Material of the Month - Tin

Materials World magazine
7 Dec 2016

Probably the first things that come to mind when thinking of tin today are the tin cans that line supermarket aisles and clutter the back of your kitchen cupboards, despite the majority now being made from aluminium. However, the metal has played a significant role in human history, and continues to be an economic driver.

Tin is a member of the carbon family, part of group 14 of the periodic table. The metal is soft, silver-white with a blue tint and has been mined for thousands of years for various purposes. Archaeological evidence suggests that people have used tin, in some form, for at least 5,500 years. It is primarily obtained from the mineral cassiterite, which is roasted in a furnace to produce tin. Making up just 0.0001% of the earth’s crust, tin is chiefly mined in China and Indonesia. 

War and trade 

Tin’s first major importance was as part of an alloy and not as a pure metal. The Bronze Age began at various dates depending on location, with the earliest in the Near East – Anatoloa and Egypt, for example, in 3300BC. Europe closely followed in 3200 BC, followed by South Asia in 3000BC and China in 2000BC. Bronze was produced by alloying copper with around 5% of tin, melting at a low temperature to produce a metal that was strong and better suited for making tools and weapons. 

Artisans from Mesopotamia – now the area covering most of Iraq, Kuwait, eastern Syria and regions along the Turkish-Syrian and Iran-Iraq borders – entered a new age of warfare with the discovery of bronze, using it to make weapons and armour that were light. The earliest form of torso armour was scale armour, made by sewing pieces of bronze to fabric. Weapons of the Bronze Age included the short blade dagger, the battle-axe, the spear, the mace and a sword with a long handle and short blade similar to a sickle. 

Bronze was seen as a luxury used by rulers and their armies, and was mostly reserved for the higher classes of society. This meant that the Stone Age lasted well into the Bronze Age for many people. Its superior properties made bronze, and its components copper and tin, valuable commodities. This created a great incentive for trade, with Cyprus gaining much wealth from its large copper deposits, and Cornwall becoming a major supplier of tin in Europe.

Cornish ‘tinners’

Tin mining in Cornwall began more than 2,500 years ago and was mined from visible cliff face veins by innovative ‘tinners’, who were awarded unique rights and privileges in charters granted by King John and Edward III that awarded them unique rights and privileges because of their important contribution to the economy. Greek and Roman traders were known to source tin from Cornwall, and it has been cited as one of the reasons for Julius Caesar’s interest in Britain.

The most productive Cornish tin mine was South Crofty, which began operating in 1670 and continued as an active mine until 1998, when all tin mining in Cornwall ceased. The mine was also known as the East Wheal Crofty from 1830–1880 when focus shifted to copper. 

Canadian company Strongbow Exploration has recently acquired South Crofty, following various other attempts over the last 15 years to revive the mine. The failure of theses projects came down to low metal prices and a lack of funding, but South Crofty still contains a substantial amount of ore and the mine retains an active mine permit, a high grade Mineral Resource, existing mine infrastructure and support from the local community. Over recent years, Strongbow has conducted a significant amount of exploratory drilling to obtain an updated NI-43101 Mineral Resource estimate, showing 2.4Mt of Indicated and Inferred Mineral Resource at a grade of 1.84%Sn. South Crofty will require dewatering over the next year to recover submerged mine workings, followed by a series of water treatment tests, before the addition of four drilling areas to widen the resources base.  

Another site attempting to reboot the Cornish tin industry is Drakelands mine near Homerton. Constructed in 2015, Drakelands is a tungsten and tin mine run by Australia’s Wolf Minerals, becoming the first producing metal mine in the UK for 40 years upon opening. The mine produces tungsten and tin concentrates, with the processing plant churning out approximately 5,000t and 1,000t, respectively, each year. 

Preservation and innovation

Tin plating is used in food cans, in a process that came about in 1809 when French inventor Nicholas Appert observed that food cooked inside a jar did not spoil until the seal was breached. He developed a way of sealing food in glass jars to claim the reward of 12,000 Francs offered by the French Government during the Napoleonic Wars for an invention that would preserve food. This method was adapted and patented in 1810 by Peter Durand, but sold to Bryan Donkin and John Half two years later, who refined the process and set up the world’s first commercial canning factory in London. The first canned goods from this factory were produced in 1813 for the Royal Navy. 

Tin plating technology originated in Bohemia in the Middle Ages, and was marketed in England in 1730. The combination of materials gave the physical strength of steel with the corrosion resistance of tin. The aluminium can was introduced in 1957, offering great malleability and ease of manufacture over tin. Today, 180 billion aluminium cans are produced globally, and constitute the largest use of aluminium. 

‘In its elemental form and through its derivatives of alloys and chemical products, tin impacts a gamut of industries that span the engineering, energy, transport, housing, agriculture and healthcare sectors’ said Professor V G Kumar Das of the University of Malaya, Malaysia, pointing to recent research highlighting the metal’s green credentials. ‘The rising demand for lead-free solders on environmental grounds has been met in the electronics industry by solders based on the tin-silver eutectic modified with small amounts of copper, bismuth or antimony to improve strength and creep resistance while maintaining a melting point close to the Sn-Ag eutectic.’ Nanosolder pastes based on SAC nanoparticles are poised to replace conventional tin-lead alternatives.

Tin is also used to make niobium-tin, which was the first known material to support high currents and fields, discovered in 1961. The alloy’s superconductivity was uncovered in 1954, leading to the finding of V3Si the next year – the first example of an A3B superconductor. 

Niobium-tin has recently been involved in upgrade plans for the Large Hadron Collider (LHC) at CERN, billed to replace niobium-titanium in the magnets. Niobium-titanium can only bear magnetic field of up to 10 Tesla, whereas the tin equivalent can handle fields beyond 10 Tesla. Niobium-tin was part of the original plans for the LHC, but due to the greater availability of niobium-titanium at the time, it was replaced. 

Niobium-tin wires will be used in the coils of the LHC magnets. The wires are made of a copper matrix, inside which are filaments of about 0.05mm in diameter. The wires are assembled into cables, which are then wound into a coil and heat-treated at about 650oC for several days, superconducting the coils.

Another tin alloy being used in technological advancement is silicon-tin. Researchers at the University of California, Riverside, USA, have created a new silicon-tin nanocomposite anode with the potential to extend the lives of lithium-ion batteries. The researchers claim that the anode can triple the charge capacity of a battery compared with that offered by graphite, and is stable over many charge-discharge cycles. The improvement is put down to the high electrical conductivity and energy storage capabilities of tin. The innovation is claimed to be a candidate for use in battery-powered vehicles because of the simple manufacturing process and long life. 

Tin has played an important role in the formation of modern civilisation, and its alloyed superconductivity will see it shape the future, too.