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Tin Pest

The usual practice within the SRG has been to store specimens after production in a freezer at –18°C to minimise microstructural instability. This led to the ‘discovery' of tin pest in the Sn-0.5Cu alloys after prolonged periods (greater than one year) at this temperature. White (beta) tin transforms to grey (alpha) tin at temperatures below 13°C with a substantial increase (26 per cent) in volume, and this results in surface wart formation and cracking. Ultimately, total disintegration of the sample occurs. There is a significant difference in coefficient of thermal expansion between the phases, which further exacerbates the potential danger of the problem during service.

Tin pest

Publication of these findings aroused considerable interest internationally. A systematic study is now underway to determine whether this phenomenon occurs in other lead-free alloys, and the kinetics involved.

A technical brief detailing the findings of the above study (190K)

 

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