Tin, a white metallic element (chemical symbol ‘Sn’, atomic number 50, atomic weight 118.71) with over thousand years of application in human history, is now mainly used in the manufacturing of tinplates, which are widely related to our daily life, particularly in food industry.
Tinplate is made of low carbon steel (normally consider as thin steel sheet) coated on both sides with extremely thin film or layer of tin. The coatings offers great protection for the plate from corrosion or other chemical reactions, while also maintain a aesthetically brilliant and luster appearance for the container. For food storage, it is vital since the weak acids or chemicals in food could be a threat harming the insides of the cans.
Tin can be easily converted into complex shapes with ease, thus tinplates are made to warp into various forms, such as tin cans. Additionally, most paper clips, safety pins and staples are made of steel or brass coated with tin.
There are two major techniques in tinplating. One is to melt the tin into a molten liquid, then dip the metal object. The other is to coat tin via electroplating technology. The latter involves dissolving tin salts into a liquid mixture, and then using electric current so that tin irons will be attached permanently onto the metal surface.
Compared with zinc plating, which also can effectively prevent metals from corrosion and rust, tin plating has its own advantages. One major reason is that zinc being overly toxic for medical or food applications. Also, tin helps to increase the ductility of metal objects, which as mentioned earlier is why tinplates can be made in various forms. On the other hand, zinc plating is better in corrosion-resistance, simply because zinc can react with the air and form new protective coating even after scratch or damage, while tin coating cannot recover itself as much effective.
Further reading: About tin deposits
Tin makes up only a small portion (about 0.001%) of the earth’s crust. As a consequence, tin quantity per year is extremely small compared with other common metals. US has little in deposit to mine, while most of the known tin deposits are in the southern hemisphere. The principal tin ore is a compound of tin and oxygen known as cassiterite. Extractive metallurgy involves extracting metals from their ores and refining them to a pure state.