Glassy and crystalline systems from gels: Chemical basis and technical application

The sol-gel synthesis of glasses, glass ceramics and ceramics was successfull in many laboratories. Now it has the change of being scaled up for technological applications. Therefore, an overview is given about specific sol-gel products and sol-gel process advantages that are connected with the recent trends in the research and development in this field.     

锰锌铁氧体材料的制备研究新进展

介绍了目前国内外制备锰锌铁氧体材料的主要方法及研究进展,包括传统的干法工艺(陶瓷工艺)和湿法工艺等,同时指出了各种制备方法的优缺点.认为煅烧条件的控制及产品粒径的分布是影响材料磁性能的关键,湿法工艺中的溶胶-凝胶法和水热法是今后研究的主要方向.     

The factors during protein crystallization: A review

Many factors have effects on crystallization. The major influencing factors during protein crystallization are summarized in this paper. Recommendations are made about the basic process of crystallization and the analysis of the thermodynamic effects on crystallization, and the dynamics factors effecting crystallization during an equilibrium process are discussed. The advantages of ionic liquid in various chemical processes, especially in the field of biochemistry, are emphasized, and some tentative conclusions are made about future short-term trends. The text was submitted by the authors in English.     

Prospects of sol-gel processes

The ultrastructural control of materials through sol-gel processes offers significant promise for the achievement of reliable performance in glass, glass-ceramics, ceramics and composites. This will be attainable only if the fundamental chemistry of the sol-gel process is understood. Several examples based on this approach will be presented for optical glass, structural ceramics and electromagnetic materials. New concepts, such as ceramic or glass molecular composites and optically active gels, will be discussed. It will be shown how these new concepts are derived from an understanding of polymer chemistry and chemical reactivity. Advanced sol-gel basic research directions and their prospects will be discussed.     

Applications of the sol-gel process

The advantages and disadvantages of the sol-gel process are reviewed. Successful applications are dependent on sufficient scientific understanding of the various stages of the process. The many factors governing the development of structure and microstructure during gelation and subsequent heating are mentioned. Examples are described for applications in the areas of composites, porous solids and coatings. Opportunities for many new applications are presently available for exploitations.     

溶胶凝胶法制备WS2-SiO2可饱和吸收体的探究

WS2二维材料独特的光吸收体特性使其成为可饱和吸收体的优选材料。溶胶凝胶法具有操作方便、设备简单、成本低廉等优点。利用溶胶凝胶法在石英基片上制备SiO2材料为主体的WS2-SiO2薄膜是一种实现可饱和吸收体的新思路。本文通过改变实验过程中原料配比、热处理条件、旋涂速度等实验参数确定出溶胶凝胶法制备SiO2薄膜的最佳条件,在此基础上再加入WS2溶液制备出WS2-SiO2薄膜可饱和吸收体,通过共聚焦显微镜、透射电子显微镜、拉曼光谱、X射线衍射等方法对制备的样品进行了测试分析,结果表明采用本文提出的制作方法可以得到外观良好的WS2-SiO2薄膜可饱和吸收体、WS2在 SiO2薄膜中呈多层的多晶颗粒,晶面指数主要为(002)、(004)、(101)、(103)、(006)、(105)。     

Glass Dispersed Liquid Crystals

Abstract

Liquid crystals can be trapped into inorganic (silica) substrates by sol-gel processes. The sol-gel process consists of hydrolysis and polycondensation reactions of metal organic monomers, i.e. organoalkoxy silanes, which allows the formation of a silica gel-glass. These processes have been used since 1984 for trapping organic molecules into inorganic oxides; usually, single molecules are trapped into isolated gel-glass (nm size) pores. However, it is possible, by chemical means, to induce larger (0.1–10 pm) cavities in the network of the gel-glass allowing the formation of embedded micron size droplets of low molecular weight nematic LC molecules. Surface variations in these cavities (e.g., providing a molecular oriented surface using Si-CH,CH, groups on the pore cage) may allow a lamellar structure and alignment of the nematogenic LC compounds at the surface. It was suggested that order arises as a consequence of the chemical affinity between the apolar character of the pore surface and the lipophilic groups of the LC. Therefore, the main concern has been to ascertain whether the sample manufacturing keeps the LC structure, thus giving gel-glass dispersed liquid crystals (GDLCs) with electrooptical response.     

Solvent effects on the condensation stage of the sol-gel process

Effects produced by changing the solvent medium on the sol-gel polymerization process have been investigated by Raman spectroscopy, the molybdenum chemical reaction and electron microscopy methods. The mechanism of particle aggregation as well as the extent of condensation of the polymeric network have been shown to be dramatically affected by the presence of organic additives, such as formamide, dimethyl formamide, acetonitrile and dioxane. These observations have been explained in terms of hydrogen bonding and electrostatic interactions which modulate the nucleophilic substitution mechanism associated with the sol-gel condensation process.     

Chemical modification of alkoxide precursors

The chemical reactivity of metal alkoxides offers a broad range of possibilities for chemical modification of these molecular precursors. The whole hydrolysis-condensation process may then be completely different leading to new products. An analysis is presented concerning some of the most common chemical additives used in the sol-gel process. Their role is explained in terms of chemical reactivity. The most important parameters appear to be the reactivity of the new ligand towards hydrolysis, the charge distribution in the new molecular precursor and the coordination numbers of the metal atom.     

化学气相沉积法制备二维过渡金属硫族化合物研究进展

二维过渡金属硫族化合物(TMDs)是继石墨烯之后的新型二维材料,由于其自身的独特物理化学性质在半导体、光电材料、能源储存和催化制氢等方面备受瞩目。化学气相沉积(CVD)是目前适合实现大规模制备二维材料的工艺之一,制备过程中参数的高度可控性使其具有很大优势。本文综述了近期通过CVD制备TMDs的研究进展,探讨了在CVD制备工艺中各种参数对产物生长和最终形貌的影响,包括前驱体、温度、衬底、辅助剂、压力和载气流量等。列举了一些改进的CVD制备工艺,并对其特点进行了总结。最后讨论了目前CVD制备TMDs所面临的挑战并对其发展前景进行展望。     

人工合成翡翠研究进展

几个世纪以来,随着工艺技术以及珠宝行业的蓬勃发展,有着“玉石之王”之称的翡翠在装饰和收藏方面的需求量日益激增。但翡翠在自然界中的形成条件极其苛刻,导致其供应量难以满足人们的需求。因此,人工翡翠合成技术的发展对于解决天然翡翠供给不足的问题大有裨益,不仅能够推进翡翠高产化,还能加快其市场化进程。现有的人工合成翡翠的主流工艺大多采用高温高压法,该方法的关键是翡翠前体的合成以及玻璃质非晶硬玉到硬玉的转化。在这个过程中,找到一种条件相对温和的翡翠前体合成方法成为了人工合成翡翠的难点和突破点。本文论述了近年来国内外翡翠合成的最新研究热点和应用情况,着重介绍了固相烧结法、化学合成法和溶胶凝胶法三种翡翠前体常规制备技术。并从不同的制备技术路线出发,评估了各种方法的优缺点,同时对未来人工合成翡翠领域的发展进行了展望。     

Application of mercury porosimetry to the study of xerogels used as stone consolidants

Alkoxysilanes, low-viscosity monomers that polymerize into the porous network of stone by a sol-gel process, are widely used in the restoration of stone buildings. We have used the mercury porosimetry technique to characterize changes in microstructure of three granites following their consolidation with two popular commercial products (Wacker OH and Tegovakon V). The suitability of this technique is questioned because a surprising increase of stone porosity is observed. In order to investigate the feasibility of porosimetry, we analyze the behavior of xerogels prepared from the two commercial products, under mercury pressure. Gels are basically compacted and not intruded by mercury. Thus, the increase of stone porosity after consolidation can actually be associated with gel shrinkage. Mercury porosimetry, therefore, has been found unsuitable for characterizing the microstructure of consolidated rocks. However, it can be employed usefully to evaluate shrinkage of gels under mercury pressure, which permits the behavior of a consolidant during the process of drying in stone to be predicted. It is a key factor because many problems of consolidants are related to their drying process within the stone. Gels under study exhibit a high rigidity and an elastic behavior, as consequence of their microporous structure. Finally, the reduction in the porous volume of gels after the porosimetry test demonstrates that the shrinkage mechanism is based on pore collapse.     

Improved Photobleaching for (1,10-phenanthroline)tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato]europium(III) Particle Embedded in Sol-Gel Derived Glass Film

In this research, we investigated improved photobleaching characteristics of (1,10-phenanthroline)tris[4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato]europium(III) by forming nano-particles embedded into a sol-gel derived silica glass film by a conventional sol-gel process. The relative photoluminescence intensities after the UV irradiation for 90 min were 88, 76, and 67% for nano-particles in the sol-gel derived glass film, powders in the sol-gel derived glass film, and raw powders, respectively. This result indicates that the phtobleaching of this Eu-complex can improved by forming nano-partcile structures by a reprecipitation method and embedding in the sol-gel derived silica glass.     

Investigation of inorganic network formation in photopatternable hybrid sol-gel films by Si liquid NMR

Liquid ²⁹Si NMR spectroscopy was used to investigate the sol-gel process of methacryloxypropyltrimethoxysilane. This hybrid precursor was involved in the realization of optical elements in laminated crack-free thick films (up to 100 μm), through spatially controlled photopolymerization. Understanding the formation of the inorganic network was of first importance to insure the creation of crack-free photopatterned thick films in a laminated configuration. Material preparation required evaporation of the volatile solvents released during the sol-gel process and limitation of the condensation degree. Both conditions were achieved by a drying process at room temperature. The structure and the composition of the sols were investigated and compared to non-dried sols. Evolution of inorganic species distribution was also studied under increasing aging time or storage temperature. NMR peak fitting of T1 species gave fruitful information on the sol structure evolution during the sol-gel process. It pointed out the presence of a large variety of oligomers in the sol. The study also allowed the identification of more constraint cyclic species in dried sols stored at room temperature. Their amount significantly decreased when increasing the storage temperature and was attributed to ring opening of cyclic species. Consequently, the structure of the dried sol will depend both of the aging time and of the storage temperature. All these results have to be taken into account when the degree of condensation has to be limited to achieved photopatternable hybrid layers for specific optical applications.     

Comparative study of the sol-gel processes starting with different substituted Si-alkoxides

In the present work a comparative study of the hydrolysis-polycondensation processes of different Si-substituted alkoxides, leading to hybrid materials with covalent -Si-C- bonds, was carried out. The following alkoxides were used: tetraethoxysilane (TEOS), methyltriethoxysilane (MTEOS) and vinyltriethoxysilane (VTEOS). Using gas chromatography coupled with mass spectrometry (CG-MS), nuclear magnetic resonance (²⁹Si-NMR) and infrared spectrometry (IR), information about the sol-gel process in the mentioned systems were obtained. The differences in the reactivity of the studied alkoxides are connected with the steric effect of the organic substituents. The reactivity of the alkoxides in the early stages of the hydrolysis-polycondensation process increased in the order TEOS < VTEOS < MTEOS.     

Engineering ZnO nanowire surfaces via a chemical method

Quasi‐aligned porous ZnO nanowire arrays are promising architectures for potential applications in catalysts, gas sensors and solar cells. However, processes for conversion of ZnO nanowire arrays into porous ones have rarely been reported. Here, we report a facile chemical method for the synthesis of ZnO nanowire array with porous surface. The morphology and structure of the obtained products have been investigated with field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy. Time‐dependent experiments have also been carried out to better understand the formation process of porous structures on the nanowire surfaces. The obtained porous ZnO nanowire arrays may find potential applications in catalysts, solar cells and gas sensors due to the large surface area of the yielded products.     

熔盐法制备三元层状MAX相陶瓷的研究进展

MAX相是一种兼具金属和陶瓷性能的新型三元层状过渡金属碳氮化物。传统合成MAX相的方法都有一定的局限性,如反应温度较高、合成时间过长、合成样品较少,且大部分无法直接一步制备所需MAX相。近些年来,采用熔盐法合成MAX相的报道越来越多,并且工艺持续改进。本文从传统熔盐法合成MAX相出发,分析并阐述了新熔盐法合成MAX相的研究进展。传统熔盐法利用较低熔点的熔盐作为反应溶剂,提高了反应效率;熔盐屏蔽法以熔盐作为反应溶剂的同时还可防止氧化,使得反应可以在空气中进行;路易斯酸盐法则是将熔盐作为反应原料来合成MAX新相;熔盐电化学法以电脱氧的方式,将合成原料由纯金属改为金属氧化物,降低了生产成本。熔盐法所合成MAX相产物较传统方法所合成产物的产量及纯度更高,所需要的温度、能耗以及成本更低。因此,熔盐合成法是未来大批量合成MAX相以及MAX新相合成的一个重要方法。     

Chemistry of material preparation by the sol-gel process

A survey over the role of chemistry in sol-gel processing is given. The basic chemistry of the sol-gel process is complex due to the different reactivities of the network forming and the network modifying components and the wide variety of reaction parameters. Despite the important progress in the investigations of the mechanisms of hydrolysis and condensation, a direct relation of reaction parameters to material properties is still very difficult.     

Luminescence of CaS and MnS nanocrystallites co-activated sol-gel derived silica xerogel

CaS and MnS nanocrystallites co-activated sol-gel derived silica xerogel has been prepared by sol-gel processing. Their photoluminescence characteristics have been evaluated and compared with those of the undoped silica xerogel. Two emission bands have been observed from the doped sample, one at 440 nm while the other at 580 nm. CaS and MnS nanocrystallites embedded in sol-gel derived silica xerogel show sharp emission band. The novel luminescence phenomenon is attributed to the luminescent centers of CaS and MnS in the silica xerogel.     

退役三元锂离子电池正极材料高效清洁回收技术研究进展

锂离子电池因其能量密度高、循环性能好、自放电低等优势在各个领域得到了广泛的应用.近年来,退役三元锂离子电池数量急剧增长,从保护环境和节约资源的角度来看,开展退役锂离子电池回收再生工艺研究是必要的.本文综述了退役三元锂离子电池回收再生技术的研究现状,指出对衰减程度不同的锂电池正极材料需采取灵活的梯级回收工艺路线,并详细介...