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1.
Bi2Sr2CaCu2Ox superconductor was studied by differential scanning calorimetry (DSC) and thermogravimetry (TG) in different atmospheres. It is discovered that there is a thermal anomaly in the DSC curve, associated with a weight loss in the TG curve before the melting of the sample. Careful thermal analysis and high temperature X-ray diffraction reveal that the thermal anomaly and the weight loss show an instability of the crystalline Iattice. By annealing the sample in oxygen and argon, respectively and then by TC measurement and thermal analysis, the coincidence of transition temperature with the instability is found. The coincidence is further confirmed by Y-doped 2212 phase. 相似文献
2.
Optimization of the Phase Diagram of CeO_2-ZrO_2 System 总被引:1,自引:0,他引:1
Lin LI Zuyao XU Qing AO 《材料科学技术学报》1996,12(2):159-160
Revised phase diagram of the CeO2-ZrO2 system is optimized and the lattice stability parameters of CeO2 of various phases as well as solution parameters of phases (liquid, cubic, tetragonal and monoclinic) are simultaneously obtained by using the Kaufman and Nesor's model for describing the ceramic solutions and the Lukas program 相似文献
3.
Crystallization peak temperature was measured for Li2O · 2SiO2 glass with various number densities of nuclei induced by long heat-treatment (405 h) at 460°C. Its crystallization process of Li2O · 2SiO2 glass was simulated numerically in order to examine the effect of the initial size of nuclei on crystallization behavior, and the relationship between crystallization peak temperature and the number density of nuclei in the glass was considered. It was found that the effect of nuclei size is not significant when the heat-treatment temperature is lower than 460°C. By considering the effect of nuclei size, number density of nuclus was evaluated by DTA method accurately. 相似文献
4.
Chi XU Ming LI Nianyi CHEN 《材料科学技术学报》1993,9(1):65-67
The structure of NaAlO_2 melt has been studied by computerized simulation using Monte Carlomethod.The radial distribution functions and Local structure of this melt are calculated.It has beenfound that NaAlO_2 melt contains ionic clusters formed by corner-sharing AlO_4 tetrahedra,sodiumions and xNa~+.yO~(2-) ionic clusters. 相似文献
5.
Modeling of symmetric 2 × 2 fused-fiber couplers 总被引:1,自引:0,他引:1
A complete analysis of symmetric 2 × 2 fused-fiber couplers in terms of supermode beating is made. The tranverse and longitudinal geometry of the couplers has been carefully modeled to take into account the fabrication parameters. The first two scalar supermodes and their polarization corrections have then been calculated for each degree of fusion and taper ratio, resulting in powerful tools for the design of particular couplers. The good agreement between the observed and the predicted responses for slightly and strongly fused couplers confirms the validity of each step of this analysis. 相似文献
6.
E. M. Godzhaev A. M. Nazarov Kh. S. Khalilova A. M. Suleimanova 《Inorganic Materials》2002,38(9):876-879
TlIn1 – x
Nd
x
Se2(0 < x 0.1) solid solutions were characterized by x-ray diffraction and temperature-dependent electrical conductivity, Hall effect, thermoelectric power, and heat capacity measurements. With increasing Nd content, the lattice parameters of the solid solutions increase almost linearly, and their band gap decreases. 相似文献
7.
V. G. Asmolov V. N. Zagryazkin E. V. Astakhova V. Yu. Vishnevskii E. K. D'yakov A. Yu. Kotov V. M. Repnikov 《High Temperature》2003,41(5):627-632
The density of a UO2–ZrO2 melt (atomic ratio U/Zr = 1.528) is experimentally measured by a pycnometric method in the temperature range of 2973–3373 K. The found temperature dependence of density has the form (T) = (7.0 ± 0.01) – (4.5 ± 0.4) × 10–4 × (T – 2973 K), g/cm3. The temperature dependence measured enables one to calculate the values of the density of UO2–ZrO2 melts depending on the temperature and composition for any atomic ratio U/Zr. 相似文献
8.
A phase transition in TlIn1 – x
Pr
x
S2 (0 <x 0.08) solid solutions was detected at 260–290 K by temperature-dependent isothermal compressibility measurements, in accordance with the thermal expansion data obtained earlier. 相似文献
9.
The production of tetragonal zirconia polycrystalline (TZP) ceramics and the identification of factors controlling retention of the tetragonal phase in the ZrO2·TiO2 system have been investigated. In this binary system, it was not possible to retain tetragonal zirconia polycrystals at room temperature for a range of compositions sintered above 1200 °C. A decrease in the martensitic transformation temperature of zirconia with titania addition was observed, but the effect was insufficient to retain the tetragonal phase at room temperature. In solid solution, the TiO2 additions act to suppress ZrO2 densification, this leading to grain growth when attempts are made to attain higher densities. The use of fine powders, fast firing or sintering in reducing conditions altered densification but was not able to generate a final grain size sufficiently small to avoid spontaneous tetragonalmonoclinic transformation on cooling. Based on the results obtained for ZrO2·MOx systems, the main factors involved in the retention of tetragonal zirconia at room temperature are discussed in an attempt to incorporate thermodynamical and the stress field effects. 相似文献
10.
The compounds Gd2Ba2Cu2Ti2-xMxO11- (M = Al, Co) were prepared and characterized by X-ray diffraction. The structure was refined by Rietveld calculations. Additional investigations such as magnetic measurements and impedance spectroscopy were performed in order to determine the physical properties of Gd2Ba2 Cu2 Ti2 M011-. SQUID measurements revealed the presence of a superconducting phase in the compound with the formal composition Gd2Ba2Cu2Ti1.6Al0.4011-. A transition temperature (Tc) of 25 K was observed. 相似文献
11.
Incorporation of SnO2 into MgO–spinel (M–S) increased mechanical properties significantly. Relationships between the parameters improving mechanical properties and microstructural variables were examined. Basic parameters improving the mechanical properties of M–S–SnO2 composites were identified as follows: (a) when microcracks come across with either Mg2SnO4 particles or pores; crack branching and deviation of interlinked microcracks or crack arresting occurred more effectively than those of spinel particles, (b) fracture type was converted to intergranular fracture with incorporation of spinel into MgO, and transgranular fracture with addition of SnO2 to M–S; additionally with the incorporation of additives, (c) critical defect size, (d) work of fracture values increased, and (e) MgO grain size decreased. Rst thermal shock parameter values of M–S–SnO2 composites were markedly higher than those of M–S materials, associated with low strength loss, high thermal shock damage resistance and thus longer service life of M–S–SnO2 composites for high-temperature industrial applications. 相似文献
12.
V. C. Sousa M. R. Cassia-Santos C. M. Barrado M. R. D. Bomio E. R. Leite J. A. Varela E. Longo 《Journal of Materials Science: Materials in Electronics》2004,15(10):665-669
This work illustrates the advancement of research on TiO2-based electroceramics. In this work will be presented that the addition of different dopants, as well as thermal treatments at oxidizing and inert atmosphere, influences of the densification, the mean grain size and the electrical properties of the TiO2-based varistor ceramics. Dopants like Ta2O5, Nb2O5, and Cr2O3 have an especial role in the barrier formation at the grain boundary in the TiO2 varistors, increasing the nonlinear coefficient and decreasing the breakdown electric field. The influence of CrTi is to increase the O and O2 adsorption at the grain boundary interface and to promote a decrease in the conductivity by donating electrons to O2 adsorbed at the grain boundary. In this paper, TiO2 and (Sn,Ti)O2-based studies of polycrystalline ceramics, which show a non-linear I–V electrical response typical of low voltage varistor systems are also presented. All these systems are potentially promising for varistor applications. 相似文献
13.
Spherical and nanoporous TiO2 and TiO2–SiO2 mixed micro-particles with four different compositions (20/80, 50/50, 80/20, 90/10 in weight ratio of TiO2/SiO2) were prepared by spray drying method from colloidal mixtures of amorphous silica and anatase titania nanoparticles. The as-prepared particles were heat-treated at 900 °C for 0.5–5 h. The TiO2 and TiO2–SiO2 particles were spherical in shape and the average particle diameter was about 1 μm. The anatase mass fraction and the specific surface area of TiO2–SiO2 (50 wt.% SiO2) mixed particles were kept to 61.5% and 30.6%, respectively, of their initial values after 5 h heat-treatment whereas these values of TiO2 particles were rapidly decreased to 13.0% and 1.2% of their initial values, respectively, within 30 min after heat-treatment. And the anatase mass fraction and specific surface area increased as SiO2 content in the TiO2–SiO2 mixed particles increased. 相似文献
14.
《Materials Research Bulletin》1987,22(6):715-722
The vapour phase crystallization process of α-HgI2 platelets in the presence of hydrocarbons and argon was investigated. The mass transport mechanism in the system and mutual relation between stoichiometries of the sources and the crystals were explained. The mass transport of HgI2 in this system can be treated as a sublimation-condensation process /PVT/. The α-HgI2 crystals were obtained in ampoules with argon or styrene added. The source HgI2 samples of various stoichiometries were applied. The shape and stoichiometry of the crystals grown depend on the starting stoichiometry of the source. No excess of iodine was found in the obtained crystals. 相似文献
15.
《材料科学技术学报》1997,(1)
16.
17.
M.Bahgat M.H.Khedr H.S.Abdelmaksoud 《材料科学技术学报》2007,23(5):697-702
Fe2O3, TiO2, CuO and ZnO powders were mixed according to the formula of (1-x)TiO2 xCuO-Fe2O3 or (1-x)TiO2 xZnO-Fe2O3 (x=0, 0.2 0.4, 0.6, 0.8, 1), and well ball-milled with H2O for 3 h to ensure homogeneity of the powdered solids, then fired at 1200℃ for 4 h. The fired samples were reduced at 500℃ with hydrogen gas. The reduced samples were subjected to recalcination at 500℃ in CO2 atmosphere. Both of fired, reduced and calcined samples were characterized by X-ray diffraction, vibrating sample magnetometry, reflected light microscopy and scanning electron microscopy. Different phases were formed after firing of Cu^+2 or Zn^2+ substituted Fe2TiO5. Magnetization (Bs) of the formed phases after firing are very low corresponding to diluted magnetic semiconductors (DMS) and increases with increasing the substituted cations (Cu^+2 or Zn^2+). The reduction of the fired samples enhanced the Bs values whereas the reducibility increases with increasing the Cu^+2 or Zn^2+ content. Samples show different tendency toward CO2 decomposition which is very important for environmental minimization for CO2. 相似文献
18.
The 90°C endotherm peak in the thermogram of a conventional dental amalgam is due to two overlapping peritectic transitions involving SnHg-2 and HgAgSn-1, respectively. The aim of the present study is to separate these two events and thus confirm that the 2 phase is indeed a part of an amalgam microstructure. The materials used in this study were: sample 1, 1+1 wt% Sn; sample 2, 1+2 wt% Sn; sample 3, 1+3 wt% Sn; and sample 4, a commercial conventional amalgam with 48 wt% Hg. In powder form, they were exposed to 1 wt% NaCl solution at 37 °C for up to 45 days. At 15 day intervals, samples were withdrawn from the solution, washed, dried and then characterized by the differential scanning calorimetry (DSC) technique. Corrosion of Sn from ternary 1 matrix and intergranular 2 in respective materials during their exposure to the NaCl solution led to the following: (a) a progressive increase in 11 transition temperature in samples 1 and 2; (b) a gradual decrease in 2 peak and its disappearance in sample 2; and (c) in samples 3 and 4, initial splitting of the 90°C peak into two distinct endotherms associated with 2 and 1, respectively. Continued corrosion of the last two materials produced further changes in 2 and 1 in a manner similar to that seen in samples 1 and 2. On the basis of these observations, we have concluded that the 90°C endotherm is a valid indicator of the existence of the 2 phase in dental amalgams. 相似文献
19.
Ricardo Guido Follador Neto Eder Carlos Ferreira de Souza André Vitor Chaves de Andrade Sandra Regina Masetto Antunes Augusto Celso Antunes 《Journal of Materials Science: Materials in Electronics》2013,24(3):938-944
This work investigated the influence of Nb2O5 dopant on the varistor behavior of the ternary system (99.95 ? x)%TiO2, 0.05 %Cr2O3, x%Nb2O5, where x = 0.10; 0.15; 0.20; 0.25 % in mol. The processing was carried out using the conventional oxide mixture method. The initial oxides were homogenized in alcoholic media in a ball mill, for 3 h, dried in oven and isostatically pressed at 210 MPa and sintered at 1,400 °C for 2 h in air atmosphere and cooled at 5 °C/min cooling rate, resulting in pellets with high densification. Electrical measurements in continuous current at different temperatures revealed that for the lowest Nb2O5 concentration the breakdown electric field, EB = 4.41 V/cm and non-linear coefficient, α = 4.6 were obtained, and for the highest Nb2O5 concentration the breakdown electric field, EB = 9.71 V/cm and non-linear coefficient, α = 15.3 were obtained. These low values in the breakdown electric field enable these varistor systems to be used in protection systems for low-voltage energy grids. Changes in the potential barrier present in the grain–grain boundaries could also be observed, in which the height increased and the width decreased with the increase in the dopant concentration. However, for x = 0.25 % in mol Nb2O5, a significant reduction in the potential barrier height and the voltage per barrier was obtained. Furthermore, the tendency to increase the volume of the unitary cell with the increase of dopant concentration, which was interrupted in the system with 0.25 % Nb2O5, was another evidence that suggested the occurrence of Nb2O5 segregation in the grain boundaries, or even that the reduction in the average grain size could possibly dilute Nb2O5 concentration in the grain boundaries. The average grain size was calculated through SEM micrographs and ranged from 7 to 16 μm, with larger sizes occurring for lower dopant concentrations and presenting higher porosity and lower uniformity in the grains shape. 相似文献
20.
Formation of machinable glass–ceramic in the system MgO–SiO2–Al2O3–K2O–B2O3–F with and without addition of MgF2 has been investigated. Crystallization of glass sample was done by controlled thermal heat treatment at nucleation and crystallization temperatures. The results showed that MgF2 in high concentration had a synergistic effect and enhanced the formation of interlocked mica crystals. Non-isothermal DTA experiments showed that the crystallization activation energies of base glasses were changed in the range of 235–405 kJ/mol, while the crystallization activation energies of samples with addition of MgF2 were changed in the range of 548–752 kJ/mol. 相似文献