I expect this to be an absolute wall of text driven by hours to think on a topic during a long late night drive. I advise not reading it.
In the quest to finish off my stone collection with some ultimate stone, I like most of ya’ll have come across the super vitrified stones a few sellers carry. Not being a professional sharpener, or even a skill sharpener I obviously have 0 use for this. But it’s not like something as trivial as a ‘need’ has stopped me from anything in this hobby or I would sell everything but the Enzo HD knife my better half got me and my buckels knife. So why start now?
Of course I caught the vitrified diamond bug when the 3-4 sellers for vitrified diamond stones are out of stock of them, and they have a tendency to sell out due to the high demand for them.
So I figure some theory crafting would be fun. Most of this is minimally educated gibberish, like most of my posts.
I went into my googlefu curious about the binders. Obviously they play as large a part in how a stone behaves as the abrasive. The mouthfeel of the stone so to speak, or as folks with more experience then I describe it, the feedback. The binder also should dictate the rate at which a stone dishes, since it forms the bulk of the stone and is what primarily gets worn away during sharpening (abrasives, provided you aren’t taking a super steel to a stone I’ll equipped to it should by definition be harder than your steel and thus allow them to cut it, including whatever your majority carbide is to avoid carbide tear out). So a softer, binder, a creamier feel but a larger chance of dishing. At least that’s the theory, wear resistance is a weird, weird topic and it definitely isn’t entirely tied to hardness, but I’ll start there and confuse myself on the topic when I know more.
So naturally I started looking into the more wear resistant ceramics, they tend to fall into the tribological ceramic category. Things like CBN, zirconia and the ilk. Hard stuff that makes for decent bearing surfaces due to the wear resistance they can provide.
The second issue came from the abrasive. Diamonds. Lovely little hunk of carbon. What else is carbon? Firewood. And like firewood diamonds burn at elevated temperature. Ok, so remove the oxygen and it can’t burn right? Nope. Diamond will just turn into graphite once you start heading north of 1500F.
So how do you make a vitrified diamond stone? Ceramic firing tends to be involve crazy temperatures, at least my knife steel standards. Low temperature vitrifying ceramics exist, but even are classified as occurring at about 1800-1900F, and many sources put it closer to 2k. So, using the lowest temperature for vitrification of a ceramic puts it above the “our diamond has turned to gas and pencil lead” temperatures.
So what now? I figured maybe sintering may be the solution, maybe the vitrification isn’t an accurate description of the process (or maybe I really am that dumb and missed some ultra low vitrifying ceramic). Sintering occurs at more normal firing temperatures, and results in the binder essentially glueing your ceramic structure together, compared to the vitirification process that turns a portion of your ceramic into a glass. In short, a lower temperature can be used.
That brought me to one of the tribological ceramics, zirconia. Specifically TTZ, which confusingly seems to get called EITHER transformation toughened zirconia or tetragonal toughened zirconia. I believe the first is more technically accurate, but the transformation is of the tetragonal morph
. Zirconia has a few forms, that are stable at various temperatures, which can be stabilized by addition of stabilizers that have a particular. The tetragonal phase is metastable, and when it transforms to monoclinic it increases the fracture toughness of the ceramic. From what I can find, it’s the type of ceramic used in most ceramic knives (not including the new rahven ones).
Of the phases that occcur, monoclinic lacks the physical properties desired, and cubic occurs at too high a temperature for diamond to happily coexist. Tetragonal though, is metastable at about 1200-2400F, since diamond doesn’t seem to start burning until about 1500F, this makes it perfect. The issue is, tetragonal is the metastability. As it cools, it transforms to monoclinic. This changes it’s volume, damaging the material and losing the sweet, sweet tetragonal properties. So you dope it. Small amounts of yttria or cerium are enough to stabilize the tetragonal morph, see the pretty chart at the bottom for info on the yttria route. Cerium (cerium stabilized zirconia, CSZ) , does better at preventing low temperature degradation, yttria (yttrium stabilized zirconia, YSZ) has better physical properties.
So a binder that is incredibly wear resistant, holding onto diamonds to prevent them from tearing out, that sinters at a low enough temperature that the diamonds don’t degrade. Interestingly enough, thanks to the low temperature it could theoretically maybe be done in any old pottery kiln since they tend to fire well above that range, even potentially a heat treat kiln.
Obviously this doesn’t begin to address the issues of preventing the stone from cracking, either during heating or cooling, flattening the inevitable warping out, or even figuring out how much abrasive to include, let alone any nicher issues (like what impact does loading a YSZ with diamond have on the properties of the YSZ?) and how do you get an even distribution and suspension of your diamond within the binder Still, it’s fun to ponder.
Also I probably wrote zirconium somewhere in here. It’s meant to be zirconia but it’s far too late for me to find and fix it.
If you made it this far then I’m sorry for making you read all this.
Sources:
Low fire clay temps
Zirconia polymorphs
Elementary info on tribological ceramics
More detailed zirconia info and some useful tables for the stability
In the quest to finish off my stone collection with some ultimate stone, I like most of ya’ll have come across the super vitrified stones a few sellers carry. Not being a professional sharpener, or even a skill sharpener I obviously have 0 use for this. But it’s not like something as trivial as a ‘need’ has stopped me from anything in this hobby or I would sell everything but the Enzo HD knife my better half got me and my buckels knife. So why start now?
Of course I caught the vitrified diamond bug when the 3-4 sellers for vitrified diamond stones are out of stock of them, and they have a tendency to sell out due to the high demand for them.
So I figure some theory crafting would be fun. Most of this is minimally educated gibberish, like most of my posts.
I went into my googlefu curious about the binders. Obviously they play as large a part in how a stone behaves as the abrasive. The mouthfeel of the stone so to speak, or as folks with more experience then I describe it, the feedback. The binder also should dictate the rate at which a stone dishes, since it forms the bulk of the stone and is what primarily gets worn away during sharpening (abrasives, provided you aren’t taking a super steel to a stone I’ll equipped to it should by definition be harder than your steel and thus allow them to cut it, including whatever your majority carbide is to avoid carbide tear out). So a softer, binder, a creamier feel but a larger chance of dishing. At least that’s the theory, wear resistance is a weird, weird topic and it definitely isn’t entirely tied to hardness, but I’ll start there and confuse myself on the topic when I know more.
So naturally I started looking into the more wear resistant ceramics, they tend to fall into the tribological ceramic category. Things like CBN, zirconia and the ilk. Hard stuff that makes for decent bearing surfaces due to the wear resistance they can provide.
The second issue came from the abrasive. Diamonds. Lovely little hunk of carbon. What else is carbon? Firewood. And like firewood diamonds burn at elevated temperature. Ok, so remove the oxygen and it can’t burn right? Nope. Diamond will just turn into graphite once you start heading north of 1500F.
So how do you make a vitrified diamond stone? Ceramic firing tends to be involve crazy temperatures, at least my knife steel standards. Low temperature vitrifying ceramics exist, but even are classified as occurring at about 1800-1900F, and many sources put it closer to 2k. So, using the lowest temperature for vitrification of a ceramic puts it above the “our diamond has turned to gas and pencil lead” temperatures.
So what now? I figured maybe sintering may be the solution, maybe the vitrification isn’t an accurate description of the process (or maybe I really am that dumb and missed some ultra low vitrifying ceramic). Sintering occurs at more normal firing temperatures, and results in the binder essentially glueing your ceramic structure together, compared to the vitirification process that turns a portion of your ceramic into a glass. In short, a lower temperature can be used.
That brought me to one of the tribological ceramics, zirconia. Specifically TTZ, which confusingly seems to get called EITHER transformation toughened zirconia or tetragonal toughened zirconia. I believe the first is more technically accurate, but the transformation is of the tetragonal morph
. Zirconia has a few forms, that are stable at various temperatures, which can be stabilized by addition of stabilizers that have a particular. The tetragonal phase is metastable, and when it transforms to monoclinic it increases the fracture toughness of the ceramic. From what I can find, it’s the type of ceramic used in most ceramic knives (not including the new rahven ones).Of the phases that occcur, monoclinic lacks the physical properties desired, and cubic occurs at too high a temperature for diamond to happily coexist. Tetragonal though, is metastable at about 1200-2400F, since diamond doesn’t seem to start burning until about 1500F, this makes it perfect. The issue is, tetragonal is the metastability. As it cools, it transforms to monoclinic. This changes it’s volume, damaging the material and losing the sweet, sweet tetragonal properties. So you dope it. Small amounts of yttria or cerium are enough to stabilize the tetragonal morph, see the pretty chart at the bottom for info on the yttria route. Cerium (cerium stabilized zirconia, CSZ) , does better at preventing low temperature degradation, yttria (yttrium stabilized zirconia, YSZ) has better physical properties.
So a binder that is incredibly wear resistant, holding onto diamonds to prevent them from tearing out, that sinters at a low enough temperature that the diamonds don’t degrade. Interestingly enough, thanks to the low temperature it could theoretically maybe be done in any old pottery kiln since they tend to fire well above that range, even potentially a heat treat kiln.
Obviously this doesn’t begin to address the issues of preventing the stone from cracking, either during heating or cooling, flattening the inevitable warping out, or even figuring out how much abrasive to include, let alone any nicher issues (like what impact does loading a YSZ with diamond have on the properties of the YSZ?) and how do you get an even distribution and suspension of your diamond within the binder Still, it’s fun to ponder.
Also I probably wrote zirconium somewhere in here. It’s meant to be zirconia but it’s far too late for me to find and fix it.
If you made it this far then I’m sorry for making you read all this.
Sources:
Low fire clay temps
Zirconia polymorphs
Elementary info on tribological ceramics
More detailed zirconia info and some useful tables for the stability
