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.     

Investigation of the structure evolution process in sol-gel derived CaO-B2O3-SiO2 glass ceramics

A sol-gel method was used to prepare CaO-B₂O₃-SiO₂ (CBS) glass powder for making low-temperature cofired ceramics. This paper was focused on the mechanism of hydrolysis and polymerization and also on the structural evolution of xerogel at various temperatures. The xerogel was transformed into glass ceramics containing CaSiO₃ and CaB₂O₄ crystalline phases through nucleation and crystallization processes. The results indicated that the xerogel exhibits [BO₄] or [SiO₄] based three-dimensional network structure whose interstices Ca ions fill in, which becomes more orderly and stable after heat treatments. The CBS glass ceramics through controlled crystallization have a potential as electronic packaging materials.     

Ca3-xCexCo4O9+δ陶瓷的制备与电输运性能

采用柠檬酸溶胶-凝胶法制备了掺Ce的钴酸钙(Ca3Co4O9+δ)陶瓷,通过TG-DSC、XRD和SEM对样品进行表征,研究了Ce掺杂对电导率、Seebeck系数和功率因子的影响。结果表明:陶瓷样品的断面形貌呈片层状。随着Ce掺杂量的增加,样品的导电机制发生变化,测试温度范围内样品的电导率和功率因子下降,Seebeck系数先增加后下降。     

溶胶-凝胶法制备Ca0.4Sr0.6Bi4Ti4O15细晶陶瓷

采用凝胶预碳化处理工艺制备了颗粒粒径较小,无硬团聚的Ca0.4Sr0.6Bi4Ti4O15纳米粉体,以Ca0.4Sr0.6Bi4Ti4O15非晶团簇粉体为陶瓷素坯的原料,同组分高浓度的Ca0.4Sr0.6Bi4Ti4O15溶胶为粘结剂,制备了Ca0.4Sr0.6Bi4Ti4O15细晶陶瓷,研究了Ca0.4Sr0.6Bi4Ti4O15粉体的相结构和微观形貌以及陶瓷的显微结构和铁电性能.实验结果表明:700 ℃焙烧粉体呈现为非晶团簇,800 ℃焙烧粉体形成了纯层状钙钛矿结构,粒径在100～150 nm之间,无硬团聚;950 ℃烧结的Ca0.4Sr0.6Bi4Ti4O15细晶陶瓷结构致密,晶粒尺寸在0.2～0.5 μm之间,其铁电性能优良,剩余极化Pr=12.5 μC/cm2,矫顽场强Ec=50 kV/cm.     

Chemical processing of rare earth chalcogenides

Chalcogenides are compounds containing sulfur, selenium and tellurium and are well known for their semiconducting and optical properties. Their characteristic absorption at low frequencies render these materials excellent for long wavelength transmission. In the past few years, the need for far infrared transmitting materials to be used in target acquisition equipment formed the basis for identifying several new crystalline sulfide materials which transmit into the extended far infrared (IR) spectral region. Rare earth sulfides exhibiting excellent transmission into the far infrared (8-14 μm) emerged as a new group of infrared window materials. This paper reviews the status of binary and ternary rare earth sulfide compounds for optical window application. Conventional and non-conventional techniques used for processing these materials will be discussed in complete detail. The use of metallorganic precursors and modification of the precursor chemistry to tailor the composition of the final ceramic will be described. The potential of these emergent low temperature chemical processing techniques such as sol-gel, precipitation and co-precipitation for synthesis of non-oxide ceramics will also be addressed, particularly in light of their successful application in processing of novel electronic oxide ceramics, glasses and composites.     

Sr掺杂对Ca3Co4O9基材料热电性能的影响

采用溶胶-凝胶法,结合常压烧结工艺制备了Ca3-xSrxCo4O9(x=0～0.5)热电陶瓷材料,并对材料的热电性能进行了测试。结果表明,Sr掺杂对Ca3Co4O9基材料的热电性能有较大影响。随着掺杂量的增加,电导率逐渐增大,Seebeck系数略有减小。Sr掺杂能显著降低热导率,而且随着掺杂量的增加,热导率的下降幅度逐渐增大。Sr掺杂显著改善Ca3Co4O9材料的热电性能,当掺杂量为0.5时获得最佳热电性能,573 K时Z值达1.07×10-4 K-1。     

Sol-gel: Science, processes and products

The connection between science, processes and products in the sol-gel field is shown. This determines what advantages sol-gel processes have and can have in the future. But it also makes clear some disadvantages which have to be circumvented for industrial use. Therefore, future products based on the sol-gel process must have product or process advantages.     

Photoinduced degradation of fluorescence and formation of copper nanoparticles in sol-gel silica doped with flavins

Copper nanoparticles were formed by photoirradiation of doped sol-gel silica, which was prepared by mixing Cu²⁺ ions, ethylenediaminetetraacetic acid (EDTA), and riboflavin into sol-gel solutions of tetramethoxysilane. The doped silica exhibited broad absorption bands at 442 nm due to riboflavin and 740 nm due to Cu²⁺-EDTA complexes. After photoirradiation, the sol-gel silica showed a reddish brown color and the absorption peak around 580 nm due to the plasmon band of copper nanoparticles. Copper nanoparticles were also formed from other sol-gel silica doped with lumichrome or lumiflavin. The photostability of the flavins dyes obtained from the fluorescence intensities was in the order of lumichrome > lumiflavin > riboflavin in the sol-gel silica without Cu²⁺ ions. On the other hand, the fluorescence intensities were considerably reduced by photoirradiation of the sol-gel silica doped with Cu²⁺ ions, irrespective of the flavin dyes doped. Considering the absorption and fluorescence spectral changes during the photoirradiation, we concluded that copper nanoparticles are produced by the photoinduced electron transfer from the flavin dyes in the sol-gel silica.     

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.     

自增韧和增强的镁铝尖晶石透明陶瓷

用化学配比n为1.0,1.3,1.5和1.8的MgO·nAl2O3粉体分别制备出了镁铝尖晶石透明陶瓷MA1.0,MA1.3,MA1.5和MA1.8.这些陶瓷是通过真空烧结和热等静压两步烧结方法制得的.由于第二相物质氧化铝晶粒的析出,陶瓷相对密度随着化学配比的增高而降低.然而,与化学配比陶瓷相比,这些非化学配比陶瓷表现出了较高的机械性能,陶瓷断面的扫描电镜照片显示非化学配比陶瓷多为穿晶断裂模式,这种断裂模式对陶瓷的强韧化作出了主要贡献.     

过滤用镁渣多孔陶瓷的制备与渗透性能

本文以镁渣,粉煤灰等为原料制备了镁渣基多孔陶瓷,评价了多孔陶瓷的孔隙参数,烧结性能,力学性能,渗透性能等,观察了多孔陶瓷的微观结构,研究了烧结温度、成型压力、原料配比和添加剂等因素等对多孔陶瓷理化性能的影响.结果表明,烧结温度1150℃,保温4 h可制得固废掺比为90;的镁渣基多孔陶瓷,成型压力对多孔陶瓷的气孔率、吸水率和体积密度具有较大影响.镁渣和粉煤灰的配比为7:2时,多孔陶瓷产品的综合性能较好.添加电石渣和碳粉为造孔剂能够匀化气孔分布,细化孔径,提高多孔陶瓷的气孔率和气体过滤性能.     

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.     

具有碳化硅纳米线编织结构的氧化铝泡沫陶瓷的制备及性能研究

本文利用简单、高效的浆料直接发泡法制备气孔率高达96%的Al₂O₃/Si泡沫陶瓷,并选用简便、易行的焦炭埋烧工艺在Al₂O₃/Si泡沫陶瓷坯体中生长出大量SiC纳米线。通过控制烧结温度来观察分析SiC纳米线的生长形貌变化。采用扫描电子显微镜(SEM)、X射线衍射仪、BET比表面积测试仪、电子万能试验机等对泡沫陶瓷的微观结构、物相组成、比表面积、气孔率、抗压强度、热导率进行分析与表征。结果表明,1 450 ℃烧结时得到的SiC纳米线最多,纳米线在泡沫陶瓷孔壁交织缠绕。同时观察到SiC纳米线的存在改变了氧化铝泡沫陶瓷固有的脆性断裂模式,SiC纳米线可有效促进泡沫陶瓷在压缩过程中的裂纹偏转。本实验制备了一种新型的纳米线缠绕在孔壁上的三维网络结构的泡沫陶瓷,为在泡沫陶瓷内部原位生长SiC纳米线提供了新的方法,更好地拓展了泡沫陶瓷在环境过滤、催化剂载体等领域中的应用。     

Influence of sodium dodecylbenzene sulfonate on the structure and properties of carbon aerogels

This letter describes the effects that the surfactant, sodium dodecylbenzene sulfonate (SDBS), has on the structure and electrical properties of monolithic carbon aerogels (CA). Using organic sol-gel chemistry, a series of novel CA materials prepared with different concentrations of SDBS were characterized to evaluate the influence the surfactant had on the network structure of the resultant material. Addition of the SDBS surfactant to the sol-gel reaction mixture was shown to generate CA structures that had different pore sizes, higher densities and improved electrical conductivity than those prepared without the surfactant. These results are discussed in comparison with relevant sol-gel literature and theory.     

透明陶瓷的研究进展

透明陶瓷性能优异,应用广泛,是一类备受关注的新型材料.目前已经成功开发的透明陶瓷有氧化铝透明陶瓷、氧化钇透明陶瓷、氮化铝透明陶瓷以及PLZT电光透明陶瓷和激光透明陶瓷等.本文介绍了几种透明陶瓷的研究进展以及性能和应用,并且对透明陶瓷的研究趋势提出展望.     

(Sr0.7Bi0.2)TiO3取代BNT基无铅陶瓷的相变及储能特性

采用弛豫铁电体(Sr0.7Bi0.2)TiO3与铁电体(Bi0.5Na0.5)TiO3构建了的新型二元系BNT基无铅陶瓷材料:(1-x)(Bi0.5Na0.5)TiO3-x(Sr0.7Bi0.2)TiO3(记为BNT-xSBT,x=10mol;、20mol;、30mol;和40mol;).通过传统固相法进行制备,研究了(Sr0.7 Bi0.2)TiO3取代对其结构、相变、铁电性能和储能特性的影响.结果表明,室温所测BNT-xSBT陶瓷为准立方结构;介温和铁电性则证实其为极性三方和非极性四方共存相结构.A位复合占位的BNT-xSBT陶瓷是典型的弛豫铁电体,其Tm随x的增大而减小.低温(Td)处的介电反常源于结构(三方和四方)起伏所引起的缓慢转变过程.(Sr0.7 Bi0.2)TiO3取代量增大时,其Td降低,四方相增多,并伴随非极性微区增长;并导致BNT-xSBT陶瓷的铁电性减弱和电滞回线变形.x=30mol;时,BNT-xSBT陶瓷具有大的Pmax=26.8μC/cm2、小的Pr=1.4μC/cm2,和较好的储能特性:W=0.74 J/cm3,η=68.5;(@70 kV/cm).     

La3+掺杂Ca1-xLaxCu3Ti4O12陶瓷的制备及性能研究

采用固相反应法制备了La3+掺杂的CaCu3Ti4O12(CCTO)陶瓷,研究了La3+掺杂量对Ca1-xLaxCu3Ti4O12(x=0;,1;,3;,5;,7;)陶瓷物相结构、微观形貌和介电性能影响,对La3+掺杂影响CCTO陶瓷介电性能的机理进行了分析.结果表明:x为3;时,开始出现杂相;x高于5;时,陶瓷晶粒开始细化;La3+掺杂可以显著提高CaCu3Ti4O12陶瓷的介电常数,同时介电损耗在高频段也相应降低,从而有助于CCTO陶瓷的综合介电性能的提升.     

Effect of method of preparation and drying time on photophysical properties of coumarin 1 laser dye embedded in HCl catalysed sol-gel glasses

Coumarin 1 (C1) dye is impregnated in transparent sol-gel glass samples prepared by sol-gel process using three methods - (I) using HCl as catalyst and glycerol as a drying control chemical additive (DCCA), (II) using HCl as catalyst at 60 °C subsequent drying at room temperature, and (III) using HCl as catalyst at 60 °C and heated at 600 °C for 3 h. The sol-gel matrices prepared by Methods I and II are given dip treatment with methanol/distilled water (50/50 volume) for 16 h before dipping into dye solution. The effect of method and drying time of matrix on spectroscopic properties of C1 dye doped glass samples has been studied. The optical density (OD) at absorption maximum wavelength and fluorescence intensity (FI) at fluorescence maximum wavelength of all C1 dye doped samples prepared by Methods I and II decrease, where as there is no change in photophysical properties (OD/FI) is observed in samples prepared by Method III with the time of drying of the sol-gel samples. These absorption/fluorescence properties of C1 dye in sol-gel glass matrices are compared with its respective properties in methanolic solution in acidic environment.     

Structural study of sol-gel silicate glasses by IR and Raman spectroscopies

A study of the structure and bonding configuration of sol-gel silicate glasses by Raman and infrared spectroscopies is presented. Moreover, a review of the Raman lines and infrared bands assignment, the identification of the non-bridging silicon-oxygen groups and the ring structures are also demonstrated. The evolution of the changes of the bonding configuration in the composition and the stabilization temperature of the bioactive glasses is discussed in terms of the structural and textural characteristics of the glasses. Raman and infrared analyses contribute to the improvement in understanding of the local symmetry for sol-gel silicate glasses. infrared spectroscopy has allowed to identify the vibration bands of the hydroxyl groups associated with various configurations of the terminal silanol bonds on the glass surface and the free molecular water in the glass matrix. Raman analysis has provided an alternative method of quantifying the network connectivity grade and predicting the textural properties of the sol-gel silicate glasses.     

Reduction and luminescence of europium ions in glass ceramics containing SrF2 nanocrystals

Reduction of Eu³⁺ → Eu²⁺ and luminescence of europium (Eu) ions in glass ceramics containing SrF₂ nanocrystals have been investigated. The formation of SrF₂ nanocrystals in glass ceramics was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Blue luminescence of the Eu²⁺ ions was observed in the Eu doped glass ceramics which were prepared by the heat treatment of the glass in air atmosphere. The double-exponential decay curves of ⁵D₀ state of Eu³⁺ in the Eu doped glass ceramics indicated that there were two different surroundings of the Eu ions in the glass ceramics.