# Which is the harder substance? **URL:** \ **Category:** Factual Questions\ **Created:** [August 8, 2004, 2:46am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843 "2004-08-08T02:46:09Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![bummerboy](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bummerboy](https://boards.straightdope.com/u/bummerboy)\ **Post date:** [August 8, 2004, 2:46am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/1 "2004-08-08T02:46:09Z")
Which is harder? Zircon-oxide used to make ceramic blades or diamonds? I’ve got some information that says “zircon oxide, which is harder than diamonds (so hard it registers beyond the Rockwell Scale)” But most information says that a diamond is the hardest substance known to man. Which is it? ---
**Author:** ![ZebraShaSha](https://avatars.discourse-cdn.com/v4/letter/z/eada6e/32.png) [@ZebraShaSha](https://boards.straightdope.com/u/ZebraShaSha)\ **Post date:** [August 8, 2004, 2:59am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/2 "2004-08-08T02:59:09Z")
From [www.wikipedia.com](http://www.wikipedia.com) - Zircon has a hardness of (Mohs) 7.5. Diamond, of course, is 10. Diamonds are still the hardest occuring gemstone or whatever. Zirconium Dioxide, what you are looking for, is a compound. I have no idea what its hardness is but it can not be compared to diamonds for that reason. Or so I think, atleast. ---
**Author:** ![ZebraShaSha](https://avatars.discourse-cdn.com/v4/letter/z/eada6e/32.png) [@ZebraShaSha](https://boards.straightdope.com/u/ZebraShaSha)\ **Post date:** [August 8, 2004, 3:04am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/3 "2004-08-08T03:04:35Z")
> [@http://www.24carat.co.uk/cubiczirconia.html](#): > > It should not be allowed to rub against other gemstones, particularly diamond, because this will cause wear and scratching. Hopefully that is self explanatory. ---
**Author:** ![bummerboy](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bummerboy](https://boards.straightdope.com/u/bummerboy)\ **Post date:** [August 8, 2004, 3:18am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/4 "2004-08-08T03:18:40Z")
Zircon oxide is short. It’s full name is Zirconium oxide (not that much longer) ---
**Author:** ![iwakura43](https://avatars.discourse-cdn.com/v4/letter/i/9de0a6/32.png) [@iwakura43](https://boards.straightdope.com/u/iwakura43)\ **Post date:** [August 8, 2004, 3:20am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/5 "2004-08-08T03:20:04Z")
> [@ZebraShaSha](#): > > From [www.wikipedia.com](http://www.wikipedia.com) - > > Zircon has a hardness of (Mohs) 7.5. Diamond, of course, is 10. Diamonds are still the hardest occuring gemstone or whatever. > > Zirconium Dioxide, what you are looking for, is a compound. I have no idea what its hardness is but it can not be compared to diamonds for that reason. > > Or so I think, atleast. I don’t think that’s true. The structure of the substance determines its hardness, not the substance’s components. Carbon has a hardness of 10 when in the form of a diamond, and 0.5 (!) as graphite. ---
**Author:** ![SnakeSpirit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snakespirit/32/7271_2.png) [@SnakeSpirit](https://boards.straightdope.com/u/SnakeSpirit)\ **Post date:** [August 8, 2004, 3:56am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/6 "2004-08-08T03:56:41Z")
> [@](#): > > Quote: > Originally Posted by [CZ - C.Z. - Cubic Zirconia](http://www.24carat.co.uk/cubiczirconia.html) > It should not be allowed to rub against other gemstones, particularly diamond, because this will cause wear and scratching. > [@ZebraShaSha](#): > > Hopefully that is self explanatory. Nooooo. Wear and scratching on the CZ or the diamond??? And are cubiczirconia and Zircon-oxide the same thing? A check of several Google pages turned up the following: [Describing it as a corundum](http://www.altech.pechiney.com/Gardanne/WebGardanne.nsf/vwUrl/MondeAlumine_Alumines_Corundum_VI) More generally, corundums represent a family of electrofused aluminas that can be divided into three large groups : • White corundums (“pure” alumina) • Brown corundum (aluminas doped at 1.5% or 3% with TiO2) • Solid solutions with corundum matrices among which zircon oxide corundums can be mentioned (25% of alumina and 42% of zircon oxide) and aluminium oxynitrides (AlON). In Nature, _corundum is the hardest mineral after diamond_. Moreover, chemically inert and more or less fragile depending on its preparation, it has always been a polyvalent abrasive and remains the most commonly used today. It is also used as an aggregate in refractories for its mechanical resistance in heat, its dimensional stability, its chemical inertia and its electric resistivity. * * * [A microceramics manufacturer](http://www.microceram.de/werkstoffe_eng.shtml) ZrO2-3Y Zircon oxide ceramics is a ceramic material on the basis Z2O3 zircon oxide part-stabilized by highly pur with 3MolY2O. Characteristics: Density: 6,05 g/cm³ Hardness: 1300 HV Pressure strength: 4000 N/mm² Bending strength (blank): 1200 MPa ZrO2-3Y20A Zircon oxide ceramics is a dispersion ceramic(s) on the basis of part-stabilized zircon oxide and alumina, which leads to an increase of the firmness and/or facture toughness oppostie pure ZrO2. Characteristics: Density: 5,5 g/cm³ Hardness: 1300 HV Bending strength (blank): 2400 MPa (1000°C: 800 MPa) * * * [More details from this site](http://www.microceram.de/media/MICROCERAM_FLYER_eng.pdf) Aluminum Oxide, Al2O3 hardness 2100 HV **Zirconium oxide, ZrO2 -Y2O3 hardness 1300 HV** Silicon Carbide, LPSSiC hardness 2990 HV * * * This reference, but the site wouldn’t open up. "Knives & Tools - compare prices, reviews and buy at NexTag - Price … Boker Infinity. Boker’s ceramic blades are constructed of zircon-oxide, which is hard as diamonds (so hard it registers beyond the Rockwell scale), resists wear … [IRL]([http://www.techshopper.com/](http://www.techshopper.com/) Knives\_\_\_Tools~2701185z110z160z0zB11y8zmainz5-htm - 57k - ) So, it depends if we can take the sales statement of a knife dealer as scientifically true… The other site lists Silicon carbide as harder yet! I’d be pretty amazed at a zirconium oxide corundum ceramic that is harder than diamonds yet with tensile strength enough to function as a knife! Hope someone can come up with more information. ---
**Author:** ![SnakeSpirit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snakespirit/32/7271_2.png) [@SnakeSpirit](https://boards.straightdope.com/u/SnakeSpirit)\ **Post date:** [August 8, 2004, 4:06am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/7 "2004-08-08T04:06:24Z")
[Again, from a knife dealer…](http://www.kniferunner.itcstore.com/store/product.aspx?prdId=1475) > [@](#): > > Boker blended its mastery of the knife making craft with its tradition of quality, then added the latest in modern material-titanium and ceramic-to create knives that set the standard for the future. Lighter than air, stronger than steel, with ceramic blades that are hard as diamonds…that stay sharp longer than steel blades…that defy rust and stains. Here are the brightest and best from Boker. We need “The Straight Dope!” ---
**Author:** ![SnakeSpirit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snakespirit/32/7271_2.png) [@SnakeSpirit](https://boards.straightdope.com/u/SnakeSpirit)\ **Post date:** [August 8, 2004, 4:35am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/8 "2004-08-08T04:35:55Z")
[A rating of ceramic knives](http://www.zvis.com/knives/folding/bokercd.shtml) > [@](#): > > Extremely high hardness - it is beyond the Rockwell scale, as I know something like 90 HRC; However it is very fragile, you drop it and there’s your chance to say bye to your lovely ceramic blade :((( > > One more thing - according to the description: Ceramic blade never needs sharpening, on the Boker’s web and some other places you see We’ll resharpen your Boker Ceramic blade for just … 🙂 They may mean that it won’t need sharpening if properly used??? Donno where this knife can get dull, when used on tomatoes & oranges? Anyways, Nice joke isn’t it 😉 You can cheek those out at: [http://www.bokerusa.com](http://www.bokerusa.com). > > It’s couple years since I wrote the initial review, things have changes since then, and I’ve got some real life experience regarding the creamic blades. This particular knife given away, as a gift(though I still have another one, just for the heck of it), and was used for 3 months in the flower shop. Just to cut flowers. After that it’s dead, dull in other words, and there’s no way to resharpen it, and I’m too lazy to send it to Boker for that. Another blade was a Keyocera ceramic blade in the kitchen for a while. All I can say is that, yes ceramics will hold the edge on soft materials beter than the premium cutlery steel, but eventually (depending on the user from 1 to 3-4 months) it’ll dull and then you have a choice, send it back to manufacturer, or throw it away. I personally like sharpening things myself, so ceramics is not an option anymore. > > Last revised - 05/09/04 Beyond the Rockwell scale, not the Mohs scale. I think that’s where the confusion comes from. I don’t think it’s harder than diamonds. ---
**Author:** ![ZebraShaSha](https://avatars.discourse-cdn.com/v4/letter/z/eada6e/32.png) [@ZebraShaSha](https://boards.straightdope.com/u/ZebraShaSha)\ **Post date:** [August 8, 2004, 5:16am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/9 "2004-08-08T05:16:53Z")
Ok, here: “Cubic zirconia is relatively hard, at about 8.5 on Mohs scale nowhere near diamond, but much harder than most natural gems” From: [http://encyclopedia.thefreedictionary.com/Cubic%20zirconium](http://encyclopedia.thefreedictionary.com/Cubic%20zirconium) ---
**Author:** ![SnakeSpirit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/snakespirit/32/7271_2.png) [@SnakeSpirit](https://boards.straightdope.com/u/SnakeSpirit)\ **Post date:** [August 9, 2004, 2:28am UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/10 "2004-08-09T02:28:56Z")
> [@ZebraShaSha](#): > > Ok, here: > > “Cubic zirconia is relatively hard, at about 8.5 on Mohs scale nowhere near diamond, but much harder than most natural gems” > > From: [http://encyclopedia.thefreedictionary.com/Cubic%20zirconium](http://encyclopedia.thefreedictionary.com/Cubic%20zirconium) From the same site: > [@](#): > > Cubic Zirconia (or CZ) is zirconium oxide (ZrO2), a mineral that is extremely rare in nature, but is widely synthesized for use as a diamond simulant. So CZ is the same as zirconium oxide, though not the same kind used in knives, but the hardness of both is 1300 HV, or 8.5 on the Mohs scale! Wow, we did it! Thanks **Zebra!** ---
**Author:** ![gfloyd](https://avatars.discourse-cdn.com/v4/letter/g/d2c977/32.png) [@gfloyd](https://boards.straightdope.com/u/gfloyd)\ **Post date:** [August 9, 2004, 5:06pm UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/11 "2004-08-09T17:06:41Z")
Speaking as chemist (Organic, not Inorganic however), I’m having trouble believing that anything could be harder than diamond, as it’s strength comes from the crystaline latice, which is damn near perfect in diamond. All of the carbons are sp3 hybridized and form a tetraheraonal structure. In graphite, however, the carbons are sp2 hybridized and are in sheets of hexagons, with an inherent aromaticity. The sheets are held together by nothing more than Vander Waals forces, which accounts for the softness. I don’t claim to know anything about zirconium oxide or cubic zirconium, other than it’s cheaper than diamonds and I like it better, but no one listens to me. ---
**Author:** ![Ethilrist](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ethilrist/32/4604_2.png) [@Ethilrist](https://boards.straightdope.com/u/Ethilrist)\ **Post date:** [August 9, 2004, 5:21pm UTC](https://boards.straightdope.com/t/which-is-the-harder-substance/258843/12 "2004-08-09T17:21:41Z")
> [@Snakespirit](#): > > Again, from a knife dealer… > > > [@](#): > > > > Boker blended its mastery of the knife making craft with its tradition of quality, then added the latest in modern material-titanium and ceramic-to create knives that set the standard for the future. **Lighter than air,** … :dubious: That sounds _really_ dangerous…