共查询到20条相似文献,搜索用时 15 毫秒
1.
Guo-Jun Zhang Jian-Feng Yang Tatsuki Ohji 《Journal of the American Ceramic Society》2001,84(6):1395-1397
Porous alumina ceramics with unidirectionally aligned continuous pores were fabricated via the slurry coating of fugitive fiber. Cotton thread was coated with ceramic slurry by pulling it through the slurry, and specimens were produced by spooling the coated thread. The obtained porous alumina ceramics had an average pore diameter of 165 μm, 35% open porosity, and a bending strength of 160 MPa. It was suggested that the pore size and the porosity could be adjusted using the diameter of the cotton thread and the solids concentration of the slurry, respectively. 相似文献
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Christopher H. Schilling Robert A. Bellman Rachelle M. Smith Honey Goel Herbert Giesche 《Journal of the American Ceramic Society》1999,82(1):57-66
Aqueous suspensions of submicrometer, 20 vol% Al2 O3 powder exhibited a transition from strongly flocculated, thixotropic behavior to a low-viscosity, Newtonian-like state upon adding small amounts of maltodextrin (0.03 g of maltodextrin/(g of Al2 O3 )). These suspensions could be filter pressed to highly dense (57%) and extrudable pastes only when prepared with maltodextrin. We analyzed the interaction of maltodextrin with Al2 O3 powder surfaces and quantitatively measured the resulting claylike consolidation, rheological, and extrusion behaviors. Benbow extrusion parameters were comparable to, but higher than, those of kaolin at approximately the same packing density of 57 vol%. In contrast, Al2 O3 filter cakes without maltodextrin at 57 vol% density were too stiff to be extruded. Measurements of rheological properties, acoustophoresis, electrophoresis, sorption isotherms, and diffuse reflectance Fourier infrared spectroscopy supported the hypothesis that sorbate-mediated steric hindrance, rather than electrostatic, interparticle repulsion, is important to enhancing the consolidation and fluidity of maltodextrin–Al2 O3 suspensions. Viscosity measurements on aqueous maltodextrin solutions indicated that free maltodextrin in solution does not improve suspension fluidity by decreasing the viscosity of the interparticle solution. 相似文献
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多孔氧化铝陶瓷具有耐高温、低热导率等特点,是工业窑炉的隔热保温的首选材料.实验以α-Al2 O3、煅烧铝矾土、苏州土为主要原料,采用物理发泡和注浆成型结合的方法制备了具有高气孔率、低热导率的多孔氧化铝陶瓷样品.通过正交实验确定了发泡剂的最佳配方为SDS添加量为0.5 g·L-1、CTAB添加量为0.3 g·L-1及水质量分数为50wt%.并探究了烧成温度对多孔氧化铝陶瓷样品的物理性能、相组成、热导率的影响,结果表明,经1500℃烧成后的最佳配方样品吸水率为13.71%,气孔率为33.14%,体积密度为2.42 g·cm-3,在300℃下测得热导率为0.83 W·m-1·K-1.本实验制备的多孔氧化铝陶瓷样品的相组成为莫来石和刚玉,由于具有大量的气孔,相同能量下气体激发出的声子数量远少于固体,热导率远远低于固体,导致热导率低. 相似文献
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以PAA-NH4与阿拉伯树胶为分散剂,采用有机泡沫浸渍和凝胶注模工艺制备了不同气孔率的氧化铝陶瓷。探讨了工艺参数对坯体的干燥和烧结状况的影响,以及有机泡沫的压缩比对多孔陶瓷的气孔率的影响。结果表明,坯体干燥最佳的升温速率为0.5℃/min;坯体的排胶温度为200~600℃.此时升温速率为0.5℃/min。大于600℃时.升温速率为10℃/min左右;可以根据有机泡沫的压缩比例,设计多孔陶瓷的气孔率的大小。 相似文献
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Effect of Powder Surface Chemistry on the Stability of Concentrated Aqueous Dispersions of Alumina 总被引:2,自引:0,他引:2
The surface chemistry differences between two alumina powders is shown to have a significant effect on the properties of concentrated aqueous dispersions of the powders. The initial dispersion pH and magnitude and sign of the initial mobility of the particles (determined by acoustophoresis) are different for the two powders because of differences in surface impurity contents. As a result, the two powders require different amounts of dispersant to achieve stability in dispersions near their isoelectric points. The surface chemistry differences between these two aluminas illustrate the importance of examining ceramic dispersion properties at the concentrations used in processing the material. 相似文献
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The dispersion of nitride and carbide ceramic particles in water is difficult, due to the absence of hydroxyl groups on their surface. Boron nitride (BN) is not an exception and despite its numerous applications, no effective dispersant has been identified so far. We demonstrate here the dispersion properties of two cellulose derivatives for hexagonal BN powders, hydroxyl ethyl cellulose and methyl cellulose. The effect of particle size and cellulose concentration was investigated. The adsorption of cellulose onto the surface of the BN particles was confirmed by isotherm adsorption. Zeta potential measurements show a charge screening effect of the cellulose The suspensions obtained were highly loaded and stable versus pH, and thus could lead to homogeneous codispersion of BN particles and sintering additives. 相似文献
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Adsorption Effects on the Rheological Properties of Aqueous Alumina Suspensions with Polyelectrolyte 总被引:15,自引:0,他引:15
Lu-Cun Guo Yao Zhang Nozomu Uchida Keizo Uematsu 《Journal of the American Ceramic Society》1998,81(3):549-556
The influence of adsorption coverage and free polymer on the rheological properties of aqueous alumina suspensions with polyelectrolyte was studied. The flow curves of the suspensions followed the Casson model very well in the observed range of shear rate. The Casson yield value, τc , was used to evaluate the stability. The coverage exerted a profound influence on the rheological properties by affecting the interaction between particles. The zeta potential increased and the value of τc decreased as the coverage increased. The free polymer could cause weak flocculation as its concentration was increased to a certain level. The opposite effects of the adsorbed polymer and free polymer on stability resulted in the presence of optimum coverage for stabilization. The concentration of free polymer increased rapidly as the adsorption coverage approached the saturation limit, and then the free polymer started to dominate the stability. Stabilization could be achieved at a condition of unsaturated adsorption and was related to the non-high-affinity adsorption at alkaline pH (9.2). The impact of adsorption affinity on stability was discussed. 相似文献
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Effect of Acid Cleaning and Calcination on Rheological Properties of Concentrated Aqueous Suspensions of Silicon Nitride Powder 总被引:2,自引:0,他引:2
Jian-Qing Dai Yong Huang Zhi-Peng Xie Xing-Li Xu Jin-Long Yang 《Journal of the American Ceramic Society》2002,85(2):293-298
The powder characteristics of two types of Si3 N4 (referred to as FD1 and FD2), as well as the rheological properties of their aqueous suspensions, were studied in this paper. There are distinctive differences in size distribution, soluble counterions, and surface groups. Highly concentrated aqueous slurries could not be prepared from these two as-received powders. Acid cleaning and calcination improved the solids loading of their aqueous slurries, but the improvement varied with the powder. For the as-received FD1 powder, poor dispersibility was caused by high-valence counterions, which can be eliminated through acid-cleaning. However, for the as-received FD2 powder, it was the surface group of amine structures and carbon-hydrogen bonding that limited the dispersibility. The calcination of FD2 can remove the amine structure and carbon-hydrogen bonding and improve the slurry's rheological properties almost perfectly. For acid-cleaned and calcined FD1, and calcined FD2, the solids loading of their aqueous suspensions reached 50 vol% with a viscosity below 300 mPa·s. 相似文献
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Beate Balzer Martin K. M. Hruschka Ludwig J. Gauckler 《Journal of the American Ceramic Society》2001,84(8):1733-1739
Electrostatically stabilized alumina suspensions can be destabilized by the enzyme-catalyzed decomposition of urea (direct coagulation casting). Depending on the conditions, this reaction can shift the pH of a suspension to the buffer pH of the reaction products or increase the ionic strength at the buffer pH. The coagulation for both mechanisms was investigated using in situ rheological measurements. Using a vane tool in oscillation mode, the measuring conditions were optimized to find a reasonable method for time-dependent measurements. Constant parameters (stress or strain) proved to be unsuitable, because the linear viscoelastic region shifted considerably during the coagulation. Furthermore, the gel structure produced on coagulation via increase of ionic strength (Δ I ) was very sensitive to the oscillation. Therefore, for long-time experiments, a short continuous measurement with a low strain was followed by amplitude sweeps with increased intervals to determine the linear values of G ' and G ". In this way, the increase of the moduli G ' and G " could be followed for longer times, and it was possible to demonstrate two results. First, the final G ' of the network was about 10 times higher for Δ I -coagulated material than for suspensions coagulated via pH shift (ΔpH). Second, particle rearrangement processes took place in Δ I -coagulated networks even after the chemical changes were finished, whereas ΔpH-coagulated samples were "frozen-in" when approaching the isoelectric point and showed no further physical changes afterward. 相似文献
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Dissolution of BaCO3 and its effect on the dispersion behavior of aqueous BaCO3 suspensions at various pH values have been investigated. The amount of leached Ba2+ decreases with increasing pH value, which agrees with thermodynamically calculated results. The dissolution of BaCO3 also causes an increase in pH value of the suspension, but the change decreases with increasing initial pH value. The isoelectric point (IEP) of leached BaCO3 powder is at a pH of ∼10–10.5 and remains unchanged with increasing solids loading. The IEP of BaCO3 shows no significant change with added KCl or K2 CO3 , but shifts to a higher pH with increasing concentration of added BaCl2 . 相似文献
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Hierarchical Structure of Porous Silicon Nitride Ceramics with Aligned Pore Channels Prepared by Ice‐Templating and Nitridation of Silicon Powder
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A unique hierarchical porous structure of silicon nitride ceramic with 76.5% porosity is fabricated by combining an ice‐templating method and nitridation for a silicon powder. The porous silicon nitride ceramics were composed of a lamellar structure with aligned pore channels and ceramic walls filled with fibrous whiskers. This study is focused on the influences of freezing rate on the microstructures and properties of the silicon nitride ceramics. The properties were characterized by compressive strength and gas permeability, which were shown to vary with controlled microstructure. The compressive strength and the permeability reached up to 32.2 MPa and 0.035?12 m2, respectively. 相似文献
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A technique was developed to pulverize agglomerates in a slurry into primary particles. Pulverization increased the powder packing density of alumina green sheets from 50 to 61 vol%. The sinterability of alumina was also increased. The internal voids in the sintered body were drastically reduced. 相似文献
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球磨助剂对氧化铝粉末细度及90氧化铝陶瓷烧结温度的影响 总被引:1,自引:0,他引:1
本文以十二烷基苯磺酸钠、OP-10和吐温80作为氧化铝粉末中的球磨助剂,探讨了不同球磨助剂及其用量对氧化铝粉末的球磨效率及对90氧化铝陶瓷烧结温度的影响。结果表明,阴离子表面活性剂十二烷基苯磺酸钠的助磨效果最佳,OP-10次之,吐温作用不大。球磨助剂通过分散、润滑、劈裂等作用强化了球磨效果,可缩短球磨时间,并提高了球磨物料的细度,使氧化铝粉体的烧结活性增强。在相同的工艺条件下,加入球磨助剂可使90氧化铝陶瓷的烧结温度降低60℃以上。 相似文献
20.
ihiro Kasuga † ‡ Tatsuya Inoue† Kenji Tsuji† Yoshio Ota† § Yoshihiro Abe † 《Journal of the American Ceramic Society》1995,78(1):245-247
High-strength calcium metaphosphate fibers for biomedical applications are extracted from crystallized products of calcium ultraphosphate glasses by aqueous leaching. In the present work, new types of porous ceramics with a skeleton composed of the crystalline fibers are prepared by heating the fibrous products extracted. The fibers in the ceramic are interlinked to each other by glassy phases formed during the heating. This porous material has a large porosity of >60%. The surface of the skeleton can be successfully converted into new calcium phosphate phases such as apatite by heating the porous material treated with a molten salt mixture of CaCl2 -Ca(NO3 )2 . 相似文献