共查询到20条相似文献,搜索用时 15 毫秒
1.
Jagadish C. Ray Asit B. Panda Chitta R. Saha Panchanan Pramanik 《Journal of the American Ceramic Society》2003,86(3):514-516
The polymer precursor method is very useful to prepare Nb5+ -stabilized nanocrystalline powders of t -ZrO2 . The precursor solution is composed of zirconium oxalate, niobium tartrate, and poly(vinyl alcohol), which help to form a network matrix to disperse the metal ions homogeneously. Nb5+ is an effective agent to stabilize t -ZrO2 , and ease of formation of the tetragonal phase increases with increasing dopant concentration. Thermal stability of t -phase is found up to 1700°C having 15 mol% Nb5+ , prepared at 600°C with particle sizes of 35 ± 5 nm. 相似文献
2.
Synthesis of Nanocrystalline Chromium Nitride Powders by Direct Nitridation of Chromium Oxide 总被引:2,自引:0,他引:2
Yaogang Li Lian Gao Jingguo Li Dongsheng Yan 《Journal of the American Ceramic Society》2002,85(5):1294-1296
Nanocrystalline CrN powder was synthesized by the direct nitridation of nanosized Cr2 O3 powder. Powder X-ray diffractometry patterns indicated that pure cubic-phase CrN powder could be obtained by nitridation at 800°C for 8 h. Transmission electron microscopy images showed that the particle sizes were 40–80 nm. The effect of the nitridation temperature and holding time on the powder properties was studied. 相似文献
3.
Nanocrystalline niobium nitride (NbN) powders were sintered by spark plasma sintering under a nitrogen atmosphere at temperatures from 1040° to 1230°C. Fully dense bulk NbN ceramic with grain sizes of 0.5–1.0 μm was obtained at 1130°C. The effects of sintering temperature on the density, phase content, electrical conductivity, Vickers hardness, and microstructure of the NbN ceramic were discussed. 相似文献
4.
Nanocrystalline ZrN powder was synthesized by reduction–nitridation of nanosized ZrO2 powder in ammonia gas with magnesium as the reducing agent. The effects of nitridation temperature, holding time, and Mg:ZrO2 mole ratio on the powder properties were investigated. Cubic phase ZrN powder with a 30–100-nm particle size was synthesized at 1000°C for 6 h, under a Mg:ZrO2 mole ratio of 10:1. 相似文献
5.
Federica Bondioli Anna Maria Ferrari Cristina Leonelli Cristina Siligardi Gian Carlo Pellacani 《Journal of the American Ceramic Society》2001,84(11):2728-2730
Nanosized zirconium oxide (ZrO2 ) powders were prepared by adding NaOH to a zirconyl chloride aqueous solution under microwave-hydrothermal conditions. The obtained results showed that the tetragonal polymorph increased with increasing NaOH concentration in the starting solution and reached the maximum value by using 1 M ZrOCl2 . The microwave-assisted hydrothermal synthesis is expected to be able to process continuously, and may lead to energy savings because of rapid heating to temperature and increased kinetics of crystallization. This method is very simple and can lead to powders with desirable characteristics such as very fine size, narrow size distribution, and good chemical homogeneity. 相似文献
6.
Jingguo Li Lian Gao Jing Sun Qinghong Zhang Jingkun Guo Dongsheng Yan 《Journal of the American Ceramic Society》2001,84(12):3045-3047
Nanocrystalline TiN powder has been synthesized by the direct nitridation of nanocrystalline TiO2 powder. Powder XRD patterns indicated that the TiN nanocrystalline powder could be obtained by nitridation at 800°C for 5 h. TEM micrographs showed that the synthesized TiN powders consisted of uniform spherical particles with an average diameter of ∼20 nm. The effect of the nitridation temperature and holding time on the powder properties is discussed. 相似文献
7.
Lokesh Chandra Pathak Ajoy Kumar Ray Samar Das C. S. Sivaramakrishnan P. Ramachandrarao 《Journal of the American Ceramic Society》1999,82(1):257-260
A new precursor technique for the carbothermal synthesis of nanocrystalline AlN powder has been developed. A precursor that contains an intimate mixture of nanocrystalline Al2 O3 and carbon has been synthesized by using a chemical pyrophoric reaction. The formation of AlN starts at 1473 K, and complete conversion has been observed at temperatures >1673 K. The synthesized AlN particles are nanocrystalline (<100 nm) in size. 相似文献
8.
Hiromichi Ichinose Masanori Taira Sachiko Furuta Hiroaki Katsuki 《Journal of the American Ceramic Society》2003,86(9):1605-1608
Niobium- or vanadium-doped anatase sols were prepared by hydrothermal treatment of 0.1 mol/dm3 peroxotitanium complex aqueous solutions dissolving 0–10 mol% niobium or vanadium at 100°C for 8 h. Niobium-doping caused the increase of lattice constants of anatase and the shape change of anatase crystal from spindle-like to cubic-like structure, but no change of the optical absorbance. Vanadium-doping caused the decrease of lattice constant of c -axis, the miniaturization of anatase crystal and the increase of optical absorbance at the wavelength from 350–700 nm. 相似文献
9.
A new process has been developed for the synthesis of nanocrystalline AlN powder by the nitridation of coarse aluminum powder in flowing NH3 gas, using NH4 Cl and KCl as additives. The resulting powders have been characterized using XRD, TEM, and XRF techniques. XRD-pure AlN nanoparticles with a diameter of 10–20 nm can be obtained by nitridation at 1273 K for 5 h. NH3 is proved to eliminate the effect of water impurity. The effects of the additives on the conversion of aluminum are also discussed. 相似文献
10.
New titanium–niobium oxynitride (Ti1− z Nb z O x N y ) powders were synthesized by ammonolysis of nanosized TiO2 /Nb2 O5 composite powders at 700°–900°C for 5 h. The products were characterized by X-ray diffraction (XRD), chemical analysis, and transmission electron microscopy. The results indicated that the as-synthesized powders were pure cubic structures with sizes of 30–60 nm. With increasing value of z , XRD peaks of Ti1− z Nb z O x N y powders tended to shift toward low 2θ angle and the cell parameter showed a linear increase. 相似文献
11.
12.
Kyung-Sik Oh Jae-Yong Jun Doh-Yeon Kim Nong M. Hwang 《Journal of the American Ceramic Society》2000,83(12):3117-3120
In niobium carbide–iron (NbC-Fe) specimens where the grains were faceted, abnormally large grains appeared during coarsening. Normal and uniform grain growth occurred when the grain shape was changed to a spherical morphology by the addition of a small amount of boron. The results have been discussed, in terms of a coarsening mechanism, depending on the atomic structure of the interface. For faceted grains with an atomically smooth interface structure, the coarsening was suggested to occur via two-dimensional nucleation and a lateral-growth mechanism. For spherical grains with an atomically rough interfacial structure, diffusion was suggested to control the coarsening process. 相似文献
13.
14.
Effect of pH of Medium on Hydrothermal Synthesis of Nanocrystalline Cerium(IV) Oxide Powders 总被引:1,自引:0,他引:1
Nan-Chun Wu Er-Wei Shi Yan-Qing Zheng Wen-Jun Li 《Journal of the American Ceramic Society》2002,85(10):2462-2468
Well-crystallized cerium(IV) oxide (CeO2 ) powders with nanosizes without agglomeration have been synthesized by a hydrothermal method in an acidic medium by using cerium hydroxide gel as a precursor. The relationship between the grain size, the morphology of the CeO2 crystallites, and the reaction conditions such as temperature, time, and acidity of the medium was studied. The experiments showed that with increasing reaction temperature and time, the CeO2 crystallites grew larger. The crystallites synthesized in an acidic hydrothermal medium were larger and had a more regular morphology than the ones synthesized in a neutral or alkaline medium when the reaction temperature and time were fixed. The CeO2 crystallites synthesized in an acidic medium were monodispersed; however, there was vigorous agglomeration among the grains synthesized in a neutral or alkaline medium. It was demonstrated that the hydrothermal treatment was an Ostwald ripening process and the acidity (pH) of the used hydrothermal medium played a key role in the dissolution of smaller grains. It is proposed that the dissolution process can control the kinetics of the growth of larger grains. 相似文献
15.
Reaction Synthesis of Magnesium Silicon Nitride Powder 总被引:2,自引:0,他引:2
Zoltán Lené Kiyoshi Hirao Yukihiko Yamauchi Shuzo Kanzaki 《Journal of the American Ceramic Society》2003,86(7):1088-1093
The synthesis of magnesium silicon nitride (MgSiN2 ) by direct nitridation of a Si/Mg2 Si/Mg/Si3 N4 powder mixture is described. A nucleation period at 550°C and stepwise heat-treatment schedule up to 1350°C was adopted for the synthesis of MgSiN2 powder, based on TG-DTA measurements. The influence of the ratio of constituents on the final phase composition also has been studied. The content of magnesium and silicon in the starting powder should fulfill the conditions Mg2 Si/Mg ≥ 3 and Si3 N4 /Sitot ≥ 0.5 to obtain single-phase MgSiN2 . The silicon particle size of <0.5 μm is preferable to decrease the time of nitridation. The oxygen content of as-synthesized powders is in the range 0.9–1.2 wt%. However, the oxygen content of MgSiN2 powder decreases further by the addition of 2 wt% CaF2 or 0.75 wt% carbon and reaching the lowest value of 0.45 wt% oxygen after carbothermal reduction in an alumina-tube furnace. 相似文献
16.
Synthesis of high-purity, single-phase gallium nitride powder has been achieved in a hot-wall tube furnace via (i) the reaction of gallium with ammonia (NH3 ) and (ii) the conversion of gallium oxide (Ga2 O3 ). For complete reaction, the optimum temperatures, NH3 flow rates, and boat positions relative to the NH3 inlet were 975°C, 400 standard cubic centimeters per minute (sccm), and 50 cm, respectively, for the gallium-NH3 reaction, and 1050°C, 500 sccm, and 50 cm, respectively, for the Ga2 O3 conversion. Polyhedra of various shapes were obtained from both processes; some rod-shaped crystals also were observed in the material derived from Ga2 O3 . 相似文献
17.
Gilles Robert Marlyse Demartin Maeder Dragan Damjanovic Nava Setter 《Journal of the American Ceramic Society》2001,84(12):2869-2872
A modified processing method for lead nickel niobate–lead zirconate titanate (Pb(Ni1/3 Nb2/3 )O3 –Pb(Zr,Ti)O3 , PNN–PZT) solid solutions is presented. This method is based on the high-temperature synthesis of a precursor that contains all the B-site cations (Ti, Zr, Ni, and Nb). This synthesis yields a diphasic mixture that contains a ZrTiO4 -like phase and a rutile-like phase. Both phases exhibit a cationic valence of 4; thus, it is concluded that the mixing of Ni and Nb cations is adequate for the preparation of PNN–PZT solid solutions. Indeed, a pure perovskite phase has been obtained after calcination with lead oxide for compositions that contain 40 and 50 mol% PNN. Moreover, their electromechanical properties have been shown to be superior to values reported for standard columbite routes. This conclusion has been interpreted in terms of enhanced chemical homogeneity. 相似文献
18.
Interfacial Characterization of Silicon Nitride Powders 总被引:6,自引:0,他引:6
The composition of the surface and the behavior in aqueous suspensions of three silicon nitride powders were investigated using electron spectroscopy for chemical analysis (ESCA), potentiometric titrations, leaching experiments, and electrophoretic mobility. ESCA shows that the as-received powders have a surface-layer composition similar to that identified as an intermediate state between silica and silicon oxynitride. The original differences in pHiep between the three powders disappears by aging the powders. The common pHiep of 6.8 ± 0.3 for the three powders is interpreted as the equilibrium pHiep for silicon nitride in aqueous suspensions. 相似文献
19.
Shaobo Zhang Liwei Shi Lanyang Zhang Haiyan Zhu Wangsuo Xia 《Journal of the American Ceramic Society》2018,101(3):1014-1019
New high‐quality microwave dielectric ceramics Mg2NdNbO6 were prepared by conventional solid‐state sintering method. The phases, micro‐structures and microwave dielectric properties of Mg2NdNbO6 ceramics were investigated at sintering temperature in the range of 1275°C‐1400°C. The X‐ray diffraction patterns showed that the peaks of the compounds were attributed to two phases, including the main crystalline phase of NdNbO4 that was indexed as the monoclinic phase and MgO as the second phase. Well‐developed microstructures of Mg2NdNbO6 ceramics can be achieved, and the grain size reached the maximum value (1.63 μm) at 1375°C. As the sintering temperature increased, the dielectric constant, temperature coefficient of resonant frequency and apparent density remained almost unchanged, however, the significant change in the quality factor was observed. At 1375°C, Mg2NdNbO6 ceramics possessed excellent microwave dielectric properties: εr = 16.22, Q × f = 116 000 GHz and τf = ?30.96 ppm/°C. 相似文献
20.
Kyung-Han Seo Joon-Hyung Lee Jeong-Joo Kim M. I. Bertoni B. J. Ingram T. O. Mason 《Journal of the American Ceramic Society》2006,89(11):3431-3436
Nanocrystalline powders of two indium tin oxide (ITO) polymorphs—rhombohedral and cubic—were prepared by a co-precipitation process. The temperature and aging time of precipitates after co-precipitation were controlled to obtain selectively the two different crystal structures. X-ray diffraction and transmission electron microscopy were used to characterize the powders. The electrical conductivity of the two ITO powders was determined by the powder solution composite method. The conductivities obtained were 0.26±0.04 and 0.65±0.17 S/cm for the rhombohedral and cubic ITO samples, respectively, the first such report for the rhombohedral phase. 相似文献