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1.
Yellow coatings have been prepared from titanium tetraisopropoxide and cerium chloride by the sol-gel dip-coating process, and the transmittance, chromaticity, thickness and acidic durability of the coating films produced on glass or aluminum were studied. The effects of the pH of the solution on the preparation of the transparent and homogeneous coating films were studied by adding the alkali or acid, and as a result transparent and homogeneous yellow coating films were prepared by dipping the substrate in a solution containing acetic acidic solution. The acidic durability of the aluminum foil was improved by dip-coating the brilliant yellow CeO 2-TiO 2 coating three times. 相似文献
2.
A series of titania-silica glasses with 0–9% TiO 2 were fabricated using a sol/gel process. The sol was prepared by dispersing colloidal silica fume in an aqueous solution of titania which was synthesized through the acid-catalyzed hydrolysis of titanium isopropoxide. The sols gelled in 2–4 days, and then were dried for 6–8 days. The dry gels were sintered at 1450–1500°C to produce clear, dense, microstructure-free glasses. The gels underwent a total shrinkage of 50% to yield glass rods about 50 mm long and 5 mm in diameter, or glass discs about 4 cm in diameter and 5 mm thick. The drying step was most critical in the production of crack-free specimens. In the gel, the transmission electron microscope (TEM) revealed the presence of 1–5 nm rutile microcrystallites uniformly distributed within a network of colloidal silica particles. After sintering to 1450–1500°C, though, a dense, transparent, microstructure-free glass was created. Fourier transform infrared spectroscopy (FTIR) verified the formation of an amorphous solid-solution of titania and silica after sintering. The thermal expansion of the glasses was measured using a differential dilatometer. The average linear coefficients of thermal expansion (CTE @ 25–675°C) varied between +5 × 10−7 and −0.2 × 10−7°C−1 in the range 0 to 9% TiO2. The glass with 7.2% TiO2 exhibited a zero thermal expansion coefficient at 150–210°C. The hysteresis in CTE on heating and cooling was of the order of 0.01–0.02 ppm. 相似文献
3.
The refractive index, optical absorption coefficient α and the thermomodulated absorption d α/d T have been measured on 70% TiO 2?30% SiO 2 glasses with up to 8% Ti 3+. The direct absorption data show intense ligand field absorption at photon energies hν = 1.9 and 3.0 eV, arising from Ti 3+ in a distorted octahedral environment. In the bandgap region at 3.5 eV α obey αhν ~ ( hν ? Eg) 2; it is qualitatively different from the bandgap absorption in crystalline TiO 2. The d a/d T spectra show peaks in the bandgap region and at 1.1 eV in the near IR. This last peak is attributed to absorption by small polarons, and its line shape is compared with theoretical predictions. 相似文献
4.
We report the infrared and Raman studies of titanium doped vitreous silica glasses for a number of titanium concentrations. The vibrational modes associated with the randomly oriented chains of SiO 4 tetrahedra show broadenings and shifts. The LO-TO splitting of some Raman active modes decreases with increasing titanium concentration. This is attributed to the decrease in long-range coulomb fields associated with the chains of SiO 4 tetrahedra which are broken by the titanium atoms. The results are discussed in the context of random network models. An increase in the average intertetrahedral angle of the SiO 4 network is calculated from the data. This explains the anomalous decrease in the density of TiO 2---SiO 2 glasses with increasing titanium content. We identify two new modes associated with the distorted titanium tetrahedra. A polarized Raman mode at 1115 cm −1 which is infrared inactive and an unpolarized Raman mode at 945 cm −1 which is infrared active are observed. 相似文献
5.
The effect of the interaction between colloidal particles in SiO 2 and TiO 2 sols on the viscosity of the sols has been examined. It was found that the interaction was significantly influenced by the zeta potential of electrical double layers and terminal bonds associated with particle surfaces. Water/alkoxide mole ratio and pH affect the zeta potential and the terminal bonds and, consequently, change the interaction between the particles and the viscosity of the sols. In addition, the relationship of viscosity with the volume fraction of the colloidal particles in SiO 2 sol has been described by a Dougherty-Kreiger equation when the viscosity reached a stable value with time. 相似文献
6.
This study demonstrates that hydrolysis should be carried out in a step manner in gel synthesis. The key to the increase in the amount of water added is the control of the hydrolysis rate of Ti(OC 4H 9) 4. The hydrolysis of Si(OC 2H 5) 4 can be carried out at about 75°C. The amount of added water (γ WI), which varied with TiO 2 content (in mol%), was about 64–88% of the total amount of added water. The hydrolysis reaction should be performed at room temperature while Ti(OC 4H 9) 4 is added. The total amount of added water (γ W) is related to the amount of solvent ( R). For example, if TiO 2 is 40mol%, γ W will vary from 3.2 to 8.0 when R varies from 0.8 to 2.0. The amount of added water was affected by the distribution of solvent in the metal alkoxides. The amount of added water can be increased when RSi(OC2H5)4 = 1, RTi(OC4H9)4 > 1. The rate of rise in temperature of the thermolysis of the dried gel should be less than 10°C per hour, and the heat treatment temperatyre is related to the TiO 2 content (in mol%). Gel glasses without devitrification can only be obtained by thermolysis at 600°C from the gel with no less than 20 mol% TiO 2. 相似文献
7.
The sol-gel dip coating technique has been used to deposit composite oxide films (NiO) x(SiO 2) 1−x with x = 0.1 on silicon wafers. Single and multilayer coatings allowed a variation of the film thickness from 70 to 400 nm. Film morphology, atomic structure and atomic composition have been investigated by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). The local environment of the Ni atoms was characterized by extended X-ray absorption fine structure (EXAFS). The samples were studied in the as-prepared state and after annealing in H 2 at 600 °C for 1 h. The structural and chemical state evolution of clusters present inside the silica matrix is discussed in terms of out-of-equilibrium reaction processes specific to low-dimensional objects and superficial effects. 相似文献
8.
70Ph 2SiO·30TiO 2 coatings on slide glass and phosphate glass substrates have been prepared by the sol-gel process. Experimental results on the characterization and chemical durability of the coatings are presented. It is shown that the coatings heated at 150°C have reasonably good acid and water resistance while their alkali durability is very poor. The XPS results are used to verify the different corrosion behaviors of the coating in pure water and 1N HC1 solutions. The chemical durability of phosphate glass can be significantly improved by this coating. 相似文献
9.
Basic glasses are prepared by chemical polymerization in a sol-gel process. Nucleation and crystallization of these glasses are analyzed in dependence of the composition of the basic glasses and “additions” of TiO 2 and LiO 2. A comparison of gel glasses with conventionally molten glasses is made. Gel glass-ceramics are prepared as bulk materials and thin coatings. 相似文献
10.
In order to better understand the distribution of tetrahedra in multicomponent tetrahedral network structures of melts and glasses, we have investigated the Raman spectra of binary SiO 2GeO 2 glasses. We compare the Raman spectral features of the end-member glasses and discuss their vibrational origins. The mixing of GeO 2 and SiO 2 melts results in a continuous random network structure of TO 4 tetrahedra (T Si, Ge) in the glass. Raman bands corresponding to the asymmetric stretch ( vas) of oxygen in GeOGe, SiOSi and SiOGe bonds are observed in the glasses having intermediate compositions along the SiO 2GeO 2 join. The presence of three distinct vas (TOT) bands in the spectrum of a glass having Si/Ge one reveals that a considerable degree of SiGe disorder exists in the glass. The presence of a single symmetric oxygen stretching band in the spectra of binary SiO 2GeO 2 glasses indicates that the symmetric stretch modes ( vs) of oxygen in SiOSi, SiOGe and GeOGe bonds are strongly coupled. An observed decrease in the halfwidth of the vs (TOT) band in the spectra of SiO 2GeO 2 glasses with increasing concentration of GeO 2 may be attributed to a decrease in the average TOT bond angle and a predominance of six-membered ring structures. Results of the present study support the assignment of the bands in the 900–1200 cm ?1 region of the alumino-silicate glasses, spectra to the vas(AlOSi) and vas(SiOSi) modes. In contrast to the alumino-silicate glasses, however, the SiO 2GeO 2 glasses have a much higher degree of disorder of the network-forming cations. 相似文献
11.
The cobalt oxide-silica and copper oxide-silica glasses are prepared by the sol-gel method. Tetra-Ethyl-Ortho-Silicate (TEOS) is used as source of the silica and transition metal nitrate is used as the dopant. The morphological, structural and optical properties of the samples are investigated by Scanning Electron Microscope (SEM), Energy Dispersion Analysis by X-ray (EDAX), X-ray diffraction (XRD) and Ultra-Violet/Visible (UV/Vis) spectrophotometer. The influences of heat treatment temperature and withdrawal rate on absorption/transmission spectra are investigated in the range 400-800 nm. In the cobalt oxide-silica, the intensity and position of absorption bands (λ max) are changed by heat treatment. These behaviors are explained through the Bathochromic and the Hyperochromic effects. In addition, the effect of the withdrawal rate on transmission curves is explained in terms of the Levich equation and Beer -Lambert law. 相似文献
12.
Ceramic materials with a very low thermal expansion coefficient are synthesized by the sol-gel process. The binary gel is obtained by hydrolysis and polycondensation reactions of organometallic compounds of aluminium and titanium. The thermal evolution of the amorphous powder is followed by DTA and TGA measurements. Structural evolution is followed using X-ray diffraction. The crystallization of the TiO 2 rutile and Al 2O 3 corindon starts at 700 and 900°C respectively. The transformation of Al 2O 3 and TiO 2 into Al 2TiO 5 appears between 1200 and 1300°C. The densification of the powder is performed by the hot pressing process. The shrinkage of the powder was previously followed by dilatometric measurements. The physical properties of the final material are studied as a function of pressing parameters. 相似文献
13.
Four glasses of the SiO 2-GeO 2 binary system have been synthesized via a sol-gel route followed by a heat treatment and a quench. Glass structure has been determined by Ge K-edge X-ray absorption spectroscopy (XAS) at low temperature and Raman spectroscopy. These mixed glasses present a continuous random network of interconnected GeO 4 and SiO 4 tetrahedra, with GeO 4 tetrahedra similar to the GeO 4 units in GeO 2 glass and continuous compositional variations from GeO 2-rich regions to SiO 2-rich regions. Such a random mixture is consistent with physical properties of these binary glasses as well as with the chemical dependence of their polyamorphism at high pressure. This EXAFS-derived mean Ge-O-Si angles are close to the Ge-O-Ge mean angle in GeO 2 glass, 134° and 130°, respectively. This misfit with the Si-O-Si angles might explain the ease of formation of isolated and pair defects centers, which are suspected to be at the origin of photo-induced modifications of optical properties in Ge-bearing SiO 2 glasses. 相似文献
14.
The immiscibility boundary and the critical point of SiO 2-Nd 2O 3 system glass were determined as a function of Al 2O 3 addition. The critical temperature of the immiscibility boundary was observed to decrease with the addition of Al 2O 3. Using the regular solution model, the observed decrease of the immiscibility boundary was directly related to the decrease of the concentration fluctuation of Nd 2O 3 in SiO 2. It is concluded that the Al 2O 3 addition to Nd 2O 3 containing silica glass is beneficial in decreasing the concentration quenching effect, deterioration of the optical efficiency due to clustering of rare earth element, because Al 2O 3 addition diminishes the concentration fluctuation of Nd 2O 3 in silica glass. 相似文献
15.
The structure of Na 2OGa 2O 3SiO 2 glasses of four different compositions containing up to 45 mol. % Ga 2O 3 has been determined by the X-ray diffraction method. The radial distribution function D( r) obtained indicates that Ga 3+ ions are in fourfold coordination and GaO 4 tetrahedra are formed in these glasses. The reduced intensity function S· i( S) and radial distribution function D( r) which were calculated based on a structural model for A-25, 0.25(Ga 2O 3)·0.75(Na 2O·2SiO 2)/3 glass agreed well with the observed ones. 相似文献
16.
Transparent glasses composition of which can be expressed by the formula: (100− x) · (K 2O · 2TiO 2 · P 2O 5) · x(K 2O · 2B 2O 3 · 7SiO 2), where x=5, 10, 15 and 20 mol% (KTP- xKBS), were obtained by melt quenching technique. The structure and crystallization behavior of these glasses have been examined by Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction. In spite of their nominal composition, the studied glasses exhibit a similar oxygen polyhedra distribution. However, significant differences were found in the trigonal BO 3 units amount. During DTA runs all the examined glasses devitrify in two steps. In the former, very small crystals of an unknown crystalline phase are produced. In KTP-5KBS and KTP-10KBS glasses anatase phase was also detected. Attempts were made in order to identify the unknown phase (UTP) for which a AB 3(XO 4) 2(OH) 6 Crandallite-type structure was proposed where the A, B and X sites were occupied by K, Ti and/or Al, and P, respectively. In the second devitrification step the crystallization of the KTiOPO 4 phase occurs while the UTP phase previously formed disappears. Isothermal heat treatments performed at temperature just above Tg have allowed one to obtain transparent crystal-glass nanocomposites, formed by crystalline nanostructure of the UTP phase uniformly dispersed in the amorphous matrix. 相似文献
17.
The preparation of ruthenium catalysts by the sol-gel method is described. The preparation consists of adding the active metal to a sol which, by hydrolysis and codensation reactions turns into a gel. The catalytic activity for benzene hydrogenation shown by these catalysts is higher than that of catalysts prepared by impregnation of a commercial silica. A superior resistance to catalytic autodeactivation is observed for catalysts prepared by this method. 相似文献
18.
The synthesis of CuO---Al 2O 3---SiO 2 glasses by the sol-gel method was investigated and the thermal expansion of bulk glasses was measured. Phase separation was observed in these glasses and apparently consisted of a copper-rich dispersed phase and a network former-rich matrix phase. The low thermal expansion coefficient of these glasses was governed by the matrix phase. 相似文献
19.
Glasses with the compositions xNa 2O · 10MgO · (90 − x)SiO 2, 10Na 2O · xMgO · (90 − x)SiO 2, 5Na 2O · 15MgO · xAl 2O 3 · (80 − x)SiO 2, xNa 2O · 10MgO · 10Al 2O 3 · (80 − x)SiO 2, 10Na 2O · 10MgO · xAl 2O 3 · (80 − x)SiO 2, 10Na 2O · 5MgO · 10Al 2O 3 · (80 − x)SiO 2 were melted and studied using UV-vis-NIR spectroscopy in the wavenumber range from 5000 to 30 000 cm −1. At [Al 2O 3] > [Na 2O], the UV-cut off is strongly shifted to smaller wavenumbers and the NIR peak at around 10 000 cm −1 attributed to Fe 2+ in sixfold coordination gets narrower. Furthermore, the intensity of the NIR peak at 5500 cm −1 increases. This is explained by the incorporation of iron in the respective glass structures. 相似文献
20.
Organic-inorganic hybrid monoliths consisting of poly(methyl methacrylate) and SiO 2 were synthesized by the sol-gel process. Three PMMA/TEOS ratios by weight were prepared, namely PMMA/TEOS = 80/20, 50/50 and 20/80. The effects of the ratio of PMMA/TEOS on thermal stability, microstructure, morphology and optical properties were systematically studied. In particular, scanning electron microscopy (SEM) demonstrated morphological variation corresponding to the degree of miscibility between organic and inorganic components. Energy dispersive spectroscopy (EDS) clearly revealed that the SiO 2 was more uniformly distributed in the hybrids with increasing PMMA content. The refractive index could be adjustable in the range of 1.474-1.486. The 80/20 monolith had the similar transparency to pure PMMA in the visible region and lower absorption than PMMA in the near infrared region, suggesting its potential applications for optical devices. 相似文献
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