Tin, the First Alloying Element
Tin (Sn) was first used as an alloying element with copper to form bronze, which is much more easily castable than copper and enabled the creation of more complex castings. It is a soft metal with a shiny silver color and is very corrosion resistant in air and water. Tin's corrosion resistance helps it serve in bronze and pewter alloys, as a durable component of electrical solder, and as protective plating for other metals.
- Strength: Tin is one of the weakest metals. You can, for example, bend or crush a tin can with your bare hands. This property does not allow tin to be used on its own as a structural metal.
- Ductility: Tin is a very ductile metal at room temperature, and is also quite malleable. When chilled below 55 F, tin slowly changes from a form known as "beta tin" to "alpha tin," which is much less ductile. Tin is also much less ductile above roughly 392 F.
- Conductivity: Tin and some of its alloys are excellent electrical conductors. Over half of the tin used industrially ends up in solder for making electrical connections.
The first alloy, bronze, was discovered around 5000 BC. It consists of copper and 5-12% tin by weight and revolutionized the way copper metal was used. The addition of tin makes bronze much harder and tougher than plain copper. Pewter, another tin alloy, was used extensively until 200-300 years ago in cooking and dining utensils. In the middle ages, tin was known as stannum, which is the origin of the modern symbol, Sn.
In the 19th and 20th centuries, many different applications for tin emerged. Electroplating was first developed around 1850 and is used to protectively coat metals that have better physical properties than tin. An example of this is the common food can, although most of them are actually made today from less-expensive aluminum. In the 1950s, Sir Alastair Pilkington invented a process in which molten glass is floated on top of molten tin, creating an incredibly flat glass surface for windows.
Tin in the Marketplace
ITRI, a tin industry advocacy group, reports that 340,000 short tons of tin are consumed globally each year. According to ITRI research, the top applications for tin are in solder and as plating, accounting for approximately 60% of global tin consumption.
Tin does not occur naturally and must be extracted from ores. Ore mining mainly occurs in China, Indonesia, Peru, Brazil, and Bolivia. The LME trades pure tin by the pound.
- Bronze: 5-12% Sn by weight. Used in coins, cymbals, and artwork.
- Pewter: 85-99% Sn by weight. Used primarily today in decorative items.
- Tin-lead solder: 5-70% Sn by weight.
- Tin-plated toys were considered among the finest in the world from the mid-1800s until the 1950s when plastic toys heavily entered the market.
- An interesting fact about tin's ductility is a phenomenon known as "tin cry." While tin is being bent, it emits a screeching nails-on-chalkboard sound. It occurs because the layers of molecules in the metal are sliding over one another and resolidifying, also known as twinning, allowing the metal to bend without breaking.