Platinum group metals have similar physical and chemical properties as well as their own unique characteristics. For example: they are all in silvery white except osmium and ruthenium in steel gray, all of them have high melting point, high strength, thermal stability, high resistance to spark erosion, excellent corrosion resistance, strong oxidation resistance and good catalytic activity. At the meanwhile, different performances determine different uses. Platinum has good plasticity, stable resistance and resistance temperature coefficient. When it is forged into platinum wires and platinum foils, it will not be combined with oxygen, not be eroded by acid or alkali as well. It is only dissolved in hot aqua regia. Palladium can be dissolved in concentrated nitric acid and it can absorb 350 ~ 850 times the volume of hydrogen at room temperature. Rhodium and iridium insoluble in aqua regia can react with molten sodium hydroxide and sodium peroxide and produce compounds dissolved in acid. Osmium and ruthenium are not soluble in aqua regia, but they are easily oxidized to four oxides.
