Platinum group metals, also known as platinum group elements. Six metallic elements, including platinum (Pt), palladium (Pd), osmium (Os), iridium (Ir), ruthenium (Ru) and rhodium (Rh), belong to cycle 5 and 6 in the periodic table. Native element in the gemological application widely, including precious metals palladium jewelry - white to be bestowed favor on newly, the international fashion jewelry platinum, palladium for pge deposit in a minimum of two kinds of mineral and metallurgical properties of the two is quite similar, because its too rare, similar purposes, so often do substitute each other in the various applications.
Platinum metals have similar physical and chemical properties as well as their own properties. Their common characteristic is: apart from osmium and ruthenium being steel gray.
The rest were silver; High melting point, high strength, stable electrothermal property, high corrosion resistance to electric spark, good corrosion resistance, high temperature oxidation resistance, good catalytic activity. Their respective characteristics determine their different USES. For example, platinum has good plasticity and stable resistance and resistance temperature coefficient, which can be forged into platinum wire and platinum foil. It is not directly combined with oxygen and is not corroded by acid and alkali. It is only soluble in hot royal water. Palladium is soluble in concentrated nitric acid and absorbs 350 to 850 times its volume of hydrogen at room temperature. Rhodium and iridium are insoluble in royal water and can react with molten sodium hydroxide and sodium peroxide to form compounds soluble in acids. Osmium and ruthenium are insoluble in royal water but easily oxidized to tetraoxide. Their main physical and mechanical properties are shown in table 3.17.1.
Platinum and rhodium have good oxidation resistance, and can keep bright in the air for a long time without being oxidized. At high temperatures platinum and rhodium interact with oxygen to produce volatile oxides, increasing its evaporation rate. Powdered iridium at 600 ℃ in air or oxygen oxidation, generate a layer of iridium oxide (IrO2) thin film. The oxide decomposition when higher than 1100 ℃, make metal to restore the original luster. Iridium is the only thing that can be used to 2300 ℃ in oxidizing atmosphere without serious loss of metal. Ruthenium and osmium are easily oxidized, and at room temperature, blue oxide film (OsO2) is formed on the surface of osmium. Osmium tetroxide (OsO4) and ruthenium tetroxide (RuO4) are volatile toxic compounds that can stimulate the mucous membrane and damage the skin.
Platinum group metals are all transition metals, and have multiple combined prices. Their stable combined prices are: ruthenium +3, rhodium +3, palladium +2, +4, osmium +3, +4, iridium +3, +4, platinum +2, +4. They both have a strong tendency to form complex complexes, with the most common ligands being 4 and 6.
Platinum has excellent thermoelectric stability, high temperature oxidation resistance and high temperature corrosion resistance. Palladium can absorb hydrogen 2,800 times its volume, and hydrogen can travel freely among palladium. Iridium and rhodium are resistant to many kinds of oxidants and have good mechanical properties. Ruthenium can bind to ammonia but does not react chemically, similar to the properties characteristic of certain bacteria. Osmium is very brittle and hard, with the largest volume elastic modulus. Osmium and ruthenium are easy to oxidize, and their oxides are irritating and toxic.
