Gold And Its Uses Term paper
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Gold's great virtues of malleability, ductility, reflectivity, resistance to corrosion and unparalleled ability as a thermal and electrical conductor mean it is used in a wide variety of industrial applications consuming close to 300 tonnes annually.
Gold (Au, from Latin "Aurum" (World Book Dictionary) is the most non-reactive of all metals -- it is benign in all natural and industrial environments. Gold never reacts with oxygen (one of the most active elements), which means it will not rust or tarnish. Gold is among the most electrically conductive of all metals. Since electricity is basically the flow of charged particles in a current, metals that are conductive allow this current to flow unimpeded. "Gold is able to convey even a tiny electrical current in temperatures varying from -55. to +200. centigrade." (Gold Institute) Gold is the most ductile of all metals, allowing it to be drawn out into tiny wires or threads without breaking. Consequently, a single ounce of gold can be drawn into a wire five miles long. Gold's malleability is also unparalleled. It can be shaped or extended into extraordinarily thin sheets. For example, one ounce of gold can be hammered into a 100 square foot sheet.
Gold is the most reflective and least absorptive material of infrared (or heat) energy. High purity gold reflects up to 99% of infrared rays. Gold is also an excellent conductor of thermal energy or heat. Since many electronic processes create heat, gold is necessary to transfer heat away from delicate instruments. Gold alloy is the most tenacious and long-performing material available for protection of these temperatures.
Geologists use the latest technology such as satellite surveys and geochemistry to locate an ore deposit. Computers are used to design the mine, which requires precise and accurate measurement of the ore deposit. Construction begins following the lengthy process of receiving permits. As holes are drilled for blasting, samples of ore are examined to determine grade and metallurgical characteristics. The broken rock is marked by type for efficient processing. Based on its metallurgical makeup, a dispatcher directs truck operators to deliver the ore to the correct processing location.
Low-grade ore is roughly broken into small chunks and placed on carefully lined pads where a dilute cyanide solution is distributed over the surface of the heap. The solution percolates through the heap and the cyanide dissolves the gold. This solution containing dissolved gold is then collected. Refractory ore containing carbon is roasted to over 1,000 degrees Fahrenheit, burning off the sulfide and carbon. The product of this process is an oxide ore, which is routed to the leaching circuit. Oxide ore is sent directly to the leaching circuit where cyanide dissolves the gold. Sulfide refractory ore without carbon is oxidized in an autoclave to liberate the gold from sulfide minerals, then it is sent to the leaching circuit. Treated, high-grade ore is leached with cyanide.
The gold is absorbed out of solution onto activated carbon. The remaining cyanide solution is recycled. The gold loaded carbon is moved into a vessel where the gold is chemically stripped from the carbon, which is then recycled. Gold is precipitated from the solution electrolytically or by chemical substitution. The pure gold is then melted into dore' bars containing up to 90 % gold. Dore' bars are then sent to an external refinery to be refined to bars of 999.9 parts per thousand pure gold.
The prime use is in electronics. Our age of high technology finds it indispensable in everything from pocket calculators to computers, washing machines to television and missiles to spacecraft. The rocket engines of American space shuttles are lined with 35% gold brazing alloys to reflect the 3300. heat, and the lunar modules of the Apollo program that put men on the moon were shrouded with gold foil acting as a radiation shield. (World Gold Council) More commonly, the humble touch telephone in your home typically contains 33 gold-plated contacts. The plating of such contacts in switches, relays and connectors is the major application of gold in electronics. Contacts are electroplated with a very thin film of gold using gold potassium cyanide (GPC), often called plating salts. This touch of gold on a contact ensures rapid dissipation of heat and guarantees freedom from oxidation or tarnishing at extreme low or high temperature, thus providing an atomically clean metal surface with an electrical contact resistance close to zero. Not surprisingly "nothing is as good as gold" to provide total reliability, whether out in space or in the home. The production of plating salts accounts for 70% of the more than 150 tonnes of gold used annually in electronics. Although new technology has enabled plating thickness to be pared down to less than one-thousandth of a millimeter of gold, gold consumption has been maintained because of the myriad new electronic applications.
Gold's other main role in electronics is in semi-conductor devices, where fine gold wire or strip is used to connect parts such as transistors and integrated circuits, and in printed circuit boards to link components. Again, the need for reliable connections makes gold indispensable. This bonding wire is one of the most specialized uses of gold; it is highly refined to 999.99 purity and the wire has a typical diameter of one-hundredth of a millimeter. Japan is the major fabricator of electronics products in the western
world, accounting for over 45% of gold consumption, followed by the United States with nearly 30%. The United Kingdom and Germany are the only other significant contributors at about 6 and 7% respectively, although South Korea is growing. Dental gold is the second important sector. Gold has been used in dentistry for almost 3000 years. The Etruscans in the 7th century BC used gold wire to fix substitute teeth when their own were lost. In the 16th century an early dental text book recommended gold leaf for filling cavities.
Gold's malleability and resistance to corrosion render it eminently suitable for dental use, although its softness means that it must be alloyed to retard wear. The most common companion metals are platinum, silver and copper. A typical alloy may contain anywhere from 620 - 900 fine gold depending on the precise end-use. In recent years the price of gold has resulted in a trend towards cheaper alloys with as little as 30% gold and towards palladium-based alloys which contain scarcely 2% gold.
Gold alloys have also suffered competition from new techniques, such as ceramic dental crowns. In addition, social security payments for gold dental work have come under tighter scrutiny; reductions in such insurance payments make gold use more price sensitive. These factors initially contributed to a sharp fall in gold use by the dental sector, from 64 tonnes in 1980 to 48 tonnes by 1987. However, there has since been a recovery because of its non-allergic properties; demand has revived to 60 tonnes annually. Japan is the leading dental gold fabricator, accounting for roughly 28% of the market, followed by Germany and the United States. There is Significant unrecorded use, however, in Asia and Latin America where it is not unknown for dentists to melt down gold coin to make their own alloy.
Other applications for gold include decorative plating of costume jewelry, watchcases, pens and pencils, spectacle frames and bathroom fittings. Gold-based points are used for decoration of china and glass. Demand for gold from this sector is around 90 tonnes per year. The gold is used in various forms, such as rolled gold and gold fill, although both of these are under competition from new techniques. On the other hand, the use of gold electroplating in watchcases and similar products is increasing. Visually, the most spectacular use of decorative gold is gold leaf which has been used for centuries to adorn the domes or ceilings of public buildings, because its resistance to corrosion means it will outlast paint by many years. Gold's ability to reflect heat in summer and help retain it in winter has also led to the use...
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