Tape Casting of Fine Alumina/Zirconia Powders for Composite Fabrication

Ceramic films, containing AI₂O₃, with up to 40 vol% ZrO₂, have been fabricated using the tape casting process. Finer powders (average mean diameter of 250–300 nm) than have generally been reported for tape casting were used in this study. The optimum formulation for tape casting is affected substantially by decreasing particle size. For example, the amount of dispersant needed is increased. Moreover, the amount of plasticizer/binder must be increased so as to maintain the solids content in the dried tapes below a critical level (about 55 vol% in this case), which decreases with particle size. Rheological studies on the effectiveness of menhaden fish oil and phosphate ester as dispersants show that phosphate ester can be used in lower concentrations, for the preparation of higher solids loading slurries, and was therefore selected for further study. The amount of dispersant required to obtain minimum slurry viscosity was found to be primarily dependent upon the effective particle surface area, defined as that available to the dispersant molecules. In the case of particles composed of agglomerated crystallites (such as the ZrO₂, powder used here), this may be considerably less than that measured by nitrogen absorption. Moreover, the porous internal structure of such powders is filled with solvent, which increases the effective solids loading of the slurry, and thus its viscosity. Particle morphology also influences the packing efficiency; i.e., the green density decreases as ZrO₂, is added.     

微晶刚玉瓷的生产

材料主晶相的细微化是提高材料性能的有效途径.在相关理论的指导下,笔者结合科研实验和长期的生产实践,总结出一些制备微晶刚玉瓷的经验,以适应微晶瓷产业化的客观实际需要.     

Preparation of Fine Alumina Powder in Alcohol

The preparation of fine alumina powder from alcoholic solutions of the metal alkoxide is described. The water for the hydrolysis reaction is generated in situ as a result of dehydration of the solvent at elevated temperature in an autoclave. The amount of water generated can be controlled according to the time temperature schedule employed. Control over the amount of water formed provides a means of controlling certain physical properties of the products, e. g., crystal structure and surface area.     

Fabrication of Macroporous Alumina with Tailored Porosity

Macroporous alumina materials were fabricated via colloidal processing using polymer spheres as the template and ceramic particles as the building blocks. The influence of the suspension conditions and volume ratio of the polymer/ceramic particles on the formation of the pore structure has been investigated. The results showed that the suspension conditions have a significant effect on the pore morphology. A well-defined three-dimensional, ordered porous structure with a controllable pore size and porosity could be obtained through the hetero-coagulation, self-assembled processing of the polymer/ceramic particles. The pore size and porosity could be easily tailored by varying the polymer size and the volume ratio of the polymer/ceramic particles.     

Fabrication of Textured Alumina by High-Temperature Deformation

Texture formation via high-temperature deformation in sintered alumina was investigated. Fine-grained, normal-purity-alumina sintered bodies deformed under stresses up to 80 MPa in a temperature range of 1200°–1300°C. Fine, disklike grains formed in the equiaxial fine-grained matrix during high-temperature deformation and aligned unidirectionally via material flow during deformation. Highly textured sintered alumina bodies were obtained via high-temperature deformation and further annealing.     

Al2O3纳米线薄膜的制备及其生成机理研究

研究了一种简单新颖的制备Al2O3纳米线薄膜的电化学方法。以阳极氧化法在高纯铝片表面制备多孔阳极氧化铝的工艺为基础,在草酸电解液中通过一次阳极氧化过程,将阳极氧化铝孔壁溶解形成Al2O3纳米线,均匀覆盖在阳极氧化铝有序孔道的上方,得到一种特殊结构的纳米线薄膜。使用扫描电镜、高分辨透射电镜和X-射线能谱仪对纳米线的形貌、结构及成分进行了表征分析。并结合扫描电镜对不同反应时间长度的产物形貌来观察纳米线的生成过程。探讨了Al2O3纳米线薄膜的生成机理。     

Fabrication of Porous Anodic Alumina with Ultrasmall Nanopores

Anodization of Al foil under low voltages of 1–10 V was conducted to obtain porous anodic aluminas (PAAs) with ultrasmall nanopores. Regular nanopore arrays with pore diameter 6–10 nm were realized in four different electrolytes under 0–30°C according to the AFM, FESEM, TEM images and current evolution curves. It is found that the pore diameter and interpore distance, as well as the barrier layer thickness, are not sensitive to the applied potentials and electrolytes, which is totally different from the rules of general PAA fabrication. The brand-new formation mechanism has been revealed by the AFM study on the samples anodized for very short durations of 2–60 s. It is discovered for the first time that the regular nanoparticles come into being under 1–10 V at the beginning of the anodization and then serve as a template layer dominating the formation of ultrasmall nanopores. Under higher potentials from 10 to 40 V, the surface nanoparticles will be less and less and nanopores transform into general PAAs.     

透明氧化铝陶瓷制备的研究进展

氧化铝陶瓷是第一个实现透明化的先进陶瓷材料,拓展了先进陶瓷材料的研究和应用领域;并作为高强度气体放电灯的关键部件一电弧管而获得实际应用.近半个世纪以来,人们在提高透过率的理论研究和优化制备工艺方面取得了众多成果.本文论述了影响透明氧化铝陶瓷透光性的各种因素,并且从氧化铝粉体、烧结助剂的选择及作用和烧结工艺等三方面综述了近年来国内外关于氧化铝陶瓷研究的工作与进展,对氧化铝透明陶瓷的制备进行了较为系统的综述,最后展望了透明氧化铝陶瓷的发展趋势.     

硅酸铝陶瓷纤维过滤管的制备与表征

本文研究制备陶瓷纤维过滤管所用硅酸铝纤维、硅溶胶和水之间的最佳配比及最佳成型工艺参数。并对陶瓷纤维过滤管的气孔率、孔径以及抗弯强度进行测试,运用SEM对试样进行微观分析。研究确定的最佳配比是硅溶胶含量为68wt%,硅酸铝纤维含量为12wt%,水含量为20wt%,真空抽滤成型时最佳抽滤压力为0.08MPa,最佳抽滤时间为5min。     

Fiber Strength After Grain Growth in Nextel™ 610 Alumina Fiber

Nextel^? 610 alumina fiber tows were heat‐treated at 1100°C–1500°C for 1 to 100 h in air. Tensile strengths and Weibull moduli were measured for 30 filaments after each heat‐treatment. 3‐D grain size and orientation distributions were described using oblate ellipsoids. The number of grains in a 1 inch gauge length and grains with the largest major and minor ellipsoid‐axes were determined from these distributions. The grain with the largest K_EFF for mixed‐mode fracture was also determined, using the maximum energy release rate criteria from grain‐size and orientation distributions. Grain‐size dependence of tensile strength and Weibull modulus was evaluated. Strength had no obvious dependence on grain size for fibers with average major‐axes smaller than 0.25 μm. For fibers with larger grains, grain‐size dependence may involve flaws originating from clumps of grains, rather than a single grain. Possible relationships between strength and grain‐size and other causes of strength degradation after heat‐treatment are discussed.     

氧化铝纤维对多孔陶瓷载体性能的影响

通过添加适量的塑性剂和造孔剂,采用挤压成型的方式制成了氧化铝纤维增强多孔陶瓷.探讨了不同烧结温度和不同纤维含量对于多孔陶瓷性能的影响.随着烧结温度的提高和纤维含量的增加,样品的线收缩率不断减小,而气孔率和抗折强度先增加后减小.在900℃烧结后,纤维含量4％时,材料最大抗折强度最高并达到4.19Mpa,比基体材料提高了35％.氧化铝纤维的加入有效地解决了多孔陶瓷开裂的问题.     

多晶氧化铝纤维对莫来石—氧化锆陶瓷材料的增强研究

以电熔莫来石、半稳定氧化锆和α-氧化铝微粉为主要原料,制备莫来石—氧化锆陶瓷材料。在材料中分别外加了（V%）0、5%、10%、15%和20%的多晶氧化铝纤维,并将试样在1500℃保温3h烧成,制备出氧化铝纤维增韧的莫来石—氧化锆复相陶瓷。研究了氧化铝纤维对试样的加热线收缩率、常温耐压强度、常温抗折强度和热震稳定性的影响。结果表明：加入适量的多晶氧化铝纤维能够显著降低莫来石—氧化锆复相陶瓷的加热线收缩率,大幅度提高其常温抗折强度和热震稳定性,而常温耐压强度只有轻微下降。     

氧化铝质陶瓷纤维的制备方法与应用

随着耐火材料的不断发展，新型功能材料在不断的研究应用。氧化铝纤维制品以其高强度、高模量、耐高温、抗氧化性、耐腐蚀性和电绝缘性等多功能特性，在高温、环保及航空航天领域的应用研究备受关注。本文简单介绍了氧化铝纤维的现有制备方法及在各领域的应用。     

氧化铝纤维/红柱石复合材料的制备与性能

笔者针对红柱石和氧化铝纤维广泛的应用前景，通过两者的复合来提高红柱石制品的使用性能，采用传统无压烧结工艺制备氧化铝纤维增强红柱石基复合材料。探讨了红柱石细粉的粒度、氧化铝纤维的加入量和烧成温度对氧化铝纤维增强红柱石基复合材料物理性能以及常温力学性能的影响。结果表明：随着红柱石细粉粒度的降低，氧化铝纤维团聚现象加剧，由于纤维与基质的界面结合力较强，原料粒度的变化对材料常温力学性能影响不大；当氧化铝纤维加入量为5％。10％时，材料的体积密度最大，常温耐压强度和抗折强度最好，超过10％后由于纤维的团聚，材，料的力学性能显著下降；当烧成温度超过1400℃后纤维与基体开始反应，随着烧成温度的进一步提高，纤维遭到破坏的程度加剧。     

甩丝法制备多晶氧化铝纤维

使用溶胶-凝胶法制备氧化铝质量分数为80%的多晶氧化铝纤维。以结晶氯化铝、铝粉和硅溶胶为主要原料制备出不同粘度的胶体,采用甩丝法制备纤维。研究了胶体粘度、甩丝盘转速对纤维直径和拉伸强度影响。并对热处理过程中升温制度对纤维拉伸强度的影响进行了研究。结果表明：当胶体粘度为20,Pa·s、甩丝盘转速为6,000,r/min、升温速度为240,℃/h时得到的纤维拉伸强度较高,该纤维经1,200,℃烧成后,平均单丝拉伸强度超过1,100,MPa,是一种性能较优异的氧化铝纤维。     

氧化铝纤维发展现状及应用前景

详细介绍了氧化铝纤维的制取工艺、生产现状、技术进展及应用前景。氧化铝纤维是新型的高性能无机陶瓷纤维,与碳纤维、碳化硅纤维等非氧化物纤维相比,不仅具有高强度、高模量、耐高温等优良性能,还有很好的高温抗氧化性、耐腐蚀性和电绝缘性,且表面活性好,易与树脂、金属、陶瓷等基体复合,形成诸多性能优异的复合材料;在工业高温炉窑、航空航天、交通运输及高新科技领域中,氧化铝纤维都有广泛的应用。并对国内今后氧化铝纤维的发展提出了一些建议。     

多层低温流延法制备片状氧化铝多孔陶瓷

为了避免金属/陶瓷复合散热片两相共烧,并减小因两相热膨胀系数不同而造成在使用过程中的开裂失效问题,采用水基Al2O3陶瓷浆料在低温下进行多层流延,经定向冷冻、低温干燥及烧结工艺,制备出具有小孔径、直通孔结构的片状Al2O3多孔陶瓷.研究了浆料固体含量和冷冻温度对多孔陶瓷片孔隙率和孔尺寸的影响,观察了孔的微观形貌并测试了其热疲劳性能.结果表明:随着浆料固体含量从30％(质量分数)增加到40％,多孔陶瓷片的孔隙率(体积分数)从62.1％减小至51.4％,随着冷冻温度从-15℃降低至-45℃,多孔陶瓷片孔道尺寸逐渐减小;固体含量为40％、冷冻温度为-45℃的多孔陶瓷片在热疲劳实验中裂纹出现最晚,达到695次,其热疲劳性能最好;多层低温流延法制备的多孔陶瓷片层间孔道相互连通.     

Fabrication and Sintering of Fine Yttria-Doped Ceria Powder

Yttria–doped ceria powder was prepared from oxalate precursors. The oxalate coprecipitation bath parameters were closely monitored and found to influence the sintering behavior of the subsequently obtained oxide powders strongly. The use of concentrated (Ce,Y) metal nitrate solutions and dilute neutralized oxalic acid for coprecipitation were identified as the most–important parameters. Following calcination at 700°C, compacts of such powders were sintered to high density (98%) at 1400°C (4 h). Ball milling of the powder further reduced the sintering temperature. Dry milling, for tape–casting applications of the powder in particular, was more effective than wet milling. Tape–cast membranes were fired at 1400°C (2 h), with resulting densities of 98%.     

Fabrication of Graded Nickel–Alumina Composites with a Thermal-Behavior-Matching Process

Composites of nickel and Al₂O₃ with compositionally graded microstructures were fabricated from powders through an empirically determined thermal-behavior-matching process that was designed to minimize processing-induced stresses. Compositions ranged from pure Al₂O₃ to pure nickel. Specimen geometries included round disks 25 mm in diameter and 5–25 mm thick, as well as rectangular bars 25 mm × 25 mm in cross section and 75 mm long. Several different gradients were produced, including samples with single interlayers. Compacts were formed by cold uniaxial pressing in a die, followed by consolidation through sintering at 1 atm or hot isostatic pressing. Several different particle sizes of nickel and Al₂O₃ comprised the composite interlayers. The compaction behavior, sintering start temperature, sintering rate, and total linear shrinkage of each composition were evaluated. Careful data analysis, coupled with sintering theory, led to a layer configuration with matched green density and sintering behavior. Thermomechanically matched layers allowed large, crack-free, graded composites to be produced.     

High Alumina Fiber Composite SiO_2 Based Nanoporous Insulation Boards

The specimens were prepared with high alumina fiber accounting for 0,5%,10% or 15% by mass of the total amount of amorphous silica and high alumina fiber,using phenolic resin as binder,and extra-adding 0 or 0. 5% ZnO as sunscreen to cut the cost of SiO_2 nanoporous insulation board. The hot volume stability and thermal conductivity(flat plate method) of the specimens were tested and multi-function simulation equipment was used to study the thermal insulation performance. The results show that:(1) with high alumina fiber addition increasing,the linear shrinkage rate decreases,but thermal conductivity changes a little;(2)adding ZnO can decrease thermal conductivity obviously;(3) for the specimen with ZnO and 15% of high alumina fiber,its cold face temperature hardly rises during the simulation experiment at 1 000 ℃ for 2 h,and the cold face temperature of the specimen with the smallest thickness of 2 cm doesn't exceed 180 ℃.