Pressure and Temperature Influence on the Desorption Pathway of the LiBH4-MgH2 Composite System

The decomposition pathway in LiBH4-MgH2 reactive hydride composites was investigated systematically as a function of pressure and temperature. Individual decomposition of MgH2 and LiBH4 is observed at higher temperatures and low pressures (T >= 450 degrees C and p(H-2) <= 3 bar), whereas simultaneous desorption of H-2 from LiBH4 and formation of MgB2 was observed at 400 degrees C and a hydrogen backpressure of p(H-2) = 5 bar. The simultaneous desorption of H-2 from LiBH4 and MgH2 without intermediate formation of metallic Mg could not be observed. In situ X-ray diffraction (XRD) and infrared (IR) spectroscopy reveal the present crystalline and amorphous phases.