Topic

Tin pest

At low temperatures, tin deposits may suffer from what is called ‘tin pest’, and also ‘tin disease’, or even ‘tin leprosy’. These all describe the modification of silvery, ductile ‘white’ tin into a non-adherent powdery grey form known as ‘grey’ tin, a phase transformation that can occur at temperatures between −40°C and 13°C, but typically only occurs below 0°C. The problem has been known since medieval times – there are some interesting historical links at this site.

Once started, the transformation is autocatalytic, and can even continue at above 13°C, but the problem may be greatly reduced by alloying with very small quantities of antimony, bismuth or lead: an addition of 0.25% antimony is often specified by military users as a preventative measure.

However, Professor Bill Plumbridge of the Open University made the point at a workshop in March 2004 that there had only been a few observations of tin pest on real joints, as distinct from on billets of material. So, tin pest should probably not be a concern for the assembler.

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