Investigation of the thermodynamics governing metal hydride synthesis in the molten state process

• Published in: Journal of alloys and compounds 2008-10, Vol.465 (1), p.41-46
• Main Authors: Stowe, Ashley C., Berseth, Polly A., Farrell, Thomas P., Laughlin, Laura, Anton, Donald, Zidan, Ragaiy
• Format: Article
• Language: English
• Subjects: 08 HYDROGEN; Cross-disciplinary physics: materials science; rheology; DESORPTION; Exact sciences and technology; HYDRIDES; HYDROGEN; Hydrogen absorbing materials; HYDROGEN STORAGE; KINETICS; Materials science; Materials synthesis; materials processing; Mechanicochemical processing; Metal hydrides; MILLING; Physics; PROCESSING; SYNTHESIS; Thermodynamic properties; THERMODYNAMICS
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2007.10.103

This work is aimed at utilizing a new synthetic technique to form novel complex hydrides for hydrogen storage. This technique is based on fusing different complex hydrides at elevated temperatures and pressures to form new species with improved hydrogen storage properties. Under conditions of elevated hydrogen overpressures and temperatures the starting materials can reach melting or near-melting point without decomposing (molten state processing), allowing for enhanced diffusion and exchange of elements among the starting materials. The formation and stabilization of these compounds, using the molten state process, is driven by the thermodynamic and kinetic properties of the starting and resulting compounds. Complex hydrides (e.g. NaK 2AlH 6, Mg(AlH 4) 2) were formed, structurally characterized and their hydrogen desorption properties were tested. In this paper we report on investigations of the thermodynamic aspects governing the process and products. We also report on the role of molar ratio in determining the final products. The effectiveness of the molten state process is compared with chemomechanical synthetic methods (ball milling).