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What is Tin Disease?
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, marching 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. The cause of the empty tins could
have been related to tin pest. Some observers blame poor quality soldering
though, as tin cans over eighty years old have been discovered in Antarctic
buildings with the soldering in good condition.
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 low 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. It is clear
though that some of the regiments employed in the campaign had tin buttons and
that the temperature reached sufficiently low values (at least -40 °C).However,
none of the many survivor's tales mentions problems with buttons and it has
been suggested that the legend is an amalgamation of a case of disintegrating
Russian tin buttons in an army warehouse in the 1860s and the
utterly desperate state of Napoleon's army turning soldiers into ragged
beggars.
Russian Army:
In the winter of 1850 Russia was particularly cold, and record low
temperatures persisted for extended periods of time. The uniforms of some
Russian soldiers had tin buttons, many of which crumbled due to these extreme
cold conditions, as did also many of the tin church organ pipes. This problem
came to be known as the “tin disease.”
Cause:
The reason of tin disease is a
specific type of allotropic change is tin. White (or β) tin, having a
body-centered tetragonal crystal structure at room temperature, transforms, at
13.20C to gray (or α) tin, which has a crystal structure similar to
diamond (i.e., the diamond cubic crystal structure). The rate at which this
change takes place is extremely slow; however, the lower the temperature (below
13.20 C) the faster the rate.
The transformation is slow to initiate
due to a high activation energy but the presence of germanium (or crystal
structures of similar form and size) or very low temperatures of roughly −30 °C
aids the initiation.
Accompanying this white tin-to-gray tin
transformation is an increase in volume (27 percent), and, accordingly, a decrease
in density (from 7.30 g/cm3 to 5.77 g/cm3). Consequently,
this volume expansion results in the disintegration of the white tin metal into
a coarse powder of the gray allotrope. For room temperature, there is no need
to worry about this disintegration process for tin products, due to the very
slow rate at which the transformation occurs.
Specimen of white tin . Another
specimen disintegrated upon transforming to gray tin (right) after it was
cooled to and held at a temperature below 13.2 0C for an extended period
of time.
(Photograph courtesy of Professor Bill
Plumbridge, Department of Materials Engineering,
The Open University, Milton Keynes, England.)
