training at stockholm university (2008 02 07 - 02 27) martynas lelis

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


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


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


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


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.


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.


Scheme of the hydrogenation tube

GASThermocouple

Sample

Results

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 (FT-IR)

80012001600200024002800320036004000wavelengh, cm-1

inte

nsi

ty, a

rb. u

nt.

DNQ417VH Clear yellowDnQ417VHspotsDNQ418VHgreenishNQ418VHBlackspots

Measurements at SU - results

80012001600200024002800320036004000wavelengh, cm-1

inte

nsi

ty, a

rb. u

nt.


Ni-H


80012001600200024002800320036004000wavelengh, cm-1

inte

nsi

ty, a

rb. u

nt.


Air elementsNi-H


80012001600200024002800320036004000wavelengh, cm-1

inte

nsi

ty, a

rb. u

nt.


Ni-HAir elements

C-H


80012001600200024002800320036004000wavelengh, cm-1

inte

nsi

ty, a

rb. u

nt.


Ni-HAir elements

C-HO-H

Measurements at SU – results (BG)

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

0,00,51,01,52,02,53,0

Energy (eV)

Measurements at SU – results (BG)

-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,51,71,92,12,32,52,72,93,1

Energy (eV)

Abso

rban

ce422Cloud422Clear417Clear411Cloud411Wcloud411Clear

Discussions

Discussions - XRD

Discussions - XRD

20 30 40 50 60 70

b)

a)(4

00

)(31

1)

(22

0)

(11

1)

(00

2)

(00

6)

(20

3)

(20

0)

(11

2)

(00

3)

Inte

nsi

ty, a

rb. u

nt.

2, degrees

c - Mg2NiH

4

h - Mg2Ni

h - MgThin 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

Discussions - TEM

Discussions – DSC - powder

Discussions – DSC – thin film

500 510 520 530 540

Second heating cycle

First heating cycle

Hea

t fl

ow

, arb

. un

t.

Temperature, K

Discussions – FT-IR

80012001600200024002800320036004000wavelengh, cm-1

inte

nsi

ty, a

rb. u

nt.


Discussion – Band gap


-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,51,71,92,12,32,52,72,93,1

Energy (eV)

Abso

rban

ce422Cloud422Clear417Clear411Cloud411Wcloud411Clear

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

0,00,51,01,52,02,53,0

Energy (eV)


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training at stockholm university (2008 02 07 - 02 27) martynas lelis

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