The structure of plasma-prepared Al2O3-TiO2 powders

The morphology and phase constitution of sub-micron Al₂O₃-TiO₂ powders prepared by oxidation of mixtures of Al₂Br₆ and TiCl₄ in an oxygen-argon high-frequency plasma have been studied. The particle size and distribution were consistent with formation of liquid particles by rapid nucleation and surface reaction followed by growth by coalescence of droplets. The particle size of the powders is related to the concentration of reactants in the gas stream and the temperature difference between condensation and solidification. A metastable solution of TiO₂ in -Al₂O₃ was formed in the range 0 to 7 wt% TiO₂, at higher TiO₂ concentrations particles consisted of a dispersion of rutile particles (~ 10 nm) within single crystals of -Al₂O₃. A metastable phase identified as 3Al₂O₃·TiO₂ was also formed in powder with compositions in the range 14 to 40 wt% TiO₂. Over the composition range 40 to 80 wt% TiO₂ the powder consisted predominantly of crystals with a two-phase Al₂TiO₅-rutile structure. Pure TiO₂ consisted largely of anatase and the addition of Al₂O₃ resulted in the formation of rutile as the major phase. The phase constitution of the powders is interpreted in terms of the nucleation kinetics of the various phases.     

氧化铝包覆石墨复合粉体的制备及性能研究

通过无机铝盐的水解,利用异相成核的方法在天然鳞片石墨表面包覆氧化铝制备了氧化铝包覆石墨复合粉体.对复合粉体进行了形貌观察、结构分析、热分析、表面电位及与水的润湿性测定.研究结果表明,在石墨表面形成了较为均匀的氧化铝包覆层,所包覆的氧化铝为无定形,其与石墨表面结合良好,包覆层厚度约1μm;氧化铝包覆石墨复合粉体与水具有良好的润湿性,其表面特性与氧化铝相似,并且抗氧化性能得到较大的改善.     

Effect of calcination on characteristics and sintering behaviour of Al2O3-ZrO2 composite powders

The effect of calcination on the characteristics and sintering behaviour of zirconia-toughened alumina (ZTA) composite powders has been investigated. TiO₂ was selected as an additive to promote the sinterability of ZTA powders. The starting materials were Al₂O₃ powder, Zr(OC₃H₇)₄ and Ti(OC₃H₇)₄, and homogeneous ZTA powder containing Zr-O-Ti bonding was prepared. Calcination affected the tetragonalmonoclinic phase transformation temperature of ZrO₂ crystallizing from the gels. Calcination improved the densification rate of ZTA powder compact during sintering, which was attributed to the optimal ZrO₂ particle size and distribution on the surface of alumina. A ZTA specimen with high bulk density and high tetragonal ZrO₂ content was obtained under the conditions of 850°C/1 h calcination and 1500°C/1 h sintering.     

Preparation of composite Al2O3-TiO2 particles from organometallic precursors and transformations during heating

Equimolar Al₂O₃-TiO₂ composite powders were prepared via controlled hydrolysis of organometallic precursors, sometimes in the presence of submicrometre commercial-Al₂O₃ or anatase-TiO₂ particles. Variations in the chemical procedures were used aimed at different submicrostructures within the resulting powders. Heating such powders in air shows that structural behaviour is influenced by the micromorphology of the composite particle. Transformation temperatures of the titania phases seem to depend upon some size parameter which would represent their morphology within the powders. Studies performed on a series of non-equimolar Al₂O₃-TiO₂ composite powders showed that the temperature of -Al₂O₃ formation may be decreased by 210° C possibly due to a seeding effect of rutile. Pseudobrookite Al₂TiO₅ was never detected at 1300° C in air.     

Preparation of Fe2O3/Al composite powders by homogeneous precipitation method

The Fe₂O₃/Al composite powders were prepared by homogeneous precipitation method. The influence of the concentration of Fe²⁺ and the molar ratio of raw materials on the preparation of Fe₂O₃/Al composite powders were investigated. X-ray diffractometer, scanning electron microscope, Fourier transform infrared spectroscopy and differential thermal analysis were used to analyze the morphology and structure of the Fe₂O₃/Al composite powders. The results show that the content of iron oxide in the composite powders could be effectively controlled by adjusting the concentration of Fe²⁺ and the molar ratio of raw materials in the plating solution. The surface of Al particle was coated with a layer of thick and dense iron oxide. The core-shell Fe₂O₃/Al composite powders with Fe₂O₃ content of 14.1% were produced, the coating efficiency of Fe₂O₃ reaches more than 77%. The iron oxide, which coated on the surface of the aluminium particle is flower-like cluster structure, each flower-like cluster is constituted by nano-flaky iron oxide.     

Microwave and conventional sintering of rapidly solidified Al2O3-ZrO2 powders

The Al₂O₃-ZrO₂ eutectic composition was rapidly solidified, forming amorphous and crystalline structures. The as-quenched material was crushed and pressed into pellets which were sintered conventionally or with microwaves. Conventional and microwave sintering at temperatures up to 1600 °C resulted in a microstructure where 100–200 nm ZrO₂ grains were present intergranularly in the -Al₂O₃ grains. Larger ZrO₂ grains (1 m) were found intergranularly. The as-quenched lamellar structure spheroidized during sintering at high temperatures. Boron contamination of the powders resulted in more homogeneous and dense as-fired samples but promoted the ZrO₂ tetragonal-to-monoclinic transformation, which was attributed to increased grain boundary diffusivity. Conventional sintering at low temperatures resulted in the formation of rods of an Al₂O₃-rich phase which grew from a low-melting B₂O₃-rich liquid.     

Al_2O_3-TiO_2纳米管制备研究

采用一种温和的制备方法首次制得Al2O3-TiO2纳米管。将TiO2粉体在常压下,于700℃熔融、110℃水热反应,制备了管径约为几纳米、单层管壁厚约为0.2纳米以及管长约为数微米的复合Al2O3-TiO2纳米管。利用TEM和XRD对其组织形貌进行表征,并对其形成机理进行了讨论。     

纳米Al2O3/ZrO2复合粉体的制备及表征

高性能的复合粉体是制备纳米复相陶瓷材料的关键.采用醇-水溶液加热法结合共沉淀过程制备纳米Al2O3/ZrO2复合粉体,研究了不同沉淀剂对粉体团聚的影响,利用透射电镜、X射线衍射、热重-差热分析、比表面积测定等技术对获得的纳米复合粉体进行了表征.结果表明:采用NH4HCO3作为沉淀剂可以得到几乎无团聚的碱式碳酸盐前驱物,该前驱物在煅烧过程中的物相变化显示四方相氧化锆(t-ZrO2)的形成温度大幅度地提高,同时在较低温度下生成了α-Al2O3,在1 100℃转变为t-ZrO2相和α-Al2O3相;粉体中两相颗粒分散良好、粒径一致、无硬团聚,其平均粒径为15～20 nm,比表面积为69.5 m2·g-1.     

Al2O3 reinforced Al/Ni intermetallic matrix composite by reactive sintering

An aluminium-nickel reinforced Al₂O₃ particulate composite was fabricated by a powder metallurgy route, where 35wt% aluminium and 30wt% nickel powders were mixed with 35wt% Al₂O₃ particles and compacted at 548 MPa. Sintering was carried out at 850 °C, where the synthesis reaction was sustained by the transient liquid phase resulting from the exothermic reaction associated with the formation of intermetallic compounds, i.e. reactive sintering. The resultant microstructure was studied using X-ray diffraction (XRD) and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS). It was found that the initial distribution of individual constituent powders affect the outcome of the reactive sintering and that the inward diffusion of aluminium in nickel was responsible for nickel aluminide formation.     

Preparation and mechanical properties of high-purity Al2O3 fibre/Al2O3 matrix composite

Al₂O₃ matrix composites with unidirectionally oriented high-purity Al₂O₃ fibre with and without carbon coating, were fabricated by the filament-winding method, followed by hot-pressing at 1573–1773 K. The composite with non-coated Al₂O₃ fibre exhibited a bending strength (594 MPa) comparable to that of monolithic Al₂O₃ (589 MPa). While the composite with a carbon-coated fibre had lower strength (477 MPa), it showed improved fracture toughness (6.5 MPa m^1/2) compared to the composite with an uncoated fibre (4.5 MPa m^1/2) and monolithic Al₂O₃ (5.5 MPa m^1/2). This toughness enhancement was explained based on the increased crack extension resistance caused by the fibre pull-out observed by SEM at the notch tip. This revised version was published online in November 2006 with corrections to the Cover Date.     

中空纤维担载Al_2O_3-SiO_2复合膜的研制

采用溶胶-凝胶法在α-Al2O3中空纤维载体上制备了Al2O3-SiO2复合膜,并对复合膜的制备条件及稳定性进行了研究.利用SEM和EDS对复合膜的微观形貌及化学组成进行了分析.结果表明,所制备的担载复合膜表面完整、无缺陷.气体渗透实验进一步说明,复合膜具有一定的气体选择性,在0.1 MPa下对H2/N2的分离因子为3.03,表明气体通过膜的扩散以Knuen扩散传质为主.用等温氮气吸附实验测定了非担载膜的孔径大小和分布,其比表面积为294.85 m2/g,总孔容为0.28 mL/g,最可几孔径小于3 nm.     

中空纤维担载Al2O3-SiO2复合膜的研制

采用溶胶-凝胶法在α-Al2O3中空纤维载体上制备了Al2O3-SiO2复合膜,并对复合膜的制备条件及稳定性进行了研究.利用SEM和EDS对复合膜的微观形貌及化学组成进行了分析.结果表明,所制备的担载复合膜表面完整、无缺陷.气体渗透实验进一步说明,复合膜具有一定的气体选择性,在0.1 MPa下对H2/N2的分离因子为3.03,表明气体通过膜的扩散以Knuen扩散传质为主.用等温氮气吸附实验测定了非担载膜的孔径大小和分布,其比表面积为294.85 m2/g,总孔容为0.28 mL/g,最可几孔径小于3 nm.     

In situ synthesis of Al2O3 particulate-reinforced Al matrix composite by low temperature sintering

The powder mixture of Al-10 wt.% SiO₂ was selected as a research system. Compared with an as-mixed powder, the phase structure and microstructure of an as-milled powder was investigated, and the temperature of the displacement reaction in the two kinds of powder was determined by thermal analysis. The preforms of the two kinds of powder were sintered based on the result of thermal analysis. The results indicate that the particle size of the Al-SiO₂ powder was refined greatly after 4 h of high energy ball milling, and diffusion couples were formed due to SiO₂ particles embedded in the Al matrix. The displacement reaction did not occur between Al and SiO₂ for the as-mixed powder, while it occurred in the range of 560–680°C for the as-milled powder. For the as-milled powder, an aluminum matrix composite reinforced with Al₂O₃ particles, which were homogeneously distributed in the Al matrix, can be fabricated by sintering at 640°C for 2 h.     

无团聚ZrO2-HfO2-Y2O3复合纳米粉体的制备

以分析纯ZrOCl2·8H2O、HfOCl2·8H2O和Y(NO3)3·6H2O为原料,采用反向滴定共沉淀-共沸蒸馏法成功地制备出无团聚的ZrO2-HfO2-Y2O3复合纳米粉体.借助XRD、TEM、BET等手段分析了制备工艺对粉体粒径和团聚状态的影响.研究表明,分散剂PEG的加入量及前驱体湿凝胶的处理方式对最终制备的ZrO2-HfO2-Y2O3复合粉体的晶粒度影响不大,但显著影响粉体的分散状态.分散剂加入量为1%(质量分数)并对湿凝胶共沸蒸馏处理条件下最终获得的粉体的分散性最好.前驱体沉淀经500℃焙烧1h后,生成了具有高氧离子电导率的立方晶型ZrO2基ZrO2-HfO2-Y2O3固溶体,粉体的平均粒径约为15nm.     

Bi2O2CO3/TiO2复合粉体的制备及其光催化性能研究

采用水热法制备了Bi2O2CO3,并将其与TiO2进行了复合。XRD数据表明此复合光催化剂中Bi2O2CO3结晶性良好,紫外-可见漫反射光谱说明Bi2O2CO3的加入使其吸收带边有一定的红移。研究了紫外-可见光照射下Bi2O2CO3/TiO2复合光催化剂对亚甲基蓝溶液的降解性能,结果表明当Bi2O2CO3与TiO2的质量比为0.032时,得到性能最优的复合光催化剂,其光催化活性优于TiO2。