Hi Dave,

You are probably right that it is only a "natural" environment exposed to
sub-zero temperatures plus unlimited exposure time that provides the ultimate
test of susceptibility to tin pest.    However, experiments such as I reported
can provide a good indication of the likelihood.   Given that nucleation is the
critical step that has to be overcome before the tin pest can proceed, testing
the doped tin in contact with pre-transformed tin should provide a sensitive
indication of the susceptibility of the resultant alloy.    At a give average
temperature the most likely effect of the natural environment would probably
be on the nucleation stage.

And in the case of field reports it is important for tin pest (as for
whiskers) to confirm that the phenomenon has been correctly identified.    The
positive test would be X-ray crystallography to confirm that the alpha-tin phase is
actually present since there are forms of electrochemical corrosion that could
be confused with tin pest.

Keith Sweatman
Nihon Superior Co., Ltd

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