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1.
Alumina as a Devitrification Inhibitor during Sintering of Borosilicate Glass Powders 总被引:5,自引:0,他引:5
Cristobalite is formed when borosilicate glass (Corning Code 7740) is sintered at temperatures ranging from 700o to 1000o C. The precipitation kinetics, determined by XRD analysis, exhibit a characteristic incubation period which decreases with increasing sintering temperature, from 60-120 min at 700o C to 3-5 min at 1000o C. Activation analysis of precipitation shows an activation energy of 75 kJ/mol, which is close to that for the diffusion of Na+ in borosilicate glass, suggesting mass-transport controlled kinetecs. 1.,5 With added alumina content greater than a critical value, however, the cristobalite formation in the borosilicate glass is completely prevented at the sintering temperatures investigated. The critical alumina content is found to decrease with decreasing alumina particle size but with increasing sintering temperature. The above result, similar to observations previously made in a binary glass mixture containing a low-softening borosilicate glass (BSG) and a high-softening high silica glass (HSG) 3 is attributed to a strong coupling between Al3+ from alumina and Na+ from borosilicate glass. The coupling reaction causes segregation of Na+ in boraosilicate glass to alumina, thus forming a Na+ -and Al3+ -rich reaction layer around alumina particles far too rapid for cristobalite formation. 相似文献
2.
Strengthening of Porous Alumina by Pulse Electric Current Sintering and Nanocomposite Processing 总被引:1,自引:0,他引:1
Sung-Tag Oh Ken-ichi Tajima Motohide Ando Tatsuki Ohji 《Journal of the American Ceramic Society》2000,83(5):1314-1316
Porous Al2 O3 and SiC–dispersed-Al2 O3 (Al2 O3 /SiC) nanocomposites with improved mechanical properties were fabricated using pulse electric current sintering (PECS). Microstructures with fine grains and enhanced neck growth, as well as high fracture strength, could be achieved via PECS of Al2 O3 . The incorporation of fine SiC particles into an Al2 O3 matrix significantly increased the fracture strength of porous Al2 O3 . Based on microstructural observations, it was revealed that the refinement of Al2 O3 grains and neck growth occurred by PECS and nanocomposite processing. 相似文献
3.
D. Doni Jayaseelan N. Kondo D. Amutha Rani S. Ueno T. Ohji S. Kanzaki 《Journal of the American Ceramic Society》2002,85(11):2870-2872
The pulse electric current sintering technique (PECS) was demonstrated to be effective in rapid densification of fine-grained Al2 O3 /3Y-ZrO2 using available commercial powders. The composites attained full densification (>99% of TD) at 1450°C in less than 5 min. The composites sintered at a high heating rate had a fine microstructure. The incorporation of 3 vol% 3Y-ZrO2 substantially increased the average fracture strength and the toughness of alumina to as high as 827 MPa and 6.1 MPa·m1/2 , respectively. A variation in the heating rate during the PECS process influenced grain size, microstructure, and strength, though there was little or no variation in the fracture toughness. 相似文献
4.
Homogeneous Distribution of Sintering Additives in Liquid-Phase Sintered Silicon Carbide 总被引:1,自引:0,他引:1
Eva Lidén Elis Carlstrom Lars Eklund Brita Nyberg Roger Carlsson 《Journal of the American Ceramic Society》1995,78(7):1761-1768
The addition of sintering additives to silicon carbide particles by electrostatic adsorption of colloidal A12 O3 and Y2 O3 sols has been studied as a way to achieve an optimum homogeneity in the microstructure. The adsorption behavior of the sol particles was examined by electrophoretic measurements and X-ray fluorescence analysis. Both A12 O3 and Y2 O3 sols could simultaneously be adsorbed on the SiC particle surfaces. Viscosity measurements showed that the colloidal sol particles had a stabilizing effect on the slip, and hence slips with relatively high solid loadings could be prepared without adding extra dispersing agent. Liquid-phase-sintered silicon carbide materials (LPS-SiC) with 2 wt% A12 O3 and 1 wt% Y2 O3 were prepared by freeze granulation/ pressing and sintering at 1880deg; C for 4 h. The homogeneity of the green compacts was quantified using a spot analysis technique in an electron probe microanalyzer. It was clearly shown that the addition of sols gave a more homogeneous microstructure than the reference sample with Y2 O3 and A12 O3 added as powders. The addition of sintering additives as sols also enhanced the sintering behavior. 相似文献
5.
Yoshinobu Fujishiro Motoyuki Miyata Masanobu Awano Kunihiro Maeda 《Journal of the American Ceramic Society》2004,87(10):1890-1894
Thermoelectric elements consisting of the layered polycrystalline materials of Al-doped ZnO and NaCo2 O4 were prepared using the pulse electric-current sintering (PECS) method at 900°C for 3 min. Direct contact between the polycrystalline Al-doped ZnO and the NaCo2 O4 was obtained in a single-step process for the stacked powders. The electrical conductivities of the polycrystalline materials prepared by PECS were higher than those of materials prepared by conventional sintering, despite their porous structure. The thermoelectric voltage of the 1-mol%-Al-doped ZnO and NaCo2 O4 polycrystalline element (measuring ∼6 mm × 3 mm × 15 mm) was 83 mV at d T = 500 K, when the junction of the elements was at 800°C. 相似文献
6.
Florence Babonneau Gian D. Sorarú Kevin J. Thorne John D. Mackenzie 《Journal of the American Ceramic Society》1991,74(7):1725-1728
Polycarbosilane was modified by reaction with an aluminum alkoxide to get a precursor for Si-Al-C-O ceramics. The precursor was essentially characterized by magic-angle spinning nuclear magnetic resonance (29 Si, 27 Al, and 13 C) and appeared as a dispersion of Al(OH)3 -based particles in a polycarbosilane chain matrix. After the material was heat-treated under argon at 1500°C, X-ray diffraction showed that it crystallized mainly as SiC 2H. The presence of this rather unusual polytype for polycarbosilane-derived ceramics seemed to be related to the presence of aluminum atoms. 相似文献
7.
Takeshi Yagi Kazuo Shinozaki Nobuo Ishizawa Nobuyasu Mizutani Masanori Kato Akihiko Tsuge 《Journal of the American Ceramic Society》1988,71(7):334-C
The thermal diffusivity of AlN ceramics was significantly decreased by the addition of SiO2 . The AlN ceramics with 4 wt% SiO2 could not be densified by pressureless sintering in the temperature range 1400° to 1800°C. The thermal diffusivity of these samples was very low because of their porous structure. The AlN ceramics containing 2, 4, and 8 wt% SiO2 were densified by hot-pressing and also had low thermal diffusivity. In these samples, the grains of the 27R polytype that resulted from the reaction between AlN and SiO2 were dispersed, obstructing the conduction of heat. The relation between the amount of 27R polytype and the thermal diffusivity of the AlN ceramics was determined. 相似文献
8.
J. K. Richard Weber Dennis R. Merkley Collin D. Anderson Paul C. Nordine Chandra S. Ray Delbert E. Day 《Journal of the American Ceramic Society》1993,76(8):2139-2141
Glass formation from melts of 44 CaO 56Ga2 O3 (mol%) was investigated under containerless conditions obtained by acoustically stabilized aerodynamic levitation in combination with laser beam heating. The critical cooling rate for glass formation was Rc <100°C/s, much less than values reported in the literature ( Rc =550o ±120o C/s and ca 350o C/s) for pendant drops of this composition attached to Pt-Rh thermocouples. High values of Rc in pendant drop experiments were confirmed for the specimens used in this work. 相似文献
9.
Influence of Copper(II) Oxide Additions to Zinc Niobate Microwave Ceramics on Sintering Temperature and Dielectric Properties 总被引:6,自引:0,他引:6
Dong-Wan Kim Kyung Hyun Ko Kug Sun Hong 《Journal of the American Ceramic Society》2001,84(6):1286-1290
The effect of CuO additions on the firing temperature of ZnNb2 O6 ceramics was investigated using dilatometry, transmission electron microscopy, and X-ray diffractometry. A 5 wt% CuO addition to ZnNb2 O6 ceramics significantly lowered the firing temperature from 1150° to ∼900°C. The presence of a CuO-rich intergranular phase in the specimen was observed and was evidence of the formation of a liquid phase during sintering. The composition of the liquid phase was (ZnCu2 )Nb2 O8 . In particular, the low-fired ZnNb2 O6 ceramics had good microwave dielectric characteristics— Q × f = 59 500, ɛr = 22.1, τf =–66 ppm/o C. These properties were correlated with the formation of a second phase, (ZnCu2 )Nb2 O8 . 相似文献
10.
Darin A. Ray Sarbjit Kaur Raymond A. Cutler Dinesh K. Shetty 《Journal of the American Ceramic Society》2008,91(7):2163-2169
The densification of silicon carbide (SiC) was studied using a variety of additives (Al, AlN, Al2 O3 , B4 C, C, Si3 N4 , and Y2 O3 ). The onset of densification of SiC with small amounts of additives occurred at temperatures between 1500° and 1900°C with 28 MPa applied pressure. Al, B4 C, and C promoted densification, while N (added as AlN or Si3 N4 ) retarded sintering. A 96.75 wt% SiC–2 wt% Al–1 wt% C–0.25 wt% B4 C starting composition yielded the same percent of theoretical density (in the range of 70%–90% theoretical density) 400°C lower than a 95 wt% SiC–5 wt% AlN material. Yttria additions promoted intergranular fracture, which increased the single-edged precracked beam fracture toughness. The appropriate selection and amount of additives allowed for the tailoring of grain size and intergranular fracture, thus controlling the mechanical properties. While oxygen was present in all materials containing aluminum, the incorporation of additional oxygen as alumina resulted in reduced sintering activity compared with Al metal. Corrosion resistance decreased in both HF and NaOH solutions at 80°C for materials containing a grain boundary phase. 相似文献
11.
Mathias Herrmann Christian Schuber reas Rendtel Heinz Hübner 《Journal of the American Ceramic Society》1998,81(5):1095-1108
The fabrication of dense Si3 N4 /SiC nanocomposite materials that contained 2.5-30 wt% SiC via gas-pressure sintering and hot pressing was investigated. The SiC particles originated from admixed commercial SiC powders, SiCN powders produced by plasma synthesis, in situ reaction pyrolysis of carbon-coated Si3 N4 particles, and pyrolysis of a polycarbosilazane-based SiCN precursor. Based on thermodynamic calculations, criteria for minimum liquid-phase decomposition during sintering were developed. The best sintering results were obtained for sintering cycles that observed this criteria. Materials that contained plasma-synthesized SiCN exhibited high strengths (835-995 MPa) and fracture toughness values (7.4-7.8 MPam1/2 ) at room temperature. Post-sintering thermal treatments led to a strength reduction. 相似文献
12.
Effect of Weight Loss on Liquid-Phase-Sintered Silicon Carbide 总被引:3,自引:0,他引:3
Tor Grande Hkon Sommerset Eirik Hagen Kjell Wiik Mari-Ann Einarsrud 《Journal of the American Ceramic Society》1997,80(4):1047-1052
The evaporation of silicon carbide (SiC) ceramics during sintering has been studied by thermogravimetry in a graphite furnace filled with argon. The SiC powder compacts contained 7.5 wt% eutectic composition of Y2 O3 –Al2 O3 to promote liquid-phase sintering. A weight loss of 1–11 wt% was observed during sintering, depending on the sintering temperature and sintering time. The weight loss severely influenced the final density and the microstructure of the SiC ceramics. Particularly, the oxide sintering aids, which were homogeneously distributed in the green ceramics, were observed to segregate and form particular patterns that were dependent on the temperature, sintering time, and the total weight loss. Possible heterogeneous reactions evolving volatile species have been discussed in relation to the experimental observations. 相似文献
13.
D. Doni Jayaseelan † Shunkichi Ueno Tatsuki Ohji Shuzo Kanzaki 《Journal of the American Ceramic Society》2004,87(1):159-161
Recently, we reported on the retention of fine-grained micro-structure in Al2 O3 /3 vol% 3Y-ZrO2 composites using the pulse electric current sintering (PECS) technique. It was demonstrated that a high heating rate is beneficial for the retention of fine grains and homogeneous microstructure. As there are few reports on microstructural inhomogeneity and excessive grain growth in compacts densified by the PECS technique, we carried out a series of experiments on monolithic alumina by varying the sintering parameters and discussed the characteristic results. All specimens that were densified under selective sintering conditions attained high density (∼99% of the theoretical density) at 1250°3C in > 5 min. The average fracture strength of monolithic alumina was observed to be 741 ± 25 MPa and the fracture toughness was 2.2 MPa.m <1/2 , and these were reasoned out to small grains. However, compacts sintered under very low compaction pressure attained ∼92%-93% of the theoretical density, and these specimens had undesirable microstructural inhomogeneity owing to differential sintering. Hence, in the present study, we address the problem of differential sintering. 相似文献
14.
Amiya S. Sanyal Joydeb Mukerji Siddhartha Bandyopadhyay 《Journal of the American Ceramic Society》1991,74(9):2312-2314
Mössbauer spectra of the products obtained by carbothermal reduction and distribution of silica in the presence of iron in the temperatures range 1200o to 1540o were studied. The preponderance of β- Si3 N4 over the α form at a higher reaction temperature were assumed to be related to the formation of an Fe-Si-N liquid. The liquid did not alter its composition with the variation of reduction-temprature, Iron had no effect on the reaction mechanism below 1300o C. 相似文献
15.
Shiro Torizuka Kaoru Sato Hiroaki Nishio Teruo Kishi 《Journal of the American Ceramic Society》1995,78(6):1606-1610
Compacts of TiB2 with densities approaching 100% are difficult to obtain using pressureless sintering. The addition of SiC was very effective in improving the sinterability of TiB2 . The oxygen content of the raw TiB2 powder used in this research was 1.5 wt%. X-ray photoelectron spectroscopy showed that the powder surface consisted mainly of TiO2 and B2 O3 . Using vacuum sintering at 1700°C under 13–0.013 Pa, TiB2 samples containing 2.5 wt% SiC achieved 96% of their theoretical density, and a density of 99% was achieved by HIPing. TEM observations revealed that SiC reacts to form an amorphous phase. TEM-EELS analysis indicated that the amorphous phase includes Si, O, and Ti, and X-ray diffraction showed the reaction to be TiO2 + SiC → SiO2 + TiC. Therefore, the improved sinterability of TiB2 resulted from the SiO2 liquid phase that was formed during sintering when the raw TiB2 powder had 1.5 wt% oxygen. 相似文献
16.
Jae-Yuk Kim Takayoshi Iseki Toyohiko Yano 《Journal of the American Ceramic Society》1996,79(10):2744-2746
The effect of aluminum and yttrium nitrate additives on the densification of monolithic Si3 N4 and a Si3 N4 /SiC composite by pressureless sintering was compared with that of oxide additives. The surfaces of Si3 N4 particles milled with aluminum and yttrium nitrates, which were added as methanol solutions, were coated with a different layer containing Al and Y from that of Si3 N4 particles milled with oxide additives. Monolithic Si3 N4 could be sintered to 94% of theoretical density (TD) at 1500°C with nitrate additives. The sintering temperature was about 100°C lower than the case with oxide additives. After pressureless sintering at 1750°C for 2 h in N2 , the bulk density of a Si3 N4 /20 wt% SiC composite reached 95% TD with nitrate additives. 相似文献
17.
Silicon carbide (SiC) porous substrates, containing alumina (Al2 O3 ) dopant levels of 3, 5, and 8 wt%, are prepared by slip casting and sintering in the temperature range of 1450°–1800°C. The linear shrinkage, bulk density, and pore size of the sintered substrate increase as the sintering temperature and the amount of dopant increase. A large amount of β-phase SiC is transformed to α-phase SiC if the dopant concentration is 5 or 8 wt%. The flexural strength of the substrate doped with 8 wt% Al2 O3 is higher than that of the substrate doped with 3 wt% Al2 O3 ; however, the Weibull modulus of the former is lower. SiC composite membranes of improved selectivity and strength are fabricated by coating the porous substrate with layers of lower Al2 O3 contents at lower sintering temperatures. 相似文献
18.
Young-Keun Jeong Atsushi Nakahira Koichi Niihara 《Journal of the American Ceramic Society》1999,82(12):3609-3612
Al2 O3 /5-vol%-SiC nanocomposites have been fabricated by using pressureless sintering with MgO and/or Y2 O3 sintering aids and post-hot isostatic pressing (HIPing), which circumvents the limitations of hot pressing. Al2 O3 /SiC nanocomposites that have been doped with 0.1 wt% MgO and 0.1 wt% MgO + 0.1 wt% Y2 O3 show an increased sintering density and a homogeneous microstructure, as well as a high fracture strength (1 GPa) after HIPing. In contrast, using Y2 O3 as a dopant has a negative impact on the microstructure and the fracture strength. The results suggest that MgO, as a sintering additive, has a key role in improving the densification and controlling the microstructure of Al2 O3 /SiC nanocomposites. 相似文献
19.
Jean-Louis Besson Dominique Billieres Tanguy Rouxel Paul Goursat Robert Flynn Stuart Hampshire 《Journal of the American Ceramic Society》1993,76(8):2103-2105
Glasses have been prepared in the Si -Y-Al O-N system by melting mixtures of silica, alumina, yttria, and silicon nitride. One particular glass containing 17 equiv% N has been investigated to Observe the crystallization at temperatures in the range 1050o -1300o C. The major crystalline phase observed is Y2 Si2 O7 , existing as the α form below 1200o C and the β form above this temperature. Properties of the glass-ceramic, including thermal expansion coefficient, hardness, electrical resistivity, and creep have been assessed. 相似文献
20.
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