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JJay
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Metal Shot Heating Bath
I have made a couple of attempts at creating a heating mantle and have so far been unsuccessful. So I was wondering what kind of metal shot might make
a good heating bath. Copper has some attractive properties but is pretty expensive.... Would steel BBs make a good heating bath for use with
mechanical stirring, or are they too large/not conductive enough? Also, what cheap and readily available shot might work well with magnetic stirring?
[Edited on 28-1-2016 by JJay]
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DutchChemistryBox
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http://www.labarmor.com/lab-armor-beads-for-lab-water-baths/
I use those, you can request a free sample. If you ask a friend to request a second sample then you have more then enough for home use.
[Edited on 28-1-2016 by DutchChemistryBox]
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JJay
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"Starting at $1399" - I think I would definitely have to try a sample before making that purchase.
Their beads look quite a bit larger than BBs. So I guess BBs would probably work for thermal transfer, although they would tend to shift/roll around
more than beads.
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Sulaiman
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Also note that those beads are rated for -80 to +180 celcius.
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MrHomeScientist
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Those are extremely expensive for just being aluminum shot. I'd like to try making some by pouring molten aluminum into water. Would be a hell of a
lot cheaper, if you have a furnace. I built one out of an old charcoal chimney and hair dryer.
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careysub
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There have been a couple of threads on this recently, which I believe you read.
There are cheaper aluminum shot/pellet sources than LabArmor:
http://www.sciencemadness.org/talk/viewthread.php?tid=64259
http://www.sciencemadness.org/talk/viewthread.php?tid=64841
Look up the vendor "handi-ramp510" on eBay: 10 lb of aluminum for $50.
Aluminum conducts heat 5 times better than steel, and is 1/3 the weight.
There is also copper metal powder on eBay $52 for 4 lb (or $120 for 10 lb). Copper conducts twice as well as aluminum (but is also 3 times denser).
Prices:
Lab Armor beads: $100/Liter
handi-ramp510 pellets: $23/Liter
Copper powder: $178/Liter
I was just looking at a chem lab handbook about "metal baths" - molten low mp bismuth-lead alloys. The really low mp alloys all either have cadmium in
them, which would make me wary of cadmium fumes, or indium which is really expensive.
Rose's metal with an mp of 98 C/208 F is the lowest mp alloy with neither cadmium or indium and is $340/Liter from Rotometals (its density is 9.7).
It occurs to me that combining the aluminum pellets with the copper powder might make a good substitute to using a liquid metal bath. The
super-efficient conducting copper powder would fill the pellet void giving a boost to thermal conductivity in two ways.
Maximum random packing density for spheres is 64%. A mix of pellets and powder would be something like 60% aluminum pellets (assuming the squat
cylinder pellets don't pack quite as tightly), 40% copper powder (copper powder is not solid, so it is something like 30% copper metal and 10% air).
This would make a dry bath costing $85/Liter, with a density of 4.3.
BTW - I don't think "shifting" is a problem with a bath. You would presumably clamp your flask in place, then pour in the bath beads.
[Edited on 28-1-2016 by careysub]
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MrHomeScientist
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A molten metal bath is an interesting idea. I've made some low-melting alloys (one liquid at room temperature, which I have a video on) so this would
be cool to try. The problem, at least with alloys I've made, is that they usually wet glass. It seems like gallium is the culprit there, and possibly
indium. So if your requirements allow you to use an alloy without these metals, it might not stick so much.
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JJay
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I've considered using zinc pennies, but I'm concerned that they might melt on the hotplate.
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XeonTheMGPony
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IMO being a one time investement with high resale value I'd just go with course copper my self (What I'll be doing personaly)
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careysub
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Quote: Originally posted by MrHomeScientist  | | A molten metal bath is an interesting idea. I've made some low-melting alloys (one liquid at room temperature, which I have a video on) so this would
be cool to try. The problem, at least with alloys I've made, is that they usually wet glass. It seems like gallium is the culprit there, and possibly
indium. So if your requirements allow you to use an alloy without these metals, it might not stick so much. |
I forgot to mention, the lab manual prescribed coating the flask with graphite to prevent metal from adhering.
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XeonTheMGPony
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IMO being a one time investement with high resale value I'd just go with course copper my self (What I'll be doing personaly)
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JJay
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Copper pennies contain more than one cent worth of copper, but who has time to gather enough to fill a bath?
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The Volatile Chemist
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| Quote: Originally posted by MrHomeScientist | | A molten metal bath is an interesting idea. I've made some low-melting alloys (one liquid at room temperature, which I have a video on) so this would
be cool to try. The problem, at least with alloys I've made, is that they usually wet glass. It seems like gallium is the culprit there, and possibly
indium. So if your requirements allow you to use an alloy without these metals, it might not stick so much. |
One could always use a container other than glass. Of course the cheapest alternative would be metal. Do gallium alloys alloy with metals like
iron/steel when hot?
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chemrox
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I would suggest using an electric lead melting pot with woods metal. Woods metal is a time honored mixture for heating glassware to high temperatures
but be careful. I destroyed a heating mantle and warped a flask running an exothermic reaction. Check the thread on oil baths and consider sand.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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JJay
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Apparently there are still lots of copper pennies. I am told that coin collectors regularly buy $25 boxes of pennies from banks. A few hundred copper
pennies weighs a kilogram.... It just might be worth sorting through enough pennies to make a copper bath.
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Herr Haber
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I once had this idea and went to my local armory to get some copper BB's.
If I remember correctly, they cold me they were only copper coated so they would eventually melt.
Instead, they suggested I go find an armory that sells non lead shot (steel) because of ecological reasons many people are fighting against the use of
lead.
I never pursued the idea, using ultra fine and pure sand from a quarry I have nearby but I guess different sizes of bird shot would provide good
thermal conductivity and be a lot easier to cleanup.
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JJay
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BBs are usually steel with a copper, zinc, or stainless coating.
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JJay
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I decided to go with copper pennies. I can get $20 worth/day from a local credit union, and about 20% are copper. This is around 300 ml of pennies at
around 1200 grams from $20 worth of pennies. Sorting them takes time, so I do it while running distillations.
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careysub
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| Quote: Originally posted by JJay | | I decided to go with copper pennies. I can get $20 worth/day from a local credit union, and about 20% are copper. This is around 300 ml of pennies at
around 1200 grams from $20 worth of pennies. Sorting them takes time, so I do it while running distillations. |
How big a fraction of copper pennies are you finding?
1982 minted both zinc and copper, are you sorting these by weight (though a few zinc in the mix is not exactly a disaster). (There are also rare 1983
pennies accidentally minted in copper!)
If you are buying pennies for this purpose presorted copper pennies are available from eBay.
When I did this from a relative's coin hoard I use a 0.1 g scale to sort the 1982, but found the situation a little more ambiguous than you might
think. The minimum weight of a copper cent (new) is 2.98 g The maximum weight of a zinc cent is 2.60 g, And I found an even wider variation from wear
(on the one hand) and oxidation (and possible other deposits) driving the weight up. Dropping the coin on tile helped in some cases.
I found about 1/3 copper but I think the hoard may have selectively enriched in copper.
Not that this is of great import, but it should be noted that the thermal conductivity of the copper penny alloy (5% zinc, some tin) is only about 2/3
that of electrolytic/tough pitch copper (the nearly pure copper used in industry) .
[Edited on 14-2-2016 by careysub]
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XeonTheMGPony
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Seeing those pennies you'd be better off with the bb's
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JJay
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How so? The major problem with BBs is that they won't work with magnetic stirring.
I set aside the 1982 pennies and weighed them later. Zinc could cause problems at high temperatures, but it doesn't have to be a huge concern.
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subsecret
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How about copper turnings/filings? They're a little expensive, though.
Take solid copper wire, and cut it into segments The smaller the better.
http://www.ebay.com/itm/PURE-COPPER-FILINGS-6-LB-BULK-BOX-GR...
Fear is what you get when caution wasn't enough.
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JJay
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$10 per pound for copper is just outrageous.
I have seen penny sorting machines, but the ones that are ready to use out of the box aren't cheap.
I am still not exactly sure about zinc pennies that may have accidentally gotten mixed in.... Perhaps heating to 700 C and looking for molten blobs
and destroying them with acid....
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XeonTheMGPony
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heat distrobution and contact area the penny's contact area seems hidious., if you could grind them then that would be better but as flat discs.....
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JJay
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I'll try some stress tests.
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