Hydrogen Sorption Properties of the Intermetallic Mg Ni ... · Inge nie ría Inv es ti ga ción y Tec no lo gía. Vol. XI. Núm. 3. 2010 325-332, ISSN 2594-0732, FI-UNAM 327 Martínez-Franco

Ingeniería Investigación y Tecnología. Vol.XI. Núm.3. 2010 325-332, ISSN 2594-0732, FI-UNAM (artículo arbitrado)DOI: http://dx.doi.org/10.22201/fi.25940732e.2010.11n3.028

Hydrogen Sorption Properties of the Intermetallic Mg2Ni Obtained by Using a Simoloyer Ball Milling

Propiedades de ab-desorción de hidrógeno del intermetálico Mg2Ni obtenido empleando un molino de bolas Simoloyer

Martínez-Franco E.GKSS, Research Center Geesthacht, Germany

CIITEC, Instituto Politécnico Nacional, Mexico CityE-mail: [email protected]

Klassen T.GKSS, Research Center Geesthacht, Germany

E-mail: [email protected]

Jaramillo-Vigueras D.

CIITEC, Instituto Politécnico Nacional, Mexico CityE-mail: [email protected]

Bormann R.

GKSS, Research Center Geesthacht, GermanyDepartment of Materials Science and Technology

Technical University Hamburg-Harburg, Eissendorfer Str. 42E-mail: [email protected]

(Recibido: septiembre de 2008; aceptado: junio de 2009)

Abstract

Intermetallic Mg2Ni was produced from elemental powder blends by mechan ical

alloying in a batch scale using a rotary hori zontal mill (Simoloyer). Fast hydro ge na -

tion kinetics are obtained: 2.2 wt.% of hydrogen is absorbed within 10 minutes at

300 °C. Hydrogen sorp tion kinetics were further improved by adding Pd (1 mol%)

powder as a cata lyst during ball milling. Crack forma tion and concom i tant particle

size reduc tion was observed by scan ning elec tron micros copy after hydrogen

cycling, which is attrib uted to in ternal stresses in the parti cles.

Keywords: High-energy ball milling (Simoloyer), hydrogen storage, particle size

evolution.

Resumen

Se pro du jo por alea ción me cá ni ca el com pues to in ter me tá li co Mg2Ni a par tir de pol vos

ele men ta les, em plean do un mo li no de al ta ener gía (pro duc ción por lo tes) ho ri zon tal ro ta -

to rio co mer cial men te co no ci do co mo Si mo lo yer. Se ob ser vó que es te com pues to pre sen ta ba

una rá pi da ab sor ción de hi dró ge no, en don de se ob tu vo 2.2 % pe so de hi dró ge no a 300 ºC

des pués de 10 mi nu tos de pro ce so. La ci né ti ca de ab sor ción de hi dró ge no se me jo ró al

inge nie

ría

INVESTIGACIÓN

Y TECNOLOGÍA

http://dx.doi.org/10.22201/fi.25940732e.2010.11n3.028

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agre gar 1 % mol de pa la dio du ran te la mo lien da. Se ob ser va ron por mi cros co pía elec tró ni ca de

ba rri do, grie tas y dis mi nu ción del ta ma ño de par tí cu la por efec to de los ci clos de ab sor ción-de -

sor ción de hi dró ge no; y los cua les se atri bu ye ron a es fuer zos in ter nos en las par tí cu las.

Des crip to res: mo lien da de bo las de al ta ener gía (Si mo lo yer), al ma ce na mien to de hi dró ge no,

evo lu ción del ta ma ño de par tí cu la.

Intro duc tion

Me chan i cal al loy ing (MA) yields chem i cally ho mo ge -neous al loys (Benjamin, 1976), ( Benjamin et al., 1974),(Koch, 1989), (Bormann, 1977) with ex tremely finecrys tal lite sizes. The pro cess is char ac ter ized by high-en ergy im pact col li sions of the mill ing tools, which lead to plas tic de for ma tion, cold-weld ing, and par ti cle frac -ture which pro vides the driv ing force for micro -structural re fine ment. Dif fer ent tech niques are avail -able to con duct MA on the lab o ra tory scale. How ever,few types of equip ment have been de signed to ob tainlarger quan ti ties of pow der for in dus trial pro duc tion,such as hor i zon tal ro tary ball mills (Simoloyer modelCM100s) (Zoz et al., 1996, 1999). The charge-dis chargeop er a tions in this equip ment can ei ther take place un -der in ert gas or vac uum to pre vent ox i da tion. The mill -ing cham ber of this mill is de signed such that al lows vi -als cool ing us ing ei ther liq uid or gas me dia. Mag ne siumand mag ne sium-based al loys have been widely stud iedas hy dro gen stor age ma te ri als by many re search groups(Zaluzski et al., 1995), (Liang et al., 1999), (Zaluski,1995), (Zaluski et al., 1999), (Kumar et al., 1995) be -cause of their high hy dro gen stor age ca pac i ties byweight (7.6 wt.% of MgH2 and 3.6 wt.% of Mg2NiH4),long-term sta bil ity, full re vers ibil ity and low raw ma te -ri als costs. A tech no log i cal break through re gard ing re -ac tion ki net ics has been achieved by pre par ing nan -ocrystalline al loys by high-en ergy mill ing and by add -ing suit able cat a lysts, e.g., metal ad di tives (Zaluzski etal., 1995), (Liang et al., 1999) or more re cently, me talox ides (Oelerich et al., 2001), (Youp et al., 2002), (Inui et al., 2002). For ex am ple, Zaluski et al. (1995) used el -e men tal Pd as cat a lyst and stored about 2.5 wt.% ofhy dro gen in Mg2Ni at 200°C/15bar in 10 min utes.For MgH2 with ox ide cat a lysts, 80% of the the o ret i -cal ca pac ity, i.e., 6.1 wt.% was ob tained at 300°C/8bar in 5 min utes (Oelerich, 2001). So far, all stud iesre lated to nanocrystalline hy drides were based onma te ri als pro duced in small mill ing ma chines on the lab o ra tory scale. For pro to type pur poses and tech ni -cal ap pli ca tions, larger quan ti ties are re quired.

How ever, re spec tive stud ies re gard ing ups caling ofthe pow der pro duc tion are still lack ing.

Expe ri mental proce dure

El e men tal pow der blends (Mg JCPDF-35-0821, NiJCPDF-04-0850) cor re spond ing to the stoichiometric ra -tio for the intermetallic Mg2Ni phase were milled in ahigh-en ergy ro tary ball mill (Simoloyer model CM01-2l,Zoz GmbH Ger many). These re sults are al ready ob -tained and pub li ca tion is avail able (Martínez et al.,2006). Dif fer ent ball-to-pow der mass ra tios were used to eval u ate ef fi ciency of the mill sys tem and sam ples with -out cat a lyst were stored for sev eral months be fore mea -sur ing hy dro gen sorp tion prop er ties. Pal la dium pow der(1 mol%) was added as a cat a lyst in a sam ple with amass ra tio of 10:1, for com par ing hy dro gen sorp tion ki -net ics with the pow ders with out cat a lyst.

For mea sure ments of hy dro gen ab sorp tion ki net ics,sam ple hold ers were sealed in side a glove box and at -tached to a hy dro gen ti tra tion ap pa ra tus, which wasspe cially de signed (Schulz et al., 1999) for fast dataac qui si tion.

Par ti cle mor phol ogy dur ing mill ing, as well as, af terhy dro gen charg ing and dis charg ing was in ves ti gated by SEM (JEOL JSM-35CF). Con tam i na tion by ox y gen andiron was quan ti fied us ing en ergy dis perse spec trom e try (EDS) avail able in the SEM.

Results and discus sion

Mechan ical alloying using the Simoloyer ball mill

The XRD pat terns for dif fer ent ball-to-pow der mass ra -tios as a func tion of mill ing time are shown in fig ure 1.Peak broad en ing in di cates microstructural re fine ment.The crys tal lite size of Mg2Ni is es ti mated be tween 4and 11 nm us ing the Scherrer-for mula (Cullity, 1978).Peaks cor re spond ing to the intermetallic Mg2Ni(JCPDF-35-1225, mainly dif fracted be tween 20°-22°and 40°-45°) are ob served af ter dif fer ent mill ing timesde pend ing on the mass ra tio. Traces of Ni were found

326 Inge nie ría Inves ti ga ción y Tec no lo gía. Vol. XI. Núm.3. 2010 325-332, ISSN 2594-0732, FI-UNAM

Hydrogen Sorp tion Proper ties of the Inter me ta llic Mg Ni2

Obtained by Using a Simo loyer Ball Milling

DOI: http://dx.doi.org/10.22201/fi.25940732e.2010.11n3.028


Inge nie ría Inves ti ga ción y Tec no lo gía. Vol. XI. Núm. 3. 2010 325-332, ISSN 2594-0732, FI-UNAM 327

Martínez-Franco E., Klassen T., Jara millo-Vigueras D. and Bormann R.

in all mill ing ex per i ments and unreacted Mg was onlyfound for a mass ra tio of 50:1. These re sults show thatMg2Ni for ma tion strongly de pends on the mass ra tio.In creas ing the mass ra tio con sid er ably re duces theMg2Ni syn the sis time from 25 hours down to 4 hoursus ing mass ra tios of 10:1 and 100:1, re spec tively.

In all mill ing pro cess the pos si bil ity ex its of con tam -i na tion due to wear of me dia (balls) and con trol pro cess

(at mo sphere). Anal y sis of pos si ble con tam i nants suchchro mium, iron and ox y gen by us ing en ergy dispersivespec trom e try (EDS) were car ried out.

EDS mea sure ments showed only the pres ence ofiron and ox y gen as is re ported in ta ble 1 for all ball-to-pow der mass ra tios. The num bers in brack ets in di catethe mill ing time of the sam ple. Av er age and cor re -spond ing de vi a tions of all mea sure ments are reported.

Figure 1. XRD patterns for Mg-Ni powders milled for several times with diffe rent ball-to-powder mass rations:

(a) 100:1, (b) 50:1, (c) 20:1, (d) 10:1

Table 1. Iron and oxygen conta mi na tion after milling

Mass ratio Average Fe (wt.%) Average O (wt.%)

100:1 [6h] 1.6 ± 0.2 5.1 ± 0.1

50:1 [10h] 0.8 ± 0.2 4.3 ± 0.05

20:1 [16h] 0.4 ± 0.15 5.6 ± 0.06

10:1 [25h] 0.4 ± 0.2 4.9 ± 0.1



Iron and ox y gen con tam i na tion took place from thevial’s ero sion and air when sam ples were taken for char -ac ter iza tion. Even though the mill ing time re quired forcom plete trans for ma tion into the Mg2Ni phase is much shorter for a mass ra tio of 100:1, the high est iron con -tam i na tion was de tected in this sam ple. This is at trib -uted to the smaller pow der quan tity and there fore,more im pacts col li sions of the balls. The ox y gen con -tam i na tion is sim i lar (ap prox i mately 5 wt.%) for allspec i mens in de pend ently of the mass ra tios, which in -di cates con tam i na tion due to han dling for sam pling toanal y sis.

Hydrogen storage prop er ties

Sorp tion prop er ties of Mg2Ni without cata lyst

The hy dro gen re ac tion ki net ics at 9 bar hy dro gen pres -sure and 300ºC of the intermetallic Mg2Ni ob tainedwith dif fer ent ball-to-pow der mass ra tios is shown infig ure 2. Ab sorp tion ki netic is best for the mass ra tio of10:1 and 2.2 wt.% of hy dro gen is ab sorbed within 10min utes at 300°C. It is ob served that in creas ing massra tios hy dro gen ab sorp tion ki net ics is lower, with ex -cep tion of the mass ra tio of 50:1. Ac cord ing to our pre -vi ously work (Martínez et al., 2006), if is taken into ac -count only the iron con tent, the sam ple with mass ra -tio of 100:1 should pres ent the lower ki netic and hy dro -gen ca pac ity, but in the sam ple with mass ra tio of 50:1Mg-traces still pres ent af ter mill ing which can eas ilyforms an ox ide layer which in hib its the re ac tion withthe hy dro gen.

Due to its high est hy dro gen ab sorp tion ca pac ity,the pow der milled with the mass ra tio of 10:1 was usedfor fur ther ki net ics char ac ter iza tion. Ab sorp tion-desor -ption curves at dif fer ent tem per a tures are shown in fig -ure 3.

As ex pected, the best ab sorp tion ki net ics are achi -eved at 300°C, tak ing about 10 min utes for com ple tion. At lower tem per a tures, the ab sorp tion ki net ics slowdown and the max i mum hy dro gen stor age is achievedonly af ter 90 min utes at 250°C. There is no sig nif i cantdif fer ence ob served be tween desorption at 300°C and250°C and is com pleted af ter 12 min utes for bothtem per a tures.




Figure 2. Hydrogen absorp tion proper ties at 9 bar and

300 °C for Mg2Ni milled with diffe rent mass ratios

Figure 3. Hydrogen sorp tion proper ties at diffe rent tempe ra tures for Mg2Ni milled with a mass ratio

of 10:1 (a) absorp tion at 9 bar, (b) desorp tion curves





Sorp tion prop er ties of Mg2Ni with cata lyst

The ab sorp tion and desorption curves of Mg2Ni+Pd (1mol%) are pre sented in fig ure 4. Ab sorp tion ki net icswere en hanced in com par i son to the ma te rial with outcat a lyst, and the to tal ca pac ity (af ter 90 min utes) wasabout 3.0 wt.%, which is very close to the re sults ob -tained by Klassen et al. (1998) for sim i lar ma te rial. Fulldesorption was achieved af ter 2 and 8 min utes for 300and 250°C, re spec tively. Com par ing with the re sultsfor Mg2Ni with out cat a lyst, desorption ki net ics wasabout five times faster at 300 °C. These re sults dem on -strate the en hance ment of the sorp tion prop er ties byadd ing Pd as a cat a lyst. The cat a lytic ef fect of Pd sug -gested by Zaluski et al. (1999) is due to small Pd par ti -cles dis trib uted on the metal sur face. They pro cess isex plained by a “spill-over” phe nomenon: hy dro gen is eas -ily chemisorbed i.e. dis so ci ated, on the Pd-sur face and

mi grates to the base stor age ma te rial, i.e. Mg, whichdoes not show easy chemisorption of hy dro gen. Al -though no di rect ev i dence is re ported in this work, issug gested that high-en ergy ball mill ing by us ing a Sim -oloyer pro duces very fine Pd par ti cles and/or dis persesPd-clus ters on the pow der sur face and ab sorp tion-desorption ki net ics are im proved.

As was re ported pre vi ously (Martínez et al.,2006) par ti cle size de crease upon in creas ing mill ingtime. The av er age par ti cle size be fore mill ing was inthe range of 40-50 µm, and re duces to 5-20 µm af ter25 hours mill ing time when a ball-to-pow der massra tio of 10:1 is used. Fig ure 5 shows back scat teredelec tron im ages of pow ders milled at 8 and 25 hourswith a mass ra tio of 10:1. While Mg-rich and Ni-rich ar eas can still be dis tin guished af ter 8 hours, thepow der ap pears mostly ho mo ge neous af ter 25 hours mill ing.

Figure 4. Hydrogen sorp tion proper ties at diffe rent tempe ra tures of Mg2Ni+1%mol Pd milled

with a mass ratio of 10:1. (a) absorp tion at 9 bar and (b) desorp tion curves

Fgure 5. Micros truc tural evolu tion during milling of Mg-Ni with a mass ratio of

10:1 (a) 8 h milling time, (b) 25 h milling time

(b) (a)



Fig ure 6 shows SEM pic tures of the Mg2Ni with cat a -lyst (mass ra tio of 10:1) af ter the sec ond ab sorp tionmea sure ment and af ter six ab-desorption cy cles. It isshown crack ing of ag glom er ates and par ti cles. We sup -pose that ex ists an ef fect of the in ter nal stresses in par ti -cles built up dur ing hy dro ge na tion-dehydrogenationpro cess (Mg2Ni+2H2ÛMg2NiH4). Re gard ing to this ef -fect, Inui and co-work ers (2002) re ported that for somema te ri als, the par ti cle size de creases dur ing ab sorp -tion-desorption cy cling be cause of in ter nal stre ssescaused by lat tice ex pan sion-con trac tion, which is a good agree ment with our re sults. Al though retic ular pa ram e -ters were not cal cu lated, and con sid er ing cell ex pan -sion-con trac tion, is sup posed that the o ret i cally the cellvol umes of an hcp (Mg2Ni) and fcc (Mg2NiH4) crys tal

struc tures are 311 and 278, re spec tively; there fore, dis -tor tion of cell is ev i dent and our ex per i men tal re sults arealso in good agree ment with this con sid er ation.

Cracks are formed and some smaller par ti cles breakloose, ex pos ing fresh sur faces that are ben e fi cial for im -prov ing the re ac tion with hy dro gen. A sam ple with Pdas cat a lyst was cy cled at 300ºC/ 9 bar hy dro gen pres -sure and re sults of the ab sorp tion pro cess is shown infig ure 7.

As is shown in fig ure 6, “fresh” sur faces gen er ateddur ing hy dro gen cy cling im proves hy dro gen ab sorp tion pro cess (fig ure 7). Hy dro gen con tent of 3.3 wt. % is ob -tained af ter 15 min utes in a sam ple with 12 cy cles;which is near to the the o ret i cal ca pac ity, 3.6 wt. %, forthe re ac tion Mg2Ni+2H2ÛMg2NiH4.

Conclu sions

1. Ma te rial stored in glass vial un der ar gon at mo -sphere for sev eral months (Mg2Ni with out cat a -lyst) shows fast ab sorp tion ki net ics at 300°C (15min utes for com plete ab sorp tion), al though its ca -pac ity is rather low (2.2 wt.%). Full desorption ofMg2Ni with out cat a lyst is readily achieved at250°C in about 10 min utes in vac uum.

2. Small amounts of Pd used as a cat a lyst (1 mol%)fur ther im prove the hy dro gen sorp tion ki net ics.Full desorption at 300°C was achieved af ter 2min utes.

3. The av er age par ti cle size de creases with in creas ingmill ing time, and a fur ther de crease due to par ti clecrack ing was ob served dur ing cy cling.




(a) (b)

Figure 6. Mg2Ni parti cles with: (a) only absorp tion in the second

absorp tion cycle, (b) after 6th absorp tion-desorp tion cycle

Fgure 7. Hydrogen absorp tion cycling of a sample with

Pd-catalyst at 300 ºC/9 bar





4. Hy dro gen ab-desorption cy cles pro duces in ter nalstresses and gen er ated new sur faces that im provehy dro ge na tion pro cess.

Acknow led ge ments

E. Martínez-Franco is grate ful for re ceiv ing a fel low shipby CONACyT-Mex ico and DAAD-Ger many, and wouldlike to ac knowl edge M. Sc. Emma Mo rales (GKSS) for as -sis tance in SEM op er a tion. Au thors are grate ful for fi nan -cial sup port from ICyTDF/SIP-IPN for this re search.

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About the authors

Enrique Martínez-Franco. Bachelor and Graduate Studies on Meta lur gical Engi nee ring at ESIQIE-IPN, Mexico. Ph.D. Studies

under a Sand wich Program at Tech nical Univer sity Hamburg-Harburg, GKSS Research Center both in Germany and

ESIQIE-IPN. The topic of the research work during Ph.D was the proces sing and deve lop ment of Light Metal Hydrides

for Hydrogen Storage. From 2004 up to now is professor at Research Center and Inno va tive Tech no lo gical of IPN

(CIITEC-IPN). Colla bo ra tion with diffe rent Research Centers like CINVESTAV Mexico, Zoz GmbH Germany in topics

on the field of proces sing mate rials for hydrogen storage, metal oxides for elec tronic appli ca tions and use of high

energy-ball milling for leaching dust from elec tric furnaces.

Thomas Klassen. Bachelor and Graduate Studies on Engi nee ring at Goet tingen Univer sity and Ph.D. studies at Tech nical

Univer sity Hamburg-Harburg, Germany. Up to now Prof. Klassen has been parti ci pated in more than 60 papers and

graduate more than 20 Graduates from diffe rent Coun tries. Leader from more than 10 years in Nano tech no logy Depart -

ment at GKSS Research Center and recently got his Habi li ta tion as Professor and since 2009 is a leader of the Depart -

ment of Mecha nical Engi nee ring at Helmut Schmidt Univer sity, Germany.

David Jara millo-Vigueras. The Professor Jara millo Vigueras got his Bachelor as Meta llur gical Engi nee ring at ESIQIE-IPN. He

got his Ph.D at Tech no logy Insti tute of Nuevo Mexico, USA. He was professor for more than 15 years at ESIQIE-IPN,

Director of CIITEC and of the Supe rior Educa tion in IPN and currently is research-professor at CIITEC. He was pioneer

in Mexico with the deve lop ment of high energy milling concept and has been lead more than 50 theses in Bachelor and

Graduate Studies. He joins the group who founded the Ph.D Graduate Studies on Mate rials at ESIQIE-IPN and all labo -

ra to ries for the respec tive research work. Has been parti ci pated in more than 100 papers.

Ruediger Bormann. Professor Bormann has been worked more than 20 years as leader in diffe rent topics on mate rials proces -

sing. He got more than 10 patents also in diffe rent topics all related to the successful research acti vi ties. He has

Graduate more than 50 Ph.D. students from diffe rent Coun tries. He was professor and leader at Tech nical Univer sity

Hamburg-Harburg and Director of Mate rials Insti tute at GKSS Research Center. He has parti ci pated in more than 150

papers. Currently he is the Presi dent of the Univer sity of Bayreuth, Germany.



Documents

Hydrogen Sorption Properties of the Intermetallic Mg Ni ... · Inge nie ría Inv es ti ga ción y Tec no lo gía. Vol. XI. Núm. 3. 2010 325-332, ISSN 2594-0732, FI-UNAM 327 Martínez-Franco