Post 352 – by Gautam Shah
Tin was one of the earliest metals to be known, and used in the form of an alloying material with copper to form the bronze. Pure copper is occasionally available as nodules, but its ore is fairly common. Tin is rare, and not found together with copper.
First Bronze was produced by smelting copper and arsenic. This was a very toxic process. The arsenic was soon replaced with tin. Tin bronze was superior to arsenic bronze, as the former alloying process was controllable. Tin-based bronze was nontoxic and produced an alloy that was stronger and easy to cast. Tin was not available at places where copper ore was available, so tin had to be bought from elsewhere. Tin resources and trade routes of ancient times had a great bearing on development of bronze cultures. The earliest tin-alloyed bronzes date to 4500 BC, but pure tin was produced after 600 BC.
Tin is a silvery malleable metal, a chemical element with symbol Sn from Latin =stannum. It does not easily get oxidized in the air. Tin has many applications other than as an alloying material. Tin, with and without lead, is used for soldering metal joints, plating electrical and other wires, steel plates and components, and for forming pewter metal items.
PEWTER is a tin alloy. The earliest piece of pewter was found in Egyptian tombs from 1450 BC. It was extensively used by the Romans for household vessels and ornamental use. The word pewter is possibly a variation of word spelter, a term commonly used for zinc alloys, with similar grey a shiny surface. Pewter is a malleable metal alloy, traditionally 85–99% tin, with the rest formed of copper, antimony, silver, bismuth and sometimes, less common today, the lead. Copper and antimony acts as hardeners, whereas lead is used in decorative (non-food) utilities. Lead containing pewters have a bluish tint. Pewter due to its low melting point (170–230 °C) is easy to cast and work with techniques like chasing, engraving, etc. Pewter was used for making flatware, tableware and church prayer items till early part of 20th C. The early pewters, due to the lead content were hazardous for health. The constituents of pewter were first controlled in the 12th C. by town guilds in France, and later elsewhere. By 16th C. three grades of pewter were common. The first type, the ‘fine metal’, was used for tableware. The second grade known as ‘trifling metal’ containing up to 4% lead was meant for statuettes and holloware. The third type of pewter, known as ‘lay or ley’ metal, with 15% lead, was used for non-food utilities and for items not used by direct contact. Pewter remained in use till porcelain and glass tableware became common.
TIN PLATING is metal coating of usually pure tin, on variety of metal surfaces, such as mild steel, copper, brass, etc. Cooking utensils were tin plated to prevent copper oxide and sulphate contamination and weather tarnishing of the surface. Romans were using tinned copper vessels for cooking. A tinned iron sheet or tin-plates were developed in Europe in the 14th -15th C. AD. Food canning industry of 1800s would not have existed without the tin plate packing. Tin-plated sheets can be drawn and worked further without any flaking damage to the coating as tin itself acts as a lubricant. Until the middle of the 20th C. tin-plates were manufactured in by immersing individual sheets in a bath of molten tin, whereas now this is done in a continuous electroplating process. Both bright and matte-finish tin coatings can be produced electroplating.
BABBITT METAL is a tin-based alloy. It was originally a casting material for bearings. However, now it is used as a thin surface layer as metal-matrix composite. It is used as a bearing metal for engines and constant-turning tools such as saw-blades.
SOLDERING is a process of joining metal components by a tin metal or its alloys. Tin is melted as a wire or its powder. Familiar electronic solder contains silver, lead and tin. Metals that are to be soldered should be clean and free of oxide film. A flux of pine rosin, hydrochloric acid or zinc chloride is usually applied, which cleans the surface and seals it from the tarnishing effect of the atmosphere.
TIN ALLOY COATINGS of tin-zinc, tin-nickel, tin-copper, and tin-lead are used. These are used as both protective and decorative finishes. Tin-zinc coatings, are used in automotive industry. Tin-nickel is highly resistant to corrosion and tarnish, finds special use in electrical equipment and scientific instruments. The tin-copper coatings show colour range from bronze to white. Tin-lead coatings are applied to create solder-able surfaces (known as terneplate) on other metals for outdoor corrosion protection and also for gasoline tanks.