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1.
High burnup is a goal for further development of advanced nuclear power in the future. However, along with the increase of burnup, it becomes more diffidult to control reactor reactivity, which affects the operation safety of the nuclear reactor. Al2O3/B4C burnable poison materials widely used in pressurized water reactor currently will not meet the requirements of burnable poison materials in high burnup nuclear power. Because of the better performance of ZrO2/Gd2O3 burnable poison materials than that of Al2O3/B4C, this paper studies the preparation of ZrO2/Gd2O3 composite ceramic materials by the coprecipitation method. The experimental results show that at the sintering temperature of 1500–1650 °C, ZrO2/Gd2O3 composite ceramic grains are small, compact and uniform with the generation of homogeneous solid solution. At 1600 °C, ZrO2–10%Gd2O3 has the highest density and mechanical strength. 相似文献
2.
TiO2 varistors doped with 0.2 mol% Ca, 0.4 mol% Si and different concentrations of Ta were obtained by ceramic sintering processing at 1350 °C. The effect of Ta on the microstructures, nonlinear electrical behavior and dielectric properties of the (Ca, Si, Ta)-doped TiO2 ceramics were investigated. The ceramics have nonlinear coefficients of α = 3.0–5.0 and ultrahigh relative dielectric constants which is up to 104. Experimental evidence shows that small quantities of Ta2O5 improve the nonlinear properties of the samples significantly. It was found that an optimal doping composition of 0.8 mol% Ta2O5 leads to a low breakdown voltage of 14.7 V/mm, a high nonlinear constant of 4.8 and an ultrahigh electrical permittivity of 5.0 × 104 and tg δ = 0.66 (measured at 1 kHz), which is consistent with the highest and narrowest grain boundary barriers of the ceramics. In view of these electrical characteristics, the TiO2–0.8 mol% Ta2O5 ceramic is a viable candidate for capacitor–varistor functional devices. The characteristics of the ceramics can be explained by the effect and the maximum of the substitution of Ta5+ for Ti4+. 相似文献
3.
Al2O3-SiC composite ceramics were prepared by pressureless sintering with and without the addition of MgO, TiO2 and Y2O3 as sintering aids. The effects of these compositional variables on final density and hardness were investigated. In the present article at first α-Al2O3 and β-SiC nano powders have been synthesized by sol-gel method separately by using AlCl3, TEOS and saccharose as precursors. Pressureless sintering was carried out in nitrogen atmosphere at 1600 °C and 1630 °C. The addition of 5 vol.% SiC to Al2O3 hindered densification. In contrast, the addition of nano MgO and nano TiO2 to Al2O3-5 vol.% SiC composites improved densification but Y2O3 did not have positive effect on sintering. Maximum density (97%) was achieved at 1630 °C. Vickers hardness was 17.7 GPa after sintering at 1630 °C. SEM revealed that the SiC particles were well distributed throughout the composite microstructures. The precursors and the resultant powders were characterized by XRD, STA and SEM. 相似文献
4.
Tian He Jinhui DaiJintao Tian Zhibin ZhuLiangzhai Guo Zhongfang LiuXiaofei Qu Zhenlei ShenPeipei Wang 《Ceramics International》2008
The Bi0.5(Na0.7K0.2Li0.1)0.5TiO3 powder synthesis through molten salt method was investigated in the temperature range of 650–700 °C for 2–4 h. The XRD results indicated that the optimal synthesizing temperature for molten salt method was 700 °C, significantly lower than that for conventional processing route of solid state reaction method, where a calcining temperature of 850 °C was needed. The SEM results revealed better crystallization of the powders obtained through molten salt method, compared with those through the conventional processing route of solid state reaction method. 相似文献
5.
A visible light active binary SnO2-TiO2 composite was successfully prepared by a sol-gel method and deposited on Ti sheet as a photoanode to degrade orange II dye. Titanium and SnO2 can promote the development of rutile phase of TiO2 and inhibit the formation of anatase phase of TiO2. Formation of SnO2 crystalline is insignificant even when the calcination temperature increases to 700 °C. Heterogenized interface between SnO2 and TiO2 inhibits growth of TiO2 linkage and leads to the particle-filled surface morphology of SnO2-containing films. The carbonaceous, Ti-O-C bonds and Ti3+ species are likely to account for the photoabsorption and photoelectrocatalytic (PEC) activity under visible light illumination. The electrode with 30% SnO2 exhibits higher photocurrent when compared with those in the region of 0-50%. The 600 °C-calcined SnO2-TiO2 electrode indicates higher activity when compared with those at 400, 500, 700 and 800 °C. PEC degradation of orange II follows the Langmuir-Hinshelwood model and takes place much effectively in a solution of pH 3.0 than those in pH 7.0 and pH 11.0. 相似文献
6.
Bo-Ra Kim Hyo-Jin Oh Kang-Seop Yun Sang-Chul Jung Wooseung Kang Sun-Jae Kim 《Progress in Organic Coatings》2013
For an electrochemical water splitting system, titanate nanotubular particles with a thickness of ∼700 nm produced by a hydrothermal process were repetitively coated on fluorine-doped tin oxide (FTO) glass via layer-by-layer self-assembly method. The obtained titanate/FTO films were dipped in aqueous Fe solution, followed by heat treatment for crystallization at 500 °C for 10 min in air. The UV–vis absorbance of the Fe-oxide/titanate/FTO film showed a red-shifted spectrum compared with the TiO2/FTO coated film; this red shift was achieved by the formation of thin hematite-Fe2O3 and anatase-TiO2 phases verified using X-ray diffraction and Raman results. The cyclic voltammetry results of the Fe2O3/TiO2/FTO films showed distinct reversible cycle characteristics with large oxidation–reduction peaks with low onset voltage of I–V characteristics under UV–vis light illumination. The prepared Fe2O3/TiO2/FTO film showed much higher photocurrent densities for more efficient water splitting under UV–vis light illumination than did the Fe2O3/FTO film. Its maximum photocurrent was almost 3.5 times higher than that obtained with Fe2O3/FTO film because of the easy electron collection in the current collector. The large current collection was due to the existence of a TiO2 base layer beneath the Fe2O3 layer. 相似文献
7.
A new method was proposed to form (Ba0.5Sr0.5)TiO3–Al2O3 composite oxide film on etched aluminum foils. The specimens were covered with (Ba0.5Sr0.5)TiO3 (BST) layer by dip-coating in citrate solution and subsequent heat-treatment under 400–650 °C, finally by anodizing in a hot boracic acid and borate solution. The BST powders heated under different temperatures were characterized by X-ray diffraction (XRD) and the specific capacitance of the coated specimens heat-treated under different temperatures and times was measured. It is found that the specific capacitance increases initially with enhancing the temperature and reaches to maximum at 550 °C, but slightly decreases with the heat-treatment time. The capacitance was increased by about 35% after BST coating. 相似文献
8.
TiO2 based ceramic/glass composites were prepared by a non-reactive liquid phase sintering (NLPS) using zinc borosilicate (ZBS) glass having the deformation temperature of 588 °C. The compounds of Zn2SiO4 and Zn4B6O13 were formed after the sintering process, indicating that the ZBS glass was a non-reactive one in this system. For TiO2/50 vol% ZBS glass composite, the two-stage sintering behavior was conducted as the sintering temperature increased. The former might be correlated to the NLPS process and the latter appeared to be related to the crystallization. The dielectric constant (?r) was mainly affected by the porosity and obeyed the logarithmic mixing rule. The quality factor (Q × f0) showed an increase and then a steep decrease after the maximum at 850 °C. TiO2/50 vol% ZBS glass composite sintered at 900 °C demonstrated 36 in the dielectric constant (?r) and 7500 GHz in the quality factor (Q × f0) for an application to LTCC filters. 相似文献
9.
Abdul Latif Ahmad Nur Aimie Abdullah SaniSharif Hussein Sharif Zein 《Ceramics International》2011,37(8):2981-2989
A SrCo0.8Fe0.2O3 impregnated TiO2 membrane (TiO2-SrCo0.8Fe0.2O3 membrane) was successfully prepared using a sol-gel method in combination with a wet impregnation process. The membrane was subjected to a single gas permeance test using oxygen (O2) and nitrogen (N2). The TiO2 membrane was immersed in the SrCo0.8Fe0.2O3 solution, dried and then calcined to affix SrCo0.8Fe0.2O3 into the membrane. The effect of the acid/alkoxide (H+/Ti4+) molar ratio of the TiO2 sol on the TiO2 phase transformation was investigated. The optimal molar ratio was found to be 0.5, which resulted in nanoparticles with a mean size of 5.30 nm after calcination at 400 °C. The effect of calcination temperature on the phase transformation of TiO2 and SrCo0.8Fe0.2O3 was investigated by varying the calcination temperature from 300 to 500 °C. X-ray diffraction spectroscopy (XRD) and Fourier transform infrared (FTIR) analysis confirmed that a calcination temperature of 400 °C was preferable for preparing a TiO2-SrCo0.8Fe0.2O3 membrane with fully crystallized anatase and SrCo0.8Fe0.2O3 phases. The results also showed that polyvinyl alcohol (PVA) and hydroxypropyl cellulose (HPC) were completely removed. Field emission scanning electron microscopy (FESEM) analysis results showed that a crack-free and relatively dense TiO2 membrane (∼0.75 μm thickness) was created with a multiple dip-coating process and calcination at 400 °C. The gas permeation results show that the TiO2 and TiO2-SrCo0.8Fe0.2O3 membranes exhibited high permeances. The TiO2-SrCo0.8Fe0.2O3 membrane developed provided greater O2/N2 selectivity compared to the TiO2 membrane alone. 相似文献
10.
Tzu-Jung ChenJer-Han Lu Hui-Di LuI-Lung Liu Pouyan Shen 《Journal of the European Ceramic Society》2012,32(4):795-805
Specific surface area change of ZrO2 (predominant tetragonal - (t) symmetry, 30-50 nm) and less refractory TiO2 anatase nanoparticles (20-50 nm) upon isothermal firing at 700-1000 °C in air was determined by N2 adsorption-desorption hysteresis isotherm. The nanoparticles underwent onset coarsening-coalescence within minutes without appreciable phase transformation for TiO2, but with extensive transformation into monoclinic (m-) symmetry for ZrO2. The apparent activation energy of such a process being not much higher for ZrO2 (77 ± 23 kJ/mol) than TiO2 (56 ± 3 kJ/mol) nanoparticles can be attributed to transformation plasticity. The minimum temperature for coarsening/coalescence of the present ZrO2 and TiO2 nanoparticles was estimated as 710 and 641 °C, respectively. 相似文献
11.
12.
The present study aims to investigate synthesis of Ti3SiC2 from TiO2 and SiO2 powder mixtures by carbothermal reduction method. Equilibrium TiO2–SiO2–C ternary phase diagram was used to predict the conditions for the formation of Ti3SiC2 at 1800 K under Ar atmosphere. A reactant mixture with a TiO2:SiO2 molar ratio of 1.5 and a C content of 68.75 mol% (26.86 wt%) was initially selected among the thermodynamically favorable reactant compositions for the experimental studies. Two different C sources, graphite flakes and pyrolytic C coating, were used to synthesize Ti3SiC2 at 1800 K under Ar atmosphere. When graphite flakes were used, the products contained a trace amount of Ti3SiC2 phase along with major TiC and minor SiC phases. Whereas, pyrolytic C coating on the oxide particles resulted in the products with much higher Ti3SiC2 contents owing to the close contact between the reactants. Optimal C concentration for the C coated oxide mixtures with a TiO2:SiO2 molar ratio of 1.5 was determined to be 30.05 wt% under the experimental conditions studied. Ti3SiC2 content of the products obtained from this reactant was observed to increase with reaction time to 31 wt% at 75 min beyond which it gradually decreased. XRD studies indicated that the product with the highest ternary carbide content also contained TiC and a trace amount of SiC. SEM-EDS analyses showed that this sample essentially consisted of spherical fine TiC particles and Ti3SiC2 nanolaminates. Equilibrium thermodynamic analysis of the TiO2–SiO2–C system suggested that the reaction of solid Ti2O3 with SiO and CO gases may play a dominant role in the formation of Ti3SiC2. 相似文献
13.
Here is described a sonosynthesis method to produce nanostructured TiO2 pure and doped (Al, C, Co, Fe and Rh). The synthesized TiO2 is amorphous and is transformed to anatase, brookite or rutile by heat treatments at temperatures between 100 and 300 °C. Pure TiO2 can be partially transformed to brookite between 100 and 300 °C. The band gap in all heat treated samples from 100–600 °C is relatively constant, 3.2 eV, except for those doped with Fe. This effect on the band gap is the results of a bi/tri-crystal (anatase:brookite:rutile) framework. Rhodium is the most effective dopant to narrow the band gap, the opposite effect is observed with C. In single phase frameworks the bandgap can be modified ranges from 2.38 to 4.10 eV depending on the dopant. TiO2 lattices are rigid enough to promote an outwards diffusion of the dopants to the surface of the particles forming nanostructured precipitates. The precipitates develop a network of quantum-dots with sizes between 5 and 10 nm. 相似文献
14.
Debao Li Cheng YangNing Zhao Huijie QiWenhuai Li Yuhan SunBing Zhong 《Fuel Processing Technology》2007
Ni modified K2CO3/MoS2 catalyst was prepared and the performance of higher alcohol synthesis catalyst was investigated under the conditions: T = 280–340 °C, H2/CO (molar radio) = 2.0, GHSV = 3000 h− 1, and P = 10.0 MPa. Compared with conventional K2CO3/MoS2 catalyst, Ni/K2CO3/MoS2 catalyst showed higher activity and higher selectivity to C2+OH. The optimum temperature range was 320–340 °C and the maximum space-time yield (STY) of alcohol 0.30 g/ml h was obtained at 320 °C. The selectivity to hydrocarbons over Ni/K2CO3/MoS2 was higher, however, it was close to that of K2CO3/MoS2 catalyst as the temperature increased. The results indicated that nickel was an efficient promoter to improve the activity and selectivity of K2CO3/MoS2 catalyst. 相似文献
15.
The complex perovskite oxide Ba(Zn1/3Nb2/3)O3 (BZN) has been studied for its attractive dielectric properties which place this material interesting for applications as multilayer ceramics capacitors or hyperfrequency resonators. This material is sinterable at low temperature with combined glass phase–lithium salt additions, and exhibits, at 1 MHz very low dielectric losses combined with relatively high dielectric constant and a good stability of this later versus temperature. The 2 wt.% of ZnO–SiO2–B2O3 glass phase and 1 wt.% of LiF-added BZN sample sintered at 900 °C exhibits a relative density higher than 95% and attractive dielectric properties: a dielectric constant ?r of 39, low dielectrics losses (tan(δ) < 10−3) and a temperature coefficient of permittivity τ? of 45 ppm/°C−1. The 2 wt.% ZnO–SiO2–B2O3 glass phase and 1 wt.% of B2O3-added BZN sintered at 930 °C exhibits also attractive dielectric properties (?r = 38, tan(δ) < 10−3) and it is more interesting in terms of temperature coefficient of the permittivity (τ? = −5 ppm/°C). Their good dielectric properties and their compatibility with Ag electrodes, make these ceramics suitable for L.T.C.C applications. 相似文献
16.
V. Baglio A.S. Aricò V. Antonucci S. Licoccia F. Serraino Fiory 《Electrochimica acta》2005,50(5):1241-1246
TiO2 nanometric powders were prepared via a sol-gel procedure and calcined at various temperatures to obtain different surface and bulk properties. The calcined powders were used as fillers in composite Nafion membranes for application in high temperature direct methanol fuel cells (DMFCs). The powder physico-chemical properties were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and pH measurements. The observed characteristics were correlated to the DMFC electrochemical behaviour. Analysis of the high temperature conductivity and DMFC performance reveals a significant influence of the surface characteristics of the ceramic oxide, such as oxygen functional groups and surface area, on the membrane electrochemical behaviour. A maximum DMFC power density of 350 mW cm−2 was achieved under oxygen feed at 145 °C in a pressurized DMFC (2.5 bar, anode and cathode) equipped with TiO2 nano-particles based composite membranes. 相似文献
17.
MgTa2O6 powders were prepared by mechanochemical synthesis from MgO and Ta2O5 in a planetary ball mill in air atmosphere using steel vial and steel balls. High-energy ball milling gave nearly single-phase MgTa2O6 after 8 h of milling time. Annealing of high-energy milled powder at various temperatures (700–1200 °C) indicated that high-energy milling speed up the formation and crystallization of MgTa2O6 from the amorphous mixture. The powder derived from 8 h of mechanical activation gave a particle size of around 28 nm. Although at low-annealing temperatures the grain size was almost the same as-milled powder, the grain size increased with annealing temperature reaching to around 1–2 μm after annealing at 1200 °C for 8 h. 相似文献
18.
Tao Chen Hongli Wang Ting Zhang Guangchang Wang Jifang Zhou Jianwei Zhang Yuhong Liu 《Ceramics International》2014
(Bi0.5Na0.5)0.94Ba0.06TiO3–xHfO2 [BNBT–xHfO2] lead-free ceramics were prepared using the conventional solid-state reaction method. Effects of HfO2 content on their microstructures and electrical properties were systematically studied. A pure perovskite phase was observed in all the ceramics with x=0–0.07 wt%. Adding optimum HfO2 content can induce dense microstructures and improve their piezoelectric properties, and a high depolarization temperature was also obtained. The ceramics with x=0.03 wt% possess optimum electrical properties (i.e., d33~168 pC/N, kp~32.1%, Qm~130, εr~715, tan δ~0.026, and Td~106 °C, showing that HfO2-modified BNBT ceramics are promising materials for piezoelectric applications. 相似文献
19.
Preparation, cross-linking and ceramization of AHPCS/Cp2ZrCl2 hybrid precursors for SiC/ZrC/C composites 总被引:1,自引:0,他引:1
Zhaoju Yu Le Yang Junying ZhanCong Zhou Hao MinQiang Zheng Haiping Xia 《Journal of the European Ceramic Society》2012,32(6):1291-1298
SiC/ZrC/C composites were prepared via pyrolysis of a polymeric precursor, namely AHPCS/Cp2ZrCl2 hybrid precursor prepared by the blend of allylhydridopolycarbosilane (AHPCS) and bis(cyclopentadienyl) zirconium dichloride (Cp2ZrCl2). The cross-linking and polymer-to-ceramic conversion of as-synthesized AHPCS/Cp2ZrCl2 were characterized by means of FTIR, 13C NMR, TGA, EDS, Raman spectroscopy and XRD. It is suggested that dehydrocoupling, hydrosilylation and dehydrochlorication are involved in the cross-linking of the hybrid precursor, which is responsible for a relatively high ceramic yield of 75.5% at 1200 °C. The polymer-to-ceramic conversion is complete at 900 °C, and it gives an amorphous ceramic. Further heating at 1350 °C induces partial crystallization, and then the characteristic peaks of β-SiC and cubic ZrC appear at 1600 °C. The effect of the composition of the hybrid precursor is also studied in the work. 相似文献
20.
This paper studies the preparation of UO2 dispersion fuel microspheres with 0.3 wt% of doped titanium by the sel–gol method. The experimental results show that between 1250 °C and 1450 °C, grain growth speeds are different with a rapid growth of some grains and a “double peaks” feature of grain sizes distribution, while at 1550 °C, the grain sizes have normal distribution with the average grain size of about 42 μm. Based on the calculation, between 1250 and 1550 °C, the average activation energy of the grain growth of (U,Ti)O2 microspheres, Ea, was 232.79 kJ/mol, which is significantly lower than that of the UO2 microspheres. In the later sintering period of (U,Ti)O2 microspheres, U4O9 is formed in some parts of the microspheres, accelerating the U-atom diffusion rate and the grain growth. 相似文献