10 Metais mais valiosos do Mundo

10 Most valuable Metals in the World
When it comes to finding that perfect piece of jewelry, many of us are concerned with the dazzling gem (or gems, depending on the size of your wallet). Much of the time, settings, bands and chains end up playing second fiddle to the sparkling jewels they hold.

However, there's a reason your neighbor hides his gold coins, and your dad locks the family silverware in a safe. Gold and silver are two extremely valuable metals -- deemed as precious because of their rarity, socioeconomic importance, non-reactivity and ability to withstand corrosive and oxidative forces. From year to year, even month to month, prices of these valuable metals fluctuate greatly.

Besides looking great around someone's neck or finger, these valuable metals also have industrial purposes. For example, platinum-group metals are used to create lab equipment, dental materials and electronics. Precious, or valuable, metals also serve as a means of investment as these commodity prices have continued to rise over the years. It's important to note that the common unit of weight for precious metals is the troy ounce -- equivalent to 1.1 standard ounces or .031 kilograms.

10. Indium
File:Indium.jpg
  Indium is a rare metal produced from zinc-ore processing, as well as lead, iron and copper ores. In its purest form, indium is a white metal that's extremely shiny and malleable. It was used first widely during World War II, as a coating for bearings in aircraft engines. Indium can also be used to create corrosive-resistant mirrors, semiconductors, alloys and electrical conductivity in flat-panel devices.
  The largest producers included China, South Korea and Japan. Indium recycling or reclamation has become more popular as the price of indium rises.
  Indium is a chemical element with symbol In and atomic number 49.

9. Silver
File:Silver crystal.jpg
  If every cloud really did have a silver lining, we'd all be enjoying lucrative rainstorms. That's because silver is one of the most valued metals on Earth. This lustrous white element, in its purest form, has the best electrical and thermal conductivity, as well as the lowest contact resistance of all the metals.
  You may know silver's common uses -- jewelry, coinage, photography, circuitry, dentistry, batteries -- but what about the surprising ones? Silver can be used to stop the spread of bacteria in cell phone covers, control odor in shoes and clothing and prevent mold in treated wood. In fact, some clouds may very well have real silver linings since silver iodide is used in cloud seeding.
  Silver can be found in such ores as horn silver and agentite. And silver is a valuable by-product of processing and smelting copper, gold and lead-zinc ores. Peru, China, Mexico and Chile were the top producers of silver. Because of its many uses, silver is one of the most valuable metals exchanged today.
  Silver is a chemical element with the chemical symbol Ag and atomic number 47.

8. Rhenium
File:Rhenium single crystal bar and 1cm3 cube.jpg
  Though perhaps not as well known as fellow precious metals like gold and platinum, silvery rhenium is one of the densest metals and has the third highest melting point.
  Because of its ability to withstand blistering conditions, rhenium, discovered in 1925, is used in high-temperature turbine engines. This cool-as-a-cucumber metal is also added to nickel-based superalloys to improve temperature strength. Other uses include filaments, electrical contact material and thermocouples.
  Rhenium is a by-product of molybdenum, which essentially is a by-product of copper mining. Chile, Kazakhstan and the United States led world production of this valuable metal.
  Rhenium is a chemical element with the symbol Re and atomic number 75.

7. Palladium
File:Palladium.jpg
 In 1803, William Hyde Wollaston discovered a way to separate palladium from its surrounding platinum ore. This grayish-white, precious metal is valued because of its rarity, malleability, stability under hot conditions and ability to absorb a considerable amount of hydrogen at room temperature.
  Palladium, named for the Greek goddess Pallas, is a member of the precious-metals group. Its valuable properties put palladium in high demand within various industries: Automobile makers rely on it for their catalytic converters to reduce emissions; jewelers use palladium to create "white gold" alloys; and electronics manufacturers have the option of plating with it, as palladium has excellent conductive traits.
  Almost half of the world's palladium came from Russia, followed by South Africa, the United States, Canada and other various countries.
  Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46.

6. Osmium
File:Osmium crystals.jpg
  One of the densest elements on Earth, osmium is a bluish-silver metal discovered by Smithson Tennant in 1803. He also discovered iridium (our valuable metal no. 5) that year as well. There's debate about whether osmium or iridium is the heavier element.
  Rare osmium usually is alloyed with the other platinum-group metals in nickel-heavy ores, and iridosuleis mined in parts of Russia and North and South America.
  This very hard, brittle metal has an extremely high melting point which can be problematic when trying to manipulate it. For the most part, osmium is used to harden platinum alloys for electrical contacts, filaments and other uses. There are dangers associated with handling osmium, as it emits a toxic oxide that can cause skin and eye damage as well as lung congestion.
  Osmium is a chemical element with the symbol Os and atomic number 76.

5. Iridium
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  If valuable metals could have mottos, iridium's would be "go big or go home." It is definitely the most extreme member of the platinum group. This whitish metal has an amazingly high melting point, is one of the densest elements around and stands as the most corrosion-resistant metal. Water, air, even acid, have no real affect on iridium.
  Because of its extreme properties, iridium is difficult to obtain and manipulate. It mostly comes from South Africa, is processed from platinum ore and as a by-product of nickel mining. Its unique traits allow this hard metal (much harder than platinum) to contribute to advancements in medicine, electronics and automobiles, as well as in such products as pens, watches and compasses.
  Even jewelers are trying to use iridium in a few exclusive pieces. With a high shine factor and a low-tarnish guarantee, iridium could make an amazing medium for those willing to front the cash.
  Iridium is the chemical element with symbol Ir and atomic number 77.

Metals from Outer Space
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The Willamette Meteorite, the sixth-largest meteorite found in the world, has 4.7 ppm iridium.
Iridium is one of the rarest elements on Earth, yet scientists discovered huge amounts of this metal at the K-T boundary (the change from Mesozoic to Cenozoic eras, referring to a huge extinction event). This provides proof to many scientists that a massive asteroid struck Earth, displacing a cloud of iridium at the moment of impact.

4. Ruthenium
File:Ruthenium a half bar.jpg
  Russian scientist Karl Karlovich Klaus discovered ruthenium, a bright gray metal, in 1844. This member of the platinum metals retains many of the group's characteristics, including hardness, rarity and an ability to withstand outside elements -- to a point. It doesn't degrade at room temperature, but going above 800 degrees Celsius (1,472 degrees Fahrenheit) will eventually impact the metal.
  Ruthenium is found among the same ores of its fellow platinum-group metals throughout areas of Russia and the Americas, including nickel-dense areas of Canada.
  After a complex chemical process, the metal can be isolated and used for various purposes. Ruthenium can be added as an alloy to platinum and palladium in order to increase hardness (for jewelry) and better resistance (against corrosive agents, especially with titanium). Ruthenium has become quite popular in the electronics field, as a way to effectively plate electric contacts.
  Ruthenium is a chemical element with symbol Ru and atomic number 44.


3. Gold
File:Gold-crystals.jpg
  Whether we're wearing it, paying with it, praying to it, starting wars over it or even being buried inside it, gold has always been a cherished commodity. Gold has enticed everyone -- from the ancient Egyptians who forged gold coffins to the 19th century prospectors who scoured California coast for nuggets.
  Because of its desirability, durability and malleability, gold remains one of the most popular metals and investment options.
  The largest miners of gold include South Africa, the United States, Australia and China. Gold is usually separated from surrounding rocks and minerals by mining and panning, upon which the metal is extracted with a combination of chemical reactions and smelting.
  Besides looking great on your fingers, neck and ears, gold has valuable industrial uses as well. Its conductivity makes it a great component of electronics, and its reflective surface helps create better radiation shields and office windows.
  Gold is a chemical element with the symbol Au and atomic number 79.

2. Platinum
File:Platinum-nugget.jpg
  The most affordable way for some of us to wear "platinum" is to dye our hair bright white and look like we walked out of an '80s music video. That's because real platinum, a dazzling, silvery metal, can drain a bank account fast.
  Found in South Africa, Russia, Canada and other countries, platinum has made a name for itself through its malleability, density and non-corrosive properties. In addition, platinum is similar to palladium in its ability to withstand great quantities of hydrogen.
  This valuable metal has become well known in the jewelry world for its lustrous look and remarkable resistance. Platinum is also used in fields like dentistry, weaponry and aeronautics.
  Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78.

1. Rhodium
File:Rhodium powder pressed melted.jpg
  Though its name may sound like a place where cowboys strut their stuff, rhodium is actually one of the world's most valuable metals. This shiny, silvery-colored metal is commonly used for its reflective properties -- in objects like search lights, mirrors and jewelry finish.
  Besides its popular metallic uses, rhodium is valuable for its catalytic applications within the automotive industry. Its high melting point and ability to withstand corrosion allow rhodium to be a crucial addition in many industrial fields.
  This extremely rare and valuable metal is found in only a few places. 60 percent of rhodium came from South Africa, followed by Russia. Though the price has been falling over the years, rhodium is still one of the most expensive metals around.
  Rhodium is a chemical element that is a rare, silvery-white, hard, and chemically inert transition metal and a member of the platinum group, it has the chemical symbol Rh and atomic number 45.

Note:
  Paul McCartney may have sung about a man with a silver hammer, but to celebrate his pre-eminent status as a recording artist, the Guinness Book of World Records presented him with a rhodium disc.

Source: http://www.discovery.com

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