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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.
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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 Mg2Ni alloys and their hydrogenation to Mg2NiH4 • There are three phases of Mg2NiH4 – 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 Mg2NiH4 samples prepared on CaF2 • To prepare fresh powder samples of LT1 and LT2 Mg2NiH4 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 - equipment • Scheme of the hydrogenation tube
Measurements at SU – results • Metallic Mg2Ni film was put in a transparent quartz tube under 500 kPa H2 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.
Measurements at SU - results Ni-H Air elements
Measurements at SU - results C-H Ni-H Air elements
Measurements at SU - results O-H C-H Ni-H Air elements
Discussions - XRD • Thin film: • a=6.440 Å • Scratched powders: • a=6.507998 Å • Powder material: • 6.5295 Å
Discussions - TEM D. Noréus, L. Kihlborg, J. Less-Comm. Met. 123 (1986) 233
