Platinum
Title: Platinum
CAS Registry Number: 7440-06-4
Literature References: Pt; at. wt 195.084; at. no. 78; valences 2,4; seldom 1, 5, 6. Group VIII (10). Six naturally occurring isotopes: 190 (0.01%); 192 (0.8%); 194 (32.9%); 195 (33.8%); 196 (25.2%); 198 (7.2%); 190 is radioactive: T½ 6.9 ´ 1011 years. Artificial, radioactive isotopes: 173-189; 191; 193; 197; 199-201. Abundance in earth's crust about 0.01 ppm. Believed to be mentioned by Pliny under the name "alutiae". Has been known and used in South America as "platina del Pinto". Reported by Ulloa in 1735; brought to Europe by Wood, and described by Watson in 1741. Occurs native alloyed with one or more members of its group (iridium, osmium, palladium, rhodium, and ruthenium) in gravels and sands. Prepn: Wichers et al., Trans. Am. Inst. Min. Metall. Eng. 76, 602 (1928). Reviews of prepn, properties and chemistry of platinum and other platinum metals: Gilchrist, Chem. Rev. 32, 277-372 (1943); Beamish et al., in Rare Metals Handbook, C. A. Hampel, Ed. (Reinhold, New York, 1956) pp 291-328; Livingstone in Comprehensive Inorganic Chemistry Vol. 3, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 1163-1189, 1330-1370; F. R. Hartley, The Chemistry of Platinum and Palladium with Particular Reference to Complexes of the Elements (Halsted Press, New York, 1973).
Properties: Silver-gray, lustrous, malleable and ductile metal; face-centered cubic structure. Also prepd in the form of a black powder (platinum black) and as spongy masses (platinum sponge). mp 1773.5 ± 1°; Roeser et al., Natl. Bur. Stand. J. Res. 6, 1119 (1931); bp about 3827°. d 21.447 (calcd). Brinell hardness: 55. Sp heat 0.0314 cal/g at 0°. Electrical resistivity (20°) 10.6 mohm-cm. Does not tarnish on exposure to air. Absorbs hydrogen at a red heat and retains it tenaciously at ord. temp, gives off the gas at a red heat in vacuo. Occludes carbon monoxide, carbon dioxide, nitrogen. Volatilizes considerably when heated in air at 1500°. The heated metal absorbs oxygen; gives it off on cooling. Not affected by water or by single mineral acids. Reacts with boiling aqua regia with formation of chloroplatinic acid, also with molten alkali cyanides. Attacked by halogens, by fusion with caustic alkalies, alkali nitrates, alkali peroxides; by arsenates and phosphates in presence of reducing agents.
Melting point: mp 1773.5 ± 1°; Roeser et al., Natl. Bur. Stand. J. Res. 6, 1119 (1931)
Boiling point: bp about 3827°
Density: d 21.447 (calcd)
CAUTION: Potential symptoms of overexposure to Pt metal are irritation of eyes, skin, respiratory system; dermatitis. Potential symptoms of overexposure to soluble Pt salts are irritation of eyes, nose; cough, dyspnea, wheezing, cyanosis; dermatitis, skin sensitization; lymphocytosis. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH 97-140, 1997) p 260. See also E. Browning, Toxicity of Industrial Metals (Appleton-Century-Crofts, New York, 2nd ed., 1969) pp 270-275.
Use: Manuf apparatus for laboratory and industrial use, thermocouples, platinum resistance thermometers, acidproof containers, electrodes, etc. In dentistry; jewelry; electroplating. As oxidation catalyst in manuf acetic acid, nitric acid from ammonia, manuf sulfuric acid; control of automotive emissions.

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