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Unpotting...Mutant tar



Hi All,
 
Been following the mutant tar string with delight, as it reaffirms my
contention that unpotting an NST is a filthy, frustrating, time consuming and
often, unrewarding undertaking.  There is really NO good way to do it.  There
is NO magic solvent.  Since tar is essentially very long aliphatic hydrocarbons
(the bottom of the pot), with various polycyclic aromatics thrown in for good
measure, most nonpolar organic solvents will work.  To make matters worse, as
the tar is baked and subjected to high voltage stresses inside an NST it
becomes very to carbonization, polymerization etc.  So, what you need is a
LARGE volume of a cheap and relatively safe solvent.  I would forget about
gasoline or any other low flash point solvent,  too dangerous.  Especially if
you use the "fish tank aerator" technique  for agitation. Forget alcohols.
Benzene, toluene, xylene are good, but expensive, flammable and toxic.  A nice
solvent is chloroform, its nonflammable, very agressive, but expensive and the
vapors could be a problem if used indoors.  I would choose kerosene.  At about
$1.75/gal its cheap, has a high flash point, has good solvent qualities and is
less toxic than gasoline by quite a bit.  You may be thinking: how bout diesel
fuel? Diesel fuel would be good, very high flash point, but be sure you get the
type with out added paraffin (is it 1 or 2? I can never remember).  It is
always best to remove as much tar with brute force using a screwdriver or
something.  This will lessen the time and solvent required.  And speaking of
time and solvent, it will take ALOT of BOTH.  Its best to use more changes of a
small amount of solvent than vice versa.  The moral of the story is: do
anything you can to avoid having to unpot an NST.  Hope this helps. 
 
Eric 
<mailto:edavidson-at-icva.gov>edavidson-at-icva.gov