Mullite Based Compositions Prepared by Sol-Gel Techniques

Ceramic powders and gels in the multi-alumina system with different compositions were prepared by sol-gel method. The preparation of gels was done in strong acidic conditions and also with the addition of ammonia. The powders were prepared by dropping the sols on a hot plate. The effect of water/alkoxide and ethanol/alkoxide ratios was studied together with the type of catalyst used (hydrochloric acid or ammonia). The thermal evolution of materials was followed by thermal analysis, X-ray diffraction, specific surface area measurements and electron microscopy. The morphology of powders was also studied. The characteristic exothermic peak attributed to a good mixing degree of the Al and Si species was observed at ∼980°C. The intensity of this exothermic peak was more pronounced in gels than in sol-gel derived powders. The crystalline phases formed are related with the preparation conditions and with the thermal treatment. The crystallisation of mullite and transient phases of alumina were observed in powder samples heat treated at 1000°C while in gel samples mullite was the only crystalline phase detected.     

Spinel-Mullite Composites with Optical Properties

The aim of this paper was to study the synthesis and characterization of spinel-containing mullite based materials, using sol-gel techniques. Several gels were prepared, with nominal compositions 3(Al_2−2xM_x Ti_xO₃)·2SiO₂ and 3(Al_2−xM_xO₃)·2SiO₂, with M=Ni⁺² or Co⁺² and 0.0≤x≤0.2, by hydrolysis and condensation of mixtures of aluminum, silicon and titanium alkoxides and nickel chloride. Dried gels were homogeneous and displayed a glass transition at around 750°C, which indicated that the system could be described as an amorphous silicoaluminate network. Crystallization pathway of gels were followed using differential thermal analysis and X-ray diffraction patterns of samples thermal treated at temperatures in the range between 800 and 1400°C. A two-phase aluminate spinel-mullite arrangement was detected at temperatures around 1200°C. The microstructure of the final product was interesting, because the minor secondary phase was homogeneously dispersed in the mullite matrix. Chemical and thermal resistance of diphasic materials were tested and the results indicate that these materials can be used as high temperature ceramic pigments.     

溶胶-凝胶法制备In-Cd纳米复合氧化物及其气敏性能研究

采用溶胶凝胶法制备了In20rCdln2O4和CdO-Cdln2O4纳米复合氧化物,利用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对复合材料的形貌和结构进行表征,并对其进行了乙醇、丙酮等多种气体的气敏性能测试.结果表明Cdln2O4材料复合h12O3和CdO后显著提高了对丙酮和乙醇气体的灵敏度和选择性.     

蒸汽相转化法原位诱导沸石化制备Y-ZSM-5双沸石复合物

针对Y型沸石在ZSM-5沸石干胶制备及晶化过程中易于溶解、坍塌的问题,采用葡萄糖在水热处理条件下对Y沸石进行包膜处理,提高了Y沸石在高温、高碱度环境中的稳定性,并采用蒸汽相转化法制备了同时含有Y和ZSM-5的双沸石复合物。对影响沸石复合物形成的因素如Y沸石表面碳包膜改性、凝胶碱度、晶化时间等进行了详细讨论。采用X射线衍射（XRD）、扫描电子显微镜（SEM）、傅立叶变换红外（FT-IR）、N₂吸附-脱附,能谱（EDS）以及NH₃-TPD等手段对制备的材料进行了表征。结果表明通过蒸汽相转化法能获得Y和ZSM-5两相共存的双沸石复合物,产物中的ZSM-5沸石相前驱体随蒸汽处理时间的延长逐渐从蠕虫状无定型向纳米多晶ZSM-5沸石转变,纳米多晶聚集体与Y型沸石晶粒之间紧密相连,相互包埋。在异丙苯催化裂化反应中,合成的沸石复合物的活性和稳定性介于Y和ZSM-5之间,优于对应的机械混合物。     

蒸汽相转化法原位诱导沸石化制备Y-ZSM-5双沸石复合物

针对Y型沸石在ZSM-5沸石干胶制备及晶化过程中易于溶解、坍塌的问题,采用葡萄糖在水热处理条件下对Y沸石进行包膜处理,提高了Y沸石在高温、高碱度环境中的稳定性,并采用蒸汽相转化法制备了同时含有Y和ZSM-5的双沸石复合物。对影响沸石复合物形成的因素如Y沸石表面碳包膜改性、凝胶碱度、晶化时间等进行了详细讨论。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、傅立叶变换红外(FT-IR)、N2吸附-脱附,能谱(EDS)以及NH3-TPD等手段对制备的材料进行了表征。结果表明通过蒸汽相转化法能获得Y和ZSM-5两相共存的双沸石复合物,产物中的ZSM-5沸石相前驱体随蒸汽处理时间的延长逐渐从蠕虫状无定型向纳米多晶ZSM-5沸石转变,纳米多晶聚集体与Y型沸石晶粒之间紧密相连,相互包埋。在异丙苯催化裂化反应中,合成的沸石复合物的活性和稳定性介于Y和ZSM-5之间,优于对应的机械混合物。     

Mullite Fibre Mats by a Sol-Gel Spinning Technique

Fine grained, microcrystalline mullite (Al_4+2x Si_2–2x O_10–x) fibre mats with a web-like structure were fabricated by a sol-gel spinning technique using a multi-orifice spinneret. Points of contact in gel fibre mats helped in the formation of a web-like fibrous body having reasonable strength and very little dust formation after calcination. Strong and resilient fibres with diameters in the range 3–12 m were obtained by a single-step sol-gel method from spinnable sols devoid of organics as the binder aid. Crystallization of -alumina and mullite at about 900°C and 1250°C, respectively was confirmed by differential thermal analysis (DTA) and X-ray diffraction (XRD). Thermogravimetry (TG) indicated the removal of most of the volatiles at about 500°C accompanied by a weight loss of about 48%. Scanning electron microscopy (SEM) shows the presence of small grains (80–150 nm in size) in the fibres calcined at 1250°C. Fourier transformed infrared spectroscopy (FTIR) indicated the sequence of transformations taking place during heat-treatment of gel fibres at different temperatures. The individual fibres in the mats calcined at 1250°C exhibited a tensile strength of 1300–1600 MPa.     

等离子体辅助球磨Si-C复合负极材料及其电化学性能研究

首次采用介质阻挡放电等离子体辅助高能两次球磨制得Si-C复合材料,其结构为微纳尺度硅颗粒均匀分散于微米级碳基体上. Si-C复合电极首周期循环放电容量为1259 mAh·g^-1,20和100周期循环的容量分别为474和396 mAh·g^-1. 该电极充放电曲线和交流阻抗测试的结果表明,复合材料中的硅和碳均参与锂离子嵌/脱反应,且其电荷传导阻抗明显低于纯Si.     

基于纳米碳填料可拉伸导电聚合物复合材料的制备

碳系材料具有导电性强、稳定性好、价格低廉等优点,被广泛用于制备可拉伸导电复合材料,并且在可拉伸、可穿戴电子设备等领域有巨大的应用潜力,引起了研究者的密切关注。本文介绍了碳系材料的种类,主要有炭黑、碳纳米管和石墨烯等;总结了3种纳米复合材料的主要制备工艺:原位聚合法、熔融共混法和溶液混合法,并介绍了传统印刷技术和新型打印技术。分析了复合材料的导电机理,介绍了渗流阈值理论;并重点探讨了其在可拉伸传感器和可拉伸能量储存设备领域的应用。针对基于纳米碳填料制备的可拉伸导电聚合物复合材料指出目前研究的不足之处:导电填料分散性差、导电网络不稳定和无法大规模生产等,并提出了多种解决方案。对基于纳米碳填料制备的可拉伸导电聚合物复合材料在微型化、可拉伸、可穿戴电子设备领域的应用前景作出了展望。     

Preparation of Mullite Fibers by the Sol-Gel Method

Mullite fibers were synthesized from an aqueous solution of aluminum isopropoxide, aluminum nitrate and tetraethylorthosilicate by the Sol-Gel method. The starting solution was prepared by adding aluminum isopropoxide and tetraethylorthosilicate simultaneously to an aluminum nitrate aqueous solution. The spinnability of the starting solution was investigated by varying the molar ratio of aluminum isopropoxide/aluminum nitrate in the solution. Gel fibers were obtained from solutions in a composition range of aluminum isopropoxide/aluminum nitrate of 3 to 5. Gels obtained from spinnable solutions appeared to have high homogeneity in the mixing of the Al/Si components, leading to a sharp 980°C exothermic peak in the DTA curve and a mullitization temperature of 1000°C. However, in the case of gels obtained from unspinnable solutions, a small 980°C exothermic peak was detected, and the mullitization temperature was as high as 1200°C, probably due to greater heterogeneity in the mixing of the Al/Si components.     

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.     

溶胶-凝胶工艺制备发光薄膜研究进展

本文综述了通过深胶－凝胶工艺制备发光薄膜的基本过程、薄膜的表征方法、发光薄膜的当前发展及应用情况。依据组成特点,对溶胶－凝胶法制备的发光薄膜乾地了分类阐述,并预言了今后该法制备发光薄膜的发展趋势。     

Piezoelectricity of ZnO Films Prepared by Sol-Gel Method

"ZnO piezoelectric thin films were prepared on crystal substrate Si(111) by sol-gel technology, then characterized by scanning electron microscopy, X-ray diffraction and atomic force microscopy (AFM). The ZnO films characterized by X-ray diffraction are highly oriented in (002) direction with the growing of the film thickness. The morphologies, roughness and grain size of ZnO film investigated by AFM show that roughness and grain size of ZnO piezoelectric films decrease with the increase of the film thickness. The roughness dimension is 2.188-0.914 nm. The piezoelectric coeocient d33 was investigated with a piezo-response force microscope (PFM). The results show that the piezoelectric coeocient increases with the increase of thickness and (002) orientation. When the force reference is close to surface roughness of the films, the piezoelectric coefficient measured is inaccurate and fluctuates in a large range, but when the force reference is big, the piezoelectric coeocient d33 changes little and ultimately keeps constant at a low frequency."     

Characterization of the Sol-Gel Process Using Raman Spectroscopy Organically Modified Silica Gels Prepared Via the Formic Acid-Alkoxide Route

For precursor mixtures containing tetraethoxysilane (TEOS) and phenyltriethoxysilane (PhTREOS), time of gelation can be reduced by up to two orders of magnitude depending on reaction conditions employed when reacting the silicon alkoxide mixture with formic acid instead of water. Results indicate that time of gelation depends on the amount of PhTREOS in the precursor mixture. Within the range of concentrations investigated, an exponential law describes best the dependence of reduced time of gelation on the molar fraction of PhTREOS. Therefore, we conclude that the phenyl ring acts as a steric hindrance to network formation. Raman spectroscopy is used to characterize the reaction between the alkoxide mixture and formic acid. During the acidolysis reaction, ethanol is formed as an intermediate. A preliminary reaction scheme is proposed to account for the time dependence of species involved. Furthermore, Raman spectroscopy is successfully employed to monitor the effects of post-gelation thermal treatment of the gel samples. The effects observed are interpreted with a model of a phenyl ring trapped in a siloxane cage.     

溶胶-凝胶法制备纳米WO_3气致变色材料

本文主要阐述了纳米WO3气致变色材料的溶胶-凝胶制备方法、气致变色机理及其应用的研究新进展,重点评述了溶胶-凝胶法中各种制备条件诸如掺杂、模板剂、溶剂、热处理温度等对这种材料的结构和性能的影响,最后展望了纳米WO3气致变色材料的研究和应用前景。我们认为,在未来的溶胶-凝胶法制备纳米WO3气致变色材料领域,如何进行最优化的掺杂设计和选择高效模板剂、如何降低气体检测温度以及气致变色机理等将是该项研究的重点。     

Vanadium-Based Organic-Inorganic Hybrid Materials Prepared by a Sol-Gel Method

Synthesis and characterization of hybrid organic-inorganic nanocomposites based on reaction of vanadium i-propoxide with an organically functionalized poly(ethylene glycol) having di-carbonyl groups is reported. The bulk gels were characterized by thermal analyses (DSC, TGA and TMA) and FT-IR spectroscopy. The results revealed that the gels consist of vanadium-oxygen-vanadium groupings which are cross-linked with the functionalized polymer through the di-carbonyl groups. Gels doped with lithium salt show significant electrical conductivity.     

Titania-Doped Silica Fibers Prepared by Electrospinning and Sol-Gel Process

Titania-doped silica fibers were prepared by electrospinning of the sol of silica containing titania. The electrospun fibers had ribbon type morphology. The fibers had significant quantities of hydroxyl groups of Si—OH and Ti—OH. The fibers did not have crystalline structure. Diameters of the fibers were reduced by solvent evaporation and calcination. The hydroxyl groups on the fibers disappeared by calcination. The hydroxyl groups, M—OH (MSi, Ti) were changed to M—O—M by intermolecular and intramolecular condensation reactions.     

Electrochemical Performance Studies of Tin Oxide Prepared by Sol-Gel

IntroductionSince the introduction of commercial lithium-ion batteries for the portable devices in the 1 990′s,the search for new anode materials with improvedenergy density and cycle- ability has never beenstopped[1— 5] .Graphite used as the early commercialanode material for lithium- ion batteries over otherkinds of materials in terms of its flat intercalationpotential and high cycle- ability[6,7] can′t keep pacewith the demand today because of its low capacity.In resentyears,the greateff…     

Thermal Transformations of Polymetallosiloxanes Prepared by the Sol-Gel Procedure

Thermal stability and crystal structure transformations of polyalkoxymetallosiloxanes (metallosilicas) prepared by the sol-gel procedure involving hydrolytic polycondensation of tetraethoxysilane with salts and oxides of Group I, II, and IV metals (Cu, Zn, Hg, Sn, and Pb) were studied.     

Preparation,Structure, and Properties of Starch/Rubber Composites Prepared by Co-Coagulating Rubber Latex and Starch Paste

Summary: Several rubber/starch composites in which the starch particles are in an amorphous state and are smaller than 1 μm, prepared by directly mixing and co-coagulating rubber latex and starch paste, exhibit higher hardness, stress at 100%, tensile strength, and tear strength relative to the corresponding rubber/starch composites prepared by direct blending.

TEM micrograph of starch/SBR composite.     

SiO2-Iron Oxide Composites Obtained by Sol-Gel Method

Composite SiO₂-iron oxide materials were prepared by three experimental procedures. In the first case (1), the iron oxides were precipitated during the sol-gel process. In the second case (2), the SiO₂ matrix was initially obtained, and the iron oxides were formed by thermal treatment after impregnation of a soluble Fe²⁺ salt in the previously processed matrix. In the third method (3), ferrite powders, prepared by wet chemical method, were embedded into a SiO₂ based sol-gel matrix. Two type of precursors (tetraethoxysilane (TEOS) or methyltriethoxysilane (MTEOS) were used as SiO₂ sources. Various properties versus both type of precursor and on the method of preparation were noticed. Materials with high porosity and nano-sized iron oxide content could be prepared using the mentioned above methods.