What is "100% silicone"?


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Oct 29, 2019
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When sealing a tank, we're told to use "100% silicone" adhesive. That made since until just now when I learned I needed "100% silicone" lubricant to seal the o-rings on my canister filters. Clearly the sticky adhesive silicone can't be the same thing as the greasy lubricant. "100%" - I don't think it means what you think it means.

This is more a rant than anything else since I'll continue to use the brands that either I or other reefers have used and which haven't yet killed my fish. But, out of curiosity, are there any chemists in the crowd that have an explanation? I suspect it's that "silicone" is not just one thing, but a class of things of various formulations (as described on Wikipedia). Does anyone know (and perhaps we'll need the marketing lawyers in addition to the chemists) if "100% silicone" really is something we can rely on when choosing aquarium products? Or are there formulations that count as "100% silicone" that wouldn't be aquarium safe? I'm specifically concerned because the Wikipedia article describes a "Platinum-based cure system". Platinum being a heavy metal, I would be reluctant to put that in my tank.


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Oct 3, 2015
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I dont think anyone is referring to 100% pure Silicon, as in the element Si.

Thats too reactive, and would be found as Silica (SiO2). Which is a primary component in these "Silicone" products.

AKA: Silicone is a broad term for products that utilize Silica. Alone, agreed the term is not particularly useful. Grease, adhesives, etc may use silica.

This is example SDS for 100% Silicone sealant, if that helps at all.

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