJ mol⁻¹, Ni₂B -67.66 ±4.12 kJ ml⁻¹, FeB-64.63 ±4.34 kJ mol⁻¹, CoB -69.52 ±6.0 kJ mol⁻¹, and NiB -40.2 ±3.77 kJ mol⁻¹. The enthalpy of fusion of NiB has been determined to be 28.25 ±1.54 kJ mol⁻¹ at its melting point of 1315 K. New data are reported also for the enthalpies of solution of iron, cobalt, and nickel in copper, and for the enthalpies of interaction between these metals and boron in dilute solutions in liquid copper.     

A novel process on preparation of ammonium metatungstate solution using bipolar membrane electrodialysis

An industrial (NH₄)₂WO₄ solution was used to directly prepare ammonium metatungstate solution using bipolar membrane electrodialysis. The effects of current density, initial concentrations of NH₄HCO₃ and WO₃ in feeds, temperature and pH of product solution on the process were investigated. A continuous running test was carried out under the optimum conditions and the results showed that the direct recovery of WO₃ reached 99.97% with average current efficiency of 72.5% and power consumption of 0.877?kWh?kg^?1 WO₃ using a feed solution containing 172.3?g?L^?1 WO₃ and a base solution containing 1.5?mol?L^?1 NH₄HCO₃ with a current density of 700?A?m^?2 and a solution pH in salt compartment of 2.8 at 31°C for 600?min, indicating easy and stable operation of the bipolar membrane electrodialysis process.     

Use of solid-electrolyte Galvanic cells to determine the activity of CaO in the CaO-ZrO2 system and the standard Gibbs free energies of formation of CaZrO3 from CaO and ZrO2

The activity of CaO in the CaO-ZrO₂ system has been measured at 1572 to 1877 K with a Galvanic cell composed of 4CaO ? P₂O₅ as the solid electrolyte. The activity ZrO₂ was calculated from the activity of CaO by integrating the Gibbs-Duhem relation. From the activities of CaO and ZrO₂, the standard Gibbs free energy of formation of CaO ? ZrO₂ was determined as follows: ΔG _f ⁰ /J mol^?1 = -25,200 (±150) - 17.58 (±0.085)T (1633 to 1873 K)     

Influence of reaction parameters on the luminescence properties of monodisperse NaGd(1−x−y)(WO4)2:xEu3+,yTb3+ phosphor by molten salt synthesis

Eu~(3+) activated and Eu~(3+), Tb~(3+) co-activated monodisperse sodium double tungstates NaGd(WO4)2 phosphors were prepared by molten salt method at 750 ℃ for 10 h using NaCl as a flux. The crystal structure and morphology of the as-synthesized phosphors were measured by XRD and SEM, respectively. The photoluminescence properties were characterized by PL spectra, decay lifetime and CIE. The presence of NaCl plays an important role in the morphology and luminescence properties. In this work,NaCl and one of the raw material Na_2 CO_3 in a certain proportion will form a low eutectic salt to decrease the reaction temperature and benefit the formation of monodisperse NaGd(WO_4)_2 crystals. The color of Eu~(3+) and Tb~(3+) co-doped NaGd(WO_4)_2 phosphors can be tuned from creamy white to orange, red and green by adjusting the doping concentration of rare earth ions, since the emission contain the broad blue-green emission origin from NaGd(WO_4)_2 host and characteristic red and green emission origin from Eu~(3+) and Tb~(3+) ions. The electroluminescent spectra and CIE measurement shows that the LED device with NaGd_((1-x))(WO_4)_2:xEu~(3+)(x = 0.24) phosphor can be excited by 365 nm and 380 nm LED chip, and their CIE coordinate is(x = 0.45, y = 0.45) and(x = 0.36, y = 0.37), Ra is 80.3 and 86.3, T_c is 3196 and4556 K, respectively. As a single-component phosphor, NaGd(WO_4)_2:Eu~(3+),Tb~(3+) have potential application in UV-pumped WLEDs.     

The transported entropy of Na+ in solid state cryolite

The transported entropy of Na⁺ in mixtures of NaF (s) and Na₃AlF₆ (s) is determined from thermocell experiments. The experiments were favorably described by the electric work method. The variation observed in the thermocell electromotive force (emf) with composition can be explained from the probable path of charge transfer in the electrolyte. The transported entropies are S*^cry _Na+ = 140 ± 7 J K^?1 mol^?1 for cryolite and S*^NaFNa+ = 81 ± 8 J K^?1 mol^?1 for sodium fluoride between 380 °C and 500 °C. The value obtained for sodium in the solid cryolite makes us predict that the transported entropy for Na⁺ in themolten electrolyte mixture for aluminum production is substantial and that the reversible heat effects in the aluminum electrolysis cell are the same.     

Thermodynamics of the system NaCl-AlCl3

Heat capacities of melts were measured in the range 400 to 1100 K and 0.48 < N_AlCl3 < 0.62, the results being expressed by C_p = 40.96 – 0.0295T + 2.01 × 10^?5 T ² J K^?1 g·atom^?1 i.e., AlCl₃ contains 4 atoms, and so forth). This equation was used in interpreting literature vapor pressure data. Measurements were made of the emf of the concentration cell $$AL\left| {_{AlCl_3 }^{NACl(sat)} } \right.\left| {_{(Na^ + )}^{Pyrex} } \right.\left| {_{AlCl_3 }^{NACl(sat)} } \right.\left| {_{AlCl_3 }^{NACl} } \right.\left| {AL} \right. $$ at temperatures 473 to 623 K, and the results were correlated with the vapor pressure data to yield activities of NaCl and AlCl₃. Measurements with a sodium electrode confirmed the accepted values for the free energy of formation of A1C1₃ within about 1.5 kJ mol^?1. The activities were used to analyze the phase diagram. Direct measurement of the eutectic temperature with a concentration-cell technique (which avoids supercooling) gave 386 K; the eutectic composition is 60.0 mol pct A1C1₃. The standard entropy of NaAlCl₄(s) is S _298.15 ^° = 199.1 J K^?1 mol^?1. The free energy for NaAlCl₄(l) = NaAlCl₄(g) is ΔG° = 82740 ?63.66T J mol^?1 at around 950 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:

Characterization,Tribological and Mechanical Properties of Plasma Paste Borided AISI 316 Steel

The AISI 316 steel was treated by the plasma paste boriding by using a gas mixture of 70%H₂–30%Ar with a boron source of 100% B₂O₃ in the temperature range of 700–800 °C for 3, 5 and 7 h. The boride layers formed on the samples were observed by scanning electron microscope. The iron borides were also identified by the use of an X-ray microanalyzer, equipped with energy dispersive X-ray spectroscopy. The XRD analysis was carried out to identify the iron and metallic borides present inside the boride layer. Based on the kinetic data, the value of boron activation energy for the AISI 316 steel was estimated as 118.12 kJ mol^?1 and compared with the data available in the literature. A regression model based on ANOVA analysis was used to predict the boride layers’ thicknesses depending on the boriding parameters: the treatment time and the boriding temperature. A good correspondence was obtained between the experimental values and those predicted by the regression model. Furthermore, the wear behavior of the sample borided at 750 °C for 5 h was investigated. The significant increase in wear resistance of plasma borided layer was observed in comparison with the untreated AISI 316 steel. The nanomechanical properties of the sample, plasma paste borided at 700 °C for 7 h, were examined using the nanoindenter with a Vickers diamond tip. The load–displacement curves, as well as, Young’s moduli and hardness were shown for the selected measurements. The obtained results depended on the phase composition of the tested area.