助熔剂法制备硼酸铝晶须

以Al（OH）3和H3BO3为原料,分别以MnO2、Fe2O3为助熔剂制备硼酸铝晶须,研究助熔剂对晶须形貌的影响。研究发现,在1350℃煅烧6h,试样的物相为硼酸铝（9Al2O3·2B2O3）。以MnO2为助熔剂的试样晶须的直径为1μm～6μm,长径比较小;以Fe2O3为助熔剂的试样晶须的直径为0．2μm～1μm,长径比〉10。     

Tin(IV) Oxide Coating of Aluminum Borate Whiskers and Alumina Particles by Chemical Vapor Deposition

Aluminum borate whiskers of 0.5–1.0 μ diameter and alumina particles of 10–20 μ diameter were coated with SnO₂ by the reaction of SnCl₄–H₂O–N₂ gas mixtures in a rotary kiln reactor. Prior to coating, the whiskers were slightly etched to ensure adhesion between the SnO₂ layer and the whisker surface. The whiskers were coated at 100°C for 1 h, and then at 300°C for 2 h. This procedure was effective for covering the entire whisker surface with a uniform SnO₂ layer. Precoating was not necessary for the alumina particles. A compressed disk of the coated whiskers had an electrical conductivity of 30–40 S/m.     

Preparation and Characterization of Aluminum Borate

Aluminum borate, 9Al₂O₃·2B₂O₃ or Al₁₈B₄O₃₃, was synthesized by the reaction of stoichiometric amounts of α-Al₂O₃ and B₂O₃. The Al₁₈B₄O₃₃ material was formed into a dense ceramic by pressureless sintering with CaO, MgO, or CaAl₂B₂O₇ additives. The material was characterized by low bulk density, moderate coefficient of thermal expansion (3 × 10⁻⁶/°C to 5 × 10⁻⁶/°C), moderate strength (210 to 324 MPa), and low dielectric constant.     

Morphology and Crystallography of Aluminum Nitride Whiskers

Highly pure and dense AIN whiskers were produced by carbothermal reaction of an alumina and a carbon source at 1800°C under flowing nitrogen. The whiskers grew via a VLS mechanism where there is a strong interaction between the liquid catalyst and the substrate/support, resulting in a complete lack of droplets at the whisker tips. The whiskers can be described as long and straight single crystals, free of planar defects, having a diameter of 2–30 μm and a length of 0.5–10 cm. They exhibited two different morphologies, planar and serrated. SADPs indicate that their lateral surfaces fall in a great circle of a stereographiv projectiov, joining two pyramidal poles such as the ( 1 101)–(10 1 1). It is suggested that branching in these whiskers occurs by keeping active one of the pyramidal planes and activating a new one.     

Polygonal Single-Crystal Aluminum Borate Microtubes

In this paper we report the synthesis of polygonal single-crystal aluminum borate microtubes by the direct calcination of alumina and boron nitride powders in air. The diameters of the obtained tubes vary between 1 and 15 μm; and the lengths are in the range of tens to hundreds of micrometers. The cross-sections of the microtubes are in the shapes of rectangular, hexagonal, and quasi-circle. A new solid–liquid–solid growth mechanism was proposed to account for the formation of microtubes instead of whiskers.     

Formation and Strength of Magnesia Whiskers

The formation of single-crystal magnesia whiskers during the compressive deformation of single crystals at room temperatures is described. These whiskers can have strengths of the order of millions of pounds per square inch. They are formed during fracture as a result of the discontinuous propagation of cracks which are mechanically relieving internal stresses resulting from plastic flow     

Combustion Synthesis of Aluminum Nitride Particles and Whiskers

Aluminum nitride (AlN) was produced via the combustion synthesis of loosely packed aluminum powder (pore fraction of ∼0.8) in a graphite reactor that was lined with permeable carbon felt. Almost-complete conversion was achieved with a forced flow of nitrogen for beds 50-150 mm deep (mass of 200-650 g). The product was in the form of a loosely aggregated bed, with regions of distinct morphology, and had a predominantly whisker morphology. Some control over the microstructure was possible by changing the processing parameters. The addition of 5% of ammonia to the nitrogen resulted in a uniform production of whiskers, whereas a 50% solid-phase dilution with AlN favored the production of particles.     

Influence of Aluminum Titanate Formation on Sintering of Bimodal Size-Distributed Alumina Powder Mixtures

The sintering behavior of green compacts, in which coarse alumina particles formed a skeletal structure and fine alumina and/or fine titania particles filled the voids of the skeletal structure, was investigated. Sinterability of the green compacts changed according to the titania content in the fine powder. The titania content of 33 mol% was the most effective for the densification. The volume expansion due to the aluminum titanate formation occurred in the voids of the skeletal structure, and the densification of the skeletal structure progressed more because the grain growth between the fine and coarse alumina particles did not proceed. As the titania content decreased, the densification did not progress more than that of the compact with 33 mol% titania content because the grain growth proceeded more. As the titania content increased, the expansion of the compacts was larger, and large grains were formed by the reaction between the titania and coarse alumina particles. Therefore, densification became difficult.     

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.     

助熔剂法合成硼酸铝晶须的研究进展

硼酸铝晶须的合成方法,从工艺上大致可以分为气相法、高温熔融法、助熔剂法和液相生长法等。本文较为系统地综述了助熔剂法合成硼酸铝晶须的研究进展,包括其优缺点、合成机理及不同助熔剂和硼源/铝源的合成体系。     

硼酸铝晶须-磷酸铝陶瓷透波材料的制备

以磷酸铝粉末为基体,以硼酸铝晶须为增强体,采用常压烧结工艺制备了硼酸铝晶须/磷酸铝陶瓷透波材料.实验结果表明:硼酸铝晶须对磷酸铝基体的析晶起到了抑制作用和增韧补强作用.硼酸铝晶须含量为30%的样品在1050℃烧结1h后,维氏硬度和抗弯强度分别达到231.8 MPa和215.3 MPa,介电常数和介电损耗分别为4.23、0.023 83(10 GHz)和4.25、0.024 54(15 GHz).     

Formation and Structure of Silicon Carbide Whiskers from Rice Hulls

A study of the distribution of Si in rice hulls was carried out to aid in understanding the observed formation of SIC whiskers by the thermal decomposition and reaction of these natural materials. Scanning electron microscopy, Auger electron spectroscopy, and energy-dispersive X-ray analysis confirm the presence of a major amount of Si in the inner and outer epidermal regions of the rice hull. The Si is present as a hydrated amorphous form of SiO₂ which is evidently bound in the inner layer to organic constituents, placing it adjacent to a source of carbon but interfering with its solubility in HF. The SIC produced by pyrolysis is in the form of ultrafine particles with cubic crystal structure and whiskers exhibiting stacking faults and twins perpendicular to the whisker axis, easily visible by transmission electron microscopy. These whiskers are very similar to ones obtained by chemical vapor deposition with SiO and CO as the primary reactants.     

Mullite Whiskers Grown from Erbia-Doped Aluminum Hydroxide–Silica Gel

Mullite whiskers and anisotropic grains that were derived from erbia-doped aluminum hydroxide–silica gel were studied. Firing 3.0-mol%-erbia-doped isostatically pressed pellets at 1600°C for 1.0–8.0 h resulted in a high surface concentration of mullite whiskers. Their c -axes were aligned preferentially along the pellet surface; the maximum length was 50 μm, and the maximum aspect ratio was 23. The pellet surface was fully covered by mullite whiskers, and small anisotropic grains with a low aspect ratio were observed in the bulk. The voids that were observed in the fracture surfaces were covered fully by mullite whiskers. The large number of voids resulted in an apparent density of 1.60 g/cm³ in the sintered pellets. The molar ratio of alumina to silica in the whiskers was in the range of 1.30–1.45 (an average value of 1.31), regardless of whether the alumina/silica powder compositions were mixed in a 3:2 or 2:1 ratio.     

碳化硅晶须连续生产烧结炉初探

采用卧式电热连续烧结炉生产碳化硅晶须,发热体选用石墨捧,耐火材料选用刚玉砖,保温材料选用高铝砖和粘土砖;在满足工艺要求前提下、炉体断面尺寸尽可能大,矩形断面尺寸宽×高为250×280mm,预热带,烧成带,冷却带长度分别为0.4m,1.6m,2.4m。     

氧化铜为助熔剂制备硼酸铝晶须

利用H3BO3和Al（OH）3为原材料,CuO为助熔剂制备硼酸铝9Al2O3·2B2O3晶须。经研究发现,试样在1350℃煅烧6h,试样的物相为硼酸铝相。以CuO为助熔剂制备的硼酸铝晶须,其直径较均匀为1～5μm,长度为10μm。     

表面活性剂CTAB辅助溶胶-凝胶法制备硼酸铝纳米棒

以仲丁醇铝（aluminum tri-sec-butoxide,ATSB）和硼酸为原料,采用阳离子表面活性剂（cetyltrimethyl ammonium bromide,CTAB）辅助溶胶-凝胶法于120℃形成白色干凝胶,再进行焙烧得到硼酸铝纳米棒。采用X射线衍射仪、扫描电子显微镜、透射电子显微镜、X射线能量色散谱仪和Fourier变换红外光谱仪对产物结构和形貌进行表征。结果表明：750℃焙烧产物为具有单晶结构的A148209纳米棒,,其形貌及直径、长度受ATSB和硼酸摩尔比影响;当ATSB与H38O3摩尔比为1：2时,AhB209纳米棒直径约为15nm,长度为200～300nm。1200℃焙烧的产物为Al18B4O33纳米棒,其直径为200～500nm,长度约为3哪。对硼酸铝纳米棒的形成机理进行了初步探讨。     

Effects of Aluminum and Zirconia Contents on the Sintering of Reaction-Bonded Aluminum Oxide Ceramics

The reaction-bonded aluminum oxide (RBAO) process is an attractive alternative to the conventional processing of Al₂O₃-based ceramics. The most attractive features of the process are the high strengths, densities, and easy machinability of the green powder compacts, and the low shrinkage and high strengths of the sintered ceramics. These advantages result from the presence of aluminum in the green bodies and are enhanced further with increasing aluminum contents. However, it is apparent that ZrO₂-containing RBAO powders with higher aluminum contents (>45 vol%) are increasingly more difficult to densify, as the start of densification is delayed (shifted to higher temperatures) and the densification rates are decreased. Ultimately, this results in a decrease in the limiting density to which the RBAO ceramic may be sintered. In this study, the cooperative effects of ZrO₂ and aluminum contents on the sintering of RBAO ceramics are discussed in terms of densification behavior and microstructural analysis.     

氧化铜为助熔剂制备硼酸铝晶须

利用H3BO3和Al(OH)3为原材料,CuO为助熔剂制备硼酸铝9Al2O3·2B2O3晶须。经研究发现,试样在1350℃煅烧6h,试样的物相为硼酸铝相。以CuO为助熔剂制备的硼酸铝晶须,其直径较均匀为1～5μm,长度为10μm。