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ceramic stones - scott.livesey - 11-30-2017
new to forum. I am a knifemaker in North Carolina. found a link to this forum on the Cliff Stamp's site "Towards 0.1 Micron." I make smaller knives for the kitchen usually of O1 I heat treat myself, usually to Rc62-65 hardness range.
on knife forums I hear talk of ceramic stones. what exactly are they talking about? are these just stones made of synthetic alumina?
Scott Livesey
"Just an old sailor glad to be home from the sea."
RE: ceramic stones - EOU - 12-01-2017
Welcome Scott! We really like new members but we especially like new members who participate so thank you! We're far from experts in the ceramics arena so I'm going to do a little footwork here and try to get someone on who is. I believe that Mark Reich has an association with a sharpening stone distributor that knows his stuff. I'm going to call Mark and see if this individual can come on the Exchange and make us all smarter.
In the meantime, anyone else with thoughts on this topic is very much welcome to step forward and share them. Once again Scott, thank you and welcome.
RE: ceramic stones - Mark Reich - 12-01-2017
Hi Scott, Welcome to to the forum, it's great to have you here!
Ceramic is an astonishingly broad term, because there are so many different types and even more different applications. As it relates to man made sharpening stones, ceramic is generally a binder for high end aluminum oxide abrasive, like Shaptons and Choseras. Both are cream of the crop. Glass stones may look thin, but they're tougher Chinese algebra.
Alumina and aluminum oxide are totally different things. Alumina has a Mohs' hardness of 3.4, or a little harder than fingernails. However, aluminum oxide has a Mohs' hardness of 9, which is not far from diamonds.
Note that there are a few ceramic stones that have no abrasive. The "roughness" of the stone's surface removes steel, which is fairly problematic. Pure ceramic stones, like Spyderco's, are like this. Good "ceramic" stones, like Shaptons and Choseras, just use ceramic as the binder for aluminum oxide grit.
There is way more to talk about, but I can't type when I get sleepy. It's been a very long day. I will continue tomorrow.
Please feel free to keep asking questions. We love to answer them.
RE: ceramic stones - Ken S - 12-02-2017
Welcome to the forum, Scott.
Life was simpler when I was younger. I had four sharpening stones: a Norton combination India stone which was my grandfather's; an unmarked worn similar stone which had belonged to my other grandfather, a smaller oilstone which had belonged to my father; and a combination carborundum oilstone which Dad gave me for Christmas as a boy. Life was simple, but more limited.
Decades later I added a set of Norton waterstones. Sharpening became quicker, but I always had to mind flatness. Then came a couple small ceramic stones and a Tormek.
I do not have Mark's expertise with sharpening. However, I am glad you asked this very pertinent question. While life presents us with more choices now, it also presents many more opportunities.
I switched from a knife steel to a ceramic rod. I like the feel of the ceramic rod and the edge surface it leaves. I especially appreciate the built in angle locating triangles.
If I was starting over, I would look very seriously at ceramic bench stones. I look forward to reading more replies. Again, excellent question.
Ken
RE: ceramic stones - Rupert Lucius - 12-02-2017
In ref to ceramics (Spyderco) do they polish their stones to what ever grit?
For a man that was sleepy you did great - whats to be when you wake up? WOW
Until tomorrow
Rupert
RE: ceramic stones - Mark Reich - 12-03-2017
Thank you, Mr Rupert. And, that is a good question.
To the best of my understanding, stones like Spyderco's are pure ceramic- no abrasive. Same with "ceramic rods". There are no abrasive particles like there are on diamond stones or diamond rods, only a semi- rough surface.
I don't know how they produce such an accurate, consistent surface texture, but it must be formed before the material is hardened/fired... whatever. There is no texturing after hardening. It would actually wear diamonds down, so I can't sharpen my sintered ceramic blade without a "disposable" $75 diamond belt. I think it would be possible to affect the edge with a TAS diamond wheel, but you'd probably hate the result on the knife and the wheel.
This form of ceramic is hard enough that the surface texture just doesn't wear out. Need proof? Have you ever heard of anyone lapping their Spyderco stone? No, because they don't wear. To clean them, you let the oxalic acid in Bar Keeper's Friend dissolve the "stuck on" steel for you, and you just rinse it off with water.
Well, Everyone laps "ceramic" Shaptons and Naniwas. Not only to keep them flat, but because it exposes new aluminum oxide abrasive, which Does leave a scratch pattern.
Anyway, the texture of ceramic is rough enough to remove steel, but the steel removed from the blade just sticks to the high spots of the stone. Since those spots are not sharp at all, you get virtually no scratch pattern from ceramic stones or rods. To make matters worse, as soon as you have steel stuck to the high spots, you're just rubbing steel against steel, galling the edge.
I've determined for myself that ceramic rods are pretty worthless (recently, I may add). No scratch pattern means no tooth, which means smooth edge, which means forgettaboutit. Sure, a ceramic rod in the kitchen isn't a sin, but I would not be able to upgrade to a diamond rod quickly enough. Once you boys get around to edge retention testing, you will figure this out immediately.
RE: ceramic stones - Jan - 12-04-2017
Mr. Mark, thank you for mentioning galling**.
Only recently I have corrected my older opinion that galling requires significant load between the rubbing surfaces. My current understanding is, that at higher speed also low contact load between the surfaces can cause galling.
I was curious to know more about the size of the surface speed, and have found one wear classification which considers speed larger than 0.7 m/s for sufficient to cause galling.
My Tormek with 90 rpm has surface speed about 1.2 m/s!
Jan
** ASTM G40-15 defines galling as "a form of surface damage arising between sliding solids, distinguished by macroscopic, usually localized, roughening, and the creation of protrusions above the original surface; it is characterized by plastic flow and may involve material transfer."
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RE: ceramic stones - scott.livesey - 12-04-2017
thanks for the replies. did some more checking. depending on the material used, ceramic stones would be mostly a combination of aluminum oxide & silicon oxide held together by glass. I guess that is why I have seen folks sharpen on the bottom of a ceramic coffee cup. I would guess it would be hard to tell the difference between a ceramic stone and a Norton India of the same grit.
RE: ceramic stones - EOU - 12-04-2017
"Once you boys get around to edge retention testing, you will figure this out immediately."
Mark you couldn't have made it more clear. It's coming...and very soon. Thank you for the "hands-on" perspective that you contribute to this subject. Jan, more than one of our customers have claimed that edge testing " was like turning on the light in their sharpening room". You may have just turned on a light for us with your comments on galling. We've noticed some strange edge phenomena and wonder if this might be the cause. We're going use the "flashlight" you've just provided and look into it.
Great thread Scott and thank you for opening it up. Thank you, as well, to Cliff Stamp's forum which provided the bread crumb that brought you our way.
RE: ceramic stones - me2 - 12-05-2017
Good evening (here anyway) all. I followed Scott from Cliff's forum.
Ceramics are a huge variety of materials. The abrasive in basically any sharpening stone can be considered a ceramic. Aluminum oxide, silicon carbide, zirconium oxide, cubic boron nitride (CBN), and a handful of others are all ceramics.
Solid ceramic stones like Spyderco and some others, and the ceramic rods people used in various V sharpeners are generally aluminum oxide (Al2O3). This is by far the most common form, and as far as I know is generally referred to as alumina. I am not familiar with the softer version Mark speaks of above, but aluminum oxide has more than the Al2O3 form, though I don't know what applications use them. Various forms of abrasive have different concentrations and quality of aluminum oxide. Emory and corundum are both aluminum oxide with various other materials mixed in with it in different amounts. Corundum works well as a sharpening abrasive, but I cannot recommend emory from my few experiences with it.
These types of stones and rods are sintered solid aluminum oxide with no binder, and the bonds between the particles are very strong, similar to the bonds between powder particles in CPM type steels. I have found them to be useful as finishing stones, thought they are not typically coarse enough to remove enough metal to be useful for rebeveling or sharpening really dull knives. I sharpen using the Spyderco Sharpmaker fairly often, and find the standard white stones to provide a very sharp edge and fine finish, though I typically stop at the brown stones, just out of saving a step.
Most stones use aluminum oxide or silicon carbide as an abrasive, combined with some form of binder/filler. These can be seen in micrographs of stones from Leonard Lee's book on sharpening. The resin and vitrified bond of water and oil stones, respectively, are quite different under magnification. Grinding/sanding belts use a larger variety of ceramics as abrasives. I use zirconium oxide (zirconia) belts for 40 and 80 grit rough grinding, then switch to aluminum oxide belts for finishing/polishing. CBN and diamond are both ceramics, and are both used in belts or on wheels. I have not tried any of these, and likely won't due to cost and my low grinding/sharpening volume.
The various oxides and other compounds used as abrasives in polishing compounds would also be considered ceramics. Chromium oxide, cerium oxide, iron oxide (for softer metals), diamond, and cbn buffing/polishing compounds are ceramics. It's really bewildering, and the imprecise use of the names by various industries/suppliers doesn't help.