共查询到20条相似文献,搜索用时 15 毫秒
1.
H. Doweidar 《Journal of Materials Science》2009,44(11):2899-2906
Refractive index and molar refraction of Li2O–, Na2O–, CaO–, and BaO–Ga2O3–SiO2 glasses have been used to test the validity of a structural model of silicate glasses containing Ga2O3 glasses. Ga2O3 enters these types of glass in a similar manner as Al2O3. It is assumed that, for (SiO2/Ga2O3) >1 and (Ga2O3/R2O) ≤1, Ga2O3 associates primarily with modifier oxides to form GaO4 units. The rest of modifier oxide forms silicate units with non-bridging oxygen ions. Silicate structural units have the
same factors as found for binary alkali- and alkaline earth silicate glasses. Differences between experimental and model values
suggest another structure for (Ga2O3/SiO2) ≥1. 相似文献
2.
The influence of SrO (0·0–5·0 wt%) on partial substitution of alpha alumina (corundum) in ceramic composition (95 Al2O3–5B2O3) have been studied by co-precipitated process and their phase composition, microstructure, microchemistry and microwave dielectric
properties were studied. Phase composition was revealed by XRD, while microstructure and microchemistry were investigated
by electron-probe microanalysis (EPMA). The dielectric properties by means of dielectric constant (ε
r
), quality factor (Q × f) and temperature coefficient of resonant frequency (τ
f
) were measured in the microwave frequency region using a network analyser by the resonance method. The addition of B2O3 and SrO significantly reduced the sintering temperature of alumina ceramic bodies to 1600 °C with optimum density (∼ 4g/cm3) as compared with pure alumina powders recycled from Al dross (3·55g/cm3 sintered at 1700 °C). 相似文献
3.
M. H. Shaaban 《Journal of Materials Science》2012,47(15):5823-5832
Glasses with composition (70 − x) B2O3·15Bi2O3·15LiF·xNb2O5 with x = 0–1.0 mol% were prepared by conventional glass-melting technique. The molar volume V m values decrease and the glass transition temperatures T g increase with increase of Nb2O5 content up to 0.2 mol%, which indicates that Nb5+ ions act as a glass former. Beyond 0.2 mol% Nb2O5 the V m increases and the T g decreases, which suggests that Nb5+ ions act as a glass modifier. The FTIR spectra suggest that Nb5+ ions are incorporated into the glass network as NbO6 octahedra, substituting BO4 groups. The temperature dependence of the dc conductivity follows the Greaves variable range hopping model below 454 K, and follows the small polaron hopping model at temperatures >454 K. σ dc, σ ac conductivity and dielectric constant (ε) decrease and activation energy for dc conduction ΔE dc which increases with increasing Nb2O5 content up to 0.2 mol%, whereas σ dc, σ ac and (ε) increase and ΔE dc decreases with increasing Nb2O5 content beyond 0.2 mol%. The impedance spectroscopy shows a single semicircle or arcs which indicate only the ionic conduction mechanism. The electric modulus formalism indicates that the conductivity relaxation is occurring at different frequencies exhibit temperature-independent dynamical process. The (FWHM) of the normalized modulus increases with increase in Nb2O5 content suggesting that the distribution of relaxation times is associated with the charge carriers Li+ or F− ions in the glass network. 相似文献
4.
A magnetic SO42−/ZrO2–B2O3–Fe3O4 solid superacid catalyst is prepared via a simple chemical co-precipitation approach. The obtained materials were characterized in detailed by X-ray powder diffraction, thermogravimetric analysis–different scanning calorimetry, Fourier transform infrared spectroscopy (FTIR), electron microscopy (SEM and TEM), and Mossbauer spectra. Powder X-ray diffraction patterns show that in this composite oxide the transformation temperature of ZrO2 from tetragonal to monoclinic phase is higher compared to the pristine SO42−/ZrO2 material. The introduction of Fe3O4 endows the superacid with a super-paramagnetic property while in a ferromagnetic state after calcination. The superacid exhibits high catalytic activity in forming ethyl acetate by esterification. 相似文献
5.
Moo-Chin Wang Huy-Zu Cheng Huey-Jiuan Lin Chien-Fu Wang Chi-Shiung Hsi 《Materials Chemistry and Physics》2013
The crystallization behavior and magnetic properties of 10Li2O–9MnO2–16Fe2O3–25CaO–5P2O5–35SiO2 (10LFS) glass have been studied using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) to observe the crystallization behavior and a superconducting quantum interference device (SQUID) for measurements of the magnetic properties. The DTA shows that the 10LFS glass has one broad exothermic peak at approximately 674 °C and one sharp (the highest) exothermic peak at 764 °C. When the 10LFS glass crystallized at 850 °C for 4 h, the crystalline phases identified by XRD were lithium silicate (Li2SiO3), β-wollastonite (β-CaSiO3), lithium orthophosphate (Li3PO4), magnetite (FeFe2O4) and triphylite (Li(Mn0.5Fe0.5)PO4). The SEM surface analysis revealed that the β-wollastonite and lithium silicate have a lath morphology. The TEM microstructure examination showed that the largest FeFe2O3 particles have a size of approximately 0.3 μm. When the 10LFS glass was heat treated at 850 °C for 16 h and a magnetic field of 1000 Oe was applied, a very small remnant magnetic induction of 0.01 emu g−1 and a coercive force of 50 Oe were obtained, which revealed an inverse spinel structure. 相似文献
6.
High-energy milling was used for production of Cu–Al2O3 composites. The inert gas-atomized prealloyed copper powder containing 2 wt.%Al and the mixture of the different sized electrolytic copper powders with 4 wt.% commercial Al2O3 powders served as starting materials. Milling of prealloyed copper powders promotes formation of nano-sized Al2O3 particles by internal oxidation with oxygen from air. Hot-pressed compacts of composites obtained from 5 and 20 h milled powders were additionally subjected to the high-temperature exposure in argon at 800 °C for 1 and 5 h. Characterization of processed material was performed by optical and scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness, as well as density and electrical conductivity measurements. Due to nano-sized Al2O3 particles microhardness and thermal stability of composite processed from milled prealloyed powders are higher than corresponding properties of composites processed from the milled powder mixtures. The results were discussed in terms of the effects of different size of starting copper powders and Al2O3 particles on the structure, strengthening of copper matrix, thermal stability and electrical conductivity of Cu–Al2O3 composites. 相似文献
7.
8.
Jigui Cheng Qiumei Jiang Haigen He Junfang Yang Yifang Wang Jianfeng Gao 《Materials Chemistry and Physics》2011
Y2O3–Sm2O3 co-doped ceria (YSDC) powder was synthesized by a gel-casting method using Ce(NO3)3·6H2O, Sm2O3 and Y2O3 as raw materials. Phase structure of the synthesized powders was characterized by X-Ray diffraction analysis. Sinterability of the powders was investigated by testing the relative density and observing the microstructure of the sintered YSDC samples. Electrical conductivity of the sintered YSDC samples was measured using impedance spectra method. Single solid oxide fuel cells based on the YSDC electrolyte were also assembled and tested. The results showed that YSDC powders with single-phase fluorite structure can be obtained by calcining the dried gelcasts at temperature above 800 °C. Average particle size of the YSDC powder is 50–100 nm. Relative density of more than 95% of the theoretical can be achieved by sintering the YSDC compacts at temperature above 1400 °C. The sintered YSDC sample has an ionic conductivity of 4.74 × 10−2 S cm−1 at 800 °C in air. Single fuel cells based on the YSDC electrolyte with 50 μm in thickness were tested using humidified hydrogen as fuel and air as oxidant, and maximum power densities of about 190 and 112 mW cm−2 were achieved at 700 and 600 °C, respectively. 相似文献
9.
Kenji Kanamori Tohru Kineri Ryohei Fukuda Takafumi Kawano Keishi Nishio 《Journal of Materials Science》2009,44(3):855-860
Amorphous ZrW2O8 powder and amorphous SiO2 powder were prepared by a sol–gel process as raw materials, and high-density ZrW2O8–SiO2 were successfully prepared at a much lower temperature of 923 K for a much shorter holding time of 10 min by spark plasma
sintering (SPS) method rather than by conventional melt-quenching method. The relative densities of 0.85ZrW2O8–0.15SiO2 and 0.70ZrW2O8–0.30SiO2 were 99.4% and 96.6%, respectively. The combined technique of a sol–gel process and SPS should enable us to prepare the varied
types of high-density composites of ZrW2O8 without severe thermal cracking caused by melt-quenching. The thermal expansion properties and dielectric properties of ZrW2O8–SiO2 were also investigated. 相似文献
10.
Ivana R?sslerová Ladislav Koudelka Zdeněk ?erno?ek Petr Mo?ner Ludvík Bene? 《Journal of Materials Science》2011,46(20):6751-6757
Thermal properties and crystallization of glasses from PbO–MoO3–P2O5 ternary system were studied in three compositional series (100 − x)[0.5PbO–0.5P2O5]–xMoO3 (A), 50PbO–yMoO3–(50 − y)P2O5 (B), and (50 − z)PbO–zMoO3–50P2O5 (C). Glass transition temperature, crystallization temperature, coefficient of thermal expansion, and dilatation softening
temperature of the studied glasses were determined by differential thermal analysis and dilatometry. Crystallization products
of annealed glass samples were investigated by X-ray diffraction and Raman spectroscopy. X-ray diffraction analysis of crystallized
glasses revealed the formation of PbP2O6, Pb3P4O13, and PbMoO4 in the samples of the B series. In the series A and C in the samples with a high MoO3 content, crystalline compounds of Pb(MoO2)2(PO4)2 and (MoO2)(PO3)2, respectively, were identified. Raman spectra of crystalline samples confirmed the results of X-ray diffraction measurements
and provided also information on thermal stability of glasses and formation of glass-crystalline phases in the studied glass
series. 相似文献
11.
12.
Wen-Chou Tsai Ying-Hung Liou Yi-Cheng Liou 《Materials Science and Engineering: B》2012,177(13):1133-1137
MgAl2O4 spinel exhibits fascinating microwave dielectric properties, but the synthesis of dense MgAl2O4 ceramics requires high firing temperatures. In this study, Co is introduced into MgAl2O4 ceramics to improve their sinterability and microwave dielectric properties. An Mg1−xCoxAl2O4 solid solution of a spinel structure was observed in the MgAl2O4–CoAl2O4 system, and dense Mg1−xCoxAl2O4 ceramics were obtained by sintering at 1475–1500 °C in air for 2–6 h. Co addition is effective in lowering the sintering temperature to 1475 °C. Q × f of Mg1−xCoxAl2O4 ceramics was increased to 49,300 GHz with an increase in Co content to 0.2, but degraded with a further increase in Co content. The temperature coefficient of resonant frequency of Mg1−xCoxAl2O4 ceramics was sustained at between −73 and −23 ppm/°C to the variation of Co content. 相似文献
13.
Manish S. Jayswal D.K. Kanchan Poonam Sharma Nirali Gondaliya 《Materials Science and Engineering: B》2013,178(11):775-784
Silver ion conducting super-ionic glass system xPbI2–(100 − x) [Ag2O–2(V2O5–B2O3)], where, 5 ≤ x ≤ 25, were prepared via melt quenching route and -characterized by XRD and DSC. Their electrical properties were measured by impedance spectroscopy in the frequency range of 2 MHz to 20 Hz from 30 to 120 °C. The electrical relaxation mechanism has been studied using AC conductivity, dielectric modulus function and frequency dependent dielectric permittivity over a wide range of frequency and temperature. Two different scaling approaches for AC conductivity as well as dielectric permittivity spectra were used to understand the nature of relaxation processes. 相似文献
14.
Atiar Rahaman Molla Anal Tarafder Basudeb Karmakar 《Journal of Materials Science》2011,46(9):2967-2976
Glasses were prepared by the melt-quench technique in the K2O–SiO2–Bi2O3–TiO2 (KSBT) system and crystallized bismuth titanate, BiT (Bi4Ti3O12) phase in it by controlled heat-treatment at various temperature and duration. Different physical, thermal, optical, and
third-order susceptibility (χ3) of the glasses were evaluated and correlated with their composition. Systematic increase in refractive index (n) and χ3 with increase in BiT content is attributed to the combined effects of high polarization and ionic refraction of bismuth and
titanium ions. Microstructural evaluation by FESEM shows the formation of polycrystalline spherical particles of 70–90 nm
along with nano-rods of average diameter of 85–90 nm after prolonged heat treatment. A minor increase in dielectric constants
(εr) has been observed with increase in polarizable components of BiT in the glasses, whereas a sharp increase in εr in glass–ceramics is found to be caused by the formation of non-centrosymmetric and ferroelectric BiT nanocrystals in the
glass matrix. 相似文献
15.
The effects of the annealing of 20BaO–30V2O5–50Bi2O3 glass on the structural and electrical properties were studied by scanning electron micrographs (SEM), X-ray diffraction (XRD), differential scanning calorimeter (DSC) density (d) and dc conductivity (σ). The XRD and SEM observations have shown that the sample under study undergoes structural changes: from amorphous at the beginning, to partly crystalline after nanocrystallization at crystallization temperature (Tc) for 1 h and to colossal crystallization after the annealing at the same temperature for 24 h. The average size of these grains after nanocrystallization at Tc for 1 h was estimated to be about 25–35 nm. However, the glass heat treated at Tc = 580 °C for 24 h the microstructure changes considerably. The nanomaterials obtained by nanocrystallization at Tc for 1 h exhibit giant improvement of electrical conductivity up to four order of magnitude and better thermal stability than the as-received glass. The major role in the conductivity enhancement of this nanomaterial is played by the developed interfacial regions “conduction tissue” between crystalline and amorphous phases, in which the concentration of V4+–V5+ pairs responsible for electron hopping is higher than inside the glassy matrix. The annealing at Tc for 24 h leads to decrease of the electronic conductivity. This phenomena lead to disappearance of the abovementioned “conduction tissue” for electrons and substantial reduction of electronic conductivity. The high temperature (above θ/2) dependence of conductivity could be qualitatively explained by the small polaron hopping (SPH) model. The physical parameters obtained from the best fits of this model are found reasonable and consistent with the glass compositions. 相似文献
16.
Soda alumina borosilicate glasses of composition (24-y)Na2O·yAl2O3·14B2O3·37SiO2·25Fe2O3, y = 8, 12, 14, 16 mol%, were melted using Fe2O3 as raw material. Besides, samples with y = 12 and Fe2O3 concentrations of 14.32, 17.8, and 25.0 mol% were prepared from FeC2O4·2H2O as raw material. The X-ray diffraction analyses showed the presence of magnetite for the samples from all the investigated
compositions. Transmission electron microscopy (TEM) evidenced that all the samples are phase separated and droplets in the
diameter range 100–1000 nm, enriched in iron, are formed. Inside these droplets, numerous small magnetite particles, with
size in the 25–40 nm interval, are crystallized. 相似文献
17.
Rare earth oxides co-doped zirconia have been developed for application in thermal barrier coating systems to promote the performance and durability of gas turbines. 8 mol%Sc2O3, 0.6 mol%Y2O3–stabilized ZrO2 (ScYSZ) powder was synthesized by chemical co-precipitation method. The phase stability, sintering resistance and thermo-physical properties of ScYSZ and 8 wt%Y2O3 stabilized ZrO2 (8YSZ) were investigated. The results indicated that both ScYSZ and 8YSZ show single tetragonal phase before heat treatment. After heat treating at 1500 °C for 300 h, ScYSZ exhibits excellent phase stability with 100% metastable tetragonal (t′) phase, whereas the content of monoclinic phase in 8YSZ reached 49.4 mol%. ScYSZ also exhibits higher sintering resistance and lower thermal conductivity than 8YSZ. ScYSZ can be considered to be explored as candidate material for TBC application. 相似文献
18.
Glass samples of the system (15Li2O–30ZnO–10BaO–(45 − x)B2O3–xCuO where x = 0, 5, 10 and 15 mol%) were prepared by using the melt quenching technique. A number of studies, viz. density, differential
thermal analysis, FT-IR spectra, a.c. conductivity and dielectric properties (constant εφ, loss tan δ, a.c. conductivity,
σac, over a wide range of frequency and temperature) of these glasses were carried out as a function of copper ion concentration.
The analysis of the results indicate that the density increases while molar volume decreases with increasing of copper content
indicates structural changes of the glass matrix. The glass transition temperature, T
g, and crystallization temperature, T
c, increase with the variation of concentration of CuO referred to the growth in the network connectivity in this concentration
range, while glass-forming ability parameter (T
c − T
g) decreases with increasing CuO content, indicates an increasing concentration of copper ions that take part in the network-modifying
positions. The FT-IR spectra evidenced that the main structural units are BO3, BO4, and ZnO4. The structural changes observed by varying the CuO content in these glasses and evidenced by FTIR investigation suggest
that the CuO plays a network modifier role in these glasses while ZnO plays the role of network formers. The dielectric constant
decreased with increase in temperature and CuO content. The variation of a.c. conductivity with the concentration of CuO passes
through a maximum at 5 mol%. In the high temperature region, the a.c. conduction seems to be connected with the mixed conduction
viz., electronic conduction and ionic conduction. 相似文献
19.
20.
Feifei Chen Baoan Song Changgui Lin Shixun Dai Junwen Cheng Jong Heo 《Materials Chemistry and Physics》2012
Glass-forming region of Bi2O3–GeO2–TiO2 (BGT) pseudo-ternary system was determined by using melt-quench method. A series of high transparent glass samples were selected and their structural characteristics were investigated by FT-IR and Raman spectra. By employing Z-scan and optical Kerr shutter techniques with femtosecond laser pulses as excitation source, third-order optical nonlinearities (TON) of the BGT glasses as well as the TON response time were investigated at wavelength of 800 nm. The ultrafast nonlinear response and high figure of merit suggest great potentials of BGT glasses in applications of all-optical switching or related optical devices. 相似文献