Abstract
Hydrogen-induced effects in alloys of type Nd 2 (Fe x Co 1-x ) 14 B have been investigated by X-ray photoelectron spectroscopy (XPS). Conclusions are drawn regarding the different behavior during the HDDR process (hydrogenation, disproportionation, desorption, recombination) upon substitution of Fe by Co. This hydrogen-induced fully reversible process is applied to produce highly coercive magnet powders. The XPS data provide information on the effect of different alloy components on hydrogen adsorption at the surface and absorption into the bulk as well as hydrogen-induced disproportionation and phase transformation in the course of the HDDR process. Specific differences in surface composition and oxidation behavior for the Fe and Co system, which are influenced by the presence of hydrogen, seem to play a major role in the primary steps of hydrogenation and disproportionation. In addition, hydrogen-induced electronic effects induced by surface hydrogenation by ion implantation under UHV conditions, which inter alia avoids surface contamination usually accompanying hydrogenation processes in an external chamber, have been studied. The XPS data allow us to explain changes of special properties of the Nd 2 (Fe x Co 1-x ) 14 B systems, such as fundamental aspects of hydrogen adsorption on the metal surface and hydrogenation and disproportionation.
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