Synthesis and Mechanical Properties of Stoichiometric Aluminum Silicate (Mullite)

Highly dense translucent polycrystalline bodies of stoichiometric aluminum silicate (mullite) were obtained by vacuum-hot-pressing of high-purity submicron mixed oxide powders. The powders were prepared by the hydrolytic decomposition of mixed metal alkoxides. X-ray diffraction and electron microscopy indicated that the initially amorphous needlelike fine particulates transform into highly crystalline orthorhombic mullite at ∼1200°C. Optimum hot-pressing conditions were 5 kpsi and 1500°C for 30 min. Densities within experimental error of the theoretical value of 3.19 g/cm³ were obtained. A typical microstructure consisted of fine interlocking needlelike grains arranged in an overall mosaic or "jigsaw" pattern. Microprobe traverses across the samples indicated homogeneous dispersion of SiO₂ in the AlO₃ matrix. Room-temperature mechanical properties were measured and correlated with the microstructure and crystal structure of the ceramic compact. A slightly higher melting temperature than has been previously reported was observed for the 3Al₂O₃·2SiO₂ studied. All specimens exhibited a smooth surface finish and excellent thermal-shock resistance from 1200°C to room temperature.     

Aluminum Nitride Prepared by Nitridation of Aluminum Oxide Precursors

Aluminum nitride (AlN) powders were prepared from the oxide precursors aluminum nitrate, aluminum hydroxide, aluminum 2-ethyl-hexanoate, and aluminum isopropoxide (i.e., Al(NO₃)₃, Al(OH)₃, Al(OH)(O₂CCH(C₂H₅)(C₄H₉))₂, and Al(OCH(CH₃)₂)₃). Pyrolyses were performed in flowing dry NH₃ and N₂ at 1000°–1500°C. For comparison, the nitride precursors aluminum dimethylamide (Al(N(CH₃)₂)₃) and aluminum trimethylamino alane (AlH₃·N(CH₃)₃) were exposed to the same nitridation conditions. Products were investigated using XRD, TEM, EDX, SEM, and elemental analysis. The results showed that nitridation was primarily controlled by the water:ammonia ratio in the atmosphere. Single-phase AlN powders were obtained from all oxide precursors. Complete nitridation was not obtained using pure N₂, even for the non-oxide precursors.     

Water Content and Water Evolution from Reaction-Bonded Aluminum Oxide (RBAO) Powder Precursors

Water evolution behavior from reaction-bonded aluminum oxide (RBAO) powder precursor was studied by the Carl-Fischer titration method. RBAO mixtures were milled for 4 and 8 h in absolute ethanol and water–ethanol mixtures containing 5 and 10 vol% water. The water content was then determined under dynamic heating conditions from 20°C to 250°C and static heating at 250°C. When the aluminum content is increased from 30 to 60 vol%, the water content of the milled powder precursor mixtures also increased. The higher water contents observed in powders milled in absolute ethanol are discussed in terms of the possible interaction of the ethanol with the surface of the aluminum particles.     

优质莫来石─—钛酸铝窑具的研制

本文简介了钛酸铝的主要性质，稳定性钛酸铝原料的合成与莫来石—钛酸铝复相材料的研制。对陶瓷窑用窑具材料的各自特长和适用条件等也作了详尽的分析讨论     

利用铝型材厂污泥和叶腊石制备莫来石材料

以铝型材厂污泥和叶腊石为主原料制备莫来石材料,属于固体废料和矿物资源的综合利用项目.采用XRD法和SEM法表征各试样的晶相结构和显微结构;用Rietveld Quantification法确定各试样中各晶相的含量.结果表明不同配方的各试样均形成三种晶相,莫来石固溶体Al4.59Si1.41O9.7、Al2O3、SiO2,其中Al4.59Si1.41O9.7是主晶相,其含量为85.3%～97.8%;分析结果确定最佳的配方组成为:污泥为75wt%,叶腊石为25wt%,Al2O3/SiO2物质的量比为2.4.     

Determination of Valence States of Chromium in Calcium Chromates by Using X-ray Absorption Near-Edge Structure (XANES) Spectroscopy

Calcium chromates with the empirical formulas Ca₁₀Cr₆−O₂₅, Ca₃Cr₂O₈, and Ca₅Cr₃O₁₂, which form at temperatures >900°C at CaO:Cr₂O₃ molar ratios of 3 in an oxidation atmosphere have been synthesized in the pure state. X-ray absorption near-edge structure (XANES) spectroscopy has been used to determine the average valence state of chromium in the samples. The presence of unusual chromium valence states, 4+ and 5+, which was proposed via X-ray diffractometry studies, is strongly supported.     

用羧酸铝和硅溶胶制备莫来石纤维

采用金属铝粉、甲酸和醋酸为原料,以氯化铝为催化剂制备了羧酸铝溶液。在羧酸铝溶液中加入硅溶胶,制备了可纺的前躯体溶胶。凝胶纤维在1400℃煅烧后,主要物相为莫来石,有少量的氧化铝和氧化硅相,得到的纤维直径均匀,但纤维表面有较多的裂纹。     

Formation of Mullite Basedon Hydromica Clay – Aluminum Oxide Compositions

The results of studying mullite formation based on hydromica clay – Al(OH)₃ compositions are described. It is shown that formation of mullite (or a solid solution of mullite with corundum) is the most intense at temperatures of 1150 – 1200°C in compositions with a content of hydromica clay equal to 50 – 60%.     

莫来石—钛酸铝复相陶瓷的高温强度与热分解

本文介绍了莫来石－钛酸铝复相陶瓷的制备工艺及其主要性能，重点对它的高温强度、热分解及抗热震性等进行了讨论并提出了我们的见解。     

Grain Boundary Grooving Studies of Yttrium Aluminum Garnet (YAG) Bicrystals

Grain boundary grooving experiments were conducted with Σ5 (210) twist boundaries in Y₃Al₅O₁₂ (YAG) with the goal of extracting information on diffusion in YAG. Planar boundaries oriented 90° to the surface were annealed in air at various times and temperatures. Atomic force microscopy was used to characterize the subsequent grooves. The Mullins approach leads to the following expression for the diffusion coefficient: D (m²/s) = 3.9 × 10⁻¹⁰ exp[−330 ± 75 (kJ/mol)/ RT ]. The relatively low activation energy agrees well with earlier oxygen tracer diffusion measurements on YAG, suggesting that oxygen is the limiting diffusing species in boundary grooving of YAG.     

Poly(methacrylate) Precursors to Forsterite

A novel polymer precursor method for the preparation of silicates including enstatite-free forsterite is being investigated. Precursors to crystalline materials were prepared via the copolymerization of the K and/or Mg salts of methacrylic acid with various combinations of a siloxane-methacrylate and a methoxysilyl-methacrylate Thermogravimetric/differential thermal, pyrolysis mass spectrometry, and high-temperature X-ray diffraction analyses were used to monitor the conversion of the precursors to inorganic oxide during air pyrolysis. Some precursors to crystalline oxides showed yields as high as 77% of theoretical.     

四环素-铜（Ⅱ）配合物与DNA相互作用的吸收光谱研究

用紫外光谱方法研究了四环素(TC)-Cu(Ⅱ)配合物与DNA的相互作用．吸收光谱研究表明，DNA能与四环素(TC)及Cu(Ⅱ)形成的配合物发生反应，配合物与DNA的作用方式随着配合物类型及DNA浓度的不同而不尽相同：当四环素与铜形成1：1型配合物时，较低浓度的DNA能与配合物以嵌插方式相互作用，而较高浓度的DNA与该配合物除了发生嵌插作用外，还存在另外的作用方式；当四环素与铜形成1：2型配合物时，DNA与该配合物则主要以嵌插方式相互作用，并且这两种配合物与DNA的嵌插作用均是通过四环素配体插入的．     

Preparation of Mullite Ceramics from Coprecipitated Aluminum Hydroxide and Kaolinite Using Hexamethylenediamine

Mullite ceramics have been prepared from an aqueous suspension of kaolinite (raw or ground) and aluminum hydroxide. The precursor was coprecipitated in the mixture using hexamethylenediamine (HMDA) or ammonium hydroxide, and a solution of aluminum chloride from acid dissolution of wastes of aluminum metal. The precursor and the resulting materials were characterized and studied by X-ray diffraction, thermal methods, and mechanical strength and porosity measurements. The feasibility of the proposed chemical processing route for mullite preparation was demonstrated, in particular using HMDA as a precipitating agent for aluminum hydroxide instead of ammonium hydroxide, which adversely affects the system reactivity. The use of HMDA, as compared with ammonium hydroxide, and ground kaolinite produces single-phase mullite and enhances the flexural strength (maximum of 49 MPa) of the resultant ceramic porous bodies (porosity ca. 52–45 vol%) fired at 1550–1600°C for 30 min.     

Preparation of Silicon Carbide/Aluminum Nitride Ceramics Using Organometallic Precursors

Solid solutions of 2H -SiC/AlN can be prepared at temperatures less than 1600°C by rapid pyrolysis ("hot drop") of mixtures of [(Me₃Si)_0.80((CH₂=CH)MeSi)_1.0(MeHSi)_0.35] _n (VPS) or [MeHSiCH₂] _n (MPCS) with [R₂AlNH₂]₃, where R=Et, i -Bu or simply by slow pyrolysis of the precursor mixture in the case of [Et₂AlNH₂]₃. In contrast, slow pyrolysis of mixtures of VPS or MPCS with [ i -Bu₂AlNH₂]₃ yields a composite of 2 H -AlN and 3 C -SiC at 1600°C, which transforms into a single 2 H -SiC/AlN solid solution on heating to 2000°C. The influences of the nature of the precursor and processing conditions on the structure, composition, and purity of the SiC/AlN materials are discussed.     

XANES Determination of Chromium Oxidation States in Glasses: Comparison With Optical Absorption Spectroscopy

The oxidation state of chromium in glasses melted in an air atmosphere with and without refining agents was investigated by Cr K-edge X-ray absorption near-edge structure (XANES) and optical absorption spectroscopy. A good agreement in the relative proportion of Cr(III) and Cr(VI) is obtained between both methods. We show that the chemical dependence of the absorption coefficient of Cr(III) is less important in XANES than in optical absorption spectroscopy. The comparison of optical absorption and XANES spectra of glasses melted under different conditions provides an indirect assessment of the molar extinction coefficient of Cr(VI) in glasses.     

Synthesis and Structural Characterization by X-ray Absorption Spectroscopy of Tin-Doped Mullite Solid Solutions

The formation of solid solutions between tin cations and mullite by calcination at 1400°C of amorphous precursors prepared by pyrolysis of aerosols is reported. The oxidation state of the tin cations and the position that they occupy in the mullite structure have been analyzed using XAS (XANES and EXAFS) spectroscopy, which shows that the tetravalent tin cations are located at the octahedral positions of the Al³⁺ ions, which induces cell expansion. The limit of tin incorporation under the experimental conditions reported here correspond to a tin/mullite mole ratio of ∼5%, which is within the range previously reported for other tetravalent cations (4%–6%).     

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.     

TiO2对用铝厂污泥和叶腊石制备莫来石材料的影响

本研究以铝型材厂污泥和叶腊石为主要原料制备莫来石材料,在研究确定最佳配方、最佳煅烧温度和最佳保温时间的基础上,探讨TiO2矿化剂对莫来石晶相结构、显微结构和性能的影响,从而确定出最佳TiO2矿化剂添加量. 采用XRD法和SEM法表征各试样的晶相结构和显微结构;用Rietveld Quantification 法确定各试样中各晶相的含量;测试各试样的性能.综合结构与性能分析结果,确定最佳TiO2添加量为1.0%,对应莫来石固溶体含量为98.5%,体积密度为2.48 g·cm-3,气孔率为13.1%,吸水率为5.30%,抗折强度为22.66 MPa,折强度保持率为83.9%.     

氮化铝和莫来石陶瓷衬底的SIMS和XRD研究

利用二次离子质谱（ＳＩＭＳ）和Ｘ射线衍射（ＸＲＤ）研究了用于电子封装的以Ｄｙ２Ｏ３,ＣａＯ为添加剂的ＡＬＮ和以堇青石,ＢａＣＯ３为添加剂的莫来石陶瓷衬底的物相组成和表面成分,尤其是表面杂质,并利用ＳＩＭＳ尝试探讨了ＡｌＮ表面热氧化问题。结果表明,ＡｌＮ和莫来石陶瓷表面不同程度地存在Ｌｉ,Ｃ,Ｆ,Ｎａ,Ｋ,Ｃｌ,Ｔｉ,Ｒｂ等杂质元素的污染;ＡｌＮ表面存在富Ｏ层,在空气中经过８５０℃１０分钟退火后,富