Precious Metals
Platinum
Properties Brief History Other Uses Alloys Working with Platinum
Precious Metals
Platinum
Properties Brief History Other Uses Alloys Working with Platinum
Platinum is a silvery-white metal that ductile and malleable when pure and when alloyed with certain other metals. Its chemical symbol is Pt and its atomic number is 78. It occurs in nature with small amounts of other platinum group metals. It does not corrode or tarnish in air or water and is unaffected by most chemicals and acids, with the exception of aqua regia. Platinum and many of the other platinum group metals are excellent catalysts and tend to absorb large volumes of hydrogen. Platinum melts at 1769 degrees celsius (3216 F), has a density of 21.45 grams per cubic centimeter and is a very poor conductor of heat. It is nearly twice as dense as silver and 10% more dense than gold. Only 15 other elements have a melting point higher than platinum, and five of these are platinum group metals. Platinum has magnetic properties when alloyed with cobalt.
The popular use of platinum dates back only a few hundred
years, though it was worked with some success by South Americans
over 1,000 years ago. It was not until the Spanish conquest of
the New World in the fifteenth and sixteenth century that news
of a new white metal with unusual properties reached Europe.
By the end of the 17th century, Spanish Conquistadors discovered
alluvial deposits of platinum while searching for gold in what
is now Columbia. The metal was considered a nuisance because
it interfered with their gold mining activities and had little
value.
European scientists found platinum's extraordinary properties of interest, and it was described as a substance that could not be melted by fire or by any of the Spanish arts, was even heavier than gold and was virtually impossible to corrode with gasses or chemicals. In 1751, a Swedish assayer named Scheffer, recognized platinum as the seventh element know to exist up to that time.
It was these qualities of platinum that made the white metal attractive for industrial uses. It was used in Berlin in the 1780's to make durable acid- and heat-resistant laboratory instruments, and in France to make crucibles for the production of glass.
In the early 19th century, new refining techniques increased platinum's availability and it was soon used in batteries and fuel cells and as components in the production of caustic chemicals.
Most platinum was still produced in Columbia, but in 1822, alluvial platinum was discovered in the Ural Mountains in Russia. Widespread mining of platinum began, but since there was little Russian demand, the government began to produce platinum rubles. Over the next 18 years the Russians minted almost 500,000 ounces of platinum.
Industry and coinage were the major uses of platinum in the 19th century and platinum jewelry remained rare until the advent of the high-temperature jewelers' torch. Until the early 20th century, diamonds were set in silver to display their near-colorless beauty without the yellow tinting caused by gold. Silver, however, is quite soft and to provide security for the stones, settings had to be made quite large and heavy. Platinum was soon embraced as the metal of choice for diamond setting.
Only between 5 and 6 million ounces of platinum are produced each year, less than 5% the production of gold. It is estimated that all the platinum ever mined would fill a room less than 25 feet square.
Today's main sources of platinum are just south of Pretoria, South Africa's capitol - producing nearly two-thirds of the worlds supply, and in the extreme north of Siberia.
Platinum, in its pure form, is too soft and easily deformed to be used in jewelry. In order to make the metal hard and strong enough to withstand daily wear and to secure gemstones, it is necessary to alloy (mix) the platinum with other metals. The two most common alloys are: 950 pt, 95% platinum and 5% ruthenium; and 900pt, 90% platinum and 10% iridium. Both these alloys provide good workability, are ductile and malleable, quite strong, wear well and take a beautiful high polish.
Every country has its own standards for precious metal content in jewelry. Some countries allow platinum jewelry to be marked "platinum" even if those pieces contain less than 50% platinum, while other only allow items to be marked "platinum" if they contain at least 90% platinum. Our alloy of choice is 95% platinum and 5% ruthenium because it is accepted as platinum in all countries, it is the only alloy allowed by our major customers, and it does not oxidize or discolor when heated or exposed to different chemicals.
There are other alloys in use in platinum jewelry around the world, some of these include:
Platinum/copper alloys - used primarily in Europe
Platinum/cobalt alloys - easy to cast in an inert atmosphere or vacuum, cannot be cast in an air atmosphere, discolors when heated and cannot be welded, has magnetic properties
Platinum/tungsten alloys - used in heat/work hardening applications such as snaps and clasps where springiness is required
Platinum/proprietary alloys - recently developed by "experts" in the platinum field, cannot be cast in an air atmosphere, must be cast in vacuum or inert atmosphere, some discolor with heat, cannot be welded, scrap cannot be reused without melting in inert atmosphere/vacuum, alloying metals not disclosed by manufacturer, available only through manufacturer at nearly prohibitive cost.
Aside from platinum's great strength, beautiful luster and substantial density, it has many properties that make it a joy to work. Unlike gold and silver alloys, the platinum/ruthenium and platinum/iridium alloys do not oxidize nor discolor when heated, are nearly impervious to most chemicals and are hypoallergenic. They conduct heat so poorly that one can hold a small piece of platinum by hand and heat one end to red hot without burning your skin. This characteristic is essential for performing intricate welds and solders on hand-made pieces of jewelry because individual components can be added without the fear of previous assemblies shifting or detaching.
Platinum is ductile and malleable, meaning it can be hammered or rolled into shape, or drawn into fine wire.
It will also bend into shape and stay in that shape without springing back. This makes platinum a fine choice for setting stones because the prongs will bend and stay to securely hold a gem.
Platinum takes a beautiful polish, but much effort is required to attain this polish. It is much more difficult to polish platinum than silver or gold, but it is this characteristic that makes platinum jewelry wear and last much longer than jewelry made of the lesser metals.
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ductile: capable of being drawn into wire
malleable: capable of being formed by beating with a hammer or by the pressure of rollers
alloy: a substance composed of two or more metals or of a metal and a nonmetal intimately united usually by being fused together and dissolving in each other
when moltenElements with a melting point higher than platinum:
| Boron | 2100 C (not found pure in nature) |
| Carbon | 3727 C |
| Chromium | 1875 C |
| Hafnium | 2222 C |
| Iridium | 2454 C |
| Molybdenum | 2610 C |
| Niobium | 2468 C |
| Osmium | 3045 C |
| Rhenium | 3180 C (not found pure in nature) |
| Rhodium | 1966 C |
| Ruthenium | 2500 C |
| Tantalum | 2996 C |
| Tungsten | 3387 C |
| Vanadium | 1900 C |
| Zirconium | 1852 C |
Platinum Group Metals: The group of 6 metals having similar properties:
| Platinum: atomic number 78, Density 21.45 g/cm, melting point 1769 C |
| Ruthenium: atomic number 44, Density 12.45 g/cm, melting point 2500 C |
| Rhodium: atomic number 45, Density 12.41 g/cm, melting point 1966 C |
| Palladium: atomic number 46, Density 12.02 g/cm, melting point 1552 C |
| Iridium: atomic number 77, Density 22.65 g/cm, melting point 2454 C |
| Osmium: atomic number 76, Density 22.6 g/cm, melting point 3045 C |
aqua regia: a mixture of nitric and hydrochloric acid
catalyst: a substance that, without being used up, enables a chemical reaction to proceed at a usually faster rate or under different conditions than otherwise possible
crucible: a vessel in which a substance can be melted.
fuel cell: a device that changes chemical energy directly into electricity
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