mortar and pestle hardness vs material - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: August 14, 2024, 11:17:48 pm
content: I am getting very confused trying to find specs on mortar and pestles.I see there is a kind of general idea for laboratory use (i.e. making powder for DIY ceramic PCB or plating) they go between agate and porcelain. I know there harder materials but that is pretty clear cut.When I look up porcelain on the MOHS scale, it says that it has a 7 hardness.When I look up agate it says between 6.5 to 7.All over its saying that agate is much tougher then porcelain. to me it looks equal or even worse.Granite is 6-7, quartz is 7.They can't be wrong, so what factor am I missing? Because a porcelain crucible website seems to say its 5. But all the tables show 7. Is there two mohs scales? Is it more complicated then this?There appears to be enough information to suggest that its not a conspiracy to sell agate. But the numbers don't make sense!

author: wraper
author_rank: Unknown
timestamp: August 14, 2024, 11:24:38 pm
content: Hardness does not say how tough the material actually is. Something can be hard but fragile, prone to chipping.

author: coppercone2
author_rank: Super Contributor
timestamp: August 14, 2024, 11:26:57 pm
content: Hmm so I wonder if that website made up their own number to give it a 5 based on some other metric if tables suggest the value is 7. fake unitsBecause the MOHS test is clear. I am guessing the truth is the MOHS scale is not good for measuring grinding performance and its data sheet front page wank.Because porcelain is used as the standard to determine a 7 on the mohs scale.

author: thm_w
author_rank: Super Contributor
timestamp: August 14, 2024, 11:50:53 pm
content: Why not link the site.As you see here properties can vary a bit:https://www.tenax4you.com/surface-material-hardness-s/2249.htmhttps://www.2spi.com/item/z01448/"Unlike porcelain, which is porous, the high quality agate used by SPI Supplies is high density (e.g. without porosity) which minimizes sample loss and reduces cross contamination between samples. For those who are geologically inclined, the specific agate used by SPI Supplies is of Brazilian origin which is recognized as being the hardest and most dense found anywhere in the world. So far as mortar and pestle sets are concerned, only zirconia mortars and pestles would be harder (e.g. Mohs Scratch Hardness of ~10 vs. ~7. The agate used by SPI Supplies is resistant to all solvents and acids except aqua regia and HF. "

author: coppercone2
author_rank: Super Contributor
timestamp: August 15, 2024, 02:23:04 am
content: https://www.isolab.de/en-us/lab-consumables-labware/mortars-porcelain-standardformit is confusing because everyone basically shows you about rocks, all the way back to science class, to try to scratch porcelain, as a hallmark of mohs 7 . but somehow you end up with 5.since everyone says agate is better then porcelain, referencing agate mohs of 7, clearly something does not align. so the people giving porcelain a 5 look basically CORRECT.Its like the high mohs of porcelain becomes irrelevant when talking about mortars, but the mohs of agate, alumina, etc... are still relevant.it seems like one of those figures that only shows up when your winning the argument!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 15, 2024, 03:02:55 am
content: Well, diamond is 10 Mohs, and cubic zirconia is ~8, so someone's lying there.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: August 15, 2024, 03:07:01 am
content: there must be confusion between minerals from earth and minerals from cardasiazirconia crucibles are listed as mohs 10 on like 3 different websitesI just wanted some tin and I got wrapped up in this conspiracy involving big agate :'(

author: coppercone2
author_rank: Super Contributor
timestamp: August 15, 2024, 03:58:15 am
content: I am not convinced that any of these materials stand up to big particles. I am suspicious they use a porcelain mortar for bulk processing then move fine powders into a better one unless its purity critical.I would think iron might be the best bet, because you can impact stuff in there, but it has to be oiled and oily powders are annoying. I have a feeling owning a porcelain mortar is not a bad idea. And maybe a stainless steel one too for difficult materialsbut it still seems like there is some funny business here with the numbers

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 15, 2024, 05:35:19 am
content: Well, porcelain is glass, mostly SiO2, with enough Ca and K (or other fluxes) to make it goop, and just enough Al2O3 to hold it together (recrystallizes into a mullite skeleton on firing). Hence the translucent quality, it's as glassy as you can get without the stuff slumping into a puddle in the kiln. Likewise the high density / low porosity, low and consistent expansion (no phase change due to free quartz/cristobalite), value as an insulator, etc.Agate is quartz, but so finely crystalline that it's basically glass anyway. Quartz doesn't have cleavage planes either, but a conchoidal fracture, so the crystallinity wouldn't make much difference in terms of hardness. (Grain boundaries can still be a point of weakness though, hence why granite for example is weaker to certain forces.)Both have a Mohs hardness of 7, or very close.Hardness is the ability to resist deformation (scratching, abrasion) by another material; it isn't bulk strength, cleavage, intergranular strength, etc. You can quite easily chip and break these materials with a steel tool (Mohs 4-5?), and I think it's pretty obvious if you have a go at one of these with a hammer and chisel, you'll be able to chip, dent or fragment them even without much difficulty.Likewise, media doesn't need to be especially hard to do the job. Steel balls in a ball mill, can be pretty hard, but they're also regularly used to break up rock and ores of quite high hardness. It's the impact that does it: say two balls clack together (giggity?) and there's some grains of rock inbetween, maybe quartz, maybe corundum, whatever. To some extent, the grains will push into the surfaces of the two balls, deforming them, maybe chipping out a bit of metal, but the deformation can also serve to simply grab onto the grains, and then the whole impact force is transmitted through those tiny grains, which quickly fail under compression. The balls aren't likely to hit straight-on either, rotation or a glancing blow turns into a shear force tearing the grains apart.A ball mill might end up contaminating the charge with a lot of iron (or whatever the balls are made of), but if that can be acid-washed out, or just doesn't matter, well, that's fine.You're working a mortar and pestle the same way, whether by impact, smashing up larger bits with the pestle, or with a thrust-and-gyrate motion, or a continuous orbital motion, either way applying large forces to sharp fragments as they stir around and catch randomly between the grinding faces. It's just a hell of a lot slower because it's your hand doing it, lol.Inevitably, some of the grinding material will come loose and contaminate the sample; if this is undesirable, harder materials should be chosen, which is where a zirconia or alumina set might be desirable.You also want to avoid reactions with the grinding material. It was, I believe, mercury compounds can react with copper on fine milling, seemingly a reaction like cold-welding but involving the transfer of compounds,https://en.wikipedia.org/wiki/Mechanochemistry. That makes silica attractive, it's pretty inert to most things. This might make steel undesirable for grinding something like tin compounds, if that's something you need to do.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: August 15, 2024, 05:40:02 am
content: I have a alumina one but I wanted another one that is cheaper for like bootleg experiments.Not sure if I want porcelain ,agate, metalThe ball mill is too big etc I just want small amounts, ball mill is not for 'discovery' research (many different samples)I am worried that the agate might be annoying to use because its so polished.I am worried about stupid things happening with alumina, for instance the silver oxide I Have is contaminated with metalic silver. I got silver smeared into my micro borosilicate crucible and I had a field day cleaning that up. I don't want this to happen to the alumina crucible. Porcelain says it can be reground with sand pretty easily.I am not quite imagining how agate works because it looks real smooth. The alumina is smooth but not polished. I think little granules would just skid around in agate so you need pre processing in a 'grinding' crucible of some kind?Do you know if agate can handle processing 'coarse pepper' material (i.e. post hammer, or maybe metal crucible 'pounding')Ill probobly end up getting all of them because it is curious. I am guessing its like pliers where you end up being able to use all of them if your smart for optimal results... playing whats the best is probobly gonna get me no where?I almost have a vauge recollection of playing with some kind of smooth mortar some where (perhaps science class) and getting pissed off and wishing I had my kitchen one (some kinda marble?) because it was just skidding around. Or maybe it was someones kitchen. I was thinking that its non functional posh looking decorative bullshit, but perhaps I was doing it wrong.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 15, 2024, 05:55:04 am
content: Like I said, trap a particle between pestle and mortar, the surfaces might be smooth but they still deform, trapping the particle there while transmitting say a few pounds of crushing force, into a particle you know 100um or whatever across. You'll figure out the pressure, angle and motion quick enough.Sounds like you need some nitric acid... will clean out that silver real quick. Not really any way around it unfortunately, working with silver pretty much necessitates it. A bit expensive and hard to obtain but well worth it (or distill your own).Tim

author: coppercone2
author_rank: Super Contributor
timestamp: August 15, 2024, 06:08:48 am
content: so with agate are you just supposed to tap it without any traditional grinding and twisting? because thats what it looks like

author: coppercone2
author_rank: Super Contributor
timestamp: August 15, 2024, 08:35:33 pm
content: What I mean is getting it started, with a coarse one, you can drag a particle along near the pestle and it disintegrates. with this one, you basically have to keep impacting it like a hammer before the pieces are small enough to grind on a smooth surface. I feel like it has a minimum mesh requirementat least I suspect that. it could be really freaking annoying

author: coppercone2
author_rank: Super Contributor
timestamp: August 18, 2024, 07:13:38 am
content: I ground ITO and borosilicate frit in a alumina mortar to prepare various samples. It was not 100% clean to begin with, and maybe it had a tiny amount of staining, but it works pretty well for mixing the powder and its not scratched up. I might try to get a agate mortar. The slippery surface might be better for mixing stuff, because I noticed that I had ab it of difficulty because the powder kinda made a uniform layer under the pestle and I needed to kinda like scrape it after mixing for a while. I am thinking if its slippery like I think, the agate might make a better powder mixing vessel (not so much for grinding but getting rid of clumps in mixtures with some pressure).But I do need to say, ITO is kind of a crappy material to work with. As a powder I consider it obnoxious compared to other powders i have seen.I realized that I basically require a slippery polished crucible, for mixing silver metal... it will basically foul anything that grinds... and for copper or aluminum when I try to make low cost ceramic conductors.

author: coppercone2
author_rank: Super Contributor
timestamp: September 10, 2024, 09:32:18 pm
content: ok I got a small onyx crucible for grinding the silver / frit mixtures.It seems to mix it well but its wasteful, even when I scrape everything with a sharp steel point, there was a substantial amount of silver and palladium embedded in the rock. The onyx ones are not super polished.To clean it, I poured in salt and ground that for a while, etc.. and it got mostly clean.What is a good material to dump the crucible out on to funnel it back into a container? Paper also wastes silver.I suppose what I should do is grind it with salt and then filter it on filter paper to try to save silver, but I suppose its acceptable losses. I did over load the crucible though, I got the smallest one because I had doubts, but it was only $10.