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Posted by George on June 11, 2008, 10:26 am
stan wrote:
>> stan wrote:
>>> I've got sort of a specail project going where I put the caulk on
>>> something about the size of a half-dollar coin.
>>>
>>> Imagine putting a small bead on the coin's face, then spreading it around
>>> with your finger. What happens of course is the caulk fills in and
>>> covers the small depressions while the higher area's (like the
>>> president's face) you can see still see because your finger sort of
>>> "squegees" it off.
>>>
>>> Now if I let the caulk cure on the coin for 24hrs what should I find on
>>> the president's face? I would think nothing but there is actually a
>>> greasy residue which I did not expect.
>>>
>>> This is 100% silicone:
>>> http://www.caulkyourhome.com/sil2_kitchen_bath.html
>>>
>>> I rub a blue colored old T-shirt on the raised area's of the coin and it
>>> comes away darker like it was wet or greasy (even after 24hr cure). If I
>>> put a small bead of caulk on a piece of paper (without smearing it) and
>>> let it cure, it looks and feels rubbery like normal caulk with no greasy
>>> residue, even if I pull it away from the paper.
>>>
>>> Any thoughts on how this is occuring?
>> Likely the acetic acid that was liberated during the curing process
>> attacked the metal. There are other formulations that are not peroxide
>> cure that will prevent that.
>
>
> Ok thank you for educating me. The label for for GE silicone II caulk says
> the curing process releases Methanol and Ammonia but I think that's not any
> better. To add some more detail, this is actually an electronics
> application but I just used the coin as an example of the surface. The
> caulk/sealant will touch solder and a silver based paint (85% silver) which
> need to remain un-corroded and electrically conductive.
>
> I may need some type of electronics grade sealant but it has to have a
> service temp of -40C to 110C when fully cured. Here are some things on my
> short list:
>
> star brite liquid electrical tape:
>
> http://www.starbrite.com/sproductdetail.cfm?ID=1076
>
>
> dow corning 744
>
>
http://www.dowcorning.com/applications/search/default.aspx?R=2127EN&DCCSF=1977EN&DCCSF=21EN
>
>
> dow corning 3140
>
>
http://www.dowcorning.com/applications/search/default.aspx?R=109EN&DCCSF=1977EN&DCCSF=21EN
>
>
>
You are looking at the right stuff. Those Dow RTV products are
specifically designed corrosion sensitive applications. I think the 744
is likely the most appropriate one for the use you described.
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