Magnesium alloys for hydrogen storage

Yuri Estrin
Department of Materials Science & Engineering, Monash University,Melbourne
Department of Mechanical Engineering, University of Western Australia,PerthALMA Meeting, Tokyo, 10 November 2018
ALMA, 9 November 2018

Collaborations with:
Monash University, Melbourne:• Rimma Lapovok
University of Queensland, Brusbane:• Arne Dahle
Technion, Haifa, Israel:• Eugene Rabkin• Vladimir Skripnyuk• Larisa Popilevsky
University of Applied Sciences and Arts Western Switzerland:• Efrain Carreño‐Morelli
General Electric, USA:
• S. Jorgensen

Why Mg?
• Advantages:• Fourth most commonelement in the Earth crust• Cheap• Can reversibly store up to7.6 wt% of hydrogen• Main drawback: slow
absorption/desorption
kinetics• MgH2 hydride is relatively
stable (desorption at 1bar requires temp. of300°C) ‐ impractical formobile applications.
• High reactivity toward
oxidation. Formed oxide
layer inhibits thedissociative adsorption ofhydrogen.
3

Hydrogen storage in Mg alloys

4Volume of 4 kg of hydrogen compacted in different
ways, with size relative to the size of a car

Mg2NiH4

LaNi3H6

H2 (liquid)

H2 (gas,200 bar)5

Benefits of Solid State Storage• Reversible metal hydrides operate at low
pressure – advantage over compressedgas storage (700 to 2,100 bar)
• No need for storage at the cryogenic
temperatures – advantage over liquidhydrogen storage.
Current mobile applications:Toyota Mirai
https://str.llnl.gov/2018-01/wood6

Solid hydrid storage (stationary)

McPhy, France
INGRID Project,
750 kg storage
capacity

7
https://mcphy.com/en/our-products-and-solutions/storage-solutions/How Can the Kinetics be Improved?
Control overparticle
size/surface
area

Addition oftransition metals
that act as
catalysts

Working with Alloying with Ni
chips (thickness upto 50μm)

Introduction oflattice defects

Severe plastic
deformation(ECAP)
8Strategies for enhancing H2 storage kinetics• Nanostructuring• Addition of catalysts(Ni, Ti, Fe, Pd, V, Oxides)

SPD techniques

Rotation forging

High pressure torsion

Equal channel angularpressing
Multidirectional forging

Radial-shift rolling

SPD techniques

Rotation forging

High pressure torsion

Equal channel angularpressing
Multidirectional forging

Radial-shift rolling

Equal channel angular pressing (ECAP) at Monash UniPPlungerDie

Highly defective, sub-m grains are
obtainedDie

Test material

Hydraulic presses
ECAP improves hydrogenation properties of Mg alloys:
V. Skripnyuk, E. Rabkin, Y. Estrin, R. Lapovok
Improving hydrogen storage properties of magnesium based alloys by equal channel angular pressing
Int. J. of Hydrogen Energy 34 (2009) 6320‐6324

Effects of grain refinement, Alloy AZ31

Degradation rate (m/day)

2.4
2.2

SC

2.0
1.8

ECAP

1.6
1.4

HR

1.2
1.0
0.8
0.6

02468

10121416182022Time (day)Fatigue strengthCorrosion in NaCl solution

Wang, Song, Estrin, Zuberova, Adv. Eng. Mater. 9 (11), 967-972 (2007)

Multi‐step ECAP, Alloy ZK60
Conical Section PC SectionK2d1d01NDTDEDOrlov et al., Acta Mater. 2011

Variation of the corrosion current density

Corrosion‐strength property space

ZK60

Enhanced Fatigue Strength

Vinogradov, Orlov, Estrin,
2011

PCT diagram of ECAP processed ZK60

Black Lines: V.M.Skripnyuk et al., Acta Mater. 52, 405 (2004)
Coloured Lines: M. Krystian, M. Zehetbauer, G. Krexner, H. Kropik,Mingler, J.Alloys Comp. (2011)B.

Sievert-type Apparatus
Before the beginning of theabsorption:

After full absorption:

Difference= moles of absorbedhydrogen:

Mass of absorbed hydrogen:20

Accelerating absorption/desorption of hydrogen, andreplacíng expensive and hazardous ball milling

From: M.Skripnyuk, E.Rabkin, Y.Estrin, R.Lapovok, Acta mater. (2004)
M.Krystian, M.Zehetbauer, G.Krexner, B. Mingler, J.Alloys Comp. (2011)

Eutectic Mg‐Ni alloy
Mg89Ni11

Eutectic Mg‐Ni alloy
As-cast1 ECAP pass

10 ECAP passes

28th February
2011

V. Skripnyuk etal. J Alloys
Comp. 2007

SEM micrographs taken after 10 passes

After ECAP

Hydrogen desorption

Pressure‐composition isotherms

573K

Effects:- Accelerated kinetics- Increase in pressure by 50%

Hypo‐eutectic Mg‐10 wt% Ni alloy

Dependence of Absorption Kinetics on the Number ofCycles
510 cycles
43 cycles

H, wt%

321 cycle

10050100t, min

150200as cast 1 cycle

as cast 3 cycles

as cast 6 cycles

as cast 9 cycles

as cast 10 cycles

post-ECAP 1 cycle

post-ECAP 3 cycles

post-ECAP 6 cyclespost-ECAP 9 cycles

post-ECAP 10 cycles

Faster kinetics are expected for the ECAP-ed alloy.
What is the reason for the reversal of kinetics?
28

Microstructures afterhydrogenation: after the first cycle

As-cast,after first cycle

Large faceted Mg crystals grew in the as-cast sample after the 1st full hydrogen
absorption/desorption cycle.

As cast Mg-Ni after 4 cycles

Facets of the grown grains are smooth. Smallest
grains are a few microns in size.

ECAP processed Mg-Ni after 4cycles

A porous structure is covered with faceted grains.
Slip lines (as dash lines indicate) cover the facets of all of the grains.
Sub-micron grains were observed.

abAs-castcd

ECAP-edChips of two alloys prepared by filing. Primary Mg grains are separated by MgMg2Ni eutectics. ECAP has broken and refined Mg2Ni lamellae, otherwise notmuch difference between the two samples.

Mechanism of Formation of Large Faceted Mg
Crystals
As-cast sample
Mg2NiMg
MgH2•Doyama et al (1982): formation of MgH2 and Mg2NiH4 is accomplished by volumetric expansion
up to approximately 30% of molar volume relatively to the Mg and Mg2Ni phase.
•Compressive stresses during hydrogenation are the driving force for the crystals growth.
•Mg particle growth has a direct influence on the kinetics, since catalyst phase is left behind.
33

Mechanism of Formation of Large Faceted Mg
Crystals
ECAP-ed sample

Mg2NiMg
MgH234

HThe Model   y  229 MPa (for the as - cast alloy)

σσGradient of chemical potential of Mg :  yH(1)Volumetric flux that leads to the formation of extrudedMg crystal:JH(2)
tH

D y tk BTt is the time of hydrogen absorption process
On the other hand :JD
 (3)
 kBT35

Comments••

•

•

•

Hydrogenation encourages growth of large faceted Mg single crystals. In ECAP-ed samples
these crystals are nucleated earlier than in as-cast sample, and they are larger. Tendency fornucleation and growth depends on stored internal energy and defect density inside the chip.
Current phenomenon is observed in chips (that are relatively large compared to BM powder)and not in ball milled powder. This indicates that faceted grain nucleation and growth are
related to the size and geometric constrains during growth of hydride phase.
The size of faceted Mg single crystals decreases with every hydrogenation cycle, but theiramount increases. This mechanism of increasing surface probably accelerates hydrogenation
kinetics. On the other hand, growth of crystals leads to areas that are rich in Mg2Ni particles,that serve as catalysts, while faceted grains are poor in catalyst.
ECAP process doesn't refine the microstructure significantly, yet influences absorption
behavior. As-received microstructures are very similar, but intermittent hydrogenation behavior
is very different.
Although there is significant morphological difference between as cast and post-ECAP
powders during first cycles, after 9 cycles topography is similar and so is the hydrogenationkinetics.

HPT Work at Kyushu University(Prof. Zenji Horita, Dr. Kaveh Edalati)

Coarse Grains

Coarse Grains with Stacking Faults

Hongo, Edalati, Arita, Matsuda, Akiba, Horita, Acta Mater. 92 (2015) 46-54.

Mg4NiPd for Room-Temperature Hydrogen StorageCalculations suggested if a
homogenous Mg4NiPd alloy
is synthesized, it should havea B2 structure with lowhydrogen binding energy.

Mg
Ni
Pd

Edalati, Uehiro, Ikeda, Li, Emami, Filinchuk, Arita,Sauvage, Tanaka, Akiba, Horita, Acta Mater.149 (2018)
88.

N: Number of HPT Turns39

Edalati, Uehiro, Ikeda, Li, Emami,Filinchuk, Arita, Sauvage, Tanaka, Akiba,Horita, Acta mater. 149 (2018) 88.

Magnesium with Carbon Nanotubes

Preparation of PMH+MWCNTs composites
Mg or Mg alloy

MWCNTsMilling of Mg: 8 h at 960 rpm(high energy ball milling,HEBM)

Mg milling
Milling ofthepowders
Milling of Mg+MWCNTs:
Sintering

Either at 800 rpm (HEBM)
or at 100 rpm (LEBM)
Compactingof themixtureProcessing of Mg-2 wt.% MWCNT composite-MWCNT: catalytic decomposition of acetylene @ 720C over Co-Fe/CaCO3;-Dry blending with 99.8 wt.%Mg (particle size of 38 m) for 4 h;-Hot pressing @ 600C in vacuum, 50 MPa for 30 min;-HIP @ 600C in argon, 1800 bar for 60 min.

MWCNTsFracture surface of thecomposite showing MWCNTpull-outs

V.M. Skripnyuk, E. Rabkin, L.A. Bendersky, A. Magrez, E. Carreño-Morelli, Y. Estrin
Hydrogen storage properties of as-synthesized and severely deformed magnesium – multiwall carbon nanotubes
composite
Int. J. of Hydrogen Energy 35 (2010) 5471-5478

Kinetics of hydrogen absorption by the composite
7oAbsorption, T=300 C
6H, wt%54321Mg+CNTMg pure00102030

405060708090100t, min

Kinetics of hydrogen desorption by the composite
6oDesorption, T=300 C
5H, wt%

4321Mg+CNTMg pure00200400600800t, min100012001400

HRSEM of ECAP-ed Mg-MWCNT after hydrogenation cycleTEM of ECAP-ed Mg-MWCNT after hydrogenation cycle-sword-sheath failure-bending sites

MWCNTs vs. Graphite

Conclusions
1. 4 h of high energy ball milling destroy MWCNTs;
2. The hydrogen desorption kinetics and mechanical integrity of Mg2wt.% MWCNT composites improve once the MWCNTs aredestroyed;
3. The addition of MWCNTs is more beneficial than that of Graphite;

Twist Extrusion: Worth trying?

Surface area

Variation of surface area during twist
extrusion2150

Surface area

Variation of surface area during TE
21

Hydrogen51

Mechanochemical Process
Hydrogen52

Conclusion:
Severe plastic deformation techniques offer awealth of interesting opportunities foracceleration of hydrogen sorption/desorption.
Research in this area should be encouraged.

53

Thank you for your attention!

yuri.estrin@monash.edu