Study of cation distribution for Cu–Co nanoferrites synthesized by the sol–gel method

Nano sized polycrystalline soft ferrite particles with composition Cu_1−xCo_xFe₂O₄ (x =0.1, 0.3, 0.5, 0.7, 0.9) were synthesized by the sol–gel technique. The existence of well-defined single cubic spinel structure was confirmed in all the samples by X-ray diffraction. The crystallite size found by XRD varied from 14.8 to 34.0 nm. The microstructure was also characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Slight expansion of the unit cell was detected with the increase of Cobalt concentration, which may be attributed due to larger ionic radius of Co²⁺. Lattice parameter ranged from 8.34 Å to 8.37 Å for Co²⁺ from 0.1–0.9. The distribution of cations amongst A- and B-sites of the lattice was estimated by X-ray diffraction by using the R-factor technique. The results showed that both Cu²⁺ and Co²⁺ ions occupy mainly the B-site while Fe³⁺ ions were equally distributed among A- and B-sites. The data obtained from cation distribution analysis was used to determine the magnetic moment for each sample and VSM studies were also carried out to validate these calculations. Magnetic measurements showed that the saturation magnetization (Ms) and coercivity (Hc) increased with increasing cobalt content.     

Chiral induction in anion–anion electron transfer in aqueous solution catalyzed by a chiral cation

The oxidation of cobalt(II) chelate complexes [CoY]²⁻, where Y=edta (ethylenediaminetetraacetate), pdta (1,2-propanediaminetetraacetate) and cydta (trans-1,2-cyclohexanediaminetetraacetate), by [Co(mal)₃]³⁻ (mal=malonate) was catalyzed by chiral [Co(en)₃]³⁺ to yield optically active products with the enantiomeric excesses which increase with increasing concentration of chiral [Co(en)₃]³⁺. Substituents on the ethylenediamine backbone of [CoY]²⁻ had significant effects on the sign and the magnitude in the stereoselectivity. The results are interpreted in terms of a chiral induction mechanism in which the ion pair between [CoY]²⁻ and chiral [Co(en)₃]³⁺ is stereoselectively oxidized by [Co(mal)₃]³⁻. A model is proposed for the relative orientation of oxidant, reductant, and catalysis complexes.     

Hybrid A–B–A type nanowires through cation exchange

Hybrid A–B–A type nanowires (NWs) with Ag5Te3–HgTe–Ag5Te3 composition have been created by the reaction of Hg2+ with Ag2Te NWs. The NW morphology of Ag2Te is preserved upon reaction with minor changes and the two separate phases formed are spatially separated within the same NW. The reaction of Hg2+ with Ag2Te NWs was monitored at different concentrations and the reactivity was attributed to cationic exchange depending on solubility products. Hybrid NWs were formed by partial cation exchange only at low concentrations (below 50 ppm) resulting in Ag5Te3 and HgTe within the same NW. However, at high concentrations (above 100 ppm), the HgTe phase alone was formed. These studies have been extended to other metal ions such as Pb2+, Cd2+, and Zn2+ whose reactivity towards Ag2Te NWs is different from that of Hg2+. These ions form a passivating Te oxide layer upon reaction with other metal ions. The mechanism of reactivity of Hg2+ is explained on the basis of free energy of formation of the ionic solid. Phase transition of Hg2+-reacted NWs occurs at a lower temperature than the parent (Ag2Te NWs) and other metal ions-reacted Ag2Te NWs. Details of the process were elucidated using microscopic and spectroscopic investigations. The physical and chemical properties of the individual components within a NW are expected to provide a novel functionality to the metal chalcogenide systems.     

Preparation of Al–Si composite from high-alumina coal fly ash by mechanical–chemical synergistic activation

High-alumina coal fly ash (HAFA) is a special solid waste because it contains more than 45% alumina and 35% silica. This material can be applied to prepare Al–Si series ceramics if the impurities can be removed and the Al/Si mass ratio can be elevated to a high level. In this work, a new mechanical–chemical synergistic activation–desilication process is proposed and optimized. During the synergistic activation, the morphology, ironic leaching ratios, efficient desilicated ratio (EDR), and mineral phases of different treatments are investigated. The reactivity of amorphous silica can be elevated to a high level (EDR>11%). After the desilication process, the contents of different impurities can be lowered up to less than 1%, and the Al/Si mass ratio can be elevated from 1.26 to 2.71. Mullite refractories are prepared from desilicated HAFA by forming and sintering process, and the bulk density and apparent porosity can reach to 2.85 g/cm³ and 2.07%, respectively.     

Mechanically induced rhombohedral to tetragonal phase transition in PMN–PT single crystals by nanoindentation

Understanding the phase transition behavior of the rhombohedral phase (R) and tetragonal phase (T) of the relaxor ferroelectric PMN–PT single crystals under mechanical load is essential for the potential voltage-free controlled ferroelectric-based nanodevices. Relaxor ferroelectric single crystals PMN–PT, under a local inhomogeneous mechanical load, were studied experimentally by the nanoindentation tests and Raman spectroscopy measurements. The observations show that the rhombohedral phase can be transformed successfully to the tetragonal phase under a mechanical stress, and the tetragonal phase in the PMN–PT single crystals presents a structural stability. The phase transition induced by the mechanical stress with different strain rates further indicates that the relaxor ferroelectric single crystals possess a potential mechanical controllability. The present study reveals the phase transition pathway of the relaxor ferroelectric single crystal under inhomogeneous stress and provides the exciting possibility of the control of mechanically induced phase transition for ferroelectrics.     

Preparation and application of epoxy–chitosan/alginate support in the immobilization of microbial lipases by covalent attachment

The aim of this work was the preparation and application of highly hydrophobic epoxy–chitosan/alginate as a support to immobilize microbial lipases from Thermomyces lanuginosus commercially available as Lipolase® (TLL1) and Lipex® 100L (TLL2) and Pseudomonas fluorescens (PFL). The catalytic properties of the biocatalysts were assayed in olive oil hydrolysis and butyl butyrate synthesis. The results indicated that 12 h was enough for TLL1 to be immobilized on the support. Covalent attachment of TLL1 turned biocatalysts highly active and around 6-fold more stable than free lipase. Based on the results, a time of incubation of 24 h was selected for further studies about the maximum immobilized protein amount and butyl butyrate synthesis. Maximum protein loading immobilized was found to be 25.4 mg g^?1 support for TLL1, followed by TLL2 (20.5 mg g^?1) and PFL (15.5 mg g^?1) offering 80 mg protein g^?1 support. The immobilization of TLL1 and TLL2 resulted in highly active biocatalysts (around 1300 IU g^?1 gel), almost fivefold higher than PFL (272.4 IU g^?1 gel). In butyl butyrate synthesis, PFL showed similar activity to TLL1 and TLL2 derivatives, up to 60 mmol L^?1. The biocatalysts displayed high activity after five successive cycles, retaining around 95% of the initial activity.     

Investigation of gas–solids flow characteristics in a conical fluidized bed dryer by pressure fluctuation and electrical capacitance tomography

It is important to investigate the gas–solids flow characteristics of fluidized bed drying processes to improve the operation efficiency and guarantee the product quality. This paper presents research into fluidized bed drying processes measured by high-frequency differential pressure fluctuation and electrical capacitance tomography (ECT). Power spectra analysis is combined with dynamic calibration for ECT to reveal the complex gas–solids flow behavior. Bubble characteristics are visualized by cross-sectional and quasi-3D ECT images. In addition, results by discrete wavelet transform analysis are given and compared with the analysis results of previous sections. It has been found that bubbles would coalesce in different ways under different operation conditions, and discrete wavelet transform sub-signals of ECT measurements are sensitive to particle moisture. This work reveals the complex hydrodynamic behavior in the fluidized bed dryer and provides valuable information for process control.     

Compressibility induced bubble size variation in bubble column reactors: Simulations by the CFD–PBE

Bubble column reactors can be simulated by the two fluid model (TFM) coupled with the population balance equation (PBE). For the large industrial bubble columns, the compressibility due to the pressure difference may introduce notable bubble size variation. In order to address the compressibility effect, the PBE should be reformulated and coupled with the compressible TFM. In this work, the PBE with a compressibility term was formulated from single bubble dynamics, the mean Sauter diameters predicted by the compressible TFM coupled with the PBE were compared with the analytical solutions obtained by the ideal gas law. It was proven that the mesoscale formulations presented in this work were physically consistent with the macroscale modeling. It can be used to simulate large industrial plants when the compressibility induced bubble size variation is important.     

Low thermal conductivity in porous SiC–SiO2–Al2O3–TiO2 ceramics induced by multiphase thermal resistance

The introduction of multiple heterogeneous interfaces in a ceramic is an efficient way to increase its thermal resistance. Novel porous SiC–SiO₂–Al₂O₃–TiO₂ (SSAT) ceramics were fabricated to achieve multiple heterogeneous interfaces by sintering equal volumes of SiC, SiO₂, Al₂O₃, and TiO₂ compacted powders with polysiloxane as a bonding phase and carbon as a template at 600 °C in air. The porosity could be controlled between 66% and 74% by adjusting the amounts of polysiloxane and the carbon template. The lowest thermal conductivity (0.059 W/(m·K) at 74% porosity) obtained in this study is an order of magnitude lower than those (0.2–1.3 W/(m·K)) of porous monolithic SiC, SiO₂, Al₂O₃, and TiO₂ ceramics at an equivalent porosity. The typical specific compressive strength value of the porous SSAT ceramics at 74% porosity was 3.2 MPa cm³/g.     

Anisotropic core–shell nanocomposites by direct covalent attachment of a side-functionalized poly(3-hexylthiophene) onto ZnO nanowires

Inorganic-organic hybrid solar cells have demonstrated great potential for the development of next generation flexible electronics to deliver efficient energy conversion. The interfacial morphology and structure between donor and acceptor are determinative to the device performance. Here, we report on novel core–shell hybrid heterojunction nanostructures by covalently grafting side-functionalized poly(3-hexylthiophene) onto ZnO nanowires without ligand linkers. Solvatochromism of polythiophene is utilized to control the polymer morphology at interface. Study into the photophysics of nanohybrids demonstrates an elongated conjugation length of the polymer backbone at the interface and fast interfacial charge transfer. These results provide critical insight into the utilization of molecular composites to control donor–acceptor interfaces and further enable the use of anisotropic nanohybrids as photovoltaic elements for the massive fabrication of high efficiency devices.     

Bubble–particle collision and attachment probability on fine particles flotation

Particle size is an important parameter in flotation and has been the focus of flotation research for decades. The difficulty in floating fine particles is attributed to the low probability of bubble–particle collision. In this research, the influence of hydrodynamic parameters on collision probability of fine particles was investigated. Collision probability was obtained using Stokes, intermediate I and intermediate II and potential equations. Maximum collision probability was 5.65% obtained with impeller speed of 1100 rpm, air flow rate of 30 l/h and particle size of 50 μm. Also, attachment probability under Stokes flow, turbulent and potential flow conditions was calculated 100, 99.49 and 81.87% respectively. Maximum attachment probability was obtained with impeller speed of 700 rpm, contact angle of 90°, particle size of 20 μm and air flow rate of 15 l/h. Collision angles were obtained between 60.71° and 60.18° and attachment angles were obtained between 9.15° and 59.83°.     

New lanthanide sulfate–oxalate hybrid solids containing different inorganic building blocks

Three new lanthanide sulfate–oxalate hybrid solids, Er₂(SO₄)(C₂O₄)₂(H₂O)₆·0.5H₂O (1), Nd₃(SO₄)(C₂O₄)_3.5(H₂O)₇·H₂O (2), and [C₄H₁₄N₂]_0.5·Nd₂(SO₄)₂(C₂O₄)_1.5(H₂O)₄ (3), have been synthesized and structurally characterized. Compound 1 has a rare ladder-like structure, while compounds 2 and 3 have different three-dimensional structures. The presence of large 12-ring channels in the structure of 3 is noteworthy. The powder X-ray diffraction, IR spectra, thermogravimetric analyses, and magnetic susceptibility measurements of compounds 1 and 2 have also been investigated.     

Preparation of Ni1−xMnxFe2O4 ferrites by sol–gel method and study of their cation distribution

The spinel ferrite nanoparticles of the system Ni_1?xMn_xFe₂O₄ with x=0.0, 0.1, 0.3, 0.5, 0.7 and 0.9 were prepared by sol–gel auto combustion technique using chlorides of Ni, Mn and Fe as a source with citric acid as chelating agent. The structure of the ferrite materials and the particle size were determined by XRD, it was observed that the structure was a single phase, face centered cubic with lattice parameter ranging from 8.365 Å to 8.394 Å and the particle size ranging from 23.86 Å to 38.30 Å. The lattice parameter showed a linear dependence on concentration in accordance with the Vegard's law. By analyzing XRD patterns, the cation distribution over A and B-sites was estimated through the R-Factor method. The magnetic moment for each sample was determined from cation distribution on the two sites. An enhancement in the net magnetic moment was observed with gradual increase in the Mn content.     

Integrated high strength and high toughness induced by elongated TiB2 grains in reactive sintered TiB2–TiC–SiC ceramics

Although the addition of other phases into TiB₂ matrix to form ceramic composites has been widely used to improve the mechanical properties of monolithic TiB₂ ceramics, it is still difficult to greatly enhance the flexural strength and fracture toughness simultaneously. In this work, TiB₂–TiC–SiC composites were successfully prepared by reactive spark plasma sintering of Ti₃SiC₂–B₄C–Ti powder mixtures. During the sintering process, TiB₂ grains grew into an elongated morphology, endowing the composites with integrated high strength and high toughness. The growth mechanism of TiB₂ grains was attributed to the evaporation–condensation kinetics induced by the presence of B₂O₃. These findings can accelerate the exploration of ceramic composites with excellent comprehensive properties.     

Pore and microstructure change induced by SiC whiskers and particles in porous TiB2–TiC–Ti3SiC2 composites

TiB₂–TiC–Ti₃SiC₂ porous composites were prepared through a plasma heating reaction using powder mixtures of Ti, B₄C SiC whiskers (SiC_w) and SiC particles (SiC_p). The effects of the SiC_w and SiC_p content on pore structures, phase constituents, microstructure, and crystal morphology of TiC were studied. The results show that TiC, TiB, Ti₃B₄ phases are formed within the 5Ti+B₄C system. With the addition of SiC_w and SiC_p, the TiB and Ti₃B₄ phases are reduced, sometimes even disappeared. Interestingly, the content of TiB₂ and TiC increased, resulting in Ti₃SiC₂ and TiSi₂ being formed. The porosity of composites increases notably with the addition of SiC_w. However, with the increase of SiC_p, the porosity of the composites first decreases, followed by an increase. After adding the specified amount of SiC_w/SiC_p, the compressive strength of composites are improved significantly. Additionally, the pore size of the composites are decreased significantly with the addition of SiC_w/SiC_p. During the plasma heating process, some Si atoms will diffuse into the TiC lattice, which in turn made the cubic TiC grains into hexagonal lamellar TiC or Ti₃SiC₂ grains.     

Discrete particle simulation of solids motion in a gas–solid fluidized bed

The solids motion in a gas–solid fluidized bed was investigated via discrete particle simulation. The motion of individual particles in a uniform particle system and a binary particle system was monitored by the solution of the Newton's second law of motion. The force acting on each particle consists of the contact force between particles and the force exerted by the surrounding fluid. The contact force is modeled by using the analogy of spring, dash-pot and friction slider. The flow field of gas was predicted by the Navier–Stokes equation. The solids distribution is non-uniform in the bed, which is very diluted near the center but high near the wall. It was also found that there is a single solids circulation cell in the fluidized bed with ascending at the center and descending near the wall. This finding agrees with the experimental results obtained by Moslemian. The effects of the operating conditions, such as superficial gas velocity, particle size, and column size on the solids movement, were investigated. In the fluidized bed containing uniform particles better solids mixing was found in the larger bed containing smaller size particles and operated at higher superficial gas velocity. In the system containing binary particles, it was shown that under suitable conditions the particles in a fluidized bed could be made mixable or non-mixable depending on the ratios of particle sizes and densities. Better mixing of binary particles was found in the system containing particles with less different densities and closer sizes. These results were found to follow the mixing and segregation criteria obtained experimentally by Tanaka et al.