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Tin
In celebration of the 50th anniversary of Education in Chemistry, John Emsley
takes a look at the 50th element: tin
Key advances
Tin was the key to three
technological advances. The
first occurred five thousand
years ago when a metal worker
found that adding tin to copper
produced bronze, a tougher metal
for tools and weapons.
The second was the realisation
that a coating of tin would protect
iron – tinplating became an
important industry in medieval
Europe.
The third was the use of molten
tin to manufacture ‘float glass’,
which is the modern method for
producing perfect window glass.
Tin cans for preserving
food were first introduced in
England, in 1812. Concerns
about incorporating tin into the
diet mean that its level is now
regulated, and the problem is
solved by lacquering the inside of
cans. This method of preserving
foods is declining, but billions of
cans of food are still produced
and the tin is reclaimed from
around a third of them. Tin foil,
where the metal was hammered
into thin sheets, was used for
centuries until it was replaced
with aluminium.
Flexible uses
The only tin ore of commercial
significance is cassiterite (SnO2).
Total output of new tin is around
300 000 tonnes per year and
the main producers are China,
Indonesia and Peru.
Half the tin produced ends
12 | Education in Chemistry | January 2013 | www.rsc.org/eic
up in solder and a fifth goes into
tin plate. The rest finds many
uses: in pewter, bell metal,
heavy bearings and even dental
amalgams.
Traditional tin-lead solder
has now been replaced by a new
solder consisting of 95.5% tin,
3.9% silver, and 0.6% copper. It
is known as SAC after the initial
letters of the elements’ chemical
symbols.
The niobium-tin alloy Nb3Sn
is used for superconducting
magnets.
Glorious colours
Tin compounds are also useful.
Tin(iv) oxide, SnO2, has been used
for ceramics for millennia. The
ancient Babylonians produced
wall tiles with a tin-based glaze.
Some tin pigments give beautiful
colours, such as tin-vanadium
(yellow) and cobalt-stannate
(sky blue, known as cerulean
blue). Tin dioxide is also used in
some carbon monoxide sensors
because as it absorbs the gas its
electrical conductivity increases.
Tin(ii) chloride, SnCl 2, is used
as a mordant in dyeing calico and
natural silk. The tin becomes
attached to the fabric and then
the dye molecules attached to the
tin. In the case of silk dyes, the
mordant and dye can more than
double the weight of the fabric.
Data file
Atomic number 50; atomic weight 118.710; melting
point: 232°C; boiling point: 2270°C; density: 7.3 g cm–3
(white tin) 5.8 g cm–3 (grey tin). Tin is a member
of group 14 of the periodic table and its preferred
oxidation states are +2 (SnCl2 is a reducing agent) and
+4 (as in SnO2).
murray robertson/visual elements
Cold plague
Pure tin undergoes a transition
when cooled below 13°C,
changing from a solid metal
known as β–tin (white tin) to a
powder known as α–tin (grey tin).
The transition is imperceptibly
slow at 0°C and is still very slow at
–10°C, although in places where
such low temperatures as –33°C
are quite common, it becomes
much quicker.
Tin ‘plague’ came to public notice
during the hard Russian winter
of 1850 when the temperature
dropped to record lows for weeks
on end. The most noticeable effect
was on organ pipes in churches,
which were 95% tin. They became
covered with scaly patches that
crumbled when touched.
Biocides
Some tin compounds are
decidedly dangerous, the
triorgano tin family especially
so. Trimethyl tin and triethyl
tin analogues are particularly
toxic because they damage the
central nervous system. Larger
organic groups were thought to be
much safer and tributyl tin (TBT)
compounds became widely used
as biocides, especially to prevent
barnacles fouling the hulls of
ships. However, by the 1980s it
was clear that species such as
oysters, marine snails and dogwhelks, which flourish in coastal
waters, were becoming infertile
due to TBT and it was banned in
the early 2000s.