silver

Silver Although silver was found freely in nature, its occurrence was rare. Silver is the most chemically active of the noble metals, is harder than gold but softer than copper. It ranks second in ductility and malleability to gold. It is normally stable in pure air and water but tarnishes when exposed to ozone, hydrogen sulfide or sulfur. Due to its softness, pure silver was used for ornaments, jewelry and as a measure of wealth. In a manner similar to gold, native silver can easily be formed. Silver's symbol is Ag from the latin argentum. Galena always contains a small amount of silver and it was found that if the lead was oxidized into a powdery ash a droplet of silver was left behind. Another development in this process was the discovery that if bone ash was added to the lead oxide, the lead oxide would be adsorbed and a large amount of material could be processed. By 2500 BC the cupellation process was the normal mode of silver manufacture. Tin Smelted copper was rarely pure, in fact, it is clear that by 2500 BC the Sumerians had recognized that if different ores were blended together in the smelting process, a different type of copper, which flowed more easily, was stronger after forming and was easy to cast, could be made. An axe head from 2500 BC revealed that it contained 11% tin and 89% copper. This was of course the discovery of @b(Bronze). However, by 2000 BC copper implements contained very little tin as local reserves of tin had been exhausted. The Sumerians were forced to travel to find the necessary ores. Bronze was a much more useful alloy than copper as farm implements and weapons could be made from it, however, it needed the discovery of tin to become the alloy of choice. Native Tin is not found in nature. The first tin artifacts date back to 2000 B.C., however, it was not until 1800 B.C. that tin smelting became common in western Asia. Tin was reduced by charcoal and at first was thought to be a form of lead. The Romans referred to both tin and lead as plumbum where lead was plumbum nigrum and tin was plumbum candidum. Tin was rarely used on its own and was most commonly alloyed to copper to form bronze. The most common form of tin ore is the oxide casserite. By 1400 BC. bronze was the predominant metal alloy. Tin's symbol is Sn from the stannum. Tin is highly malleable and ductile and has two allotropic forms which lead to tin initially having its own disease (tin pest or blight) which was actually formation of alpha-tin below 13 C. As alpha-tin is a highly friable cubic structure with a greater specific volume than beta-tin, during the phase change, which is kinetically limited, nodules of alpha-tin become visible on the surface of beta-tin giving rise to early belief of sickness and the first true doctors of metallurgy. Tin is highly crystalline and during deformation is subject to mechanical twinning and an audible tin cry. Tin is also quite resistant to corrosion. Tin is found as vein tin or stream tin. The tin ore is stannic oxide and is generally found with quartz, feldspar or mica. The ore is a hard , heavy and inert substance and is generally found as outcroppings as softer impurities are washed away. Mercury Mercury was also known to the ancients and has been found in tombs dating back to 1500 and 1600 BC. Pliny, the Roman chronicler, outlined purification techniques by squeezing it through leather and also noted that it was poisonous. Mercury, also known as quicksilver, is the only metal which is liquid at room temperature. Although it can be found in its native state, it is more commonly found in such ores as calomel, livingstonite, corderite and its sulfide cinnabar. Extraction is most simply carried out by distillation as mercury compounds decompose at moderate temperatures and volatilize. Mercury was widely used because of its ability to dissolve silver and gold (amalgamation) and was the basis of many plating technologies. There is also indications that it was prized and perhaps worshipped by the Egyptians. In 315 B.C., Dioscorides mentions recovery of quicksilver (which he called hydrargyros, liquid silver) by distillation, stating " An iron bowl containing cinnabar is put into an earthenware container and sealed with clay. It is then set on a fire and the soot which sticks to the cover is quicksilver". Methods changed little until the 18th century. Mercury's symbol is Hg from hydragyrum, liquid silver. Iron Iron was available to the ancients in small amounts from meteors. This native iron is easily distinguishable because it contains 6-8% nickel. There is some indication that man-made iron was available as early as 2500 B.C., however, ironmaking did not become an everyday process until 1200 BC. Hematite, an oxide of iron, was widely used by the ancients for beads and ornaments. It is also readily reduced by carbon. However, if reduced at temperatures below 700-800 C it is not suitable for forging and must be produced at temperatures above 1100 C. Wrought iron was the first form of iron known to man. The product of reaction was a spongy mass of iron intermixed with slag. This was then reheated and hammered to expel the slag and then forged into the desired shape. In the early days iron was 5 times more expensive then gold and its first uses were as ornaments. Iron weapons revolutionized warfare and iron implements did the same for farming. Iron and steel was the building block for civilization. Interestingly, an iron pillar dating to 400 A.D., remains standing today in Delhi, India. Corrosion to the pillar has been minimal a skill lost to current ironworkers. Iron is rarely found in its native state the only known sources being Greenland where the iron occurs as nodules in basalt that erupted through beds of coal and two very rare nickel-iron alloys. Iron's symbol is Fe from the latin ferrum. These seven metals: gold, silver, copper, lead, tin, mercury and iron, and the alloys bronze and electrum were the starting point of metallurgy and even in this simple, historic account we find some of the basic problems of process metallurgy. The problems are: The ores must be found, separated and sized before use. The ores must be reacted under a controlled temperature and gas atmosphere. The liquid metal must be collected and cast into a desired shape. The metal must be worked to achieve desired final properties and shape.