共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
Oleg Vasylkiv Yoshio Sakka Valeriy V. Skorokhod 《Journal of the American Ceramic Society》2006,89(6):1822-1826
CeCl3 ·7H2 O and GdCl3 ·6H2 O that were dissolved in water were precipitated with urea (NH2 CONH2 ) to produce matrix agglomerates for three-component nano-reactors. Mixing hexamethylenetetramine with dilute nitric acid resulted in the formation of well-dispersed nano-particles of cyclotrimetilene trinitramine (C3 H6 N6 O6 ) (RDX) in the solvent. Nano-reactors were produced by impregnating the nano-C3 H6 N6 O6 into the matrix agglomerates of an intermediate complex of cerium and gadolinium compounds. Blast initiation of the C3 H6 N6 O6 resulted in extremely rapid detonation and gaseous products formation at temperatures of 2000°–5000°C, which were compressed into a volume nearly equal to the initial volume of each RDX nano-particle. Multiple "nano-blasts" occurred in the volume of each nano-reactor. The impact of the blast waves led to fragmentation of the surrounding matter. The evolution of a large volume of gaseous products dissipated the heat of the process and limited temperature increase, thus reducing the possibility of local sintering among the primary particles. The short-term high temperature generated during the blasts enhanced the solid solubility of the metal oxides. Uniform aggregates of 22∼74 nm consisting of 6∼14 nm crystallites of gadolinia in ceria solid solution were synthesized. 相似文献
3.
Liang Fang Hui Zhang Qian Yu Heping Su Bolin Wu Xueming Cui 《Journal of the American Ceramic Society》2009,92(2):556-558
The microwave dielectric properties of dense ceramics of a new A4 B3 O12 type cation-deficient hexagonal perovskite Sr3 LaNb3 O12 are reported. Single-phase powders can be obtained from the mixed-oxide route at 1320°C and dense ceramics (>96% of the theoretical X-ray density) with uniform microstructures (5–12 um) can be obtained by sintering in air at 1430°C. The ceramic exhibits a moderate dielectric constant ɛr ∼36, a high quality factor Q × f ∼45 327 GHz, and a low temperature coefficient of resonant frequency τ f of −9 ppm/°C. 相似文献
4.
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
5.
Ritesh Rawal Antonio Feteira Neil C. Hyatt Derek C. Sinclair Kumaravinothan Sarma Neil McN. Alford 《Journal of the American Ceramic Society》2006,89(1):332-335
The dielectric properties of dense ceramics of the n =0 member of a newly identified homologous series Ba3+ n LaNb3 Ti n O12+3 n , where n =0, 1, and 2, are reported. Single-phase powders can be obtained from the mixed-oxide route at 1350°C and dense ceramics (>97% of the theoretical X-ray density) with uniform microstructures (3–5 μm) can be obtained by sintering in air at 1500°C. The ceramics are excellent dc insulators with a band gap >2.6 eV that resonate at microwave frequencies with a relative permittivity, ɛr ∼44, a quality factor, Q × f r , of ∼9000 at f r ∼5.5 GHz and a temperature coefficient of resonant frequency, TCf ,∼−100 ppm/K. 相似文献
6.
Atsushi Kitaoka Ken Hirota Masaru Yoshinaka Yoshinari Miyamoto Osamu Yamaguchi 《Journal of the American Ceramic Society》2000,83(5):1311-1313
NiAl/10-mol%-ZrO2 (3Y) composites of almost full density have been fabricated via spark plasma sintering (SPS) for 10 min at 1300°C and 30 MPa. The former intermetallic compound, which contains a trace amount of Al2 O3 , has been prepared via self-propagating high-temperature synthesis. The composite microstructures are such that tetragonal ZrO2 (∼0.2 μm) and Al2 O3 (∼0.5 μm) particles are located at the grain boundaries of the NiAl (∼46 μm) matrix. Improved mechanical properties are obtained: the fracture toughness and bending strength are 8.8 MPa·m1/2 and 1045 MPa, respectively, and high strength (>800 MPa) can be retained up to 800°C. 相似文献
7.
SiO2 -Al2 O3 melts containing 42 and 60 wt% A12 O3 were homogenized at 2090°C (∼10°) and crystallized by various heat treatment schedules in sealed molybdenum crucibles. Mullite containing ∼78 wt% A12 O3 precipitated from the 60 wt% A12 O3 melts at ∼1325°± 20°C, which is the boundary of a previously calculated liquid miscibility gap. When the homogenized melts were heat-treated within this gap, the A12 O3 in the mullite decreased with a corresponding increase in the Al2 O3 content of the glass. A similar decrease of Al2 O3 in mullite was observed when crystallized melts were reheated at 1725°± 10°C; the lowest A12 O3 content (∼73.5 wt%) was in melts that were reheated for 110 h. All melts indicated that the composition of the precipitating mullite was sensitive to the heat treatment of the melts. 相似文献
8.
A coating approach for synthesizing 0.9Pb(Mg1/3 Nb2/3 )O3 –0.1PbTiO3 (0.9PMN–0.1PT) and PMN using a single calcination step was demonstrated. The pyrochlore phase was prevented by coating Mg(OH)2 on Nb2 O5 particles. Coating of Mg(OH)2 on Nb2 O5 was done by precipitating Mg(OH)2 in an aqueous Nb2 O5 suspension at pH 10. The coating was confirmed using optical micrographs and zeta-potential measurements. A single calcination treatment of the Mg(OH)2 -coated Nb2 O5 particles mixed with appropriate amounts of PbO and PbTiO3 powders at 900°C for 2 h produced pyrochlore-free perovskite 0.9PMN–0.1PT and PMN powders. The elimination of the pyrochlore phase was attributed to the separation of PbO and Nb2 O5 by the Mg(OH)2 coating. The Mg(OH)2 coating on the Nb2 O5 improved the mixing of Mg(OH)2 and Nb2 O5 and decreased the temperature for complete columbite conversion to ∼850°C. The pyrochlore-free perovskite 0.9PMN–0.1PT powders were sintered to 97% density at 1150°C. The sintered 0.9PMN–0.1PT ceramics exhibited a dielectric constant maximum of ∼24 660 at 45°C at a frequency of 1 kHz. 相似文献
9.
Do-Kyun Kwon Teppei Akiyoshi Hyeongjae Lee Michael T. Lanagan 《Journal of the American Ceramic Society》2008,91(3):906-909
Manganese dioxide (α-MnO2 ) thin films have been explored as a cathode material for reliable glass capacitors. Conducting α-MnO2 thin films were deposited on a borosilicate glass substrate by a chemical solution deposition technique. High carbon activities originated from manganese acetate precursor, (Mn(C2 H3 O2 )2 ·4H2 O) and acetic acid solvent (C2 H4 O2 ), which substantially reduced MnO2 phase stability, and resulted in Mn2 O3 formation at pyrolysis temperature in air. The α-MnO2 structure was stabilized by Ba2+ insertion into a (2 × 2) oxygen tunnel frame to form a hollandite structure. With 15–20 mol% Ba addition, a conducting α-MnO2 thin film was obtained after annealing at 600–650°C, exhibiting low electrical resistivity (∼1 Ω·cm), which enables application as a cathode material for capacitors. The hollandite α-MnO2 phase was stable at 850°C, and thermally reduced to the insulating bixbyte (Mn2 O3 ) phase after annealing at 900°C. The phase transition temperature of Ba containing α-MnO2 was substantially higher than the reported transition temperature for pure MnO2 (∼500°C). 相似文献
10.
Tomohiro Yamakawa Junichi Tatami Toru Wakihara Katsutoshi Komeya Takeshi Meguro Kenneth J. D. MacKenzie Shinichi Takagi Masahiro Yokouchi 《Journal of the American Ceramic Society》2006,89(1):171-175
Aluminum nitride (AlN) powders were synthesized by gas reduction–nitridation of γ-Al2 O3 using NH3 and C3 H8 as the reactant gases. AlN was identified in the products synthesized at 1100°–1400°C for 120 min in the NH3 –C3 H8 gas flow confirming that AlN can be formed by the gas reduction–nitridation of γ-Al2 O3 . The products synthesized at 1100°C for 120 min contained unreacted γ-Al2 O3 . The 27 A1 MAS NMR spectra show that Al–N bonding in the product increases with increasing reaction temperature, the tetrahedral AlO4 resonance decreasing prior to the disappearance of the octahedral AlO6 resonance. This suggests that the tetrahedral AlO4 sites of the γ-Al2 O3 are preferentially nitrided than the AlO6 sites. AlN nanoparticles were directly formed from γ-Al2 O3 at low temperature because of this preferred nitridation of AlO4 sites in the reactant. AlN nanoparticles are formed by gas reduction–nitridation of γ-Al2 O3 not only because the reaction temperature is sufficiently low to restrict grain growth, but also because γ-Al2 O3 contains both AlO4 and AlO6 sites, by contrast with α-Al2 O3 which contains only AlO6 . 相似文献
11.
The electrical properties of a series of CaCu3 Ti4 O12 ceramics prepared by the mixed oxide route and sintered at 1115°C in air for 1–24 h to produce different ceramic microstructures have been studied by Impedance Spectroscopy. As-fired ceramics are electrically heterogeneous, consisting of semiconducting grains and insulating grain boundaries, and can be modelled to a first approximation on an equivalent circuit based on two parallel RC elements connected in series. The grain boundary resistance and capacitance values vary as a function of sintering time and correlate with the ceramic microstructure based on the brickwork layer model for electroceramics. The large range of apparent high permittivity values for CaCu3 Ti4 O12 ceramics is therefore attributed to variations in ceramic microstructure. The grain-boundary resistance decreases by three to four orders of magnitude after heat treatment in N2 at 800°–1000°C but can be recovered to the original value by heat treatment in O2 at 1000°C. The bulk resistivity decreases from ∼80 to 30 Ω·cm with increasing sintering time but is independent of heat treatment in N2 or O2 at 800°–1000°C. The origin of the bulk semiconductivity is discussed and appears to be related to partial decomposition of CaCu3 Ti4 O12 at the high sintering temperatures required to form dense ceramics, and not to oxygen loss. 相似文献
12.
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
13.
Xia Wang Wei Li Jin-lou Gu Yong-sheng Li Liang Li Jian-lin Shi 《Journal of the American Ceramic Society》2009,92(10):2412-2414
Li2.06 Nb0.18 Ti0.76 O3 powder has been successfully prepared at low temperatures via a facile and manageable, activated pretreatment on the inert raw Nb2 O5 . It is demonstrated that with triethanolamine, citric acid, and hydrogen peroxide, this simple pretreatment process could activate Nb2 O5 efficiently. Pure Li2 TiO3 solid solution phase was thus obtained by calcining the mixture of the activated Nb2 O5 , LiOH·H2 O, and Ti(C4 H9 O)4 at temperatures as low as 650°C, which is about 200°C lower than that of the traditional solid-state method. To the best of our knowledge, this temperature is the lowest one for preparing Li2 TiO3 solid solution. Additionally, the phase transformation and the morphology of the final powder are also discussed. 相似文献
14.
Antonio Feteira Derek C. Sinclair Ian M. Reaney Michael T. Lanagan 《Journal of the American Ceramic Society》2005,88(11):3055-3062
BaTi1−2 y Ga y Nb y O3 (BTGN) (0≤ y ≤0.35) powders were synthesized at 1300°C by the conventional solid-state method. Room temperature x-ray diffraction patterns for y ≤0.025 and 0.05≤ y ≤0.30 can be indexed as the tetragonal ( P 4 mm ) and cubic ( Pm m ) polymorphs of BaTiO3 , respectively, whereas y =0.35 consists of a mixture of the cubic polymorph of BaTiO3 and an 8H hexagonal-type perovskite ( P 63 / mcm ) isostructural with Ba8 Ti3 Nb4 O24 . Scanning electron microscopy shows the microstructures of BTGN ceramics ( y ≤0.30) sintered at 1500°C to consist of fine grains (1–3 μm) within a narrow grain size and shape distribution. Room temperature transmission electron microscopy for y ≤0.08 reveals core–shell structures and (111) twins in some grains; however, their relative volume decreases with y . Energy dispersive spectroscopy reveals the cores to be Ga and Nb deficient with respect to y . For y >0.08 there is no evidence of core–shell structures, however, some grains have a high density of dislocations, consistent with chemical inhomogeneity. BTGN ceramics exhibit a diverse range of dielectric behavior in the temperature range 120–450 K and can be subdivided into two groups. 0.025≤ y ≤0.15 display modest ferroelectric relaxor-type behavior, with high room temperature permittivity, ɛ25 ', (>300 at 10 kHz), whereas 0.25≤ y ≤0.30 are temperature and frequency stable dielectrics with ɛ25 '<100 that resonate at microwave frequencies with modest quality factors, Q × f , ∼3720 GHz (at ∼5 GHz) for y =0.30. 相似文献
15.
Qiwei Chen Ying Shi Liqiong An Jiyang Chen Jianlin Shi 《Journal of the American Ceramic Society》2006,89(6):2038-2042
A novel co-precipitation process was adopted for the preparation of highly sinterable europium-doped lutetia powders using ammonium hydroxide (NH3 ·H2 O) and ammonium hydrogen carbonate (NH4 HCO3 ) as the mixed precipitant. The resultant powders calcined at 1000°C for 2 h showed good dispersity and excellent sinterability. Highly transparent polycrystalline lutetia ceramics with a relative density of ∼99.9% were fabricated by pressureless sintering in flowing H2 atmosphere at 1850°C for 6 h without any additives. The average grain sizes of the transparent material were estimated to be 50–60 μm. Optical in-line transmittance in the visible wavelength region for Lu2 O3 ceramics (1 mm in thickness) reached 80%. The luminescence and decay behavior of the obtained transparent plate and the corresponding nanophosphors were also investigated. 相似文献
16.
Zhong Zhuang Xian Ping Wang Dan Li Tao Zhang Qian Feng Fang 《Journal of the American Ceramic Society》2009,92(4):839-844
Dense, crack-free, and uniform La2 Mo2− x W x O9 ( x =0, 0.1, and 0.2) nanocrystalline films were successfully synthesized on poly-alumina substrates via a modified sol–gel method, with inorganic salt of La(NO3 )3 ·6H2 O, (NH4 )6 Mo7 O24 ·4H2 O, and (NH4 )6 H2 W12 O24 as precursors. Pure La2 Mo2 O9 phase was confirmed by X-ray diffractometer when the annealing temperature was >500°C. The average grain size of the La2 Mo2− x W x O9 films is in the range of 90–400 nm, depending upon the conditions of thermal treatment, and the thickness of films can reach 1 μm by repetitive spin-coating. The electrical conductivity increases with decreasing grain size and reaches 0.074 S/cm at 600°C in the film with a grain size of 90 nm, which is one order of magnitude higher than that in the corresponding bulk materials. W-doping can suppress the phase transition that occurs at 580°C in pure La2 Mo2 O9 and enhance the low-temperature ionic conductivity. Furthermore, the activation energy of conductivity in the nanocrystalline La2 Mo2 O9 films decreases to about 0.6 eV in comparison with 1.0 eV in the bulk ones, which implies that the grain resistance prevails in the total resistance, when grain size reduces to nanometer domain. 相似文献
17.
Toshiaki Yamaguchi Wataru Sakamoto Toshinobu Yogo Shin-ichi Hirano 《Journal of the American Ceramic Society》2002,85(4):909-914
The effects of the substitution of transition-metal ions and/or reductant gases on the catalytic properties of barium hexaaluminogallate were investigated. Transition-metal-substituted hexaaluminogallates (BaM(Al,Ga)11 O19 , M = transition metal, Al/Ga = 9/3) were synthesized from aqueous metal nitrates and ammonium carbonate by the coprecipitation followed by crystallization at 1100°C. The direct NO x reduction was observed over BaM(Al,Ga)11 O19 to be around 10%. The NO x removal activity of BaM(Al,Ga)11 O19 powders was improved by addition of C3 H6 as a reductant gas. Co-, Ni- and Cu-substituted BaM(Al,Ga)11 O19 catalysts exhibited about 40% NO x reduction with C3 H6 in excess oxygen at a high space velocity of 10 000 h−1 . The NO x reduction on Mn- and Fe-substituted BaM(Al,Ga)11 O19 catalysts was less than 10% even in the presence of C3 H6 . The temperature of the effective NO x reduction on BaM(Al,Ga)11 O19 catalysts could be adjusted from 350° to 500°C by the selection of the transition-metal substitution in the catalysts. The catalysts hold high activities for NO x reduction even at 500°C in water vapor produced in the combustion system of reductant gases. 相似文献
18.
Ping-Hua Xiang Yoshiaki Kinemuchi Koji Watari Fei Cao Xian-Lin Dong 《Journal of the American Ceramic Society》2006,89(2):684-687
Highly textured Bi3 NbTiO9 ceramics are fabricated by normal sintering from molten salt-synthesized plate-like crystallites. Fine Bi3 NbTiO9 plate-like crystallites (∼1 μm) not only facilitate the densification, but also enhance texture in Bi3 NbTiO9 ceramics. Weak-agglomerated platelets exhibit higher sinterability and can be densified at a temperature as low as 1000°C, which is about 100°C lower than that of equiaxed powders prepared by directly calcining Bi3 NbTiO9 precursor. Meanwhile, the orientation degree of textured Bi3 NbTiO9 ceramics increases with sintering temperature. Highly oriented Bi3 NbTiO9 (orientation degree of ∼0.91) ceramic with a relative density of ∼92% is obtained at 1150°C. Because of the oriented grain microstructure, textured Bi3 NbTiO9 ceramic exhibits anisotropic electrical properties. 相似文献
19.
Jing Pei Zhenxing Yue Fei Zhao Zhilun Gui Longtu Li 《Journal of the American Ceramic Society》2007,90(10):3131-3137
Tungstenbronze-type Ba4 (Nd0.7 Sm0.3 )9.33 Ti18 O54 (BNST) microwave dielectric ceramics doped with 0–10 wt% silver (Ag) particles were successfully fabricated by a citrate sol–gel method. The influence of Ag doping on the sinterability, microstructure, bulk conductivity, and dielectric properties of BNST was investigated. The desired tungstenbronze-type phase was obtained at 900°–950°C. The sintering temperature of BNST decreased to 1100°C with the aid of a small amount of Ag addition (1 wt%). No chemical reaction between the tungsenbronze phase and Ag was detected. The particle size of the powders decreased with increasing Ag content up to 1 wt% and it then increased with a further increase in the Ag content. The dense fine-grained ceramics with submicrometer grains (∼300 nm) were obtained with 1 wt% Ag addition. The submicrometer-grained ceramics had excellent dielectric properties of ɛr ∼81 and Q × f ∼11 000 GHz. Both the dielectric constant and dielectric loss significantly increased with large additions (>3 wt%) of Ag due to the percolation effect. 相似文献
20.
The effect of Al2 O3 inclusions with a greater average size (0.6 μm) than the average particle size of the major phase powder (<0.1 μm) on grain gowth was examined by sintering ZrO2 /Al2 O3 composites (0,3,5,10, and 20 vol%) at 1400°C and then heat-treating at temperatures up to 1700°C. Normal grain growth was observed for all conditions. The inclusions appeared to have no effect on grain growth until the ZrO2 grain size was ∼1.5 times the average inclusion size. Grain growth inhibition increased with volume fraction of the Al2 O3 inclusion phase. At temperatures 1600°C, the inclusions were relatively immobile and most were located within the ZrO2 grains for volume fractions <0.20; at higher temperatures, the inclusions could move with the grain boundary to coalesce. Grain growth was less inhilited when the inclusions could move with the boundaries, resulting in a larger increase in grain size than observed at lower temperatures. Analogies between mobile voids, entrapped within grain at lower temperature due to abnormal grain growth during the last state of sintering, and the observations concerning the mobile inclusions are made suggesting that grain-boundary movement can "sweep" voids to grain boundaries and eventually of four-grain junctions, where they are more likely to disappear by mass transport. 相似文献