Training at Stockholm University (2007 09 12 - 10 02)

Martynas Lelis

Contents

Background Objectives and tasks of the visit Measurements at SU

Equipment Results

Discussions

Background

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

Background

Initial investigation of Mg2NiH4 samples prepared at LEI seems to be pseudo cubic HT phase (even at room temperatures)

Moreover, it exhibits unusual stability

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

Differential scanning colorimeter (DSC) and spectrophotometer

to prepare and to measure samples from LEI

to analyze the results and to make conclusions

Measurements at SU - equipment

Differential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature.

Measurements at SU - equipment

The basic principle underlying this technique is that, when the sample undergoes a physical transformation such as phase transitions, more (or less) heat will need to flow to it than the reference to maintain both at the same temperature.

Measurements at SU - equipment

Perkin Elmer Pyris 1

It can be used to find Heat Flow, Melting Temperature, Phase Transition Temperature etc.

Typical sample weights are 5-10mg

Measurements at SU - results

500 510 520 530 540

Second heating cycle

First heating cycle

Hea

t fl

ow

, arb

. un

t.

Temperature, K

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

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

Discussion – Band gap

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)

Discussion – Band gap

Discussion - model

MgO

Thin film

Powder

Mg2Ni zones

Mg zones

Conclusions

1. During the visit to Stockholm university new analytical techniques were successfully learned and employed for sample characterization

2. Measurement of thin film samples has given some proving evidence (not complete) for the existence of pseudo cubic HT phase of Mg2NiH4

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