Synthesis of TiC-TiB2-Ni cermets by thermal explosion under pressure

TiC/TiB₂-based cermets were fabricated in situ by means of the thermal explosion under pressure technique starting from Ti-B₄C powders with the addition of varying contents of Ni metal binder to achieve near-net-shape bulks. The combustion reaction was ignited in a graphite die heated by current. Full conversion of the reactants was obtained by thermal explosion and the process yielded TiC-TiB₂-Ni materials characterised by a fine microstructure. Appreciable differences in terms of microstructure, hardness and fracture toughness by indentation were observed between core and external surface of the products due to fast cooling caused by heat transfer to the die walls. Cermets with a high content of Ni showing high hardness and fracture toughness were obtained, with values of HV₅ = 2182 and K_Ic = 8.8 MPa m^1/2 for 30 wt.% Ni and of HV₅ = 1684 and K_Ic = 12.7 MPa m^1/2 for 47 wt.% Ni.     

Synthesis and characterization of nanocrystalline MgAl2O4 spinel via sucrose process

Nanocrystalline MgAl₂O₄ spinel powder was synthesized using metal nitrates and a polymer matrix precursor composed of sucrose and polyvinyl alcohol (PVA). The precursor and the calcined powders were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to XRD results, the inceptive formation temperature of spinel via this technique was between 600 and 700 °C. The calcined powder at 800 °C for 2 h has faced shaped morphology and its crystallite size is in the range of 8-12 nm. Further studies also showed that the amount of polymeric matrix to metal ions has significant influence on the crystallite size of synthesized magnesium aluminate spinel powder.     

Synthesis of PbS/poly (vinyl-pyrrolidone) nanocomposite

A simple solution growth method for synthesis of nanocomposite of PbS nanoparticles in poly(vinyl-pyrrolidone) (PVP) polymer is described. The nanocomposite is prepared from methanolic solution of lead acetate (PbAc), thiourea (TU) and PVP at room temperature (∼27 °C). Optical absorption spectrum of PbS/PVP nanocomposite solution shows strong absorption from 300 to 650 nm with significant bands at 400 and 590 nm which is characteristic of nanoscale PbS. Spin-coated nanocomposite films on glass have an absorption edge at ∼650 nm with band gap of 2.55 eV. Fourier transform infrared (FTIR) spectroscopy of PbS/PVP nanocomposite and PVP shows strong chemical bond between PbS nanoparticles and host PVP polymer. The transmission electron microscope (TEM) images reveal that 5-10 nm PbS particles are evenly embedded in PVP polymer. The formation of PbS is confirmed by selective area electron diffraction (SAED) of a typical nanoparticle.     

Synthesis of FePO4 cathode material for lithium ion batteries by a sonochemical method

Hydrated amorphous FePO₄ was synthesized by a sonochemical reaction method, in which a solution of (NH₄)₂HPO₄ and FeSO₄·7H₂O was irradiated by an ultrasonic wave. From this material, two kinds of cathode materials were easily prepared: (1) an amorphous sample prepared by heating at 350 °C and (2) a crystalline sample prepared by heating at 700 °C. Both samples consisted of homogeneous sub-micron particles. The amorphous sample of FePO₄ exhibited high discharge capacities with more than 100 mAh g⁻¹ in the range of 3.9-2.0 V versus Li/Li⁺ at a current rate of 0.2 C. The sonochemical synthesis proposed herein has the following advantages: no use of oxidation agents for production of trivalent iron ions, reduction in reaction time, control of particle size, and enlargement in surface area for the preparation of the cathode material.     

Characterization of nanosized Al2(WO4)3

Nanosized aluminum tungstate Al₂(WO₄)₃ was prepared by co-precipitation reaction between Na₂WO₄ and Al(NO₃)₃ aqueous solutions. The powder size and shape, as well as size distribution are estimated after different conditions of powder preparation. The purity of the final product was investigated by XRD and DTA analyses, using the single crystal powder as reference. Between the specimen and the reference no difference was detected. The crystal structure of Al₂(WO₄)₃ nanosized powder was confirmed by TEM (SAED, HRTEM). In additional, TEM locality allows to detect some W₅O₁₄ impurities, which are not visible by conventional X-ray powder diffraction and thermal analyses.     

Synthesis and characterization of Fe(III)-silicate precipitation tubes

Fe(III)-silicate precipitation tubes synthesized through “silica garden” route have been characterized using a number of analytical techniques including X-ray diffraction, infrared spectroscopy, atomic force microscopy, scanning and transmission electron microscopy. These tubes are brittle and amorphous and are hierarchically built from smaller tubes of 5-10 nm diameters. They remain amorphous at least up to 650 °C. Crystobalite and hematite are the major phases present in Fe(III)-silicate tubes heated at 850 °C. Morphology and chemical compositions at the external and internal walls of these tubes are remarkably different. These tubes are porous with high BET surface area of 291.2 m²/g. Fe(III)-silicate tubes contain significant amount of physically and chemically bound moisture. They show promise as an adsorbent for Pb(II), Zn(II), and Cr(III) in aqueous medium.     

Effect of anionic surfactant on vaterite CaCO3

Calcium carbonate (CaCO₃) crystals with various shapes have been synthesized by aging calcium chloride and urea hybrid solution containing sodium dodecylsulfonate (SDSN) or sodium dodecylbenzenesulfonate (SDBS) in a 90 °C bath. The effects of SDSN and SDBS on the morphology and polymorph of precipitated CaCO₃ are investigated with the help of scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectrometer and X-ray diffraction (XRD). Flower-like vaterite changes from monolayer to multilayer structure with the increase of SDSN concentration. While the crystal shape changes from plate-like, through rose-shaped, hat-like, to bicone-like as the concentration of SDBS is increased.     

Synthesis, deposition and characterization of magnesium hydroxide nanostructures on zeolite 4A

The precipitation and self-assembly of magnesium hydroxide Mg(OH)₂ nanopetals on dispersed zeolite 4A particles was investigated. Mg(OH)₂/zeolite nanocomposites were produced from magnesium chloride solutions and characterized via X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), Fourier transform infrared analysis (FTIR), and solid state NMR. It was determined that Mg(OH)₂ interacted with bridging hydroxyl protons (SiOHAl) on the zeolite surface, but not with silanol or aluminol groups. NMR analysis showed that 13% of the tetrahedral Al sites on the zeolite were converted to octahedral Al. The zeolite structure and crystallinity remained intact after treatment, and no dealumination reactions were detected. This suggests that the deposition-precipitation process at ambient conditions is a facile method for controlling Mg(OH)₂ nanostructures on zeolites.     

Powder synthesis and characterization of nanocrystalline CeO2 via the combustion processes

Nanocrystalline CeO₂ powders were synthesized by the combustion reactions using citric acid and glycol as fuels and nitrate as an oxidant. The adiabatic flame temperatures in the auto ignition processes of the precursors were calculated theoretically. XRD measurements indicated that the powders produced in the combustion processes were cubic fluorite CeO₂ phase. The size and morphology of the particles and extent of agglomeration in the powders were studied using transmission electron microscopy (TEM) and the particle size analyzer respectively. Blue shifts of the absorption peak of the as-prepared powders were observed.     

Sonochemical preparation and characterization of SrZrxTi1−xO3/CdS composites

CdS nanoparticles coating SrZr_xTi_1−xO₃ (x=0.27) microparticles were obtained by sonochemical reaction, and the as-prepared composites products were characterized by TEM, XRD, FT-IR and other techniques and the fabrication mechanism was also discussed. Moreover, the photocatalystic properties of the final products were investigated by degradation of methylene blue. By coating CdS nanoparticles, the absorption of the UV-Vis spectrum of SrZr_xTi_1−xO₃ red-shifted, but the emission fluorescence spectrum blue-shifted. Adjusting the reactant concentration can control the thickness of the CdS layer.     

Polyol method synthesis and characterization of nanoscale Sb2Se3 wires

Sb₂Se₃ nanowires ([0 0 1] orientation) with diameter of ∼100 nm and high aspect ratio were successfully synthesized in large scale by a facile nonaqueous polyol method, where home-prepared NaHSe alcohol solution is used as selenium source and PEG-400 serves as an excellent solvent and structure director. The product was characterized by XRD, TEM, SAED, HRTEM, EDS and diffuses reflectance spectroscopy, respectively. The effects of the experimental conditions on the final morphologies were also investigated. The method is promising to be extended to synthesize other V₂VI₃ compound semiconductor 1D nanostructure.     

Solvothermal synthesis of fusiform hexagonal prism SrCO3 microrods via ethylene glycol solution

Fusiform hexagonal prism SrCO₃ microrods were prepared by a simple solvothermal route at 120 °C, and characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FT-IR) spectroscopy. By controlling the content of ethylene glycol (EG), it was found that ethylene glycol (EG) played an important role in the formation of such SrCO₃ microrods. Finally, effects of other solvents on the products, including 1,2-propanediol and glycerin, were also investigated.     

Efficient rapid microwave-assisted route to synthesize InP micrometer hollow spheres

The efficiencies of two methods of synthesizing InP micro-scale hollow spheres are compared via the analogous solution-liquid-solid (ASLS) growth mechanism, either through a traditional solvothermal procedure, or via a microwave-assisted method. Scanning electronic microscopy (SEM) images show that most of the as-grown samples are micrometer hollow spheres, which indicates the efficiency of both methods. For traditional solvothermal route, long time (10 h) is necessary to obtain the desired samples, however, for the microwave-assisted route, 30 min is enough for hollow spherical products. An optimal choice of microwave irradiating time allows reducing the reaction time from hours to minutes. The proposed ASLS growth mechanism has also been discussed in detail.     

SiC-dopped MCM-41 materials with enhanced thermal and hydrothermal stabilities

SiC-dopped MCM-41 mesoporous materials were synthesized by the in situ hydrothermal synthesis, in which a small amount of SiC was added in the precursor solvent of molecular sieve before the hydrothermal treatment. The materials were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, N₂ physical adsorption and thermogravimetric analysis, respectively. The results show that the thermal and hydrothermal stabilities of MCM-41 materials can be improved obviously by incorporating a small amount of SiC. The structure collapse temperature of SiC-dopped MCM-41 materials is 100 °C higher than that of pure MCM-41 according to the differential scanning calorimetry analysis. Hydrothermal treatment experiments also show that the pure MCM-41 will losses it's ordered mesoporous structure in boiling water for 24 h while the SiC-dopped MCM-41 materials still keep partial porous structure.     

Grain growth and microstructural evolution of yttrium aluminum garnet nanocrystallites during calcination process

An yttrium aluminum garnet (YAG) precursor precipitate was synthesized by urea method using yttria (Y₂O₃) and aluminum nitrate (Al(NO₃)₃·9H₂O) as raw materials. The fresh wet precipitate was dried by supercritical carbon dioxide (CO₂) fluid and the resulting powder was calcined at temperatures from 600 to 1600 °C. Crystallization of YAG was detected at 800 °C, and completed at 900 °C. HRTEM images of the YAG product obtained above 900 °C revealed crystallographically specific oriented attachment along the [1 1 2] direction. Based on the observation of the particle morphology a possible growth mechanism of YAG nanoparticles was presented. The fast increase on the average crystallite size of YAG at temperatures from 900 to 1300 °C is attributed to the crystallographically specific oriented attachment growth process. As the growth process proceeds at higher temperatures, oriented attachment based growth becomes less important because of the increase on particle size, and the self-integration assisted by the Ostwald ripening becomes dominant.     

Synthesis and characterisation of chromium lutetium gallium garnet solid solution

The chromium lutetium gallium garnet system has been studied. Samples with 2xCaOxCr₂O₃(3 − 2x)Lu₂O₃5Ga₂O₃ (x = 0.025, 0.05, 0.075, 0.1, 0.2 and 0.3,) and xCr₂O₃(3 − x)Lu₂O₃5Ga₂O₃ (x = 0, 0.05, 0.075 and 0.3) compositions have been prepared in Ca,Cr:LGG and Cr:LGG systems, respectively. Samples were prepared by ceramic method, fired at 1250 °C/6 h and characterised by XRD, lattice parameters, UV-vis-NIR spectroscopy, CIE L^*a^*b^* measurements and SEM/EDX. Results indicate that Ca,Cr:LGG and Cr:LGG solid solutions are obtained. In Cr:LGG system only Cr(III) is stabilised in octahedral positions substituting for Lu(III) and Ga(III). Both Cr(III) and Cr(IV) are present in Ca,Cr:LGG. The calcium is a charge compensator to stabilise Cr(IV) and this is the predominant oxidation state up to x = 0.075 composition. From this composition, Cr(III) becomes more stabilised in garnet lattice. Cr(IV) occupies generally tetrahedral and dodecahedral sites substituting for Ga(III) and Lu(III), while Cr(III) is in octahedral site substituting for Ga(III).     

Synthesis reactions for Ti3SiC2 through pulse discharge sintering TiH2/Si/TiC powder mixture

Ternary compound Ti₃SiC₂ was rapidly synthesized by pulse discharge sintering the powder mixture of 1TiH₂/1Si/1.8TiC without preliminary dehydrogenation. Almost single-phase dense Ti₃SiC₂ was synthesized at 1400 °C for 20 min. The grain size of synthesized Ti₃SiC₂ strongly depends on sintering temperature. The synthesis mechanism of Ti₃SiC₂ was revealed to be completed via the reactions among the intermediate phases of Ti₅Si₃, TiSi₂ and the other reactants in the starting powder. The Ti-Si liquid reaction occurring above the Ti-Ti₅Si₃ eutectic temperature at 1330 °C was found to assist the synthesis reaction and densification of Ti₃SiC₂. The dehydrogenation of TiH₂ was accelerated by the synthesis reactions.     

Fabrication and characterization of mesoporous TiO2/polypyrrole-based nanocomposite for electrorheological fluid

Mesoporous TiO₂/polypyrrole (PPy)-based nanocomposite for electrorheological fluid was synthesized through one-pot method. By exploiting the combination conductivity of PPy and high dielectric constant of TiO₂, the ER fluid exhibited an enhanced effect. The shear stress was 3.3 times as high as that of mesoporous TiO₂. Powder X-ray diffraction (XRD), TEM and Fourier transform infrared (FT-IR) spectroscopy were employed to characterize the as-made samples. Using a modified rotational viscometer, the electrorheological effect was measured. Dielectric spectra were also given to explain the mechanism.     

Synthesis and characterization of FeVO4 nanoparticles

Iron vanadate (FeVO₄) nanoparticles were synthesized by simple co-precipitation method using various surfactants such as ethylene glycol, polyethylene glycol 200 and polyethylene glycol 400 as the structure directing agents. Systematic investigations on the structural, morphological and magnetic properties of the materials have been studied. The lattice constants of the triclinic structure of FeVO₄ were calculated from the X-ray diffraction (XRD) analyses. The average grain size was estimated to be around 35 nm, which increased with increasing the calcination temperature. The stretching and bending vibrations of Fe-O were evaluated from the FT-IR spectra. Using VSM magnetometer, magnetic property was investigated through magnetic susceptibility and magnetization measurements. FeVO₄ exhibits two magnetic ordering temperatures at T ≈ 20 K and 14 K, which is due to two different chemical environments of Fe ligands such as octahedral FeO₆ and trigonal bipyramidal FeO₅ in a six-column doubly bent chain, respectively.     

Synthesis of nanocrystalline Mn3O4 at 100 °C

A simple gel to crystal conversion route has been followed for the preparation of nanocrystalline tetragonal Mn₃O₄ powders at 80-100 °C under refluxing conditions. Freshly prepared manganese hydroxide gel is allowed to crystallize under refluxing and stirring conditions for 4-6 h. Formation of nano crystallites of Mn₃O₄ is confirmed by X-ray diffraction (XRD) study. Transmission electron microscope (TEM) investigations revealed that the average particle size is 50 nm for these powders.