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Solvent Selection and the Control of Sol-Gel Reactions

Published online by Cambridge University Press:  28 February 2011

K Jones ,
J M Boulton  and
H G Emblem
K Jones
Affiliation:
Department of Chemistry, University of Manchester Institute of Science & Technology, UMIST, Manchester M60 1QD, United Kingdom.
J M Boulton
Affiliation:
Department of Chemistry, University of Manchester Institute of Science & Technology, UMIST, Manchester M60 1QD, United Kingdom.
H G Emblem
Affiliation:
Department of Chemistry, University of Manchester Institute of Science & Technology, UMIST, Manchester M60 1QD, United Kingdom.
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Abstract

The hydrolysis and gelation sequence occurring in the formation of a filament or a rigid coherent gel from an organic silicate requires a mutual solvent for the organicsilicate and water if it is to proceed successfully. The solvent is usually a water-miscible alcohol. This alcohol can also be a reaction product, which makes the sequence very solvent dependent. The best control of both hydrolysis and gelation is obtained when the alcohol solvent and the organic silicate each contain the same alkoxy group. The gel resulting is also the best binder for refractory grain. Suitable systems are ethyl silicate and ethanol also isopropyl silicate and isopropanol. The formation of rigid coherent gels, or filaments which on firing convert to ceramic fibres, from hydrolysates of ethyl silicate and aluminium chlorhydrate species is also very solvent dependent. With glycol solvents, aluminium chlorhydrates do not form filaments nor ceramic fibres. With ethanol as solvent, aluminium chlorhydrate-polyol complexes readily form rigid coherent gels and filaments, hence ceramic fibres, because the polyol complex is formed by displacing coordinated water in the aluminium chlorhydrate. This reduces the amount of water available for reaction, which optimises filament and fibre formation.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 180: Symposium A – Better Ceramics Through Chemistry IV , 1990 , 277
Copyright
Copyright © Materials Research Society 1990

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References

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