The aim of this research is to obtain a meaningful rheological characterization of deflocculated china clay suspensions. It is generally true that in the study of suspensions relatively little successful work has been carried out on the flow properties of highly concentrated suspensions as compared with dilute suspensions; it was decided therefore that the work, presented in this thesis, should be confined to the study of higher concentration suspensions. A survey is given of previous work on the rheological characterization of suspensions and the reasons for choosing the clay suspensions in particular, are discussed. Since a knowledge of the microscopic nature of the particles in suspension is important for the understanding of the macroscopic behaviour of the suspensions, a detailed account of the relevant aspects of clay and its rheological behaviour is presented. The investigation consists of a theoretical and experimental study of the suspensions. The experimental results are obtained by using a commercial rheometer, the Weissenberg Rheogoniometer. Experiments are performed which include steady shear studies, oscillatory shear studies and studies of a combined steady and low-amplitude oscillatory shear flow. A theory is developed for this latter flow situation and expressions for the percentage increase in couple are obtained based on different rheological equations of state. Concentration effects are examined and it is shown that, with increasing concentration, an initial shear thinning region is followed by a shear thickening one. It is also found that marked elastic properties are exhibited by these highly concentrated clay suspensions. Qualitative agreement is obtained between theory and experiment for all suspensions considered and at the highest concentrations it is shown (for the first time) that it is possible to characterize shear thinning and shear thickening properties of a fluid using one equation of state. The experimental results indicate that this programme of work may have important implications for certain industrial nearly viscometric flow situations as well as the whole approach being applicable to other concentrated suspension systems.

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