SPI-DRY™ Critical Point Dryers
Some comments about the selection of the grade of carbon dioxide
(CO2)
Generally speaking, the grade we "recommend" is the "normal" grade, that is,
the one most commonly offered by industrial gas suppliers.
In most parts of the world, this "normal" grade of
CO2, from the suppliers, is specified as
"N4.5" or 99.995% minimum purity with a maximum level of 50 ppm
of impurities.
There are, however, two other grades available, and for most gas suppliers,
it would be by special order. One is "N4.0" or 99.99% (less pure than
"normal" grade), the other is "N5.5" or 99.9995% minimum purity. The N4.0
purity is easier to find in those parts of the world where there is high
level of activity in electronics, since those customers often times demand
the higher purities.
We are not aware of anyone who has ever reported either superior results
using N5.5 purity (vs. N4.5) or inferior results using N4.5 vs. N5.5.
However, we do want our customers to have the benefit of such detail about
gas procurement in the event they should ever find reason to believe that
their particular samples might benefit from the higher purity gas.
Finally, in order to keep this information in its proper context, and
perspective, one person involved with the manufacturing and distribution of
CPD units for nearly thirty years said to us recently, when we asked him his
opinion on this subject:
"......... yours has been the first inquiry on CO2
purity in almost 30 years. I cannot recall seeing any reference to CO2
purity in the old CPD papers. I think therefore that we are safe in
advising users that the normal commercial grade of CO2
(99.995) is ideal for the vast majority of applications, but that the higher
grade, 99.9995% may be beneficial for semiconductor or more critical
applications."
We therefore would invite anyone who has other opinions on this topic, or
if anyone has experimental data showing that the results one achieves can
be to some degree a function of the purity of the CO2
used in their drying procedures. And of course, we hope this page has been
useful, and
we would certainly welcome any comments, pro or con, regarding this
kind of presentation of this kind of potentially valuable if not also
interesting information.
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Thursday July 02, 2009
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