From ???@0x00000B93 Thu May 09 08:53:28 2002 Path: pitt.edu!newsflash.concordia.ca!nntp.cs.ubc.ca!newsfeed.stanford.edu!sn-xit-01!sn-xit-04!sn-post-01!supernews.com!corp.supernews.com!not-for-mail From: rfwilson@intergate.nospam.bc.ca (Bob Wilson) Newsgroups: sci.electronics.design Subject: Re: Is there a glue or epoxy I can enclose a circuit in? Date: Thu, 09 May 2002 04:01:23 -0000 Organization: Your Organization Message-ID: X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit) References: <6y2C8.2327$pc6.221253@newsread2.prod.itd.earthlink.net> MIME-Version: 1.0 Content-Type: Text/Plain; charset=US-ASCII X-Complaints-To: newsabuse@supernews.com Lines: 41 Xref: pitt.edu sci.electronics.design:297653 Status: N In article , speff@interlog.com says... > >The renowned Dick Johnson wrote: >> Silicon Bathtub sealer or silicone glue also works and it can be found at >> Home Depot, et al. > >Avoid the stuff with acetic acid! On a minor point of order, NO RTV has acetic acid in it. There are 2 common types of RTV. One is "acetic acid cure" and the other is "alcohol cure". This refers the reactant that is liberated upon curing. RTV cures by a condensation reaction. The "acetic acid cure" stuff reacts with moisture in the air and the reaction byproduct is acetic acid (the acid that makes vinegar). The alcohol cure types release one of the higher alcohols as a byproduct. Neither of these types contains the byproduct; it is created as a reaction byproduct. But the main point is that using RTV in thick sections (or many layers of thinner sections) is downright silly. It is simply the wrong thing to use for potting. As far as avoiding the acetic acid cure stuff, it really is mainly harmless in most instances. Acetic acid is benign unless it is in the presence of liquid water. Further, no "common" acid (i.e. a non-oxidizing acid) will attack any metal below hydrogen in the electromotive scale. This includes copper, tin and lead. You can use acetic acid cure RTV quite successfully if you simply allow the stuff to cure at room temperature, with lots of ventilation. Once the stuff is cured, there is no more reaction, and no more acetic acid is produced. But curing in thick sections takes forever. In general, people just seem scared off by the word "acid". One final point is that the alcohol cure varieties are 2 or 3 times more expensive, and they take far longer to cure. There is one interesting one available from Shin-Etsu Silicones that seems to be an alcohol cure type, but cures lightning-fast. The stuff is amazing. In 5 minutes, a blob that is 1/8" thick is already well on its way to being fully cured! Bob.