| Platinum |
|
Platinum and gold are from the few metals that can be found in their pure state, uncombined with other elements. Platinum’s extreme natural hardness, strength and ductility are some of its most valuable properties. On the contrary, its steely grey appearance was not prized till the 19th century. Platinum’s metallic bonding makes it stronger than gold and it can shine like silver without tarnishing. This lustrous silver-white metal is much better than gold to complement the glitter of diamonds. Platinum is in fact one of the six closely related metals that all belong in the platinum-group (platinum, palladium, rhodium, iridium, osmium, ruthenium). Palladium is, like platinum, malleable and highly resistant to oxidation and corrosion, but it has a much lower melting point and significantly less density. Rhodium is extremely rare and the most expensive of all metals. Rhodium typically occurs in proportions of 1 part rhodium to 18 parts platinum. Of all the platinum metals, rhodium has the highest electrical and thermal conductivity. Its great reflectivity and high melting point make it ideal for surfaces that are subjected to high temperatures. Iridium is insoluble in all acids except hydrochloric, and its extreme hardness makes it an ideal alloy to strengthen softer platinum in jewellery. Osmium is the heaviest metal on earth. It also has the highest melting point of all the platinum metals. But, it is so highly toxic, that there is little commercial use of it, mostly in staining tissues for electron microscopy. Ruthenium is used as a catalyst in petroleum refining and in electrical contacts. When combined with platinum, it forms one of the hardest metals known and is used in fine surgical instruments. Roughly 90% of all platinum supplies come from South Africa and Russia. Part of platinum's appeal lies in the fact that it dulls very little over time and never tarnishes. Platinum is a hypoallergenic metal that will not irritate the skin. Typically platinum is alloyed with copper, iridium, palladium, rhodium, osmium, titanium, ruthenium or gold. Pure platinum is marked 999 (999 parts per 1000 or 99,9% pure). Most platinum jewellery is 95% pure platinum, and 5% iridium or palladium alloy. This is marked 950 (950 parts per 1000) and is a recognised standard of “fineness”. Accordingly, there are two more standards 900 (90%) and 850 (85%). Of the many industrial uses of platinum the most important is its role as a catalyst vital to the production of nitric acid used in making fertilisers, explosives and nylon manufacturing. For this catalytic property, platinum is also used in catalytic converters, incorporated in automobile exhaust systems, as well as tips of spark plugs. |
