Pure Nickel Films Research Articles

Adsorption and reaction of cyclopropane and hydrogen on nickel: Changes in selectivity with temperature

A comparative study was made of the cyclopropane chemisorption on pure nickel film surfaces and of the hydrogenation and hydrocracking of cyclopropane on both the films and a reduced nickel catalyst. In a range of higher coverages, the chemisorption of cyclopropane at 273 °K was accompanied by selfhydrogenation to propane, and, as a characteristic feature of the process on nickel, cracking to methane and ethane was also observed. Some further data concerning composition and properties of the chemisorbed layers are also given. Cyclopropane was reacted with hydrogen on nickel films in an UHV apparatus at 195 and 273 °K, and in the range of 300–600 °K using a microcatalytic-pulsed reactor coupled to a gas chromatograph. For the purpose of comparison, hydrocracking of propane was also investigated under the same conditions on the nickel powder catalyst. From the temperature variation of the product composition thus obtained, two types of cyclopropane cracking could be distinguished. With the low-temperature selective hydrocracking, the percentage of methane and ethane in overall product was constant over the range of 195–500 °K. Beyond this range the nonspecific hydrocracking began, characterized by the increasing proportion of cracking in products and by the prevalence of methane over ethane. No distinction could be made between the latter process and the propane or propylene hydrocracking. Some mechanistic consequences of the experimental findings are discussed. A concerted simultaneous splitting of two bonds in the chemisorbed cyclopropane ring is suggested as the reaction path for the low-temperature fragmentation.

Heterogeneity of adsorptive bond of carbon monoxide on the surfaces of pure iron and nickel films: K Fricke,PhD Thesis, techn hochschule Hannover, 62 pages (in German), (Sci Tech Aerospace Reps, 6 (6), 786, N68-15043).

Heterogeneity of adsorptive bond of carbon monoxide on the surfaces of pure iron and nickel films: K Fricke,PhD Thesis, techn hochschule Hannover, 62 pages (in German), (Sci Tech Aerospace Reps, 6 (6), 786, N68-15043).

Magnetic Anisotropy in Single-Crystal Thin Films

Thin, single-crystal films of Ni, Fe, Ni-Fe and Ni-Co have been grown by vacuum deposition onto heated rock salt. The cubic crystalline anisotropy constant, K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> , of these films has been measured at room temperature by a torque method. In the case of the Ni-Fe alloys, K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> was found to be the same for thin films as for bulk materials of the same composition. The measured anisotropy in the Ni-Co films differs quantitatively but has the same qualitative variation with composition as is reported for bulk crystals. The results of one magnetic annealing experiment on a 75% Ni - 25% Fe film lends support to the short-range ordering model of uniaxial anisotropy in alloys. Pure nickel films exhibit a pronounced uniaxial anisotropy superimposed on the crystalline anisotropy. This uniaxial term disappears after the film is removed from the substrate, indicating that its origin is in an anisotropic stress in the deposited film.