Processing of Yttria-Alumina Coated Silicon Nitride Slips by Slip Casting

Si₃N₄powders coated with 6 wt% Y₂O₃and 4 wt% Al₂O₃were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH₄PA) to produce 32 vol% slips. The influence of the amount of NH₄PA solution added and pH on the rheological properties of 32 vol% coated Si₃N₄slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH₄PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m²at pH 9.2. High NH₄PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si₃N₄slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH₄PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s^–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values.     

氧化铝/锌合金复合材料界面的SEM观察

利用挤压铸造制备氧化铝／锌合金复合材料，在扫描电镜（ＳＥＭ）上观察复合材料的界面。结果表明，在复合材料中纤维与基体间存在致密界面层，合金元素通过适当的化学反应可改善纤维与基体间的结合；在凝固过程中，纤维／基体界面上的硅在共晶体的共生生长过程中起了领先相作用，导致复合材料的共晶转变是由铝硅共晶转变和锌铝共晶转变两者组成。     

Anodising potential influence on well-ordered nanostructures formed by anodisation of aluminium in sulphuric acid

High-density structures with relatively well-ordered nanopore arrays have been obtained by the self-ordering growth of nanopores occurring during anodisation of aluminium in sulphuric acid. The resulting array of well-ordered nanopores strongly depends on an applied voltage of anodising, temperature and a procedure of synthesis. Regular arranged hexagonal arrays on aluminium with a relatively uniform pore diameter, interpore distance, and depth of pores exceeding 90 μm, can be formed by the self-ordering two-step anodising at 1 °C. The interpore distance and the pore diameter were evaluated on anodised aluminium layers obtained at different cell potentials ranging from 15 to 25 V. The detailed analyses of their uniformity were performed from SEM images. The analysis of a pore arrangement defects was made from SEM top view images taken on samples anodised at various cell potentials. The defect maps, known as Delaunay triangulations, of the arrangement of about 1000 pores were constructed for different applied anodising potentials. The percentage of pores that are not six-fold coordinated by the neighbouring pores indicates the percentage of defected surface.     

降低氧化铝生产中熟料折合比的探讨

在氧化铝生产过程中，熟料折合比是烧结法一项重要的综合性指标，本文通过对熟料折合比的定义、计算公式的剖析，分析了生产过程中影响熟料折合比的主要因素，对有效降低熟料折合比的措施进行了探讨。     

棕刚玉粉中Al2O3含量分析方法的探讨

对耐火材料——棕刚玉粉的质量分析控制，提出了用实用性的检测方法测定其Al2O3含量。通过与国家标准分析方法的对比试验，证实快速实用分析方法测定棕刚玉粉中Al2O3含量是可行的。     

碳酸化分解工艺的改进与实践

本文针对烧结法生产氧化铝过程中,铝酸钠溶液的碳酸化分解工艺,由间断分解到连续分解的改进进行了论述,指出连续分解是碳酸化分解的发展方向。     

The interfacial microstructure of joined single crystal and polycrystalline alumina

The interfacial microstructures of 96 and 98% polycrystalline alumina joined with single crystal sapphire have been investigated in relation to the joining parameters. Joining has been evaluated based on either using a thin spin-on silica interlayer or by placing the alumina and sapphire in direct contact. The materials were joined by placing the coated or uncoated surfaces in contact and heating in the range of 1340–1475 °C with minimum external load. With the aid of a silica interlayer, sapphire and 98% polycrystalline alumina were successfully joined in 180 min at 1400 °C and above, while samples without a silica interlayer failed to join under these conditions. However, sapphire and 96% polycrystalline alumina were joined both with and without the use of silica interlayer. A variety of interfacial morphologies have been observed, including amorphous regions, fine crystalline alumina, and intimate contact between the sapphire and polycrystalline alumina.     

Thermoreversible Gelcasting: A Novel Ceramic Processing Technique

A new ceramic processing method, thermoreversible gelcasting (TRG), has been developed. The method uses a gelation process that can be reversed multiple times. Two Al₂O₃ systems have been explored with the use of a specific triblock copolymer to form a binding gel network. The mixture becomes a free-flowing liquid on heating above 60°C. However, on cooling below 60°C, the slurry instantaneously transforms to a physical gel. This process can be reversed easily (essentially with an infinite processing time window) while the solvent is present in the system, which is advantageous when trying to produce high-quality dense pieces if initial casting irregularities occur. Near-theoretically dense specimens have been produced with properties consistent with reported values of high-density Al₂O₃.     

Asymmetric alumina membranes electrochemically formed in oxalic acid solution

Alumina membranes were fabricated by anodizing aluminium metal in 0.15 M oxalic acid. The growth kinetics of the porous layer were investigated in the temperature range –1 to 16 °C using linear potential scans up to 70 V. The faradaic efficiencies of metal oxidation and of porous layer formation, determined by applying Faraday's law, were found to be independent of both temperature and electrical charge. SEM analysis of the metal-side and solution-side surfaces revealed different morphologies. After dissolution of the barrier layer in phosphoric acid, the metal-side surface showed circular pores whose size of about 90 nm was found to be uniform and independent of temperature. The pore population was also practically independent of temperature and a value of about 4 × 10¹³ pores m^–2 was determined. On the solution-side surface the presence of a deposit partially occluding the mouths of pores was observed. This coating could be removed by chemical etching in NaOH or thermal treatment at 870 °C, where decomposition of oxalate occurs. This supports the hypothesis that the deposit consists of an aluminium salt containing oxalate anions precipitated from the solution. The results show that it is possible to control the morphological characteristics of the anodic alumina membranes by careful choice of experimental conditions.     

试论入世对中国氧化铝工业的影响

随着中国加入WTO，给企业带来了发展的机会，也带来了挑战。本文通过对中国氧化铝工业的现状及其与世界水平的差距的分析，阐明了入世后随着关税等贸易壁垒的消除，国内、国际市场的竞争更加激烈。明确指出了我国氧化铝工业面临的多重挑战，以及给中国氧化铝工业带来的机遇。强调充分利用WTO给企业创设的权利，借入世东风，促进我国氧化铝工业快速发展，只有发展，中国氧化铝工业才有出路。