Papers by Keyword: Non-Hydrolytic Sol-Gel

Abstract: Mullite whiskers were prepared via non-hydrolytic sol-gel process combined with molybdate molten salt using tetraethoxysilane and anhydrous aluminum chloride as precussor, anhydrous ether as oxygen donor, molybdate as molten salt. The effects of heat treatment temperature, molten salt amount, holding time on synthesis and morphology of mullite whiskers were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The results show that the mullite whiskers appeared at the lowest temperature of 800°C, and optimized mullite whiskers could be prepared at 900°C for 8 h with the mass ratio of xerogel and molybdate as 1:2, the diameter of the whiskers was in the range of 0.15-0.22 μm with the aspect ratio of more than 40.

Abstract: Composite sol with spinnability was prepared from an aqueous solution using polyvinyl butyral (PVB), Al (NO₃)₃·9H₂O (AN) and tetraethylorthosilicate (TEOS) via non-hydrolytic sol-gel method. The mullite fibers with good flexibility were also obtained. The viscosity of composite sol increased with the increasing PVB content, water-bathing temperature and aging time. FTIR spectroscopy of composite gel showed a new absorption peak due to the C=O group, which implied the presence of new reaction product. It could be explained by the reaction among PVB, AN and TEOS.

Abstract: Corundum structure alumina (α-Al₂O₃) powders were prepared via a non-hydrolytic sol-gel (NHSG) method using aluminum as raw material, ethanol as solvent, and iodine as catalyst. X-ray diffraction (XRD), differential thermal analysis (DTA), thermo gravimetric analysis (TG) were used to characterize the crystal phase of the products, while scanning electron microscopy (SEM) and transmission electron microscope (TEM) were employed to analyze the morphology. The results indicated that γ-Al₂O₃ was completely changed to α-Al₂O₃ at 1100 ^o C with a bit of aggregation. When 3 wt.% polyethylene glycol 600 (PEG 600) was introduced on the NHSG process, the dispersion was improved and the particle size decreased to100 nm.

Abstract: Zircon nano–powder has been synthesized via the non-hydrolytic sol–gel route, using industral zirconium tetrachloride (ZrCl₄) and tetraethoxysilane (TEOS) as precursors, lithium fluoride (LiF) as mineralizer, PEG1000 as dispersant. The effects of solvents on the synthesis and dispersion of zircon nano-powder were investigated by means of XRD and TEM. The results indicate that the aprotic solvent N, N-dimethyl formamide (DMF) is not conducive to the nucleophilic substitution reaction, which directly affect the zircon synthesis, and the particles are easy to agglomerate due to the large surface tension; the powder with size of 30nm and good dispersion can be obtained using dichloromethane (CH₂Cl₂) as solvent; different anhydrous alcohols as solvents influence zircon synthesis, the order of the synthesis ratio is listed as EtOH›propanol (PrOH)› isopropanol (PrⁱOH). Powder particles are larger than 50nm with wide distribution and serious agglomeration when taking PrOH and PrⁱOH as solvents. Nano-zircon with good dispersion and synthesis ratio up to 94.5% can be obtained via using ethanol as solvent.

Abstract: TiO₂ nanopowders were synthesized by non-hydrolytic sol−gel method. Effects of TiCl₄ concentration and acidity on the properties of TiO₂ nanopowders were investigated. The results showed that the average grain size of TiO₂ decreased with the increasing of TiCl₄ concentration. H⁺ can inhibit the growth of TiO₂ particles and Cl^- is conducive to the formation of rutile phase. When 2.06M HCl was used as the reaction solution, TiO₂ microspheres with diameter 2μm was obtained, and TiO₂ microspheres was composed of anatase and rutile phase.

Abstract: Magnesium aluminate (MgAl₂O₄) spinel nanoparticles were prepared by non-hydrolytic sol-gel method using anhydrous alcohols as oxygen donor. XRD and FTIR were used to characterise the effect of anhydrous alcohols on synthesis of MgAl₂O₄ spinel nanoparticles.The results showed that when the oxygen donor used in stoichiometric ratio for synthesizing MgAl₂O₄, anhydrous ethanol was the more effective oxygen donor than anhydrous isopropanol. But there was no remarkable effect on synthesis of MgAl₂O₄ spinel when the amount of anhydrous ethanol exceeded the stoichiometric ratio. The mean particle size MgAl₂O₄ spinel nanoparticles was in the range of 40 to 50 nm.

Abstract: Zirconium titanate and magnesium aluminate spinel precursors were prepared by non-hydrolytic sol-gel method using ethanol as oxygen donor. The gels and calcined powders were investigated by differential thermal analysis (DTA), thermogravimetry analysis (TG), X-ray diffraction (XRD). The results show that the ZrTiO₄ and MgAl₂O₄ crystallized at low temperature of 550 °C and 700 °C, respectively. It indicated that the highly homogeneous zirconium titanate and magnesium aluminate gels were aslo obtained by nonhydrolytic sol-gel process using ethanol as oxygen donor. The particle size distribution measured by laser scattering exhibit that ZrTiO₄ and MgAl₂O₄ powders were large soft agglomerates which could be broken through milling process.

Abstract: A novel flame retardant polymethylsilsesquioxane (PMSQ) was successfully obtained via combination of non-hydrolytic and hydrolytic sol-gel routes. Chemical structure of the resultant PMSQ was determined by nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectrometry and powder X-ray diffraction, respectively. All the measurements demonstrated that the product possessed regular structure with chain-to-chain width of 0.87nm and chain thickness of 0.40nm. Weight average molecular weight of PMSQ was measured to be 3.5×105 using gel permeation chromatography. Numerical simulations of the molecular structure suggested that PMSQ should exhibit cis-isotactic configuration and double helical conformation at undisturbed condition.