Sciencemadness Discussion Board - Suitable Flux for Calcium Metal Fusion

Suitable Flux for Calcium Metal Fusion

bfesser - 13-3-2009 at 13:17

I have calcium metal granules that I would like to melt into a small ingot. Does anyone have any suggestions of a good flux to prevent oxidation and to help remove oxides/nitrides/sulfides? Also, is there any special way in which I should prepare the flux compound (e.g. removal of water)?

I'm thinking that an inorganic salt would be best, but which? Maybe sodium borate?

I have plenty of Ca, so I'm not really concerned with wasting it on experimenting--I would just rather not have it react with the flux violently while heating it with a torch.

not_important - 13-3-2009 at 16:29

Try anhydrous CaCl2, as it is the electrolyte used for making calcium and some processes depended on it coating the calcium being withdrawn. Just dehydrate with heat, them fuse it before adding the calcium.

As magnesium reacts with boric oxide, heating borates and elemental calcium might be a bad idea.

UnintentionalChaos - 13-3-2009 at 16:34

I'd just pull a vacuum on the whole thing if you can or flood the vessel with inert gas. That's probably your best bet since the Ca metal will react with a lot of things and needs a flux that is molten at very low temperatures to avoid substantial oxidation before the flux even melts.

Quote:

Originally posted by not_important
Try anhydrous CaCl2, as it is the electrolyte used for making calcium and some processes depended on it coating the calcium being withdrawn. Just dehydrate with heat, them fuse it before adding the calcium.

As magnesium reacts with boric oxide, heating borates and elemental calcium might be a bad idea.

As above, it doesnt melt until very high temperatures. 772C whereas Ca melts at 842C. Also, Ca is somewhat soluble in molten CaCl2, which may cause issues later on.

[Edited on 3-13-09 by UnintentionalChaos]

[Edited on 3-13-09 by UnintentionalChaos]

bfesser - 13-3-2009 at 19:36

I'll give the CaCl2 a shot and report back with results. Thanks for the suggestions.

not_important - 13-3-2009 at 20:27

Add Na/K/Li chloride LiCl-KCl-CaCl2 has an eutectic melting at 425°C for example. There's tables of such around.

kclo4 - 13-3-2009 at 20:29

Isn't calcium chloride more dense then calcium? That might defeat the purpose.

bfesser - 15-3-2009 at 16:21

Results of my preliminary tests:

My calcium is in the forms of small (coarse sand sized) mixed granules--ranging from white and crusty, to dull dark grey spheres, to small silvery spheres and pieces.

1. I could not get CaCl2 to melt with my torch (micro butane).
2. Ca heated alone in an open test tube burns spectacularly! White-grey residue remains.
3. CaCl2 mixed with KCl melts nicely (just a scoop of calcium chloride dihydrate plus a scoop of potassium chloride--obviously not the lowest eutectic), but the Ca does simply float on top, then reacts.

I will try inert gas (Ar, He) when possible, but does anyone else have any suggestions in the mean time?

If anyone else would like to try contributing to this, I could perhaps mail small vials of calcium to a few people in the continental US. The vials would probably only be around 5 ml of impure granules, but it's better than starting from salts.

kclo4 - 15-3-2009 at 16:50

I'd just like to have Ca for the heck of it haha

Why not just cork the test tube or something, and prevent any further oxidation after the first bit of the Ca has reacted? To me it seems like you could perhaps get a small one way valve to fit into a cork and then only allow the air.. that will be building up pressure as heated, to leave.

Or for an inert atmosphere perhaps use propane, butane, or some other easily obtainable gas? I doubt those would react.. of course it would be dangerous but on a test tube scale you might be able to pull it off.. I don't know?

len1 - 15-3-2009 at 16:52

50ml of air say will react with

~ (0.05/27)*0.2*(40/32)=2mg of Ca

That is nothing compared to the impurities the Ca already contains.

So a reasonable approach is to high temperature seal (say braze or weld) a copper/iron tube full of Ca. Hold it at dull red heat with strong shaking for 1/2hr or so. Cut open + remove ingot at low temp. The surface tension of the Ca provided it was agitated violently enough should have coalesced it.