Wednesday, January 26, 2011

CBN Cubic Boron Nitride - Scanning Electron Microscope (SEM) images

In the previous posting, Part 2 : A Comparison of Three "Quarter Micron Polycrystaline Diamond" Slurries, I mentioned that I sent out seven samples to the SEM facility for analysis. Six of them were quarter micron monocrystaline and polycrystaline diamond formulations. The seventh sample, which was not included in either Part 1 or Part 2 of the above study was 0.125 or eighth micron Cubic Boron Nitride, abbreviated as CBN.

My CBN products are available along with all of my monocrystaline and polycrystaline diamond products at Ken's Corner.  This is an area set aside for some of my products that are sold through Chef Knives to Go.

CBN is available at  Chef Knives to Go in 0.75, 0.50 and 0.25 micron sizes as well as my finest CBN 0.125 micron product. I had SEM micrographs of the finest particle size made at various resolutions that demonstrate both the consistency of particle size, the purity of the preparation and shapes of the individual particles. Also of note is the complete absence of any agglomeration of the slurry.

Agglomeration is the clumping together of individual particles into larger structures which would result in effectively making a coarser grit mixed in with the slurry. In colloidal suspensions, this process of agglomeration is also referred to as flocculation . A good example of this would be curd formation - where the cottage cheese curds separate from the whey in milk  Flocculation is also advantageous in brewing and sewage treatment, but to be avoided at all costs in abrasive particle preparations. Agglomeration or flocculation is more likely to occur as particles get smaller as the surface area to volume ratio increases and electrostatic charges become greater. To reduce this effect of agglomeration, the absence of charged particles in the carrier is essential and the reason for using deionized water in these preparations. You do NOT want to dilute these CBN or Diamond slurries with tap water and the deionized water used is of the highest purity, 'cleaner' than filtered water. Also, too high of a particle concentration can increase the odds of agglomeration. In the process of formulating my compounds, several concentrations were tried to see where these limits were. My preparations are well enough below these limits, taking into account dehydration over time.

The samples were prepared by mixing the bottle before use and spraying a light coating of the slurry from the atomizer bottle that the product comes in. This sample is allowed to dry on standard metal cylinders used for mounting samples for SEM analysis - the same conditions as you would see on a strop sprayed with the product. As you will see in the micrographs, no agglomeration is present, just a carpet of particles.

SEM Images

I will present the images in order of increasing magnification. In each image a calibration bar is in the legend at the bottom of the micrograph This bar specifies the length that a particular number of nanometers or microns represent. Remember that 1 micron is 1000 nanometers, so 500 nanometers would be half a micron for instance The magnification is also noted to the left of the measurement bar.

This first image is taken at lower magnification, 2,000 times magnification or 2.00 KX noted in this image's legend. This is just beyond the limits of conventional light microscopy. The bar show how much distance in the image is equal to 5 microns. Of note is the carpet like effect of the particles, looking much like a layer of salt on a countertop. Not a thick pile of particles and not sparse particles, but an optimum distribution. Just enough to cover the surface with a nice layer with some 'light spots'.

Now let's go in a bit closer - 5 times closer -  first at 10,000X and then at 20,000X. At 10000 x the measurement bar would be 1000 nanometers so this first image is at a slightly higher magnification and the bar slightly smaller than 1 micron or 990 nanometers.

Now we can make out the individual particles and see the uniform coating of particles present.

Next is a 20,000X magnification image - 10 times closer than the first iimage presented,  with a 500 nanometer or half micron bar. The individual particles are more clearly resolved and you can see the surface characteristics of these particles.

Now, in Part 1, I showed Particle Size Distributions (or PSDs) of various diamond preparations. Here is the PSD of my eighth micron CBN product. Please refer to the Part 1 posting for a more detailed explanation of these graphs.

1 comment:

  1. No one can say that "boron is boring"! Here's some levity for you - "The Boron Song" sung by a young scientist: