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1.
Jingxian Zhang Qiang Xu Mikio Iwasa Feng Ye Dongliang Jiang 《Journal of the American Ceramic Society》2006,89(2):702-705
A new solidifying agent, 4-aminobenzene sulfonic acid (sulfanilic acid), is reported in this paper. The consolidation process and mechanism were followed using on viscoelastic, FTIR, SEM, and Hg porosimetry measurements. It was shown that the Al2 O3 slurries with PAA-Na as dispersant exhibited a high degree of particle stabilization. After the addition of sulfanilic acid, we observed an exponential increase in the storage modulus ( G ') as a function of consolidation time. Correspondingly, Al2 O3 slurries exhibited a transition from a viscous to an elastic state (in 62 min). FTIR analysis indicated that the consolidation process might follow two steps: first, the adsorption of sulfanilic acid on the Al2 O3 particle surface; second, the acid–base interaction between the adsorbed PAA-Na molecules and the sulfanilic acid molecules. This interaction could possibly induce the formation of three-dimensional networks through a bridging or charge neutralization mechanism. The as-consolidated Al2 O3 green samples were homogeneous, with the relative green density being 54.69%. Results showed that it was feasible to introduce sulfanilic acid for the consolidation of Al2 O3 slurries in aqueous media. 相似文献
2.
Kathy Lu Chris S. Kessler Richey M. Davis 《Journal of the American Ceramic Society》2006,89(8):2459-2465
Poly(acrylic acid) (PAA) dispersant concentration, suspension pH, and Al2 O3 solids loading effects on PAA adsorption onto Al2 O3 nanoparticles were studied; the stability and rheology of the Al2 O3 nanoparticle suspensions were examined. The most desirable suspension conditions were 7.5–9.5 for pH and 2.00–2.25 wt% of Al2 O3 for the PAA concentration. Electrical double-layer thickness and PAA adsorption layer thickness comparison showed that electrosteric stabilization was dominant. 45.0 vol% Al2 O3 solids loading can be achieved for freeze casting. The maximum solids loading was predicted to be 50.7 vol%. The freeze-cast sample showed that pre-rest before freezing was critical for achieving desirable microstructures. 相似文献
3.
Jingxian Zhang Mikio Iwasa Dongliang Jiang 《Journal of the American Ceramic Society》2005,88(4):1013-1016
It has been well accepted that polyethylene imine (PEI) is an effective dispersant for silicon carbide (SiC) in aqueous media. However, after the addition of sintering additives (Al2 O3 and Y2 O3 ), this dispersing effect is reduced significantly. In this work, a second dispersant, citric acid, was used to resolve this problem. It was found that citric acid could decrease the slurry viscosity (without sintering additives) and enhance the PEI adsorption on SiC particle surface. The optimal amount of citric acid required to achieve a minimum viscosity for 55 vol% SiC suspensions was equal to ∼0.87 wt% (at pH ∼6.8). With the aid of citric acid, well-stabilized SiC suspensions (containing sintering additives) were realized, which exhibited slight shear thinning rheologies. After tape casting and SPS sintering, dense SiC samples were obtained with a homogeneous fine-crystalline microstructure. Results showed that citric acid was an effective dispersant for improving the dispersion of SiC particles containing sintering additives. 相似文献
4.
YiHua Sun WeiHao Xiong ChenHui Li Lu Yuan 《Journal of the American Ceramic Society》2009,92(9):2168-2171
The rheological behavior of concentrated ZnO–Al2 O3 aqueous suspensions has been studied in order to obtain an ultrahigh-density ZnO–Al2 O3 composite ceramic target by slip casting. The influence of the mass fraction of polyacrylic acid (PAA) on the fluidity of slurries and the density and strength of the green and sintered bodies was investigated. The slurries exhibited a near-Newtonian flow behavior and had a lower viscosity with 0.3 wt% PAA. The excess of PAA enhanced the green strength and the density and strength of the sintered bodies. An ultrahigh density sintered body (>99.7% theoretical density) could be obtained after pressureless sintering at 1400°C. The Al species were well distributed in the sintered bodies, which showed a homogeneous, defect-free microstructure with no abnormal grain growth. 相似文献
5.
The fracture toughness of 3 mol% Y2 O3 -ZrO2 (3Y-PSZ) composites containing 10–30 vol% Al2 O3 with different particle sizes was investigated. It was found that Al2 O3 dispersion of up to 30 vol% increased the fracture toughness by 17% to 30%, and the toughness increase was more remarkable in the composite dispersed with Al2 O3 particles of larger sizes. By combining the effects of the dispersion toughening and phase transformation toughening, the toughness change in the present materials was theoretically predicted, which was in good agreement with the experimental data. 相似文献
6.
The optimization of concentrated Si3 N4 powder aqueous slurry properties to achieve high packing density slipcast compacts and subsequent high sintered densities was investigated. The influence of pH, sintering aid powder (6% Y2 O3 , 4% Al2 O3 ), NH4 PA dispersant, and Si3 N4 oxidative thermal treatment was determined for 32 vol% Si3 N4 slurries. The results were then utilized to optimize the dispersion properties of 43 vol% solids Si3 N4 -sintering aid slurries. Calcination of the Si3 N4 powder was observed to result in significantly greater adsorption of NH4 PA dispersant and effectively reduced the viscosity of the 32 vol% slurries. Lower viscosities of the optimized dispersion 43 vol% Si3 N4 -sintering aid slurries resulted in higher slipcast packing density compacts with smaller pore sizes and pore volumes, and corresponding higher sintered densities. 相似文献
7.
Jian-Feng Yang Guo-Jun Zhang Naoki Kondo Tatsuki Ohji Shuzo Kanzaki 《Journal of the American Ceramic Society》2005,88(4):1030-1032
Porous Si3 N4 ceramics were synthesized by pressureless sintering of green compacts prepared using slip casting of slurries containing Si3 N4 , 5 wt% Y2 O3 +2 wt% Al2 O3 , and 0–60% organic whiskers composed of phenol–formaldehyde resin with solids loading up to 60 wt%. Rheological properties of slurries were optimized to achieve a high degree of dispersion with a high solid-volume fraction. Samples were heated at 800°C in air and sintered at 1850°C in a N2 atmosphere. Porosities ranging from 0% to 45% were obtained by the whisker contents (corresponding to 0–60 vol% whisker). Samples exhibited a uniform pore distribution. Their rod-shaped pore morphology originated from burnout of whiskers, and an extremely dense Si3 N4 matrix. 相似文献
8.
Philippe Boch Thierry Chartier Muriel Huttepain 《Journal of the American Ceramic Society》1986,69(8):191-C
Fracture toughness of ZrO2 -toughened alumina could he increased by macroscopic interfaces, such as those existing in laminated composites. In this work, tape casting was used to produce A/A or A/B laminates, where A and B can be Al2 O3 , Al2 O3 /5 vol% ZrO2 , and Al2 O3 /l0 vol% ZrO2 . An increase of toughness is observed, even in the Al2 O3 /Al2 O3 laminates. 相似文献
9.
The composite sol—gel (CSG) technology has been utilized to process SiC—Al2 O3 ceramic/ceramic particulate reinforced composites with a high content of SiC (up to 50 vol%). Alumina sol, resulting from hydrolysis of aluminum isopropoxide, has been utilized as a dispersant and sintering additive. Microstructures of the composites (investigated using TEM) show the sol-originating phase present at grain boundaries, in particular at triple junctions, irrespective of the type of grain (i.e., SiC or Al2 O3 ). It is hypothesized that the alumina film originating from the alumina sol reacts with SiO2 film on the surface of SiC grains to form mullite or alumina-rich mullite-glass mixed phase. Effectively, SiC particles interconnect through this phase, facilitating formation of a dense body even at very high SiC content. Comparative sinterability studies were performed on similar SiC—Al2 O3 compositions free of alumina sol. It appears that in these systems the large fraction of directly contacting SiC—SiC grains prevents full densification of the composite. The microhardness of SiC—Al2 O3 sol—gel composites has been measured as a function of the content of SiC and sintering temperature. The highest microhardness of 22.9 GPa has been obtained for the composition 50 vol% SiC—50 vol% Al2 O3 , sintered at 1850°C. 相似文献
10.
Hae-Won Kim Young-Hag Koh Hyoun-Ee Kim 《Journal of the American Ceramic Society》2000,83(11):2863-2865
The densification behavior and mechanical properties of B4 C hot-pressed at 2000°C for 1 h with additions of Al2 O3 up to 10 vol% were investigated. Sinterability was greatly improved by the addition of a small amount of Al2 O3 . The improvement was attributed to the enhanced mobility of elements through the Al2 O3 near the melting temperature or a reaction product formed at the grain boundaries. As a result of this improvement in the density, mechanical properties, such as hardness, elastic modulus, strength, and fracture toughness, increased remarkably. However, when the amount of Al2 O3 exceeded 5 vol%, the level of improvement in the mechanical properties, except for fracture toughness, was reduced presumably because of the high thermal mismatch between B4 C and Al2 O3 . 相似文献
11.
Ken-ichi Tajima † Hae Jin Hwang Mutsuo Sando Koichi Niihara 《Journal of the American Ceramic Society》2000,83(3):651-653
Hard lead zirconate titanate (PZT) and PZT/Al2 O3 composites were prepared and the alternating-electric-field-induced crack growth behavior of a precrack above the coercive field was evaluated via optical and scanning electron microscopy. The crack extension in the 1.0 vol% Al2 O3 composite was significantly smaller than that in monolithic PZT and the 0.5 vol% Al2 O3 composite. Secondary-phase Al2 O3 dispersoids were found both at grain boundaries and within grains in the composites. A large number of dispersoids were observed at the grain boundaries in the 1.0 vol% Al2 O3 composite. It appears that the Al2 O3 dispersoids reinforce the grain boundaries of the PZT matrix as well as act as effective pins against microcrack propagation. 相似文献
12.
Activity–composition relations of FeCr2 O4 –FeAl2 O4 and MnCr2 O4 –MnAl2 O4 solid solutions were derived from activity–composition relations of Cr2 O3 –Al2 O3 solid solutions and directions of conjugation lines between coexisting spinel and sesquioxide phases in the systems FeO–Cr2 O3 –Al2 O3 and MnO–Cr2 O3 –Al2 O3 . Moderate positive deviations from ideality were observed. 相似文献
13.
Yoshikazu Suzuki Masahiro Tsukatsune Susumu Yoshikawa Peter E. D. Morgan 《Journal of the American Ceramic Society》2005,88(11):3283-3286
Porous Al2 O3 /20 vol% LaPO4 and Al2 O3 /20 vol% CePO4 composites with very narrow pore-size distribution at around 200 nm have been successfully synthesized by reactive sintering at 1100°C for 2 h from RE2 (CO3 )3 · x H2 O (RE = La or Ce), Al(H2 PO4 )3 and Al2 O3 with LiF additive. Similar to the previously reported UPC-3Ds (uniformly porous composites with a three-dimensional network structure, e.g. CaZrO3 /MgO system), decomposed gases in the starting materials formed a homogeneous open porous structure with a porosity of ∼40%. X-ray diffraction, 31 P magic-angle spinning nuclear magnetic resonance, scanning electron microscopy, and mercury porosimetry revealed the structure of the porous composites. 相似文献
14.
Ziqi Sun Xinwen Zhu Meishuan Li Yanchun Zhou Yoshio Sakka 《Journal of the American Ceramic Society》2009,92(1):54-61
The dispersion of aqueous γ-Y2 Si2 O7 suspensions, which contain only one component but have a complex ion environment, was studied by the introduction of two different polymer dispersants, polyethylenimine (PEI) and polyacrylic acid (PAA). The suspension without any dispersant remains stable in the pH range of 9–11.5 because of electrostatic repulsion, while it is flocculated upon stirring due to the readsorption of hydrolyzed ions on the colloid surface. However, suspensions with 1 dwb% PEI exhibit greater stability in the pH range of 4–11.5. The addition of PEI shifts the isoelectric point (IEP) of the suspensions from pH 5.8 to 10.8. Near the IEP (pHIEP =10.8), the stability of the suspensions with PEI is dominated by the steric effect. When the pH is decreased to acid direction, the stabilization mechanism is changed from steric hindrance to an electrosteric effect little by little. PAA also has the effect of reducing the hydrolysis speed via a "buffer effect" in the basic pH range, but the lack of adsorption between the highly ionized anionic polymer molecules and the negative colloid particle surfaces shows no positive effect on hydrolysis of colloids and on the stabilization of Y2 Si2 O7 suspensions. 相似文献
15.
Chunfeng Hu Yanchun Zhou Yiwang Bao Detian Wan 《Journal of the American Ceramic Society》2006,89(11):3456-3461
Tribological properties of Ti3 SiC2 and Al2 O3 -reinforced Ti3 SiC2 composites (10 and 20 vol% Al2 O3 ) were investigated by using an AISI-52100 bearing steel ball dryly sliding on a linear reciprocating athletic specimen. The friction coefficients were found varying only in a range of 0.1 under the applied loads (2.5, 5, and 10 N), and the wear rates of the composites decreased with increasing Al2 O3 content. The enhanced wear resistance is mainly attributed to the hard Al2 O3 particles nail the surrounding soft matrix and decentrale the shear stresses under the sliding ball to reduce the wear losses. 相似文献
16.
Hyun M. Jang Jong H. Moon Cheol W. Jang 《Journal of the American Ceramic Society》1992,75(12):3369-3376
Al2 O3 –ZrO2 –SiC whisker composites were prepared by surface-induced coating of the precursor for the ZrO2 phase on the kinetically stable colloid particles of Al2 O3 and SiC whisker. The fabricated composites were characterized by a uniform spatial distribution of ZrO2 and SiC whisker phases throughout the Al2 O3 matrix. The fracture toughness values of the Al2 O3 –15 vol% ZrO2 –20 vol% SiC whisker composites (∼12 MPa.m1/2 ) are substantially greater than those of comparable Al2 O3 –SiC whisker composites, indicating that both the toughening resulting from the process zone mechanism and that caused by the reinforced SiC whiskers work simultaneously in hot-pressed composites. 相似文献
17.
Yu Jia Yuji Hotta Kimiyasu Sato Koji Watari 《Journal of the American Ceramic Society》2006,89(3):1103-1106
ZrO2 –Al2 O3 nanocomposite particles were synthesized by coating nano-ZrO2 particles on the surface of Al2 O3 particles via the layer-by-layer (LBL) method. Polyacrylic acid (PAA) adsorption successfully modified the Al2 O3 surface charge. Multilayer coating was successfully implemented, which was characterized by ξ potential, particle size. X-ray diffraction patterns showed that the content of ZrO2 in the final powders could be well controlled by the LBL method. The powders coated with three layers of nano-ZrO2 particles, which contained about 12 wt% ZrO2 , were compacted by dry press and cold isostatically pressed methods. After sintering the compact at 1450°C for 2 h under atmosphere, a sintered body with a low pore microstructure was obtained. Scanning electron microscopy micrographs of the sintered body indicated that ZrO2 was well dispersed in the Al2 O3 matrix. 相似文献
18.
Naoki Omura Yuji Hotta Kimiyasu Sato Yoshiaki Kinemuchi Shoichi Kume Koji Watari 《Journal of the American Ceramic Society》2006,89(9):2738-2743
A wet jet milling process was used as a novel method to prepare Al2 O3 slurries. The wet jet-milled slurries showed very low viscosity compared with the ball-milled slurries. Moreover, the viscosity of the wet jet-milled slurries was constant for long times, whereas that of the ball-milled slurries increased rapidly with time. Al2 O3 particles after wet jet milling retained initial surface conditions, although Al2 O3 particles after ball milling yielded more OH groups on the surface. Casting rate was sensitive to the solid content and preparation method of slurry. The relative density of the green bodies prepared from the wet jet-milled slurries was about 65% or more and was independent of the slurry solid content. On the other hand, the relative density of the green bodies prepared from the ball-milled slurries increased with increasing solid content and was higher than 60% at the solid content of 50% by volume. Linear shrinkage of the sintered bodies prepared from the wet jet-milled slurries was very low and independent of the solid content of the slurry whereas that of the sintered bodies prepared from the ball-milled slurries increased with decreasing solid content. 相似文献
19.
Preparation and Microstructure of Multi-Wall Carbon Nanotubes-Toughened Al2 O3 Composite 总被引:1,自引:0,他引:1
Jinpeng Fan Daqing Zhao Minsheng Wu Zening Xu Jun Song 《Journal of the American Ceramic Society》2006,89(2):750-753
With multi-wall carbon nanotubes (MWNTs) as reinforcement, a 12 vol% MWNTs/alumina (Al2 O3 ) ceramic composite was obtained by hot pressing. A fracture toughness of 5.55±0.26 MPa·m1/2 , 1.8 times that of pure Al2 O3 ceramics, was achieved. Experimental results showed that the enveloping of carbon nanotubes (CNTs) with sodium dodecyl sulfate (SDS) is effective in changing the hydrophobicity of CNTs to hydrophilicity and improving the dispersion of CNTs in aqueous solution. Enveloped with SDS, CNTs can be homogeneously mixed with Al2 O3 at a microscopic level by heterocoagulation. This mixing method can obviously improve the chemical compatibility between CNTs and Al2 O3 , which is important for enhancement of interfacial strength between them. 相似文献
20.
Osamu Yamaguchi Daijo Tomihisa Tatsuji Uegaki Kiyoshi Shimizu 《Journal of the American Ceramic Society》1987,70(11):335-C
In the system Ta2 O3 -Al2 O5 solid solutions of metastable δ-Ta2 O5 (hexagonal) are formed up to 50 mol% Al2 O3 from amorphous materials prepared by the simultaneous hydrolysis of tantalum and aluminum alkoxides. The values of the lattice parameters decrease linearly with increasing Al2 O3 , content. The to β-Ta2 O5 (orthorhombic, low-temperature form) transformation occurs at ∼950°C. The solid solution containing 50 mol% Al2 O3 transforms at 1040° to 1100°C to orthorhombic TaAlO4 . Orthorhombic TaAlO4 contains octahedral TaO6 groups in the structure. 相似文献