Re: gEDA-user: Isopropyl alcohol vs. ethanol

[Bill Sloman <bill.sloman@xxxxxxxxx>]

At 23:54 23-4-2006, you wrote:
> On 4/23/06, Karel Kulhavy <clock@xxxxxxxxxxxxx> wrote:

> > >Is it true that PCB's should be washed by isopropyl alcohol and 
> not > ethanol because ethanol has small molecules that creep into 
> the part > cases and wreak havoc >>there?



> >I've never personally heard this, but it is feasible I suppose. 
> Ethanol is only C2H3OH, which is a much smaller molecule than isopropanol.

Ethanol is CH3.CH2.OH . Iso-propanol  is CH3.CH(OH).CH3, which is one 
CH3 group larger - not a vast difference. Both are much larger than 
water  - HOH - and nobody seems to worry about water creeping into 
the parts, or a least not since they perfect the plastic package some 
thirty-odd years ago.

Iso-propanol is a less polar solvent than ethanol, and more effective 
at dissolving grease and oil, and it is somewhat less volatile, which 
means you can wipe it off the surface you are cleaning before it evaporates.

> >In California supermarkets, isopropanol is vastly more popular (in 
> fact, you cannot even purchase a bottle of ethanol at most 
> supermarkets; the closest you get is >Vodka), so I honestly cannot 
> remember a time when I actually possessed a bottle of actual ethanol.


> >> Is it OK to use denaturated ethanol (burning spirit) to clean PCB's?

> Probably not, because the "denatured" part simply means infused 
with *methanol*, which is an even smaller molecule yet.  BTW, 
methanol is used specifically because > it acts as a poison, thus 
hoping to deter would-be drunkies from ingesting otherwise 200-proof alcohol.

Denatured alcohol is mostly ethanol, plus additives that make it 
unpleasant to drink. In England it is called "methylated spirits" but 
methanol is rarely used these days - see 
http://en.wikipedia.org/wiki/Methylated_spirits

>>What's maximum safe time to leave a PCB inside the bath?

>I always spot-wash individual solder joints.  I personally never 
bathe a whole PCB.

Me too - more because you seem to need to scrub the surface to get 
rid of the excess flux

>> Is it allowed to pour isopropyl alcohol into the sink? Is the 
same allowed with denatured ethanol?

>It depends on your locality, of course, but in the US, it is legal. 
Both are not only biodegradable, but also evaporate quickly (contrary 
to popular belief, ethanol [at least] >dissolves water, not the other 
way around, so after it evaporates, all that's left is water). You 
*probably* don't want to make a habit of it though, as I'm unaware of 
any long->term environmental effects.  What follows is 100% pure 
hypothesis. Alcohol vapors in the sewer system may allow easier 
ignition of the methane gas (it's like adding fuel >additive to 
petrol), thus somewhat increasing the hazard of explosion.  If vapors 
come into regular contact with PVC or other plastic pipes, it may 
also contribute to their >dissolving, thus prematurely aging the 
pipe, or causing leaks. -- Samuel A. Falvo II

Small quantities of ethanol and iso-propanol aren't going to damage 
the sewers or the sewage treatment plants - there is going to be 
ethanol and iso-propanol in waste water from time to time from 
natural fermentation. Nobody working on an industrial scale could get 
away with flushing either solvent into the sewers, nor should they, 
but hobbyists don't work with big enough volumes of solvent to 
produce detectable levels of contamination.

--
Bill Sloman, Nijmegen