To All Listmembers,

At Reading we use Louwers-Hapert HV stopcocks and Vacutaps
in a wide variety of applications on our stable isotope
extraction lines and associated glassware to provide vacuum
seals down to 1 E-7 mbar.

Their HV stopcocks have performed very well over several years
constant use but we have found serious corrosion problems with
the more expensive Vacutaps in one specific application -
when used to seal glass reaction vessels containing 100%
Orthophosphoric acid during the preparation of CO2 gas from
carbonates for subsequent analysis of 13-C and 18-O.

After about 40-50 such preparations, the white plastic part
of the Vacutap starts to corrode, first by patchy discolouration
which gets progressively worse until the material begins to
flake off, eventually rendering the Vacutap unusable.  Once
started, the corrosion apparently continues even during off-
line storage.  When the HV stopcocks are used in the same
glassware, no such corrosion problems have been encountered.

I would be interested to hear if anyone else on the list has
experienced similar problems with these Vacutap valves and if so,
what solutions may have been adopted to overcome it.

Many thanks.

Michael Isaacs
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Dept. P.R.I.S,
University of Reading,
Whiteknights,
Reading RG6 6AB,
U.K.

Tel: +44-118-9875123x7974
Fax: +44-118-9310279
Email: [log in to unmask]
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