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Crystal structure, thermal expansion and melting point of americium metal

1962; Pergamon Press; Volume: 24; Issue: 9 Linguagem: Inglês

10.1016/0022-1902(62)80246-2

1878-1225

D. B. McWhan, B.B. Cunningham, J.C. Wallmann,

Hydrogen Storage and Materials

The methods for preparing milligram quantities of pure, well crystallized americium metal are discussed in detail. A versatile high and low temperature X-ray powder camera for small radioactive samples is presented. americium metal prepared by the reduction of americium trifluoride with barium vapour has been indexed as hexagonal close-packed with a = 3·4681 ± 0·0008 Å and c = 11·241 ± 0·003 Å at 20°C. The proposed structure type is that of lanthanum metal (P63/mmc with metal atoms in 2 (a) 000; 0012 and 2 (c) 13, 23, 14; 23, 13, 34). Americium metal condensed on a tantalum wire or quartz fibre from the vapour phase was found to be face-centred cubic (a = 4·894 ± 0·005 Å) with a density similar to the dhcp structure. Evidence for the existence of a face-centered cubic form of americium metal above 600°C, is presented. The following physical properties of americium metal have been determined: (1) Melting point: 994 ± 7°C. (2) Density (X-ray): 13·671 ± 0·005 g/cm3 (20°C). (3) Metallic radius (CN 12): 1·730 Å. (4) Coefficient of thermal expansion: (20°C) αa = 7·5 ± 0·2 × 10−6°C−1αc = 6·2 ± 0·4 × 10−6°C−1