Tin pest

Tin pest is an autocatalytic, allotropic transformation of the element tin, which causes deterioration of tin objects at low temperatures. Tin pest has also been called tin disease, or tin leprosy (Lèpre d'étain).

It was observed in medieval Europe that the pipes of church pipe organs were affected in cool climates. As soon as the tin began decomposing, the process sped up, and seemed to feed on itself.

With the adoption of RoHS regulations in Europe, and similar regulations elsewhere, tin pest is an increasing problem, with some manufacturers using pure tin to comply with RoHS regulations by removing the lead from formerly tin/lead alloys.

The allotropic transformation is crap :) haha

At 13.2 degrees Celsius (about 56 degrees Fahrenheit) and below, pure tin transforms from the (silvery, ductile) allotrope of β-modification white tin to brittle, α-modification grey tin. Eventually it decomposes into powder, hence the name tin pest.

The decomposition will catalyze itself, which is why the reaction seems to speed up once it starts; the mere presence of tin pest leads to more tin pest. Tin objects at low temperatures will simply disintegrate.

Possible historical examples

Scott expedition to Antarctica

In 1910 British polar explorer Robert Scott hoped to be the first to reach the South Pole, but was beaten by Norwegian explorer Roald Amundsen. On foot, the expedition trudged through the frozen deserts of the Antarctic, making for caches of food and kerosene deposited on the way in. In early 1912, at the first cache, there was no kerosene; the cans — soldered with tin — were empty. Members of the expedition later died in the cold and blizzards, only eleven miles from a massive depot of supplies.

The cause of the empty tins could have been related to tin pest, and some observers blame poor quality soldering, although tin cans over eighty years old have been discovered in Antarctic buildings with the soldering in good condition. In any case, the lack of kerosene would only have led to hypothermia, one of many ailments the expedition were suffering from. One source observes,

The likely cause of death for Scott's polar party was some combination of scurvy, gangrene, starvation, dehydration, and hypothermia.

Napoleon's buttons

The story is often told of Napoleon's men freezing in the bitter Russian winter, their clothes falling apart as tin pest ate the buttons. Whether failing buttons were indeed a contributing factor in the failure of the invasion remains disputed; critics of the theory point out that the tin used would have been quite impure and thus more tolerant of cold temperatures. Laboratory tests provide evidence that the time required for unalloyed tin to develop significant tin pest damage at lowered temperatures is about 18 months, which is more than twice the length of Napoleon's Russian campaign.[1]

Modern tin pest since adoption of RoHS

With the adoption of Restriction of Hazardous Substances Directive (RoHS) regulations in Europe banning most uses of lead, and similar regulations elsewhere, the problem of tin pest has come back with some manufacturers using pure tin, who previously used tin/lead alloys. For example, the leads of some electrical and electronic components are plated with pure tin. In cold environments, this can change to α-modification grey tin, which is not electrically conductive, and fall off the leads. After heating back up, it changes back to β-modification white tin, which is electrically conductive, and can cause electrical short circuits and failure of equipment. Such problems can be intermittent as the particles of tin move around. Tin pest can be avoided by alloying with small amounts of antimony or bismuth, which prevent the decomposition. Silver, indium, and lead have also been used, but lead has been mostly banned by RoHS.