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1.
Various oxide films on SiO 2 glass substrates were irradiated by a laser beam. A continuous CO 2 laser source (wavelength 10.6 μm) was used for this purpose; the composition change at the surface layer was determined by Rutherford backscattering spectrometry (RBS). All the alkaline-earth oxides as well as those of lanthanum and yttrium, entered the glass after treatment. ZrO 2 and CeO 2, however, did not enter the SiO 2 glass due to laser irradiation. It is interesting, however, that a film of ZrO 2 + Al 2O mixture easily entered into the SiO 2 glass by laser processing. The conditions and mechanism of laser-enhanced interaction of ZrO 2 or other oxide films with SiO 2 glass surfaces are discussed especially in view of their structural behaviour in glass. 相似文献
2.
The type and the amount of silicate groupings existing in glassy and crystalline 2PbO·SiO 2 have been determined by direct chemical methods: paper chromatography, trimethylsilylation combined with gas-liquid partition chromatography and by the molybdate method. The results obtained by these three different methods are in good agreement and demonstrate, that glassy 2PbO·SiO 2 and each of the three main crystalline polymorphs are characterized by its own specific silicate anion distribution: the distribution in vitreous 2PbO·SiO 2 is of a polyanionic nature; in T---Pb 2SiO 4 dimetic groups [Si 2O 7] 6− prevail; M 1---Pb 2SiO 4 contains predominantly [Si 4O 12] 8− rings and H---Pb 2SiO 4 is a typical polysilicate with chain anions [SiO 32−] n. The results fit a structural model according to which glass is a random array of discrete polyatomic groupings; the gradual transition from the glassy state to the stablest crystalline structure is connected with degradation and polymerization of silicate anions. 相似文献
3.
A process for production of thick (>10 μm) titania-doped silica films on Si substrates by repetitive spin-coating of sol-gel material and rapid thermal annealing for 10 s in the range 800–1200°C is described. The dependence of overall thickness and etch rate in buffered HF on annealing temperature is described, and it is shown that films annealed at low (< 1175°C) temperatures have a relatively large thickness and etch rate. However, films having the properties of fully densified material (minimum thickness and etch rate) can be produced by subsequent consolidation. The film stress characteristics are similar to those phosphosilicate glass formed by the same process: films annealed below a critical temperature (< 1075°C) are under tensile stress at the annealing temperature, and crack before a thick film can be built up. Refractive index data are given; these show that only fully consolidated films have the refractive index expected from their SiO 2 and TiO 2 compositions. Finally, discrepancies in results for thickness of unconsolidated single-layer and multilayer films are explained using a simple model that accounts for the effect of cumulative densification. 相似文献
4.
无机填料作为齿科复合树脂的主要成分,对其性能影响最为显著。本文以阿拉伯胶为结构导向剂,用热水解法合成了多孔、分级结构的刷状ZnO介晶,其厚度和直径分别为1.2 μm和1.0 μm。通过微流控制法在其表面包覆了4~6 nm无定形SiO 2,以利于其表面硅烷化。通过场发射扫描电镜(FE-SEM)、X射线衍射仪(XRD)、热重分析仪(TGA)等对其进行了表征。对ZnO@SiO 2进行硅烷改性处理后,将其作为辅助填料,与改性纳米SiO 2主填料一起添加到Bis-GMA/TEGDMA树脂体系中,光固化得到齿科复合树脂。力学测试表明,ZnO@SiO 2填充质量分数控制在5%以内时可有效提高复合树脂力学性能。与单一二氧化硅填料的复合树脂相比,添加填充质量分数3% ZnO@SiO 2,复合树脂的力学性能表现最佳,其弯曲强度、弯曲模量和压缩强度分别提高了12.9%、6.6%和3.7%,同时还表现出优良的抗菌活性,对变异链球菌抗菌率达98.7%。此外,添加了ZnO@SiO 2介晶填料的复合树脂还具备更好的耐磨性。 相似文献
5.
The fabrication of a highly efficient Nd 3+-doped single-mode fiber laser operating at 1.06 μm is described. The Nd 3+ is introduced by doping Nd 2O 3 into a multicomponent (flint) lead-silicate glass host, Schott commercial optical glass F7. A fabrication technique for doping rare-earth evenly into commercial optical glasses is demostrated. Spectroscopic properties relevant to laser operation in the Nd 3+-doped lead-silicate glass fibers were measured and the influence of Pb 2+ ions on the spectral properties was analyzed. Owing to the long lifetime and large absorption and emission cross-sections of Nd 3+ in this lead-silicate glass host, a high-performance Nd 3+-doped lead-silicate fibre laser device operating at 1.06 μm has been successfully demonstrated. 相似文献
6.
Optical third-harmonic generation from some high-index glasses was investigated. The highest χ (3) was obtained from As 2S 3 glass 2.2 × 10 −12 esu/ This value was 100 times higher than that of pure SiO 2 glass and comparable with that of the polymer with monomer-doping, which are known as organic materials with quite high χ (3). From the relationship between χ (3) and composition, sulfide glasses were found to have higher χ (3) than oxide or semiconductor-doped oxide glasses with similar refractive indices. 相似文献
7.
We obtained the chemical shielding constants of 29Si in Li 2S–SiS 2 glass system on the basis of molecular orbital calculations. The relative chemical shieldings calculated at the HF/6-31G* level is −16.1 and −23.8 ppm for E(1) and E(0), respectively. These calculations are in good agreement with the previous NMR study: σ( E(2))>σ( E(1))>σ( E(0)). It is found theoretically that incorporation of Li 2S into SiS 2 does not influence the 29Si chemical shift, while incorporation of Li 2O into SiO 2 does to a significant extent. It is also found that the existence of oxygen in Li 2S–SiS 2 glasses increases the chemical shielding of 29Si by about 25 ppm, which is in good agreement with the experimental result. 相似文献
8.
In order to investigate the effect of sol-gel coatings on the mechanical behavior of a high strength glass substrate, HF etched glass rods were used. Coatings with different compositions (SiO2, ZrO2 and 20%ZrO2---80%SiO2) and different thicknesses were produced to study the influence of these parameters on strength. Functions of integral probability versus strength were used to analyze data. Coated glass rods exhibit higher strength in comparison with uncoated control rods that have undergone the same treatment. It seems evident that there is an effect of composition on strengthening. SiO2 coated rods displayed higher strength. A lowering in strength at thickness higher than 0.2 μ was observed, independently of composition. The effect of a saturated Ca(OH)2 solution was also studied. 相似文献
9.
Infrared (IR) reflectivity and Raman scattering spectra of LaBSiO 5 glass and glass–crystal composites were studied in the temperature range 25–260 °C. Using an analogy with the LaBGeO 5 crystal it was possible to assign the main spectral features of the LaBSiO 5 glass and glass–crystal composites. The BO 4 chain arrangement and the bending vibrations of SiO 4 are influenced by the loss of the long-range order in the glass whereas the stretching vibrations of the SiO 4 groups are practically unaffected. The structural disorder in LaBSiO 5 crystallites is caused by rotation of BO 4 tetrahedra. 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.
The infrared absorption spectra of sodium-disilicate glasses containing various amounts of Fe 2O 3 ([Na 2O · 2 SiO 2] 1−x [Fe 2O 3] x, where X = 0.05, 0.1 and 0.2) were investigated in the wavenumber range from 200–2000 cm −1. The addition of Fe 2O 3 to the sodium-disilicate glass does not seem to introduce any new absorption band as compared with the spectrum of a pure sodium-disilicate glass; nevertheless, a general shift of the existing absorption bands toward lower wavenumbers is observed. The amount of shift is, in fact, proportional to the content of Fe 2O 3 in the glass. This observation is consistent with the recently proposed structural model for the bonding of Fe 3+ ions in the iron-sodium-silicate glass system. Annealing of 20 mol% iron oxide glasses at 550 and 580°C produced an extra sharp infrared absorption peak at about 610 cm−1 wavenumber. This new peak is believed to be related to the crystallized particles of the glass as concluded from both a scanning electron micrograph and an electron diffraction pattern. 相似文献
12.
The La L 1 and L 3 XANES and L 3 EXAFS have been investigated for the series of glasses 10K 2O---50SiO 2--- x La 2O 3 ( x = 1, 5, 10) and (10 − x)K 2O---40SiO 2−( x/3)La 2O 3 ( x = 7.5, 5, 2.5) and model compounds La 2O 3, LaAlO 3, LaPO 4, La 2NiO 4, La 2CuO 4 and La(OH) 3. An edge resonance at 25 eV above the L 1 edge in the glass spectra is concentration-dependent, decreasing in intensity with increasing lanthanum concentration. The 2s → nd forbidden transition increases with La 2O 3 concentration, indicating a reduction in the ‘average’ site symmetry of the first coordination shell of La. Mapping X( k) space, which is a new and promising technique, was employed to extract bond distance, coordination number and thermal parameters from the EXAFS. By this method, one calculates the complete X( k) space a function of all physically reasonable values of the adjusted parameters in all possible combinations. The advantage in this method is the assurance of a global minimum. Bond lengths were comparable to those obtained by Fourier transforming the phase corrected EXAFS. The values are 2.42 Å (± 0.03 Å) for La---O. The coordination numbers ( N ≤ 7 ± 1.5) were derived by mapping and comparison to the published structures for other La compounds. X( k) mapping is compared with least-squares fitting the data, and the correlation between the Debye-Waller factor and coordination number is also discussed. 相似文献
13.
Valuable information on the geometric and electronic structure of both predominant and defect species in the bulk and on the surface of amorphous SiO 2 can be obtained from solid state 29Si and 17O NMR. Most previous NMR.studies have made assignments of structure types to NMR signals by relying on a comparison to crystalline reference materials. Using the quantum mechanical technique of Coupled Hartree-Fock Perturbation Theory (CHFPT) we can directly calculate NMR shielding tensors, σ, for Si and O and electric field gradients tensors, q for O in silicates. Previous CHFPT calculations on (SiH 3) 2O at Si--- O--- Si = 180° to 140° semiquantitatively reproduced observed trends in σ for SiO 2 polymorphs. These calculations have been improved and extended to Si---O---Si = 120° in (SiH 3) 2O and to the small siloxane rings H 4Si 2O 2, H 6Si 3O 3, H 8,Si 4O 4 which are models for the ring structures which may occur in the bulk and surface of amorphous SiO 2. Thus, predictions can be made of the 17O and 29Si NMR characteristic of such species. We have also calculated NMR shieldings and other properties for three and five coordinate Si and for three coordinate O. The 29Si NMR shielding increases with coordination, as expected, and five coordinate Si shows an anisotropy which although large is still smaller than that inferred from spin-lattice relaxation times in silicate melts. O q values are also calculated for (BH 2) 2O and H 3B 3O 6. The results are consistent with O EFGs and Raman frequencies observed in B 2O 3 glass, supporting a boroxol ring model. 相似文献
14.
Vitreous BeF 2 was prepared by two techniques; (1) remelting of a technical grade material, and (2) vacuum distillation/fluoridation. Infrared spectroscopy studies have established that the first material contains about 0.5 wt.% hydroxyl, predicted to be coherently incorporated into the vitreous network as edge-linked [Be(OH) 4] 2− units. The distilled BeF 2 is water-free. The dc electrical conductivity of the remelted BeF 2 was measured as σ = (7.9 × 10 3/ T) exp(−24500 cal/mol/ RT) ω −1 cm −1 and for the distilled BeF 2 as σ = (3.0 × 10 5/ T) exp(−36700 cal/mol/ RT ω −1 cm −1 at temperatures to 280°C. Ionic transport studies utilizing a dc electrolysis polarization technique with N 2−F 2 and H 2−HF gas electrodes have demonstrated that the fluorine ion is the transport species. A general model for fluorine transport is proposed based upon a modified anti-Frenkel defect model. The difference in the fluorine transport process for the undistilled grade of BeF 2 is seen as a consequence of the anti-Frenkel defect pair interaction with the [Be(OH) 4[ 2− groupings. 相似文献
15.
Long-wavelength vertical cavity surface emitting lasers (VCSELs) are considered the best candidate for the future low-cost reliable light sources in fiber communications. However, the absence of high refractive index contrast in InP-lattice-matched materials impeded the development of 1.3–1.5 μm VCSELs. Although wafer fusions provided the alternative approaches to integrate the InP-based gain materials with the GaAs/AlAs materials for their inherent high refractive index contrast, the monolithic InP-based lattice-matched distributed Bragg reflectors (DBRs) are still highly attractive and desirable. In this report, we demonstrate InP/InGaAlAs DBRs with larger refractive index contrast than InP/InGaAsP and InAlAs/InGaAlAs DBRs. The switching between InP and InGaAlAs layers and growth rate control have been done by careful growth interruption technique and accurate in situ optical monitoring in low-pressure metal organic chemical vapor deposition. A 35 pairs 1.55 μm centered InP/InGaAlAs DBRs has the stopband of more than 100 nm and the highest reflectivity of more than 99%. A VCSEL structure incorporating 35 pairs InP/InGaAlAs DBR as the bottom mirror combined with a 2λ thick periodic gain cavity and 10 pairs SiO 2/TiO 2 top dielectric mirrors was fabricated. The VCSELs lased at 1.56 μm by optical pumping at room temperature with the threshold pumping power of 30 mW. 相似文献
16.
A solubility limit of ≈6 mol% PuO 2 in sodium disilicate (Na 2O · 2 SiO 2) glass has been determined. Magnetic susceptibility measurements on these glasses yield approximate Curie—Weiss behavior, in contrast to the temperature-independent susceptibility of crystalline PuO 2. This result is interpreted to indicate that the local site symmetry around the Pu ion in the sodium disilicate glass is very different than in crystalline PuO 2. The effective paramagnetic moments determined from the temperature dependence of the susceptibility are found to be consistent with calculated free-ion values based on the most likely 5f electron configurations. 相似文献
17.
We determined the internal nucleation, crystal growth and overall crystallization kinetics of fresnoite crystal (2BaO · TiO 2 · 2SiO 2) in an almost stoichiometric fresnoite glass. Due to the extremely high nucleation rates (10 17 m −3 s −1) that limit the maximum crystal size to 700 nm the nucleation densities and crystal sizes were estimated by scanning electron microscopy (SEM). The volume fraction crystallized was measured by X-ray diffraction. The nucleation rates obtained directly from SEM measurements reasonably agree with those calculated from the combination of overall crystallization with crystal growth kinetics. The activation enthalpies for viscous flow, transport of structural units across the nucleus/melt interface (nucleation) and crystal growth: Δ Hη, Δ Hτ and Δ HU respectively, follow a similar trend to that observed for other stoichiometric silicate glasses that nucleate internally: Δ Hη=294>Δ Hτ=87>Δ HU=61 kJ/mol. Fresnoite glass displays the highest internal nucleation rates so far measured in inorganic glasses. These rates are comparable to some metallic glasses and can lead to nanostructured glass-ceramics. 相似文献
18.
Glasses of composition 65 mol% LiNbO 3:: 35 mol% SiO 2 have been shown to be Li + ion conductors with a conductivity at 200° C > 1 × 10 −5 (η cm) −1 and an activation energy of 0.54 eV. The addition of approximately 0.1 mol% Fe 2O 3 leads to an enhancement of conductivity to ≈10 −3 (η cm) −1 at 200°C and an activation energy of 0.67 eV. The effect of Fe is shown to be in the control of microstructure in the glass, with Fe 2O 3 concentrations < 1 mol% acting as a grain growth inhibitors and larger concentrations acting as a nucleating agents. A model for this process based on the expected stoichiometry of the melt and the effect of Fe 2+ and Fe 3+ in charge compensation is in excellent agreement with experimental data from electron spin resonance. 相似文献
19.
Binary glasses containing no modifying oxides, such as SiO 2---GeO 2, SiO 2---B 2O 3, SiO 2---P 2O 5, GeO 2---B 2O 3, Al 2O 3---P 2O 5 and ternary glasses SiO 2---GeO 2---P 2O 5, Al 2O 3---B 2O 3---P 2O 5, B 2O 3---SiO 2---P 2O 5, Al 2O 3---ZrO 2---P 2O 5 have been prepared by melting and CVD methods. The Raman spectra have also been measured. Structural characteristics of SiO 2, GeO 2, B 2O 3, P 2O 5 in different glass systems are analysed. There exist coordination number changes in B 2O 3- and GeO 2-containing glasses and linkage changes between tetrahedra (SiO 4) and (PO 4) in SiO 2 and P 2O 5 containing glasses. The structure of Al 2O 3 containing glasses is homogeneous and the structure of B 2O 3 containing glasses is inhomogeneous. These experimental results are in coincidence with the X-ray small angle scattering analysis. 相似文献
20.
III–V semiconductor Indium Arsenide (InAs) nanocrystals embedded in silica glasses was synthesized by combining the sol–gel process and heat treatment in H 2 gas. The size of InAs nanocrystals can be easily controlled via changing the In and As content in the starting materials and the heating temperature in a H 2 gas atmosphere. Absorption measurements indicate a blue shift in energy with a reduction on the In and As content in the SiO 2 gel glasses as a result of quantum confinement effects. A near-infrared photoluminescence with peak at 3.40 μm was observed at 6 K under 514.5 nm Ar + laser excitation from InAs nanocrystals embedded in the silica gel glasses. 相似文献
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