Preparation and thermochromic property of VO2/mica pigments

Thermochromic VO₂/mica pigments were fabricated by an aqueous sol-gel and spray-drying method. XRD and SEM were used to investigate the structure and morphology of pigments, and the results show that the VO₂ layer was composed of randomly oriented worm-like particles less than 300 nm in width. A thermochromic composite was prepared with the pigments and UV curing resin. The infrared transmittance change in the composite was measured from 24 °C to 100 °C by FTIR, showing very good thermochromic performance. The composite exhibits a transmittance of 50-55% in the visible range.     

Facile fabrication of SiO2/Al2O3 composite microspheres with a simple electrostatic attraction strategy

SiO₂/Al₂O₃ composite microspheres with SiO₂ core/Al₂O₃ shell structure and high surface area were prepared by depositing Al₂O₃ colloid particles on the surface of monodispersed microporous silica microspheres using a simple electrostatic attraction and heterogeneous nucleation strategy, and then calcined at 600 °C for 4 h. The prepared products were characterized with differential thermal analysis and thermogravimetric analysis (DTA/TG), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption and X-ray photoelectron spectroscopy (XPS). It was found that uniform alumina coating could be deposited on the surface of silica microspheres by adjusting the pH values of the reaction solution to an optimal pH value of about 6.0. The specific surface area and pore volume of the SiO₂/Al₂O₃ composite microspheres calcined at 600 °C were 653 m² g⁻¹ and 0.34 ml g⁻¹, respectively.     

Synthesis and magnetic properties of Ni–SiO2 nanocomposites

Nanocomposite Ni_(1 − x)/(SiO₂)_x soft magnetic materials were synthesized by a simple sol–gel combined hydrogen reduction method. The crystal structure of the particles was determined by X-ray diffraction (XRD). The shapes and sizes of the metal particles embedded in the SiO₂ matrix were determined by transmission electron microscopy (TEM), and magnetic properties were measured by the vibrating samples magnetometer (VSM). The obtained nanocomposite material is composed of nanoparticles coated with a thin SiO₂ layer, and with the content of the silicon increase, the thickness of the silica shells increase and the saturation magnetization decrease. The diameter of Ni particle in the sample is about 30–40 nm. The influence of the Ni content and preparation conditions on the microstructures and magnetic properties were discussed.     

Wear behavior of plasma sprayed composite coatings with in situ formed Al2O3

In the present study, the wear behavior of in situ formed Al₂O₃ reinforced hypereutectic Al–18Si matrix composite coatings have been investigated. These coatings were successfully fabricated with mechanically alloyed Al–12Si and SiO₂ powder deposited on aluminum substrates by atmospheric plasma spraying (APS). The produced samples were characterized by means of microscopic examinations, hardness measurements and wear tests. The obtained results pointed out that the amount of in situ formed Al₂O₃ particles increased with increasing spray distance and decreasing in-flight particle velocity and temperature, which was accompanied by an improvement in hardness and wear resistance.     

The large modification of phase transition characteristics of VO2 films on SiO2/Si substrates

The vanadium oxide (VO₂) films have been prepared on SiO₂/Si substrates by using a modified Ion Beam Enhanced Deposition (IBED) method. During the film deposition, high doses of Ar⁺ and H⁺ ions have been implanted into the deposited films from the implanted beam. The resistance change of the VO₂ films with temperature has been measured and the phase transition process has been observed by using the X-ray Diffraction technique. The phase transition of the IBED VO₂ films starts at a low temperature of 48 °C and ends at a high temperature of 78 °C. It is found that the phase transition characteristics can be adjusted by changing the annealing temperature or the time and the phase transition characteristics of the IBED VO₂ films depend on the quantity and location of argon atoms in the film matrix.     

Mixture of fuels approach for the solution combustion synthesis of Al2O3-ZrO2 nanocomposite

A modified solution combustion approach was used for the first time in the preparation of nanosize zirconia toughened alumina (ZTA) composite. ZTA-1 with an average particle size of ∼37 nm was prepared using corresponding metal nitrates and urea. ZTA-2 with an average particle size of <10 nm was prepared by using mixture of fuels such as ammonium acetate, urea and glycine. The products formed were characterised by powder X-ray diffractometry, Transmission electron microscopy and BET surface area analysis. By using mixture of fuels, the energetics of the combustion reaction and eventually the properties of the combustion product have been changed. A series of combustion reactions were carried out to optimise the fuel ratio combinations required to obtain <10 nm ZTA particles. The microstructure of ZTA consisted of crystallites of Al₂O₃ and ZrO₂ both of which were nanocrystalline as evident from TEM.     

Fine particle Sr2SiO4:Tb phosphor for the plasma display panel prepared by a combined approach

Sol-gel with microwave heating was employed to prepare fine particles Sr₂SiO₄:Tb phosphor. X-ray diffractometer was used to characterize the structural of the samples. The Scanning Electron Microscope image shows that the particle size is about 300 nm. The phosphor particles have several advantages in the morphology, such as excellent surface quality, spherical shape, and narrow size distribution with no aggregation. The VUV luminescence measurements indicate that the phosphor presents an intense excitation band at 173 nm. Because the wavelength of excitation source in PDP is mainly at 147 and 172 nm, it makes Sr₂SiO₄:Tb a potential candidate for green emitting phosphor for plasma display panel (PDP) application. Photoluminescence (PL) measurements indicate that the Sr₂SiO₄:Tb particles present excellent green emission at 542 and 547 nm excitated at 236 and 172 nm, respectively.     

Fabrication of porous TiO2 nanofiber and its photocatalytic activity

Porous TiO₂-based nanofiber was fabricated via a combined electrospinning and alkali-dissolution method. TiO₂/SiO₂ composite nanofiber was firstly prepared by electrospinning and sintering, and then silica was leached out with alkaline solution from the bulk of TiO₂/SiO₂ composite nanofiber to produce porous microstructure. The thermal decomposition and phase structure of the composite nanofiber precursor was investigated with TG/DSC and XRD, and optimal sintering temperature was obtained. SEM-EDX and FT-IR characterization show that most silica can be dissolved out from the composite nanofiber and thus porous nanofiber with excellent microstructure can be spontaneously formed. The effect of composite nanofiber composition on porous microstructure was studied, and it is found that the composite nanofiber with 20wt% silica can produce better porous microstructure compared to those with 10wt% and 30wt% silica. Meanwhile, porous TiO₂ nanofiber with 20wt% silica shows higher degradation efficiency to Congo Red.     

Effect of the SiO2/TiO2 ratio on the solid acidity of SiO2-TiO2/montmorillonite composites

SiO₂-TiO₂/montmorillonite composites with varying SiO₂/TiO₂ molar ratios were synthesized and the effect of the SiO₂/TiO₂ ratio on the solid acidity of the resulting composites was investigated. Four composites with SiO₂/TiO₂ molar ratios of 0, 0.1, 1 and 10 were synthesized by the reaction of colloidal SiO₂-TiO₂ particles prepared from alkoxides with sodium-montmorillonite at room temperature. The composites showed slight expansion and broadening of the XRD basal reflection, corresponding to the intercalation of fine colloidal SiO₂-TiO₂ particles into the montmorillonite sheets and incomplete intercalation to form disordered stacking of exfoliated montmorillonite and colloidal SiO₂-TiO₂ particles. The colloidal particles crystallized to anatase in the low SiO₂/TiO₂ composites but remained amorphous in the high SiO₂/TiO₂ composites. The specific surface areas (S_BET) of the composites measured by N₂ adsorption ranged from 250 to 370 m²/g, considerably greater than in montmorillonite (6 m²/g). The pore size increased with decreasing SiO₂/TiO₂ molar ratio of the composites. The NH₃-TPD spectra of the composites consisted of overlapping peaks, corresponded to temperatures of about 190 and 290 °C. The amounts of solid acid obtained from NH₃-TPD were 186-338 μmol/g in the composites; these values are higher than in the commercial catalyst K10 (85 μmol/g), which is synthesized by acid-treatment of montmorillonite. The present sample with SiO₂/TiO₂ = 0.1 showed the highest amount of acid, about four times higher than K10.     

Mechanical and dielectric properties of porous Si3N4–SiO2 composite ceramics

In order to prepare a structural/functional material with not only higher mechanical properties but also lower dielectric constant and dielectric loss, a novel process combining oxidation-bonding with sol–gel infiltration-sintering was developed to fabricate a porous Si₃N₄–SiO₂ composite ceramic. By choosing 1250 °C as the oxidation-bonding temperature, the crystallization of oxidation-derived silica was prevented. Sol–gel infiltration and sintering process resulted in an increase of density and the formation of well-distributed micro-pores with both uniform pore size and smooth pore wall, which made the porous Si₃N₄–SiO₂ composite ceramic show both good mechanical and dielectric properties. The ceramic with a porosity of 23.9% attained a flexural strength of 120 MPa, a Vickers hardness of 4.1 GPa, a fracture toughness of 1.4 MPa m^1/2, and a dielectric constant of 3.80 with a dielectric loss of 3.11 × 10⁻³ at a resonant frequency of 14 GHz.     

Synthesis and characterization of ZnO/SiO2 core/shell nanocomposites and hollow SiO2 nanostructures

In this paper, we prepared the ZnO nanoparticles by a simple hydrothermal method and fabricated the ZnO/SiO₂ core/shell nanostructures through a sol-gel chemistry process successfully. The hollow SiO₂ nanostructures were obtained by selective removal of the ZnO cores. The structure, morphology and composition of the products were determined by the techniques of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicated that the ZnO nanoparticles were sphere-like shape with the average size of 60 nm and belonged to hexagonal wurtzite crystal structure. With the coating of SiO₂, the vibration modes of Si-O-Si and Si-OH were found. Furthermore, the measurement results of optical properties showed that spectra of bare ZnO nanoparticles and ZnO/SiO₂ core/shell nanocomposites exhibited similar emission features, including a blue emission peak and an orange emission band.     

Hydrogen sorption properties of MgH2–NiCo2O4 composites activated mechanically under argon and hydrogen atmospheres

The effect of the mechanical activation medium on the hydrogen absorption–desorption properties of MgH₂ with NiCo₂O₄ additives is investigated. The composite 90 wt.% MgH₂–10 wt.% NiCo₂O₄ mechanically activated for 180 min under hydrogen reaches a higher absorption capacity as compared to the composite ground for the same time in an argon medium. At T = 573 K and P = 1 MPa the composite activated mechanically in a reactive medium shows a value of 5.67 wt.% while for the composite ground under argon the value is 4.36 wt.% only, both samples preserving a high absorption capacity at temperatures below 573 K. Addition of nickel cobaltite is found to have a favorable effect on the hydriding kinetics of magnesium. In order to elucidate this effect, a composite containing a large amount of NiCo₂O₄ (50 wt.%) is also investigated.     

Low-temperature sintering characteristics of nano-sized BaNd2Ti5O14 and Bi2O3–B2O3–ZnO–SiO2 glass powders prepared by gas-phase reactions

Nano-sized BaNd₂Ti₅O₁₄ (BNT) powders were prepared by spray pyrolysis from solutions containing ethylenediaminetetraacetic acid and citric acid. Treatment at temperatures ≥900 °C and subsequent milling resulted in nanoparticle powders with orthorhombic crystal structures. The mean particle size of the powder post-treated at 1000 °C was 160 nm. Nano-sized Bi₂O₃–B₂O₃–ZnO–SiO₂ glass powder with 33 nm average particle size was prepared by flame spray pyrolysis and used as a sintering agent for the BNT. BNT pellets sintered at 1100 °C without the glass had porous structures and fine grain sizes. Those similarly sintered with the glass had denser structures and larger grains.     

Effects of hydrolysis on dodecyl alcohol modified β-CaSiO3 particles and PDLLA/modified β-CaSiO3 composite films

In this research, β-CaSiO₃ particles were surface modified with dodecyl alcohol, and Poly-(DL-lactic acid) (PDLLA)/modified β-CaSiO₃ composite films were fabricated with a homogenous dispersion of β-CaSiO₃ particles in the PDLLA matrix. The aim of the study was to investigate the properties of the composite films before and after hydrolytic treatment. SEM images showed retained homogenous dispersion of β-CaSiO₃ particles after hydrolysis and tensile test also showed maintained mechanical property. Simulated body fluid (SBF) incubation experiment suggested that hydrolytic treatment did not affect the formation of hydroxyapatite on the surface of the composite films. The hydrophilicity of the composites was greatly recovered (from 69.82° to 50.28°) after hydrolysis. In addition, cells cultured on composite films after hydrolysis presented the highest cell proliferation rate and differentiation level. All of these results suggested that the surface modification of silicate particles with dodecyl alcohol along with reversible hydrolytic treatment was an effective and feasible approach to fabricate polymer/silicate composite materials with improved properties.     

Oxidative dehydrogenation of cyclohexane with Mg3(VO4)2 synthesized by the citrate process

Citric acid complexation under mild condition was proposed to prepare monophasic and well crystallized Mg₃(VO₄)₂ particle to be used as an active catalyst for the oxidative dehydrogenation of cyclohexane to cyclohexene. The catalyst prepared above was characterized by N₂-physisorption, X-ray diffraction, scanning electron microscopy, and thermal gravimetric analysis. The characterization results displayed that the Mg₃(VO₄)₂ particle was typically 100-160 nm and the specific surface area was 12.0-26.7 m²/g. Moreover, it showed that the purity and the structure of the catalyst were principally subjected to the calcination temperature and the amount of citric acid used in the sol-gel procedure. The Mg₃(VO₄)₂ catalyst calcined at 823 K for 6 h with a molar ratio of (Mg + V):citric acid = 1:1.2 exhibited the best catalytic performance with an excellent thermal stability.     

Fabrication and optical properties of NUV-emitting SiO2–SrB4O7:Eu glass–ceramic thin films

SiO₂–SrB₄O₇:Eu²⁺ glass–ceramic thin films were fabricated for possible application in near ultraviolet (NUV) emitting devices. Nano-sized SrB₄O₇:Eu²⁺ powders were prepared by a Pechini-type sol–gel method and a subsequent ball-milling treatment. The powders showed NUV emissions centered at 367 nm, upon irradiation with UV of shorter wavelengths, due to an allowed 4f⁶5d¹ → 4f⁷ electronic transition of Eu²⁺ ions. The glass–ceramic thin films were prepared by dip-coating of tetraethylorthosilicate (TEOS) solutions dispersed with the nano-sized SrB₄O₇:Eu²⁺ powders and a subsequent heat-treatment. It was found that the glass–ceramic thin films had relatively high thermal stability up to 800 °C in terms of the Eu²⁺ emissions. SiO₂ layers surrounding SrB₄O₇:Eu²⁺ appeared to be effective for the surface passivation of the phosphor particles.     

VO2(R) nanobelts resulting from the irreversible transformation of VO2(B) nanobelts

VO₂(R) nanobelts were prepared by the irreversible transformation of VO₂(B) nanobelts at the elevated temperature. The morphology and size of the VO₂(R) nanobelts were dependent on that of the precursor. VO₂(B) nanobelts were synthesized by a hydrothermal route, and the process of the VO₂(B) nanobelts' formation was also discussed. The product was characterized by a combination of techniques including XRD, TEM, FE-SEM, HRTEM, DTA and FT-IR. The as-obtained VO₂(R) nanobelts have a monoclinic structure with a length of 350-600 nm, a wideness of 100-150 nm and a thickness of 20-30 nm.     

Synthesis and characterization of hollow glass microspheres coated by SnO2 nanoparticles

The composite of hollow glass microspheres coated by SnO₂ nanoparticles has been successfully fabricated via sol-gel method. The phase structures, morphologies, particle size, shell thickness, chemical compositions of the composite have been characterized by XRD, FESEM, and EDX. The results show that SnO₂ coating on hollow glass microspheres can be achieved, and the coating layers are constituted by SnO₂ nanoparticles of mean size ca. 15 nm. The SnO₂ coating layers grow thicker with the increased concentration of SnCl₄. The effects of parameters (reaction temperature, concentration of NaOH and SnCl₄, and time) were investigated to yield SnO₂ coating on hollow glass microspheres, and the UV-vis absorption spectra of the composites were studied.     

Carbon nanotube growth at the tip of SiO2 nanocone

A well aligned growth of carbon nanotube (CNT) at the tip of SiO₂ nanocone using chemical vapor deposition (CVD) method is described. Fe particle at the tip of a nanocone has been observed to work as the catalyst for CNT growth. Initially, a number of self organized SiO₂ nanocones were grown via thermal annealing of MnCl₂ on Si substrate in the presence of H₂ gas. The average diameters of the tip and base of the nanocones were nearly 50 nm and 1 μm, respectively, with length up to 2.4 μm. At the tip of the nanocone a CNT was grown successfully. The CNT grows from the tip of the nanocone where Fe particles accumulate after the reduction of FeCl₃ at 950 °C. The accumulation point of Fe particles depends on the orientation of the nanocone tip inside the reaction tube during CVD process. Therefore, the alignment of nanotube at the tip of SiO₂ nanocone can be controlled by orientation of the nanocone in the reaction tube.     

Structural, dielectric, impedance and optical properties of CaBi2B2O7 glasses and glass-nanocrystal composites

Optically clear glasses were fabricated by quenching the melt of CaCO₃–Bi₂O₃–B₂O₃ (in equimolecular ratio). The amorphous and glassy characteristics of the as-quenched samples were confirmed via the X-ray powder diffraction (XRD) and differential scanning calorimetric (DSC) studies. These glasses were found to have high thermal stability parameter (S). The optical transmission studies carried out in the 200–2500 nm wavelength range confirmed both the as-quenched and heat-treated samples to be transparent between 400 nm and 2500 nm. The glass-plates that were heat-treated just above the glass transition temperature (723 K) for 6 h retained ≈60% transparency despite having nano-crystallites (≈50–100 nm) of CaBi₂B₂O₇ (CBBO) as confirmed by both the XRD and transmission electron microscopy (TEM) studies. The dielectric properties and impedance characteristics of the as-quenched and heat-treated (723 K/6 h) samples were studied as a function of frequency at different temperatures. Cole–Cole equation was employed to rationalize the impedance data.