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Author: Subject: Low melting salt mixtures
Fulmen
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[*] posted on 12-7-2015 at 05:52
Low melting salt mixtures


I need appr 4kg of a low melting salt mixture for a tempering bath. I'd like to get below 200°C, which in it self isn't that hard, the challenge is availability of chemicals. Basically I have sodium and calcium nitrate, and assuming the reduction with lead works sodium nitrite as well.
I've been searching like mad, but most mixtures uses potassium nitrate and even more exotic salts like lithium. Does anybody have a good source for useful compositions?
One source claims 145°C for 50/50 NaNO3/NO2 while other sources say 220+, so it's hard to know where to start.




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[*] posted on 12-7-2015 at 08:02


Calcium nitrate tetrahydrate melts at around 40 oC, and loses water at 132 oC.



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[*] posted on 12-7-2015 at 08:29


Quote: Originally posted by DraconicAcid  
Calcium nitrate tetrahydrate melts at around 40 oC, and loses water at 132 oC.


It loses water and becomes a solid again. Which decomposes at ~500C before melting.

Have a look at this: http://www.crct.polymtl.ca/fact/documentation/FTsalt/FTsalt_...

A LiNO3/NaNO3 eutectic can get you to 195C. KNO3/NaNO3 eutectic will get you to 223C.

LiNO3/KNO3 is very low-melting at 125C.

Of course, LiNO3 is fairly expensive and that website doesn't have nitrites included.
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[*] posted on 12-7-2015 at 09:48


I have used the tin/bismuth eutectic (mp =139°C) but I needed less than a kg.



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[*] posted on 12-7-2015 at 14:39


To elaborate a bit, I need a annealing/tempering-bath that can operate in the <200-400+°C range for hardening and tempering steel. And as I need at least 2l (4-5kg in the case of nitrate salts) I need something cheap and available. The Bi/Pb/Sn-alloys are interesting, but the density would make steel float. And then there's the fact that I would need 20kg...

UC235: Wonderful source, but sadly it does not contain any useful candidates. Unfortunately I am completely out of KNO3, as most mixtures seems to rely on that. And KNO3 has become increasingly hard to get in recent years. I would prefer to avoid the nitrites as well (suspected carcinogenic and teratogenic), but compared to the dangers of hot molten salts I'm not sure if that is any real issue. And as I have both sodium nitrate and lead it is at least something I could make.

Best candidate so far is 46:24:30 K-Na-Ca nitrate with a listed mP of 160 C.




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[*] posted on 13-7-2015 at 23:51


I've been searching for low melting NaCl mixtures so I can make sodium metal and came across this excellent compilation of eutectic mixtures:

http://www.nist.gov/data/nsrds/NSRDS-NBS-61-1.pdf

There's a lot more nitrate mixtures that you could try.

AlCl3 mixtures also have very low melting points but getting the anhydrous salt is pretty hard. Putting Al in hydrochloric acid will produce the hydrate, which according to Wikipedia, cannot be heated to get the anhydride.

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[*] posted on 14-7-2015 at 02:02


Thank you sir, this was exactly what I was looking for.

I'm focusing on nitrates only as I know these are used for heat treatment. And I have been advised against chlorides by a metallurgist, and while he didn't give any detailed reasons I have no reason to doubt his expertise.

What I was hoping for was a Ca/Na NO3 mix below 200C, but no such luck. At 31 mol% it has a mp of 214C, which isn't that bad really.

Edit: Dang, I thought I found a good one at 154C, but that was with Ca(NO2)2. So 214°C it is, I can live with that as long as I don't have to make any chemicals.

[Edited on 14-7-15 by Fulmen]




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[*] posted on 14-7-2015 at 11:20


Huh! I threw together a quick test, but got nowhere. The mix was listed as Ca(NO3)2-NaNO3, 31 mol%, which I assumed was 31 m% NaNO3. Could it be 31% Ca?



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[*] posted on 14-7-2015 at 18:41


Generally the material with the highest concentration is listed first. So most likely sodium is 31%.



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[*] posted on 21-7-2015 at 17:59


http://www.sciencemadness.org/talk/viewthread.php?tid=10529#...



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[*] posted on 22-7-2015 at 00:59


Thank you, I'll have a look and see if there is anything useful there as well.



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[*] posted on 22-7-2015 at 12:34


I took a look at that PDF and it seems the first concentration is for the first of the two components. For example the concentration of #86 is listed as 8.1-87.6-4.3. You need 31% Ca(NO3)2.



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[*] posted on 22-7-2015 at 13:36


Quote: Originally posted by franklyn  
http://www.sciencemadness.org/talk/viewthread.php?tid=10529#...

Now there is a Franklyn that i respect. Nice one.




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[*] posted on 22-7-2015 at 15:27


Quote:
Chlorine trifluoride should be officially designated "liquid fire"

I just looked that up, and fail to see how it exists.

F and Cl each have 7 electrons in their outers, so are looking for just 1.

Surely F & Cl should form FCl and be rather pleased with themselves.

How does it get to ClF3 ?

[Edited on 22-7-2015 by aga]




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[*] posted on 22-7-2015 at 16:06


Fluorine is so electronegative, it even forms ClF5!

https://en.wikipedia.org/wiki/Chlorine_pentafluoride




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[*] posted on 22-7-2015 at 16:41


Quote: Originally posted by aga  

How does it get to ClF3 ?



Much in the same way the other +1, +3, +5 and +7 Oxidation Number chlorine compounds exist: see hypochlorites, chlorates and perchlorates.

[Edited on 23-7-2015 by blogfast25]




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[*] posted on 23-7-2015 at 09:49


Albino Moose: Logic dictates it has to be either one or the other, right? I'll try the reverse proportions when I feel like working again.



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[*] posted on 23-7-2015 at 15:37


Fulmen, what part of the world are you in?

Are you heat treating steel tooling, knives, or ??? Any particular alloys and profiles you could disclose?

There's over 500lb. of Potassium nitrate, plus good quantities of all the other common nitrates on site here, and one of my crew is an amateur blacksmith.




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[*] posted on 23-7-2015 at 18:58


Here's a useful table for mixed nitrates eutectics made anhydrous by heating

http://www.sciencemadness.org/talk/viewthread.php?tid=4457&a...


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[*] posted on 23-7-2015 at 21:09


That Ca/NH4/Na nitrate 18/69/13 eutectic mixture melting @ 107 C. sounds quite interesting for other things than an annealing bath... Given that pyrotechnic reactions tend to start in earnest at the temperature where the oxidizer becomes molten .

Unfortunately, it would likely be rather hygroscopic.




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[*] posted on 24-7-2015 at 14:15


This project must be put on hold for now, most of my access to proper tooling is gone so I might not work too much on machining. But I'll keep it alive on the back burner, scouting for what I need.

[Edited on 24-7-15 by Fulmen]




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[*] posted on 24-7-2015 at 14:47


Quote: Originally posted by Bert  
Unfortunately, it would likely be rather hygroscopic.

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[*] posted on 25-7-2015 at 03:25


Eutectic nitrates sounds like a good way to improve casting properties of sugar propellants. The K/HN4-mix is especially interesting if it improves burn rate over straight NH4, although I have seen tests (20 years ago) that showed signs of reaction with the fuel when molten (liberation of gas). Don't remember which fuel they tested though, could have been charcoal.



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[*] posted on 25-7-2015 at 03:42


59 wt. KOH and 41 wt. % NaOH eutectic at 170°C. See US 20050072837 A1 patent application for this and others. HIGHLY dangerous of course!



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[*] posted on 20-8-2015 at 08:01


In my "chemistry tables" book I've found the following compositions, none of them being nitrates:

50% ZnCl2 + 50% KCl m.p=.230C

60% ZnCl2 + 20% NaCl + 20% KCl m.p.=203C

67% AlCl3 + 33% KCl m.p.=128C

And finally unbelievable:

60% AlCl3 + 26% NaCl + 14% KCl m.p.=94C (!)

I assume zinc and aluminium chlorides are not hydrates here.

Note that anhydrous zinc and aluminium chlorides cannot be prepared with aqueous HCl!
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