Jean-Paul,

It is worth noting that in the Plumbridge experiment you cited it was
reported that the alpha tin nucleated only on the ends of the tensile test specimens
that had been machined.   From what seem to be the fairly coarse machining
marks I suspect that there was quite a bit of deformation below the surface in
those areas.

The experiments carried out by what was then the International Tin Research
Institute many years ago found that even at the optimum temperature for
transformation the transformation from beta to alpha tin is difficult to nucleate.
Considerable energy is required to get over the energy "hill" to the point
where some tin atoms reorient to form an area of face centred cubic alpha crystal
structure large enough and stable enough to grow.    In the Plumbridge
experiments that energy probably came from that stored in the deformed surface layer
and it would be interesting to see whether unmachined specimens would
transform in the same way.

The question is whether, in normal circumstances a soldered joint would be
subjected to sufficiently intense mechanical damage to provide the energy
necessary to nucleate alpha tin.

Nihon Superior has samples of as cast SN100C alloy (Sn-0.7Cu+Ni) that have
been in refrigerated storage for several years without showing signs of "tin
pest".

Keith Sweatman
Nihon Superior Co., Ltd

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