It appears that lithium will react with nitrogen at room temperature to form solid lithium nitride. It looks like it will also oxidize. So if some quantity of finely powdered mostly pure lithium is placed in a sealed container, possibly up to 99% of the air will react and turn to a solid, creating a low vacuum. I was starting to try to figure out if other gasses could be captured, like CO2, etc, but realized that's pointless since almost 1% of air is argon, which won't react with anything.
So what would this be good for? Well vacuum pumps are expensive, and if you just need to create a vacuum on rare occasions, this might be just the thing. Ideally this could be sold in a tea-bag-like pouch sealed inside a foil wrapper. Tear the foil open, toss it in the container and close the lid. You might want to shake it around a bit (after eh lid is closed) to help the air distribute throughout the powder more quickly. I envision using this for the feather drop experiment in classrooms with a long clear tube. When you first throw the pouch and feather into the tube, turning the container over will result in the pouch falling faster than the feather. As the vacuum is improves, the feather will fall faster and faster.
To get a higher vacuum, the container could be purged with nitrogen to reduce the concentration of argon and any other gasses that won't react with lithium.
Still unresolved (since I'm too lazy to research this at the moment): Just how dangerous is pure lithium? I don't suppose the US Postal Service would want to deliver this. If it's packed to look like a tea-bag, how do we ensure that no one drops it in a cup of hot water? How do you safely dispose of the lithium Nitride when you're done? How much finely powdered lithium would be needed per quart of air at sea level, and how expensive would that be?-- scad mientist, Nov 17 2020 Lithium properties https://www.webelem...hermochemistry.htmlWell, the thermochemical properties; links there to physical etc... [neutrinos_shadow, Nov 17 2020] Why? Why_3fby xenxag [pashute, Nov 19 2020] If you can make lithium hypochlorite, there's a world-wide shortage of it now for pools and spas. All the lithium makers ditched it to make batteries but too many came online and the price of lithium dropped. I bought a couple years' worth of lithium hypochlorite but I'm almost out.-- AusCan531, Nov 17 2020 For a cheaper method, purge the tube with oxygen and use moist iron (e.g. steel wool).
Lithium is reasonably dangerous. In the presense of moisture, it causes chemical burns and can spontaniously combust. You can make your own metallic lithium by electrolysing a molten lithium salt, but it is kind of dicey and should be done in a vacuum :-/.-- spidermother, Nov 17 2020 The problem is leakage. No vacuum system is ever perfect, and hydrogen can diffuse through metal at a disconcertingly high rate. So your absorber (and sorbtion pumps are Baked and WKTE) will eventually saturate and the volume will start to move back towards equilibrium with its environment.
There are cryopumps, sputter-ion pumps that capture gas molecules, and thermionic valves (tubes) often have a titanium "getter" which presents a reactive surface to grab gas ... but just about all vacuum systems have to be constantly pumped to maintain the pressure.
Reactive pumps for creating vacuum are not an innovation.
Also, Lithium is very boring and lacks entertainment value compared to the other alkali metals.-- 8th of 7, Nov 17 2020 That's just the normalizing feeling you get after you take your dosage of it to help with the desires to take over the galaxy and "mood swings," 8th.-- RayfordSteele, Nov 17 2020 [8th] Thanks for the search term "reactive pumps" and "getter pumps" which get a lot more hits than chemical vacuum pump.
I guess what I reinvented is a getter, though it sounds like most of those are heat activated (probably for good reason). Since this is WKTE do I need to MFD?
I wasn't concerned about maintaining a vacuum long term. Just long enough to complete some task or run some experiment. Of course diffusion through the foil wrapper would be a problem with storage of the lithium before use. I guess that explains the heat activated getters...
[spidermother] I like the idea of your cheaper method. But then thought: wouldn't all the moisture turn to water vapor, reducing the vacuum? Then I checked the vapor pressure of water at 25C. That's 0.03 atmospheres: not quite as good as I was theoretically aiming for, but reasonably close.
With that in mind, rather than trying to get oxygen to flush the chamber, just flush it with steam, cap it and let it cool. Throw it in the freezer (-18C) to get it down to 0.0012 atmospheres assuming the temperature and fogged glass don't mess with the experiment you're trying to perform. ... Which I see after a quick google is a widely used method of demonstrating vacuum ...
Thanks for the feedback!-- scad mientist, Nov 18 2020 If you add the right amount of water to the iron, it ends up as water of hydration; the water is chemically bound to the iron oxide, so it doesn't end up as water vapour. In theory.
I wouldn't delete it. Your idea is to chemical vacuums as those coffee machine single packs are to coffee.-- spidermother, Nov 18 2020 As in "More expensive on a per-unit basis, ties you to a specific supplier, more environmentally damaging, and the result is no better than existing methods" ?
// [8th] Thanks //
There's no need to thank us; we welcome the opportunity to expose your pitiful ignorance to the world. Don't hesitate to ask us if you feel in need of a further bout of gratuitous denigration and public humiliation.
// Since this is WKTE do I need to MFD? //
We ddn't MFD it as it's the equivalent of a corpse hanging in a gibbet-cage; a horrible warning to onlookers, and something tasty for the crows to peck at...-- 8th of 7, Nov 18 2020 //lithium hypochlorite, there's a world-wide shortage of it now for pools and spas.//
I wonder why the cation matters? I can't see why sodium, potassium, calcium or magnesium wouldn't work just fine? Potassium might be expensive and Calcium might give some precipitation issues in hard water, but that could be dealt with using EDTA.
It's a shame H2O2 isn't cheaper, that's a great disinfectant and has the good manners to disappear discretely after a short while.
//There's no need to thank us; we welcome the opportunity to expose your pitiful ignorance to the world.//
The problem is the sheer productivity of the ignorant vs hours in a day.-- bs0u0155, Nov 18 2020 "While there is clearly an upper limit to human intelligence, there is no such limit to human stupidity".-- 8th of 7, Nov 18 2020 >and should be done in a vacuum. - MFTagline
> Also, Lithium is very boring... That's what Boredom specialist and [["Why?"]] are for. (see link)-- pashute, Nov 18 2020 random, halfbakery