Sciencemadness Discussion Board

heating media's for heat bath ?!

avi66 - 18-6-2010 at 23:59

there are chemical process's which i got to reach high temperature as 290c, and apply them on my vacuum system.... so i cant use direct heat source(i could make thermal cracking on my glass vessels).
i was looking for a readily available chemical to melt in my steel pot and allow me transfer the heat to my system, i already try calcium chloride mono hydrate, this chemical loose his lest water molecule under 290 Celsius and become solid.
i was looking in wikipedia for month to find a good salt and cheap which allow me to do this, and i field !!!
so if someone know a material which melts in 200->350c +- ,easy to get, and friendly to steel and glass, please write it here.

not_important - 19-6-2010 at 00:44

Mixed alkali metal nitrates and nitrites are the old standards, as are sand or small metal (steel) shot, and low melting point alloys. A mix of 53% KNO3, 7% NaNO3, and 40% LiNO3 is used over the range of 150 to 450 C. Silicon oils can be used up to ~300 C, but are expensive.

Eclectic - 19-6-2010 at 07:23

Mg(NO3)2, KNO3, NaNO3 mixture is good too...not sure of exact proportions

oh...KNO3, NaNO2 is old standby for metal heat treating...

[Edited on 6-19-2010 by Eclectic]

avi66 - 19-6-2010 at 09:11

i don't have access to lithium .... the 150 to 450 range is perfect, someone know similar mixture which allot me to work in those temperatures ?!?! the mixture don't corrode my steel pot?

Picric-A - 21-6-2010 at 15:00

I would be scared of dropping anythign organic in that molten nitrate/ite bath! :O
How about wax? you can buy high m.p/b.p. wax for such purposes.

not_important - 21-6-2010 at 17:10

Waxes generally don't go above 250 C, most are limited to below 200 C.

Nitrate baths are used because they have reasonable low melting points and are compatible with many ferrous alloys. Alkali hydroxides have lower melting points, but absorb water and CO2 from the air, and needless to say are hard on skin and many fabrics. Chlorides either have too high a melting point, or react with moisture; chlorides and ferrous metals don't get along well especially if they are exposed to air.

From Vogel:
Quote:
A satisfactory bath suitable for temperatures up to about 250° may be prepared by mixing four parts by weight of 85 per cent, ortho-phosphoric acid and one part by weight of meta-phosphoric acid; the mixed components should first be heated slowly to 260° and held at this temperature until evolution of steam and vapours has ceased. This bath is liquid at room temperatures. For temperatures up to 340°, a mixture of two parts of 85 per cent, ortho-phosphoric acid and one part of meta-phosphoric acid may be used : this is solid (or very viscous) at about 20°.


Ordinary phosphoric acid can be used if you first heat it with stirring to about 20 C higher than the intended temperature of use, it partially dehydrates to polyphosphoric acids.

Molten metal baths are another choice, Wood's metal being the classic but because of its cadmium content it presents fume toxicity problems.


50/50 In/Sn 118-125 C

58/42 Bi/Sn 138 C

In 157 C

63/37 Sn/Pb 183 C

Sn 231.8 C

Pb 327.5 C



Metal baths generally are bothersome to work with, with some alloys the oxide film can reach with the glassware, slowly damaging it over many uses. Salt baths are much easier to clean up after, because of their water solubility. Often glassware was coated with soot or graphite before being placed in a metal bath, this lower the amount of metal and oxides sticking to the glass. Both metal and salt baths need to be melted before the flask can be placed in them, and when done you'd best remove the flask while the bath is still liquid.


There's a handy discussion at http://www.ilpi.com/inorganic/glassware/heatsources.html including 2 salt mixes - one K/Na NO3 and the other those plus NaNO2



heating_baths.png - 21kB

watson.fawkes - 21-6-2010 at 20:10

Quote: Originally posted by not_important  
Molten metal baths are another choice, Wood's metal being the classic but because of its cadmium content it presents fume toxicity problems.
RotoMetals has a selection of low melting point alloys, many of which don't have cadmium (although most of the lower-melting ones do). In addition to cadmium, they're various alloys of bismuth, lead, tin, and indium, and in one case, antimony.

As a small digression, the antimony bearing one is an equivalent to Indalloy 217-440. The numbers are temperature in Fahrenheit. It's a non-eutectic, and these numbers are the solidus and liquidus temperatures. I mention this as interesting because that temperature range seems remarkably large. It's evidently used for fixtures in machines, as it expands almost half a percent a day after solidifying. So don't let it harden around your glass.

CouchHatter - 26-3-2020 at 15:10

Could someone explain why the "useful up to __°C" metric is roughly half of the compounds' boiling points? Diphenyl can be used right up to its bp.

I have lots of glycerol and wonder about using it at slightly higher temperatures. I know it won't blow up or anything, but I'm curious how they arrived at the specific temperatures.

wg48temp9 - 26-3-2020 at 16:37

I would use a material that in the event that the flask fails its contents does not react violently with the material. For example organics and molten nitrates are probably very bad. As almost 300C and vacuum is beyond the recommended operating conditions for a borosilicate flask its got a higher chance of failing.

Consider using molten tin.

DavidJR - 26-3-2020 at 16:48

The eutectic mixture of biphenyl and diphenyl ether (aka Dowtherm A) is apparently a useful heat transfer medium usable at high temps.

Attachment: preprints201806.0048.v1.pdf (1.1MB)
This file has been downloaded 562 times

Sulaiman - 26-3-2020 at 20:03

Heating mantles are usable to 450oC

You could also wind-your-own nichrome or kanthal heating coil directly on the pot (with e.g. fibreglass insulation layers)

Also, AFAIK hot phosphoric acid is not compatible with borosilicate glass,
and may also corrode steel (despite the phosphate passivation layer.

rockyit98 - 26-3-2020 at 21:30

what you need is "sand" bath with instead of sand try using sand sized aluminium grains. you can look for them in local metal working shops they have Metal swarf from from machining.they even give them for free.because of Al much higher thermal conductivity so much better than sand or a liquid that can spill allover .i use this set up to make con.H2SO4 .

yobbo II - 9-4-2020 at 16:20


Could brake fluid be used?

unionised - 10-4-2020 at 05:22

At a pinch, you can use cooking oil.
https://en.wikipedia.org/wiki/Smoke_point
or engine oil
https://en.wikipedia.org/wiki/Motor_oil

[Edited on 10-4-20 by unionised]

S.C. Wack - 10-4-2020 at 10:07

Quote: Originally posted by CouchHatter  
Could someone explain why the "useful up to __°C" metric is roughly half of the compounds' boiling points? Diphenyl can be used right up to its bp.

I have lots of glycerol and wonder about using it at slightly higher temperatures. I know it won't blow up or anything, but I'm curious how they arrived at the specific temperatures.


Short answer: Vogel 5th ed. starting on page 71; or give it a try, you'll see.

Refinery - 15-5-2020 at 13:12

I was wondering of using nuts and shims that are sold at hardware store for like 5 bucks a kg. Find the smallest one, like 4mm and so on, and get a kg or two and use them as steel heating bath?

Actually.. Could one use these to form a sort of heating mantle pit?

Or would it be a potential for catastrophy to go so far as to cast half-sphere from aluminum that is about the size of a flask?

EDIT: Oh, if anyone wouldn't have thought it already. How about this?

https://www.amazon.com/Chemglass-CG-1992-54-Anodized-Aluminu...

[Edited on 15-5-2020 by Refinery]

Fulmen - 15-5-2020 at 13:55

According to simple physics the most important factor should be bulk thermal conductivity. Low conductivity would cause more delay and thermal losses, but it won't stop heat from flowing.

Refinery - 17-5-2020 at 10:19

I recently formed lead shots by pouring molten lead through a sieve.

Could aluminum be formed the same way? Small Al shots would form a great heating bath.

mackolol - 17-5-2020 at 11:59

You can use Wood's alloy or various metal low-melting alloys, but it's more as a possibility, as it is quite expensive.

Mateo_swe - 6-6-2020 at 21:20

Wouldnt buying a heating mantle be easier and less work?
You could buy these cheap replacement heating mantle sleeves and use them if you have a powersupply or a variac to control the power.
I have ordered some of those and plan to control them with a PID Temperature Controller, a solid state relay and a thermocouple.
Only thing is they dont have stirring, but that is quite easily made with a fanmotor and a magnet.
Is there any applications where a bath would be preferred over a heating mantle (except with low temps and sensitive materials as for example distilling ether)?