挤压铸造Al_2O_3／Al─Si合金复合材料的凝固组织与凝固模型

利用挤压铸造技术制备了Ａｌ２Ｏ３／Ａｌ─Ｓｉ合金复合材料，研究了这种复合材料的凝固组织．结果表明，氧化铝纤维可作为铝硅合金中硅相非自发形核的衬底，但是未观察到纤维对α相的细化作用；氧化铝纤维与浸渗压力影响了复合材料的凝固过程，复合材料具有不同于普通基体合金的最终凝固组织．基于实验结果和凝固理论，提出了Ａｌ２Ｏ３／Ａｌ─Ｓｉ合金复合材料的凝固模型．     

Characterization and Photoluminescence Properties of AluminaNanowires Elaborated by Arc-Plasma

Ultrafine powders containing alumina nanowires are synthesized by DC arc plasma from pure aluminium metal. Nanowires grow only when reactive gases are composed of nitrogen and less than ten percent of oxygen. Nanowires have the diameters ranging from 20 to 80 nm and lengths ranging from hundreds nanometers to tens of micrometers. A first assumption of the mechanism process is proposed, in which nanowires grow starting directly from the aluminium. Photoluminescence measurements show that the powders have three emission peaks around 435, 530 and 750 nm resulting from different kinds of defects such as oxygen vacancies, aluminium interstitial ions and surface defects.     

Migration behavior of aromatic amines on alumina thin layers developed with water-in-oil microemulsion

Water-in-oil (w/o) microemulsions consisting of surfactant [sodium dodecyl sulfate (SDS) or N-Cetyl-N,N,N-trimethyl ammonium bromide], water, heptane or hexane, and a cosurfactant (1-pentanol or butanol) have been used as a mobile phase in combination with alumina, microcrystalline cellulose, silica gel G, silica gel H, and Kieselguhr thin layers to study the retention efficiency of amines. The separation of amines from their ternary and binary mixtures is achieved. Thin layers of alumina as the stationary phase and SDS/water/heptane/1-pentanol microemulsion as mobile phase is identified as the best chromatographic system for amine analysis. The limits of identification and dilution are reported for amines. Effects of heavy metals, anions, and phenols on the separation efficacy of diphenylamine-p-chloroaniline-p-nitroaniline have also been examined. The effect of electrolyte in the microemulsion on amine mobility is investigated. The o- and p-isomers move faster compared to the m-isomer of aniline.     

Rapid determination of polycyclic aromatic hydrocarbons in natural tocopherols by high-performance liquid chromatography with fluorescence detection

A simple and rapid method has been developed and validated for the determination of seventeen polycyclic aromatic hydrocarbons (PAHs) in natural tocopherol products. Samples were dissolved in n-hexane, cleaned by an alumina column, and separated and determined by reversed-phase high-performance liquid chromatography (HPLC) with fluorescence detection. The recoveries were greater than 77.9%, except for the lowest molecular weight PAHs (Na, 1-Me, 2-Me, AC, F) which were between 15.9% and 75.8%. The limits of quantification were less than 0.38 ng/g for the heavy PAHs and less than 1.50 ng/g for the light PAHs. Good repeatabilities were achieved with RSD less than 10.7% for all the objective compounds. This method has been applied to evaluating PAHs contents in various natural tocopherol products and controlling natural tocopherol product quality.     

陶瓷空心球/镁合金复合多孔材料制备及压缩性能

本文选用两种不同的陶瓷空心球(商购氧化铝空心球和自制含硅复合氧化物陶瓷空心球)作为增强体,采用粉末烧结的方式在烧结温度600℃、保温时间3 h 20 min的烧结条件下,成功制备出两种轻质、含孔的镁合金复合多孔材料。通过扫描电子显微镜观察烧结样品的微观结构,发现含硅陶瓷空心球与镁合金的界面处发生了界面反应,生成了含有MgO、Mg₂Si等成分的合金相。研究了采用不同种类陶瓷空心球对样品表观密度、压缩强度和比强度的影响。结果表明,采用商购氧化铝空心球制备的复合样品的体密度最低,与镁合金致密体的密度相比,平均表观密度下降了33.3%,为1.20 g·cm^-3;选用自制含硅陶瓷空心球制备的复合样品的平均表观密度下降了16.1%,为1.51 g·cm^-3;在压缩过程中两种样品都表现出了弹性阶段、屈服平台和致密化阶段的多孔材料典型的压缩特征;自制含硅陶瓷空心球所制样品的压缩强度明显高于氧化铝空心球所制样品,自制含硅陶瓷空心球所制复合样品的比强度也高于商购氧化铝空心球所制复合样品。     

Synthesis of α-Al2O3 platelets and kinetics study for thermal decomposition of its precursor in molten salt

The precursor, ammonium aluminum carbonate hydroxide (AACH) was synthesized via solid-state reaction at 60 °C. The experimental results show that the AACH is orthorhombic NH₄Al(OH)₂CO₃, and the calcined powder products are hexagonal platelets of α-Al₂O₃ which can be obtained from calcining AACH in molten salt at 1000 °C. The linear and nonlinear methods were used to calculate the activation energies of the thermal process of AACH. The calculated results indicated the decomposition process involved two stages which were single-step kinetic processes. The most probable reaction mechanisms of the two stages were estimated by two comparative methods. The values of pre-exponential factor A of the two stages were obtained on the basis of E_α and the reaction mechanisms.