Aqueous magnetorheological (MR) polishing fluids used in magnetorheological finishing (MRF) have a high solids
concentration consisting of magnetic carbonyl iron particles and nonmagnetic polishing abrasives. The properties of MR
polishing fluids are affected over time by corrosion of CI particles. Here we report on MRF spotting experiments
performed on optical glasses using a zirconia coated carbonyl iron (CI) particle-based MR fluid. The zirconia coated
magnetic CI particles were prepared via sol-gel synthesis in kg quantities. The coating layer was ~50-100 nm thick,
faceted in surface structure, and well adhered. Coated particles showed long term stability against aqueous corrosion.
"Free" nano-crystalline zirconia polishing abrasives were co-generated in the coating process, resulting in an abrasivecharged
powder for MRF. A viable MR fluid was prepared simply by adding water. Spot polishing tests were performed
on a variety of optical glasses over a period of 3 weeks with no signs of MR fluid degradation or corrosion. Stable
material removal rates and smooth surfaces inside spots were obtained.