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1.
Fine-sized ZnO–B 2O 3–CaO–Na 2O–P 2O 5 glass powders with spherical shape were directly prepared by high temperature spray pyrolysis. The ZnO–B 2O 3–CaO–Na 2O–P 2O 5 powders prepared by spray pyrolysis at temperatures above 1200 °C had broad peaks at around 30° in the XRD patterns. The glass transition temperatures ( Tg) of the glass powders obtained by spray pyrolysis at preparation temperatures between 900 °C and 1400 °C were near 480 °C regardless of the preparation temperatures. The dielectric layers formed from the glass powders prepared by spray pyrolysis at preparation temperatures above 1300 °C had clean surface and dense inner structure at the firing temperature of 580 °C. The transmittance of the dielectric layer formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1400 °C was 90% at the firing temperature of 580 °C, in which the thickness of the dielectric layer was 13 μm. The UV cutoff edges gradually shift towards longer wavelength with increasing the preparation temperature of glass powders and the firing temperature of dielectric layers. 相似文献
2.
The preparation of glass-lined coating mould from gels in the ternary system of SiO 2–ZrO 2–B 2O 3 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-ZrO 2 as well as the tetragonal to monoclinic phase transformation are, respectively, retarded and impeded owing to the encasement of SiO 2 matrix. While the inhibitive effect of B 2O 3 on crystallization of the SiO 2–ZrO 2–B 2O 3 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 SiO 2–ZrO 2–B 2O 3 coating mould has an ideal nucleation inhibition for superalloy. 相似文献
3.
11B ( I=3/2) MAS NMR in the binary glass system xV 2O 5–B 2O 3 ( x=0.053, 0.43) and the ternary glass system xV 2O 5–B 2O 3–PbO (0.1 x1.5) has been investigated at room temperature. In the xV 2O 5–B 2O 3 glasses, one NMR line due to BO 3 unit was observed. Meanwhile in the xV 2O 5–B 2O 3–PbO, two NMR lines which arise from BO 3 and BO 4 units were detected, where the appearance of BO 4 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 BO 3 units in xV 2O 5–B 2O 3, and those for BO 3 and BO 4 units in xV 2O 5–B 2O 3–PbO were obtained as a function of x. As the V 2O 5 content increases in xV 2O 5–B 2O 3–PbO, the e2qQ/ h and η values of the BO 3− associated resonance are found to slightly decrease and increase, respectively. Meanwhile, the e2qQ/ h and η values of BO 4− associated resonance in xV 2O 5–B 2O 3–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 BO 3 and BO 4 units contained in xV 2O 5–B 2O 3–PbO with those of respective standard samples of 0.053V 2O 5–B 2O 3 and NaBH 4, the quantitative fractions of BO 3 and BO 4 in xV 2O 5–B 2O 3–PbO were obtained as a function of x. 相似文献
4.
Single crystals of ruby have been obtained from fluxed melts based on the systems Li 2O–MoO 3, Li 2O–WO 3, Na 2O–WO 3, 2PbO–3V 2O 5, PbO–V 2O 5–WO 3, PbF 2–Bi 2O 3 and Na 3AlF 6 by both the TSSG method and spontaneous crystallization at the temperatures 1330–900 °C. Al 2O 3 solubility has been measured for the flux composition of 2Bi 2O 3–5PbF 2 in the temperature range 1200–1000 °C and dissolution enthalpy has been defined as 29.4 KJ/Mol. The composition of grown crystals was studied by electron microprobe analysis. The synthetic ruby contains from 0.51 to 6.38 at% of chromium admixture depending on the crystal growth conditions. Experimental results on growth conditions, composition and morphology of grown crystals are presented for each flux and temperature interval. 相似文献
5.
An EMF cell using a Na-β″-alumina electrolyte has been designed for the quantification of the thermodynamic activity of Na 2O ( aNa 2O) in a series of sodium-bearing silicate liquids at high temperature. Initial experiments have been performed using Na 2O–0.663WO 3 and Na 2O–0.555MoO 3 as reference liquids. Values of aNa 2O derived for Na 2O–2SiO 2 binary melt are found to be in excellent agreement with data from the literature, confirming the validity of the method. To extend use of this experimental set-up to higher temperature, the aNa 2O of industrial C-glass has been calibrated as a reference liquid at temperatures up to 1263 °C. The influence of additions of CaO, Al 2O 3 and B 2O 3 on the Na 2O activity of binary sodium-silicates has been quantified. For each glass composition, measured values of aNa 2O are a function of temperature, log( aNa 2O) varying as a function of inverse absolute temperature. Activation energies derived from these data are all generally similar with the exception of industrial E-glass, which is rich in Al and poor in Na. At constant temperature, additions of network forming Al 2O 3 and B 2O 3 to a Na 2O–SiO 2 binary melt yield a decrease of the activity of Na 2O, while addition of network modifying CaO results in an increase in ( aNa 2O). These changes are qualitatively consistent with predictions based upon expected modifications of melt structure. However, measured values of log( aNa 2O) do not correlate perfectly with theoretical models of glass basicity, suggesting that either sodium activity is decoupled from melt basicity, or that current models are insufficient to calculate that parameter, in particular for the case of liquids poor in Na and rich in Al. 相似文献
6.
Alkoxide derived gels were prepared in the system Na 2O---B 2O 3---SiO 2. The gel compositions were situated in the liquid-liquid immiscibility area of the phase equilibrium diagram. Hydrolytic resistance tests were performed on the gels heat-treated at temperatures ranging between 120 to 850 °C. The Na2O, B2O3 and SiO2 extracted from the attack gels were analyzed. The experimental results indicate that the amount of B2O3 has a significant influence on the chemical durability of the heat-treated gels. At temperatures of 850 °C the greater the B2O3 mol% the greater are the amounts of Na2O and B2O3 extracted. Different behaviour was observed for gels heat-treated at 600 °C where the amounts of B2O3 and Na2O extracted slightly increases as the B2O3 mol% increases. Small amounts of extracted SiO2 were always observed. These results are complemented with other measurements so that an explanation of the controlling mechanism is given. 相似文献
7.
Glasses in the system Na 2O/B 2O 3/Al 2O 3/In 2O 3 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 Al 2O 3, In 2O 3 could not be crystallized from homogeneous glasses, because either spontaneous In 2O 3 crystallization occurred during cooling, or other phases such as NaInO 2 were formed during tempering. The addition of alumina, however, controlled the crystallization of In 2O 3. 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 In 2O 3-powders. 相似文献
8.
Ag +/Na + ion-exchanged R 2O–Al 2O 3–SiO 2 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 AlØ 4 site were exchanged by Ag + ions after full replacement of NBO sites, where Ø represents the bridging oxygen. 相似文献
9.
Mössbauer absorption measurements have been made at room temperature on 57Fe in iron sodium silicate glasses containing 3–15 mol% Fe 2O 3 and various iron alkali silicate crystals in order to study the state of iron in these glasses. The spectra of all the glasses gave one doublet with a quadrupole splitting varying from 0.73–0.78 mm s −1, while those of Na 2O · Fe 2O 3 · 4 SiO 2 and 5 Na 2O · Fe 2O 3 · 8 SiO 2 crystals showed much smaller quadrupole splitting, 0.28 mm s −1 and 0.10 mm s −1, respectively, and an asymmetrical doublet of much narrower linewidth. When sodium was replaced by other alkali metals of larger size, such as K and Cs, in MFeSi 2O 6 and MFeSi 3O 8 crystals, the quadrupole splitting became wider and approached to 0.73 mm s −1. Such a variation was not observed for glasses. These results suggest that a larger number of non-identical sites exist in iron sodium silicate glasses than in the corresponding crystals. 相似文献
10.
The 11B, 27Al, 29Si and 31P magic angle spinning (MAS) NMR spectra of MO–P 2O 5, MO–SiO 2–P 2O 5 and MO(M ′2O)–SiO 2–Al 2O 3–B 2O 3 (M=Mg, Ca, Sr and Ba, M ′=Na) glasses were examined. In binary MO–P 2O 5 (M=Ca and Mg) glasses, the distributions of the phosphate sites, P(Q n), can be expressed by a theoretical prediction that P 2O 5 reacts quantitatively with MO. In the ternary 0.30MO–0.05SiO 2–0.65P 2O 5 glasses, the 6-coordinated silicon sites were detected, whose population increases in the order of MgO xCaO–0.05SiO2–(0.95−x)P2O5 glasses, its population increases with an increase in f (=([P2O5]−[MO]−[B2O3]−[Na2O])/[SiO2]) and has maximum at f=9. The signal due to the 5-coordinated silicon atoms is also observed when x is smaller than 0.45. When three network-forming oxides such as SiO2, Al2O3 and B2O3 coexist, Al2O3 reacts preferably with MO. The populations of 4-coordinated boron atoms, N4, are expressed well with r/(1−r), where r=([Na2O]−[Al2O3])/([Na2O]−[Al2O3]+[B2O3]). The correlation of the Raman signal at 1210 and 1350 cm−1 with the NMR signal of Si(Q6) at −215 ppm is also seen. 相似文献
11.
New glasses in the PbBr 2–PbCl 2–PbF 2–PbO–P 2O 5 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 PbBr 2–PbCl 2–P 2O 5 ternary system has a broad glass-forming region which extends to 30 mol% P 2O 5. 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% PbF 2 is introduced into the PbBr 2–PbCl 2–P 2O 5 system, the glass-forming region becomes smaller and the glass transition temperatures increase. However, the introduction of 2.5% PbF 2 and 2.5% PbO into the ternary system increases the glass transition temperature and broadens the glass-forming region. The introduction of PbF 2 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 electrical and dielectric properties for three series of MoO 3–Fe 2O 3–P 2O 5 and one series of SrO–Fe 2O 3–P 2O 5 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 MoO 3 is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe 2O 3 content and Fe(II)/Fe tot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe 2O 3 content in MoO 3–Fe 2O 3–P 2O 5 glasses with O/P at 3.5 the dc conductivity, σ dc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe 2O 3 and is independent of the MoO 3 content. Also, the dielectric properties such as ′(ω), ″(ω) and σ ac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO 3. On the other hand, the dc conductivity for MoO 3–Fe 2O 3–P 2O 5 glasses with O/P > 3.5 increases with the substitution of MoO 3 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 MoO 3 content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe 2O 3–P 2O 5 glasses the conductivity and dielectric permittivity remained constant with increasing SrO. 相似文献
13.
Melts with the basic compositions 10Na 2O · 10MgO · xAl 2O 3 · (80− x)SiO 2 ( x=0, 5, 10, 15 and 20), 10Na 2O · xMgO · 10Al 2O 3 · (80− x)SiO 2 ( x=5, 10, 15 and 20) and xNa 2O · 10MgO · 10Al 2O 3 · (80− x)SiO 2 ( x=5, 10 and 15) all doped with 0.25 mol% Fe 2O 3 were studied using square-wave voltammetry. The temperatures applied were in the range of 1000–1600 °C. The square-wave voltammograms recorded show peaks caused by the reduction of Fe 3+ to Fe 2+. The attributed peak potentials measured decreased linearly with decreasing temperatures. Increasing the MgO-concentration led to more negative peak potentials. Introducing alumina in the melt first resulted in less negative peak potentials. If the molar Al 2O 3-concentration is equal to that of Na 2O (=10 mol%) the peak potentials are least negative. Further increase of the Al 2O 3-concentration led to more negative peak potentials. The variation of the Na 2O-concentration led to a maximum in the peak potentials at an Na 2O-concentration of 10 mol%. An empirical formula which allows the calculation of standard potentials from the chemical composition is proposed. Furthermore, a structural explanation for the effect of the chemical composition is given. Especially, the incorporation of Al 2O 3 as AlO 4−-tetrahedra at [Al 2O 3] < [Na 2O] and as network modifier at larger concentrations was structurally explained by the similarities of Fe 2+ and Mg 2+, with respect to cation radii and metal–oxygen bond lengths. 相似文献
14.
Phase relations around langasite (LGS, La 3Ga 5SiO 14) were studied on the basis of phase assemblage observed during calcination and crystallization process of samples of various compositions in the ternary system La 2O 3–Ga 2O 3–SiO 2. A ternary compound of apatite structure, La 14Ga xSi 9–xO 39–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
15.
Single crystals of PbMg 1/3Ta 2/3O 3 (PMT) were grown by the flux method. The PbO–Pb 3O 4–B 2O 3 system was used as a solvent. Transparent and light yellow PMT single crystals of rectangular shape and dimensions up to 10×6×4 mm 3 were obtained. For the applied growth conditions only, the crystals of the perovskite structure were grown. X-ray diffraction tests showed that at room temperature PMT exhibits cubic symmetry with lattice parameter a=4.042(1) Å. Dielectric studies pointed to relaxor properties of PMT. The characteristic broad and frequency-dependent maximum of dielectric permittivity was observed at 179.7 K (1 kHz). 相似文献
16.
The effect of alumina on the phase separation and the crystallization of the glasses of composition (mol%) 18ZnO·30B 2O 3·52SiO 2 and O-40 Al 2O 3 was studied using an electron microscope and IR spectroscopy. The main crystalline phase appears in the microphase for which the compositions are not nearer to the crystal stoichiometry than the mean. The addition of Al 2O 3 suppresses the immiscibility but enhances the crystallizability. 相似文献
17.
Glasses of compositions 5ZrO 2·5SiO 2(ZS), 5ZrO 2·Al 2O 3·4SiO 2(ZAS) and 5 5ZrO 2·0.5Al 2O 3·0.5Na 2O·4SiO 2(ZANS) were prepared by the sol-gel process from metal alkoxides and sintered to make glass-ceramics. Tetragonal ZrO 2 was precipitated by heat treatment at 900 to 1300°C. The activation energy for tetragonal ZrO 2 crystal growth was extremely high in Al 2O 3 containing glasses. ZAS and ZS were sintered to the near theoretical densities above 1200°C, at which the predominant phase was tetragonal ZrO 2. On the other hand, for ZANS, high densification was not attained owing to the large pores enclosed by the glass phase. Strength and fracture toughness increased with the densification and the crystal growth of tetragonal ZrO 2, reaching 450 MPa and 9 MN/m 1.5, respectively. 相似文献
18.
The colorless and transparent glasses in the Al 2O 3---B 2O 3---SiO 3 system with high B 2O 3 and SiO 2 content were prepared from gels at low temperature. Their IR spectra not only revealed the evolution of the gel to glass conversion, but also showed that the formation of mixed bonds in the glasses obtained did not show any effect due to the B 2O 3 content. The accuracy of the glass composition is dependent upon the SiO 2/B 2O 3 molar ratio. The higher the ratio, the less the deviation of the analyzed compositions of the resulting glasses from their original calculated values. It is obvious that the higher the ratio, the lower the thermal expansion coefficient and the higher the transformation temperature of the glass, and the temperature at which the thermal contraction reaches an equilibrium is higher. 相似文献
19.
11B Fourier transform spectra have been used to study the structure of Na 2O---B 2O 3---SiO 2 glasses of mid-alkali content. Based on the measurements of the fraction N4 of four-coordinated borons, it has been found that for K = mol.% SiO 2/mol.% B 2O 3 8 and R = mol.% Na 2O/mol.% B 2O 3 = 1, N4 is obviously smaller than 1 rather than equal to 1 as assumed in the relevant literature. Only when R reaches a value appropriately greater than 1, can the case where N4 = 1 occur. A structural model suggested in this paper can satisfactorily explain the fact. 相似文献
20.
Tellurite containing vanadate (50− x)V 2O 5– xBi 2O 3–50TeO 2 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 Bi 2O 3 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 Bi 2O 3 content. The observed results confirm that the addition of Bi 2O 3 modifier changes the rigid formula character of TeO 2 to a matrix of regular TeO 3 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 TeO 4 trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi 2O 3 content are more stable than with high Bi 2O 3 content. 相似文献
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