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1.
The Rayleigh scattering of the mixed-alkali glass system K2 O–Na2 O–MgO–SiO2 (KNMS) was investigated, both experimentally and theoretically. The lowest Rayleigh scattering coefficient (38% of that for pure SiO2 glass) was obtained when the glass composition was 22K2 O–8Na2 O–10MgO–60SiO2 (in mol%). These values are equal to or less than the minimum values reported for the ternary sodium silicate glass Na2 O–MgO–SiO2 . The Rayleigh scattering caused by concentration fluctuation was believed to have been reduced greatly in this KNMS glass, because the mobility of the alkali-metal ions was reduced by the mixed-alkali effect. 相似文献
2.
Decomposition of Mullite 总被引:2,自引:0,他引:2
ROBERT F. DAVIS ILHAN A. AKSAY JOSEPH A. PASK 《Journal of the American Ceramic Society》1972,55(2):98-101
Free surfaces of 2:1 mullite (2Al2 O3 ·SiO2 ) specimens decomposed with the evolution of SiO and O2 when they were heated at high temperatures under low partial pressures of O2 ; this reaction was analyzed thermodynamically. In addition, bubbles were observed at internal interfaces between mullite and fused-SiO2 diffusion couples. These bubbles, when formed at 1 atm ambient pressure between 1650° and 1800°C, resulted from reaction of Si particles and residual SiO2 -rich glass in the fused cast mullite. 相似文献
3.
Fibers of Li2 O.Al2 O3 .2SiO2 glass were ion-exchanged for 1 to 300 min in an NaNO3 bath at 366°C. The internal friction and the Li and Na concentration profiles were measured. As Na progressively replaced Li, the alkali internal friction peak became smaller while a new peak (mixed-alkali peak) appeared and increased in magnitude. These changes in internal friction are similar to those that occur when a second alkali is added to glasses prepared by conventional melting. The magnitudes of both internal friction peaks in the ion-exchanged glass depended on the overall composition of the glass; that of the alkali peak depended on the composition of the unexchanged glass core, whereas that of the mixed-alkali peak depended on the composition of the exchanged layer on the glass surface. When the exchanged surface layer was dissolved, the original alkali peak was restored, and the mixed-alkali peak disappeared. Changing the alkali distribution did not affect the mixed-alkali peak much; however, it caused the alkali peak to shift to higher temperatures and become smaller. The height of the alkali peak can be used to determine the maximum depth of penetration of the second alkali. 相似文献
4.
Ian M. Reaney Peter F. James William E. Lee 《Journal of the American Ceramic Society》1996,79(7):1934-1944
Phase evolution in calcium phosphate-based glass ceramics has been examined. Pure CaO:P2 O5 readily formed a glass which surface nucleated upon annealing, but volume nucleation at 680°C was observed only after the addition of the nucleating agents, TiO2 and A12 O3 . Phase separation of Ti and Al occurred along with the nucleation and growth of a calcium phosphate phase, similar to β-Ca2 P2 O7 . Heat treatments at higher temperatures and/or for longer times resulted in crystallization of A1- and Ti-rich, phase-separated regions. A glass with a higher CaO:P2 O5 ratio (approximately 2:1) could be prepared only when a total of 25-35 mol% of TiO2 , A12 O3 , and SiO2 were present in the batch. The glass phase-separated into respective SiO2 - and CaO/P2 O5 -rich regions on cooling. The SiO2 -rich regions did not influence crystallization and remained amorphous throughout the heat treatments. In the CaO/P2 O5 -rich regions, homogeneous volume nucleation of a Ti-rich phase readily occurred followed by the heterogeneous nucleation and growth on these nuclei of a calcium phosphate phase. Although this phase was macroscopically composed of spherulites, TEM revealed that they consisted of intertwined nanodendrites whose individual arms were approximately 20 nm wide and 50 nm long. 相似文献
5.
Yaping Zhang Yunxia Yang Yuwen Ou Wei Hua Jiahua Zheng Guorong Chen 《Journal of the American Ceramic Society》2009,92(8):1881-1883
Glasses with compositions 50Bi2 O3 – x Sb2 O3 –10B2 O3 –(40– x ) SiO2 ( x =0, 1, 3, 5, 8, 10) have been prepared by conventional melt quench technique. Substitution of Sb2 O3 for SiO2 exerted an obvious effect on properties of glasses, especially, increased glass transition temperature ( T g ) and crystalline temperature ( T c ) greatly. Results of infrared transmission spectra attributed the effect to the formation of new bridging bonds of Sb–O–B and Sb–O–Si in glass network. 相似文献
6.
Amorphous SiO2 fracture surfaces created under different partial pressures of water vapor ( p H2 O ) were analyzed using temperature-programmed static secondary ion mass spectroscopy. The results were used to develop an atomistic model for the formation of a fracture surface. It was found that substantial reconstruction of the SiO2 fracture surface took place immediately after the fracture event. Formation of the fracture surface was modeled as three individual steps-rupture of Si-O-Si bonds to form dangling Si* and Si-O* bonds, reconstruction and relaxation of the surface to form both strained and unstrained siloxane bonds, and, lastly, reaction of H2 O molecules with strained siloxane bonds to form surface silanol groups. The final concentration of surface silanol groups was found to have only a weak dependence on the p H2 O in the ambient atmosphere during the fracture process. It was also found that the number of strained siloxane bonds on the SiO2 fracture surface could be substantially reduced by heat treatment of the glass under vacuum. 相似文献
7.
Clear glasses which included droplet-like microphases were produced when SiO2 in sodium borosilicate glasses was replaced by Sc2 O3 . Phase separation and/or crystallization occurred after heat treatment. The porous skeleton of leached glasses consisted of hexagonal ScBO3 . The specific surface areas and pore radii are comparable to those of porous SiO2 glass. The sintering temperature of porous Sc-based material is higher than that of porous SiO2 . Alumina contamination influenced the structure of the porous material. 相似文献
8.
OMER O. VAN DER BIEST JOHN BARNES JOHN CORISH JAMES FRANK NORTON 《Journal of the American Ceramic Society》1987,70(7):456-459
Experimental observations and thermodynamic calculations are described which show that formation of SiS vapor from SiO2 in a high-sulfur, low-oxygen atmosphere is a viable corrosion mechanism. This mechanism will become more important than the well-known decomposition of SiO2 to SiO in those sulfur-bearing atmospheres where the oxygen activity is close to the Si/SiO2 phase boundary on a volatility diagram. 相似文献
9.
Laurent Cormier Daniel R. Neuville Georges Calas 《Journal of the American Ceramic Society》2005,88(8):2292-2299
The anomalous behavior of the glass transition temperature ( T g ) in low silica calcium aluminosilicate glasses has been related to the structural modifications observed by neutron and X-ray diffraction. The diffraction data indicate that Al and Si are in tetrahedral sites and that Ca atoms are in distorted octahedral sites. By subtracting the correlation functions for glasses at constant SiO2 or constant Al2 O3 content, we have shown that Si and Al atoms are introduced in a different way within the glass structure. Si is present in various Q n sites, while Al resides in Q3 and Q4 sites for glasses with high CaO content and enters fully polymerized Q4 sites with increasing SiO2 or Al2 O3 content. The higher proportion of Al in Q3 positions at high CaO content yields a depolymerization of the network. The lower connectivity will contribute to a decrease of the viscosity, which may be at the origin of the decrease of T g for glasses at low silica content. 相似文献
10.
Bo-Yun Jang Young-Hun Jeong Suk-Jin Lee Kyong-Jae Lee Sahn Nahm Ho-Jung Sun Hwack-Joo Lee 《Journal of the American Ceramic Society》2005,88(5):1209-1212
BaTi4 O9 thin films were grown on a Pt/Ti/SiO2 /Si substrate using rf magnetron sputtering and the structure of the thin films were then investigated. For the films grown at low temperature (≤350°C), an amorphous phase was formed during the deposition, which then changed to the BaTi5 O11 phase when the annealing was conducted below 950°C. However, when the annealing temperature was higher than 950°C, a BaTi4 O9 phase was formed. On the contrary, for the films grown at high temperature (>450°C), small BaTi4 O9 grains were formed during the deposition, which grew during the annealing. The homogeneous BaTi4 O9 thin films were successfully grown on Pt/Ti/SiO2 /Si substrate when they were deposited at 550°C and subsequently rapid thermal annealed at 900°C for 3 min. 相似文献
11.
Chemical diffusion coefficients for Si were measured in potassium silicate compositions containing from 64 to 85 wt% SiO2 ; unidirectional diffusion couples were heated for 0.1 to 720 h at 600° to 1400°C. The diffusion coefficients, which were calculated by the Boltzmann-Matano method, are described for a silicate containing 70 wt% SiO2 by:
The diffusion coefficients decreased with increasing O2 pressure. Below 800°C, the coefficients decreased with increasing SiO2 concentration; above 800°C, their dependence on SiO2 concentration was too weak to detect by the methods used. On the basis of a simple structural model for the glass, it was possible, from a phenomenological analysis of the diffusion, to establish a relation between the oxygen self-diffusion coefficient and the chemical diffusion coefficient for a given composition. 相似文献
The diffusion coefficients decreased with increasing O
12.
Microstructure and Properties of Co2+ : ZnAl2 O4 /SiO2 Nanocomposite Glasses Prepared by Sol–Gel Method
Xiu-Lan Duan Duo-Rong Yuan Xiu-Feng Cheng Hai-Qing Sun Zhi-Hong Sun Xin-Qiang Wang Zeng-Mei Wang Dong Xu Meng-Kai Lv 《Journal of the American Ceramic Society》2005,88(2):399-403
Transparent bulk Co2+ : ZnAl2 O4 /SiO2 nanocomposites containing nanocrystalline Co2+ : ZnAl2 O4 dispersed in silica glass matrix were obtained by the sol–gel method. The gels of composition 89SiO2 –6Al2 O3 –5ZnO− x CoO ( x =0.2, 0.4, 0.6, 0.8, 1.0) (mol%) were prepared at room temperature by using two different aluminum salts, aluminum nitrate and aluminum alkoxide (aluminum-iso-propoxide, Al(OPri )3 ), as starting materials. The transparent gels were converted to the crystalline phase of gahnite by heating above 900°C. The microstructural evolution of gels was characterized. The effect of Co2+ concentration on spectroscopic properties was also discussed. Co2+ : ZnAl2 O4 nanocrystals dispersed in the SiO2 -based glass are formed at lower heat-treatment temperature and shorter heating time by using Al(OPri )3 as raw material. 相似文献
13.
Susan Trolier-McKinstry Pong Chindaudom Kuppuswami Vedam Basavaraj V. Hiremath 《Journal of the American Ceramic Society》1995,78(9):2412-2416
Spectroscopic ellipsometry was used to rapidly and nonde- structively characterize ion-plated SiO2 and Ta2 O5 films on glass substrates as a function of temperature. The analysis provided the density (as a function of depth) and optical properties of the films. The SiO2 film had a higher refractive index than is typical for thermally grown SiO2 . This was attributed to compaction of the film during the deposition process. Similarly, the ion-plated Ta2 O5 film had the high refractive index characteristic of a high-density film. The films were not affected strongly by temperature during heating >100°C. 相似文献
14.
Robert R. Sickafoose Jr. Dennis W. Readey 《Journal of the American Ceramic Society》1993,76(2):316-324
In a reducing atmosphere, SiO2 as an impurity in SiC can react to form SiO and CO gases. Likewise, oxygen in the atmosphere can also lead to the same gaseous species. Experimental data are reported on the rate of weight loss in H2 -H2 O atmospheres of porous SiC containing residual SiO2 . The amount of residual SiO2 was varied by passive oxidation of the porous SiC prior to heating in the reducing atmosphere. The data are compared to a model of active corrosion to determine the mechanism of weight loss and to identify the gas species present in SiC with SiO2 as an impurity. 相似文献
15.
C. R. DAS 《Journal of the American Ceramic Society》1981,64(4):188-193
A sodium silicate glass and ternary glasses derived from it by substituting AI2 O3 and ZrO2 for SiO2 were exposed to water and aqueous solutions of pH 1.4 to 12.7; the kinetics of the reactions were studied. Diffusion of alkali ions and leaching of alkali and SiO2 from the glasses were influenced by the occupancy of surface sites by alkali ions above a critical pH; however, the activation energies of the processes varied linearly with the logarithm of mole fraction of surface sites occupied by Hplus; . Identical slopes were obtained for all glasses for a given process. The results are explained on the basis that transport of alkali ions is retarded as a result of increased boundary concentration and that suitable sites for reaction are lacking. 相似文献
16.
James Zaykoski Inna Talmy Marriner Norr Manfred Wuttig 《Journal of the American Ceramic Society》1991,74(10):2419-2427
High-temperature evaporation from 80% porous, rigid mullite (3Al2 O3 ·2SiO2 ) whisker felt was studied under vacuum and at various helium pressures using gravimetry, X-ray diffractometry, SEM, and EDS. Heat treatments at 1350° to 1550°C resulted in evaporation of SiO2 from mullite with a rate strongly dependent on temperature and pressure. A concentration gradient of SiO2 was observed through the cross section of samples after heating under vacuum, indicating that SiO2 preferentially evaporated from whiskers on the periphery of the samples. The SiO2 concentration gradient was accompanied by sharp microstructural changes across the specimens. The gradient was decreased by raising the ambient helium pressure during heat treatment. A mathematical model was developed to predict the SiO2 concentration profile. The model agrees well with experimental results and demonstrates that the diffusivity of SiO2 in the vapor phase controls the gradient of SiO2 through the cross section of mullite felt. 相似文献
17.
Minoru Tomozawa Won-Taek Han William A. Lanford 《Journal of the American Ceramic Society》1991,74(10):2573-2576
Hydrogen concentration depth profiles on surfaces of SiO2 glass fractured slowly in water and rapidly in oil were determined by nuclear reaction analysis. It was found that water enters SiO2 glass during slow crack growth in water. 相似文献
18.
Masayuki Fujimoto Tomoya Ohno Hisao Suzuki Hiroshi Koyama Junzo Tanaka 《Journal of the American Ceramic Society》2005,88(11):3264-3266
We characterized SiO2 –TiO2 nano-hybrid particles, prepared using the sol–gel method, using high-resolution transmission microscopy. A few nanometer-ordered TiO2 anatase crystallites could be observed on the monodispersed SiO2 nanoparticle surface. The quantum size effect of the TiO2 anatase crystallites is attributed to the blue shift of the absorption band. The rough surface of the SiO2 –TiO2 nano-hybrid particles was derived from the developed growth planes of the TiO2 anatase crystallites, grown from fully hydrolyzed Ti alkoxide that did not react with acetic acid during the crystallization process at 600°C thermal annealing. 相似文献
19.
Sol–Gel Synthesis and Characterization of Ag and Au Nanoparticles in SiO2 , TiO2 , and ZrO2 Thin Films
Mauro Epifani Cinzia Giannini Leander Tapfer Lorenzo Vasanelli 《Journal of the American Ceramic Society》2000,83(10):2385-2393
Silver and gold nanoparticles were synthesized by the sol–gel process in SiO2 , TiO2 , and ZrO2 thin films. A versatile method, based on the use of coordination chemistry, is presented for stabilizing Ag+ and Au3+ ions in sol–gel systems. Various ligands of the metal ions were tested, and for each system it was possible to find a suitable ligand capable of stabilizing the metal ions and preventing gold precipitation onto the film surface. Thin films were prepared by spin-coating onto glass or fused silica substrates and then heat-treated at various temperatures in air or H2 atmosphere for nucleating the metal nanoparticles. The Ag particle size was about 10 nm after heating the SiO2 film at 600°C and the TiO2 and ZrO2 films at 500°C. After heat treatment at 500°C, the Au particle size was 13 and 17 nm in the TiO2 and ZrO2 films, respectively. The films were characterized by UV–vis optical absorption spectroscopy and X-ray diffraction, for studying the nucleation and the growth of the metal nanoparticles. The results are discussed with regard to the embedding matrix, the temperature, and the atmosphere of the heat treatment, and it is concluded that crystallization of TiO2 and ZrO2 films may hinder the growth of Ag and Au particles. 相似文献
20.
John S. Wright Joseph M. Schwartz Lanny D. Schmidt Lorraine Falter Francis 《Journal of the American Ceramic Society》1995,78(9):2360-2366
The crystalline phase development and microstructural changes with heating of sol-gel-derived lead titanate (PT) particles and films on silica with and without a fugitive (or removable) diffusion barrier layer were investigated. Amorphous gel-derived PT particles were deposited on SiO2 -coated TEM grids with and without polyimide (PI) or carbon barrier layers between SiO2 and PT. TEM analysis showed that PI or carbon barriers prevented reaction between the gel-derived PT particles and SiO2 . PT particles crystallize and then the PI or carbon film decomposes. Sol-gel-derived PT films were deposited on oxidized Si substrates (Si/SiO2 ) with and without a PI barrier layer. Perovskite PT films were prepared on Si/SiO2 substrates with a PI barrier; however, some porosity remained in the films. Identically prepared films without the PI barrier formed a mixture of pyrochlore and perovskite. X-ray photoelectron spectroscopy results indicate that the PI film pre- vents the diffusion of Si into the PT film. 相似文献