共查询到20条相似文献,搜索用时 31 毫秒
1.
Xiaowei Yin Nahum Travitzky Peter Greil 《International Journal of Applied Ceramic Technology》2007,4(2):184-190
A porous ceramic preform was fabricated by printing a powder blend of TiC, TiO2 , and dextrin. The presintered preforms contained a bimodal pore size distribution with intra-agglomerate pores ( d 50 ≈0.7 μm) and inter-agglomerate pores ( d 50 ≈30 μm), which were subsequently infiltrated by aluminum melt spontaneously in argon above 1050°C. A redox reaction at 1400°C resulted in the formation of dense Ti–Al–O–C composites mainly composed of Ti3 AlC2 , TiAl3 , Al, and Al2 O3 , which attained a bending strength of 320 MPa, a Young's modulus of 184 GPa, and a Vicker's hardness of 2.5 GPa. 相似文献
2.
Kiyoshi Itatani Toshio Nishioka Satoru Seike F. Scott Howell Akira Kishioka Makio Kinoshita 《Journal of the American Ceramic Society》1994,77(3):801-805
Mixed solutions of Ca(NO3 )2 and (NH4 )2 HPO4 with Ca/P = 1.50 were spray-pyrolyzed at 600°C to produce β-calcium orthophosphate (β-Ca3 (PO4 )2 ) powder; the spray-pyrolyzed powder was ground and then calcined at 600°C for 1 h. The best crystalline β-Ca3 (PO4 )2 powder was obtained from the solution with 1.80 mol.L–1 Ca(NO3 )2 , 1.20 mol.L–1 (NH4 )2 HPO4 . The resulting powder was composed of primary particles with sizes of <0.5 μm. Dense β-Ca3 (PO4 )2 ceramics with a relative density of 96.1% could be fabricated by firing this compressed powder at 1070°C for 5 h. 相似文献
3.
Zong-Yang Shen Yuhua Zhen Ke Wang Jing-Feng Li 《Journal of the American Ceramic Society》2009,92(8):1748-1752
Microstructure characteristics, phase transition, and electrical properties of (Na0.535 K0.485 )0.926 Li0.074 (Nb0.942 Ta0.058 )O3 (NKN-LT) lead-free piezoelectric ceramics prepared by normal sintering are investigated with an emphasis on the influence of sintering temperature. Some abnormal coarse grains of 20–30 μm in diameter are formed in a matrix consisting of about 2 μm fine grains when the sintering temperature was relatively low (980°C). However, only normally grown grains were observed when the sintering temperature was increased to 1020°C. On the other hand, orthorhombic and tetragonal phases coexisted in the ceramics sintered at 980°–1000°C, whereas the tetragonal phase becomes dominant when sintered above 1020°C. For the ceramics sintered at 1000°C, the piezoelectric constant d 33 is enhanced to 276 pC/N, which is a high value for the Li- and Ta-modified (Na,K)NbO3 ceramics system. The other piezoelectric and ferroelectric properties are as follows: planar electromechanical coupling factor k p =46.2%, thickness electromechanical coupling factor k t =36%, mechanical quality factor Q m =18, remnant polarization P r =21.1 μC/cm2 , and coercive field E c =1.85 kV/mm. 相似文献
4.
Sunuk Kim Myong-cheol Jun Soon-cheol Hwang 《Journal of the American Ceramic Society》1999,82(2):289-296
Crack-free, undoped PbTiO3 ceramics were fabricated successfully using sol–gel-synthesized powder prepared from chelated titanium alkoxide and lead acetate. The sintered ceramics, 8.3 mm in diameter and 6–8 mm thick, were 96% dense. In the present study, PbTiO3 ceramics with excess lead (Pb:Ti = 1.1:1.0) had large grains, averaging 14.3 μm. Lower-lead ceramics (Pb:Ti = 1.0:1.0 and 0.9:1.0) had smaller grains, averaging 1.8 μm. The PbTiO3 ceramics with a high lead content cracked during sintering at 1150°C, whereas the other ceramics did not crack. Excess lead, in a more-than-stoichiometric ratio, promoted grain growth and caused disintegration of the ceramics. Therefore, uncracked PbTiO3 ceramics apparently can be fabricated by avoiding excess lead, possibly because restricted grain growth in low-lead ceramics causes low residual stress over many small grains during transition. The electrical properties measured in the present study for PbTiO3 ceramics with a Pb:Ti ratio of 1:1 are d 33 = 35 pC/N, K 3 = 64, k p = 0.59, and k t ≈ 0. 相似文献
5.
Powders of composition Ba0.65 Sr0.35 TiO3 were prepared from catecholate precursor phases, BaTi(C6 H4 O2 )3 and SrTi (C6 H4 O2 )3 . The physical and chemical properties of the base powders, and those doped with 0.2 wt% manganese, are reported in detail. The dimensions of the primary particles in the starting powders were of the order of 20–50 nm, but the occurrence of abnormal grain growth during sintering promoted grain sizes in the ceramic of up to ∼100 μm. In some microstructures, coarse grains coexisted with a ∼1-μm fraction to produce a characteristic bimodal grain size distribution. By contrast, under comparable sintering conditions, namely 1350° or 1400°C for 1 h, grain growth in Mn-doped samples was suppressed, leading to uniform microstructures with a grain size of only a few micrometers. The pellet densities were nevertheless similar, 97% of theoretical in both doped and undoped samples. No significant difference was observed in the dielectric permittivity of the two compositions: the peak relative permittivity occurred at ∼20°C, with a maximum value of ∼22 000. 相似文献
6.
Pierre E. Debély Eric A. Barringer H. Kent Bowen 《Journal of the American Ceramic Society》1985,68(3):76-C-
A fine, uniform A12 O3 -SiO2 powder was prepared by heterocoagulation of narrow Al2 O3 and SiO2 powders. This composite powder was dispersed, compacted, and fired in air at 900° to 1580°C for 1 to 13 h. Full density was achieved at 1550°C with the formation of a mullite phase. Relative densities of 83% and 98% (0.3 μm grain size) were measured for samples sintered at 1200°C for 13 h and at 1400°C for 1 h, respectively. 相似文献
7.
The orthorhombic, low-temperature α-modification of Nb2 C has a structure similar to that of ζ-Fe2 N (a = 12.36 A, b = 10.895 A, c = 4.968 A) and transforms at ∼1200°C into the hexagonal ε-Fe2 N type. A second transition at approximately 2500°C is associated with the destruction of long range order in the carbon sublattice. Alpha-divanadium carbide (orthorhombic, a = 11.49 A, b = 10.06 A, c = 4.55 A) is isostructural with α-Nb2 C and transforms at ∼800°C into the hexagonal high-temperature modification. The structures of α-V2 C and α-Nb2 C are distorted modifications related to the ε-Fe2 N type. 相似文献
8.
Ji-Guang Li Takayasu Ikegami Toshiyuki Mori 《Journal of the American Ceramic Society》2005,88(4):817-821
We report here the fabrication of transparent Sc2 O3 ceramics via vacuum sintering. The starting Sc2 O3 powders are pyrolyzed from a basic sulfate precursor (Sc(OH)2.6 (SO4 )0.2 ·H2 O) precipitated from scandium sulfate solution with hexamethylenetetramine as the precipitant. Thermal decomposition behavior of the precursor is studied via differential thermal analysis/thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffractometry, and elemental analysis. Sinterability of the Sc2 O3 powders is studied via dilatometry. Microstructure evolution of the ceramic during sintering is investigated via field emission scanning electron microscopy. The best calcination temperature for the precursor is 1100°C, at which the resultant Sc2 O3 powder is ultrafine (∼85 nm), well dispersed, and almost free from residual sulfur contamination. With this reactive powder, transparent Sc2 O3 ceramics having an average grain size of ∼9 μm and showing a visible wavelength transmittance of ∼60–62% (∼76% of that of Sc2 O3 single crystal) have been fabricated via vacuum sintering at a relatively low temperature of 1700°C for 4 h. 相似文献
9.
Superplasticity of Hot Isostatically Pressed Hydroxyapatite 总被引:1,自引:0,他引:1
Fumihiro Wakai Yasuharu Kodama Shuji Sakaguchi Tooru Nonami 《Journal of the American Ceramic Society》1990,73(2):457-460
Dense and translucent hydroxyapatite polycrystals (Ca10 (PO4 )6 (OH)2 with a grain size of 0.64 μMm) were obtained by hot isostatic pressing at 203 MPa and 1000°C for 2 h in argon. The material exhibited superplastic elongation (>150%) in a tension test at temperatures from 1000° to 1100°C and at strain rates from 7.2×10−5 to 3.6 × 10−4 s−1 . Extensive strain hardening was observed. The stress exponent of the yield stress was larger than 3. 相似文献
10.
Preparation and Sintering of Macroporous Ceramic Membrane Support from Titania Sol-Coated Alumina Powder 总被引:2,自引:0,他引:2
Yong Hong Wang Ji Gui Cheng Xing Qin Liu Guang Yao Meng Yan Wei Ding 《Journal of the American Ceramic Society》2008,91(3):825-830
The preparation of ceramic support at relatively low sintering temperature of 1350°–1500°C was investigated with a powder processing route, namely, titania sol coated on coarse alumina powder (median particle size d 50 , 27.5 μm). The sintering kinetics analysis indicates that the microstructure control of support is closely related to the sol coating and the sintering conditions. The mechanisms of sintering process were discussed in detail with the corresponding kinetics parameter, i.e., activation energy E a and exponent n as well as the microstructure characterization. The prepared support provides practical applications with tunable pore size and desired mechanical strength. 相似文献
11.
Ultrafine (<0.1 μm) high-purity θ-Al2 O3 powder containing 3–17.5 mol%α-Al2 O3 seeds was used to investigate the kinetics and microstructural evolution of the θ-Al2 O3 to α-Al2 O3 transformation. The transformation and densification of the powder that occurred in sequence from 960° to 1100°C were characterized by quantitative X-ray diffractometry, dilatometry, mercury intrusion porosimetry, and transmission and scanning electron microscopy. The relative bulk density and the fraction of α phase increased with annealing temperature and holding time, but the crystal size of the α phase remained ∼50 nm in all cases at the transformation stage (≤1020°C). The activation energy and the time exponent of the θ to α transformation were 650 ± 50 kJ/mol and 1.5, respectively. The results implied the transformation occurred at the interface via structure rearrangement caused by the diffusion of oxygen ions in the Al2 O3 lattice. A completely transformed α matrix of uniform porosity was the result of appropriate annealing processes (1020°C for 10 h) that considerably enhanced densification and reduced grain growth in the sintering stage. The Al2 O3 sample sintered at 1490°C for 1 h had a density of 99.4% of the theoretical density and average grain size of 1.67 μm. 相似文献
12.
Sangeeta D. Ramamurthi Zhengkui Xu David A. Payne 《Journal of the American Ceramic Society》1990,73(9):2760-2763
ZrO2 powder was prepared by a sol–emulsion–gel method at temperatures below 140°C from ZrO(NO3 )2 · n H2 O. The asprepared powder was amorphous, but crystallized into the tetragonal structure by 600°C. The metastable tetragonal powder (600°C) was comprised of ultrafine 4- to 6-nm size particles. On heat treatment, the tetragonal form completely transformed into the monoclinic state at 1100°C. Preliminary studies indicate good sinterability with densities greater than 94% at 1100°C and with a grain size of 0.25 μ. 相似文献
13.
Shuichi Kawano Junichi Takahashi Shiro Shimada 《Journal of the American Ceramic Society》2003,86(9):1609-1611
Nano-sized TiO2 powders were prepared by controlled hydrolysis of TiCl4 and Ti(O-i-C3 H7 )4 solutions and nitrided in flowing NH3 gas at 700°–1000°C to form TiN. Nano-sized TiN was densified by spark plasma sintering at 1300°–1600°C to produce TiN ceramics with a relative density of 98% at 1600°C. The microstructure of the etched ceramic surface was observed by SEM, which revealed the formation of uniformly sized 1–2 μm grains in the TiCl4 -derived product and 10–20 μm in the Ti(O-i-C3 H7 )4 -derived TiN. The electric resisitivity and Vickers micro-hardness of the TiN ceramics was also measured. 相似文献
14.
Peter den Exter Louis Winnubst Theo H. P. Leuwerink Anthonie J. Burggraaf 《Journal of the American Ceramic Society》1994,77(9):2376-2380
The densification behavior of ZrO2 (+ 3 mol% Y2 O3 )/85 wt% Al2 O3 powder compacts, prepared by the hydrolysis of metal chlorides, can be characterized by a transition- and an α-alumina densification stage. The sintering behavior is strongly determined by the densification of the transition alumina aggregates. Intra-aggregate porosity, resulting from calcination at 800°C, partly persists during sintering and alumina phase transformation and negatively influences further macroscopic densification. Calcination at 1200°C, however, densifies the transition alumina aggregates prior to sintering and enables densification to almost full density (96%) within 2 h at 1450°C, thus obtaining a microstructure with an alumina and a zirconia grain size of 1 μm and 0.3–0.4 μm, respectively. 相似文献
15.
Hwi-Yeol Park Cheol-Woo Ahn Kyung-Hoon Cho Sahn Nahm Hyeung-Gyu Lee Hyung-Won Kang Duk-Hee Kim Kyeong-Soon Park 《Journal of the American Ceramic Society》2007,90(12):4066-4069
The sintering temperature of 0.95(Na0.5 K0.5 )NbO3 –0.05BaTiO3 (NKN–BT) ceramics needs to be decreased below 1000°C to prevent Na2 O evaporation, which can cause difficulties in poling and may eventually degrade their piezoelectric properties. NKN–BT ceramics containing CuO were well sintered at 950°C with grain growth. Poling was easy for all specimens. Densification and grain growth were explained by the formation of a liquid phase. The addition of CuO improved the piezoelectric properties by increasing the grain size and density. High piezoelectric properties of d 33 =230 pC/N, k p =37%, and ɛ3 T /ɛ0 =1150 were obtained from the specimen containing 1.0 mol% of CuO synthesized by the conventional solid-state method. 相似文献
16.
Nader Marandian Hagh Kazuhiro Nonaka Mehdi Allahverdi Ahmad Safari 《Journal of the American Ceramic Society》2005,88(11):3043-3048
Highly grain-oriented lead metaniobate (PbNb2 O6 ; PN) ceramics were prepared by a layered manufacturing (LM) process. This process has enabled us to obtain a net-shaped piezoelectric ceramic component with grain orientation of f ∼89%, and improvement in electromechanical properties. The LM feedstock (filament) includes equiaxed (matrix; 90 vol%) and anisometric PN templates (10 vol%), both dispersed uniformly in a thermoplastic binder. The needle-like PN templates were synthesized by molten salt synthesis technique, while the equiaxed PN powder was prepared by conventional ceramic processing methods. The processing conditions were studied and optimized to obtain orthorhombic phase fine powder and anisometric templates.
Samples were obtained through layer-by-layer deposition of the filament through a small diameter (500 μm) nozzle. After binder removal, the PN samples were sintered in a temperature range of 1150°–1300°C for 1 h. SEM observation revealed strong grain orientation perpendicular to the deposition direction. Relative permittivity at the Curie point ( Tc : 560°C) was 18 100 and 14 600 for the LM and random polycrystalline samples, respectively. Improved properties in piezoelectric figure of merit by 71%, d 33 by 23%, and g 33 by 31% were observed in the grain-oriented samples. Remnant polarization also showed about 80% improvement, increasing from 4.5 to 8.1 μC/cm2 for the grain-oriented LM samples. 相似文献
Samples were obtained through layer-by-layer deposition of the filament through a small diameter (500 μm) nozzle. After binder removal, the PN samples were sintered in a temperature range of 1150°–1300°C for 1 h. SEM observation revealed strong grain orientation perpendicular to the deposition direction. Relative permittivity at the Curie point ( T
17.
Grain-oriented Bi2 WO6 ceramics were fabricated by normal sintering techniques. Platelike crystallites were initially synthesized by a fused salt process using an NaCl-KCI melt. When calcined at <800°C, the Bi2 WO6 crystallites are 3∼5 μ m in size and, at >850°C, =100 μm. After dissolving away the salt matrix, the Bi2 WO6 particles were mixed with an organic binder and tapecast to align the platelike crystallites. Large particles were easily oriented by tapecasting but the sinterability of the tape was poor. Preferred orientation of small particles was increased by tapecasting and grain growth during sintering further improves the degree of orientation. Sintering above the 950°C phase transition, however, results in discontinuous grain growth and low densities. Optimum conditions for obtaining highly oriented ceramics with high density occur at sintering temperatures of 900°C using fine-grained powders which yield orientation factors of =0.88 and densities of 94% theoretical. 相似文献
18.
Lead-based piezoelectric ceramics typically require sintering temperatures higher than 1000°C at which significant lead loss can occur. Here, we report a double precursor solution coating (PSC) method for fabricating low-temperature sinterable polycrystalline [Pb(Mg1/3 Nb2/3 )O3 ]0.63 -[PbTiO3 ]0.37 (PMN–PT) ceramics. In this method, submicrometer crystalline PMN powder was first obtained by dispersing Mg(OH)2 -coated Nb2 O5 particles in a lead acetate/ethylene glycol solution (first PSC), followed by calcination at 800°C. The crystalline PMN powder was subsequently suspended in a PT precursor solution containing lead acetate and titanium isopropoxide in ethylene glycol to form the PMN–PT precursor powder (second PSC) that could be sintered at a temperature as low as 900°C. The resultant d 33 for samples sintered at 900°, 1000°, and 1100°C for 2 h were 600, 620, and 700 pm/V, respectively, comparable with the known value. We attributed the low sintering temperature to the reactive sintering nature of the present PMN–PT precursor powder. The reaction between the nanosize PT and the submicrometer-size PMN occurred roughly in the same temperature range as the densification, 850°–900°C, thereby significantly accelerating the sintering process. The present PSC technique is very general and should be readily applicable to other multicomponent systems. 相似文献
19.
Preparation of Ultra-Fine Nickel Manganite Powders and Ceramics by a Solid-State Coordination Reaction 总被引:2,自引:0,他引:2
Dao-lai Fang Zhong-bing Wang Ping-hua Yang Wei Liu Chu-sheng Chen A. J. A. Winnubst 《Journal of the American Ceramic Society》2006,89(1):230-235
A solid-state coordination reaction was adopted to prepare negative temperature coefficient ceramics. A mixed oxalate NiMn2 (C2 O4 )3 ·6H2 O, a coordination compound, was synthesized by milling a mixture of nickel acetate, manganese acetate, and oxalic acid for 5 h at room temperature. An ultrafine NiMn2 O4 powder was obtained by calcining the mixed oxalate in air at 850°C for 2 h. Ceramics with a relative density of more than 97% were achieved by sintering powder compacts at a temperature as low as 1050°C for 5 h. The specific electrical resistivity ρ25°C and the thermal constant B 25°/85°C were 2174 Ω·cm and 3884 K, respectively. The drift of the resistivity after aging at 150°C for 1000 h was 3.0%. 相似文献
20.
Sol-Gel Synthesis of Amorphous Calcium Phosphate and Sintering into Microporous Hydroxyapatite Bioceramics 总被引:13,自引:0,他引:13
Pierre Layrolle Atsuo Ito Tetsuya Tateishi 《Journal of the American Ceramic Society》1998,81(6):1421-1428
A new route for preparing hydroxyapatite (Ca10 (PO4 )6 (OH)2 ) bioceramic has been described. An amorphous, nanosized, and carbonate-containing calcium phosphate powder that had a Ca:P ratio of 1.67 was synthesized from calcium diethoxide and phosphoric acid in ethanol via a sol-gel method. The powder was pressed at 98 MPa into green specimens and then heated to a temperature range of 500°-1300°C. At 600°C, the powder crystallized to a carbonated hydroxyapatite and a trace of ß-tricalcium phosphate before converting to hydroxyapatite at 900°C. The thermal crystallization was associated with grain growth, shrinkage, and active surface diffusion. The activation energy of grain growth was 37 ± 2 kJ/mol. After sintering at 1100°C, the decomposition of carbonated hydroxyapatite generated a microporous ceramic with an average pore size of 0.2 µm and an open porosity of 15.5%. This microporous bioceramic can be used as a bone filler. 相似文献