共查询到20条相似文献,搜索用时 15 毫秒
1.
J. SCHROEDER R. MOHR P. B. MACEDO C. J. MONTROSE 《Journal of the American Ceramic Society》1973,56(10):510-514
The intensity and spectral distribution of light scattered by K2 O-SiO2 glasses (K2 O content up to 40 mol%) were measured. The transverse and longitudinal sound-wave velocities and the photoelastic constants were evaluated from the results. The total intensity of the scattering (and therefore the attenuation caused by it) exhibited a minimum at a concentration of ∼25 mol% K2 O. For this composition the attenuation is ∼2/2 of that in pure SiO2 . This behavior results from the existence of anomalously small concentration fluctuations in the melt of K2 O·3SiO2 glass. A qualitative explanation of this result, involving low-temperature immiscibility regions, is presented. 相似文献
2.
N. L. LABERGE V. V. VASILESCU C. J. MONTROSE P. B. MACEDO 《Journal of the American Ceramic Society》1973,56(10):506-509
The density fluctuations contributing to light scattering in a glass are governed by the flctive temperature of the glass and the equilibrium compressibility of the melt. Using ultrasonic velocity data for K2 O–SiO2 melts, these compressibilities were evaluated, and the magnitude of the density fluctuations were calculated. In this system, the mean–square amplitude of the fluctuations reaches a minimum value (about half that of pure SiO2 ) for a composition of ∼20 mol% K2 O. By extrapolating the equilibrium compressibilities to zero K2 O content, the density fluctuations can be calculated for pure SiO2 glass; this calculation agrees well with the result obtained from light–scattering measurements. 相似文献
3.
Ping Wu Gunnar Eriksson Arthur D. Pelton 《Journal of the American Ceramic Society》1993,76(8):2059-2064
Available thermodynamic and phase diagram data have been evaluated for all phases in the Na2 O-SiO2 and K2 O-SiO2 systems at 1 bar pressure from 298 K to above the liq-uidus temperatures. All reliable thermodynamic and phase diagram data have been simultaneously optimized in order to obtain one set of model equations for the Gibbs energies of all phases as functions of temperature and composition. The thermodynamic properties and phase diagrams calculated from these parameters are self-consistent. The modified quasi-chemical model was used to represent the Gibbs energies of the molten slag phases. 相似文献
4.
Debao Zhang Baoyu Chen Zhuping Liu Shunguang Li Lili Hu 《Journal of the American Ceramic Society》2004,87(12):2228-2231
Er3+ -doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO2 ·0.3Al2 O3 )· x Na2 O·8.2La2 O3 · 0.6Er2 O3 ·0.2Yb2 O3 ·1Sb2 O3 (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω t ( t = 2, 4, 6) decreases with increasing Na2 O. Ω2 decreases rapidly with increasing Na2 O while Ω4 and Ω6 decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na2 O. Fluorescence spectra of the 4 I 13/2 to 4 I 15/2 transition have been measured and the change with Na2 O content is discussed. It is found that the full width at half-maximum decreases with increasing Na2 O. 相似文献
5.
Anna Musinu Giorgio Piccaluga Mauro Magini 《Journal of the American Ceramic Society》1988,71(5):256-C
The radial distribution functions of ZnO–K2 O–SiO2 glasses with 7 and 10 wt% ZnO are compared with that of the corresponding K2 O–SiO2 matrix leading to "difference distribution curves'representative of the zinc structural arrangement. Analysis of the curves indicates that Zn2+ ions are prevalent (65% to 80%) in the glasses in tetracoordinated form. 相似文献
6.
Time-dependent deformation behavior induced by an indentation, called indentation creep, was investigated for Na2 O · 3SiO2 glasses with various water contents by measuring the indentation depth as a function of time using a conical indenter. It was found that the indentation creep behavior of the glasses could be best explained as steady-state inhomogeneous (non-Newtonian viscous) flow. Water in the glasses appeared to reduce the stress (or yield stress) needed to cause this flow. Crack initiation of the glasses was promoted by water through this inhomogeneous flow. 相似文献
7.
Samples of Sr2 Fe2− x Mo x O6 were prepared by solid-state reaction in air and 5%H2 –95%N2 . X-ray diffractometry was used to identify the phases and evaluate the lattice parameters. It is found that molybdenum ions can dissolve in the SrFeO3 even if the sample is heated in air but the solubility is limited. The solubility can be enhanced by heating the sample in low oxygen partial pressure, which is attributed to the larger ionic radii of Fe3+ and Mo5+ than that of Fe4+ . The degradation of Sr2 Fe2− x Mo x O6 in water and air is also reported. 相似文献
8.
Yong Su Lee Won Ho Kang Byeoung Il Kim Sun Dal Song 《Journal of the American Ceramic Society》2001,84(10):2433-2435
A 355-nm neodymium:yttrium aluminum garnet laser, produced by a harmonic generator, was used for the nucleation process in photosensitive glass containing Ag+ and Ce3+ ions. The pulse width and frequency of the laser were 8 ns and 10 Hz, respectively. Heat treatment was conducted at 570°C for 1 h, following laser irradiation, to produce crystalline growth, after which a LiAlSi3 O8 crystal phase appeared in the laser-irradiated Li2 O–Al2 O3 –SiO2 glass. The present study compares the effect of laser-induced nucleation on glass crystallization with that of spontaneous nucleation by heat treatment. 相似文献
9.
The effect of niobia on the dielectric properties of glasses in the system Nb2 O5 –Na2 O–SiO2 has been studied from 100 to 1010 cps. The dielectric constant is high even at frequencies up to 1010 cps. The Nb5+ ion, with its small ionic radius and high charge, reinforces the network and raises the dielectric constant. 相似文献
10.
Daniel Caurant Odile Majérus Edward Fadel Marion Lenoir Christel Gervais Olivier Pinet 《Journal of the American Ceramic Society》2007,90(3):774-783
Crystallization of the poorly durable Na2 MoO4 phase able to incorporate radioactive cesium must be avoided in SiO2 –Al2 O3 –B2 O3 –Na2 O–CaO glasses developed for the immobilization of Mo-rich nuclear wastes. Increasing amounts of B2 O3 and MoO3 were added to a SiO2 –Na2 O–CaO glass, and crystallization tendency was studied. Na2 MoO4 crystallization tendency decreased with the increase of B2 O3 concentration whereas the tendency of CaMoO4 to crystallize increased due to preferential charge compensation of BO4 − entities by Na+ ions. 29 Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd3+ ) were shown to enter into CaMoO4 crystals formed in glasses. 相似文献
11.
In an attempt to understand the liquid–liquid phase separation in the B2 O3 –MgO, B2 O3 –CaO, B2 O3 –SrO, and B2 O3 –BaO systems, the liquid miscibility gaps were calculated using the optimized interaction parameters of liquid phases. The Gibbs energies of liquid phases were derived in the form of a subregular solution from an optimization procedure based on phase diagram data. In addition, metastable liquidus boundaries and spinodal curves were also assessed by using the Gibbs energies of liquid phases. The present results were compared and discussed with other experimental and assessed data available in the literature. 相似文献
12.
Measurements of the densities of glasses in the series x Na2 S + (1 − x )B2 S3 are reported for the first time. As has been found in the corresponding oxyborate series x Na2 O + (1 − x )B2 O3 , the addition of Na2 S to B2 S3 causes the density to increase, from 1.80 g/mL for pure B2 S3 to 1.99 g/mL at the limit of the low-alkali sulfide glass-forming range of x = 0.25. These data provide evidence for the formation of tetrahedral boron units (BS4 − ) as alkali is added. Volumes for the trigonal BS3 and tetrahedral BS4 − groups of 57.55 and 51.79 Å3 , respectively, were determined. As has also been found in the oxyborates, the tetrahedral boron group occupies a smaller volume than the trigonal boron group and causes the increase in density with added Na2 S. 相似文献
13.
Bh. V. JANAKIRAMA RAO 《Journal of the American Ceramic Society》1963,46(3):107-114
By a progressive weight percent substitution of TiO2 for SiO2 at various rations of concentration of K2 O and PbO, the entire region of glass formation in the quaternary system K2 O–PbO–SiO2 –TiO2 was covered with 51 glass compositions. The properties of these glasses were determined and studied with respect to the role of TiO2 in the system. The results indicated that the dielectric constant increased progressively with increasing TiO2 concentration whereas the dissipation factor showed an overall decrease, when measured at 1 Mc and 25°C. Density and the refractive index increased progressively with increasing TiO2 concentration but deviated from the additive relation. Chemical durability, expansivity, and softening temperature vs. composition curves showed definite inflections. The effect of TiO2 on oxygen packing indicated that Ti4+ strengthens the network in lower concentrations and weakens the network in higher concentrations in this system. It appears to be likely that Ti4+ changes its coordination number form 4 to 6. 相似文献
14.
Duk-Jun Kim Jin-Woo Hahn Gee-Pyeong Han Sang-Seok Lee Tae-Goo Choy 《Journal of the American Ceramic Society》2000,83(4):1010-1012
The sinterability and microwave dielectric properties of (Zr0.8 Sn0.2 )TiO4 with additions of 1 mol% of magnesium, calcium, strontium, or barium were examined. All the alkaline-earth metals were effective for densification, and the order of effectiveness was as follows: Mg < Ca < Sr < Ba. The dielectric constant and the temperature coefficient of the resonant frequency were not influenced very much by the additives; however, a strong deterioration of the quality factor ( Q ) did occur when magnesium was added. The presence of grain-boundary phases was confirmed via microstructural observation, using transmission electron microscopy. In addition, energy-dispersive X-ray analysis was performed to investigate the cause of the deterioration in the Q value. 相似文献
15.
The internal friction of R2 O·Al2 O3 ·6SiO2 glasses was measured from-180° to 700°C at 0.4 Hz. Glasses containing Li2 O or Na2 O exhibited only the one internal friction peak characteristic of the stress-induced movement of the alkali ions. Substitution of a second alkali resulted in two significant changes in the internal friction: (1) a rapid reduction in the magnitude of the original alkali peak and (2) the appearance of a new internal friction peak whose magnitude was especially sensitive to the concentration of the second alkali. Each combination of two alkali ions resulted in a new peak, with peaks being observed for the combinations Li-Na, Na-K, and Li-K. A mechanical damping spectrum is predicted for aluminosilicate glasses containing more than two alkali ions. 相似文献
16.
Samar J. Kalita Himesh A. Bhatt Abhijeet Dhamne 《Journal of the American Ceramic Society》2006,89(3):875-881
Effects of MgO–Na2 O–P2 O5 -based sintering additives on densification, microstructure, hardness, compression strength, and biodegradability of β-tricalcium phosphate (β-TCP) ceramics were studied. Three additive compositions were prepared and introduced into β-TCP. Uniaxially compacted ceramic structures, sintered at 1250°C in air, were characterized. Scanning electron microscopy was used to study the microstructure. The X-ray diffraction technique was used for phase analysis. Results showed that these additives modified the microstructure and improved the sintered density and mechanical properties. An increase of 9% in density, 40% in hardness and 38% in compression strength were achieved. Biodegradation analysis revealed that these additives could tailor the rate of resorption and hardness degradation of β-TCP. 相似文献
17.
MASASUKE TAKATA JOYCE E. MOLINELLI MINORU TOMOZAWA E. BRUCE WATSON 《Journal of the American Ceramic Society》1984,67(2):106-109
Dielectric characteristics of Na2 O·3SiO2 glasses with water contents up to ∼12 wt% were found to be drastically affected by incorporated water. The high-frequency dielectric constant increased with water content, while both the static dielectric constant and the low-frequency dielectric relaxation strength showed a pronounced minimum at a water content of ∼3 wt%. 相似文献
18.
Phase equilibria along the nonbinary join between cordierite (2MgO · 2Al2 O3 · 5SiO2 ) and spodumene (Li2 O · Al2 O3 · 4SiO2 ) were investigated in the temperature range 800° to 1550°C. using the quench technique on fourteen compositions. The phase diagram at high temperatures is characterized by a very small region of solid solution on the cordierite side, appreciable solid solution on the spodumene side, and regions of three and four phases toward the center of the system, including liquid, α-cordierite, mullite, spinel, corundum, and β-spodumene and its solid solutions. The liquidus has a flat minimum between 40 and 50% cordierite at 1347°, and rises on one side to the congruent melting point of β-spodumene (1421°) and on the other side to the temperature of complete melting of cordierite (1530°). The lowest temperature at which liquid appears is 1325°. At low temperatures a complete series of metastable solid solutions exists between μ-cordierite and β-spodumene. The significance of the data in the preparation of thermal-shock-resisting bodies is discussed. 相似文献
19.
Masayuki Nogami Yoichi Goto Toshihiro Kasuga 《Journal of the American Ceramic Society》2003,86(9):1504-1507
The effect of zirconium ions on glass structure and proton conductivity was investigated for sol-gel-derived P2 O5 –SiO2 glasses. Porous glasses were prepared through hydrolysis of PO(OCH3 )3 , Zr(OC4 H9 )4 , and Si(OC2 H5 )4 . Chemical bonding of the P5+ ions was characterized using 31 P-NMR spectra. The phosphorous ions, occurring as PO(OH)3 in the ZrO2 -free glass, were polymerized with one or two bridging oxygen ions per PO4 unit with increased ZrO2 content. The chemical stability of these glasses was increased significantly on the addition of ZrO2 , but the conductivity gradually decreased from 26 to 12 mS/cm at room temperature for 10P2 O5 ·7ZrO2 ·83SiO2 glass. A fuel cell was constructed using 10P2 O5 ·5ZrO2 ·85SiO2 glass as the electrolyte; a power of ∼4.5 mW/cm2 was attained. 相似文献
20.
Jau-Ho Jean Yu-Ching Fang Steve X. Dai David L. Wilcox Sr. 《Journal of the American Ceramic Society》2001,84(6):1354-1360
The devitrification kinetics and mechanism of a low-dielectric, low-temperature, cofirable K2 O–CaO–SrO–BaO–B2 O3 –SiO2 glass-ceramic have been investigated. Crystalline phases including cristobalite (SiO2 ) and pseudowollastonite ((Ca,Ba,Sr) SiO3 ) are formed during firing. Activation energy analysis shows that the nucleation of the crystalline phases is controlled by phase separation of the glass. The crystallization kinetics of both cristobalite and pseudowollastonite obey Avrami-like behavior, and the results show an apparent activation energy close to that of the diffusion of alkaline and alkali ions in the glass, suggesting that diffusion is rate limiting. The above conclusion is further supported by analysis of measured growth rates. 相似文献