Preliminary Polishing

Preliminary Polishing

Diamond polishing compounds or slurries are good for preliminary stages for most materials. Polishing is a similar action to grinding, accept that the supporting medium used to hold the abrasive is capable far greater 'shock absorbency' i.e. the ability of the medium to allow the abrasive to move to some degree and conform to the surface aspirates of the specimen. Thus different polishing surface materials have differing characteristics: soft cloths allow the greatest shock absorbency and therefore allow for gentle polishing with little damage associated. However soft cloths allow the abrasive to abrade different areas at different rates, giving rise to 'relief'. 'Relief' is the term used to describe the undulations that form in a polished surface. Extreme undulations or relief in the polished surface is to be avoided, although a certain amount can be tolerated (or even desirable) because the SEM generally has high depth of field. Harder polishing surfaces or cloths, conversely, produce a flatter or 'plane' surface, but may leave polishing damage in the surface of the material, and promote superficial scratching.

Therefore, it is usually the case that polishing is started on a hard cloth with a coarser abrasive and finished on a softer cloth with a finer abrasive. Final polishing should not be prolonged, but just sufficient to achieve the desired surface finish without causing excessive relief.