XPS and XAES studies of air-exposed Mg2Cu and Mg2Ni alloys showed surface decomposition and preferential segregation of Mg by the influence of oxygen and moisture. The segregated magnesium is mostly present as oxide and hydroxide on the surface. The second metallic component namely Ni or Cu is also present in the oxidized state. The passivation of these alloys arises by the oxidation of the transition metal component. We suggest that the activation of these alloys involves reduction of the oxidized 3d elements and the formation of metallic clusters. © 1989.

P Selvam

Department Of Chemistry

Balasubramanian Viswanathan

MAGNESIUM AND ALLOYS--SPECTROSCOPIC ANALYSIS

Spectroscopy, Auger Electron

Spectroscopy, X-ray

X-RAY INDUCED AUGER ELECTRON SPECTROSCOPY

X-ray photoelectron spectroscopy

Hydrogen

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

XPS and XAES studies on hydrogen storage magnesium-based alloys

International Journal of Hydrogen Energy

Although a number of surface analysis reports are available on the LaNi5 system, yet a clear picture of the actual species involved and their consequences on the activation and deactivation processes has not been reached. Moreover, differences of opinion have been seen among the researchers. The present results distinctly indicate that the air exposed samples are completely contaminated with a variety of oxygenated species (such as oxides, hydroxides and carbonates) of the constituent elements, hitherto not reported by others. The protective nature of such species in regard to the durability of the alloy and the formation of supported-metal type species upon activation accounts for its excellent behaviour. The relative higher stability of LaNi5 over CaNi5 under cyclic operating conditions has been explained based on surface energy criteria of the constituent elements rather than the deterioration initiated by hydrogen and/or gaseous impurities alone. In addition, the specific importance of X-ray induced Auger electron spectroscopy (XAES) technique in conjunction with X-ray photoelectron spectroscopy (XPS) has been highlighted in the identification of different species. © 1990.

Surface properties of LaNi5: A reinvestigation

X-ray photoelectron and Auger electron spectroscopic studies on TiFe demonstrate that ion bombardment of the alloy not only results in sputter cleaning or even destruction of the surface but also leads to the formation of compact carbide layers. Such carbide species are of considerable importance in elucidating the reaction mechanism of hydrocarbon synthesis. They are also expected to play a significant role in the hydrogen sorption properties of materials. A better understanding of the nature of sputtered carbon is needed for its use as protective (against corrosion) thin films in magnetic recording applications. A comparison of photoelectron and Auger electron spectra of the surface carbides of TiFe would also be of interest since it is unusual for both types of data to be produced on the same samples where chemical shifts are involved. © 1990.

Journal of The Less-Common Metals

Ion-induced carbide formation of TiFe: evidence from XPS and AES studies

X-Ray photoelectron spectroscopic (XPS) studies of air exposed samples of LaNi5, CaNi5, Mg2Ni, Mg2Cu and FeTi indicate that the interaction of atmospheric carbon dioxide results in the formation of surface carbonates in addition to the usual oxides and hydroxides. The reaction of carbon dioxide, in fact, is favoured by the oxidized surface which in turn produces the carbonate species on the top few layers, hitherto not reported. In particular, the carbonates seem to be predominant in the case of CaNi5. The adsorption of carbon dioxide also gives an idea of the segregated elements of the different systems. Even though such carbonate species on the alloy surfaces seem to be expected rather than surprising, there is no evidence available in the literature. To our knowledge, this forms the first report on such a problem. The results also provide valuable information concerning the understanding of various surface reactions and the nature of activation processes which often differ between materials involved in hydrogen uptake. © 1990.

Evidence for the formation of surface carbonates on some hydrogen storage intermetallic compounds: an XPS study

Features of the effect of ion bombardment and its influence on the composition of solid surfaces are considered. During ion bombardment, not only does cleaning (sputtering) of the surface take place, but the formation of carbides through the implantation of carbon from contamination also occurs. Such species were recognized clearly from their chemical shifts of XPS on intermetallic compounds, namely LaNi5, CaNi5, TiFe, MgaNi and Mg2Cu and on the hydride Mg2NiH4. These surface carbides, for example, can seriously restrict data analysis owing to their contribution to the core level alterations, and the rate of sputtering owing to their extreme hardness. However, ion bombardment would serve as an unusual method of preparation of some compounds which cannot be obtained by conventional means. Types of problems, methods and results of their investigation are described. © 1990.

Journal of Electron Spectroscopy and Related Phenomena

Note on the formation of surface carbides

The influence of atmospheric CO2 on the surface properties of Mg2NiH4 and a comparison with some hydrogen storage alloys

Intermetallics used for hydrogen storage purposes require prior activation. Mild activation conditions are sufficient for AB5 type intermetallics like LaNi5 and CaNi5 as compared to other intermetallics used for the purposes of hydrogen storage. In this communication a model for the activation process is proposed for the behaviour of LaNi5 and CaNi5 alloys. © 1989.

Some comments on modes of activation of LaNi5 and CaNi5 alloys for hydrogen storage

X-ray photoelectron and X-ray induced Auger spectroscopic (XPS and XAES) investigations show that, in Mg2NiH4, both Mg and Ni are in the metallic state. Support for this observation has been obtained from thermopower and magnetic measurements. © 1988.

X-ray photoelectron spectroscopic, electrical and magnetic studies on Mg2NiH4

Activation of FeTi alloy could either give rise to surface segregation and subsequent oxidation of titanium and the formation of iron clusters or the formation of metastable TiFeO, suboxide. The validity of either of the postulates could be gauged by monitoring the nature and concentration of each of the oxidation states of iron and titanium by depth profile analysis by XPS. These studies showed that fresh samples contained multiple oxidation states of iron and titanium though the concentrations of lower valent oxides are usually small. Sputtering studies showed that this oxide layer is of considerable depth and during activation, iron oxides are easily reduced to the metallic state as compared to the oxides of titanium. The chemical reaction induced, segregation may be the contributing factor for the enhanced concentration of titanium on the surface of these alloys. © 1987.

X-ray photoelectron spectroscopic investigations of the activation of FeTi for hydrogen uptake

This review addresses the question of using magnesium and magnesium-based alloys as "rechargeable hydrogen storage" media. The effect of addition of organic compounds as well as other metals (both transition and non-transition elements) on the sorption characteristics of magnesium is considered in detail. The current status of information in this field is reviewed with a view to evaluating the potential of these materials for use as hydrogen storage media in vehicular applications. © 1986.

Journal	Data powered by TypesetInternational Journal of Hydrogen Energy
Publisher	Data powered by TypesetElsevier Ltd
ISSN	03603199
Open Access	No