abrasives

In this series of blogs I, and some of my colleagues, would like to share some of our experience in particle sizing for industrial applications. I thought we’d do this by going through an A to Z of industrial applications and as Aardvarks are too big for our instruments, we’ll start with A for abrasives.

To be an abrasive, a material needs to be harder than the material that you want remove or polish (unless you have got a very, very long time to wait – think glacial!). The original scale for quantifying hardness is based on this principle, by looking for the ability of one mineral to scratch another.  Moh’s scale assigns hardness values to ten minerals, from soft talc at 1, to extremely hard diamond at 10. Although too simplistic for industrial abrasives, it explains why using calcite, 3, as an abrasive in toothpaste removes dirt and plaque but doesn’t grind away your teeth, which have a harness similar to topaz, 8. Common abrasive materials include alumina, silicon carbide, cubic boron nitride, zirconia, colloidal silica and diamond.

Abrasives literally come in all shapes and sizes, and that’s where we come in. The bigger the particles the more material is removed from the surface (greater polishing efficiency). However for greater accuracy in polishing you want smaller particles, and in that case controlling both the size and shape of the particles can increase the polishing efficiency.

If we start with particle size, it really is a very broad range, from colloidal silica in the tens of nanometres up to millimetre sized grit.  Because of this broad size range, the dynamic range of a laser diffraction instrument such as the Mastersizer 3000 is very useful for measuring abrasives, allowing both the nanometre sized colloidal silica and millimetre size silicon carbide to be measured on the same instrument, see Figure 1, along with the many different grades in between.

Particle size distributions of colloidal silica and silicon carbide, measured on the Mastersizer 3000

Figure 1: Particle size distributions of colloidal silica and silicon carbide, measured on the Mastersizer 3000

Controlling the shape of an abrasive can also improve the polishing efficiency. The circularity of particles is directly related to polishing efficiency, the closer the shape of a particle to a perfect circle the less effective it is as an abrasive, Figure 2.

Circularity, measured on the Sysmex FPIA 3000, vs polising efficiency

Figure 2: Circularity, measured on the Sysmex FPIA 3000, vs polising efficiency

The size and shape of particles in suspension can be measured quickly using a dynamic imaging system such as the Sysmex FPIA 3000. For more information about particle size and shape measurements of abrasives please follow the links below:

App Note: Particle shape characterization for abrasive quality control

Recorded Webinar: How size and shape of abrasive affects the efficiency of silicon wafer wire saw cutting processes

App Note: Particle size analysis of calcium carbonates by laser diffraction

And next time, on to the letter B…

If you have any suggestions for applications or materials that you would like to see covered as part of this series, please email events@malvern.com.