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排序方式: 共有102条查询结果,搜索用时 15 毫秒
1.
Co-precipitation of nano Mg–Y/ZrO2 ternary oxide eutectic system: Effects of calcination temperature
《Ceramics International》2022,48(16):23452-23459
In the family of inorganic nanomaterials, zirconia is a highly promising functional ceramic with a high refractive index, hardness, and dielectric constant, as well as excellent chemical inertness and thermal stability. These properties are enhanced in nano-zirconia ceramics, because nanopowders have a small particle size, good morphology, and uniform and dispersive distribution. In this study, a co-precipitation process was proposed to synthesise highly dispersed MgO–Y2O3 co-stabilized ZrO2 nanopowders. The effects of different calcination temperatures on the crystallisation degree and particle dispersion of zirconia nanopowders were characterised by X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption using the Brunauer–Emmett–Teller (BET) theory, transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). The optimum synthesis conditions were obtained as follows: 6 h of high-energy planetary grinding and calcination at 800 °C in an electric furnace. Under these optimum conditions, the average particle size of the prepared powder was 28.7 nm. This process enriches the literature on the controllable preparation of Mg–Y/ZrO2 nanopowders obtained by the co-precipitation method. 相似文献
2.
V.I. Popkov O.V. Almjasheva V.N. Nevedomskiy V.V. Panchuk V.G. Semenov V.V. Gusarov 《Ceramics International》2018,44(17):20906-20912
Formation and structural transformations of yttrium orthoferrite crystals have been studied using X-ray diffractometry, Mössbauer spectroscopy and transmission electron microscopy combined with electron microdiffraction. Said processes have been studied under heat treatment of glycine-nitrate combustion products. There have been identified formations of three structural yttrium orthoferrite modifications – amorphized hexagonal <h1>-YFeO3 (P63cm) and nanocrystalline hexagonal h2-YFeO3 (P63/mmc), as well as nanocrystalline orthorhombic o-YFeO3 (Pbnm), which are selectively formed depending on available three-dimensional confinements. Based on the analysis of changes in the fluid and size composition formulation, it has been proposed mechanism for formation and transformation of YFeO3 nanocrystals, including growth stage of h2-YFeO3 crystals due to amorphized phase of <h1>-YFeO3 up to critical size of about 15?nm and their subsequent transformation into orthorhombic form o-YFeO3. 相似文献
3.
V.V. Zyryanov N.F. Uvarov V.A. Sadykov Y.V. Frolova G.M. Alikina A.I. Lukashevich M.I. Ivanovskaya J.M. Criado S. Neophytides 《Catalysis Today》2005,104(2-4):114-119
Nanopowders of LaGaO3- and LaMnO3-based complex perovskites (P) and ceria-based fluorites (F) were prepared by mechanosynthesis. Compatible nanocomposites F + P and P + P with mixed ion and electron conducting (MIEC) properties were prepared and sintered at moderate temperatures up to dense ceramics. The obtained materials were studied by means of XRD, SEM, TEM, electrical conductivity measurements, temperature programmed (TP) reduction/oxidation and preliminary estimations of permeability were obtained. A new strategy based on the advantages of the mechanochemical ceramic approach is proposed to design multilayer ceramic membranes for CMR. Casting technology and one-step sintering were used for the production of thin film membranes with MIEC properties on porous substrates. The coarse fraction of as-milled powders from agglomerates with density 70% was used for the porous substrate, and fine fractions of aggregates with sizes <1 μm were used in preparation of composites for thin dense films. Ceria-based composites prepared by the Pechini route and/or mechanochemical method are proposed as materials for protecting thin films. 相似文献
4.
Valentina Medri Francesca Servadei Riccardo Bendoni Annalisa Natali Murri Angelo Vaccari Elena Landi 《Journal of the European Ceramic Society》2019,39(7):2453-2462
Cold Sintering Process (CSP) was applied on commercial nanopowders to produce nanostructured TiO2 anatase with nano-to-macro porosity. Nanoporous TiO2 based materials were obtained by applying CSP at 150 °C and pressures up to 500 MPa on three TiO2 nanopowders with different specific surface area (s.s.a. = 50, 90 and 370 m2/g), using water as transient aqueous environment. Although TiO2 is insoluble in water, a density of 68% and s.s.a. = 117 m2/g were achieved from the powder with the highest specific surface area. A post annealing process at 500 °C increased the density up to 73% with a s.s.a. = 59 m2/g, and the crystallites dimensions passed from 110 Å in the powder to 130 Å in CSP material and 172 Å after post annealing. Finally, macroporosity was produced by using thermoplastic polymer beads as sacrificial templates within TiO2 nanopowder during CSP, followed by a debonding at 500 °C. 相似文献
5.
Ceramics with perovskite-type structure and 0.94(Bi0.5Na0.5)TiO3–0.06BaTiO3 (BNBT) composition have been studied by conventional powder X-ray diffraction in Bragg–Brentano geometry. Ceramics were obtained from sol–gel autocombustion nanopowders and processed either by hot pressing and subsequent recrystallisation or pressureless sintering in two steps. These methods provided single-phase, sub-micron grain size (<700?nm), dense ceramics with good piezoelectric performance (96–94% of theoretical density and d33?=?143–124?pC?N–1, respectively). For the considered ceramics, the splitting of the peaks of the cubic perovskite-type structure with 111 and 200 Miller indices has been repeatedly used as a symmetry identification criterion. In this work a simple, yet powerful, procedure to validate the consistency of the mentioned splitting interpretation is presented. Based on peaks fitting and well-known crystallographic expressions, the rhombohedral and tetragonal symmetries' coexistence is verified. The suggested procedure can be applied to the study of peak splitting in ceramics at Morphotropic Phase Boundaries in a general way. In a given series of BNBT ceramics, inconsistencies for interplanar distances, intensities' ratios and the evolution of these from not-poled to poled samples have been found. In poled ceramics, special care has been taken when carrying out this analysis, due to the anisotropic strains arising from ferroelectric (FE) domain orientation. Poling gives rise to a displacement of the peaks angular positions and modification of the intensity ratios. However, the interplanar distance changes associated with the angular deviations here observed are one order of magnitude higher than those expected from anisotropic strains. These results set up a doubt on the sufficiency of the [rhombohedral?+?tetragonal] model to characterise the considered ceramics. A model of a mesoscopic FE phase with rhombohedral symmetry, a mesoscopic and globally weakly polar phase, with cubic symmetry, and a nanosised phase, also cubic, is presented as a plausible alternative. 相似文献
6.
《Journal of the European Ceramic Society》2020,40(5):1983-1988
Nanosized Ag-doped ceria (Ce1-xAlxO2-δ)powders (0.1 ≤ x ≤ 0.04) were obtained by self-propagating room temperature reaction. The solid solubility of Ag into ceria lattice was the highest reported so far. X-ray diffraction analysis and field emission scanning microscopy results showed that the doped samples are single phase solid solutions with fluorite-type structure and all prepared powders were nanometric in size. The average size of Ce1-xAgxO2-▯ particles lies at about 4 nm. Raman spectra revealed an increase in the amount of oxygen vacancies with the increase of Ag concentration, such as is foreseen. The thermal stability of solid solution was followed by XRD. Microstructure development was studied by scanning electron microscopy. By controlling the processing variables, it was possible to obtain high density samples with homogeneous microstructure at low sintering temperature. 相似文献
7.
《Ceramics International》2017,43(14):10637-10644
In this paper we have studied the properties of ZnO ceramics sintered from the ZnO-Zn nanopowders (NPs) produced by a pulsed electron beam evaporation of heterogeneous targets (oxide or metal) and to establish the influence of NPs prehistory on the luminescence and dilatometry properties of ceramics produced from them. Pressing was performed on uniaxial presses: static and the magnetic pulsed one. Sintering of ceramics was produced in air by heating to 1200 °C in 60 min. Maximal density of the ceramics did not exceed 81,25% of the theoretical density. The behavior of the shrinkage curves of ZnO-Zn NPs depends on their prehistory. Evolution of properties of ZnO-Zn nanoparticles (NPles) during annealing in air is studied by XRD and pulsed cathodoluminescence methods. The suppression of the ultraviolet emission in NP obtained by electron beam evaporation, and in ceramics sintered of them was established. 相似文献
8.
O. Khamman 《Materials Letters》2007,61(13):2822-2826
A perovskite phase of lead zirconate, PbZrO3, nanopowder was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of milling time on the phase formation and particle size of PbZrO3 powder was investigated. Powder samples were characterized using TG-DTA, XRD, SEM and laser diffraction techniques. It was found that an average particle size of 50 nm was achieved at 25 h of vibro-milling after which a higher degree of particle agglomeration was observed upon continuation of milling to 35 h. In addition, by employing an appropriate choice of milling time, a narrow particle size distribution curve was also observed. 相似文献
9.
Yong-Cheng Wong Yung-Jin Weng Yung-Chun Weng 《Polymer-Plastics Technology and Engineering》2013,52(8):853-860
This study developed creative imprinting technology, combining nano-imprint lithography and array-type UV-curing technology. It used nanopowders as the method to transmit imprint force, and integrated technical features, such as soft lithography, light-curing resistant and gas-assisted imprint technology, in order to study the development of technological processes of micro-lens array manufacturing, and mature the application and technology of nano-imprinting. According to research results, SUS 304 stainless steel sheet with a micro-hole array could be smoothly fabricated into an original micro-lens array mold upon gas-assisted micro-hot embossing. At the same time, a micro-lens array structure with a complementary external form could be precisely remolded and reproduced by PDMS. Complete molding of micro-lens could be effectively achieved by combining imprints of gas-assisted lithography developed in this study, and even UV-NIL. The effective imprinting area and reproducibility of transfer printing could be greatly improved when a micro-lens contacts perfectly with a substrate surface. Moreover, since PDMS soft molds have short remolding times, and are easily feathered during manufacturing, production costs could be effectively reduced through features such as, low surface free energy, resistant to adhering to the mold during imprinting, and collocation of gas-assisted nanopowder imprinting of micro-structural processes. 相似文献
10.
Rare-earth (RE: Lu, Gd, Nd, 0.10 mol%)-doped alumina nanopowders were prepared by a new sol-gel route using polyhydroxoaluminum (PHA) and RECl3 solutions under α-alumina (∼ 75 nm) seeding. Among the rare-earth dopants studied, Lu yields the most suitable nanopowders for low-temperature densification. The 0.10 mol% Lu-doped nanopowders, which were obtained at a calcination temperature of 900 °C under 5 mass% α-alumina seeding, consisted of ∼ 80-nm α-alumina particles and γ-alumina nanoparticles. Using these Lu-doped alumina nanopowders, fully densified alumina ceramics with a uniform microstructure composed of fine grains with an average size of 0.61 μm could be obtained at 1400 °C by pressureless sintering. Clearly, the Lu-doped nanopowders obtained here represent a viable option for fabricating dense, finer-grained alumina ceramics because an undoped sample with 5 mass% seeds gave a microstructure with an average grain size of 1.78 μm at 1400 °C. 相似文献