Showing papers on "Sol-gel published in 1985"

Organic fluorescent dyes trapped in silica and silica-titania thin films by the sol-gel method. Photophysical, film and cage properties

Abstract: The sol-gel process is utilized to solve the notorious problem of incorporating an organic dye in an inorganic oxide thin film. Fluorescent thin films are prepared by this low temperature process with the aid of a surface active agent, with good homogeneity and reproducability. A variety of organic fluorescent molecules are embeded either in silica or in silica-titania films. The dye molecules are not leached out by water. Absorption and emission spectra, enhanced photostability, longer lifetimes and energy transfers between the trapped dye molecules are described and discussed in terms of the effects of molecule matrix-isolation on these properties. Potential uses of the special thin films are numerous, e.g., as laser or solar light guides.

Ceramers: Hybrid materials incorporating polymeric/oligomeric species with inorganic glasses by a sol-gel process

Abstract: A sol-gel process has been successfully utilized to produce hybrid materials incorporating polymeric/oligomeric components of polydimethyl siloxane(PDMS) with silicon glasses. All the samples made were transparent and flexible. Dynamic mechanical studies indicate that a portion of the siloxane species is phase-separated while the remainder is well dispersed. The effect of acid content were proven to be significant on the dispersion of the siloxane components and on the structure and properties of final products.

Preparation of glass by sintering

Abstract: Preparation of glass articles by sintering of glass and amorphous powders is considered. The classification of sintering processes includes: (a) sintering of premelted and pulverized glasses; (b) sintering of premelted chemically treated glasses; (c) sintering without melting; (d) sintering with melting. The most interesting class of processes is sintering without, or simultaneously with, melting and it includes preparation of preforms for optical fibres and the sol-gel route for glass preparation. This last route is reviewed in detail. Two main versions are considered: preparation of gels by hydrolysis and polymerization of alkoxides, and sintering of amorphous colloidal powder compacts. The sol-gel processes represent an embryo of a new technology for the production of high-melting glasses (including quartz glass) at relatively low temperatures.

Sol-gel-derived PbTiO 3

Abstract: The sol-gel process is a technique which is applicable for forming ceramic materials. In this process, liquid precursor materials are reacted to form a sol which then polymerizes into an inorganic polymeric gel. Advantages of this process over standard powder preparation of ceramics are: purity, homogeneity, control of macro- and micro-structures, and low processing temperatures. In our laboratory the sol-gel process has been used to form lead titanate. We detail a procedure which has produced dried monolithic gels up to 1.5 cm in diameter. The as-dried gels have not been exposed to temperatures above 40‡ C and are X-ray amorphous. Samples of the gels were crushed into powder and heated at 8‡ C min−1 to various temperatures up to 500‡ C, held for a variety of times, and then cooled to room temperature. After certain annealing procedures crystalline phases were observed. The initial crystalline phase to emerge has not yet been identified. Upon further annealing this phase transforms to tetragonal PbTiO3.

Glass preparation of the ZrO2SiO2 system by the sol-gel process from metal alkoxides

Abstract: Glasses in the ZrO 2 SiO 2 system containing up to 50 mol.% ZrO 2 were prepared by heating the gels made from the mixed solutions of Zr(OC 3 H 7 ) 4 and partially prehydrolyzed Si(OC 2 H 5 ) 4 . The anionic network structure similar to that of glass was already formed in the gels. And it was observed that the properties of the gels were determined by the porosity in the gel rather than the gel constituting structure. Porous gels converted into the non-porous impervious glasses through three major reactions with increasing temperature: the removal of the adsorbed water, dehydration-condensation and sintering. Density, refractive index and hardness of the non-porous glasses increased with the increase of ZrO 2 content. Infrared spectra and molar refractivity showed that the Zr 4+ ion was incorporated in the interstices of the silica network structure.

Preparation of transparent non-crystalline stoichiometric magnesium aluminate gel-monolith by the sol-gel process

Abstract: Transparent non-crystalline stoichiometric magnesium aluminate gel-monolith was prepared by chemical polymerization reaction between aluminium alkoxide and magnesium salt. The reaction mechanisms of gel formation are discussed. The ovendried gel was freed from residual organics by chemical treatment with hydrogen peroxide solution. X-ray analysis of organic-free gel powder after heat treatment for 4h at 2000‡ C did not show any indication of phase separation. It is suggested that the use of sol-gel-derived powders could largely eliminate most of the problems associated with the conventional method of fabrication of optically transparent stoichiometric magnesium aluminate spinel.

Thermal stability of aluminium oxides prepared from gel

Abstract: On etudie la stabilite thermique des formes d'oxyde d'aluminium preparees par le procede sol-gel

Process for low temperature curing of sol-gel thin films

Abstract: A process for curing and densifying a sol-gel derived inorganic thin film at lower temperatures (between 10° C. and 400° C.) by applying the films to a substrate, drying the film at a low temperature, exposing the film to a low pressure plasma. The film may be an oxide (e.g. SiO 2 ), nitride (e.g. Si 3 N 4 ), oxynitride (e.g. SiO x N y ) or sulfide (e.g. GeS 2 ).

Large sol-gel SiO2 monoliths containing transition metal and their production

Abstract: Sol-gel monoliths containing SiO 2 and optionally B 2 O 3 , Na 2 O, Li 2 O, TiO 2 , Al 2 O 3 and mixtures thereof, and a transition metal having an atomic number from 21-28 made by mixing water, a SiO 2 precursor, a non-precipitating salt of a transition metal and mellitic acid to form a sol, gelling the sol, aging the gelled sol, drying the aged gelled sol and densifying by heating to from about 500° C. to about 1350° C.

Experimental Study of Porous Gel Sintering

Abstract: Formation and disappearance of closed pores in silica gel during sintering were experimentally detected using a light-scattering technique. The disappearance of closed pores is strongly influenced by the atmosphere in which the gel is sintered.

Use of Sol-Gel Thin Films In Solar Energy Applications

Abstract: The sol-gel process uses metal alkoxides of network forming cations, such as Si, B, or Al, in alcohol/water solutions to form glass-like, polymeric networks in liquid solution. Thin films are formed by depositing the solution on a substrate by spinning, dipping or spraying. When the film is then heated to moderate temperatures (400-500°C), dense glass films or stable porous films are obtained.

Viscoelastic Effects Occurring the Sol-Gel Transition

Abstract: The gels can be defined as a composite material made of two phases: a three-dimensional polymeric network embedded in a fluid. The main characteristic of such materials is that only a few per cent (w/w) of network is sufficient to give a weak elastic solid behavior, and to prevent the flow of the fluid phase due to the friction of solvent molecules with the network.

Mercury porosimetry of dry silica gels

Abstract: A recent explosion in research of silica gels has been stimulated by prospects of glass preparation at temperatures significantly lower than temperatures of conventional melting and by opportunities to prepare unusual glasses which cannot be produced by melting (1,2). Dried gels represent highly porous structures which can be sintered to monolithic glasses at temperatures below the liquidus. Two types of sol-gel glass preparation have emerged: 1) hydrolysis and polymerization of alkoxides (1,2), and 2) gelation of colloidal sols, which includes dispersion of a powder in water, drying, redispersion, gelation, drying and sintering (2–5). In both cases the size and mutual distribution of pores are very important for processing after gelation: drying and sintering. Mercury porosimetry (6–8) provides information about pore size distribution. This paper deals mainly with methodological problems of gel study by this method.