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1.
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
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.
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
4.
The gel formation of the (100- x)TiO 2· xSiO 2 ( x = 0–10 mol%) system has been studied. The progressive elimination of residues was followed by DTA and TGA curves. DTA curves showed that the formation of anatase during heat treatment could be sensibly slowed down with the increase of SiO 2. The relationship between the gel composition and crystallization temperature of anatase has been systematically investigated. The X-ray diffraction spectra demonstrated that the crystallization temperature of anatase is 400°C for TiO 2 gel and 430°C for 90TiO 2 - 10SiO 2 gel. The infrared absorption spectra were used to follow the structural transformation of gels heat-treated at different temperatures. With the help of EPR it is evident that titanium ions exist only in tetravalence. 相似文献
5.
Evaporated amorphous silicon (a-Si) films, oxidized in air or O 2 at room temperature, present two native oxides with different structures. The surface oxide is constructed from SiO 4-tetrahedron structural units with a 110° O---Si---O angle, which is the common structural unit of stable silicon oxides. The internal oxide has a different structure having a 120° O---Si---O angle. The results of molecular orbital (MO) calculations for (SiO 3) m− and (SiO 4) n− anionic clusters support the presence of the two stable structures of silicon oxides and also reveal the importance of the ionic character of the oxidized sites. 相似文献
6.
Thermally stimulated luminescence (TSL) and infrared (IR) spectroscopy were measured in plasma grown Si 1−xGe xO 2 ( x=0, 0.08, 0.15, 0.25, 0.5) with different thicknesses (12–40 nm). A comparison with the TSL properties of thermally grown SiO 2 and GeO 2 was also performed. A main IR absorption structure was detected, due to the superposition of the peaks related to the asymmetric O stretching modes of (i) Si–O–Si (at ≈1060 cm −1) and (ii) Si–O–Ge (at 1001 cm −1). Another peak at ≈860 cm −1 was observed only for Ge concentrations, x>0.15, corresponding to the asymmetric O stretching mode in Ge–O–Ge bonds. A TSL peak was observed at 70°C, and a smaller structure at around 200°C. The 70°C peak was more intense in all Ge rich layers than in plasma grown SiO 2. Based on the thickness dependence of the signal intensity we propose that at Ge concentrations 0.25 x0.5 TSL active defects are localised at interfacial regions (oxide/semiconductor, Ge poor/Ge rich internal interface, oxide external surface/atmosphere). Based on similarities between TSL glow curves in plasma grown Si 1−xGe xO 2, thermally grown GeO 2 and SiO 2 we propose that oxygen vacancy related defects are trapping states in Si 1−xGe xO 2 and GeO 2. 相似文献
7.
Thin films of crystalline lithium niobate (LN) grown on Si(1 0 0) and SiO 2 substrates by electron cyclotron resonance plasma sputtering exhibit distinct interfacial structures that strongly affect the orientation of respective films. Growth at 460–600 °C on the Si(1 0 0) surface produced columnar domains of LiNbO 3 with well-oriented c-axes, i.e., normal to the surface. When the SiO 2 substrate was similarly exposed to plasma at temperatures above 500 °C, however, increased diffusion of Li and Nb atoms into the SiO 2 film was seen and this led to an LN–SiO 2 alloy interface in which crystal-axis orientations were randomized. This problem was solved by solid-phase crystallization of the deposited film of amorphous LN; the degree of c-axis orientation was then immune to the choice of substrate material. 相似文献
8.
Preparation of radial gradient refractive index ( r-GRIN) glass rods has been undertaken by a sol-gel process using metal alkoxides. Two binary systems, Si(OCH 3) 4---Ge(OC 2H 5) 4 and Si(OCH 3) 4−Ti(O− n-C 4H 9) 4 have been investigated. It has been shown that immersion of rod-shaped wet gels in neutral or acidic water gives rise to leaching of the dopants (germanium and titanium components). Since this leaching is controlled predominantly by diffusion, the dopants remaining in the gels are expected to form concentration gradients. Optical measurements of the glass rods obtained after drying and sintering of the leached gels have shown that the concentration gradients are retained in the glass rods and they give r-GRIN profiles. 相似文献
9.
The first determinations of critical stress intensity factors KIC and of fracture surface energy Λ of wet SiO 2 gels are presented. The examples comprise: (a) pure LUDOX gels, (b) LUDOX-AEROSIL composites, and (c) sonogels from alcoholates. KIC is shown to increase with the progress of syneresis but Λ stabilises itself close to the surface energy of the solid phase exposed during fracture. 相似文献
10.
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
11.
In electric fields >10 7 V/cm, we have observed that the conduction current through Si( n+)/SiO 2/poly-Si( n+) capacitors is larger than that predicted by the classical Fowler–Nordheim law for the case of a triangular potential barrier. This phenomenon appears for both gate polarities just before electric breakdown occurs. An attempt to model this excess current by direct tunneling or by other well-known conduction mechanisms such as Schottky, Poole–Frenkel or hopping effects has been unsuccessful. We have succeeded in interpreting experimental data by considering the SiO 2 layer as a non-triangular potential barrier, which leads to a non-linear relationship between the tunneling length and the applied voltage. By using a semi-linear approach, an oxide conduction band model presenting two potential wells located at approximately from 2.5 nm to within ±0.2 nm from each oxide interface has been obtained. These two singularities may be related to the presence of a non-uniformly distributed positive charge in SiO 2. 相似文献
12.
The surface morphology of Na 2O–B 2O 3–Al 2O 3–SiO 2 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 Na 2O–B 2O 3–Al 2O 3–SiO 2 vitrified bond presented a porous surface, and its bending strength declined with increasing sintering temperature. However, the Na 2O–CaO–B 2O 3–Al 2O 3–SiO 2 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
13.
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
14.
0.01Fe 2O 3---0.99SiO 2 gels were prepared by three different sol-gel methods and the effects of the heat-treatment temperature of the gels on the ESR and Mössbauer parameters were investigated to obtain information about the change in the state of iron ions in the gel. All the gels were found to be amorphous under 600 °C, and among these three methods, the best dispersed state of Fe 3+ ions was obtained by the method where TEOS was partially hydrolyzed with the same mole content of water before the addition of Fe(OEt) 3. It was indicated that the reaction at the sol-stage plays an important role in the degree of dispersal of Fe 3+ ions in this system. 相似文献
15.
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
16.
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
17.
Small-angle X-ray scattering was used to examine in situ formation of ZrO 2---SiO 2 structures in alcoholic solution of tetraethoxysilan (TEOS) as a function of the ratio of ZrO 2 to SiO 2. For the moment of the first measurement (15 min after the preparation) primary particles with Rg ≈ 1.5 nm exist in all investigated mixed gels. These particles aggregated to secondary clusters. The resulting clusters can be described by means of fractal theory, where the determining mechanism of formation is cluster-cluster aggregation (diffusion or chemical limited). The time of gelation is a function of the ZrO 2 concentration. The higher the ZrO 2 concentration in the solution, the faster is the aggregation to secondary clusters. Gelation times were between 170 and 970 h. 相似文献
18.
Effects of SiO 2 additive on sodium perborate tetrahydrate crystallization (via chemical reaction of NaBO 2 and H 2O 2) has been studied in a MSMPR-type reaction crystallizer. CSD and microscopic observations are used to evaluate the secondary nucleation behaviour. Secondary nucleation rate decreases in case of SiO 2 addition of up to 200 ppm. Higher SiO 2 content results in higher primary nucleation rates. Abrasion resistance increases with the amount of SiO 2 additive. 相似文献
19.
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
20.
Thin films of CdS-doped SiO 2 glass were prepared by using the conventional pulsed laser deposition (PLD) technique. The laser target consisted of a specially constructed rotary wheel which provided easy control of the exposure-area ratio to expose alternately the two materials to the laser beam. The physical target assembly avoided the potential complications inherent in chemically mixed targets such as in the sol–gel method. Time-of-flight (TOF) spectra confirmed the existence of the SiO 2 and CdS components in the thin-film samples so produced. X-ray diffraction (XRD) and atomic force microscopy(AFM) results showed the different sizes and structures of the as-deposited and annealed films. The wurtzite phase of CdS was found in the 600 oC-annealed sample, while the as-deposited film showed a cubic–hexagonal mixed structure. In the corresponding PL (photoluminescence) spectra, a red shift of the CdS band edge emission was found, which may be a result of the interaction between the CdS nanocrystallite and SiO 2 at their interface. 相似文献
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