The Ca(SO<Subscript>4</Subscript>)-Na<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)-Ca<Subscript>3</Subscript>(AsO<Subscript>4</Subscript>)<Subscript>2</Subscript>-Na<Subscript>3</Subscript>(AsO<Subscript>4</Subscript>) phase diagram

The phase diagram of the CaSO₄-Na₂SO₄-Ca₃(AsO₄)₂-Na₃(AsO₄) system was measured by differential thermal analysis and by an equilibration and quenching technique. Thermodynamic models were developed giving the Gibbs energies of all phases as functions of temperature and composition. Optimized model parameters were obtained by assessment of all available thermodynamic and phase equilibrium data. The models, which reproduce all the data within experimental error limits, were used to calculate the liquidus surface of the system. The modified quasi-chemical model in the quadruplet approximation was used for the liquid solution. For the various solid solution phases, the modified quasi-chemical model, which accounts simultaneously for short-range-ordering among first-nearest-neighbor (FNN) and second-nearest-neighbor (SNN) pairs, was used for the first time within the framework of the compound energy formalism. The distinction between true model parameters and formalism parameters is made. Implications of the work for the potential use of sulfate fluxes for copper refining are discussed.     

Phase transitions in the magnetic superconductor (Dy<Subscript>0.8</Subscript>Y<Subscript>0.2</Subscript>)Rh<Subscript>4</Subscript>B<Subscript>4</Subscript>

A new (Dy_0.8Y_0.2)Rh₄B₄ superconductor (the superconducting transition temperature is T _c ≈ 5.5 K), which has an inherent magnetic subsystem whose properties are determined by the crystal structure of the superconductor, is synthesized at a high pressure (∼8 GPa) and t ≈ 1800°. The magnetic sublattice of the (Dy_0.8Y_0.2)Rh₄B₄ compound is found to substantially affect its superconducting properties and, in a number of cases, to lead to their anomalous variations, namely, to the absence of the traditional Meissner effect and an anomalously abrupt increase in magnetic induction B _k2 (upper critical field) upon a transition of the magnetic subsystem into the antiferromagnetic state. Upon cooling from 250 to 1.6 K, the (Dy_0.8Y_0.2)Rh₄B₄ compound undergoes a number of phase transformations, namely, a paramagnet-ferrimagnet transition at a Curie temperature T _C ≈ 30 K, a superconducting transition at T _c ≈ 5.5 K against the background of a ferrimagnetic order, and a ferrimagnet-antiferromagnet transition (the Neel temperature is T _N ≈ 2.8 K) in the retained superconducting state.     

[(Fe<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>)<Subscript>0.75</Subscript>B<Subscript>0.20</Subscript>Si<Subscript>0.05</Subscript>]<Subscript>96</Subscript>Nb<Subscript>4</Subscript> Metallic Glasses with Small Cu Additions

Recently, (Fe-Co)-B-Si-Nb bulk metallic glasses (BMGs) were produced. Such BMGs exhibit high glass-forming ability (GFA) as well as good mechanical and magnetic properties. These alloys combine the advantages of functional and structural materials. The soft magnetic properties can be enhanced by nanocrystallization. To force the nanocrystallization, small content of Cu was added to the starting composition. In this article, {[(Fe_0.5Co_0.5)_0.75Si_0.05B_0.20]_0.96Nb_0.04}_100–x Cu _x glassy alloys (x = 1, 2, and 3) were chosen for investigation. The GFA and the thermal stability of these alloys were evaluated. The effects of crystallization during heat-treatment processes on the phase evolution and the magnetic properties, including M _s , H _c , and T _c , in these alloys were investigated. The phase analyses were done with the help of the X-ray diffraction patterns recorded in situ by using the synchrotron radiation in transmission configuration.     

Synthesis and Characterization of Microwave Absorbing SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanocomposite

Zinc ferrite and strontium hexaferrite; SrFe₁₂O₁₉/ZnFe₂O₄ (SrFe_11.6Zn_0.4O₁₉) nanoparticles having super paramagnetic nature were synthesized by simultaneous co-precipitation of iron, zinc and strontium chloride salts using 5 M sodium hydroxide solution. The resulting precursors were heat treated (HT) at 850, 950 and 1150°C for 4 h in nitrogen atmosphere. The hysteresis loops showed an increase in saturation magnetization from 1.040 to 58.938 emu/g with increasing HT temperatures. The ‘as-synthesized’ particles have size in the range of 20–25 nm with spherical and needle shapes. Further, these spherical and needle shaped nanoparticles tend to change their morphology to hexagonal plate shape with increase in HT temperatures. The effect of such a systematic morphological transformation of nanoparticles on dielectric (complex permittivity and permeability) and microwave absorption properties were estimated in X band (8.2–12.2 GHz). The maximum reflection loss of the composite reaches −26.51 dB (more than 99% power attenuation) at 10.636 GHz which suits its application in RADAR absorbing materials.     

Thermodynamic characteristics of the Pb-Bi alloys in the KCl-PbCl<Subscript>2</Subscript> melt

The thermodynamic properties of the Pb-Bi alloys containing from 1.5 to 95 mol % Pb are investigated in a molten mixture of potassium and lead chlorides in a temperature range of 723–873 K by measuring the equilibrium values of the electromotive force. The partial and integral thermodynamic characteristics of the system are calculated, and its small negative deviations from ideality are established.     

Modeling of the solubilities of NiO/NiAl<Subscript>2</Subscript>O<Subscript>4</Subscript> and FeO/FeAl<Subscript>2</Subscript>O<Subscript>4</Subscript> in cryolite melts at 1300 K

Experiments to measure the solubilities of NiO/NiAl₂O₄ and FeO/FeAl₂O₄ were performed, and the results confirmed existing literature values. The solubilities of NiAl₂O₄ and FeAl₂O₄ in Al₂O₃-saturated cryolite melts at 1300 K were modeled thermodynamically in terms of the Ni-containing complexes Na₂NiF₄ and Na₄NiF₆, and the Fe-containing solutes FeF₂, Na₂FeF₄, and Na₄FeF₆. The experimental solubility data were fitted to multiple simultaneous equilibria. Equilibrium constants and ΔG _f ⁰ values for the formation reactions of the these solutes were thereby estimated. The solubilities of NiO/NiAl₂O₄ and FeO/FeAl₂O₄ and solute distributions in Al₂O₃-undersaturated cryolite melts were calculated for a number of melt compositions from the present model. The existence of several competitive solute species is inherent to highly buffered ionic cryolite solutions where the traditional log-log methodology had previously failed to identify dominant single solutes. In such solutions, individual solutes of oxides are not likely to dominate over a wide composition range so that a more global modeling is required. The principal solute species identified in the present study exhibit reasonable three-dimensional (3-D) anion geometries.     

Leaching of sulfidized chalcopyrite with H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-NaCl-O<Subscript>2</Subscript>

The recovery of copper from chalcopyrite by leaching is complex not only due to the slow dissolution kinetics of this mineral in most aqueous media but also due to the production of solutions that are heavily contaminated with iron. On the contrary, the leaching of sulfidized chalcopyrite is very attractive because of a faster and more selective dissolution of copper compared to the leaching of the untreated chalcopyrite. In this work, the results of leaching in H₂SO₄-NaCl-O₂ solutions of sulfidized chalcopyrite concentrate are discussed. Experiments were carried out with chalcopyrite concentrates previously reacted with elemental sulfur at 375 °C for 60 minutes. The results showed that the concentration of chloride ions below 0.5 M, temperature, and leaching time are important variables for the extraction of Cu. On the other hand, Fe extraction was little affected by the same variables, remaining below 6 pct for all the experimental conditions tested. Microscopic observations of the leached particles showed that the elemental sulfur produced by the reaction does not form a coherent layer surrounding the particle, but rather concentrates in certain locations as large clusters. The leaching kinetics can be accurately described by a nonreactive core-shrinking rim topochemical expression for spherical particles 1 − (1 − 0.45X)^1/3=kt. The activation energy found was 76 kJ/mol for the range 85 °C to 100 °C.     

Li-Ion Battery with LiFePO<Subscript>4</Subscript> Cathode and Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> Anode for Stationary Energy Storage

Li-ion batteries based on commercially available LiFePO₄ cathode and Li₄Ti₅O₁₂ anode were investigated for potential stationary energy storage applications. The full cell that operated at flat 1.85 V demonstrated stable cycling up to 200 cycles followed by a rapid fade. A Li-ion full cell with Ketjen black modified LiFePO₄ cathode and an unmodified Li₄Ti₅O₁₂ anode exhibited negligible fade after more than 1200 cycles with a capacity of ~130 mAh/g at C/2. The improved stability, along with its cost-effectiveness, environmental benignity, and safety, make the LiFePO₄/Li₄Ti₅O₁₂ combination Li-ion battery a promising option for storing renewable energy.     

Reaction kinetic,magnetic and microwave absorption studies of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>/CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrite nanocrystals

Mixture of cobalt ferrite and strontium hexaferrite nanocrystals i.e. SrFe₁₂O₁₉/CoFe₂O₄ exhibiting super paramagnetic nature were synthesized by modified flux method. The resulting precursors were heat treated (HT) at 900 and 1200°C for 4 h in nitrogen atmosphere. During heat treatment, transformation proceeds as instantaneous rate of nucleation and three dimensional growth with activation energy of 135.835 kJ/mole. The hysteresis loops showed a hike in saturation magnetization from 1.045 to 84.362 emu/g with an increase in HT temperature. The ‘as synthesized’ particles have size in the range of 10–20 nm with spherical shape. Further, these spherical shape particles tend to change their morphology to hexagonal plates with increase in HT temperatures. The relative complex permittivity and permeability of the composite powder are investigated. The minimum reflection loss of the composite powder reaches to −27.6 dB at 10.8 GHz which suits its application in RADAR absorbing materials.     

Deoxidation of Liquid Copper with Reducing O<Subscript>2</Subscript>/CH<Subscript>4</Subscript> Flames

The rate of deoxidation of molten copper during top blowing with various reducing gases has been investigated using thermogravimetry. It was observed that the rate of deoxidation increases with an increasing flow rate of H₂ or CO and that H₂ is a more effective reducing reagent than CO. The rate of deoxidation using methane was measured for O₂/CH₄ ratios from 1.5 to 2.0. As expected, the deoxidation rate decreased with an increasing O₂/CH₄ feed ratio because the flame became less reducing. For all tests, initially there is a linear decrease in mass as oxygen is removed. However, for some experiments, after some time, a sudden acceleration in the rate of mass loss occurs. Using video and X-ray imaging, it was found that this pattern corresponded to gas evolution from within the molten copper. This finding can be explained by the sudden water vapor evolution because the hydrogen dissolved in the copper reacts with the remaining oxygen, and “boiling” takes place, leading to an enhanced stirring of the copper.     

Reduction of Fe<Subscript>2</Subscript>MoO<Subscript>4</Subscript> by hydrogen gas

In the present work, the reduction kinetics of iron molybdate (Fe₂MoO₄) by hydrogen gas was investigated by thermogravimetric analyses (TGA). Both isothermal and nonisothermal experiments were conducted. By using fine particles, very shallow powder bed, and high hydrogen flow rate, the study could be focused on the chemical reaction. The activation energy obtained from the isothermal experiments was found to be 173.5 kJ/mol, which was in reasonable agreement with the value of 158.3 kJ/mol obtained from the nonisothermal experiments. The reduction product was found to be an intermetallic compound, Fe₂Mo, of microcrystalline structure.     

The Thermal Stability of R<Subscript>3</Subscript>Pt<Subscript>4</Subscript> Compounds

Alloys of the rare earths R (including La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er) with platinum, having the composition R₃Pt₄, have been synthesized and investigated by X-ray diffraction (XRD) and differential thermal analysis (DTA). At temperatures above about 900 °C and below 250 °C, all the single phases R₃Pt₄ are formed, which crystallize with the same structure of the rhombohedral Pu₃Pd₄ type. Over the temperature range of about 250 °C to 900 °C, they occur at an eutectoid decomposition into RPt and RPt₂ compounds neighboring in the corresponding phase diagram, R₃Pt₄ → RPt + RPt₂. The stability of these phases R₃Pt₄ may be restricted to a radius ratio r _R/r _Pt range of 1.27 to 1.35.     

Electrochemical Behavior of an Amorphous and Nanocrystalline Fe<Subscript>79</Subscript>P<Subscript>13</Subscript>Si<Subscript>5</Subscript>V<Subscript>3</Subscript> Alloy in a Damp SO<Subscript>2</Subscript>-Contaminated Atmosphere

The electrochemical behavior of amorphous and nanocrystalline soft magnetic Fe₇₉P₁₃Si₅V₃ alloy in a 0.1 M Na₂SO₄ solution has been studied. Mössbauer studies show that the electrochemical characteristics of the alloy are comparable with those of an Finemet Fe₇₇Si₁₃B₇Nb_2.1Cu_0.9 alloy, whereas the studied alloy is inexpensive and can be prepared using natural alloy ferrophosphorus containing vanadium and silicon.     

Phase analysis of multicomponent alloys using an Ni<Subscript>50</Subscript>Co<Subscript>25</Subscript>Mo<Subscript>25</Subscript> alloy as an example

method for phase analysis of three-component alloys is proposed. It is based on a pair interaction model and an experimental determination of the sign of pair chemical interaction energy and includes an electron-microscopic investigation of microstructures above and below the ordering–separation phase transition temperature for each diffusion couple. This method is used to study an Ni₅₀Co₂₅Mo₂₅ alloy. The phases that precipitate in this alloy over the entire heating temperature range, including the liquid state, are detected.     

Reduction-Carburization of NiO-WO<Subscript>3</Subscript> Under Isothermal Conditions Using H<Subscript>2</Subscript>-CH<Subscript>4</Subscript> Gas Mixture

Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of NiO-WO₃ oxide precursors using H₂-CH₄ gas mixtures in the temperature range of 973 to 1273 K. The kinetics of the gas–solid reaction were followed closely by monitoring the mass changes using the thermogravimetric method (TGA). As a thin bed of the precursors were used, each particle was in direct contact with the gas mixture. The results showed that the hydrogen reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. Consequently, the reaction rate could be conceived as being controlled by the chemical reaction. From the reaction rate, Arrhenius activation energies for reduction and carburization were evaluated. Characterization of the carbides produced was carried out using X-ray diffraction and a scanning electron microscope (SEM) combined with electron dispersion spectroscopy (SEM-EDS) analyses. The grain sizes also were determined. The process parameters, such as the temperature of the reduction–carburization reaction and the composition of the gas mixture, had a strong impact on the carbide composition as well as on the grain size. The results are discussed in light of the reduction kinetics of the oxides and the thermodynamic constraints.     

No-current diffusion saturation of nickel with gadolinium in the LiCl-KCl-GdCl<Subscript>3</Subscript> melt

The kinetic characteristics of alloy formation during the diffusion saturation of nickel with gadolinium in the LiCl-KCl-GdCl₃ molten mixture are determined experimentally. The results of a chemical analysis, an electron probe microanalysis, and an X-ray phase analysis of coatings showed that intermetallic compounds, which are the Laves phase of the GdNi₂ composition, are formed during the no-current transfer in the surface layer of alloys. The coefficients of reactive diffusion and activation energy for the GdNi₂ compound are calculated.