Hydriding/dehydriding

Zirconium is a highly active metal which, like aluminum, seems quite passive because of its stable, cohesive, protective oxide film which is always present in air or water. Massive zirconium does not bum in air, but oxidizes rapidly above 600°C in air. Clean zirconium plate ignites spontaneously in oxygen of ca 2 MPa (300 psi) the autoignition pressure drops as the metal thickness decreases. Zirconium powder ignites quite easily. Powder (<44 fim or—325 mesh) prepared in an inert atmosphere by the hydride—dehydride process ignites spontaneously upon contact with air unless its surface has been conditioned, ie, preoxidized by slow addition of air to the inert atmosphere. Heated zirconium is readily oxidized by carbon dioxide, sulfur dioxide, or water vapor. 

Above 40 wt % hydrogen content at room temperature, zirconium hydride is brittle, ie, has no tensile ductiHty, and it becomes more friable with increasing hydrogen content. This behavior and the reversibiHty of the hydride reaction are utilized ki preparing zirconium alloy powders for powder metallurgy purposes by the hydride—dehydride process. The mechanical and physical properties of zirconium hydride, and thek variation with hydrogen content of the hydride, are reviewed in Reference 127. 

The alloy powder (used in hydrogen-storage systems) may ocasionally be pyrophoric after hydriding-dehydriding operations, igniting when placed on a combustible surface (e.g. weighing paper). 

A. Yonkeu, I.P. Swainson, J. Dufour, J. Huot, Kinetic investigation of the catalytic effect of a body centered cubic-aUoy TiV, Mn, (BCC) on hydriding/dehydriding properties of magnesium, J. Alloys Compd. 460 (2008) 559-564. 

H. Chi, C. Chen, Y. An, T. Ying, X. Wang, Hydriding/dehydriding properties of La Mg i alloy prepared by ball milling in different miUing environments, J. Alloys Compd. 373 (2004) 260-264. 

I.G. Fernandez, G.O. Meyer, F.C. Gennari, Hydriding/dehydriding behavior of Mg2CoH5 produced by reactive mechanical milling , J. Alloys Compd. 464 (2008) 111-117. 

It is known that the electrochemical hydriding/ dehydriding reactions taking place at a hydrogen storage electrode in an alkaline solution may be simply expressed as follows ... 

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