[CentOS] died again
warren at etr-usa.com
Wed Dec 4 18:44:53 UTC 2013
On 12/3/2013 22:09, Michael Hennebry wrote:
> On Tue, 3 Dec 2013, Patrick Lists wrote:
> They mention "high-purity isopropyl alcohol".
> The highest purity I've ever seen is 70%.
The vast majority of the impurity in commercial grade alcohol is water.
Capillary action sucks the fluid into all kinds of areas you might not
expect -- like under chips -- and it stays there longer than you might
guess because restricted airflow goes hand in hand with capillary
action. Also, water evaporates far less readily than alcohol,
increasing drying time.
The rest of the impurity is dissolved solids, which gets left behind
when the liquid evaporates. It also makes the fluid conductive. (Pure
alcohol and pure water are *not* conductive.) Conductive liquid is
obviously bad for computers, especially if it's still present when you
apply power. See previous paragraph. :)
Bottom line: 70% is too impure for this task.
I hesitate to use even 90% for this. The last time I used 90% isopropyl
on a PCB, it left behind a white haze that I had to scrub off with a dry
I bought a box (!) of 99% isopropyl years ago: http://goo.gl/7DYP8Y
It's fairly expensive to ship, but even so, it comes out cheaper than
the alternatives you're likely to have locally. Figure $0.30 - $0.40
per ounce, all told. You'll probably be set for life. (Tip: Add a
Menda bottle for your work table to your order, so you can keep the box
safe, like in a shed or garage.)
Radio Shack used to sell tape head cleaner for $1 an ounce. I'd guess
it's no longer available because there's not as much call for tape head
cleaning products these days.
While looking for up-to-date info on Radio Shack's web site, I came
across this relevant item: http://goo.gl/nLzub7 At $11 for a couple of
tiny bottles, both of which you have to use together, it's another 2-3x
more expensive than tape head cleaner. Plus, if you look into the MSDS,
the first part is acidic, so you must need the second pass to neutralize
what's left behind on the first pass. Sounds like a bad plan to me.
Everclear 190 proof should also work for this. At $20 per fifth, it
comes out under $1/oz, so cheaper than the RS fluids, but still more
expensive than the box o' isopropyl. Some households will find it a
more widely useful commodity, so there's that. :)
For what it's worth, you can get even purer isopropyl alcohol intended
for lab use. Prices I found online ranged from about $60-100 per liter,
or $2-3/oz, shipped. 100% is possible if you synthesize it, at even
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