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haracterization and modification of waste magnesium chip utilizeds an Mg-rich intermetallic composite
ysel Kantürk Figen, Sabriye Pis kin ∗
epartment of Chemical Engineering, Yildiz Technical University, Istanbul 34210, Turkey
r t i c l e i n f o
rticle history:eceived 22 February 2013eceived in revised form 18 January 2014ccepted 25 January 2014
eywords:aste magnesium chip
a b s t r a c t
In this study, the characterization and modification of waste magnesium chips (WMCs), which wereproduced by plastic molding in a gold manufacturing factory and are used as Mg-rich intermetalliccomposites in storing hydrogen, were discussed in detail. WMCs were analyzed using X-ray diffraction(XRD), X-ray fluorescence (XRF) spectroscopy, differential scanning calorimetry (DSC), scanning electronmicroscopy (SEM), and Brunauer–Emmett–Teller (BET) analysis to characterize the materials’ structuralproperties. Mechanical milling, organic treatment, and inorganic salt addition were carried out to modify
haracterizationodificationydrogen storage
ntermetallic composite
the WMCs’ surface to prepare Mg-rich intermetallic composites for storing hydrogen. The modified sam-ples were analyzed using high-pressure volumetric analyses to calculate their hydrogen storage capacity.The authors conclude that modified WMC was promising as an Mg-rich intermetallic composite that wassuitable for use in hydrogen storage with a 4.59 wt% capacity at 320 ◦C under a hydrogen pressure of 60 bar.
Magnesium (Mg) and Mg-based alloys as well as magnesiumydride (MgH2) are generally considered for use in hydrogen stor-ge owing to their high hydrogen storage capacity. MgH2 provides
7.6 wt% hydrogen storage capacity via the following reversibleeaction:
g + H2 � MgH2. (1)
However, the practical application of MgH2 for hydrogen stor-ge is limited due to the slow hydrogenation/dehydrogenationeaction kinetics (Zaluski, Zaluska, & Ström-Olsen, 1997). One of theactors that limits the hydrogenation reaction is the formation ofn oxide layer on the surface of Mg. To eliminate the effect causedy the oxide layer, magnesium must be perforated and cracked,nd in the literature, it is suggested that annealing at temperaturesbove 400 ◦C causes the oxide layer to crack. Another limiting fac-
Please cite this article in press as: Kantürk Figen, A., & Pis kin, S. Characan Mg-rich intermetallic composite. Particuology (2014), http://dx.doi
or is the dissociation rate of hydrogen molecules on the surface ofg. Pure Mg is not active toward hydrogen gas but is necessary for
educing the dissociation barrier (Zaluska, Zaluski, & Ström-Olsen,
999). The sorption kinetics of the Mg–H system are very slow andnly occur at high temperatures of at least 300–400 ◦C over a timecale of several hours. The complete conversion of Mg to MgH2equires more than 50 h at 350 ◦C (Shang, Bououdina, Song, & Guo,004).
It is, therefore, essential to develop non-conventional meth-ds to overcome the limitations of the kinetics of Mg with respecto hydrogen storage. In recent years, several methods have beennvestigated to improve the sorption kinetics of the Mg–H sys-em by modifying the surface of Mg. For example, catalytic metalsan be used to eliminate the dissociation barrier. Palladium (Pd)r nickel (Ni) can be used as a catalyst to improve the hydrogenbsorption rate. In addition, Mg can be combined with indium (In),luminum (Al), copper (Cu), lithium (Li), silver (Ag), and other rarearth elements, and it has been shown that these metals have aositive effect on hydrogenation (Zaluska et al., 1999). It has alsoeen observed that hydrogen storage materials should be mixturesn the nanometer scale and should include a metal selected fromhe following group of elements: Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Li,
g, Ca, Na, K, Pd, Au, Ag, and alloys containing one or more ofhese metals (Bobet, Chevalier, Song, Darriet, & Etourneau, 2003;
terization and modification of waste magnesium chip utilized as.org/10.1016/j.partic.2014.01.005
ehouche et al., 2000, 2002; Eklund et al., 2005; Gutfleisch et al.,003; Higuchi et al., 2002; Huot, Pelletier, Liang, Sutton, & Schulz,002; Liang, Huot, Boily, Van Neste, & Schulz, 1999; Liang, Huot,oily, & Schulz, 2000; Oelerich, Klassen, & Bormann, 2001a, 2001b).
and Institute of Process Engineering, Chinese Academy of Sciences.
Bobet, Chevalier, and Darriet (2002) demonstrated the effect ofeactive mechanical grinding on the chemical and hydrogen sorp-ion properties of Mg containing 10 wt% Co. The authors indicatedhat the hydrogen absorption of a mixture could be described by
two-step process, the first step being nucleation and the sec-nd diffusion. Gutfleish, Dal Toè, Herrich, Handstein, and Pratt2005) reported on the hydrogen sorption properties of Mg–1 wt%i–0.2 wt% Pd prepared by reactive milling. This material exhibitedxcellent hydrogen absorption/desorption kinetics, which weretable upon cycling. Milanese et al. (2008) investigated a binaryixture of Mg and nine other metals (Al, Cu, Fe, Mn, Mo, Sn, Ti, Zn,
r) prepared using ball milling. The mixtures as well as the inter-etallic Mg-metal phase formed after milling were analyzed. The
uthors highlighted the fact that Cu, Al, and Zn played an active rolen the hydrogenation/dehydrogenation of Mg, but only the addi-ion of Cu was effective in the destabilization of MgH2. Imamurat al. (2005) investigated the syntheses of nano-sized magnesiumith high hydrogen storage capacity by high-energy ball milling.
he authors showed that during the ball milling of Mg, organicdditives, e.g., benzene or hexane, were necessary to achieve sat-sfactory hydriding/dehydriding performance. On the other hand,
Mg-based nano-composite system prepared by the mechanicalrinding of Mg or MgH2 with a small amount of 3d transitionetals, e.g., Ti, V, Mn, Fe, Co, or Ni, showed a significant improve-ent in hydrogen storage properties (Imamura, Takesue, Akimoto,
Many studies have been carried out regarding the preparation ofg composites. Imamura et al. (1999), Imamura, Tabata, Takesue,
akata, and Kamazaki (2000), and Imamura, Tabata, Shigetomi,akesue, and Sakata (2002) proposed that preparing Mg compos-tes by the mechanical grinding of Mg with graphite in the presencef organic modifiers was a novel method for developing a hydrogentorage material. The authors studied how mechanical grindingn the presence of benzene affected the structure and hydridingroperties of Mg-graphite composites. Furthermore, they preparedarbon nano-composites by the high-energy mechanical millingf graphite and Mg (Imamura et al., 2003; Imamura, Kitazawa,anabe, & Sakata, 2007). In addition, Palma, Iturbe-Garcıa, Lopez-unoz, and Jimenez (2010) synthesized intermetallic Mg/Al alloys
o be used for hydrogen storage. Hydrogenation tests were carriedut using a micro-reactor, and the hydrogen content of the alloysas determined to be 3%. The authors proposed the use of alloys
n hydrogen storage applications to optimize the absorptionapacity.
In addition to hydrogen storage applications, Mg and Mg alloysre used in the automotive industry, aerospace engineering, metal-urgy, chemical industry and electrochemistry (batteries, cathoderotection, etc.) and consequently contribute to the rapid increase
n Mg accumulation on Earth. The worldwide production of Mgncreased from 20,000 t/year in 1937 up to 400,000 t/year in theear 2000. Most Mg waste is generated in Mg alloy foundries. Inroducing die-casting Mg alloy, approximately 50% of the mate-ial becomes the finished product, and the remainder is waste. Inccordance with the increasing number of areas of application ofg, significant quantities of fresh Mg waste are being generated
Ilıc, Korac, Kamberovıc, & Pavlovıc, 2004)The present study focused on the characterization and modi-
cation of waste magnesium chips (WMCs) for use in hydrogentorage applications. The WMCs were analyzed using X-ray diffrac-ion (XRD), X-ray fluorescence (XRF) spectroscopy, differential
Please cite this article in press as: Kantürk Figen, A., & Pis kin, S. Characan Mg-rich intermetallic composite. Particuology (2014), http://dx.doi
canning calorimetry (DSC), scanning electron microscopy (SEM)nd Brunauer–Emmett–Teller (BET) analysis to characterize theaterials’ structural properties. The surface of the WMCs was mod-
fied by mechanical milling, organic treatment and inorganic salt
ttat
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ddition. Although there have been many studies on Mg-basedaterial/alloys, there is no published study on the utilization ofg waste in hydrogen storage. The results obtained from using Mgaste as an Mg-rich intermetallic composite for hydrogen stor-
ge applications are very promising. In addition, a new perspectiven the utilization of Mg waste as a hydrogen storage medium isresented.
. Experimental
.1. Characterization of waste magnesium chips
In the present study, WMCs provided from a gold manufactur-ng factory were used as the main material (Fig. 1). Waste Mg was
olded into chips by a plastic machining process and characterizedsing the following equipment.
XRD analysis: The crystal structures of the samples were deter-mined by X-ray diffraction using a Philips Panalytical X’Pert-Prodiffractometer with CuK� radiation (� = 0.15418 nm) operated at40 mA and 45 kV. Phase identification of the samples was per-formed using the Inorganic Crystal Structure Database (ICSD). Inaddition, crystal structure refinement and quantitative analysisof the WMCs were conducted by Rietveld analysis of the X-raydiffraction data.XRF analysis: Samples were analyzed quantitatively by X-ray flu-orescence spectroscopy. The “STANDARDLESS” analysis softwareon a Minipal4-Panalytical XRF spectrometer was used to deter-mine the major constituents and trace elements in the samples.Samples were analyzed three times, and average values werereported with ±5% error.SEM analysis: Microstructure studies of the WMC samples wereperformed using a JEOL (JSM 5410 LV) SEM. The SEM was usedfor the elemental mapping of the WMC samples’ microstructure.BET analysis: The specific surface area of the samples wasmeasured by Brunauer–Emmett–Teller (Quantachrome) analy-sis under N2 adsorptive gas in multipoint mode. Samples weredegassed at 320 ◦C overnight before the measurement. Sampleswere analyzed twice, and average values were used as a singleobservation with a maximum error of ±10%.DSC analysis: Differential scanning calorimetry analyses of thematerial were performed with a Perkin Elmer Diamond instru-ment, calibrated by means of the melting points of indium(Tm = 156.6 ◦C) and tin (Tm = 231.9 ◦C) under the same conditionsapplied to the sample. An analysis was carried out using a rate of10 ◦C/min in an inert atmosphere with an Al crucible.
.2. Modification of the waste magnesium chips
Mechanical milling, organic treatment and inorganic salt addi-ion were carried out to modify the surface of the WMCs to createn Mg-rich intermetallic composite for storing hydrogen. Duringechanical milling, the WMCs were mechanically ground using a
lanetary ball mill (Fritsch Planetary Mono Mill PULVERISETTE 6).illing was performed at a speed of 300 rpm for different grinding
imes (3, 6, 9, 15, and 30 h), and the ball-to-powder ratio was 70:1.he milling parameters were kept constant for all runs. XRD andET analyses of the milled powders were performed to determinehe crystal structure, the specific surface area and the changes in
icrostructure as a function of milling time. The optimum milling
terization and modification of waste magnesium chip utilized as.org/10.1016/j.partic.2014.01.005
ime was determined to be 15 h, as indicated by the results of par-icle size analysis. In addition, after more than 15 h of milling, thegglomeration of the Mg particles was inadequate for the absorp-ion of hydrogen. During organic treatment, mechanical milling
A. Kantürk Figen, S. Pis kin / Particuology xxx (2014) xxx–xxx 3
Cs use
w(wptti
2
pcaavvfM3MfM
3
3
sPap
Df(nacacpanpt(with crystalline phase concentration in the structure less than5%) in the XRD pattern were not detected because of the providedcriterion.
Fig. 1. Raw WM
as performed in the presence of tetrahydrofuran (THF) solution10 mL THF solution/g Mg powder) for 15 h. Sodium chloride (NaCl)as used as an oxide crushing agent, and the organic treatmentrocess was carried out in the presence of 5 wt% NaCl to improvehe surface properties of the Mg layer during the inorganic salt addi-ion process. Following milling, powder handling was conductedn an inert atmosphere in a glove box to avoid possible oxidation.
.3. Determination of hydrogen storage property
Hydrogen storage capacity tests were performed in a high-ressure volumetric analyzer to calculate the hydrogen storageapacity. The instrument was designed to measure high-pressuredsorption isotherms utilizing hydrogen, methane, carbon dioxidend other gases via the static volumetric method. High-pressureolumetric analysis was conducted at a pressure ranging from highacuum to 200 bar. The sample temperature during analysis rangedrom cryogenic temperatures to 500 ◦C. After loading the modified
g powder into the micro-reactor, the sample was degassed at20 ◦C under vacuum to remove the humidity and oxide from theg surface. The high-pressure volumetric analysis system allowed
or the calculation of the hydrogen storage capacity of the modifiedg powder.
. Results and discussion
.1. Characterization of waste magnesium chips
Fig. 2 shows the XRD pattern of the WMCs. The XRD results
Please cite this article in press as: Kantürk Figen, A., & Pis kin, S. Characan Mg-rich intermetallic composite. Particuology (2014), http://dx.doi
how that the main phase was composed of magnesium (Mg,DF: 01-089-5003) and aluminum (Al, PDF: 01-089-2769). Rietveldnalysis was performed using the X’Pert High Score Plus analysisrogram with data acquired from the Inorganic Crystal Structure
d in this study.
atabase (ICSD). The results were evaluated by their reliabilityactors: the profile R-factor (Rp) = 12.95%, the expected R-factorRexp) = 12.52%, the weighted pattern (Rwp) = 19.00%, and the good-ess of fit (GoF) = 2.3. Rietveld analysis of the WMCs, which wereimed to be used as a possible hydrogen storage medium, indi-ated that the Mg belonged to the P63/mmc hexagonal space groupnd the unit cell parameters were a = 3.203642, b = 3.203642, and
= 5.200827, with the main phase constituting 94.7% of the com-osition. The other 5.3% was composed of Al (Fm 3 m space groupnd cubic unit cell parameters a, b, c = 4.070235). It should also beoted that XRD analysis is suitable for determining the crystallinehase of materials; in this study, more than 5% of the WMC struc-ure was crystalline. Diffraction peaks associated with other phases
terization and modification of waste magnesium chip utilized as.org/10.1016/j.partic.2014.01.005
tion were applied to modify the WMC surface to prepare an Mg-rich
93.12 3.54 1.72 1.02 0.21 0.14 0.25
XRF analysis was performed to determine the elemental compo-ition of the WMCs (Table 1). The main elements were Mg (93.30%)nd Al (3.67%) in the chips, and it was determined that other metalsere also present. To compare the results of the elemental analysis,
DS analysis was performed. The analysis of the XRD, XRF, and EDSesults indicated that the results were compatible.
Fig. 3 shows optical and SEM images of a WMC at 39× (Fig. 3a),50× (Fig. 3b) and 2000× (Fig. 3.1, 3.2 and 3.3) magnifications. Itan be observed that there were no cracks or voids on the metallicurface, making the material suitable for storing hydrogen. Threeifferent locations were selected in Fig. 3(b), indicated as 1, 2, and
enclosed within the rectangular areas. EDS analyses were per-ormed on the three areas. Table 2 shows the element contents inhese three areas. As shown, the area marked in white was com-osed of 81.86% Mn.
Additionally, SEM elemental mapping was carried out for theajor elements, and their distribution in the WMCs was deter-
Please cite this article in press as: Kantürk Figen, A., & Pis kin, S. Characan Mg-rich intermetallic composite. Particuology (2014), http://dx.doi
ined. Fig. 4 displays an elemental map showing the distributionf Mg, Zn, Al, and Mn, where white spots indicate the locationshere the different elements occurred in the metal shavings. Mg,
iwd
Fig. 3. Optical and SEM im
Zn 1.88 1.72 –Ni 0.69 – –
n, Al, and Mn were determined to be homogeneously distributedn the waste.
The thermal behavior of the raw WMCs under a nitrogen atmo-phere was investigated by DSC. Two endothermic peaks at 427.95nd 455.65 ◦C are shown in the DSC curve presented in Fig. 5. Melt-ng reactions occurred in two steps due to the Mg content as wells the content of various metals in the WMCs, and the reactionsere initiated at approximately 405 ◦C.
Based on the results of the above-mentioned analyses, the wasteg chips used in this study were referred to as an “Mg-rich inter-etallic material”.
.2. Modification of the waste magnesium chips
Mechanical milling, organic treatment and inorganic salt addi-
terization and modification of waste magnesium chip utilized as.org/10.1016/j.partic.2014.01.005
ntermetallic composite. Mechanical milling (ball:powder = 70:1)as carried out over 3, 6, 9, 15, and 30 h to determine the grindinguration for the WMCs. Following grinding, the crystal sizes of all
A. Kantürk Figen, S. Pis kin / Particuology xxx (2014) xxx–xxx 5
Fig. 4. SEM elemental mapping of WMC.
otmtMmg3
Fr
o2ssc
Fig. 5. Differential scanning calorimetry curve of WMCs.
f the samples obtained were determined using the Scherrer equa-ion based on the results of XRD analysis. Fig. 6 shows that, as the
illing time increased, the hexagonal phase of Mg decreased withhe decreased sizes of the crystal. However, after 3 h of grinding,
g particles could not be identified from the WMCs. After 3 hours
Please cite this article in press as: Kantürk Figen, A., & Pis kin, S. Characan Mg-rich intermetallic composite. Particuology (2014), http://dx.doi
illing, Mg waste was still in the chip form and it required morerinding time to obtain Mg waste in powder. After 6, 9, 15, and0 h of grinding, the crystal size decreased gradually. After 15 h
ig. 6. X-ray diffraction patterns of milled-Mg samples with Mg-1, -2, -3, -4, and -5epresenting milling duration of 3, 6, 9, 15, and 30 h respectively.
sdmcB
i
TB
Fig. 7. Change in Mg crystal size with milling time.
f grinding, the crystal size was 28.46 nm, and after 30 h, it was5.20 nm (Fig. 7). Therefore, it was concluded that 15 h of grindinghould be applied. However, at the end of each grinding period, theamples were subjected to multipoint BET analysis, and their spe-ific surface areas were determined (Table 3). This increase in BETurface area with increasing grinding time could be explained by aecrease in the average size of the Mg crystals and by an increase inicro-porosity. The samples that were ground for more than 15 h
ould not be efficiently evaluated due to a significant increase in
terization and modification of waste magnesium chip utilized as.org/10.1016/j.partic.2014.01.005
ET surface area.An average crystal size of 28.46 nm was obtained after grind-
ng for 15 h. To increase the BET surface area of the Mg-Al
able 3ET specific surface area of raw WMCs and modified-Mg samples.
Milling duration (h) Sample BET specific surfacearea (m2/g)
0 Raw WMC 0.083 M1 1.516 M2 1.719 M3 1.9715 M4 2.2930 M5 2.5215 with THF M6 177.0015 with THF and NaCl 5% M7 239.79
Fig. 8. High-pressure volumetric analysis curve of the sample Mg-7.
ntermetallic material, organic solvent tetrahydrofuran (THF) andhe oxide-degrading salt (NaCl) were used. It should be noted thataCl remained unchanged after grinding without the formation ofew structures in the metal samples.
In Table 3, sample Mg-7 showed a maximal specific surface areaf 238.79 m2/g. The results were obtained after 15 h of grinding,ith the addition of 5% NaCl together with THF at a concentration
f 25.87%, showing an increased surface area. Addition of NaCl mayamage the oxide layer on the metal surface, causing oxide layer-hinning and the formation of cracks, thus improving the hydrogenbsorption characteristics of the base material.
The hydrogen storage capacity of sample Mg-7 measured at20 ◦C is shown in Fig. 8. Each pressure step was held for 40 mino reach equilibrium. The hydrogen storage capacity at 10 bar wasalculated to be 1.40%. At 60 bar of pressure, the hydrogen stor-ge capacity increased to 4.59%. Afterwards, Mg-rich intermetallicomposite could be used in the synthesis of MgH2 (Kantürk Figen,011) and the thermochemical production of sodium borohydrideNaBH4) (Kantürk Figen & Pis kin, 2013).
. Conclusion
In the present study, the applicability of waste Mg chips inydrogen storage was explored in detail. The crystal size achievedas suitable because further milling caused extensive agglomera-
ion among the Mg particles, leading to undesirable results in termsf hydrogen absorption. The results of the elemental analysis indi-ated that significant amounts of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Pd,g, and Sn were present in Mg waste chips. Mg waste required
he use of a metal as a catalyst to improve the kinetics of theg-based compound. Therefore, the content of this type of wasteas considered suitable for hydrogen storage applications. Surfaceodification must be applied to increase the storage hydrogen
apacity of WMCs. The authors proposed that 15 h of mechani-al milling should be carried out in the presence of THF solutionnd NaCl salt to attain the best hydrogen storage medium, whichan be referred to as an “Mg-rich intermetallic composite”. High-ressure volumetric analysis indicated that hydrogen can be stored
n a rechargeable manner at 320 ◦C at a capacity of 4.59 wt%. Theseesults indicated that waste Mg chips represent a promising mate-ial for use in hydrogen storage applications. Furthermore, it wasbserved that such Mg waste collected from different industriesan be recovered and applied in the hydrogen energy sector.
cknowledgments
Please cite this article in press as: Kantürk Figen, A., & Pis kin, S. Characan Mg-rich intermetallic composite. Particuology (2014), http://dx.doi
The authors would like to thank the Turkish State Planningrganization (Project No. 98-DPT-07-01-02) for its financial sup-ort. The authors are thankful to UNIDO-ICHET, Istanbul, Turkey,
M
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or providing the necessary facilities for the measurements. Theuthors also express their special thanks to Dr. Osman Maliktanur from the Analytic Laboratory at UNIDO-ICHET for helpfuliscussions and comments on the measurements.
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