Investigation of the heat treatment of metal hydride powder for restoring the hydrogen capacity

Abstract

The introduction of fuel cell technology in the new 212CD submarines has brought hydrogen storage in metal hydrides, a topic of interest. Metal hydride tanks are a promising solution for hydrogen storage, offering safer and more efficient alternatives to conventional methods such as high-pressure tanks or cryogenic storage. However, solid-state storage solutions are challenged with certain difficulties. During hydrogen absorption the metal hydride expands, causing stress on the container walls. Atomization of metal hydride alloys is a proposed solution, but during the atomization process, an oxide layer is formed, making it incapable of storing hydrogen effectively. This bachelor thesis investigates the reactivation of atomized Hydralloy C5, a metal hydride alloy, through various heat treatment procedures. The goal is to restore its hydrogen storage capacity to approximately 1.8 wt.%. A quantitative and experimental approach was applied, using high-pressure treatments, vacuum heat treatments, and hydrogen purging treatments. Testing was performed using the SONJA II apparatus, and the results were further analyzed using Scanning Electron Microscopy (SEM) and particle size distribution (PSD) to observe material changes and detect surface contamination. The results demonstrated that a hydrogen storage capacity of at least 1.29 wt.% was achieved after specific heat treatment procedures. This study highlights the potential of heat treatment processes to restore hydrogen absorption capabilities, in atomized metal hydride alloys. Furthermore, the possibility of increasing the relative hydrogen capacity of the powder to 1,67 wt.% by sieving smaller inactive particles, is demonstrated.