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evil_lurker
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Suggestions for high temp oil bath?
Looking for some type of oil that will withstand at least 210C without decomposition or smoking.
Was considering using DOT 4 brake fluid which is rated as having a minimumm 230C boiling point.
Suggestions?
[Edited on 16-7-2006 by evil_lurker]
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12AX7
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Heh, at work we have some silicone oil hot pots. Some are frosty, some are room temp, and some are hot enough to do soldering (the thermostat says
500°F, or 260°C).
For hydrocarbons, *shrug*...
Tim
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chromium
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There are special oils for this purpose. I have no idea where to get them.
Other than that: Glycerine to 200C, saturated solution of CaCl2 (aprox 3 parts salt and 1 part water) to 178C. Ethylene glycol to 190C.
Woods metal Rose metal and other low melting alloys to 300C (and more if fume hood is used).
Eutectic mixture of potassium nitrate and sodium nitrate (aprox 1:1), mp 219C, can be used from 230 to 500C. This is what quick search from books
gave. I have no experience with any of these.
Whatever you use you should be very careful because even small amount of water causes powerful steam explosion if it gets in contact with so hot
liquid (at least in case of oil bath).
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Magpie
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I have a bottle of NAPA silicone DOT 5 brake fluid that I use for determination of melting points. Its listed boiling point is 289C.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Mr. Wizard
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Something to keep in mind about hot baths and 'boiling points' is that the boiling point is just when the vapor pressure of the liquid reaches
atmospheric 760 mm. Many liquids can be giving off a significant vapor long before the actual boiling point is reached. Think about the toxicity of
the chemical you are using. A well known example of such a liquid you shouldn't use is Mercury  . I'm sure you can think of others. For very high temperature baths consider molten tin.
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12AX7
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Ah yes, tin boils at a very high temperature- it's a good candidate. Lead too boils at a rather high temperature, and an alloy of them melts somewhat
lower, I recall something like 330°F, whatever that is in C.
Tim
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DeAdFX
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I recall reading that sand works ok but takes forever to eat and cool.
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evil_lurker
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That DOT 5 brake fluid is probably gonna be the solution, but goshdammit, they will absolutely KILL your wallet when it comes time to check out.
I may just have to go bite the bullet and pick some up this afternoon.
I just hope my hot plate can take a 1 liter flask in an oil bath up to 200C... I know it will take a 3 liter in an oil bath up to 140C...
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unionised
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Sunflower oil?
http://www.answers.com/topic/smoke-point
Certainly cheaper than most of the alternatives and you can fry your lunch in it too.
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chromium
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I once tested boiling point of cheap cooking oil. This was Risso brand and based on rapeseed oil. It boiled at 390C! There was some smoke and bad
smell around but no burning or noticeable decomposition. (I was very surprised and did some additional tests to be sure that thermometer does not lie)
Experiment was carried out in test tube and i am not sure what happens if it is heated in bath were there is lot of oxygen around especially if this
lasts long.
I did not recall this before reading what unionised wrote.
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Mr. Wizard
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Be careful with the hot combustible food oils. A pot full of hot oil on fire might just as well be burning kerosine. The flames will be just as hot,
and it will often re-ignite even if covered to extinguish a fire. You won't be able to move it for fear of splashing, and if you put limited water on
it it will foam and make an even bigger fire. It will ruin your day and your house. If you have a liter or two of smoking cooking oil you are very
close to a serious problem. For example common Corn Oil gives off enough flammable vapors to flash (flash point) at 490F and will auto ignite at 740F,
Cottonseed Oil will auto ignite at 650F. Soybean oil will not auto ignite until 833F. Kerosine auto ignites at 444F. People are often surprised at the
fact that oils and fuel oil will often ignite at a lower temperature than gasoline (about 900F depending on octane).
Flashpoint = temp at which material will give off enough vapor in air to flash when provided with an ignition source, such as a spark. Example
gasoline 100 octane is -35F
Ignition temperature= temperature when the material will catch fire in air without an additional heat source. Example gasoline 100 octane 853F
Don't confuse volatility with ease of ignition.
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chromium
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| Quote: | Originally posted by Mr. Wizard
You won't be able to move it for fear of splashing, and if you put limited water on it it will foam and make an even bigger fire.
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Hot oil will almost explode if in contact with water. No mater its burning or not. It will be spreaded over entire room within fraction of second. I
have seen this.
Covering it with fireproof cloth, perfectly dry sand or Na2CO3 my work.
In my opinion oil bath is dangerous anyway. In my not-too-well equiped lab i use it only for heating test tubes or small flasks. No more than 100ml
oil used at time.
[Edited on 16-7-2006 by chromium]
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Fleaker
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It will definitely stink up the laboratory. Of course, as I'm sure you know, you should *not* use it to flasks for distilling oxidizing agents (i.e.
nitric acid) because if the flask should crack, you will likely regret it. As mentioned before, silicone oils will probably be the way to go, but yes,
it will be a hard time for your wallet. Just think of the lack of stench and the reliability  as you fork over the cash.
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BromicAcid
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Use mineral oil, I've used it to very high temperatures. There are many MSDS's rolling around for it stating different temperatures but it is readily
avalible and they are all fairly high at least.
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Fleaker
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I tried using mineral oil as a cover for molten bismuth (circa 515F/268C) and it caught on fire.
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Twospoons
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I was under the impression that brake fluid was quite toxic, even when cold.
In my kitchen I have a can of rice bran oil that claims a smoke point of 260C. I can certainly get a pan of it searing hot without noticeable
decomposition.
Helicopter: "helico" -> spiral, "pter" -> with wings
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evil_lurker
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I got some Havoline synthetic brake fluid with a purported boiling point of 500F.
It started smoking badly around 120C and the distillation I was working on was aborted out of safety concerns.
I should have my vacuum pump I ordered last week in the next few days. I'm hoping that will cure my problems.
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neutrino
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>I tried using mineral oil as a cover for molten bismuth (circa 515F/268C) and it caught on fire.
I tried using it for the same purpose and it smoked heavily. I suggest avoiding mineral oil altogether.
I've melted Bi under corn oil many times without a problem. It does tend to smell a little at high temperatures, so be prepared.
Don't heat it much hotter than this because it will decompose and fill your lab with a nasty stench. Also, corn oil residue oxidized at high
temperatures is next to impossible to clean off glass. Think ajax powder + steel wool + very heavy pressure concentrated down to a tiny point. Not
impossible, but your joints will hurt afterwards.
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unionised
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I know the difference between flash points, autoignition temperatures, and smoke points. Ideally you want to be below any of them. If you can afford
that much gallium lucky you, the rest of us trade toxicity, volatillity, price and flammability against each other. Cooking oil (especially the fully
hydrogenated sort that nobody uses because it is unhealthy) works quite well.
Whatever is in the flask you are heating is probably flammable too.
The sugestion I gave was from a very old textbook- it lists arachlor as a suitable high temp bath- which says that lard is good to 250C. So's
glycerine but you need to keep it dry which is a problem. I think that may have been the problem in that havoline fluid.
Burned-on fats tend to come off better with NaOH than with scrubbing in my experience.
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evil_lurker
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This morning at my local dollar store I found some extra heavy mineral oil... this stuff should be sufficiant to meet my needs... going to find out in
a bit.
Edited to add:
The stuff worked. I conducted a distillation of a material boiling at 180C using $4 worth of laxative. 
Who would of thunk it?
[Edited on 18-7-2006 by evil_lurker]
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Flip
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The most convienent answer is Peanut oil from the grocery store... just make sure that you're not allergic to peanuts. You'll smell it, but it won't
be overpowering.
Hmmmm... that gives me an idea... with the right high boiling fragranced oil you might turn your heating bath into a giant Glade Plug-In.
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Fyndium
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I happened to waste a load of money into silicone oil, which is quite watery and it starts smoking pretty much point on 150C, although the packaging
states it is stable from -35 to 200C. I heated it up to 200C and while it appears very stable itself, it just gives out significant amount of smoke.
I'm gonna keep it hot for a while and see if it stops smoking by getting rid of the more volatile compounds in it, but we'll see. I've been simmering
the oil at 170-180C for an hour now and the smoking has dissipated significantly.
The fact is, CaCl2 bath is still by far my favorite and it is very stable up to 160C, but it will very quickly turn into crust when heated over that,
and last reading I was able to get was 170 something, and over half of it was just solidified and appeared like calcium chloride anhydrite looks like
when got out of the oven. This surface layer insulates the bottom though, which remained liquid till the end, but with very narrow play there might be
issue of running dry or hotspots or something else, so I consider 160 in the very high end of it. Below that, it works like charm though, remaining
fully liquid and stable even for hours and it gives zero odor or fumes and is cheap as dirt.
My problem lies right on that area between 160C and 220C. I just gave a though for sand bath, because I might need higher temp for now only for
distilling sulfuric acid under vacuum (180-200C bath temp req), and a couple of high temp reactions which want about 160-170C of heat. Glycerin is
another shot, but I wouldn't like to buy EVERY single compound around just to test it out and fail.
Paraffin oil, the crystal clear ntp liquid form sold in g stores as baby oil, wood treatment(ikea also) etc is stable up to 150+ and then it starts to
faintly smoke and kept doing that up to 175C when I stopped heating. It also has the paraffinous smell, which I find pleasant, buy someone might not.
[Edited on 11-9-2020 by Fyndium]
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Heptylene
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Has anyone tried vacuum pump oil? The vapor pressure is low by design:
< 1e-8 atm at room temperature
< 1e-6 atm at pump operating temperature, which can be around 80 °C.
Indeed, hot pump oil has no smell!
The flash point is incredibly high, which is important for an oil bath. One example: Leybold LVO100, which is a general purpose oil, has a flash point
above 255 °C according to Leybold. All pump manufacturers have similar general purpose oils (Edwards makes "Ultragrade 19", etc.)
Anyway I'd be interested to hear if anyone has used this.
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Sulaiman
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Given the cost and/or hazards of all of the oils mentioned above,
it would probably be cheaper/safer/easier to buy or diy a heating mantle.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Fyndium
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I was just looking for a one. Considered ordering a MESE mantle but after seeing negative rant about their hotplates just not heating and stirrers
jamming I'll look into elsewhere.
Main issue with mantles seem to be their size sensitivity. I have rather wide range of flasks, generally 0.5L, 1L, 2L and 4L which I routinely heat
depending on case so I would still need the bath. Otherwise, if it would be used only for high temp ops, I could probably do with 1L.
For the record, I've been heating the silicone oil now for several hours at 160C and it has pretty much stopped smoking. It can only be seen with a
strong flashlight when other lights are shut.
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