The sample preparation techniques have been described in detail elsewhere [4], but will be briefly presented here. To prepare a polished specimen for viewing in the SEM, approximately 25 grams of the powder to be imaged is blended with an epoxy resin to form an extremely viscous paste. The resin/powder mixture is pressed into a mold and cured at 60 ºC for 24 hours. The cured specimen is then cut to obtain a plane surface for imaging.
Saw marks are removed by grinding with 400 grit followed by 600 grit
sandpaper. Final polishing is done on a lap wheel with (6, 3, 1, and 0.25)
µm diamond paste for 30 seconds each. After each polishing, the
specimen is cleaned using a clean cloth and after the final polishing step,
ethanol is used to remove any residual polishing compound. The final polished
specimen is coated with carbon to provide a conductive surface for
viewing in the SEM.