Allan Schrøder Pedersen

Magnesium for Hydrogen Storage

Abstract A study of the hydrogenation characteristics of fine magnesium powder during repeated cycling has been performed using a high-pressure microbalance facility. No effect was found from the cycling regarding kinetics and storage capacity. The reaction rate of the absorption process was fast at temperatures around 600 K and above, but the reversed reaction showed somewhat slower kinetics around 600 K. At higher temperatures the opposite was found. The enthalpy and entropy change by the hydrogenation, derived from pressure-concentration isotherms, agree fairly well with those reported earlier.

Bulk amorphous (Mg0.98Al0.02)60Cu30Y10 alloy

Recently, Inoue and Masumoto have found that Mg-Cu-Y alloys show high glass-forming ability (GFA), hence making it possible to produce bulk amorphous samples of such alloys. The aim of the present work was to characterize in some detail one of these new bulk amorphous alloys, (Mg{sub 0.98}Al{sub 0.02}){sub 60}Cu{sub 30}Y{sub 10}. Its stability and crystallization process was examined by using x-ray diffraction (XRD), differential scanning calorimetry (DSC) and small-angle neutron scattering (SANS). One finding was the formation of nanocrystalline particles on annealing. It was also found that the addition of Al increases the hardness.

On the hydrogenation mechanism in magnesium I

Abstract The first time hydriding of spherical magnesium particles covered by a thin oxide layer and sieve-fractionated into narrow size distributions within the range 40–90 μm was followed by microgravimetry. The size distributions of the fractions were determined by semiautomatic image analysis. The hydridings were run at 402°C and 3 MPa hydrogen pressure after heating in helium. A dependence of the rate of hydriding on the heat treatment prior to reaction was observed and it is proposed that the heat treatment causes oxygen atoms to diffuse into the bulk metal and thereby break up the protective oxide layer. Based on the observed hydride propagation in the metal particles, a statistical model for the hydriding of a particle is applied to the hydriding curves for a series of samples. The data are found to be in fine agreement with the proposed model. It is concluded that care must be taken when generalizing results from the hydriding of magnesium powders.

Long-Term Cycling of the Magnesium Hydrogen System

Abstract Magnesium powder with a grain size of approximately 50γm was hydrogenated for 30 min and dehydrogenated the same time at 390°C, 515 times. A moderate loss in hydrogen storage capacity was observed and was ascribed to a measured decrease in reaction kinetics as the cycle number increased. The time for maximum hydrogen absorption was found to depend significantly on cycle number while the time for maximum desorption was found to be virtually independent of cycle number.

The effect of particles in different sizes on the mechanical properties of spray formed steel composites

Abstract The main objective of the work was to investigate the effect of addition of ceramic particles with different size distributions on the mechanical properties, e.g. wear resistance and tensile strength, of spray formed materials. The experiments were carried out in a spray-forming unit at Riso National Laboratory, Denmark, where composites with a low alloyed boron steel (0.2 wt.% carbon) matrix containing alumina particles were produced. A comparison between cast hot-rolled material without particles, spray formed material without particles and the spray formed composites with an average ceramic particle size of 46 and 134 μm were carried out with respect to their mechanical properties e.g. wear resistance and tensile strength. It was found that the addition of Al2O3 particles to the steel improves its wear properties and reduces the elongation and tensile strength of the material, but the material still showed good ductility. The composite material was also forged and showed good forgeability.