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ampakine
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Registered: 04/23/11
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DIY variable oil bath (chemistry heat source)
#14337057 - 04/23/11 04:27 AM (12 years, 9 months ago) |
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Heres what I'm thinking. I take the heating element out of a kettle use it as the heat source to heat up oil in a metal pot. To control the temperature I'll connect a potentiometer up to the heating element. To control the temperature even more I'll hook a thermostat up to the circuit so that it will cut off the power source if the temperature of the oil goes above whatever I set it to. Thats pretty much all there is to the electronic circuit for this device.
As for the design of the whole thing I'm thinking I can cut a hole through the bottom of the metal pot so and inserting the heating element through it then I'll epoxy any gaps. Then I'll attach the pot on top of some kinda sturdy, heat resistant plastic casing that'll hold the thermostat and the transformer from the kettle. I'll cut out a hole in the front of the casing for the potentiometer and glue a plastic dial to it. Beside that dial I'll cut out a space for the digital thermostat. Then at the back of the case I'll cut out a hole for the power cord. This is gonna look real slick
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Flashmob
something something dark side
Registered: 04/20/11
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Re: DIY variable oil bath (chemistry heat source) [Re: ampakine]
#14338276 - 04/23/11 12:35 PM (12 years, 9 months ago) |
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I have a distillation running right now 7 feet away. I've done lots and Lots of chemistry. I much prefer a sand bath. Head to the playground and get a bucket of clean sand rinse it well and dry it. For the heating, when I kill one I go garage sale hunting for a new metal crock pot, deep fryer or steamer (or cheap from walmart). They already have the necessary heat controls built right in, a measure of electrical safety and are built to handle the heat. As well they are all waterproof, having the element mounted outside the pot, either under or around the steel inner lining.
Oil will bite you in the end. It degrades with every use and will start to smell and smoke after a dozen or so uses at high temp. A hot rbf slipping out of your hands from split oil is a sure way to ruin the day. Sand isn't temperature limited your glassware will be slumping from the heat before you hit the highs with it. It has excellent thermal mass and my favourite... When bumping occurs in other mediums your whole assembly trembles regardless of how many stands and clamps your have, which is no good for the joins on necks and bends. Sand maintains a very positive grip on things buried in it, bumps are heard but not seen in any way.
I applaud your idea of DIY chemistry lord knows I do it myself constantly. I know of no epoxies, including high temp aircraft grade that will handle much above 200C. Your way is asking for a failure at your most vulnerable point, right as everything is in the extreme danger zone. One final note don't use a potentiometer for your power source it's going to get murderously hot from the kinda amperage that a kettle element takes >1000 Watts. Take apart a stove and use the burner controls. They utilize an internal switch that is all or none, switching the duty cycle based on what you select. Throttling the kinda energies were talking about takes a variac or the above.
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ampakine
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Re: DIY variable oil bath (chemistry heat source) [Re: Flashmob]
#14339789 - 04/23/11 05:52 PM (12 years, 9 months ago) |
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This is the first time I heard of a crock pot, if I knew about these I would have been using them years ago I have a hot plate + magnetic stirrer but I like improvising things so I decided to see what kinda heat sources I can improvise. Yeah I'm not a big fan of oil myself either. A few weeks ago I had a bit of an incident where I accidentally let some polar solvent get superheated and when the magnetic stir rod got unjammed the RB flask regurgitated the hot polar solvent most of it landing in the oil bath. As you can imagine things got a bit messy. Amazed I escaped all that without any 3rd degree burns lol. Sand actually bumps? I smashed a ceramic egg cup and used the pieces as boiling chips for my oil baths. They work well, nice small streams of bubbles form on them. I'm definitely gonna switch to sand cuz it has basically none of the dangers associated with oil.
Yeah I had a feeling epoxy would melt at those temperatures. I'd have to do some research to find a suitable material. Thanks for the info on potentiometers. Wont have to learn that one the hard way now.
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Prisoner#1
Even Dumber ThanAdvertized!


Registered: 01/22/03
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Re: DIY variable oil bath (chemistry heat source) [Re: Flashmob]
#14341091 - 04/23/11 10:43 PM (12 years, 9 months ago) |
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Quote:
Flashmob said: I know of no epoxies, including high temp aircraft grade that will handle much above 200C.
there's high temperature epoxies, some up to 400c, maybe higher. even JB Weld can handle temps around 320c for around 10 minutes, temps in the 200c range for weeks
http://www.cotronics.com/vo/cotr/
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Flashmob
something something dark side

Registered: 04/20/11
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Re: DIY variable oil bath (chemistry heat source) [Re: Prisoner#1]
#14341866 - 04/24/11 02:04 AM (12 years, 9 months ago) |
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Does JB go that high ? Good lord, I've not used it much (or ever), preferring to repair with welds or plate and clamps things that it would patch. *Reads* Ahh yes it's more metal and ceramic particles in suspension rather than just epoxy. Similar to the gold and silver clays your can buy and then kiln, creating a metal object. Less organics and volatiles however (thats a good thing, less shrinkage when curing)
Good point, I was thinking more along the lines of what you would laminate composite aircraft with (a hobby). My motor mounts are rated to 260C the kevlar, way beyond that.
You do make my point as well however. It may hold for weeks at 200C the day it fails and spills hot oil will NOT be a good one and the day it fails as you hit 320 (sulphuric acid distillation at standard atp anyone ?) would be a disaster of possibly epic proportion. Why take that risk? I didn't mention above the other major danger of flask breakage and mixing with the heat transfer medium. Hot acid mixes with a (slightly contaminated from use) hydrocarbon oil.... Checked the status of your ABC fire extinguishers lately ? Even if it's legitimate chemistry (no reason to suspect otherwise) I don't ever want to have to call the fire dept. to put out part of my house and explain whats up with the glassware that was in the fire...
After even more reading I may trust such a product in car repair for my oil lines etc where it's not running in the place I also like to sleep in. Burnt car means I still have a home.
However, with holes drilled very close to tolerance for the pipe your putting through it (epoxy performs best when it has structural reinforcement, and not used as a bridging medium all on it's own, cracks and small fills are best) and cured exactly according to the instructions (a simple oven will do the job), simply running the device to running temp is likely not going to cut it. Provided the system had a failsafe, say running in a deep metal pan meant for cooking or the like. I could see my way to using such a product if nothing else was available.
If your DIY project burns your house down, insurance won't cover it, when they find out. Not dismissing DIY things here, just advocating caution. If your deep fryer, crock pot, springs a leak as your heating oil and a flask in it and sets fire to your house... Well someone built it AS a deep fryer, saddle up to the law firms of your choice and go NUTS.
Edit, Good to hear about your sand decision, less messy etc. Bumping isn't an effect of the medium but the contents of the flask itself. When heating in sand it can still bump. I had sodium sulphate precipitate out of solution as my distillation went along and it got pretty loud at times no movement to speak of. Until it really got going and started to jump the whole 15 pound assembly.....
Edited by Flashmob (04/24/11 02:13 AM)
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ampakine
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Re: DIY variable oil bath (chemistry heat source) [Re: Flashmob]
#14344250 - 04/24/11 04:32 PM (12 years, 9 months ago) |
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Quote:
Flashmob said: I don't ever want to have to call the fire dept. to put out part of my house and explain whats up with the glassware that was in the fire...
That would be a nightmare. They police would be called and I'd most likely have my lab equipment confiscated and be forced to dismantle the entire lab. I got a fright a while ago when I went out to check on the distillation and smelled burning plastic. For a few seconds I thought the lab had somehow caught fire so I got the sand bucket and braced myself but was relieved to find there was no fire. The sand bucket is my first line of defence but I have a fire extinguisher mounted on the wall of the lab and one just inside my kitchen ready for fires I can't get at with the sand bucket. My labs out in the shed so a fire wouldn't reach my house. On top of that I built my fume hood with fireproof grade gypsum walls so if the hot plate, contents of the flask or oil were to catch on fire it should be able to contain the fire long enough for me to realise theres a fire and put it out. When it comes to chemistry you really can't be too careful.
Quote:
Flashmob said: Edit, Good to hear about your sand decision, less messy etc. Bumping isn't an effect of the medium but the contents of the flask itself. When heating in sand it can still bump. I had sodium sulphate precipitate out of solution as my distillation went along and it got pretty loud at times no movement to speak of. Until it really got going and started to jump the whole 15 pound assembly.....
You mean the contents of the flask bumping? I wasn't really thinking when I asked you if the sand bumps lol. Of course sand doesn't bump unless its a molten sand bath your using and your hitting temperatures so insanely high that the molten sand is becoming superheated lol. Anyhow bumping is pretty easy to prevent, all it takes is some stirring and/or some boiling chips. I learned my lesson from that incident I described in a previous reply. I never let solutions get superheated anymore and if I do let it happen I handle the superheated solution with great caution knowing that a slight sudden agitation could cause it to flash boil. Stirring prevents superheating but sometimes the stir rod gets stuck so its best to add some boiling chips as a 2nd line of defence. With oil baths the oil itself starts bumping so its best to add some boiling chips to that too. I just smash ceramic plates or cups, they're a great source of nucleation sites. Tempered glass works really well too so if you ever spot the remnants of a smashed wind shield grab a handful of glass cubes. I highly recommend you start taking anti bumping measures. If your whole apparatus is shaking then there must be some extremely heavy bumping going on in the flask. If you put a single cube of tempered glass in the flask beforehand I bet no superheating would occur at all. Superheated solutions are dangerous as hell, I learned that the hard way when I experienced a flash boil.
Edited by ampakine (04/24/11 04:59 PM)
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Flashmob
something something dark side

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Re: DIY variable oil bath (chemistry heat source) [Re: ampakine]
#14355221 - 04/26/11 01:16 PM (12 years, 9 months ago) |
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Oh they were anti bumping measures. However when the bar gets buried in a solid inch of precipitate and stops it goes from gurgle gurgle gurgle to bang bang. Keep in mind when under vacuum the air (and almost all of the nucleation ability) is quickly removed from ceramics, activated carbon, glass etc. A stir bar is your only option other than none, and if it stops... My reactions weren't under reduced pressure, just saying for those new to chemistry reading this.
My problem was I had identical reactions one carried out 24 hours before the previous and one had significantly more cooling time to crystallize out the sodium sulphate (beautiful crystal formations). I didn't weigh the crystals (appeared similar) or I would have found about half the weight of the other, so when I treated both reactions identically I was unprepared for the amount of precipitate. Upside the sand maintained enough grip to keep everything stable, I put a couple bricks on top of the foil thats above the sand to hold everything down and killed the heat, major bumping stopped within about 30 min, filtered and resumed.
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ampakine
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Re: DIY variable oil bath (chemistry heat source) [Re: Flashmob]
#14356133 - 04/26/11 04:31 PM (12 years, 9 months ago) |
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Quote:
Flashmob said: Keep in mind when under vacuum the air (and almost all of the nucleation ability) is quickly removed from ceramics, activated carbon, glass etc. A stir bar is your only option other than none, and if it stops...
Never thought of that. My stir bars always getting stuck so this will be a problem when I start doing vacuum distillations. One solution would be to sit the stir bar on some kind of pivot so theres little or no tension to stop it from turning. A problem there is that my stir rod is a pretty weak magnet and is cylindrical shaped so it'd just fall off the pivot. I have some flat rectangular shaped neodymium magnets that would be perfect for this, all I need to do is coat them with an inert material.
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Flashmob
something something dark side

Registered: 04/20/11
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Re: DIY variable oil bath (chemistry heat source) [Re: ampakine]
#14356995 - 04/26/11 06:43 PM (12 years, 9 months ago) |
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Sweet, good magnets like that are getting harder and harder to get. Nanny state, kids eat em and 2 magnets stick together part of your intestine... Ban magnets, not teach kids, don't eat magnets, is the obvious answer...
Regarding inert material: HDPE number 2 is what paint buckets are made from and drain cleaner bottles both NaOH and H2SO4. It's highly resistant to chemical attack.
Clean, new white ones can be had at home depot. Cut out the plastic form to roll around your magnet. Careful use of an oven will let you melt it around the shape of your magnet (have pliers and gloves handy, it has some serious thermal mass when molten). Something I discovered by accident as I was drying a new oil fired DIY furnace body (still in the home depot bucket, yah yah, I was lazy and it hadn't set to a solid yet) made for making my own glass frit.
For higher temps check out your local pottery houses. They often have borosilicate tubing for glassblowers these days, take your magnet to match a rough internal diameter. A regular propane torch will let you melt and then with pliers pinch closed the ends around your magnet. Don't let the magnet get too hot when doing that however, once you reach the curie temperature your magnet isn't a magnet anymore and re magnetizing it is difficult (understatement). Melt one side shut, allow to cool insert magnet and heat the other end as quickly as possible without thermal shock obliterating your work. For both types try to make an egg shape so there is less surface contact. With a rbf this is more difficult as the whole vessel is egg shaped..
I do mention however there are a good many ebay sellers these days who sell teflon stir bars in 1 or 3 packs for very reasonable amounts of money, last look was 15 bucks for a 3 pack of 3cm by 1cm. That said I have a couple homemade glass ones for those times when PTFE would become part of the chemical reaction.
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