Solid Solution of Titanium Dioxide in Aluminum Oxide

The solid solution limit of titanium dioxide in Al₂O₃ was investigated using diffuse reflectance and cathodoluminescence measurements on polycrystalline Al₂O₃ doped with 1.0 mole % or less TiO₂. The samples had been fired in air at 1300°C. The diffuse reflectance spectra indicated that the solid solubility limit is between 0.25 and 0.30 mole %. Cathodoluminescence spectra indicated that both Ti³⁺ and Ti⁴⁺ are present in air-fired samples whereas only Ti³⁺ is present in hydrogen-fired samples.     

烧结温度对陶瓷体氧化铝固体电解质性能的影响

在Al2O3电解质体系中,利用X射线衍射分析仪、扫描电子显微镜和交流阻抗谱仪考察了烧结温度对陶瓷体Al2O3固体电解质(BASE)的β″/β相的形成、体密度和离子电导率的影响。研究表明:固相法合成BASE时,陶瓷体的最佳的陶瓷烧结温度为1 600℃。离子电导率、β″含量、体积密度随烧结温度的升高先上升后下降。离子电导率不仅与相结构有关,还与材料的致密性有关。导电过程在温度升高过程中,会由晶界控制转变为晶粒控制。随着烧结温度的升高,晶界控制的温度范围逐渐减小。     

Dispersion-Strengthened Aluminum Oxide

Finely divided molybdenum particles were dispersed in aluminum oxide to serve as inclusions for the inhibition of grain growth and secondary recrystallization during sintering. Conventional powder metallurgy techniques were used to fabricate compacts of aluminum oxide containing up to 16 vol% molybdenum. Three methods for developing a uniform dispersion of molybdenum particles in aluminum oxide are compared on the basis of the resulting microstructures. Specimens sintered in vacuum had densities approaching 98% of theoretical density with an average grain size of 2μ or less with no evidence of secondary recrystallization. The grain refinement is reflected in transverse rupture strength data with average strengths exceeding 80 kpsi and maximum strengths exceeding 100 kpsi.     

TiO2的添加对铝铬固溶体烧结动力学的影响

铝铬固溶体被广泛应用于耐火材料,其烧结致密化较难,添加一定量的烧结助剂有利于提高铝铬固溶体的致密程度,但对于致密化过程中的晶粒生长规律尚不清楚.在本工作中以纳米η-Al2 O3和工业铬绿为原料,加入烧结助剂TiO2,并以PVA作为结合剂,经过冷等静压成型后在常压下1400～1700℃进行固相烧结制备摩尔比1:1的烧结铝...     

Synthesis of Aluminum Oxide Platelets

Aqueous solutions of boehmite and hydrofluoric acid (HF) were used to prepare homogeneous mixtures of alumina and aluminum fluoride. Calcination at temperatures as low as 1000°C resulted in the formation of well-defined hexagonal-shaped α-alumina platelets. Containment of the aluminum fluoride by covering the calcination crucible promoted crystal growth presumably by a reaction of continuous evaporation–condensation of aluminum fluoride. Hexagonal-shaped platelet α-alumina was observed with average diameters ranging from 7 to 33 μm. Large platelets with a narrow size distribution and average diameter of over 25 μm were prepared by controlling the initial concentration of HF and the calcination time, temperature, and atmosphere.     

Hot Pressing of Aluminum Oxide

The hot-pressing characteristics of two aluminum oxides were studied in order to acquire a better understanding of the densification process and to develop a method of predicting the effects of experimental conditions other than those actually tested. A rapid hot-pressing technique was developed which greatly reduced the time element. The rate equation proposed by Murray, Livey, and Williams for hot-pressing ceramics was found to hold for the two aluminas, thus making it possible to predict the effects of changes in hotpressing conditions. The equation used was     . Viscosity, η, was calculated as a function of temperature using this equation and the experimental hot-pressing results. Values varied from 1.2 × 10¹² poises at 1300°C. to 4.6 × 10¹⁰ at 1600°C.     

Low-Temperature Sintering of Aluminum Oxide

A fine-sized (∼0.1 μm), agglomerate-free Al₂O₃ dispersion was used to prepare homogeneous green bodies with ∼69% relative density and ∼10-nm median pore radius. Samples could be sintered at 1150°C to a relative density >99.5% and an average grain size of 0.25 μm.     

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.     

Optimization of Synthesis of Aluminum Hydroxides and Highly-Disperse Aluminum Oxide

The results of producing highly-disperse cubic aluminum oxide by the chemical precipitation method from aluminum hydroxide solutions with subsequent dehydration are described.     

Hydrogen Permeability of Sintered Aluminum Oxide

Hydrogen permeability of high-density, high-purity sintered alumina tubes was measures is a function of temperature and pressure using tritium as a tracer. The permeability, ø, at 1200° to 1450°C and hydrogen partial pressure between 2 and 50 kPa is:
φ(H atoms cm cm⁻² s⁻¹ kPa^−0.43) = exp(48.95±0.61)
exp[−318.2±18.8 kJ(g·atom)⁻¹ (RT)⁻¹]
Diffusion coefficients and solubility values deduced from the permeation experiments are consistent with earlier independent measurements. No accelerated permeation due to micro-structural defects or changes during the experiments was observed. Comparison of hydrogen permeability of alumina with the values observed for metals shows that alumina may be a suitable coating material for use as a hydrogen permeation barrier.     

氧化铝中钯的测定

试验了氧化铝为载体的含钯催化剂中钯的AAS测定条件,方法具有良好的精密度,分析结果准确。     

Iron Tracer Diffusion in Aluminum Oxide

Iron-59 tracer diffusion in undoped and magnesium-doped sapphire was studied between 1480° and 1600°C and 10⁻⁴ Pa oxygen and air. Silicon was the predominant impurity. Diffusion was measured perpendicular to (1102) in undoped samples, parallel to (1102) in samples designated low magnesium, and perpendicular and parallel to (1102) in samples designated high magnesium. No anisotropy was evident. All of the samples exhibited silicon-dominated behavior. Iron diffused mainly by vacancy mechanisms. The oxygen pressure dependence of the diffusivity increased with increasing temperature, indicating the presence of associates and competing diffusion mechanisms. Dimers were dominant-al low temperatures and unassociated, fully ionized defects at high temperatures.     

Feedback-Controlled Firing of Reaction-Bonded Aluminum Oxide

The reaction-bonded aluminum oxide (RBAO) process utilizes the oxidation of intensely milled aluminum/alumina powder compacts that are heat treated in air to make alumina-based ceramics. RBAO samples are typically oxidized in a furnace which is heated at 1^°C/min to 1100^°C. Heat-treating samples with a characteristic dimension >1 mm, without adjusting the furnace temperature program, usually results in a cracked ceramic. Cracking is caused by the excessive thermal and chemical stresses that result from steep temperature gradients (>30^°C/mm) and compositional gradients (>5000 mol·(m³·mm)⁻¹), which develop under the deleterious ignition and shrinking core reaction regimes. While adjustments to the furnace temperature program based on continuum models have had some success, the use of feedback-controlled firing is investigated as a means to avoid the furnace temperature program design step and to decrease the firing time. Feedback-controlled firing is shown to improve yields and significantly reduce the time required to completely oxidize the aluminum. For example, a 16 g sample with a characteristic dimension of 7.56 mm, which previously took >100 h to oxidize completely, was successfully oxidized crack free in 18.3 h using feedback control. Using the typical heat-treatment cycle, a 1 mm sample was fired in 18 h. With feedback-controlled firing, the same sized sample was fired in only 5 h.     

纳米氧化铝刹车油特性

纳米氧化铝刹车油(Brake nanofluid)由本校自行设计的电浆放电纳米制造系统生产,电浆电弧放电所产生的高温将铝钯材瞬间汽化产生纳米颗粒氧化铝,以压力差将汽化金属吸入冷却液(Dot3),而纳米氧化铝会均匀融入冷却液而得纳米氧化铝刹车油.对所生产出的纳米悬浮氧化铝颗粒大小进行检测分析,经由透射电子显微镜(TEM),X光衍射仪来鉴定所生产纳米悬浮液外观以及组成成分,并对刹车油共沸点及粘度特性作具体探讨;生产的纳米氧化铝粒粒径约为30 nm,平均粒径也可达到50 nm左右,而且纳米氧化铝流体颗粒外形呈现圆形度,分布均匀,能提供刹车系统较低起始摩擦力,同时提升刹车油共沸点及粘度性,能增加刹车安全性.     

Epoxy Infiltration into Nanoporous Aluminum Oxide

This research uses spatially-resolved electron energy-loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) to study epoxy infiltration into a nanoporous aluminum surface oxide. Imaging by scanning electron microscopy (SEM) shows that the oxide surface of an as-anodized aluminum wire consists of columnar nanopores with diameters ranging from approximately 5 -150 nm. Anodized wires were embedded in a 100 g: 28 g mixture of DGEBA (diglycidyl ether of bisphenol-A) resin and PACM20 (bis(p-aminocyclohexyl)methane) curing agent followed by a two-step cure. Electron-transparent sections were cut by ultramicrotomy. Spatially-resolved carbon and oxygen EELS profiles from the oxide are anti-correlated indicating that oxide pore walls are separated by pore interiors containing epoxy. Spatially-resolved low-loss spectral data are transformed into a measure of apparent specimen thickness. Comparisons of such data with simulations based on experimentally derived oxide topologies indicate that the pores are fully filled.     

Reactions During Milling of Aluminum Oxide

Exothermic reactions are observed at ∼400°C in alumina powders ball-milled in isopropanol. These are believed to be due to the oxidation of an Al₂O₃-alcohol reaction product formed during milling.     

Hydrothermal Synthesis of Nano Ce–Zr–Y Oxide Solid Solution for Automotive Three-Way Catalyst

Nano Ce–Zr–Y (CZY) oxide solid solution was synthesized using hydrothermal method using the nitrate of cerium, zirconium, and yttrium as raw materials and urea as a hydrolysis agent. The sample was characterized using a X-ray diffraction and FT-Raman spectra to show whether Zr and Y ions were incorporated into the crystal cell of CeO₂. Scanning electronic microscopy and transmission microscopy images were recorded to examine the particle morphology. Meanwhile, the palladium-only three-way catalyst (TWC)-containing CZY was prepared and evaluated under the condition of simulated exhaust. The results show that CZY has a cubic fluorite structure and the as-synthesized solid solution has a particle diameter less than 100 nm. The TWC-containing CZY has a higher catalytic activity including a wider operation window of air/fuel ratio and a lower lighter-off temperature.