|
|
Atomic Number: |
78 |
Melting Point: | 1768.4 șC | |
| Atomic Symbol: | Pt | Boiling Point: | 3825 șC | ||
| Atomic Weight: | 195.09 amu | Density: | 21090
kg/m 3 |
||
| Atomic Radius: |
138 pm |
Oxidation States: | 2, 4 | ||
| Covalent Radius: | 128 pm | Electron Configuration: | [Xe]6s14f145d9 | ||
| van der Waals Radius: |
175 pm |
State of Matter: | solid |
(Sp. platina: silver) Discovered in South America by Ulloa in 1735 and by Wood in 1741. The metal was used by pre-Columbian Indians.
Platinum is a beautiful silvery-white metal, when pure, and is malleable and ductile. It has a coefficient of expansion almost equal to that of soda-lime-silica glass, and is therefore used to make sealed electrodes in glass systems. The metal does not oxidize in air at any temperature, but is corroded by halogens, cyanides, sulfur, and caustic alkalis.
It is insoluble in hydrochloric and nitric acid, but dissolves when they are mixed as aqua regia, forming chloroplatinic acid.
Platinum is now considered more precious than gold, so that a platinum award is better than a golden one. The price of platinum changes along with its availability, but normally it costs up to 8 times as much as gold.
Platinum occurs natively, accompanied by small quantities of iridium, osmium, palladium, ruthenium, and rhodium, all belonging to the same group of metals. These are found in the alluvial deposits of the Ural mountains, of Columbia, and of certain western American states. Sperrylite, occurring with the nickel-bearing deposits of Sudbury, Ontario, is the source of a considerable amount of metal.
The large production of nickel makes up for the fact that is only one part of the platinum metals in two million parts of ore.
The metal is extensively used in jewelry, wire, and vessels for laboratory use, and in many valuable instruments including therocouple elements. It is also used for electrical contacts, corrosion-resistant apparatus, and in dentistry.
The metal is used for coating missile nose cones, jet engine fuel nozzles, etc., which must perform reliably at high temperatures for long periods of time. The metal, like palladium, absorbs large volumes of hydrogen, retaining it at ordinary temperatures but giving it up when heated.
In the finely divided state platinum is an excellent catalyst, having long been used in the contact process for producing sulfuric acid. It is also used as a catalyst in cracking petroleum products. Much interest exists in using platinum as a catalyst in fuel cells and in antipollution devices for automobiles.
Platinum anodes are extensively used in cathodic protection systems for large ships and ocean-going vessels, pipelines, steel piers, etc. Fine platinum wire will glow red hot when placed in the vapor of methyl alcohol. It acts here as a catalyst, converting the alcohol to formaldehyde. The phenomenon has been used commercially to produce cigarette lighters and hand warmers. Hydrogen and oxygen explode in the presence of platinum.
Platinum-cobalt alloys have magnetic properties. One such alloy made of 76.7% Pt and 23.3% Co, by weight, is an extremely powerful magnet that offers a B-H (max) almost twice that of Alnico V. Platinum resistance wires are used for constructing high-temperature electric furnaces.90/10 Platinum/osmium alloy is used to make pacemakers, replacement valves and other surgical implants.
Naturally occurring platinum is composed of five stable isotopes and one radioisotope, Pt-190, which has a very long half-life of over 6 billion years. There are also many other radioisotopes with the most stable being Pt-193 with a half-life of 50 years.
This metal doesn't normally cause health problems due to its unreactive nature but all compounds of platinum should be considered to be highly toxic. Platinum compounds rarely occur in nature.
