Presentations at PARTEC 2004

PARTEC 2004 International Conference for Particle Technology

Nuremberg, Germany 16 - 18 March

Thursday March 18 at 12:10
paper 25.6 - subtopic Adhesion & Surface-Particle Forces

Characterization of interparticle forces in dispersions by analytical centrifugation
Titus Sobisch, Dietmar Lerche
L.U.M. GmbH, Rudower Chaussee 29 (OWZ), 12489 Berlin Germany, info@lum-gmbh.de

condensed preprint at the Preprint Server of Chemweb.com shifted to the Preprint Archive
Chemistry Preprint Archive, Volume 2003, Issue 7, July 2003, Pages 198-218

The behaviour of dispersions in liquid media, i.e. dispersion stability, flow and packing behaviour and processes at the solid-liquid interface, is determined by the nature and degree of interparticle forces. This is of fundamental importance for their application in diverse fields such as nanomaterials, coating, paper making, ceramics, sludge dewatering, to name just a few.
The present work reports on the use of analytical centrifugation for investigation of the packing and compression behaviour to characterize the colloidal stability and microstructure in aqueous dispersed systems. To this end interactions have been studied in monodisperse silica dispersions and in dispersions of cellulose fibres.
Packing density, obtained after compression, is related to the total interparticle potential energy. By using different additives interaction between particles can be shifted from nearly hard sphere behaviour to strong attraction which results in flocculated systems. Both substrates differ in particle shape, swelling, surface charge density and exhibit therefore different packing behaviour. Additional information could be obtained about the strength and elasticity of particle networks by analysing the relative change in sediment volume after increasing/decreasing the excess pressure.
The multisample technique applied implies the potential for more systematic studies for targeted colloidal stability.

Wednesday March 19 at 17:10
paper 20.6 - subtopic Filtration

Identification of particle size distribution based on transmission profiles measured by photocentrifuges

Stefan Berres, Raimund Bürger
Universität Stuttgart, IANS, Pfaffenwaldring 57, 70569 Stuttgart, Germany

Dietmar Lerche

The particle size distribution of a suspension of fine particles of the same material and with a continuous size distribution is calculated from an extinction profile measured by a photocentrifuge. Photocentrifuges provide a useful tool for the characterization and quality control of suspensions. While visual inspection of the light extinction curve under centrifugal segregation allows a qualitative description, a rigorous formulation, for example as an optimization problem, gives access to a quantitative characterization. The aim of parameter identification formulated as an optimization problem is to minimize a cost function, which indicates the distance of parameter-dependent simulations from measurements. The dependence of the model solution on the parameters is induced by continuum mechanic model equations describing the continuity of mass of the solid phases. As a result, particle size distributions can be obtained from extinction profiles by computational postprocessing if basic fluid and material properties are known. Thus, the utility of photocentrifuges for recovering physical properties of suspensions from light permeability measurements is highlighted.