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Showing papers on "Sol-gel published in 1984"


Journal ArticleDOI
TL;DR: In this paper, polymethacrylates were incorporated as linear crosslinking elements using a methacrylsoxy substituted alkoxysilane as a hook between the siliceous network and the polymer chain.
Abstract: Methods of synthesizing materials for hard contact lenses were developed by hydrolysis and condensation of an epoxide substituted alkoxysilane and Ti-alkoxides. To enforce sufficient tensile strength, polymethacrylates were incorporated as linear crosslinking elements using a methacryloxy substituted alkoxysilane as a hook between the siliceous network and the polymer chain. The incorporation of titania led to dense monolithic products which could be cured only with some minor shrinkages. Good wettabilities [contact angles with water: (25 ± 5)°] are due to glycol groupings formed by the epoxide radicals. O 2 -permeabilities of P = (13 ± 1) × 10 −11 ml O 2 cm 2 ml −1 s −1 mm Hg −1 result from the silicone-like structure elements, where R denotes a silicon-carbon bound organofunctional radical.

450 citations


Patent
03 May 1984
TL;DR: The sol-gel process for forming dense, alumina-base ceramics, the process comprising 1. preparing a dispersion of aluminum oxide monohydrate containing a precursor of a modifying additive in the form of a soluble salt, 2. gelling the dispersion; 3. drying the gel dispersion to form a solid; 4. calcining the solid; and 5. sintering the calcined solid, is improved by adding to the dispixture at least about 10 weight percent, based on the oxide equivalent of the soluble salt precursor, of at least one densification aid
Abstract: The sol-gel process for forming dense, alumina-base ceramics, the process comprising 1. preparing a dispersion of aluminum oxide monohydrate containing a precursor of a modifying additive in the form of a soluble salt; 2. gelling the dispersion; 3. drying the gel dispersion to form a solid; 4. calcining the solid; and 5. sintering the calcined solid, is improved by adding to the dispersion at least about 10 weight percent, based on the oxide equivalent of the soluble salt precursor, of at least one densification aid selected from the group consisting of alcohols, glycols and polyether compounds having a vaporization point in excess of the temperature at which the dispersion is dried. This improved process is particularly useful for manufacturing abrasive grains.

77 citations


Journal ArticleDOI
TL;DR: In this paper, a comparison between two sol-gel processing routes to oxide ceramics, the first using colloidal dispersions of hydrous oxides, the second using metal alkoxide intermediates, is made.
Abstract: A comparison has been made between two sol-gel processing routes to oxide ceramics, the first using colloidal dispersions of hydrous oxides, the second using metal alkoxide intermediates. Methods of making shaped products (e.g. spheres) are described together with the range of oxides that have been produced utilising sol-gel routes. Advantages and disadvantages of using the two methods on large-scale preparations are described.

71 citations


Patent
January James R1
17 Dec 1984
TL;DR: In this paper, a method of preparing carbon-containing monolithic glassy ceramics from organosilsesquioxanes, metal oxides and metal alkoxides through pyrolysis of their gels is presented.
Abstract: What is disclosed is a method of preparing carbon-containing monolithic glassy ceramics from organosilsesquioxanes, metal oxides and metal alkoxides through pyrolysis of their gels. Also disclosed are certain gel compositions used in the method and the glassy ceramics.

70 citations


Journal ArticleDOI
TL;DR: In this article, the authors used X-ray diffraction and infrared spectroscopy to obtain the structural variation of the gels during heat treatment and the results suggest the different function of Zr4+ ions from Ti4+ ion in this kind of glass.
Abstract: ZrO2- and/or TiO2-containing silicate glasses have been attracting more and more scientists and technologists due to their low thermal expansion and excellent resistance to alkali corrosion. But it is difficult to make these glasses by the conventional melting method because of their extraordinarily high melting temperatures. In the present work, however, glasses in the ZrO2TiO2SiO2 systems have been successfully synthesized by the sol-gel route using Zr(NO3)4 · 5H2O, Si(OC2H5)4 and Ti(C4H9)4 as starting materials. Transparent glass pieces were obtained containing 20 mol.% TiO2 and up to 30 mol.% ZrO2. Detailed studies were carried out on the whole synthesis process including hydrolysis, polymerization, gelling and conversion from gel to glass. Research results on the viscosity evolution of the reaction systems showed that environmental humidity and catalyst had important effects on the gelling process. During heat treatment, the colour of the dry gels gradually changed and DTA data indicated that at about 650°C the conversion from gel to glass would be completed. The information about the structural variation of the gels during heat treatment has been obtained by means of X-ray diffraction, infrared spectroscopy and the results suggest the different function of Zr4+ ions from Ti4+ ions in this kind of glass, i.e. Ti4+ ions act as network formers, while Zr4+ ions act as network modifiers.

50 citations


Journal ArticleDOI
TL;DR: In this article, a sol-gel process is described for the preparation of diphasic composite materials, which involves the growth of extremely fine crystalline or non-crystalline materials inside a pre-made gel structure by soaking the gel in metal nitrate solution and subsequent precipitation of the metal with the selected anions (using mineral acids) followed by a densification step.

46 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of heat treatment and sintering atmospheres on hydroxyl content of these bodies is discussed, as well as their effect on optical fiber losses.
Abstract: Large silica bodies have been made from colloidal silica by doubly dispersing fumed silica, casting and drying to a porous silica body. These were subsequently dehydrated and sintered to transparency at 1200–1300°C. Tubes made in this way were used as substrates to fabricate optical fiber by MCVD. One low model fiber exhibited losses of 0.7 dB/km at 1.15 μm. The effect of heat treatment and sintering atmospheres on hydroxyl content of these bodies is discussed.

46 citations


Journal ArticleDOI
TL;DR: In this article, the authors report on work done to prepare deliberately diphasic materials by mixing two sols, mixing 1 sol with 1 solution, and post formation diffusion of either one or two solutions.
Abstract: Instead of aiming to prepare homogeneous gels and xero-gels, this paper reports on work done to prepare deliberately diphasic materials. This has been achieved by three different paths: (1) mixing 2 sols; (2) mixing 1 sol with 1 solution; and (3) post formation diffusion of either one or two solutions. By the last named process we have made SiO2, mullite and alumina based composites, with silver halides, BaSO4, CdS, etc., as the dispersed phase. The crystal size can be confined to the initial pores by rapid diffusion giving rise to extremely fine second phases in the submicron range. Subsequent reduction of appropriate metallic salts can be used to give finely dispersed metals (e.g. Cu, Ni) in essentially any xerogel matrix. The open porosity makes these metal atoms very accessible. By the first two processes we have made both single phase and di-phasic gels of the same composition (prototype: mullite) and shown that though they cannot be distinguished by XRD, SEM, and TEM, by DTA and thermal processing, they are radically different. Such di-phasic gels store more metastable energy than any other solids.

46 citations


Journal ArticleDOI
TL;DR: In this paper, both the processing and resultant properties for ferroelectrics such as BaTiO3, KTaO3 and KNbO3 made by both methods are directly compared.
Abstract: The sol-gel method for the preparation of ceramics and glasses has frequently been mentioned as more advantageous as compared to conventional methods. However, there are few known examples of a direct comparison for the same material. In the present work both the processing and resultant properties for ferroelectrics such as BaTiO3, KTaO3, KNbO3 and K(Ta,Nb)O3 made by both methods are directly compared. The uniformity is evaluated by high-angle x-ray diffraction, electron microscopy and EDAX and the dielectric properties are compared. The advantages and disadvantages of the sol-gel method are discussed.

25 citations



Book ChapterDOI
01 Jan 1984
TL;DR: In this paper, it was shown that the volume change of gelling fibers occurring during the solidification process is related to the shape of the cross-section of the resulting glass fibers.
Abstract: In the sol-gel preparation of oxide glasses using metal alkoxides as raw materials, the content of water added for hydrolysis of the alkoxides must be controlled depending on the desired shape of the resulting glass. Larger water contents of the starting solution are preferred for the production of bulk glasses, while smaller water contents lead to the formation of fiber glasses. The cross-section of glass fibers made by the sol-gel method is circular or non-circular, depending on the composition of the starting solution. This effect is examined, and it is shown that the volume change of gelling fibers occurring during the solidification process is related to the shape of the cross-section of the resulting glass fibers.

Journal ArticleDOI
TL;DR: The formation and characterization of thin ceramic coatings is currently an active area in materials science as discussed by the authors, however, only a few papers have been published in this area and no method yet exists for the formation of nitrides by the sol-gel method.
Abstract: The formation and characterization of thin ceramic coatings is currently an active area in materials science. Specifically, there has been increased interest in these materials as dielectric and optical layers for advanced microelectronic circuitry [1]. This is in addition to their continued use and evaluation as protective coatings in a variety of applications [2]. One method of forming these coatings is via the sol-gel technique. However, only a few papers have been published in this area [3–7]. Dense silicon dioxide, aluminium oxide and various glass compositions have been deposited in thin film form on various substrates. Further, silicon dioxide films, formed by the sol-gel method, have been nitrided in ammonia at high temperatures and partially converted to an oxynitride [8–11]. These films were shown to be highly non-homogeneous, with a predominance of nitrogen at the surface. Despite the desirability of dense uniform well bonded coatings of the nitrided ceramics, i.e. Si 3 N 4 and the oxynitrides, no method yet exists for the formation of nitrides by the sol-gel method.

Journal ArticleDOI
TL;DR: In this article, a solution prepared by reacting a titanium alkoxide with barium hydroxide in methanol was used for preparing thin films of barium titanate on silicon and metal substrates.
Abstract: Sol-gel techniques provide a convenient method of applying barium titanate films on solid substrates at ambient temperature A significant advantage in using this technique is the capability of maintaining compositional homogeneity while coating large areas of surfaces with complex geometries Solutions prepared by reacting a titanium alkoxide with barium hydroxide in methanol were used for preparing thin films (1000–3000A…) of barium titanate on silicon and metal substrates Electrical properties of the films depended both on solution parameters and subsequent heat treatment of the films Highest field strengths (8−9 A— 106 V/cm) were observed in amorphous films prepared from partially hydrolyzed solutions

Journal ArticleDOI
TL;DR: In this article, the shrinkage of gels prepared by the sol-gel process from metal alkoxides in the systems B2O3-SiO2 and ZrO2-SiOsO2 was determined by measuring the shrinkages of the gel on heating.
Abstract: Dehydration of gels prepared by the sol-gel process from metal alkoxides in the systems B2O3-SiO2 and ZrO2-SiO2 was determined by measuring the shrinkage of the gel on heating. Dehydration was enhanced with increased ZrO2 content, whereas it decreased with B2O3 content. Diffusion of water was also measured in the nonporous glasses obtained by heating the gels. The diffusion rate was independent of the composition of the glass.

01 Jan 1984
TL;DR: In this paper, a tetraethylorthosilicate (TEOS) solution was prepared from alcoholic solutions of TEOS using a two-step hydrolysis process; small angle X-ray scattering (SAXS), gas-liquid chromatography, and 1H NMR spectroscopy were employed to study their formation.
Abstract: Silica gels were prepared from alcoholic solutions of tetraethylorthosilicate (TEOS) using a two-step hydrolysis process; small angle X-ray scattering (SAXS), gas-liquid chromatography, and 1H NMR spectroscopy were employed to study their formation. The first step (1 mol. H20/mol. TEOS with HCI catalyst) resulted in a rather wide species distribution comprised of hydrolyzed and unhydrolyzed monomers, dimers, and chains. The second step (additional water plus acid or base) resulted in completely hydrolyzed polymers in the acid system which apparently were highly overlapped prior to gelation. In the base system, hydrolysis was incomplete due to unhydrolyzed monomer and the resulting polymers were more highly condensed (or collapsed) and discrete compared to the acid system. The formation of colloidal silica was not observed in either case.



Patent
20 Apr 1984
TL;DR: In this paper, a silicon alkoxide (e.g., ethyl orthosilicate, etc.) is hydrolyzed in an ammonia alcohol to give fine particles of silica, precipitating them, drying them under heating.
Abstract: PURPOSE:To obtain quartz glass mass with a little volume shrinkage by relative short time heating without causing cracking, by hydrolyzing a silicon alkoxide in an ammonia alcohol to give fine particles of silica, precipitating them, drying them under heating. CONSTITUTION:A silicon alkoxide (e.g., ethyl orthosilicate, etc.) is hydrolyzed in an ammonia alcohol (e.g., mixed solution of ammonia water and methanol, etc.). Fine particles of amorphous silica are formed in the reaction solution. Usually, thye are precipitated naturally, and the precipitate has the closet packing structure. A supernatant liquid is removed from the solution, and the precipitate is dried naturally or under heating to give a dried chalky material with a fixed shape. It is heated at >=1,000 deg.C and processed into transparent glass. Since this process is carried out at lower temperature with smaller energy consumption than melting process, the material can be converted into glass in a shorter time than sol gel process, cracking is few, and volume shrinkage is low, and a final molded article such as lens can be molded simultaneously with preparation.


Proceedings ArticleDOI
26 Dec 1984
TL;DR: The sol-gel process is a chemical approach to making optical materials at low temperature as discussed by the authors, where a metal alkoxide such as tetraethyl-orthosilicate (TEOS) is converted to high surface area silica gel at room tempera-ture.
Abstract: The sol-gel process is a chemical approach to making optical materials at low temperature. Through hydrolysis and condensation reactions, a metal alkoxide such as tetraethyl-orthosilicate (TEOS) is converted largely to high surface area silica gel at room tempera-ture. After drying, the result is a rigid monolithic shape of bulk density about half that of conventional fused silica. The reduced weight of the shape is due to interconnected microporosity. The average pore size is generally smaller than 10 nm, and the material is transparent to visible light.