Characterization of magnetorheological fluids

Keywords

Microscopy, Viscosity, Zeta potential

Abstract

A novel polishing technique using magnetic media has evolved over the past decade, called magnetorheological (MR) finishing. As in conventional finishing, the glass polishing efficiency of MR fluid depends strongly on glass surface - abrasive slurry interaction which is dictated by the nature and chemistry of the polishing slurry's constituents. In comparison to the behavior of normal aqueous, metal oxide slurries used in conventional polishing, MR fluids have marked differences in behavior, are driven largely by the presence of its key magnetic component, carbonyl iron (CI). This study probes the behavior of CI and other individual species present in the MR fluid, as well as their modified response to electrochemical and magnetic stimuli, when combined with other slurry ingredients. Solutions or slurries examined were prepared in relative proportions similar to that found in the "standard", commercially used, MR fluid. The MR fluid components examined in addition to CI include abrasive particles (aluminum or cerium oxide), and stabilizers to control corrosion and maintain stability. The effect on CI behavior as influenced by slurry/solution pH, CI concentration, abrasive type and purity have been examined. Zeta potential measurements, complemented by microscopy, viscometry and sedimentation measurements, with and without an applied magnetic field have been performed, and results are presented relative to slurry stability.

Abrasive type and purity were shown to affect the isoelectric point (IEP) of CI particles and correspondingly influence CI soluti.on and slurry aggregate size distribution and sedimentation behavior. Higher purity abrasives improved stability, as determined by stable (small, well-dispersed) aggregate size distribution, and lower sedimentation rate. The IEP of solutions/slurries, largely determined the regions of highest stability (well dispersed, similarly sized [fine] aggregates with good (low) sedimentation rates in CI containing solutions, and regions of extreme high and low pH, lead to extensive agglomeration and destabilization, as detennined by microscopy and viscometry. Such discrepancy from normally accepted behavior (i.e. that destabilization occurs near the point of zero charge) is believed to be offset by the large change in surface chemistry (iron-iron oxide formation, magnetic/non-magnetic particle interactions, adsorbed impurities on metal) seen in aqueous solutions/slurries containing CI examined in this study. Microscopy and viscometry measurements of dilute MR-like slurries and binary CI solutions, both showed the presence of a "threshold" magnetic field level, required to overcome the natural interparticle forces, to allow alignment and ordering of the iron particles. As this is a key feature of CI in the polishing process whereby chains are believed to push abrasive particle to the top of a polishing "spot", this threshold, and its variation with chemical conditions, oxide abrasives and other stabilizers, is important. Although the individual response of solutions/slurries made with MR fluid constituents do not illustrate maintained stability outside of a finite pH regime, MR slurries prepared with all ingredients, characterized with the tools developed in this study, exhibited resistance to aggregation over a working region near pH 9-10.

Notes

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Graduation Date

1999

Semester

Summer

Advisor

Richardson, Kathleen

Degree

Master of Science (M.S.)

College

College of Arts and Sciences

Department

Chemistry

Format

PDF

Pages

118 p.

Language

English

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

Identifier

DP0028701

Subjects

Arts and Sciences -- Dissertations, Academic; Dissertations, Academic -- Arts and Sciences

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