热压烧结AlON透明陶瓷的烧结行为及性能

本文以醇盐水解法自制的γ-Al2O3粉体为原料,利用热压反应烧结技术,在N2气氛中一步制备得到γ-AlON透明陶瓷,并着重研究了Y2O3和MgO两种氧化物烧结助剂及其含量对产物的烧结性能及透光性的影响。结果显示加入Y2O3或MgO作为烧结助剂,不但有助于促进固相反应进行,还可通过形成固溶体大大改善烧结性能。较MgO而言,采用Y2O3作为烧结助剂的产物的硬度及相对密度均更好。添加1wt%Y2O3,在1950℃热压条件下即可得到γ-AlON透明陶瓷。XRD、SEM及密度测试结果表明产物的物相组成单一、内部结构致密,其相对密度可达99.22%。IR分析结果显示该样品在1.5~4.5μm的红外波段内具有可透过性,最大透过率为18.42%(2.5μm处)。     

Skeletal isomerization of 1-butene into isobutene over Mg-ZSM-22 modified by the deposition of silicon alkoxide

Mg-ZSM-22, modified by the deposition of silicon ethoxide, was prepared and investigated as a catalyst for the skeletal isomerization of 1-butene to isobutene in a fixed-bed flow reactor. The prepared catalysts were characterized by XRD, TPD, SEM-EDX, ICP and FT-IR. The deposition of silicon alkoxide on Mg-ZSM-22 led to a decrease in the amount of strong acid sites, confirmed by TPD experiments with ammonia and γ-collidine. The treatment also affected the size of pore opening, as evidenced by constraint index measurement and chemisorption experiment using -hexane. As the deposition time increased, the conversion of 1-butene decreased as the result of reduced acidity, while selectivity to isobutene increased. The deposition of silicon alkoxide resulted in the suppression of side reactions and coke deposition, thus enhancing the skeletal isomerization. The modification of Mg-ZSM-22 by deposition of silicon alkoxide was very effective in terms of catalytic stability and coke removal. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of Potassium Niobate from Metal Alkoxides

Preparation of potassium niobate from metal alkoxides was investigated. Potassium-niobium ethoxide, KNb(OC₂H₅)₆, and potassium-niobium propoxide, KNb(OC₃H₇)₆, were synthesized and subsequently hydrolyzed using several water concentrations (0.75 to 6.0 mol of water/(mol of alkoxide)). Rapid precipitation of potassium-deficient particles occurred when higher concentrations of water were used. This resulted in the formation of a multiphase material after calcination, as X-ray diffraction showed the presence of both KNbO₃ and potassium-deficient oxide phases(s). Single-phase KNbO₃ could be prepared by two methods: (1) hydrolysis of KNb(OC₃H₇)₆/propanol solutions using 1 mol of water (per mole of propoxide) added as a water/propanol solution and (2) hydrolysis of KNb(OC₂H₅)₆/ethanol solutions using 1 mol of water (per mole of ethoxide) added as a water/methanol solution. The latter method provided advantages of low calcination temperature for the formation of single-phase KNbO₃ and low weight loss after calcination.     

Chemical Processing and Microwave Characteristics of (Zr,Sn)TiO4 Microwave Dielectrics

Monosized spherical particles of (Zr, Sn)TiO₄ with an average diameter of about 0.3 μm were synthesized by the controlled hydrolysis of metal alkoxides. The as-prepared, amorphous, particles were compacted without any sintering aid, crystallized, and then sintered at 1600°C for 3 h into bodies with >96.0% of theoretical density. The dense sintered bodies of (Zr_0.80Sn_0.20)TiO₄ showed good microwave characteristics; ɛ_r= 40.0, Q = 5000, and τ_t= 3 ppm/°C at 10 GHz. The dielectric constant was remarkably dependent upon the relative densities of the sintered bodies and the change of the lattice parameters, while Q value was mainly affected by the oxygen deficiency. An increase of the dielectric constant with the substitution of Sn⁴⁺ in ZrTiO₄ was attributable to the enhancement of ionic polarization with the increase of the c -axis length.     

Synthesis and characterization of abrasion resistant coating materials prepared by the sol-gel approach: I. Coatings based on functionalized aliphatic diols and diethylenetriamine

The synthesis of inorganic organic hybrid materials has been undertaken and used as abrasion resistant coatings for polymeric substrates by the sol-gel method. The organic components are diethylenetriamine (DETA), glycerol, and a series of aliphatic diols which are functionalized by 3-isocyanatopropyltriethoxysilane. The inorganic components are tetramethoxysilane (TMOS), aluminum tri-see-butoxide, titaniumsec-butoxide and zirconiumn-propoxide. Solutions of these materials are spin coated onto bisphenol-A polycarbonate sheet and thermally cured to obtain a transparent coating of a few microns in thickness. Following the curing, the abrasion resistance is measured and compared with a control having no coating. It was found that the abrasion resistance of inorganic organic hybrid coatings in the neat form or containing additional silicon, titanium, zirconium, and aluminum alkoxides can be very effective to improve abrasion resistance. The adhesion tests show that the adhesion between coating and substrate can be greatly improved by treating the polymeric substrate surface with an oxygen plasma or a primer solution of isopropanol containing 3-aminopropyltriethoxysilane. Other experiments, such as the abrasion resistance tests following conditioning in a hot-wet condition (boiling water treatment), microhardness tests. UV absorption behavior, and the observation of abraded surfaces, were also undertaken in order to evaluate these coating materials.     

Preparation of Colloidal Boehmite Needles by Hydrothermal Treatment of Aluminum Alkoxide Precursors

Fairly monodisperse colloidal boehmite fibrils with a high aspect ratio were synthesized by hydrothermal treatment at 150°C of an acidified aqueous alkoxide solution, prepared by adding an aqueous HCl solution to an aluminum alkoxide precursor. The average particle length could be controlled between about 100 and 500 nm by varying the initial amounts of alkoxide and acid. Using two different alkoxides in a 1:1 molar ratio yielded the most needlelike product, having a particle length standard deviation of 40%. The boehmite particles were polycrystalline and contained 0.14 mol of excess H₂O per mol of AlOOH, bound to the particle surface.     

SiO2单分散溶胶微球制备的工艺条件研究

在乙醇介质中,以氨作为催化剂,正硅酸乙酯作为硅源,制备了单分散的二氧化硅溶胶微球。通过激光粒度分析仪及透射电镜测定溶胶粒子的大小。研究了不同工艺参数如催化剂和水的量、硅源的量以及溶剂的类型对二氧化硅粒子大小及形貌的影响,并考察了粒子的形成机理。结果显示:随着氨浓度的升高,溶液初始解离的[OH-]增大,二氧化硅粒子的粒径增大;随着硅源浓度的增加,溶液中水解的中间产物增加,二氧化硅微球的粒径显著增加;在r(水/正硅酸乙酯)值远大于4的情况下,随着初始加入水量的增加,二氧化硅微球的粒径有所增加,但当水量太多时,粒径反而下降;使用不同溶剂作为制备二氧化硅的介质,在丙醇和丁醇中二氧化硅严重团聚,没有得到单分散微球。     

60%(CH3)2Si(OEt)2/40%Si(OEt)4有机-无机复合醇盐水解聚合过程的研究

研究了有机－无机复合醇盐：60％二甲基二乙氧基硅烷（DDS）／40％正硅酸乙酯（TEOS）的水解聚合过程。通过测定不同水解时间后形成产物的结构及含量变化,分析了这种有机－无机复合材料水解聚合过程中有机与无机组分的相互作用机制及各种产物的形成规律。指出：DDS的添加抑制TEOS的自聚合,使得体系中形成了大量的TEOS和DDS的共聚合分子,有机与无机组分通过化学键合连接起来而成为一种凝胶网络组成体。同时还检测到许多DDS的自聚合环状分子[(CH3)2Si-O-]n的生成。     

Deformation Mechanism of Fine-Grained Magnesium Aluminate Spinel Prepared Using an Alkoxide Precursor

Polycrystalline MgAl₂O₄ spinel with high purity and stoichiometric composition was prepared using alkoxide precursors. The average grain size of the polycrystal was fine (1.7 μm). The deformation mechanism of the polycrystal was investigated in air at temperatures of 1300°–1400°C. At 1300°C, oxygen lattice diffusion controlled the deformation, despite the fine grain size; however, increases in the temperature and applied stress caused cavities to nucleate and grow. Spinel possessed better creep resistance than alumina of comparative grain size. The effective diffusion coefficient was determined as follows: [formula omitted]