Also called fire assay, the method involves treating ores or alloyed metals under high temperatures and carefully controlled operations to separate gold from base metals (copper, zinc, or lead), which may be present in the ore. Once the base metals are heated at high temperatures, the gold (as well as the other precious metals that may be present) remains apart and the other non-precious metals react forming other compounds. mol-1 Heat of Vaporization: 563 kJ.mol-1 Atomic: Oxidation States: -3, -1, 0, 1, 2, 3, 4, 5, 6 Electronegativity: 2.20 (Pauling scale) Atomic Radius: 136 picometre Covalent Radius: 141 6 picometre Because of its characteristic of being very brittle, pure iridium is quite difficult - almost impossible, in fact - to machine. These are Australia, Austria, Canada, China, Mexico, Poland, South Africa, Switzerland, the United Kingdom, and the United States. While bullion coins are issued as legal tender, with nominal values assigned to them on minting, such face values are far below the commodity value of the metals themselves. The two coin versions can be distinguished from one another by the number of serrations they have - the proof version has 220, while the bullion has 40 less than the former's. Other nations, such as Canada, Australia, the United States, and the United Kingdom, started producing their own precious metal coins one after the other beginning in 1979. 1/10 ounce coin - With 3.11 g platinum content, 3.112 g in weight, and 16.5 mm in diameter. 3. 1/4 ounce coin - With 7.776 g platinum content, 7.78 g in weight, and 22 mm in diameter. 4. 1/2 ounce coin - With 15.552 g platinum content, 15.6 g in weight, and 27 mm in diameter. 5. 1 ounce coin - With 31.103 g platinum content, 31.119 g in weight, and 32.7 mm in diameter. In order of increasing mass abundance (parts per billion), the precious metals are rhenium, rhodium, iridium, ruthenium, osmium, gold, platinum, palladium, and silver. These metals are not radioactive and are mostly used for industrial purposes and for jewelry. Still, precious metals have some safety issues attached to them: Rhenium: Since rhenium is used in very small amounts, its toxicity is virtually unknown.
Share This Page