H.W. Myron

Particle aggregation in colloids in high magnetic fields

Abstract The influence of high magnetic fields on the stability of colloidal dispersions of paramagnetic and diamagnetic particles has been investigated. The theory of Svoboda is extended to allow examination of the dynamics of particle aggregation in colloids. Particle trajectories are calculated leading to binary pair formation. Experimental results are presented on particle aggregation in high magnetic fields (flocculation). Here binary pairs seem to form and to be stable at enhanced rates of settling.

Limits of magnetic flocculation in colloidal dispersions

The limits of particle aggregation in high magnetic fields are described. These limits are determined, for any given colloid-field system, by electrochemical factors and by particle size. The latter is discussed in terms of thermal diffusion processes at the lower size limit and by the influence of differential gravitational settling in larger particle systems.

Kinetics of magnetic flocculation in colloidal dispersions

Abstract A description is given of the kinetics of particle agglomeration in colloidal dispersions in applied magnetic fields, a phenomenon referred to as magnetic flocculation. The influence of monosize particles and dissimilar particle sizes on the position and field value for secondary flocculation minima is re-examined. The concept of isochronal volume is introduced through which a relaxation time parameter as well as a flocculation frequency is described for the case of magnetically induced agglomeration. The flocculation half life (the relaxation time parameter) and flocculation frequency both have characteristics similar to parameters used in the literature to describe rapid coagulation in the absence of a magnetic field.

Study of particle behaviour in high field magnetic flocculation

A recently developed dynamic theory of magnetic field-induced particle-particle aggregation in suspensoids is further extended in terms of characteristic velocity coefficients in the manner of the inertialess theory of H.G.M.S. This is done by expressing the flocculation process in terms of familiar parameters such as magnetic velocity and capture radius. Hybrid flocculation of diamagnetic-paramagnetic pairs is described. Also demonstrated here is the importance of the suspensoid settling velocity following the occurrence of binary flocculation.

Application of magnetic flocculation in a continuous flow magnetic separator

A Continuous Flow Magnetic Separation (CFMS) technique is introduced, capable of processing slurries in a continuous mode. The separation process is based on creating differences in the magnetically induced settling rate of the individual particles. Results concerning separator performance are given for both two-component test slurries and slurries of naturally occurring mixtures under a variety of experimental conditions.

Flocculation of diamagnetic particles in high magnetic fields

The combined influence of high magnetic fields and concentration of a paramagnetic electrolyte on the stability of a suspension of diamagnetic quartz particles has been investigated. For the first time, formation of magnetically induced binary pairs of particles has been observed over a broad range of electrolyte concentration and is explained in terms of an extended Derjaguin–Landau–Verwey–Overbeek (DLVO)‐theory. Anomalous effects at low fields are shown to be caused by particle rotation due to an anisotropic magnetic susceptibility.

Sedimentation of colloids in high magnetic fields

Magnetic flocculation experiments are described for a number of mineral suspensions in high fields. Their sedimentation behaviour has been observed in situ by a novel optical monitoring technique. Anomalous negative enhancement of sedimentation rates in these suspensions has been observed at low fields, and this phenomenon is explained in terms of particle anisotropy. Results are shown of field-induced selective sedimentation in heterogeneous suspensions of fly ash. Finally, for the first time, binary magnetic flocculation is reported for a diamagnetic colloid.

Particle diffusion effects in high gradient magnetic filtration of ultra-fine colloids

Abstract The influence of particle diffusion on high gradient magnetic filtration of ultra-fine colloids has been investigated. The] diffusion process is shown to be related to the electrical double layer interaction between the colloidal particles. Experimental results are presented concerning the recovery of CuO colloids using random matrices.

Phase transitions in high magnetic fields

The purpose of this paper is to summarize some of the research activities recently performed at the Laboratorium voor Hoge Magneetvelden at the University of Nijmegen The scope here and unifying aspect is magnetically induced phase transitions. Here we summarize transitions in the settling velocity of paramagnetic aggregates, suppression of spin fluctuations in UAl2, the phase diagram of a ferroelectric chiral smectic liquid crystal near the Lifshitz point and the transition from 3D to 2D conduction in a GaAs FET. In no way does this represent a complete review of transitioi but rather a summary of phase transitions observed at the magnet laboratory during the past year.