Diamond polishing

Abstract

The first major scientific study of diamond polishing was by Tolkowsky. His model dominated until recent years, when high-resolution microscopes allowed detailed studies of polished diamond surfaces. In this paper, new research shows that diamond polishing involves two-and three-body wear processes. The third body consists of the sp 2 detritus formed while wearing diamond, and also minute diamond particles following comminution in the scaife preparation process. Microscopy also shows that diamond particles embedded in the scaife orient themselves to positions favourable for polishing. These particles are responsible for the formation of nano-grooves observed on diamond surfaces. In addition, measurements are presented that show that the wear mechanism for diamond is velocity dependent, and related to changes in material properties caused indirectly by the heat induced through frictional sliding.

Investigating the mechanisms of diamond polishing using Raman spectroscopy

“…As mentioned earlier, chemical, mechanical, and thermal wear have all been argued to play a part in the removal process. It is, however, becoming clear that a number of competing processes may act, and that these are a function of the velocity of the sliding [3,4]. It is also clear that polishing on the scaife differs from low-speed frictional sliding due to the vastly different contact conditions, the materials involved and the velocity of sliding; comparisons should thus be made with caution.…”

“…It does appear, however, that plastic deformation is present as a direct consequence of another process. This is the plane-or chisel-like action of the grit particles on a scaife which cause plastic flow on the surface of diamond in a similar fashion to that produced on metals during conventional machining operations [3]. Analysis of diamond wear debris provides another approach to the problem and is attractive since samples can be taken from numerous sources and analysed off-site.…”

“…Thermal wear has previously been dismissed due to reports [22] that material removal was linearly proportional to the abrading (NB: not polishing) velocity. These experiments were not carried out under industrial polishing conditions, rather on miniature grinding wheels and more recent research [3,4,17] challenges their view. van Bouwelen et al [27] suggest that a structural change due to the large shear stresses present at the diamond-scaife interface is responsible for the non-diamond carbon wear debris.…”

“…Preparation is carried out in the workshop in which they are to be used. Inevitably, experimental results on this subject are conflicting (see [3] for a thorough review), though several recent papers have addressed these issues using a different approach [3,4]. Diamonds are also expensive and as a consequence reported research has been hampered by the lack of suitable specimens with regular geometry, in the necessary quantities to render the work statistically valid.…”

Prospects for the synthesis of large single-crystal diamonds

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