Neat. If I was in dentistry or oncology I'd print a tungsten apron like a suit of armour for kids, or perhaps a nice comfy/adjustable thyroid collar which isn't too tight or tall. With filament at $230 a kilo it might not be economically feasible but it sure would look cool.
this is my approximation of the pareto frontier; that is, each of the items on the list is conjectured to be cheaper than everything that's denser than it is, and denser than everything that's cheaper. corrections are welcome
i was thinking baryta (46¢/kg, 4.48 g/cc), mercury, litharge, minium, cinnabar, cupric oxide (US$3.90/kg, 6.315 g/cc), zinc oxide (US$29/kg, 5.6 g/cc), and manganese dioxide (5.026 g/cc) might be interesting in this context too
i hadn't thought of your suggestion of galena (just cinnabar) and generally i'm skeptical of metal sulfides because of their tendency to produce hydrogen sulfide; i don't think that's an issue with those two. litharge, minium, and mercury are a lot more worrisome toxicologically
i don't have solid pricing information for mercury, litharge, minium, cinnabar, or galena, and i'd be interested
tungsten is probably more chemically inert for medical purposes than a lot of these
Density alone is a weak parameter. For photons with energy below 200 keV — that is, most of them — the attenuation is proportional to Z^2, so barium with atomic number 56 is four times as attenuating as nickel with atomic number 28, and lead with atomic number 82 is about twice as effective as barium — all of this before you account for density.
I've done a bit of searching for materials myself. Barium is mined as barite (BaSO4) or witherite (BaCO3), not baryta (BaO*xH2O, caustic), and USGS lists the price of barite as $180/t, or $0.20/kg.
You also have a K-edge effect, which prompted me to wonder whether you can easily produce barium zirconate from the respective ores, which are both cheap — BaZrO3 (sg ~5.5) is not currently manufactured (Zircon sand was <$1/kg until a COVID-related shortage). But at this point I decided I was overthinking it.
you seemed to be saying that this filament might be a better alternative to lead sometimes, but i couldn't tell when that might be. pure tungsten is clearly a better choice sometimes, for example because it shields better than lead, is harder, is denser, and is more refractory, but none of those seems to be true of this filament
from your other comment at https://news.ycombinator.com/item?id=35206874 it looks like you're saying that, although this composite is inferior to lead in those ways, it's easier to print
We have issues working with lead at work, mostly due to toxicity. Putting a hole in a sheet isn't as simple as getting out the drill, not mechanically, but due to all the swarf that needs to be cleaned up. 3D printing a bolt-on cover would be lower risk than drilling lead, a quicker turnaround than getting a die made and lead cast, and give a prototype that doesn't need to be handled with gloves.
For the right application, there are some good wins here.
what do you think about copper-filled or baryta-filled filaments as cheaper alternatives
maybe this is wrong but i feel like both tungsten and copper are in the 'if you have it embedded in your body you are going to need surgery to get it out before you get gangrene' while lead and baryta are not
The article explains the beneficial properties of tungsten with rad shielding. Tungsten sheilds better than lead. Lead is easier to form to simple shapes (flats, straight forward wraps). It is essentially impossible to form it in to complex shapes. Tungsten has a high temperature resistance, and low deformation under load. Broadly speaking it can be relied upon to stay in the shape it's machined to. But getting in to that shape is very expensive and difficult - an understatement.
I can't explain everything in every comment. You can research the materials if you want to understand the discussion in more context.
Tbh I have no idea how you came away thinking I said lead is hard. "also difficult". "this" is the material that is the center point of the discussion. Context, yo.
i appreciate you being willing to clarify the things that were hard to understand or that we were wrong about
(i actually had the impression that working lead on a lathe was very easy indeed due to its softness, but i've never tried doing it myself, and my bachelor's degree from youtube is worth what i paid for it)
i think you may have misunderstood something in the comment you were replying to yourself
Lead is a nightmare to machine. It's gummy. You'd think aluminum was easy because it's softer than steels, but that comes with it's own challenges. Lead is worse so. You're right that this isn't so bad on a lathe as opposed to a mill or (lol) a grinder, but you're not going to see a need for a lot of solid round shielding.
A little bit of lead in steel will increase machinability, but only a teeny amount. Similar to adding a small bit of phosphorus.
It's also hard to hit dimensions in lead, and if you do hit them, the second the temperature changes you'll lose them. Additionally, whatever you make can't see any stress, or the part is donezo.
Idk if you've ever handled lead - but considering you can bend thick sheets of it by hand and melt it on your stove, I'm sure you can imagine the kind of issues you might have integrating expensively machined chunks of it in to hot high pressure environments with moving parts.
Even though lead is cheap and this filament is expensive, actually getting the lead to shape by machining or working it is also a costly process. 3d printing has a sort of cost ceiling. Once a part is designed, all of the real work is done. For fabrication and machining - once the part is designed the work has only begun.
What might look like a small and simple combination of geometric shapes can cost thousands to machine.
I'd rather spend 500 on filament and a day's engineering labor on a part than the same day's engineering, 100$ of lead, and 1k or more on manufacturing. Not to mention the lead times on machined parts can be wild.
i think all the post-manufacturing problems you describe with lead — dimensional instability, thermal creep, plastic deformation, incompatibility with hot high pressure environments, vulnerability to wear — are even worse with this filament
maybe an exception is that petg's maximum elastic strain is larger than lead's
Considering lead's modulus of elasticity is essentially zero, yes :) You can drill, tap, and generally rely on this material to stay in the shape it was printed at in maaaaaany more situations than lead.
Of course the petg in there is a limiting factor, but even plain petg is an order of magnitude better than lead at retaining its shape under a wide range of loads. You can print gears for lathes in petg! And they last years! (If you're wondering why you might do this - it's a good idea to have a cheap point of failure on devices that have enough power to rip themselves to shreads.)
Not to mention this is only v1 of the material. We could see exotic plastics that are far more heat resistant like PEEK get a secondary filler for niche radioactive usecases.
(at such low filler loadings the tungsten will change the modulus of elasticity very little)
petg does have higher yield stress than pure lead (53 megapascals vs. what https://nickelinstitute.org/media/1771/propertiesofsomemetal... says is 17 megapascals) but there are lead alloys that are in the same range of yield stress, including regular lead-tin solder. but they won't last if you try to make change gears out of them precisely because they're harder than petg
by the same token, though, i think you're going to get a lot of springback and long-term distortion out of petg you aren't going to get with lead
> Tbh I have no idea how you came away thinking I said lead is hard.
I did not, in fact, come away thinking lead is hard. I did, however, explain and spell out for you how @kragen probably did so; I'm not sure how I can make it any more clear.
21 comments
[ 4.3 ms ] story [ 50.9 ms ] thread- Osmium: [US$13000/kg][8], 22.65 g/cc, or possibly iridium at more than twice that price
- Tungsten: [US$30/kg][9], 19.3 g/cc
- Tungsten carbide? Not sure what it costs but its density is 15.6 g/cc.
- Lead scrap: 95¢/kg, 11.3 g/cc
- Steel scrap: [21¢/kg][10], 7.9 g/cc
- Magnetite: [10¢/kg][11] [or so][12], 5.2 g/cc
- Quartz (as construction sand): 3¢/kg, 2.6 g/cc
- Water: [.06¢/kg][22] or so, 1 g/cc
[8]: https://www.metalary.com/osmium-price/ [9]: https://www.metalary.com/tungsten-price/ [10]: https://www.usgs.gov/centers/nmic/iron-and-steel-scrap-stati... [11]: https://www.usgs.gov/centers/nmic/iron-ore-statistics-and-in... [12]: https://stockhead.com.au/resources/barry-fitzgerald-why-magn... [22]: http://www.scientificamerican.com/article/israel-proves-the-...
this is my approximation of the pareto frontier; that is, each of the items on the list is conjectured to be cheaper than everything that's denser than it is, and denser than everything that's cheaper. corrections are welcome
i was thinking baryta (46¢/kg, 4.48 g/cc), mercury, litharge, minium, cinnabar, cupric oxide (US$3.90/kg, 6.315 g/cc), zinc oxide (US$29/kg, 5.6 g/cc), and manganese dioxide (5.026 g/cc) might be interesting in this context too
i hadn't thought of your suggestion of galena (just cinnabar) and generally i'm skeptical of metal sulfides because of their tendency to produce hydrogen sulfide; i don't think that's an issue with those two. litharge, minium, and mercury are a lot more worrisome toxicologically
i don't have solid pricing information for mercury, litharge, minium, cinnabar, or galena, and i'd be interested
tungsten is probably more chemically inert for medical purposes than a lot of these
I've done a bit of searching for materials myself. Barium is mined as barite (BaSO4) or witherite (BaCO3), not baryta (BaO*xH2O, caustic), and USGS lists the price of barite as $180/t, or $0.20/kg.
You also have a K-edge effect, which prompted me to wonder whether you can easily produce barium zirconate from the respective ores, which are both cheap — BaZrO3 (sg ~5.5) is not currently manufactured (Zircon sand was <$1/kg until a COVID-related shortage). But at this point I decided I was overthinking it.
i think the price i cited for it is retail, locally
i was interested in density for psychological effects when i made the list
thanks for the tip about barium zirconate; it sounds very promising. how about lead zirconate?
you seemed to be saying that this filament might be a better alternative to lead sometimes, but i couldn't tell when that might be. pure tungsten is clearly a better choice sometimes, for example because it shields better than lead, is harder, is denser, and is more refractory, but none of those seems to be true of this filament
from your other comment at https://news.ycombinator.com/item?id=35206874 it looks like you're saying that, although this composite is inferior to lead in those ways, it's easier to print
For the right application, there are some good wins here.
what do you think about copper-filled or baryta-filled filaments as cheaper alternatives
maybe this is wrong but i feel like both tungsten and copper are in the 'if you have it embedded in your body you are going to need surgery to get it out before you get gangrene' while lead and baryta are not
that is depressing
Tungsten is ok
https://pubmed.ncbi.nlm.nih.gov/29300000/
don't confuse government power with wisdom; in many ways they are opposites
I can't explain everything in every comment. You can research the materials if you want to understand the discussion in more context.
Tbh I have no idea how you came away thinking I said lead is hard. "also difficult". "this" is the material that is the center point of the discussion. Context, yo.
(i actually had the impression that working lead on a lathe was very easy indeed due to its softness, but i've never tried doing it myself, and my bachelor's degree from youtube is worth what i paid for it)
i think you may have misunderstood something in the comment you were replying to yourself
A little bit of lead in steel will increase machinability, but only a teeny amount. Similar to adding a small bit of phosphorus.
It's also hard to hit dimensions in lead, and if you do hit them, the second the temperature changes you'll lose them. Additionally, whatever you make can't see any stress, or the part is donezo.
Idk if you've ever handled lead - but considering you can bend thick sheets of it by hand and melt it on your stove, I'm sure you can imagine the kind of issues you might have integrating expensively machined chunks of it in to hot high pressure environments with moving parts.
Even though lead is cheap and this filament is expensive, actually getting the lead to shape by machining or working it is also a costly process. 3d printing has a sort of cost ceiling. Once a part is designed, all of the real work is done. For fabrication and machining - once the part is designed the work has only begun.
What might look like a small and simple combination of geometric shapes can cost thousands to machine.
I'd rather spend 500 on filament and a day's engineering labor on a part than the same day's engineering, 100$ of lead, and 1k or more on manufacturing. Not to mention the lead times on machined parts can be wild.
maybe an exception is that petg's maximum elastic strain is larger than lead's
Of course the petg in there is a limiting factor, but even plain petg is an order of magnitude better than lead at retaining its shape under a wide range of loads. You can print gears for lathes in petg! And they last years! (If you're wondering why you might do this - it's a good idea to have a cheap point of failure on devices that have enough power to rip themselves to shreads.)
Not to mention this is only v1 of the material. We could see exotic plastics that are far more heat resistant like PEEK get a secondary filler for niche radioactive usecases.
(at such low filler loadings the tungsten will change the modulus of elasticity very little)
petg does have higher yield stress than pure lead (53 megapascals vs. what https://nickelinstitute.org/media/1771/propertiesofsomemetal... says is 17 megapascals) but there are lead alloys that are in the same range of yield stress, including regular lead-tin solder. but they won't last if you try to make change gears out of them precisely because they're harder than petg
by the same token, though, i think you're going to get a lot of springback and long-term distortion out of petg you aren't going to get with lead
I did not, in fact, come away thinking lead is hard. I did, however, explain and spell out for you how @kragen probably did so; I'm not sure how I can make it any more clear.