Sanitaryware article published in Ceramic Forum International (March 2009)

Abstract

This article focuses on the ball clay components of casting slips, in particular on how ball clays are characterised by two variables, a) the solids concentration of the ball clays used in the slip, and b) deflocculant demand. The traditional and proven method within Imerys has been to use a Brookfield viscometer for this purpose. This state of deflocculation is characterised by the addition of further deflocculant leading to an increase in viscosity. The requirement of experience and operator skill, together with the need for a large amount of ball clay per measurement, typically 700g, led us to investigate whether a suitable alternative for the Brookfield method could be successfully developed. In so doing, the dual aims of reducing ‘operator influence', i.e. increasing reproducibility, and reducing sample amounts have been pursued.

Three experimental techniques have been investigated to this end: (1) specific surface area (SSA) measurements by the BET method; (2) spectrophotometric determination of the Methylene Blue Index (MBI); (3) viscosity and thixotropy determination by means of a Bohlin Gemini 150 rheometer. The use of this rheometer also opens up new possibilities for the rheological characterisation of ball clays.

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