Hydrogenation Properties of TiFe Doped with Zirconium
The goal of this study was to optimize the activation behaviour of hydrogen storage alloy TiFe. We found that the addition of a small amount of Zr in TiFe alloy greatly reduces the hydrogenation activation time. Two different procedural synthesis methods were applied: co-melt, where the TiFe was melted and afterward re-melted with the addition of Zr, and single-melt, where Ti, Fe and Zr were melted together in one single operation. The co-melted sample absorbed hydrogen at its maximum capacity in less than three hours without any pre-treatment. The single-melted alloy absorbed its maximum capacity in less than seven hours, also without pre-treatment. The reason for discrepancies between co-melt and single-melt alloys was found to be the different microstructure. The effect of air exposure was also investigated. We found that the air-exposed samples had the same maximum capacity as the argon protected samples but with a slightly longer incubation time, which is probably due to the presence of a dense surface oxide layer. Scanning electron microscopy revealed the presence of a rich Zr intergranular phase in the TiFe matrix, which is responsible for the enhanced hydrogenation properties of these Zr-doped TiFe alloys.
Hydrogen storage properties of Ti0.95FeZr0.05, TiFe0.95Zr0.05 and TiFeZr0.05 alloys
Abstract In this paper, we report the microstructure and hydrogen storage properties of Ti 0.95 FeZr 0.05 , TiFe 0.95 Zr 0.05 and TiFeZr 0.05 alloys prepared by arc melting. We found that all these alloys are made of a TiFe phase with small amount of zirconium in solid solution and a secondary phase which is zirconium rich. This special microstructure is actually responsible for the enhanced activation (first hydrogenation) kinetics of these alloys. First hydrogenation of Ti 0.95 FeZr 0.05 alloy proceed faster than for the other two alloys. This is probably due to a finer distribution of the bright secondary phase. Pressure-composition isotherms of TiFeZr 0.05 and Ti 0.95 FeZr 0.05 alloys are similar while the alloy TiFe 0.95 Zr 0.05 shows the highest capacity. These results demonstrate that a very slight variation of composition could have an important effect of microstructure and hydrogen storage behaviours.
Mathematical Modeling of Scour and Deposition
Electronic computers are opening up the field of sedimentation engineering by permitting the analysis of problems which heretofore have required too much time and effort. Movable stream bed profiles are being calculated in addition to water surface profiles. The initial gradation of sediment material in the stream bed may be prescribed to facilitate the calculation of an armor layer. This gradation is continually changed by the computer program in response to sediment particles being deposited on the stream bed and material on the stream bed being removed to satisfy transport capacity. Hydraulic sorting of sediment by grain size is accomodated. The stream bed does not have to be represented by a single grain size. Retardance of motion because of armor layer is calculated.