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.

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Ken

Part 2 : A Comparison of Three "Quarter Micron Polycrystaline Diamond" Slurries

The first part of this comparative analysis of quarter micron polycrystaline diamond slurries has generated a great deal of interest and generated some additional questions that I will address in the initial discussion of the second part of this posting. Then I will go on to show what these compounds actually look like under the microscope and describe the testing methodology and then discuss these additional findings.

CARATS

Apparently this picture described more fully in Part 1, deserves yet a third look. Just to be clear, the product on the left labeled OUR's is a competitor's product and the one on the right,  labeled  Their's,  is a product sold by a another vendor who I have the greatest respect for - both his products and his professionalism. He is considered by most in the industry to have the best products available. For that reason, I do not offer the same products he does. If you want the specific product he is selling I recommend you buy his product. It is a 0.25 micron monocrystaline diamond slurry.

The bottle on the right contains 21 carats of monocrystaline diamond. The bottle on the left was determined to only have 3.33 carats. My methods for determining this have been questioned.

The bottle on the right was determined to have 21 carats two ways. The most simple and obvious way was by weighing the carats that were put into the compound before it was formulated. The product is purchased by the carat weight. This of course is so obvious that it shouldn't even be a question - yet some have questioned it. If you want more carats, it costs more. Want less, it costs less. It's just like buying food in a grocery store by the pound. Weak solutions are cheaper and have less particles and therefore abrade less when used for sharpening edges. It is easy to show this. The only exception to this is if the product isn't what you think it is, but is an adulterated formulation. The honest way to sell product is to say how much of it you are selling, not disguise it in rhetoric about needing ideal compound concentrations in your product or a 'weak tea tastes better than strong tea' type of argument.

So what is the 'ideal concentration'? Some vendors are going for lower undisclosed concentrations, some only saying 'heavy' concentrations, some just not saying what their concentrations are at all and some even suggest that it cannot be determined. Surely they know what they are buying when they formulate it or have it formulated for them.  If they are not specifying their product concentrations, you are buying an unknown quantity of product. I have a bridge in Brooklyn that is on sale right now that I'm holding in reserve just for you. :)  (Or perhaps they formulated it themselves in their kitchen sink or worse?)  If they aren't telling you this information, either they don't know it or don't want you to know it.

The vendor on the right side of the picture above specifies his concentrations as 21 carats per 4 oz bottle. My products also have the same concentration..There is a reason for this concentration. My products were tested at various concentrations for a specific purpose - to give my customers a product of the highest quality and at a concentration not so high as to produce particle agglomeration. This applies to any of the particle sizes in the compounds that I sell.

Another way to determine the concentration of a sample is to take a known volume and dehydrate it and weigh the volume before and after dehydration to determine percent by weight loss. Some have mistakenly suggested that this was done by decanting the liquid off the top into a sink and weighing the remainder. Yet, even after saying this wasn't the case, they insist that it was. It's not how I do science.  My background includes over 25 years of research, and includes peer reviewed publications in electron microscopy, multiple disciplines of medicine, and computer science. I have also held faculty positions and run several research laboratories. I couldn't imagine doing something so unintelligent.

If a suspension based sample was dehydrated and weighed, perhaps some of the components of the suspension would remain in the sample. Think of this as marbles in syrup. My formulation uses deionized water and is a slurry, so there is no residue that would remain. Think of this as marbles in water. There is a reason I chose a slurry over a suspension which will be explained shortly.

You get an extremely accurate determination using this analysis technique with a slurry. How do I know this? Because if a known amount of carats is put in the sample, this test accurately determines it. It's just that simple. So this is yet a second way to determine that the bottle on the right is correctly specified as having a 21 carats per 4 oz concentration. The sample on the left does contain a "permanent suspension", so perhaps some residue might remain from simple dehydration much like dehydrated syrup would have weight. If this were the case, than it would have OVERESTIMATED the concentration of this product. BUT ...

This was considered in the determination. The testing methodology was done in a lab, not some home brew experiment. This lab does these types of determinations all the time and takes this into account. Diamond can sustain higher heats than suspensions can, so the high heat drying process reduces this artifact to a negligible level. Again if anything this would argue for the product on the left having even LESS carats. Perhaps 3.3 rather than 3.33 - but this is speculation. In short, this testing methodology is very accurate and is routinely used by this lab for testing both slurries and suspensions.

SLURRIES AND SUSPENSIONS

Much has been made of permanent suspensions. A slurry is simply particles floating around, much like the slurry we all use in our sharpening or honing when we use waterstones. These are water based slurries. Therefore it is a wet technique. Sandpaper is a dry technique, usually. Suspensions add additional components to their formulations, hoping to keep the particulates floating in a permanent state rather than settling to the bottom.  Using a suspension does help to keep the particulates from settling to the bottom, but this may not be an appropriate solution or answer for all abrasive requirements.

In particular for products used in dry hand or powered situations where the abrasive remains in a relatively fixed position, it is, IMO suboptimal. It is suboptimal, especially so for submicron particulates where the suspensions may actually interfere with the abrasive. I will show this later on in this discussion. For applications requiring continuous streams of abrasives in a liquid environment, it may be more appropriate, but in that instance, the suspension should be a true permanent suspension and / or have arrangements made to keep the particulates evenly distributed at all times - magnetic stirrers, various mixers, etc. This is irrelevant to the sharpening and honing processes used to sharpen edges by hand.

For PRECISE SHARPENING, as opposed to industrial systems using pumped abrasive based liquids for non-sharpening applications but rather part dimensioning applications and surface preparation, what is relevant is disbursing an even coating on a strop. Doing this is largely a matter of technique - NOT keeping the particulates suspended. A perfect permanent suspension does not guarantee uniform dispersion from a spray bottle.

Good technique optimizes uniformity and is far more relevant. Not even the most obsessed user will go to extreme lengths to do more than a visual inspection to set an acceptable level of uniformity of dispersed particulates. A good sharpener / honer can deduce uniformity from the feedback he receives and can adjust his technique - even at particle sizes as fine as 15 nanometers (1.2 million grit). If you haven't been there, it's just theory. I've been there. I'd like to see others join me there in the future.

This brings us to the topic of permanent suspensions. Are there permanent suspensions? Yes, there are suspensions that for all practical purposes are permanent, but yet in some there is settling that takes place. This first picture is an Alumina suspension. I have yet to see settling after several months. Next are two products that claim to be permanent suspensions - the two products that were compared in part one. As you can see this is clearly settling. It is visually obvious to the most untrained eye.

Now, a supposed 'expert' claims, "A permanent suspension may appear to one eyes as being separated or settled out however it is impossible for separation to occur even if one thinks it appears to be."  If that were the case, then 1) either these two products are not permanent suspension systems or 2) if the suspension is uniform, then the upper area reveals it to be of extremely weak concentration..

If I were to use these so called permanent solutions, I would most certainly shake them up before use. For hand sharpening or honing applications, it's just not that hard to redistributes the particulates by shaking the bottle gently a couple of times. Trying to believe that these bottles contain a uniform particle distribution that is as uniformly distributed as a freshly shaken slurry strains my sense of credibility. Just shake the bottle. It would be prudent and won't hurt anything .

Here's the truly permanent Alumina slurry:

It is uniform throughout.

Here are the two so called permanent slurries. I see two distinct regions. I can't imagine a reason not to mix it back to a uniform distribution as uniform as a freshly mixed slurry. Just can't.

And the second sample tested in Part 1:

I'll let the reader draw their own conclusions if they think these solutions don't require mixing - just like a slurry. In either case a suspension either must be truly permanent or you should remix before use. Remixing is just not a big deal for honing applications. It is a minor task - nothing more and certainly not a reason to avoid slurries.  Application technique is far more important. What's MUCH more important is making sure that the individual particles don't stick together in big lumps. This is called particle agglomeration.

PARTICLE AGGLOMERATION

Particle agglomeration is one of the sins of using particulates for sharpening or honing applications. Indeed it is a sin for any type of sharpening application and to be avoided at all costs. Why? Well if two particles each a quarter micron in size stick to each other, they act like a half micron particle (yes, this is simplified, ignoring shape characteristics, etc.). If four particles stick together, it acts like an even coarser particle. This is even a worse problem than particles of random sizes or a very broad distribution in a slurry or suspension. Of course you can have both problems.

Now as the particles get smaller, the suspension can interfere with the particulates. If it is not designed to be used for the intended application, it may contribute to particle agglomeration as you will soon see. Charged particles in solution or ions can greatly contribute to this problem as well. For this reason, charged ions in the slurry solution will cause particle agglomeration and this one reason I specifically use deionized water for the vehicle. The other reason is that when it evaporates, it leaves no residue, as previously discussed.

My preparation is meant to be used as a dry technique, not a wet one. For edge sharpening, a wet technique offers no advantage. I know this from experience, based on years of sharpening.

One of the techniques I use is to take the slurry from flattening a synthetic stone and applying it to paper or balsa and letting it dry, effectively creating sandpaper that has the characteristics of the stone it came from. I have used this technique for coarse 120 grit stones through 30,000 grit stones. Again it is a dry technique. The results after years of use on many synthetic AND natural stones is that the abrasion characteristics are even finer than using the stones that they come from using a wet technique.

For dry techniques, lubricity has NO place in the discussion. The particulates become embedded in the substrate - balsa or paper and the results are excellent. This is the principle employed in platens, where the particles stay in place as the material being abraded is drawn across the bed of particles removing metal in the process. Now when you use a suspension that has been dried, it is only of modest concern for coarse particulates, but as the particulates go down into the submicron range, it becomes a disadvantage, literally gumming up the works, submersing the particulates in 'gunk'. This may be fine in a wet system, but not in a dry system. Simply put, it is the wrong tool for the job.


Is this simply idle speculation on my part or based on hard scientific data? I'll let you decide.

In the first part of this post, the particle size distributions were determined. This was a good first step in preparation for the next part of this post - actually looking at the particles themselves. Direct observation of these particulates is beyond the range of a light microscope. A transmission electron microscope is also the wrong tool for the job. A perfect tool for the job is a scanning electron microscope or SEM, which easily resolves particulates in the nanometer range. A quarter micron or 0.25 microns is a 250 nanometer particle. This will be useful to know when interpreting the following micrographs.


Seven samples were sent to the SEM facility of a major university. The person performing the analysis did not know anything about the samples. They were simply numbered one through seven. Each sample was shaken before extracting the samples that were sent to the lab. The containers were never previously used and specifically used for containing microabrasives. The instructions were to shake each sample and spray small stubs that were inserted into the microscope's chamber, which is a high vacuum environment. A light spray was applied to each stub and the sample was dried in a manner appropriate for placing it in a vacuum environment. The resolution of the scope was calibrated prior to taking the micrographs to assure very accurate measurements. You can see the bar at the bottom of the micrographs with a number next to it indicating a distance, usually in nanometers. Thus if a 1000 nanometer or 1 micron bar is present, a quarter micron particle would be a fourth as long as the bar. These bars are extremely important in evaluating the images and accurately sizing the particles.


So what do you look for? Well, you look at the shapes of the particles. Are they consistent? Are they the right size? Are they cleanly separated from the other particles or stuck together in lumps? If there are lumps how big are the lumps. remember if a lump of particles or an agglomerate is a mass of particles that is 8 microns in size, even if the individual particles are a quarter micron, you are looking at a slurry that will give an 8 micron finish or 2000 grit.

What were the samples?

There was a monocrystaline quarter micron product - the product that appears in the first image in this post.

We will call it sample one. It is a slurry using deionized water.


The second sample is my product - a quarter micron polycrystaline product. Also a deionized water preparation.


The third sample is a 0.3 micron Alumina permanent suspension


The fourth sample is advertised as a quarter micron polycrystaline diamond preparation in a permanent unspecified suspension.


The fifth sample is a water based suspension, also advertised as polycrystaline diamond.


The sixth sample is an oil based suspension, also advertised as polycrystaline diamond.

The seventh sample is eighth micron CBN. It will be shown elsewhere and is not a part of this study.

SEM IMAGES

This is sample one , quarter micron monocrystaline diamond deionized water slurry

The bar at the bottom of the image shows a 500n (nanometer) or half micron 'ruler' bar, magnification at 20,000 x an image number and the voltage of the beam, 15,000 volts. Here we are looking at clearly defined particles of an appropriate size. They are very uniform in size with no agglomeration. Just clean particles. Exactly what we want. It is clearly monocrystaline diamond. It is textbook perfect high quality product.


 Next is my product - a quarter micron polycrystaline product in a deionized water slurry:

Note the 333n or third micron bar, slightly different than the previous image. 30,000 x magnification. Again, individual particles of appropriate size, a uniform particle distribution, no particle agglomeration. Clearly polycrystaline diamond. A product I can easily stand behind and feel comfortable putting my name on.


Next is the 0.3 micron Alumina permanent suspension

At the same magnification as the previous image. Particle sizes are appropriate, but with a bit more variation not so tightly controlled and some degree of agglomeration. Individual particles are still clearly recognized
Clearly an alumina suspension.


Next is the Polycrystaline diamond preparation in an unknown suspension. The range of particle sizes required several micrographs at various magnifications.

 Note the scale factor of 50 microns! Only 200x magnification. The large structure in the middle that looks like you are looking down the throat of a volcano is more that three barlengths across or 150 microns - not nanometers but microns. To give a comparison a 120 grit glassstone particle has particles of 123 microns, so it is a coarser particle than the particles used in the coarsest stone Shapton makes.! There are other large particles clearly greater than anything you would want in as quarter micron preparation. No particular uniform size just pretty much random debris, not identifiable as being any particular type of abrasive.


Here's a closer look at the same sample

 The scale factor is still hugh - 10 microns!. Remember that 1 micron is a tenth the length of the bar and a quarter micron would be 1/40 th the length of the bar. This object is at least 12 bars long or 120 microns, similar in size to the 120+ grit 'volvano' It is a glob of something not clearly identifiable, not at all looking like my polycrystaline diamond preparation. As of yet, no one has identified what the glob is made of.


Let's get closer:

Now we are looking at a 1 micron bar and should be expecting to see particles 1/4 the length of the bar, but instead are presented with a closeup of this blob. Hardly any freestanding particles to be seen. By now you should be reading these yourself pretty well.
 
Here's one last overview.at 200 microns. This crater valley is strewn with hugh lumps of 'stuff'

Now the other product reviewed in the first part - the one with two humps in the particle distribution This is the water based suspension

At a 1 micron measurement bar, the particles are almost identifiable, but still look stuck together in clumps, with the clumping probably explaining the bimodal distribution. Clearly not ideal but not what I would want to use compared to my product with distinct particulates.


Now the oil based version of this product

 At a half micron measurement bar size, we can see than the particle size fills the screen, which is fully compatible with the hugh particles picked up by the particle analyzer data.

 SUMMARY

It's a lot of information to digest in this posting, so lets summarize what we found out. We began by reviewing my testing methodologies showing that I have very accurately measured carat concentrations. Then we reviewed slurries and suspensions, showing that not all suspensions are the same and that some suspensions should be mixed up before use, just like slurries, but that the application technique to the strop was of far greater importance. While suspensions are most useful at coarser grits, at finer submicron grits, their use, particularly when the product is used in a dry preparation may actually hinder the product's use causing massive clumping and agglomeration. This may or may not be the case for liquid preparations used in abrasive flows, a topic not addressed in this discussion because it is not applicable to sharpening / honing of edges. Then we actually look at the preparations. The slurry preparations showed distinct particulates, while the suspensions showed a very moderate amount of agglomeration when used in a dry state (alumina peparation that showed no evidence of settling) to severe agglomeration, to the point where it was difficult to even recognize the particulates as even being diamond or alumina or something else. There are electron microscopy techniques for performing elemental analysis, such as EELS (Electron Energy Loss Spectroscopy), but at this point I, and I hope the reader can clearly see why I consider my products to be of the highest quality available. ALL of my particulate products have undergone this level of testing, assuring my my customes of a most pleasant and rewarding experience. I am serious about providing a quality product specifically designed for producing superior edges and I hope you can see that what goes into my product, including the level of research and the rationale for it's design, is what separates it from it's competition.

Finally, I have to say the most basic statement about my products. They work. My customers love the edges these compounds produce. In the end, that's what matters most to me.

If you have gotten through both postings, I truly commend you and know you are serious about your edges. Thank you for your time reading this.

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Ken