共查询到20条相似文献,搜索用时 15 毫秒
1.
Somnath Bhattacharyya Thomas Hche Nicols Hemono María J. Pascual Peter A. van Aken 《Journal of Crystal Growth》2009,311(18):4350-4355
Aiming at tailoring optical properties, the precipitation of LaF3 nano-crystals in LaF3–Na2O–Al2O3–SiO2 glass-ceramics is studied thoroughly on the nano-scale using advanced transmission electron microscopic techniques. Nano-sized phase-separation droplets enriched in lanthanum and silicon are formed already in the base glass. Within these less than 20 nm large droplets, LaF3 crystallizes upon heat treatment. The nano-crystallization mechanism revealed is self-limited since growth is restricted by the size of the droplets. An average crystallite size of around 12 nm is achieved with a narrow size distribution since the phase-separation droplets also contain silicon not incorporated into the growing crystal. Instead, excess silicon relocated to the periphery of the pre-existing phase-separation droplets forms a diffusion barrier around the LaF3 nano-crystals preventing further crystal growth and/or ripening. 相似文献
2.
The solubility of Ag2O was measured for the Na2O–B2O3 and Na2O–B2O3–Al2O3 system with the rotating crucible method and static method, respectively, under air atmosphere at temperatures ranging from 1273 to 1423 K. The contamination of melts from crucibles could be avoided by the rotating crucible method, with which it became possible to measure the solubility of Ag2O for the Na2O–B2O3 system above the melting point of Ag for the first time. It was found that the addition of Na2O decreases the solubility of Ag2O while the addition of Al2O3 had little effect on the solubility. The effect of Na2O and Al2O3 on the solubility of Ag2O is expressed by interaction coefficients and is analyzed in terms of the basicity of melts. The solubility of Ag2O in Na2O–B2O3–Al2O3 melts increased with increased temperature. This phenomena was explained by a small enthalpy change in oxidation of silver. 相似文献
3.
《Journal of Non》2003,330(1-3):128-141
The electrical and dielectric properties for three series of MoO3–Fe2O3–P2O5 and one series of SrO–Fe2O3–P2O5 glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO3 is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe2O3 content and Fe(II)/Fetot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe2O3 content in MoO3–Fe2O3–P2O5 glasses with O/P at 3.5 the dc conductivity, σdc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe2O3 and is independent of the MoO3 content. Also, the dielectric properties such as ′(ω), ″(ω) and σac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO3. On the other hand, the dc conductivity for MoO3–Fe2O3–P2O5 glasses with O/P > 3.5 increases with the substitution of MoO3 which has been explained by an increase in the number of non-bridging oxygens and formation of Fe–O–P bonds that are responsible for formation of small polarons. The increase in the dielectric permittivity, ′(ω) with increasing MoO3 content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe2O3–P2O5 glasses the conductivity and dielectric permittivity remained constant with increasing SrO. 相似文献
4.
The surface morphology of Na2O–B2O3–Al2O3–SiO2 vitrified bond with and without calcium oxide was studied by soaking vitrified bonded microcrystalline alumina composites in water. The content of water introduced to the vitrified bond was determined by thermal gravity analysis, and the effects of water and calcium on the phase separation and nucleation of the vitrified bond were investigated using scanning electron microscope and energy-dispersive X-ray spectrometer. Soaked in water for 72 h, the Na2O–B2O3–Al2O3–SiO2 vitrified bond presented a porous surface, and its bending strength declined with increasing sintering temperature. However, the Na2O–CaO–B2O3–Al2O3–SiO2 vitrified bond was more durable against aqueous coolant even needle-shape crystals were found clustered on the surface of the vitrified bond. The crystals were enriched with aluminosilicate tested by energy-dispersive X-ray spectrums. The appearance of crystals lessened the dissolution of the vitrified bond and made the bending strength increase in the sintering temperature region between 870 °C and 930 °C. 相似文献
5.
11B (I=3/2) MAS NMR in the binary glass system xV2O5–B2O3 (x=0.053, 0.43) and the ternary glass system xV2O5–B2O3–PbO (0.1x1.5) has been investigated at room temperature. In the xV2O5–B2O3 glasses, one NMR line due to BO3 unit was observed. Meanwhile in the xV2O5–B2O3–PbO, two NMR lines which arise from BO3 and BO4 units were detected, where the appearance of BO4 units is produced by the presence of PbO. From the computer-simulation of the 11B NMR central transition line (m=−1/2↔1/2), the quadrupole parameters (e2qQ/h and η) for BO3 units in xV2O5–B2O3, and those for BO3 and BO4 units in xV2O5–B2O3–PbO were obtained as a function of x. As the V2O5 content increases in xV2O5–B2O3–PbO, the e2qQ/h and η values of the BO3− associated resonance are found to slightly decrease and increase, respectively. Meanwhile, the e2qQ/h and η values of BO4− associated resonance in xV2O5–B2O3–PbO are found to slightly increase and decrease, respectively. By comparing the intensities of the total transitions (m=−3/2↔−1/2,m=−1/2↔1/2, and 1/2↔3/2) for the 11B NMR line of BO3 and BO4 units contained in xV2O5–B2O3–PbO with those of respective standard samples of 0.053V2O5–B2O3 and NaBH4, the quantitative fractions of BO3 and BO4 in xV2O5–B2O3–PbO were obtained as a function of x. 相似文献
6.
In MoO3–Nd2O3–B2O3 and MoO3–Nd2O3–La2O3–B2O3 systems, glasses were obtained in the region between 20 and 30 mol% Ln2O3. A liquid-phase separation region was observed near the MoO3–B2O3 side up to 20 mol% Ln2O3 (La, Nd). The amorphous phases were characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), UV–VIS and infrared spectroscopy (IR). According to DTA data B2O3-rich glasses are stable up to 630 °C while glasses rich in MoO3 are stable up to 430 °C. The glasses are transparent in the visible region. Structural models for the glasses network were suggested on the basis of IR spectral investigations. It was established that BO3 (1380 cm−1), BO4 (1100–950 cm−1) and MoO4 (860 cm−1) groups build up the glass network. MoO6 units (band at 880 cm−1) together with BO3 units participate in the formation of the glass network with a high MoO3 content (80–90 mol%). 相似文献
7.
The densities have been systematically measured in xLi2O–(1−x)B2O3 melts of different compositions with Li2O content varying from x=0 to 0.68 from their respective melting points up to about 1450 K with a modified Archimedean method. The density decreased with increasing temperature for all the melts measured in this work. When x<0.15, the plot of temperature versus density could be well fitted by a quadratic polynomial function, and when x0.15, density decreased linearly with increasing temperature. At a fixed temperature, the density of the melts increased rapidly with Li2O content, went through a maximum at about x=0.333 (Li2O–2B2O3), and then decreased slowly as Li2O content was further increased. In addition, the volume expansion coefficient (β) was calculated based on the densities measured in this work, and it was found that a maximum value appeared in the dependence of β on the molar ratio of Li2O at about x=0.333. 相似文献
8.
A complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and thermodynamic properties of all oxide phases in the ternary Al2O3–B2O3–SiO2 system at 1 bar pressure are presented. The molten oxide phase is described by the Modified Quasichemical Model and the Gibbs energy of the mullite solid solution is modeled using the Compound Energy Formalism. A set of optimized internally consistent thermodynamic functions for all the phases is presented. With the thermodynamic dataset, all available and reliable thermodynamic and phase equilibrium data can be reproduced within experimental error limits from 25 °C to above the liquidus temperatures. In addition, the reasonable predictions obtained for phase relations in the experimentally unexplored composition ranges suggest that the thermodynamic database can be used along with appropriate Gibbs energy minimization routines to calculate thermodynamic properties, phase equilibria, and phase diagrams of interest. 相似文献
9.
B.A. Sava Adriana Diaconu Lucica Boroica Daniela Ursu T. Visan M. Elisa Alina Balu 《Journal of Non》2009,355(37-42):2020-2022
The paper studies the materials from ZnO–TiO2–B2O3 ternary system, obtained by sol–gel method [1] and [2], starting from organic and inorganic precursors. The obtained samples are investigated by FTIR and Raman spectroscopy, which provide structural information, at molecular level. FTIR absorption maxima are identified and discussed according to literature data. Raman spectra are acquired by a Raman Jasco NRS-3100 spectrometer, at 532 nm wavelength and put in evidence characteristic vibration modes for all three oxide components. ESR spectra were plotted with the aid of a JES-FA 100-JEOL Japan spectrometer and titanium surrounding is investigated. 相似文献
10.
Measurements of two-photon absorption (TPA) coefficients β at 532 nm in binary Bi2O3:B2O3 glasses are reported. The β obtained ranges from 12.9 to 16.4 cm/GW with the larger value observed in higher Bi2O3 glass. The relationship between β and glass composition is discussed in terms of the electronic structure of glasses: β can be scaled with optical band gap. 相似文献
11.
New glasses in the PbBr2–PbCl2–PbF2–PbO–P2O5 system have been prepared and characterized. The glass-forming regions have been explored and the stability of the glasses against crystallization studied. Results show that the PbBr2–PbCl2–P2O5 ternary system has a broad glass-forming region which extends to 30 mol% P2O5. Most of the glasses in this system show strong stability against crystallization and some have glass transition temperatures as low as 146°C. When 5% PbO or 5% PbF2 is introduced into the PbBr2–PbCl2–P2O5 system, the glass-forming region becomes smaller and the glass transition temperatures increase. However, the introduction of 2.5% PbF2 and 2.5% PbO into the ternary system increases the glass transition temperature and broadens the glass-forming region. The introduction of PbF2 alone improves the glass-forming ability of the system while the introduction of PbO alone lowers the glass-forming ability. 相似文献
12.
The preparation of glass-lined coating mould from gels in the ternary system of SiO2–ZrO2–B2O3 has been investigated. The crystallization characterization and high temperature structure stability of this coating mould are demonstrated. We can find that the crystallization of t-ZrO2 as well as the tetragonal to monoclinic phase transformation are, respectively, retarded and impeded owing to the encasement of SiO2 matrix. While the inhibitive effect of B2O3 on crystallization of the SiO2–ZrO2–B2O3 coating mould is explained. Finally, DD3 single crystal superalloy melt can realize highly undercooled rapid solidification by adopting this coating mould, which further evinces that SiO2–ZrO2–B2O3 coating mould has an ideal nucleation inhibition for superalloy. 相似文献
13.
Tetsuji Yano Tomonori Nagano Jaeho Lee Shuichi Shibata Masayuki Yamane 《Journal of Non》2000,270(1-3):163-171
Ag+/Na+ ion-exchanged R2O–Al2O3–SiO2 glasses with uniform concentration profile of Ag+ and Na+ were prepared by heat treatment in molten silver salt followed by holding at the same temperature in an ambient atmosphere. Their glass transition temperature (Tg) and thermal expansion coefficient (TEC) were measured and structures were investigated using 29Si-MAS NMR, 27Al-MAS NMR, IR and Raman spectroscopies. Both Tg and TEC decreased with increase of the exchange ratio, but Tg was still above the ion-exchange temperature of 400°C even for the fully exchanged sample. The 29Si- and 27Al-MAS NMR spectra were mostly unchanged and no sign of the structural alteration of the glass network was observed. On the other hand, the vibrational spectra showed remarkable peak shifts depending on the exchange ratio. From these structural results, it was found that when the exchange ratio was low, the introduced Ag+ ions were stabilized at the non-bridging oxygen (NBO) site, and then Na+ ions in AlØ4 site were exchanged by Ag+ ions after full replacement of NBO sites, where Ø represents the bridging oxygen. 相似文献
14.
Tellurite containing vanadate (50−x)V2O5–xBi2O3–50TeO2 glasses with different bismuth (x=0, 5, 10, 15, 20 and 25 wt%) contents have been prepared by rapid quenching method. Ultrasonic velocities (both longitudinal and shear) and attenuation (for longitudinal waves only) measurements have been made using a transducer operated at the fundamental frequency of 5 MHz in the temperature range from 150 to 480 K. The elastic moduli, Debye temperature, and Poisson’s ratio have been obtained both as a function of temperature and Bi2O3 content. The room temperature study on ultrasonic velocities, attenuation, elastic moduli, Poisson’s ratio, Debye temperature and glass transition temperature show the absence of any anomalies with addition of Bi2O3 content. The observed results confirm that the addition of Bi2O3 modifier changes the rigid formula character of TeO2 to a matrix of regular TeO3 and ionic behaviour bonds (NBOs). A monotonic decrease in velocities and elastic moduli, and an increase in attenuation and acoustic loss as a function of temperature in all the glass samples reveal the loose packing structure, which is attributed to the instability of TeO4 trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi2O3 content are more stable than with high Bi2O3 content. 相似文献
15.
S. Agathopoulos D.U. Tulyaganov J.M.G. Ventura A. Saranti J.M.F. Ferreira 《Journal of Non》2006,352(4):322-328
Glasses, whose basic composition was based on the CaO-MgO-SiO2 system and doped with B2O3, P2O5, Na2O, and CaF2, were prepared by melting at 1400 °C for 1 h. Raman and infrared (IR) spectroscopy revealed that the main structural units in the glass network were predominantly Q1 and Q2 silicate species. The presence of phosphate and borate units in the structure of the glasses was also evident in these spectra. X-ray analysis showed that the investigated glasses devitrified at 750 °C and higher temperatures. The crystalline phases of diopside and wollastonite dominated, but weak peaks, assigned to akermanite and fluorapatite, were also registered in the diffractograms. The presence of B2O3, Na2O, and CaF2 had a negligible influence on the assemblage of the crystallized phases, but it caused a reduction of crystallization temperature, comparing to similar glasses of the CaO-MgO-SiO2 system. 相似文献
16.
Homogeneous and transparent V2O5–TiO2 composite nanometer thin films were prepared on glass substrates by sol–gel processing and dip-coating technique. The films as well as the dried powder of bulk gel were characterized by different techniques like X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), atomic force microscope (AFM) and thermogravimetry–differential thermal analysis (TG–DTA). The hydrophilicity of the films was determined by measuring the water contact angles on the films. The results showed that the dopant of V2O5 on TiO2 thin films could produce a visible-light response to the films, and the introduction of V2O5 could suppress the structural phase transition and crystal growth of TiO2 crystal. Finally, the relationship between crystalline size and hydrophilicity under sunlight was investigated in this article. 相似文献
17.
Jn Kaluný Marian Kubliha Vladimír Laba Marcel Poulain Yasmina Taibi 《Journal of Non》2009,355(37-42):2031-2034
Electric measurements, including temperature dependencies of direct electrical conductivity and temperature dependencies of complex electrical modulus, have been implemented using Sb2O3–V2O5–K2O glass samples. These glasses absorb ambient humidity but their resistance to water attack depends on composition. The significant decrease of conductivity up to 100 °C can arise from water desorption. Cycling measurements of direct electrical conductivity versus temperature were also implemented. They show that the 30Sb2O3–30V2O5–40K2O and 70Sb2O3–30K2O glasses are irreversibly damaged with the formation of the hydrated layer. In addition, it was observed that the evolution of DC conductivity is ruled by Arrhenius relation, while activation energy decreases as Sb2O3 concentration increases. 相似文献
18.
Phase relations around langasite (LGS, La3Ga5SiO14) were studied on the basis of phase assemblage observed during calcination and crystallization process of samples of various compositions in the ternary system La2O3–Ga2O3–SiO2. A ternary compound of apatite structure, La14GaxSi9–xO39–x/2 was found for the first time. Crystallization of this compound was observed in the cooling process of molten samples of stoichiometric LGS as well as LGS single crystal, demonstrating that LGS is an incongruent-melting compound. A phase diagram was established primarily based on the crystallization sequence in the cooling process. 相似文献
19.
The kinetics of structural relaxation and of glass transition of the 45Na2O-40B2O3-10Al2O3-5In2O3 glassforming melt is studied by means of standard DSC and of temperature modulated DSC. In this way the dependence of the fictive temperature on cooling rate is determined simultaneously with the determination of the dependence of the dynamic glass transition temperature on modulation frequency. Both sets of data are fitted together in terms of the equation of Ritland-Bartenev. It was found that the activation energy of the structural relaxation exhibits a moderate dependence on temperature with the dimensionless fragility parameter α=3.3 (for strong systems, α is about 1 and increases to about 8 for some very fragile polymeric systems). 相似文献
20.
Glasses in the system Na2O/B2O3/Al2O3/In2O3 were melted and subsequently tempered in the range from 500 to 700 °C. Depending on the chemical composition, various crystalline phases were observed. From samples without Al2O3, In2O3 could not be crystallized from homogeneous glasses, because either spontaneous In2O3 crystallization occurred during cooling, or other phases such as NaInO2 were formed during tempering. The addition of alumina, however, controlled the crystallization of In2O3. Depending on the crystallization temperature applied, the crystallite sizes were in the range from 13 to 53 nm. The glass matrix can be dissolved by soaking the powdered glass in water. This procedure can be used to prepare nano-crystalline In2O3-powders. 相似文献