Metall preciós
De Viquipèdia
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Un metall preciós és aquell element químic metàl·lic poc freqüent a la natura i d'elevat valor econòmic. Químicament parlant els metalls preciosos són menys reactius que la majoria dels elements, amb marcada lluentor o lluïssor, són més tous i dúctils i tenen uns punts de fusió superiors a la de la resta de metalls. Històricament han estat importants en l'encunyació de monedes, però avui en dia són reservats principalment com a elements d'inversió i matèries primeres industrials. Tant l'or, com la plata, el platí i el pal·ladi tenen cadascú el seu codi ISO 4217.
Els metalls preciosos més ben coneguts són l'or i la plata. Tot i que ambdós tenen usos industrials, són més coneguts pels seus usos en art, joieria i coinage. Entre els altres metalls preciosos s'hi inclouen els metalls del grup del platí : ruteni, rodi, pal·ladi, osmi, iridi i platí, dels quals el platí és amb el qual es comercia més. El reni és un metall preciós que no forma part del grup del platí ni dels metalls preciosos tradicionals.
La demanda dels metalls preciosos no està originada només pel seu ús pràctic, but also by their role as investments and a store of value. Palladium, as of January 29, 2008, is valued at $388 USD per troy ounce, which is almost half the price of gold, at $995 USD/ounce. Platinum's price of $1,706 USD/ounce is almost twice that of gold. Rhodium is usually the most expensive of the precious metals, over 4.5 times more expensive than platinum, with a current price of $7,150. However, the price of rhenium has been fluctuating wildly recently and at the moment it is selling at 6,650 USD per ounce, just below rhodium. Meanwhile, ruthenium is valued at $525 USD per ounce and silver has fluctuated as well lately, trading at $16.69 USD/ounce. Silver is substantially less expensive than all of the other precious metals, presently less than 1/50 the price of gold, but is often traditionally considered a precious metal for its role in coinage and jewellery. [1]
With precious metal prices on the rise recyling precious metals has become more and more attractive.
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[edita] Llengots
A metal is deemed to be precious if it is rare. The discovery of new sources of ore or improvements in mining or refining processes may cause the value of a precious metal to diminish, as in the example of aluminium, which was considered a precious metal before the development of the Hall-Héroult process made it possible to extract aluminium on a large scale. The status of a "precious" metal can also be determined by high demand or market value. Precious metals in bulk form are known as llengots, and are traded on commodity markets. Bullion metals may be cast into ingots, or minted into coins. The defining attribute of bullion is that it is valued by its mass and purity rather than by a face value as money.
Many nations mint bullion coins, of which the most famous is probably the gold South African Krugerrand. Although nominally issued as legal tender, these coins' face value as currency is far below that of their value as bullion. For instance, Canada mints a gold bullion coin (the Gold Maple Leaf) at a face value of $50 containing one troy ounce (31.1035 g) of gold — as of September 2007, this coin is worth about $737 as bullion. Bullion coins' minting by national governments gives them some numismatic value in addition to their bullion value, as well as certifying their purity.
The level of purity varies from issue to issue. 99.9% purity is common. The purest mass-produced bullion coins are in the Canadian Gold Maple Leaf series, which go up to 99.999% purity. Note that a 100% pure bullion is not possible, as absolute purity in extracted and refined metals can only be asymptotically approached. Usually a bullion coin contains a stated quantity (such as one troy ounce) of the slightly-impure alloy; the Krugerrand is unusual in containing one troy ounce of actual gold, with the impurity making the coin heavier than one ounce.
One of the largest bullion coins in the world is the 10,000 dollar Australian Gold Nugget coin minted in Australia which consists of a full kilogram of 99.9% pure gold. There have been a small number of larger bullion coins, but they are impractical to handle and not produced in mass quantities. China has produced coins in very limited quantities (less than 20 pieces minted) that exceed 260 troy ounces (8 kg) of gold. Austria has minted a coin containing 31 kg of gold. As a stunt to publicise the 99.999% pure one-ounce Canadian Gold Maple Leaf series, in 2007 the Royal Canadian Mint made a 100 kg 99.999% gold coin, with a face value of $ 1 million, and now manufactures them to order, but at a substantial premium over the market value of the gold.
Gold and silver are often seen as hedges against both inflation and economic downturn. Silver coins have become popular with collectors due to their relative affordability, and unlike most gold and platinum issues which are valued based upon the markets, silver issues are more often valued as collectables, far higher than their actual bullion value.
[edita] L'alumini en el passat
L'alumini va ser considerat un metall preciós en el passat. Malgrat ser un dels materials més comuns del planeta, la dificultat per extreure'l de les seves menes va fer que l'alumini pur s'obtingués a un cost molt elevat, condició que durant un temps el va fer ser més car que l'or. Així:
- Barres d'alumini van ser exposades a l'Exposició Universal de 1855 juntament amb les joies de la corona francesa.
- Napoleó III va fer servir àpats en plats d'alumini per alguns dels seus més selectes convidats.
- La punta de la piràmide del monument a Washington està feta d'alumini pur, donat que en el moment de la seva construcció l'alumini era més car que el platí.
La invenció del procés de Hall-Héroult l'any 1886 va significar la fi dels preus alts de l'alumini.
[edita] Vegeu també
[edita] Enllaços externs
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