Abrasive Grains 101 | Superabrasives

As noted above, some manufactured abrasives, commonly diamond and cubic boron nitride (CBN), are characterized as superabrasives due largely to their extreme hardness. These are used in a variety of demanding high-tech applications. Standard sizes of these materials and approved testing methods are defined in ANSI B74.20-2004, currently under pre-publication formatting as of this writing.

In general, standard sizes for these materials are defined as a size range (e.g. 1-2 microns, 6-12 microns). The standard specifies that materials in these sizes must include at least 90% of the particle size distribution within the size ranges specified (maximum of 5% each above and below the range). For example, for a 1-2 micron size, at least 95% of the sample must be above 1 micron in size, and no more than 5% of the sample may be over 2 microns in size. The sample's average size must be near the center of the desired distribution (1.28-1.72 microns for a 1-2 micron material). Additionally, the coarsest particle detected must be below a maximum limit (e.g. 6 microns for size 1-2, 20 microns for size 6-12).

ANSI B74.20 also describes a variety of methods that are commonly used to characterize the particle size, including a number discussed above (such as electrical resistance, direct microscopy, laser diffraction, and photosedimentation) and a few methods unique to characterizing extremely fine particles (such as photon correlation spectroscopy). For further details on these materials, relevant calibration standards, and an excellent detailed discussion of methods of measurement, please refer to B74.20.