In part, this is because the numerous variables that must be optimized to obtain a given material with a specific shape and particular properties cannot be readily defined based on fundamental principles.
In part, the problems arise because the basic chemistry of common chemical processing systems has not been fully delineated. The prupose of this paper is to provide an overview of the basic chemical problems associated with chemical processing.
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The emphasis will be on sol-gel processing, a major subset pf chemical processing. Two alternate approaches to chemical processing of glasses are also briefly discussed. One approach concerns the use of bimetallic alkoxide oligomers and polymers as potential precursors to mulimetallic glasses. The second approach describes the utility of metal carboxylate precursors to multimetallic glasses.
Theory and application of spectroscopically active glasses prepared by the sol-gel method Author s : Renata Reisfeld Show Abstract. The sol-gel technique allows preparation of pure inorganic glasses or composite glasses of inorganic and organic nature at low temperature. Incorporation of organic molecules with desired spectral characteristics is the subject of our research. Specific cases include preparation of stable tunable lasers in the visible based on photostable dyes; glasses doped with dyes characterized by double-proton transfer with good separation between absorption and emission; new materials having nonlinear properties; and glasses with dyes sensitive to ambient acidity and basicity.
Four types of these glasses are discussed. Transition metal oxide T. O gels exhibit extrinsic or specific optical properties. This duality is related to the fact that they can be used as transparent amorphous matrices from which high refractive index is expected, or for their mixed valence behaviour. Titanium or Zirconium oxide based gels have been used as transparent matrices in which large concentration of inorganic Eu III or organic luminophores Rhodamine 6G , Rhodamine , Coumarine 4 have been incorporated. Several specific optical properties related to Titanium oxide based gels such as electrochromism photoelectrochemistry and photochemistry are also described.
Cylindrical monolithic silica dry gel bodies, up to grams in weight, are routinely produced from alkoxide sols free of colloidal particles, using tetraethylorthosilicate precursor.
These dry gel bodies, after sintering in controlled chlorinated atmosphere, yielded clear, bubble free, dense glass rods 3. Uv-vis--ir spectra, of properly dehydrated and sintered glass samples tested from 1 80 nm to urn, showed no detectable absorption peak at nm and a UV band edge at around nm; implying that resultant glasses are reasonably free of impurities and hydroxyl ions.
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Effect of sol composition on gel ultrastructure was carefully investigated. It was found that by careful choice of sol composition, type and amount of catalyst and aging conditions, it is possible to tailor the gel ultrastructure for ease of drying. As a result of this ability to tailor gel ultrastructure, including pore size, bulk density and skeletal density of the gel bodies, we have been able to optimize gel ultrastructure to maximize its strength, so that it can withstand capillary forces generated during the drying processes.
The result of this preliminary investigation has led us to believe that high quality fused silica glass of much larger sizes can be produced by the alkoxide route; and experiments to scale up the process is under way. Up to date results of this investigation will be presented at the conference.
Pregrooved glass disks were prepared by the application of the sol-gel coating technique; the soda-lime-silica glass disks were coated with polyethylene glycol PEG -containing SiTi02 gel films, in which fine patterns were formed by pressing a stamper. The refractive index of the pregrooved layer was matched with that of the glass disks by adjusting the TiO2 content. The noise level of the glass disks with the pregrooved SiO2-Ti02 layer was lower by dB than that of the disks with pure 5i02 layer in the frequency range from 0.
The lower noise level of the former can be ascribed to the agreement in the refractive index between the pregrooved layer and the glass disks. The effects of the addition of polyethylene glycol PEG on the formation of gel-derived glass films in the SiTiO2 system were studied, aimed at their application to the optical memory disks.
The viscosity of the as-prepared sols increased almost linearly with increasing PEG content.uramhalli.tk
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The increase in viscosity of the sols during the storage was retarded with decreasing molecular weight of PEG added and with increasing amount of PEG added. The viscosity increase of the sols during the storage, however, showed a similar temperature dependence, i. The gel films containing PEG of the smaller average molecular weight showed the higher hardness and the steeper increase in hardness with increasing the heat-treatment temperature than those containing PEG of the larger average molecular weight.
For a high performance in the fine patterning process and densification of the resultant patterned films, PEG of the smaller amount and the smaller molecular weight is favorable, provided the PEG-containing gel films are initially soft enough to emboss fine patterns by pressing a stamper.
New developments in sol-gel imaging Author s : Nicholas J. Phillips Show Abstract. This paper addresses the properties of sol-gel silica in relation to its potential to provide new devices for optical imaging. Although the sol-gel method opens the door to unprecedented levels of purity of silica materials, it is also beset with problems of the achievement of extreme optical homogeneity. The work reported discusses experiences with sol-gel silica intra cavity elements in ion lasers and new concepts of imaging and laser structures based on fabrication via porous gel-silica.
A new physical model for etalons is proposed which shows advantages of porous gel-silica over conventional fully dense materials. Rodenberger; Anthony F. Garito Show Abstract. Since the basic phthalocyanine structure intrinsically possesses high thermal and oxidative stabilities, phthalocyanines incorporated into sol-gel glasses provide an attractive approach for realizing highly stable nonlinear optical media. Experimental results recently obtained for the nonresonant and resonant third order optical properties of metallophthalocyanines are reviewed in this paper. Bagnall; J.
Zarzycki Show Abstract. Various methods of obtaining fine colloidal precipitates of cadmium sulfo-selenides in Si02 gel matrices are described. These materials, which are of interest in opto- electronic applications, can be prepared by diffusion of various reactants in wet gels. The influence of different preparative parameters on the diffusion characteristics, the possibility of obtaining distribution gradients and, in particular, the interest of sonocatalysis ultrasonic irradiation are briefly presented. Preparation of semiconducting sulfides microcrystalline-doped silica glasses by the sol-gel process Author s : Masayuki Nogami ; Michie Watabe; Katsumi Nagasaka Show Abstract.
The sol-gel process has been applied successfully to the preparation of small-particle-size ZnS, CdS or PbS-doped silica glasses with a significant quantum size effect.
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From X-ray diffraction analyses and transmission electron mlcrographs, these crystals were cubic ZnS, hexagonal CdS and cubic PbS crystal, respectively, and their sizes were 2 to 8 nm in diameter. In the optical absorption spectra, the absorption edge exhibited a blue shift compared with those of the bulk sulfides crystals.
Sol-Gel-Derived Doped ZnO Thin Films: Processing, Properties, and Applications
Size dependence of energy shift was discussed in relation to size quantization of electron-hole in microcrystals. The nonlinearity was estimated to be 1. CdS-doped Si02 glasses have been prepared through the sol-gel process. A methanol solution of cadmium nitrate and thiourea in a molar ratio of was added to the Si02 sol prepared from silicon tetraethoxide. For these CdS microcrystallite-doped glasses, the peak of photoluminescence was shifted to shorter wavelengths relative to the absorption edge of CdS crystal, in agreement with the blue shift of the optical absorption edge; these shifts were indicative of the quantum size effects.
A gradient-index glass rod of about 13 mm in diameter and 20 mm in length with the refractive index difference of about 0. A bubble free wet gel of about 35 mm in diameter and 50 mm in length was obtained by adding acetic acid to the precursor solution as a buffering agent. The liquid in the micropores of the wet gel was totally replaced with acetone. Then the compositional gradient of lead was formed in radial direction of the gel by soaking in an ethanolic solution of potassium acetate.
Sol-gel derived gradient index optical materials Author s : Tessie M. Che; J. Brian Caldwell; Robert M. Mininni Show Abstract. Gradient index optics will play an increasingly important role in applications such as fax machines, photocopiers, fiber optic couplers and cameras. In this paper, we present an overview of various sol-gel methods for making gradient index materials. A new technique for producing radial gradient refractive index r-GRIN titanium-doped silica lenses has been developed employing a sol-gel leaching method.
The obtained lenses possess a parabolic index distribution and give good images with high resolution. They also show high coupling efficiency with optical fibers and enable a low-loss large distance space transmission of light between optical fibers. Furthermore the sol-gel r-GRIN lenses show a high degree of environmental stability as expected for the doped-silica lenses.
Sol-gel processed inorganic and organically modified composites for nonlinear optics and photonics Author s : Paras N. Prasad Show Abstract. The newly emerging field of Nonlinear Optics and Photonics offers tremendous opportunities for optical engineers and materials scientists.