Effect of rogue particles on the sub-surface damage of fused silica during grinding/polishing

Abstract

The distribution and characteristics of surface cracks (i.e., sub-surface damage or scratching) on fused silica formed during grinding/polishing resulting from the addition of rogue particles in the base slurry has been investigated. Fused silica samples (10 cm diameter x 1 cm thick) were: 1) ground by loose abrasive grinding (alumina particles 9-30 µm) on a glass lap with the addition of larger alumina particles at various concentrations with mean sizes ranging from 15-30 µm, or 2) polished (using 0.5 µm cerium oxide slurry) on various laps (polyurethanes pads or pitch) with the addition of larger rogue particles (diamond (4-45 µm), pitch, dust, or dried Ceria slurry agglomerates) at various concentrations. For the resulting ground samples, the crack distributions of the as-prepared surfaces were determined using a polished taper technique. The crack depth was observed to: 1) increase at small concentrations (>10 -4 fraction) of rogue particles; and 2) increase with rogue particle concentration to crack depths consistent with that observed when grinding with particles the size of the rogue particles alone. For the polished samples, which were subsequently etched in HF:NH 4 F to expose the surface damage, the resulting scratch properties (type, number density, width, and length) were characterized. The number density of scratches increased exponentially with the size of the rogue diamond at a fixed rogue diamond concentration suggesting that larger particles are more likely to lead to scratching. The length of the scratch was found to increase with rogue particle size, increase with lap viscosity, and decrease with applied load. At high diamond concentrations, the type of scratch transitioned from brittle to ductile and the length of the scratches dramatically increased and extended to the edge of the optic. The observed trends can explained semi-quantitatively in terms of the time needed for a rogue particle to penetrate into a viscoelastic lap. The results of this study provide useful insights and 'rules-of-thumb' relating scratch characteristics observed on surfaces during optical glass fabrication to the characteristics rogue particles causing them and their possible source.

Subsurface mechanical damage during bound abrasive grinding of fused silica glass

“…Distribution of abrasive contact forces. This result agrees with experiments by Suratwala et al [28]. They showed that in a lapping experiment where a very small fraction (0.1%) of rogue particles were added to a slurry with abrasive grains that were half the size, this increased SSD depth to the same level as in experiments with a slurry containing only the same rogue particles.…”

Structural, morphological and electrical properties of Ce1−Ru O2−δ (x=0.005–0.02) solid solutions

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