Presentation on theme: "Training at Stockholm University (2008 02 07 - 02 27) Martynas Lelis."— Presentation transcript:
Training at Stockholm University (2008 02 07 - 02 27) Martynas Lelis
Contents Reminders about last results Objectives and tasks of the current visit Measurements at SU Equipment Results Discussions
Reminders about last results In latter years in LEI there were experiments of formation of Mg 2 Ni alloys and their hydrogenation to Mg 2 NiH 4 There are three phases of Mg 2 NiH 4 – LT1, LT2 (with microtwining) and HT At ~235° C LT transforms to HT
Reminders about last results XRD – shows pseudo cubic structure related to structure of HT phase DSC – no phase change on first run TEM – cubic with impurities BG – band gap of about 2.2 eV
Objectives and tasks Objective To acquire new skills and better understanding in analyzing and characterization of hydrogen storage materials
Objectives and tasks Tasks To learn the working principles of FT-IR spectrometer and to measure our Mg 2 NiH 4 samples prepared on CaF 2 To prepare fresh powder samples of LT1 and LT2 Mg 2 NiH 4 and to measure band gap in reflectance mode
Objectives and tasks Tasks To adjust custom made glass tube hydrogenation cell for our thin film samples and to make qualitative estimation of hydrogenation kinetics as well as chromatic properties
Measurements at SU - equipment An FTIR (Fourier Transform InfraRed) is a method of obtaining infrared spectra by first collecting an interferogram of a sample signal using an interferometer, then performing a Fourier Transform on the interferogram to obtain the spectrum.
Measurements at SU - equipment The FTIR is based on a Michelson Interferometer, that consists of, at least a beam splitter and two mirrors. This instrument produces interference between two beams of light waves propagated through two separate optical path lengths.
Measurements at SU – results Metallic Mg 2 Ni film was put in a transparent quartz tube under 500 kPa H 2 pressure and heated it up. Just after 2 min the film changed its colour to dark brown loosing its reflectivity (as the temperature reached 353 K). After 4-5 min (temperature 433 K) the film had become orange and transparent indicating formation of the hydride. Upon further heating (to 573 K) it remained transparent but got a deeper reddish colour. Upon cooling down to room temperature the orange colour returned.