Up to the discovery of the alleged Yamashita treasure, not so many of us know what platinum is and what it is all about. All that we are familiar with are that it is used for jewelry, for dental fillings, tips of pen, and that is is more expensive than gold, among others. But why it is so special?
Science books say that platinum is the most important of the group of elements called platinum metals, consisting of palladium, rhodium, ruthenium, iridium, osmium; often alloyed together; mostly iron and palladium in substantial amounts. Each has uni que properties and special uses.
Platinum (symbol: Pt) is so named after the Spanish plata (silver) because of its color. It is opaque, slightly bluish-gray like steel; some describe it as a grayish-white metal. And because it always contains iron, iron-rich varieties are dark gray t o nearly black streak shining grayish white, or luster metallic. Scientifically, platinum has an atomic number of 78, atomic weight of 195.08, specific gravity of 21.4520° , boiling point over 3,800°C, and does not melt in ordinary torch flames because it s melting point is 1770°C. It also has a high fusing point, is malleable and ductile - can be formed, and is very tough. It expands very slightly upon heating and has a high electric resistance. Clinically, it is a "noble" metal, that is, is inert and re sists attack by air, water, single acids and ordinary reagents (it does not react to most strong acids) it dissolves slowly only in hot aqua regia, forming chloroplatinic acid, it attached by halogens (it reacts with carbon, phosphorous, silicon, lead, a rsenic and antimony, and combines upon ignition with sodium hydroxide, sodium nitrate or sodium cyanide.
Platinum and palladium are far more important commercially than the other members of the platinum group metals. In general, because of platinum's chemical inertness and high fusing point, it is valuable in laboratory apparatus such as crucibles, tongs , funnels, combustion boats and evaporating dishes. It is also used in electrical apparatus (for contact points) and in instruments used for measuring high temperatures, It is also widely used as a catalyst in the chemical industry, where it is becoming more in demand. A great amount of platinum goes into jewelry in the United States, often alloyed with gold.
Specifically, others in this group are used as follows:
Rhodium, the whitest of the platinum metals, makes it widely used as an electroplate in applications ranging from the finishing of jewelry to the production of the 60-inch search light reflectors. Rhodium has useful catalytic properties that have been found suitable for electrical contacts, and is particularly useful as an electroplated surface on rubbing electrical contacts. The use of rhodium as an alloy with platinum for high temperature use, platinum-10% rhodium thermocouple, is standard for measu rement of temperatures up to about 1,500°C. For higher temperatures, thermocouples made of platinum with 7% and 30% rhodium are available. Platinum-rhodium alloys are used for heating windings in laboratory furnaces. Pure rhodium, as well as pure iridium crucibles are used in growing crystals for laser and related applications.
Iridium, the most corrosion-resistant of the platinum group, is a very effective hardener for platinum. Its extremely high melting point renders it useful is special situations where oxygen can be limited, as in growing special crystals. In addition t o the small percentage of iridium with osmium are found in most platinum deposits, natural alloys of iridium with osmium, found in a few places around the world. In addition, a few thousand ounces of osmiridium are recovered yearly from the gold ores of S outh Africa.
Iridium has outstanding resistance to lead compound at high temperatures , one of the reasons for its use in the ultra long life spark plugs. Small amounts of iridium are usually added to increase the hardness and durability of this metal.
Ruthenium is a good hardener too for platinum, the 12% alloy being used for contacts in voltage regulators, thermostats and magnetos. It is used to harden platinum, and particularly palladium for use in jewelry. Ruthenium content alloys are also use d for tipping the nibs of foundation pens. The electrodeposition of ruthenium is possible, and its hardness makes it useful in instruments where a low pressure rubbing contact is required.
Osmium is the rarest and hardest of the group and has the highest melting point, but its ready oxidation is a limitation. It has been used in the sunthesis of cortisone.
How does platinum look as raw material? Geology books say that platinum comes predominantly in nuggets or grains; large nuggets are rare and very few collections have specimens exceeding the size of a pea, although nuggets of the metal weighing up to 21 pounds have been found. This occurs in the metallic state, alloyed with other platinum metals except for the mineral sperrylite, a platinum arsenide found only in very few places. Nuggets are very small cubes and octahedrons from alluvial deposits, and grains are very rarely isometric crystals, that is having equal lines or sides.
Platinum is mined all over the earth, but the main sources are South Africa, the U.S.S.R. and Canada; other leading producers are Colombia in South America, New South Wales and New Zealand, Australia, and very small grains in the Alaskan alluvial depo sits and in California, U.S.A from the sands of the Trinity River in Trinity Country.
According to records, platinum metals were first mentioned in European literature in the early 16th century, and so were probably used then in Greece and Rome. The first platinum to reach Europe came from placers in the Choco district of what is now C olombia. The new thing was brought to England by a certain Sir Charles Wood in 1741. As its wonders became gradually known, scientific interest also grew. A method for separating quite pure platinum from the ore was devised, and they found the metal to be ductile. But then, its high melting point was a drawback for their intentions. Researchers in England, France, Germany and Russia however, devised methods for consolidating and working platinum into other useful forms. The separation of platinum for use in jewelry came about in 1906.
How is platinum recovered from its ore? Depending on the use or goal or recovery, different producers use different methods. Here are two examples.
Mining in South Africa is directed chiefly to the production of platinum metals; in the U.S.S.R., platinum metals as well as copper and nickel are involved; in Canada, nickel and cop