Hybrid Organic-Inorganic Materials by Nonhydrolytic Sol-Gel Processes: Organosilsesquioxane-Metal Oxide Hybrids

Organosilsesquioxane-metal oxide hybrid materials prepared by the Sol-Gel process are mainly heterogeneous. In this paper we report the preparation of methylsilsesquioxane-titanium oxide, and methylsilsesquioxane-aluminium oxide hybrid materials by a nonhydrolytic sol-gel process involving the etherolysis-condensation of a mixture of methyltrichlorosilane and metal chloride. The Si/M ration in the xerogels were very closed to the one of the starting solutions. ²⁹Si MAS NMR study has revealed that the methylsilsesquioxane-titanium oxide xerogel was heterogeneous at the atomic level. The spectrum of the hybrid containing aluminium, has shown beside a peak at –66 ppm corresponding to MeSi(OSi)₃ environment, another peak at –47 ppm which was ascribed to MeSi(OAl)₃ environment. The presence of only these two sites might be due to their stability.     

Zirconium titanate synthesis by diethanol amine based sol-gel route

ZrTiO₄ powder are synthesized by a modified sol-gel route via bimetallic diethanol amine complex of zirconium and titanium alkoxides. Samples are cured at 140°C and calcined between 500–800°C. Powders are characterized with XRD, TGA, DTA, SEM and TEM methods. The ZrTiO₄ powders are obtained at 650°C from the amorphous form. No identified peaks can be attibuted to other phases, namely, zirconia and titania are not observed.     

Electrochromism in Materials Prepared by the Sol-Gel Process

Electrochromism is defined as the persistent but reversible optical change (usually transmission) produced electrochemically. The preparation by the sol-gel process of thin films made of amorphous or crystalline nanoparticles of WO₃, V₂O₅, Nb₂O₅, TiO₂, CeO₂, Fe₂O₃ and mixed compounds such as WO₃−TiO₂, CeO₂−TiO₂, CeO₂−SnO₂, have opened remarkable new opportunities for obtaining electrochromic layers exhibiting large optical transmission variation in the UV, visible or infrared range and acceptable kinetics under H⁺ or Li⁺ insertion. In this paper we give an overview of what has been recently achieved in this field, with emphasis for cathodic electrochromic coatings of Nb₂O₅ and TiO₂ composition. Finally we stress the future developments in this fast growing field.     

Sol-Gel Poly-Component Nano-Sized Oxide Powders

Nano-sized, amorphous and monodispersed poly-component powders in the Al₂O₃–TiO₂–MgO and Al₂O₃–TiO₂–SiO₂ systems have been obtained by the sol-gel method. These powders have been characterized by XRD, IR spectroscopy, DTA/TGA and EDAX spectrometry. This last method confirmed the composition of the ternary powders, which are formed during the gelation process.The powders were tested as precursors for obtaining advanced ceramics, as tialite, Al₂TiO₅. The samples prepared with powders obtained by sol-gel method have shown a high reactivity, and the formation of tialite was improved.     

Sol-Gel Derived TiO2-SiO2 Fibres

TiO₂−SiO₂ fibres with 0, 5, 10 and 20 volume % SiO₂ have been prepared by drawing from a gel followed by sintering at different temperatures. Nearly one meter long fibres can be drawn easily in conditions of about 50% relative humidity. Addition of SiO₂ inhibits the crystallisation of TiO₂ and also the anatase → rutile transformation and improves the strength of the fibres. While the pure TiO₂ fibres are brittle, those with 5, 10 and 20 volume % SiO₂ are flexible and strong. Tensile strength values as high as 3 GPa have been achieved in the 10 volume % SiO₂−TiO₂ fibres. Fibres heated above 900°C are brittle. The shape of the cross section of the fibres is found to depend on their diameters.     

Two-Dimensional Sol-Gel Synthesis of Ultrathin Zirconia and Hetero-Layered Titania/Zirconia Films

Synthesis of ZrO₂ and hetero-layered TiO₂/ZrO₂ ultrathin films was investigated by two-dimensional sol-gel process assisted by n-octadecylacetoacetate (C₁₈AA). When a hexane solution of tetrabutoxyzirconium (TBZ) and C₁₈AA was spread on the water surface, Zr-based gel films stabilized with C₁₈AA were formed at the air/water interface. After deposition on substrates, the gel films were successfully transformed into ZrO₂ ultrathin films by heating at 773 K for 0.5 h, the thickness of which was controllable on the order of sub-nanometer level by the number of gel-layer deposition and the molar ratio of [TBZ]/[C₁₈AA]. Well-organized hetero-multilayers composed of ultrathin TiO₂ and ZrO₂ layers could be fabricated by the alternate deposition of C₁₈AA-stabilized Ti- and Zr-gel films.     

Microstructure Control of RF and Carbon Aerogels Prepared by Sol-Gel Process

A novel sol–gel process has been successfully developed for preparing strontium bismuth tantalate (SrBi₂Ta₂O₉, known as SBT) with ethylene alcohol as a solvent and acetic acid as a catalyst. The size of phase-pure SBT nanoparticles could be 4 nm in diameter by avoiding the formation of the fluorite phase at the low temperatures (550–600C). The behavior of the crystallization in SBT is investigated by XRD, TG-DTA, FT-IR and TEM. The nanoparticle size as a function of the annealing temperature is also investigated. By fitting the Arrhenius curve, we obtain the crystalline and vitreous growth activation energies, i.e, E_a1 = 0.709 eV and E_a2 = 0.093 eV. The two other fitting parameters, transition temperature T₀ = 814 K (541C) and transition width = 0.022, directly show the behavior of the phase transition from vitreous phase to crystalline phase.     

Sol-Gel Derived Functionally Graded TiO2/HAP Films on Ti-6Al-4V Implants

Functionally graded TiO₂/HAP coatings were prepared on Ti6Al4V implants by sol-gel process using calcium nitrate and phosphoric acid dissolved in ethylene glycol monomethyl ether, and titanium isopropoxide chelated by acethylacetone, isopropanol and water as starting materials. TiO₂/HAP coating sols with variable HAP concentrations from 0% to 100% at 10% intervals were orderly spin coated on the substrates and pyrolyzed at 500°C in air. Well-crystallized HAP coatings between coating and substrate confirmed by X-ray diffraction and field emission-scanning electron microscopy were obtained by final annealing at 500°C in argon. In this work, bioactivities of the coating were studied by examining the variation of ion concentration of Ca and P in simulated body fluid after soaking using an inductively coupled plasma-atomic emission spectrometer. Coating surfaces after soaking in simulated body fluid indicated significant morphological changes by field emission-scanning electron microscopy.     

Densification of Sol-Gel Thin Films by Ultraviolet and Vacuum Ultraviolet Irradiations

Structural changes in SiO₂ and TiO₂ gel films were investigated using ultraviolet (UV) and vacuum ultraviolet (VUV) irradiations. A significant compaction with dehydration of SiO₂ gel films was induced by irradiation of photons in the range of 9–18 eV. The refractive index and the shrinkage of the irradiated SiO₂ gel films were comparable to those obtained by sintering at 1000°C. Densification of TiO₂ gel films was also observed with irradiation of 5–14 eV photons. However, effects of the irradiation on TiO₂ gel were smaller that those on SiO₂ gel. The structural changes in the gel films are attributed to electronic excitations which are induced by irradiation with photons having higher energies than the bandgap of the oxides. The photo-induced effects are presumed to depend on the optical properties and structure of the gels.     

Calorimetric Investigations of Some Phases in the System Sodium Fluoride - Aluminium Fluoride

Beside the two well-known minerals cryolite, Na₃AlF₆, and chiolite, Na₅Al₃F₁₄, the binary system NaF-AlF₃ also contains a third compound, NaAlF₄, sodium tetrafluoroaluminate. Solid NaAlF₄ has been prepared from its vapour under controlled conditions. The stability of NaAlF₄ has been investigated by differential scanning calorimetry. It is shown that the disproportionation of the compound: 5NaAlF_4(s)=Na₅Al₃F_14(s)+2AlF_3(s) takes place at considerable rate between 700 and 900 K. The enthalpy of this reaction is calculated and found to be -66.9 kJ. Enthalpies of the two solid state transitions α-Na₃AlF₆ → β-Na₃AlF₆ and α-AlF₃ → β-AlF₃ have also been measured and new values are reported. The enthalpy of formation of chiolite, Na₅Al₃F₁₄, at 900 K has been recalculated from enthalpy increment data obtained by drop calorimetry. A value of ΔH₉₀₀ ^o = -7513.6±12.0 kJ mol^-1 has been obtained. This value is in disagreement with the recommended value given in JANAF Thermochemical Tables given at 900 K ΔH_f ^o = -7559.2 kJ mol^-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ba Titanate and Barium/Strontium Titanate Thin Films from Hydroxide Precursors: Preparation and Ferroelectric Behavior

Randomly oriented ferroelectric BaTiO₃ and (Ba_0.6Sr_0.4) TiO₃ thin films on platinum coated Si (100) were prepared by a sol-gel method. The precursor solutions were derived from barium hydroxide or a mixture of barium/strontium hydroxides dissolved in acetic acid and titanium butoxide. Polarization versus applied voltage hysteresis studies indicated a remanent polarization of 3 µC/cm² and a coercive field of 43.4 kV/cm for BaTiO₃ films annealed at 800°C for 1 h. Corresponding parameters for (Ba_0.6Sr_0.4)TiO₃ films annealed at 800°C were found to be 7.2 µC/cm² and 102.7 kV/cm, respectively. Microstructural study of the surface morphology of these films indicated grains of less than 0.1 µm in size. The leakage current for (Ba_0.6Sr_0.4)TiO₃ films was found to be two orders of magnitude lower than that for BaTiO₃ films.     

Photocatalytic Activity and Photo-Induced Wettability Conversion of TiO2 Thin Film Prepared by Sol-Gel Process on a Soda-Lime Glass

We have developed the transparent photoactive TiO₂ thin film coated on soda lime glass (SLG) by sol-gel process. Titanium dioxide thin films coated on SLG exhibit lower photocatalytic activity due to the thermal diffusion of Na ion from the SLG substrate. Thin SiO₂ film precoating is very effective to prevent the thermal diffusion of Na ion. We have evaluated the photocatalytic decomposition of gaseous acetaldehyde and the photo-induced surface wettability of TiO₂ films with and without SiO₂ precoating layer. As expected, the TiO₂ film on SiO₂/SLG is more photoactive to decompose acetaldehyde than that on SLG. However, as for wettability conversion, there was little difference in the conversion rate between TiO₂ film without SiO₂, and TiO₂ film with SiO₂. Different dependence of Na ion diffusion on two kinds of photo-induced reaction on TiO₂ is discussed based on the difference of the photo-induced reaction mechanism.     

纳米二氧化钛粉末的溶胶-凝胶法合成及晶相转化

Nanosized TiO₂ powder with anatase and rutile structures was synthesized by a sol-gel method using TiCl₄ ethanol solution as a precursor.The grain size of TiO₂ powder was about 63nm after the precursor was calcined at 600℃ for 2 hours .The experimental techniques of XRD,TEM and Particle Distribution were used to characterize the synthesized specimens. Various special effects were investigated for their contribution to crystal structure and the size of TiO₂ powder .The formation of anatase as well as the rutile phase of TiO₂ was indicted from the XRD when the reaction temperature was above 30℃ and when the sol was irradiated by infrared rays .However, an anatase TiO₂ powder formed after the heat treatment of the dried gel in a temperature range from 300℃ to 500℃.Under the vacuum drying and with the calcined time below 3hours ,the anatase phase was gained .As well as with the increase of gelatinizing time, the anatase TiO₂ powder was obtained.     

后处理温度对Sol-Gel法制备的镍基负载型催化剂性能的影响

以正硅酸乙酯、钛酸丁酯、硝酸镍为原料,用Sol-Gel法制备得到超细镍基负载型催化剂前体NiO/TiO₂-SiO₂。采用BET、UV-Vis、FT-IR 、XRD、TPR等方法,研究了焙烧温度对催化剂前体物化性能及其催化剂活性（苯加氢生成环已烷反应）的影响。结果表明：用Sol-Gel 法制备得到的NiO/TiO₂-SiO₂的织构具有较高的热稳定性。随着焙烧温度的升高,比表面积、孔体积略有减少,表观堆密度增大。焙烧至92     

Synthesis of Silica Aerogels: Influence of the Supercritical CO2 on the Sol-Gel Process

The synthesis of silica aerogels was modified by addition of supercritical CO₂ during the sol-gel process. It was shown, that CO₂ acts as a catalyst and accelerates the gelation significantly. This effect was studied under a multitude of experimental conditions. The influence of the precursor concentration, temperature and the nature of the catalysts and solvent on the gel formation in presence of CO₂ was studied. Several gels obtained by this method were dried and transparent silica aerogels were produced.     

Preparation of Alumina Supported Palladium Catalysts by Sol-Gel Method

The chemical reactivity of the aluminium-sec-butoxide (ASB) and the palladium acetylacetonate Pd(acac)₂, used as precursors for the preparation of the alumina supported palladium catalysts by sol-gel method was investigated by the spectroscopic study of the precursor mixture during ageing, using FTIR, UV-VIS and ²⁷Al NMR. The obtaind results showed that acetylacetonate ligands were linked to aluminum when the mixture was aged at 40°C. This was proved by the bands observed at 1530 and 1600 cm^–1 in the FTIR spectra, the band obtained at 289 nm in the UV-VIS spectra and the ²⁷Al NMR sharp peak at 3 ppm. Furthermore, in order to avoid the Pd(acac)₂ reduction to metallic palladium by the SB occurring when the mixture is aged for 3 h, an optimum ageing time should be selected. The precursors modification and the preservation of the palladium oxidation state during ageing could be the required conditions to create a bond between palladium and aluminium during the gelation step. This should be the reason of the thermal stability improvement of the alumina supported palladium catalyst prepared by the sol-gel method.     

Rheological Measurements in Titania Gels Synthesized from Reverse Micelles

Abstract

TiO₂ sol and gel systems have been synthesized by hydrolysis of titanium butoxide in microemulsions W/O. Different systems compositions were prepared at constant W _o = [H₂O]/[AOT] and changing R = [H₂O]/[Ti(BuO)₄]. Experimental measurements show a progressive increase of the viscosity with time, characteristic of a sol-gel transition. The rheology of the transition was studied by following the behavior of viscoelastic parameters (G′, G″ and η?) as a function of time at different frequencies.

The possibility to apply standard percolation theory was discussed. The application of two alternative growth models-either “fractal growth model” or “nearly linear growth model”-has been analysed.     

ZnSnO3透明导电薄膜：溶胶-凝胶法制备及性能

采用溶胶-凝胶(Sol-Gel)过程和旋涂法制备了Zn-Sn-O系统薄膜。通过对干凝胶的热重-差示扫描同步热分析(TG-DSC),研究了干凝胶在烧结过程中的反应历程。采用X射线衍射(XRD)、X射线光电子能谱(XPS)、场发射扫描电镜(FE-SEM)以及紫外-可见透过率(UV-Vis)等表征了烧结后薄膜的晶相、晶格缺陷、微观形貌以及紫外-可见光透过率。本文还研究了烧结温度、N2气氛热处理以及组成变化对薄膜电阻率的影响,结果表明:偏锡酸锌ZnSnO3晶体薄膜具有较低的电阻率;当nZn/(nZn+nSn)=50.3at%时,薄膜的电阻率达极小值,约为8.0×102Ω.cm。偏锡酸锌ZnSnO3晶体的导电机理研究表明:晶格中间隙阳离子含量的增加有利于薄膜电阻率的降低,而氧空位的形成则使其电阻率升高。薄膜的紫外-可见光透过率(UV-Vis)表明:偏锡酸锌ZnSnO3晶体薄膜在400~900 nm的可见光波段透过率可达80%以上。     

Fabrication of Single-Phase BaTi4O9 Nanocrystalline Powder by Sol-Gel Process

BaTi₄O₉ nanocrystalline powder was prepared by sol-gel method using Ti(OC₄H₉)₄ and Ba(CH₃COO)₂ as raw materials. The optimum process was obtained by analyzing the synthesis condition of the single-phase BaTi₄O₉ nanocrystalline powder as follows: the content of acetyl-Titanium = 1 mol/L. pH = 4.2, molar ratio of water/alkoxide = 15, and the powder is kept at 1200°C for 2 h. The XRD and TEM analysis showed that the single-phase BaTi₄O₉ nanocrystalline powder of 30 nm in size was well prepared.     

Photo-Induced Hydrophilicity of TiO<Subscript>2</Subscript> Films Deposited on Stainless Steel via Sol-Gel Technique

The photo-induced hydrophilicity of TiO₂ films deposited on stainless steel substrates and silicon wafers using two different sol-gel routes has been investigated. The results indicate that crystalline titanium oxide films with excellent hydrophilic properties can be obtained on silicon wafer with both routes. XPS and XRD data reveal that films deposited on stainless steel exhibit crystallization features similar to those of films deposited on silicon wafers, and only differ by their oxidation degree owing to a TiO₂ reduction process associated to a diffusion of iron ions during deposition of the acidic sol and/or high temperature post-treatment. Consequently, hydrophilic properties of films deposited on stainless steel are inhibited. The deposition of a SiO_x barrier layer at the film/substrate interface allows preventing such a detrimental substrate influence. A low temperature deposition route of the TiO₂ film associated to the presence of a barrier layer yields best results in preventing iron contamination of the films.