PbO–B2O3–SiO2 glass powders with spherical shape prepared by spray pyrolysis

PbO–B₂O₃–SiO₂ glass powders were directly prepared using spray pyrolysis. The powders were spherical and fine-sized. One glass particle was obtained from one droplet by melting the precursors inside a hot wall tubular reactor. The characteristics of these powders were compared with those of the commercial product, which was prepared using the conventional melting process. The spherical powders, which were prepared using spray pyrolysis at 1000 °C, had broad peaks at around 28° in the XRD spectrum. The glass phase was formed during the spray pyrolysis process even within a short residence time of the powders inside the hot wall tubular reactor. The mean size of the prepared glass powders was 1 μm. The dielectric layers formed from the spherical, fine-sized glass powders had a high transparency at firing temperatures above 520 °C. The maximum transparency of the dielectric layer formed from the glass powders obtained from spray pyrolysis was 95.3% at the firing temperature of 560 °C. The dielectric layer formed from the spherical, fine-sized glass powders had a smooth surface and no void inside the dielectric layer.     

Preparation of strontium chloride hexahydrate by batch‐cooling crystallization: Control of crystal size and morphology

The effects of initial supersaturation, cooling rate, and stirring rate on the morphology of strontium chloride hexahydrate (SrCl₂·6H₂O) crystals were investigated by batch‐cooling crystallization, providing optimal operating conditions. Uniform needle‐like crystals with a length of 1200.50 μm and a width of 100.92 μm on average were obtained. The corresponding aspect ratio of length to width was about 11.90. Moreover, the morphological modification of SrCl₂·6H₂O crystals using cetyltrimethylammonium chloride (CTAC) was studied. When 20.30 mmol·L⁻¹ of CTAC was added, the length and width of crystals were 792.71 μm and 233.25 μm, respectively, and the corresponding aspect ratio decreased to 3.40. The shape of SrCl₂·6H₂O crystal changed to granule‐like, probably because of the strong interaction of CTAC with the SrCl₂·6H₂O facets with a denser distribution of Cl⁻ ions. This study offers a simple, flexible, and highly efficient approach to regulate the morphology of SrCl₂·6H₂O crystals and opportunities for multiple applications of SrCl₂·6H₂O.     

Crystallisation and performance characteristics of high‐temperature annealed electroless Ni‐W‐P coatings

Electroless deposition of Ni–P based alloys is a well‐known commercial process that has numerous applications because of their excellent anticorrosive and wear properties. However, for some special occasions, like the components for gas making furnaces in chemical fertiliser industry, the coatings must be reinforced to withstand short‐term high temperatures between 600 °C and 700 °C as well as light erosive wear. Therefore, co‐deposition of high melting point metallic element, W, has been considered as a preferred choice. In the present study, two Ni–W–P alloy coatings were deposited on mild steel panels from different alkaline baths. The microstructures of the annealed coatings were characterised by quantitative XRD, XPS and SEM/EDS analysis techniques and their microhardness, friction and wear behaviour, corrosion mechanism as well as microstrain and residual stress are discussed in comparison with the as‐plated state. The results indicate that the hardness mainly depends on the volume fraction and crystallite size of Ni₃P phase; the uniform corrosion in sulfuric acid solution is closely related to the ratio of I_Ni/I_Ni3P as well as grain size. The wear mechanism of the high‐temperature annealed coating is dominated by abrasive wear, but the wear in the early stages started from mild adhesive wear caused by adhesion between the friction couples. Electroless deposited Ni‐W‐P alloys with high phosphorus present relatively good properties, including hardness, wear and corrosion resistance when 700 °C is applied for annealing process.     

Preparation of Li2CO3 by gas‐liquid reactive crystallization of LiOH and CO2

A spinning disk reactor (SDR) was used in this research to prepare Li₂CO₃ by gas‐liquid reactive crystallization of LiOH and CO₂. It was found that the end pH value of the above reaction should be controlled within the range of 9.0‐9.5 to obtain a high yield of Li₂CO₃. The effects of operational parameters (including the temperature, the concentration of LiOH solution, the rotation rate of the spinning disk, the circulation rate of LiOH slurry, the flow rate of CO₂ and the ultrasound field) on the particle size and the yielding rate were investigated by an orthogonal experiment. The results show the significant factors influencing the particle size are the ultrasound field, the temperature and the flow rate of CO₂. As for the yielding rate, the temperature, the concentration of LiOH solution and the flow rate of CO₂ exert obvious impacts, while the effects of ultrasound field and the rotation rate of the spinning disk are limited. The SEM images show the Li₂CO₃products are flower‐like particles, which are composed of plate‐like primary crystals. The size analysis shows the volume mean particle size of the Li₂CO₃products ranges 37‐90 μm depending on the various experimental conditions. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Particle size of powders under hydrothermal conditions

Various non‐oxide (CuI, AgI, AgCl, PbS, CuS and ZnS) and oxide (ZnO, TiO₂, SnO₂, CeO₂ and ZrO₂) powders were prepared under hydrothermal conditions to investigate the effects of temperature, pH and precursors on the particle size of powders. It was found that the particle sizes of PbS, CuS and ZnS powders were much smaller than that of CuI, AgI and AgCl powders prepared under the same conditions. The particle sizes of TiO₂, SnO₂, CeO₂ and ZrO₂ powders are much smaller than that of ZnO powders prepared under the same conditions. It is concluded that the solution conditions have a certain effect on the particle size of powders under the hydrothermal conditions. The particle size of powders increased with the rising of temperature. Additional factors affecting the particle size were uncovered through studying the nucleation mechanism. The particle size was mainly related to the Madelung constant and the electric charge number of ions. Powders with smaller particle size resulted from systems that possessed the larger Madelung constant and ionic charge number. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and thermomagnetic properties of powders produced from melt spun FeNbBCu ribbons

Amorphous ribbons of Fe₇₇Nb₇B₁₅Cu₁ prepared by melt-spinning and powders produced from them by ball-milling were characterized by means of calorimetry, X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. Upon thermal treatment the amorphous alloy experiences a primary crystallization that leads to bcc-Fe nanocrystals dispersed in an amorphous matrix. Magnetic measurements indicate that this alloy in the amorphous and nanocrystalline state is a good soft magnetic material. Values of saturation magnetization and coercivity are 120 Am²/kg and 5 A/m respectively, for the alloy in the nanocrystalline state. Pre-annealing, post-relaxation and nanocrystallization as well as various milling parameters were explored and the structural and magnetic changes induced have been studied. The analysis of the particle size distribution and morphology of the powders show that the brittleness resulting from pre-annealing of the ribbons is very effective in reducing the particle’s size. Recovery of the high coercitive field induced by milling is achieved by post-annealing to an extent that depends mostly on the milling conditions.     

On‐line monitoring of lithium carbonate dissolution

Dissolution of lithium carbonate (Li₂CO₃) in aqueous solution was investigated using three on‐line apparatuses: the concentration of Li₂CO₃ was measured by electrical conductivity equipment; CLD (Chord Length Distribution) was monitored by FBRM (Focused Beam Reflectance Measurement); crystal image was observed by PVM (Particle Video Microscope). Results show dissolution rate goes up with a decrease of particle size, and with an increase in temperature; stirring speed causes little impact on dissolution; ultrasound facilitates dissolution obviously. The CLD evolution and crystal images of Li₂CO₃ powders in stirred fluid were observed detailedly by FBRM and PVM during dissolution. Experimental data were fitted to Avrami model, through which the activation energy was found to be 34.35 kJ/mol. PBE (Population Balance Equation) and moment transform were introduced to calculate dissolution kinetics, obtaining correlation equations of particle size decreasing rate as a function of temperature and undersaturation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low‐temperature urea‐assisted hydrothermal synthesis of Bi2S3 nanostructures with different morphologies

Different morphologies of single‐crystalline orthorhombic phase bismuth sulfide (Bi₂S₃) nanostructures, including sub‐microtubes, nanoflowers and nanorods were synthesized by a urea‐assisted hydrothermal method at a low temperature below 120 °C for 12 h. The as‐synthesized powders were characterized by X‐ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and UV‐vis spectrophotometry. The experimental results showed that the sulfur sources had a great effect on the morphology and size of the resulting powders. The formation mechanism of the Bi₂S₃ nanostructures with different morphologies was discussed. All Bi₂S₃ nanostructures showed an appearance of blue shift relative to the bulk orthorhombic Bi₂S₃, which might be ascribed to the quantum size effect of the final products. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sintering of nanoparticles of α-Fe2O3 using gelatin

We have demonstrated in this work that single phase of α-Fe₂O₃ nanoparticle can be prepared using gelatin. It was characterized by X-ray powder diffraction (XRPD) technique, gas sorption technique (BET), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). The nanoparticle was obtained from an aqueous solution of gelatin and FeCl₃ · 6H₂O, as Fe source, annealed in the temperature range of 200–600 °C for 12 h. The mean particle size of this powder measured with XRPD is about 100 nm and this size agrees well with TEM experiments. Also, the TEM result shows agglomeration that was confirmed by BET technique. These results show that gelatin could be an alternative organic precursor to produce metal oxide powders with nanometer dimensions.     

Growth,structural and optical properties of 12%‐deuterated KDP crystals

K(D_0.12H_0.88)₂PO₄ crystals were chosen to be used for quadratic nonlinear medium of wideband frequency doubling at 1 μm. A key limitation on this application is that little information can be found in the previous reports. In this work, growth as well as structural and optical properties of this crystal were investigated in detail. Experimental results in comparison with KDP indicate that lattice parameter along a‐axis changes much more than lattice parameter c and infra‐red absorption edge shift by 0.08 μm accompanied with increasing of transmittance in the whole region. With the introduction of deuterium atom, peak of ν₁(PO4) shifts to lower wave number and transverse stimulated Raman scattering was effectively suppressed. Extra‐ordinary and ordinary indices were also measured as function of wavelength. Good crystalline perfection and great performance of damage threshold also indicate that 12%‐DKDP is an appropriate choice in the application of wideband frequency doubling at 1 μm.     

Magnetic anisotropy of large floating‐zone‐grown single‐crystals of SrRuO3

SrRuO₃ is a highly interesting material due to its anomalous‐metal properties related with ferromagnetism and its relevance as conductive perovskite layer or substrate in heterostructure devices. We have used optical floating zone technique in an infrared image furnace to grow large single crystals of SrRuO₃ with volumes attaining several hundred mm³. Crystals obtained for optimized growth parameters exhibit a high ferromagnetic Curie temperature of 165 K and a low‐temperature magnetization of 1.6 μ_B at a magnetic field of 6 T. The high quality of the crystals is further documented by large residual resistance ratios of 75 and by crystal structure and chemical analyzes. With these crystals the magnetic anisotropy could be determined.     

Dielectric properties of fine-grained triglycine sulphate (TGS)

The dielectric permittivity ε′ values of triglycine sulphate (TGS) compressed powders with different grain sizes: (1–300) μm have been measured from 300 to 350 K. It has been shown that ε′_max and transition temperature T_c for the average grain size of about 30 μm behave as predicted by the theory of Wang et al. [J. Phys: Condens. Matter 7 (1995) 7163] for cylindric particle geometry.     

Pt immobilization on TiO2‐embedded carbon nanofibers using photodeposition

Currently, the use of fuel cell electrodes containing Pt catalysts has been limited due to technological problems in this system, primarily the system's high cost. The improvement of Pt catalyst use has been achieved by changes in the Pt immobilization method. In this study, we have studied Pt immobilization on carbon nanofiber composites using the photodeposition method. First, we prepared the carbon nanofibers, which were homogeneously embedded TiO₂ using the electrospinning technology. These TiO₂‐embedded carbon nanofiber composites (TiO₂/CNFs) were then immersed in a Pt precursor solution and irradiated with UV light. The obtained Pt‐deposited TiO₂/CNFs contained Pt that was immobilized on the carbon nanofibers, and the Pt particle size was 2‐5 nm. The XPS spectra showed that the amount of Pt increased with an increasing UV irradiation time. The current densities and total charge also increased with an increase in the UV irradiation time, possibly due to an increase of active specific area by finely dispersed Pt nanoparticles. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electron microscopy investigations on structures of ZrO2‐rich phases in the quasibinary system ZrO2‐Zr3N4

Slowly cooled nitrided zirconia samples were investigated and characterized by means of transmission electron microscopy (TEM). Besides the well‐known different modifications of ZrO₂ some ZrO₂‐rich oxynitride phases could be further found, called β‐type phases. An overview regarding the formation of such different structural modifications could be gained, supported by previously performed measurements using powder X‐ray diffractometry (XRD). Similar to fast cooled nitrided zirconia samples Zr(N,O), the slowly cooled ones also contain different kinds of ZrO₂ precipitates, which can be obviously emphasized by using the methods of diffraction contrast. A super cell was successively built, derived from the unit cells of the β and β′ phase, in order to explain the structure of the observed modulated β″ phase. Agreements from the comparisons between experimental high resolution images and the simulated ones of such modulated structures confirm the suggested starting points. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and spectral properties of Er3+/Tm3+ co‐doped LiYF4 single crystal

High quality Er³⁺/Tm³⁺:LiYF₄ single crystals were grown by a Bridgman method. The absorption spectra and luminescent properties of the crystals were studied to characterize the effect of Tm³⁺ on the spectroscopic properties upon excitation of an 800 nm laser diode. The broaden 1.5 μm and the enhanced 2.7 μm emission were observed in the Er³⁺/Tm³⁺ co‐doped LiYF₄ single crystals. Meanwhile, the up‐conversion and 1.5 μm emission intensities from Er³⁺ decrease with increasing the ratio of Tm³⁺ to Er³⁺. The energy transfer processes between Tm³⁺ and Er³⁺ in the Er³⁺/Tm³⁺ co‐doped samples were analyzed. The energy transfer efficiency η_ETE from Er³⁺ to Tm³⁺ is calculated. The highest η_ETE of 65.30% for the sample with 0.296 mol% of Er³⁺, 0.496 mol% of Tm³⁺ concentration was obtained. The present work indicates that Er³⁺/Tm³⁺ co‐doped LiYF₄ single crystal can be a promising material for the potential application in infrared devices.     

The effect of calcination temperature on the crystallinity of TiO2 nanopowders

TiO₂ nanopowders have been prepared using 0.1 M titanium tetraisopropoxide (TTIP) in varied pH aqueous solution containing TMC and NP-204 surfactants. Only the powder acquired from a solution of pH=2 has a regular particle size distribution. Anatase phase powders are obtained by calcination in nitrogen in the 250–500°C temperature range. When calcined at 400°C, the diameter of the nanoparticles is approximately 10 nm with a specific surface area of 106.9 m²/g. As the calcination temperature is increased, the particle size increases. Rutile phase powders are formed at calcination temperatures above 600°C.     

Crystallization of silicalite‐1 from clear synthesis solutions: Effect of template concentration on crystallization rate and crystal size

Synthesis of silicalite‐1 powders and membranes from initially clear solutions with different tetrapropylammonium hydroxide or bromide concentrations was studied. While tetrapropylammonium bromide acts only as template, tetrapropylammonium hydroxide provides both the template and hydroxyl ions to the synthesis medium. The effects of template and hydroxyl ion concentration on the product yield, crystallization rate and crystal size were investigated. Pure and highly crystalline silicalite‐1 was obtained with all compositions. The nucleation time decreases from 100 h to 20 h and the crystal size decreases from 3.5 μm to 0.35 μm as the template amount x is increased from 5 to 30 moles at a batch composition of 80SiO₂.xTPAOH.1500H₂O at 95 °C. Yield of silicalite‐1 passes through a maximum at intermediate TPA concentration. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth improvement and quality evaluation of ZnGeP2 single crystals using vertical Bridgman method

ZnGeP₂ single crystals were grown using two-temperature zone vertical Bridgman method. The effect of crucible material, crucible shape, and cooling program on the growth of the ZnGeP₂ crystal was investigated. The qualities of the crystals were evaluated by high resolution X-ray diffraction, X-ray fluorescence spectrometry, and IR transmittance spectra. The results show that the full width at half maximum of the rocking curves for (200), (004), and (220) faces are 45″, 37″, and 54″, respectively. The concentration of the P, Zn and Ge are almost homogeneous along the growth axis, but P and Zn are slightly deficient compared with Ge in the as-grown ZnGeP₂ crystals. The increase of annealing temperature from 600 °C to 700 °C has little effect on the reduction of the absorption losses in ZnGeP₂ powders, and has negative effect on the reduction of the absorption losses in ZnP₂ powders. Annealed in ZnP₂ powders at 600 °C for 300 h, the optical absorption loss at 2.05 μm reduce by 37%, compared with that of 27% reduction annealed in ZnGeP₂ powders.     

Synthesis,structure and electrochemical performance of cobaltite‐based composite cathodes for IT‐SOFC

The development of novel and high‐performance cathodes is a critical issue to be addressed in order to reduce Solid Oxide Fuel Cells (SOFCs) operation temperature to the 600‐800 °C range or less. The performance of CeO₂‐based composite cathodes is very attractive to such operational temperatures. In this work, La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) and Ce_0.8Sm_0.2O_1.9 (SDC) powders were synthesized by different synthesis methods and mechanically mixed to prepare LSCF‐SDC composite cathodes. Screen‐printed LSCF‐SDC/CGO/LSCF‐SDC symmetrical cells were sintered at 1150 °C for 4 h and characterized by electrochemical impedance spectroscopy in static air. X‐ray diffraction and scanning electron microscopy were employed to characterize the powders. Area specific resistance values of 0.72 and 2.77 Ω cm² at 800 °C were found for composite cathodes containing SDC powder synthesized by modified Pechini and microwave‐assisted combustion methods, respectively. Furthermore, the activation energy of the composite cathode containing SDC derived from modified Pechini method is 1.18 eV, i.e., much lower than 1.73 eV, value determined for LSCF with SDC from microwave‐combustion method.     

Preparation and mechanical properties of a bulk icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy

A bulk Ti₄₅Zr₃₅Ni₁₇Cu₃ alloy, which consisted of the icosahedral quasicrystalline phase, was prepared by mechanical alloying(MA) and subsequent pulse discharge sintering. Ti₄₅Zr₃₅Ni₁₇Cu₃ amorphous powders (with particle size <50 μm) were obtained after mechanical alloying for more than 150 h from the mixture of the elemental powder. The transformation temperature range from amorphous phase to the quasicrystalline phase was from 400 K to 900 K. The mechanical properties of the bulk quasicrystalline alloy have been examined at room temperature. The Vickers hardness and compressive fracture strength were 620 ± 40 and 1030 ± 60 MPa, respectively. The bulk quasicrystalline alloy exhibited the elastic deformation by the compressive test. The fracture mode was brittle cleavage fracture.