The polishing performance of magnetorheological (MR) fluids prepared with a variety of magnetic and non-magnetic ingredients was studied on four types of initial surfaces for CVD ZnS flats from domestic and foreign sources. The results showed that it was possible to greatly improve smoothing performance of magnetorheological finishing (MRF) by altering the fluid composition, with the best results obtained for nanoalumina abrasive used with soft carbonyl iron and altered MR fluid chemistry. Surface roughness did not exceed 20 nm p-v and 2 nm rms after removing 2 µm of material. The formation of “orange peel” and the exposure of “pebble-like” structure inherent in ZnS from the CVD process were suppressed. Removal of diamond turning marks from a single point diamond turned (SPDT) surface was also accomplished.

Altered MR fluid chemistry reduced removal rates for CVD ZnS, but greatly improved the ability to polish out the surface.

S. D. Jacobs, “Manipulating mechanics and chemistry in precision optics finishing,” Science and Technology of Advanced Materials   8 153-157 (2007).

I. A. Kozhinova, H. J. Romanofsky, A. Maltsev, S. D. Jacobs, W. I. Kordonski, and S. R. Gorodkin, "Minimizing Artifact Formation in Magnetorheological Finishing of CVD ZnS Flats," Applied Optics 44, pp. 4671-4677 (Aug., 2005).