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Author: Subject: Waterproofing heating mantle?
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[*] posted on 16-5-2019 at 01:32
Waterproofing heating mantle?


I was looking into making a heating mantle, as mine died not long ago. I want to seal the fiberglass mantle surface (and insulation) to prevent damage from solvents and humidity.

In kilns and fireplaces, a material known as "ceramic fiber rigidizer" is used to form a hardened water resistant surface. This website reveals the R12 rigidizer is a colloidal silica solution. Unfortunately, the solution is fairly expensive, and coats some 50 square feet per gallon, much more than I'd need. Even better is that the manufacturer claims the solution has a shelf life of 6 months once opened. The MSDS and this website reveal the rigidizer to be a slightly basic aqueous solution of approximately 30% colloidal silica.

Colloidal silica, or fumed silica, is sold in a powdered form to be mixed with an epoxy to form an adhesive resin. It's also much cheaper and shelf stable. I've found a few videos of people making a sodium silicate solution.

https://www.youtube.com/watch?v=-Mx1-o1_MWo
https://www.youtube.com/watch?v=Ip-jDuM25FE

It seems that this "sodium silicate" should be analogous to commercially available "ceramic fiber rigidizer". While not totally waterproof, this should harden the surface of a heating mantle and leave a literal glass-like coating. I don't really value a heating mantle for being flexible. It only needs to conform to a flask. Is there any reason that I shouldn't be able to make and apply this sodium silicate solution to my heating mantle?
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[*] posted on 16-5-2019 at 07:02


Quote: Originally posted by advanced warning  


It seems that this "sodium silicate" should be analogous to commercially available "ceramic fiber rigidizer". While not totally waterproof, this should harden the surface of a heating mantle and leave a literal glass-like coating. I don't really value a heating mantle for being flexible. It only needs to conform to a flask. Is there any reason that I shouldn't be able to make and apply this sodium silicate solution to my heating mantle?


sodium silicate would be sprayed as a water solution, so you should dry it first without using the heating mantle itself to not make a short circuit.
you need multiple coats to build a glass like surface.
using big heavy flasks would crack the hard coating in my opinion making all of this useless





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[*] posted on 16-5-2019 at 07:39


Multiple sodium silicate coats might work, but even after drying and heating it can become soluble again (this wouldn't be the case if converted the silicate to silica but then you lose the ease of applying the silicate). One problem would be that the silicate wouldn't be a good conductor so you'd lose some heating power and responsiveness. I think a better solution might be to use a hotplate and a water bath, instead of a mantle.
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[*] posted on 16-5-2019 at 07:54


Quote: Originally posted by RedDwarf  
Multiple sodium silicate coats might work, but even after drying and heating it can become soluble again (this wouldn't be the case if converted the silicate to silica but then you lose the ease of applying the silicate).


sodium silicate can be cured with CO2 to make silica in situ, this way you apply sodium silicate, and turn it into silica on the substrate (the heating mantle)





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[*] posted on 16-5-2019 at 08:52


Thermowell mantles have solid heating surfaces, and can sometimes be found used at good prices.

I also like them because they don't use a special plug like glass-col does.

Of course, making your own might be more interesting and cheaper.




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[*] posted on 16-5-2019 at 08:58


Yeah my concern would be that it wouldn't serve any purpose ultimately, as the coating would crumble and flake off with use. It's more meant to seal the walls of a kiln or fireplace, rather than a flexible surface being regularly manipulated. Perhaps a better idea would be layering a tightly woven fiberglass sheet over the mantle surface.

I'm trying to prevent future failure of my heating mantle. Solvent exposure is a guarantee, but minimizing ingress seems like a good way to extend the life of the equipment.
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[*] posted on 17-5-2019 at 05:43


Why does it need to be waterproof anyway?
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