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.     

Synthesis and Characterization of Lithium Borate Glasses Containing La<Subscript>2</Subscript>O<Subscript>3</Subscript>

The glass series with general formula 15 Li₂O–(85 − x) B₂O₃–x La₂O₃ was prepared. Electrical and optical properties of these glasses were studied. It is observed that the conductivity of these glasses decreases while density, glass transition temperature and refractive index increases with the addition of La₂O₃. Ion concentration of La³⁺ in glasses, polaron radius, field strength, molar refractivity and molar electronic polarizability were calculated. The absorption coefficient and direct optical band gaps are evaluated using the absorption edge calculations. The different factors that play a role for controlling the refractive indices such as electronic polarizability, field strength of cations and rigidity of glass structure are discussed in accordance with the obtained index data.     

Effect of Ce<Subscript>2</Subscript>O<Subscript>3</Subscript> on Structure,Viscosity, and Crystalline Phase of CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Li<Subscript>2</Subscript>O-Ce<Subscript>2</Subscript>O<Subscript>3</Subscript> Slags

Aiming at devising new mold flux for Ce-bearing stainless steel, a fundamental investigation on the effect of Ce₂O₃ on properties of the CaO-Al₂O₃-Li₂O-Ce₂O₃ slag was provided by the present work. The results show that adding Ce₂O₃ could decrease the viscosity of the slag due to its effects on decreasing the polymerization of the slag. The crystalline process was restrained by increasing the content of Ce₂O₃, and the crystalline phases also can be influenced by the slag structure. The crystalline phases were transferred from LiAlO₂ and CaO to LiAlO₂ and CaCeAlO₄ with the addition of Ce₂O₃ to the slag, which could be well confirmed by the structure of the unit cell of the crystals.     

Preparation of V<Subscript>2</Subscript>O<Subscript>5</Subscript> from Ammonium Metavanadate via Microwave Intensification

Parameters of technique to prepare of V₂O₅ by microwave intensification from ammonium metavanadate were optimized using central composite design of response surface methodology. A quadratic equation model for decomposition rate was built and effects of main factors and their corresponding relationships were obtained. The microwave heating behavior indicated that ammonium metavanadate had weak capability to absorb microwave radiation, while V₂O₅ had good capability to absorb microwave radiation. The results of the statistical analysis showed that the decomposition rate of ammonium metavanadate was significantly affected by calcination temperature and calcination time in the range studied. The optimized conditions were as follows: calcination temperature 645.35 K, calcination time 9.66 min and 4.3 g, respectively. The decomposition rates of ammonium metavanadate were 99.13%, which coincided well with experiments values 99.33% under these conditions. These suggest that regressive equation fits the decomposition rates perfectly. XRD reveals that it is feasible to prepare the V₂O₅ by microwave intensification from ammonium metavanadate, which mixed with small amounts of V₂O₅.     

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.     

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.     

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.     

Experimental Investigation and Thermodynamic Modeling of the B<Subscript>2</Subscript>O<Subscript>3</Subscript>-FeO-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript> System for Recycling of NdFeB Magnet Scrap

NdFeB magnet scrap is an alternative source of neodymium that could have a significantly lower impact on the environment than current mining and extraction processes. Neodymium can be readily oxidized in the presence of oxygen, which makes it easy to recover neodymium in oxide form. Thermochemical data and phase diagrams for neodymium oxide containing systems is, however, very limited. Thermodynamic modeling of the B₂O₃-FeO-Fe₂O₃-Nd₂O₃ system was hence performed to obtain accurate phase diagrams and thermochemical properties of the system. Key phase diagram experiments were also carried out for the FeO-Nd₂O₃ system in saturation with iron to improve the accuracy of the present modeling. The modified quasichemical model was used to describe the Gibbs energy of the liquid oxide phase. The Gibbs energy functions of the liquid phase and the solids were optimized to reproduce all available and reliable phase diagram data, and thermochemical properties of the system. Finally the optimized database was applied to calculate conditions for selective oxidation of neodymium from NdFeB magnet waste.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Concentration on Density and Structure of (CaO-SiO<Subscript>2</Subscript>)-xAl<Subscript>2</Subscript>O<Subscript>3</Subscript> Slag

The effect of Al₂O₃ concentration on the density and structure of CaO-SiO₂-Al₂O₃ slag was investigated at multiple Al₂O₃ mole percentages and at a fixed CaO/SiO₂ ratio of 1. The experiments were conducted in the temperature range of 2154 K to 2423 K (1881 °C to 2150 °C) using the aerodynamic levitation technique. In order to understand the relationship between density and structure, structural analysis of the silicate melts was carried out using Raman spectroscopy. The density of each slag sample investigated in this study decreased linearly with increasing temperature. When the Al₂O₃ content was less than 15 mole pct, density decreased with increasing Al₂O₃ content due to the coupling of Si (Al), whereas above 20 mole pct density of the slag increased due to the role of Al³⁺ ion as a network modifier.     

Thermodynamic evaluation and optimization of the MnO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and MnO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> systems and applications to inclusion engineering

All available thermodynamic and phase-diagram data have been critically evaluated and optimized for the liquid-slag phase and for all solid phases at 1 bar pressure from 298 K to above the liquidus temperatures for the systems MnO-Al₂O₃ and MnO-Al₂O₃-SiO₂, and a database of model parameters has been prepared. The modified quasichemical model was employed for the molten-slag phase. Calculations using the database were performed with applications to inclusion engineering for Mn/Si killed steel.     

Wear of Plasma Sprayed Conventional and Nanostructured Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>, Based Coatings

An ever increasing demand for high-performance ceramic coatings has made it inevitable for developing techniques with precise control over the process parameters to enable the fabrication of coatings with the desired microstructure and improved structural properties. The literature on plasma sprayed nanostructured ceramic coatings such as of Al₂O₃, Cr₂O₃, and their composites obtained using reconstituted nano sized ceramic powders has been reviewed in this study. Ceramic coatings due to their enhanced properties are on the verge of replacing conventional ceramic coatings used for various applications like automotive systems, boiler components, power generation equipment, chemical process equipment, aircraft engines, pulp and paper processing equipment, land-based and marine engine components, turbine blades etc. In such cases, the advantage is greater longevity and reliability for realizing the improved performance of ceramic coatings. It has been observed that the plasma sprayed nanostructured ceramic coatings show improvement in resistance to wear, erosion, corrosion, and mechanical properties as compared to their conventional counterparts. This article reviews various aspects concerning the plasma sprayed ceramic coatings such as (i) the present understanding of formation of plasma-spray coatings and factors affecting them, (ii) wear performance of nanostructured Al₂O₃, Cr₂O₃ and their composite ceramic coatings in comparison to their conventional counterparts, and (iii) mechanisms of wear observed for these coatings under various conditions of testing.     

Phase-equilibrium data and liquidus for the system “MnO”-CaO-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> at Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> of 0.55 and 0.65

Phase-equilibrium data and liquidus isotherms for the system “MnO”-CaO-(Al₂O₃+SiO₂) at silicomanganese alloy saturation have been determined in the temperature range of 1373 to 1723 K. The results are presented in the form of the pseudoternary sections “MnO”-CaO-(Al₂O₃+SiO₂) with Al₂O₃/SiO₂ weight ratios of 0.55 and 0.65. The primary-phase fields have been identified in this range of conditions.     

The Thermodynamic Behavior of Copper in the CaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> and BaO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> Slag System

The Cu solubility was measured in the CaO-B₂O₃ and BaO-B₂O₃ slag systems to understand the dissolution mechanism of Cu in the slags. The Cu solubility had a linear relationship with oxygen partial pressure in the CaO-B₂O₃ slag system, which corresponds with previous studies. Also, the Cu solubilities in slag decreased with increasing the slag basicity, which value of slope was close to –0.5 in logarithmic form. From the results of experiment, the Cu dissolution mechanism established as follows:

<Emphasis Type="Italic">In-Situ</Emphasis> Synthesis of Cu/Cr-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanocomposite by Mechanical Alloying and Heat Treatment

In this article, a novel method has been used to prepare a copper matrix nanocomposite containing Cu-10 wt pct Cr-10 wt pct Al₂O₃ by heat treatment of the mechanically activated Cu, Al, and Cr₂O₃ powder mixture. Structural evolutions were investigated using the X-ray diffraction (XRD) technique. The microstructure of samples was examined using scanning electron microscopy (SEM). It was found that during the milling process, Cu(Al) solid solution and Cu₉Al₄ phase were formed as the intermediate products, and therefore, Al activity was decreased. Hence, the reduction of Cr₂O₃ with Al was prevented during the ball milling stage. Further heat treatment carried out under argon atmosphere at 900 °C for 8 hours resulted in completion of Cr₂O₃ reduction by Al.     

Synthesis and Non-isothermal Carbothermic Reduction of FeTiO<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Solid Solution Systems

To investigate the carbothermic reduction behaviors of xFeTiO₃·(1 ? x)Fe₂O₃ solid solutions, the solid solutions with different x values were synthesized and used in the corresponding reactions. With an increase in x, the temperature pertaining to the onset of carbothermic reduction increased, while the rate of reduction of the solid solutions, α, decreased. The lattice parameters calculated from XRD patterns indicated that the solid solution with a higher x led to a larger lattice distortion. The non-isothermal kinetics were calculated, and an average activation energy E value of 3.0 × 10² kJ/mol was obtained.     

Ferroelectric and Dielectric Behavior of Samarium-Substituted Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Nanomaterials Synthesized by Gel Combustion Method

Samarium (Sm) substituted bismuth titanate (Bi₄Ti₃O₁₂, BT) nanoparticles with compositions of Bi_4?xSm_xTi₃O₁₂ (BSmT) (where x = 0.0, 0.25, 0.50, 0.75, 1.0) were prepared by using the gel combustion method. X-ray diffraction pattern of prepared nanoparticles confirmed that all the BSmT compositions were of the single phase orthorhombic structure with the space group of B2ab. The dielectric loss at 100 Hz varied from 0.0925 to 0.056 with an increase in Samarium content. Dielectric loss confirmed the lower leakage current of BSmT nanoparticles. The ferroelectric behavior of BSmT nanoparticles showed that the Bi_3.50Sm_0.50Ti₃O₁₂ had good ferroelectric property and also had minimum leakage current. The increase of coercive field (Ec) and the increase of remnant polarizations (Pr) were pronounced with the increase in Sm content confirming to the fact that the substitution of Sm³⁺ had improved the ferroelectric properties of BT.     

Effect of LiF as Sintering Agent on the Densification and Phase Formation in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-4 Wt Pct Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> Ceramic Compound

Different amounts of LiF were added to an Al₂O₃-4 pct Nb₂O₅ basic ceramic, as sintering agent. Improved new ceramics were obtained with LiF concentrations varying from 0.25 to 1.50 wt pct and three sintering temperatures of 1573 K, 1623 K, and 1673 K (1300 °C, 1350 °C, and 1400 °C). The addition of 0.5 wt pct LiF yielded the highest densification, 94 pct of the theoretical density, in association with a sintering temperature of 1673 K (1400 °C). Based on X-ray diffraction (XRD), this improvement was due not only to the presence of transformed phases, more precisely Nb₃O₇F, but also to the absence of LiAl₅O₈. The preferential interaction of LiF with Nb₂O₅, instead of Al₂O₃, contributed to increase the alumina sintering ability by liquid phase formation. Scanning electron microscopy (SEM) results revealed well-connected grains and isolated pores, whereas the chemical composition analysis by energy dispersive energy (EDX) indicated a preferential interaction of fluorine with niobium, in agreement with the results of XRD. It was also observed from thermal analysis that the polyethylene glycol binder burnout temperature increased for all LiF concentrations. This may be related to the formation of hydrogen bridge bonds.