Characterisation of Concentrated Colloidal Suspensions for Ceramic Processing
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CHARACTERISATION OF CONCENTRATED COLLOIDAL SUSPENSIONS FOR CERAMIC PROCESSING R F STEVJART AND D SUTION ICI Corporate Colloid Science Group, P 0 Box 11, The Heath, Runcorn, Cheshire, England. ABSTRACT Characterisation and control of the structure and properties of particulate solids suspensions is of widespread importance with respect to many operations, such as separation, dispersion and densification in the ceramics and related industries. In this paper we describe techniques which have been used to study the effects of changes in basic parameters, for example solids content, particle size, electrolyte concentration and added polymer on the aggregated suspension morphology and characteristics. Suspension morphology was examined by a number of methods, notably freeze-etch microscopy. The mechanical properties of suspensions such as their compressional modulus and rheological behaviour was also examined. INTRODUCTION In the formation of ceramics from suspensions of fine particles the properties of the material are not only dependent upon the process selected but they are also very much determined by the properties of the suspension itself [1 ,2]. In many cases the latter are responsible for placing limits on the quality of the final product. Problems involving the manipulation of colloidal suspensions are also prevalent in the chemical industry. There is a need to improve the efficiency with which such systems are handled and this requires the ability to control suspension structure and its derivative properties such as densification, filtration and rheological behaviour. To achieve an improved understanding of the behaviour of such systems we have investigated how the structure and properties of standard suspensions of flocculated colloidal materials vary with basic parameters, for example solid loading, particle size, electrolyte concentration and added polymer type. In the main, well characterised polymer latices have been used for the work in order to allow unambiguous examination of one variable at a time, though a number of inorganic materials such as A1203 and Ti02 have also been studied. Suspension structure has been probed directly using a range of microscopic techniques, freeze-etch microscopy being extensively used for the examination of concentrated suspensions as it avoids the need to perturbate the system by, for example, dilution or drying. Parallel investigations into the properties of the samples such as their consolidation behaviour, shear moduli and rheology have also been conducted. From the experimental data we map out some general principles concerning the influence of changes in some basic parameters on the morphology and properties of colloidal systems.
Mat. Res.
Soc.
Symp.
Proc. Vol.
32 (1984)QElsevier Science Publishing Co.,
Inc.
282
MARIALS The principal dispersions used for the work were surfactant-free, anionic charge stabilised polystyrene latices prepared by methods following those suggested by Goodwin et al. [3]. Monodisperse species with diameters ranging from 0.2-4.0 micro
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