Twospoons
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Suggestion for keeping oil dry?
I am making a high voltage variable capacitor by submerging a variable air-spaced capacitor in oil, which will both increase the capacitance 2 fold
and increase the breakdown voltage at least four fold. Oil will be either paraffin or silicone - haven't decided which yet.
While the container will be well enclosed there is still some possibility of moisture absorption by the oil, which I'd like to avoid. So I want to
include a drying agent in the container to maintain the oil in a reasonably dry state. The drying agent must not alter the oil or be even slightly
soluble in the oil, as I don't want the dielectric properties to change.
Can anyone suggest a suitable agent? I have silica gel and Bentonite available, but I'm unsure if these would affect paraffin or silicone oil.
[Edited on 15-7-2012 by Twospoons]
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kristofvagyok
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Melt some metallic sodium or potassium in paraffin oil, stir it for a while and let it cool down.
This method for silicone oil should be okay also, but I'm not sure, because a friend made NaK alloy in it and it reacted with the silicone oil, while
it shouldn't....
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-Pictures from chemistry, check it out(:
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Dave Angel
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I'd wager anhydrous magnesium sulphate would have limited (if any) solubility / reactivity in oil, but haven't been able to pull up anything concrete
with a cursory google...
Go on - what's the project? 
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Twospoons
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Vacuum tube Tesla coil 
The variable cap is so I can easily tune the primary side oscillator into resonance with the secondary coil.
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Dave Angel
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Lovely!
Always had a Tesla Coil on my 'to do one day' projects list - good luck with it.
Assuming you've seen videos of them being made to play music...?
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Lambda-Eyde
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Molecular sieves. No ions to screw up the conductivity.
Please keep us posted on your project. I've always wanted to do a Tesla coil or something similar, but I'm useless with electronics, so I'm shying
away from HV until I've got the lower voltages sorted out.
[Edited on 15-7-2012 by Lambda-Eyde]
This just in: 95,5 % of the world population lives outside the USA
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Twospoons
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I've seen the musical ones. Thats a feature thats going to have to be some way down the track. I just want big arcs to start with. Its been on my
to-do list for ages too - was bored a few weeks back so decided to kick this one off by investing in a massive Soviet pentode (GU81M).
Molecular sieves - which type would you recommend? I've never used them before. I have access to a humidity controlled oven, so drying them should be
no problem.
On the reactive metal front, a strip of lithium from a coin cell would be easier to obtain than sodium, for me.
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Dave Angel
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Good call on the molecular sieves Lambda; 3A or 4A should be fine for water removal. Hope you can get hold of them where you are -
I'm sure if you were at a loss then one of us with some stashed away might be able to dig some out...
With regards to the reactive metal, do you not risk putting ions into solution / some kind of suspension that way - i.e., hydroxide formation?
Look forward to seeing how it turns out!
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m1tanker78
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Lithium will float on oil. I've been using sodium-potassium (NaK) alloy for a while now with good success to keep my oil dry. I don't know the exact
percentage of potassium in the alloy but it's probably no more than 10% by weight - maybe less. As time passes, a dark sludge-like layer has built up
on the bottoms of the containers. In my case it doesn't interfere with what I use the oil for so no biggie.
I can't attest to silicone oil nor molecular sieves though. The sieves seem like an even better option if they sink in the oil and don't disintegrate.
Good luck with your TC. I'm really surprised no one has posted nice arc pics in the pretty pictures thread.. Ahem
Tank
Chemical CURIOSITY KILLED THE CATalyst.
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Pyro
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you should check out myst32YT's vid on sodium wire for keeping things dry. he uses an extruder
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Twospoons
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I've settled on silicone oil, as it isn't flammable and seems to be more compatible with the polypropylene container I'm going to use.
Thanks for all the suggestions. I promise I'll post something when its all running.
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