Papers by Keyword: Sol-Gel Processing

Abstract: In this investigation, anatase nanocrystalline TiO₂ (nc-TiO₂) films are deposited by using sol-gel dip coating method on ITO substrates followed by annealing at 200, 300, 400 and 500 °C / 2 hr in air. To examine the structure and morphology of films, XRD, Raman spectroscopy, SEM and HRTEM techniques are used. The XRD studies showed the evolution of pure anatase TiO₂ phase with average crystallite size = 12-15 nm in resultant films. The morphological studies using SEM and HRTEM indicated ~ uniform size distribution of spherical agglomerates in films and nanocrystalline state of films (average particle size ~ 20 nm) respectively. The optical properties calculated from UV-Visible transmission spectra are found to be indirect band gap energy = 3.20 eV, absorbance coefficient = 9.2 x 10⁴ cm^-1, transmittance = 88.5 %, refractive index = 2.12 and porosity ratio = 36.6 % for the 400 °C annealed film. The better photovoltaic performance: J_SC = 2.34 mA/cm², V_OC = 0.562V, FF = 35.23 % & η = 0.46 % is obtained for eosin-Y dye sensitized solar cell made with 400 °C annealed film.

Abstract: 2ZnO.3B₂O₃.nH₂O (Zinc borate) having the industrially important composite and used as flame retardant, anti-smoke and semiconductor in the electronic circuits was examined different crystal structures. In this study, nanofibers of PVA /zinc nitrate/ boric acid composite were prepared by using sol-gel processing and electrospinning technique. By high temperature calcinations of the above precursor fibers, nanofibers of 2ZnO.3B₂O₃.5H₂O composite with diameters of 110 nm could be successfully obtained. The products have been characterized by X-ray powder diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), scanning electron microscopy (SEM) and FT-IR (Fourier transform-infrared spectroscopy). The effects of experimental conditions on the products were investigated.

Abstract: We reported the apatite-forming ability of CaO-SiO₂ spherical particles obtained through a sol-gel processing. In this study, we synthesized the CaO-SiO₂ containing silver (Ag) ions using silver standard solution to induce antibacterial property and evaluated the effects of Ag on their apatite forming ability in a simulated body fluid (SBF). The particles with 30CaO·70SiO₂ starting composition in Ag standard solution with range 0 to 500 ppm Ag content were synthesized through the sol-gel processing. The prepared 30CaO·70SiO₂ could be obtained as spherical particles with regardless of Ag contents. The prepared Ag-contained 30CaO·70SiO₂ particles formed apatite on their surfaces after soaking in SBF regardless of Ag contents. Consequently, Ag-contained 30CaO·70SiO₂ spherical particle could be obtained without decrease of its apatite forming ability.

Abstract: La₂(Ce_xZr_1-x)₂O₇ powders were synthesized by the Pechini routine with citric acid as a chelating agent. TG-DTA, XRD and SEM were used to characterize as-prepared powders. Experimental results show that the crystalline structures of La₂(Ce_xZr_1-x)₂O₇ transform to cubic fluorite phase with Ce substitution for Zr from x=0.1 to 1.0, no longer keeps the cubic pyrochlorite structure of La₂Zr₂O₇. La₂(Ce_xZr_1-x)₂O₇ powders present nanoporous low-density microstructurally, and successively lump-like, fluff-like and cotton-like morphologically with the increase of citric acid addition, this typical nanoporous microstructure results from a pore-crating mechanism initiated by self-propagation reactions between citric acids and nitrates. It is shown that the thermal conductivity k of powder compacts decreases sharply down from 1/10 to 1/32 of that of its single crystal bulk. as compact porosity increases from 60% to 95%. Therefore thermal barrier coatings (TBCs) of La₂(Ce_xZr_1-x)₂O₇ with such nanoporous structures by an appropriate processing may work with quite a high insulative performance and very promising for TBC applications of high-efficiency and large propulsion engines.

Abstract: By sol-gel processing and electrospinning technique, ultrathin fibers of PVP/ ZnTiO3:Pb2+ composites were synthesized. After calcined of the fibers at 600°C, the spinel ZnTiO3:Pb2+ nanofibers, with a diameter of 100-200nm, were successfully obtained. The scanning electron microscopy (SEM), fourier transform infrared (FT-IR), X-ray diffraction (XRD) and photoluminescence (PL) were employed in the study. The results displayed that the morphology and crystalline phase of the fibers were greatly affecteded by the calcination temperature. The PL spectra of the samples measured at different excitation wavelength reveal a novel luminescent phenomenon in blue and green region, which can be attributed to the Pb2+-related charge-transfer transitions in ZnTiO3 nanofibers.

Abstract: Ultrathin fibers of PVP/ZnTiO3 composite were prepared through sol-gel processing and electrospinning technique. After calcined of the above precursor fibers at 600°C, the spinel ZnTiO3 nanofibers, with a diameter of 50-150nm, were successfully obtained. The fibers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fourier transform infrared (FT-IR), respectively. The results displayeded that the morphology and crystalline phase of the fibers were largely influenced by the calcination temperature. The reported strategy will be useful for fabricating one-by-one continuous nanofibers, which are suitable for applications in catalysis, chemical sensors, nanoelectrodes, and nanodevices.

Abstract: Sol-Gel technology was used to develop carbon, silicon and oxygen based ceramics as well as their composites with Carbon fiber and nano siliconcarbide as reinforcements. Gels with different composition were prepared from TEOS, HMDSO and DEDMS. Dried gels were post-cured in air and pyrolyzed at 1000oC in nitrogen atmosphere. Each step of sol-gel process was characterized for density, thermal behaviour and functionality. Composites were prepared using different sols (derived from TEOS, HDMSO and DEDMS) as matrix precursors and carbon fabric as reinforcement. To some composites another phase of solid, micro/nano powder precursor of SiC was added to decrease number of impregnation cycles. Latter composites resulted in higher density. Green composites were post-cured and pyrolyzed. These composites were characterized for density and microstructure. It revealed that the resulting matrix was solid glasses and addition of SiC powder facilitated the rapid densification. Composites prepared with SiC nanparticles as well as Carbon fabric as reinforcement exhibit higher flexural strength than those made without nanoparticles. The fracture behaviour is also seen to be of mixed mode failure type.

Abstract: A modified complex sol-gel process was developed to synthesize LiMn2O4 and LiNixCo1-xO2 powders. Sols were prepared from 1.5 M of Mn2+ or 1 M of xNi2+ and (1-x)Co2+ acetates plus ascorbic acid aqueous solutions by alkalizing them with LiOH and NH4OH. Ascorbic acid was added to prevent precipitation in the precursor solutions. When the sols were concentrated to one-third of their initial volume under reduced pressure and then gelled by drying for 10 days, heat treatment to ≥700 °C was accompanied by foaming, violent self-ignition, and formation of carbonates in the Ni-containing species. Significant improvements to the process and resulting powders were gained by modifying the gelation step. When gelation and drying were carried out under reduced total pressure, subsequent heating produced self-ignition, but no foaming, for all heating rates. The resulting products were determined to be nearly phase pure and carbonate free by thermogravimetric, differential thermal, X-ray, and infrared spectroscopy methods.

Abstract: The present chapter deals with the difficult task of giving a brief survey of the synthetic routes employed to prepare materials with characteristic features on the nanometer scale. Definitions and general concepts regarding nanostructured and nanometer-sized materials are shortly tackled in the introductory part, which is followed by an overview of the most important approaches developed to synthesize such materials. No attempt is made to create a comprehensive and detailed synopsis of the experimental methods currently available. Rather, attention is focused on a selected number of general methodologies, the choice of which can be usually motivated by a mix of historical perspective, scientific significance and technological potential. So-called “top-down” approaches are discussed first, whereas the second part of the chapter is devoted to “bottom-up” ones. The former group includes mechanical processing, melt quenching, and de-vitrification methods. Sonochemistry, pulsed laser ablation, wet chemical synthesis, sol-gel processing, microwave processing, spray pyrolysis, flame synthesis, inert gas condensation, vapor deposition, and vapor-liquid-solid growth form instead the latter group.

Abstract: Ga doped SiO2 nanosized particles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. The size of the particles and the thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethyl orthosilicate(TEOS) within the micro-emulsion. The average size of synthesized Ga doped SiO2 nanoparticles were about in the size range of 10-15 nm and Ga particles 2-5 nm. The effects of synthesis parameters, such as the molar ratio of water to TEOS, and the molar ratio of water to surfactant, are discussed.