NMR imaging of pastes in a ram extruder

Nuclear magnetic resonance (NMR) imaging was used to investigate the extrusion behaviour of pastes with a ram extruder. Extrusions of limestone pastes with moisture contents of 23–29% and pastes of an oxide ceramic (Pural) with moisture contents of 72–76% have shown that NMR is a suitable method for the detection and quantification of structural changes and flow processes in pastes, e.g. the relative motion between the liquid and the solid phases, the beginning and time-dependent development of fissures within the cylinder filling and the extrudate, peptization and agglomeration. With NMR one can distinguish between free and bound water and determine the spatial distribution of the respective fractions of a phase within a specific volume element. Furthermore the time- and location-dependent displacement profiles of the solid and the liquid can be observed.