research article magnesium removal from an...

Research ArticleMagnesium Removal from an Aluminum A-332 Molten AlloyUsing Enriched Zeolite with Nanoparticles of SiO2

R Muntildeoz-Arroyo1 H M Hdz-Garciacutea1 J C Escobedo-Bocardo2 E E Granda-Gutierrez1

J L Acevedo-Daacutevila1 J A Aguilar-Martiacutenez3 and A Garza-Gomez1

1COMIMSA-Saltillo Ciencia y Tecnologıa No 790 Colonia Saltillo 400 25290 Saltillo COAH Mexico2CINVESTAV Unidad Saltillo Avenida Industria Metalurgica 1062 Parque Industrial Saltillo-Ramos Arizpe25900 Ramos Arizpe COAH Mexico3CIIIA-FIME-UANL Carretera a Salinas Victoria km 23 66600 Apodaca NL Mexico

Correspondence should be addressed to R Munoz-Arroyo ritamunozcomimsacom

Received 30 July 2014 Revised 6 December 2014 Accepted 7 December 2014 Published 24 December 2014

Academic Editor Haiming Lu

Copyright copy 2014 R Munoz-Arroyo et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

In order to improve theMg removal from an A-380 molten alloy mixtures of zeolite and SiO2nanoparticles (SiO

2(NPs)) were testedZeolite was enriched with 25 5 75 10 or 125 wt- of amorphous SiO

2(NPs) The SiO2(NPs) and zeolite were mixed for 30min in

ethanol for each experiment and then dried in a furnace at 80∘C for 12 h The enriched zeolites were analyzed by scanning electronmicroscopy transmission electron microscopy and N

2gas adsorption analysis The Mg removal was carried out injecting each

mixture into the molten aluminum alloy at 750∘C using argon The Mg content of the molten alloy was measured after differentperiods of the injection time Zeolites enriched with 25 and 5wt- of SiO

2(NPs) were demonstrated to be the better mixturesremoving Mg from an initial content of 16 to a final content of 00002 and 00101 wt- respectively in 45min of injection

1 Introduction

Al-Si alloy is one of the aluminum casting alloys widely usedin automotive industries due to its excellent microstructurecasting and mechanical characteristics as is the A380 alloyAbedi et al [1] showed that magnesium can refine the sizeof primary 120572(Al) phase and eutectic silicon Voncina et al[2] established the grain refining influence by Ce in A380alloy On the other hand the increase of ultimate tensilestrength and elongation in A380 alloy can be obtained bySDAS (secondary dendrite arm spacing) values ranging from570 to 10 120583m on the squeeze cast parts as shown by MuratLus [3] But it is noticeable that in the case of the A380 alloyfor automotive use the standard indicates a maximum of01 wt- of Mg because the presence of this element in thealloy increases its oxidation tendency [4] However when thealloy is produced from scrap the resultant Mg content of

the alloy is higher than 01 wt- and the excess of Mg needsto be removed Vieira et al [5] used the chlorine method anddiscuss bubble-formation theories and magnesium kineticremoval from aluminum scraps using chlorine and inert gasfluxing In spite of that Neff and Cochran [6] showed thatthe kinetics of the magnesium removal as MgCl

2is rapid

but the unreacted chlorine and the gaseous coproduct AlCl3

can limit the environmental acceptability of the processElectrochemical method and the incorporation of powderreagents (fluorides) are used for Mg removal [7] Both havedisadvantage the first is not profitable because of the highcost of electricity and the second produces toxic wastes Ascan be seen the secondary aluminum industry has beenfocused on the development of processes that overcome thementioned limitations One option is represented by theuse of purified silica-based powders because the generatedproducts in the treatment are not pollutants Reports on

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2014 Article ID 747451 7 pageshttpdxdoiorg1011552014747451

2 Advances in Materials Science and Engineering

literature establish the effect of SiO2on the Mg removal as

presented by Munoz et al [8] and Escobedo et al [9] whichis performed according to the following

Mg(l) + 2Al(l) + 2SiO2(s) 997888rarr MgAl

2O4(spinel) + 2Si(s)

Δ119866∘

750∘C = minus37709 kJ

(1)

However silica requires supplementary processes for itsconcentration resulting in additional costs Additionally thekinetics of the Mg removal using silica is relatively slow[10] However in recent studies Munoz et al [8 11] havedemonstrated the feasibility of Mg removal from aluminummolten alloys by injecting zeolite (containing more than50wt- of SiO

2) and silica using an inert carrier gas

On the other hand nanotechnology has been applied infoundry processes to improve mechanical properties of somematerials according to studies in Al alloy treatment withnano-SiC powders in order to improve toughness [12] Liet al [13] improved the tensile strength and toughness aswell as wear resistance with the addition of SiC nanopow-ders in the performance of traditional cast iron Thereforethe nanotechnology may be used for removing undesirableelements during the adjustment of the final chemical alloyscomposition Zeolite with its high porosity is ideal to beimpregnated with amorphous SiO

2(NPrsquos) Further amorphousSiO2(NPrsquos) can act as chemical catalyst to remove magnesiumof molten aluminum improving the efficiency of the processDue to the fact that the surface structural defects (ieundercoordinated units) strongly increase with decreasingnanoparticle size diffusion of atomic species to the surface ofnanoparticles significantly increases as suggested by Huynhet al [14] and Carmona-Munoz et al [15] Therefore suchconsiderations are appropriate for impregnating the porousinner part of zeolite It is noteworthy that the nanoparticlescan increase the surface area of zeolite to reduce the time ofmagnesium removal from molten aluminum alloys

The aim of this work was the study of the Mg removalfrom a molten aluminum alloy by using mixtures of zeoliteand amorphous SiO

2(NPs) asMg remover agentsThe capacityof Mg agents was evaluated by comparing its effect with thatcorresponding to the pure zeolite

2 Experimental Procedure

21 Raw Materials and Characterization of Zeolites withoutAmorphous 1198781198941198742(NPs) The mineral zeolite was crushed in aball mill and classified obtaining powders with an averageparticle size smaller than 150 120583m The chemical composi-tion of the minerals was determined by atomic absorptionspectroscopy inductively coupled plasma atomic emissionspectroscopy and gravimetric method Amorphous SiO2(NPs)(Aldrich 9999) with size smaller than 10 nm were selectedfor this work These nanoparticles were characterized byTEM

22 Impregnation and Characterization of Zeolites with Amor-phous 119878119894119874

2(119873119875119904) The impregnation of zeolite with amor-

phous SiO2(NPs) was reached mixing the selected amount of

nanoparticles (25 5 75 10 or 125 wt-) with zeolite for30min in ethanol and drying the mixture in a furnace at80∘C for 12 h Samples of the enriched zeolites were analyzedby TEM and SEM and their surface area was measured byAutosorb 1-C using liquid nitrogen adsorption

23 Selection of the Al Alloy and Mg Removal by InjectionThe selected alloy was the A-332 aluminum base alloy (Al-1164Si-0338Fe-205Cu-16Mg-154Ni) An induction electricfurnace equipped with a silicon carbide crucible of 12 kg ofcapacity and temperature control was used to melt and holdthe alloy Injection equipment with devices to measure andcontrol the gas and powder flows was used to introducethe powder mixtures into the melt The injection lance(internal diameter of 698mm) was made of graphite andcovered externally with refractory material The selectedparameters for the submerged powder injection experimentswere argon (ultrahigh purity) flow of 44 Lmin powderflow of 162 gmin mass of aluminum alloy of 8 kg andaluminum alloy treatment temperature of 750∘C The lancewas submerged at the 85 of the depth of the melt Thevariable in the experiments was the composition of thepowder mixtures zeolite-SiO

2(NPs) to be injected (0 25 575 10 or 125 wt- of SiO

2(NPs)) The mass of the powdersto be injected was calculated considering the SiO

2as the

solid reagent and spinel and silicon as products accordingto the chemical reaction (1) For each experiment samplesof the melt were obtained every 10min and the produceddross (oxidized material) was collected at the end of theexperiment The solidified samples were analyzed by sparkatomic emission spectrometry to determine their chemicalcompositions and a sample of the dross was analyzed byXRDFinally the quantity of dross was weighted and the efficiencyof process was calculated with

120578 () =Mg(start) minusMg

(end)

Mg(start)

lowast 100 (2)

where 120578() is efficiencyMg(start) is initialMg content (wt-)

and Mg(end) is final Mg content (wt-)

24 Characterization of Reaction Products byDRX and SEMofSamples after the Magnesium Removal by Injection In orderto determine the reaction products of slags formed duringthe injection of enriched zeolite with different percentages ofSiO2(NPs) the samples were characterized by X-ray diffraction

(XRD) In the case of semireacted particles founded inthe metallic samples these samples were characterized andanalyzed by SEM and EDX respectively

3 Results and Discussions

31 RawMaterials Characterization Figure 1(a) shows a SEMimage of a particle of pure zeolite (irregular morphology)Two zones can be observed (1) a clear zone (labeled LZ)corresponding to the Carlsbad twins and (2) a dark zone(labeled DZ) containing mainly Si and O and Al Ca Na andK traces (classical chemical composition of Feldsparrsquos group)

Advances in Materials Science and Engineering 3

O

Al

KNa Ca

Si

K

Si

AlO

100 200 300LZ

DZ

LZ

200100 300 400DZ

(a)

(b)

Figure 1 (a) SEM image of pure zeolite with Carlsbad twins and (b) TEM image of amorphous SiO2(NPs) as received

Table 1 Compounds identified by XRD

Compound Chemical formulaHeulandite Ca(Si7Al2)O18sdot6H2OSanidine KAlSi3O8

Table 1 shows the compounds identified in zeolite by XRDFigure 1(b) shows a TEM image of pure nanoparticles It ispossible to observe agglomerates of nanoparticles of sphericalmorphologies These nanoparticle characteristics allow highchemical reactivity because this kind of surfaces has a highspecific surface energy

32 Characterization of the Enriched Zeolites with Amor-phous 119878119894119874

2(119873119875119904) A sample of enriched zeolite (125 wt- of

SiO2(NPs)) was analyzed by SEM Figures 2(a) and 2(b) show

backscattered electron SEM images of the scanned area athigh magnifications Small agglomerates of less than 1 120583m(Figure 2(b)) can be appreciated Due to the size of thescanning spot it is not appropriate to perform chemicalanalysis by EDX

Examining other zones of the same sample agglomeratedparticles of spherical morphology were observed (Figure 3)This fact can be due to the effects of sonication by ultrasoundThe EDS analysis of the surface of the agglomerate shows that

(a)

(b)

Figure 2 SEM images of (a) zeolite with 125 of SiO2(NPs) and (b)

SiO2(NPs) agglomerates at high amplifications

its chemical composition approaches SiO2 The advantage of

such spherical morphology is that it increases the reactionkinetics due to its high surface energy

Representative samples of enriched zeolite (25 and125 wt- of SiO

2(NPs)) were analyzed by TEM Studies suchas that by Tomokazu and Hidekazu [16] suggest that bydecreasing the silicoaluminate particle size (lt300 120583m) therate of Mg removal decreases However this disadvantagecan be avoided with the impregnation of SiO

2(NPs) on the


Si

O

C

200100

Figure 3 Secondary electron SEM image of a spherical particle rich in SiO2(NPs)

1120583m

200nm

(a)

1120583m

(b)

Figure 4 TEM images of enriched zeolites with SiO2(NPs) (a) 25 and (b) 125

surface of the zeolite changing in this way the surface areaof the material At high amplification it is observed thatthe SiO

2(NPs) are immersed in a stretch gap approach to1 120583m between zeolitic materials (dark zone) (Figure 4(a)) Bycontrast the enriched zeolite with 125 of SiO

2(NPs) showsa high quantity of agglomerated nanoparticles (Figure 4(b))Both surface aspects can affect the rate and time of Mgremoval by injection

The characterization of zeolite without and with 25 575 10 and 125 of SiO

2(NPs) by Autosorb yielded importantinformation that is necessary for understanding the rolebetween the pores of zeolite and the SiO

2(NPs) As it can beseen in Table 2 the zeolite shows a pore size of 15 nm thatis sufficient to get inside the SiO

2(NPs) These pores can befilled and enrichedwith nanoparticles with a size smaller than15 nm Likewise the amorphous nature of nanoparticles canincrease the rate ofmagnesium removal before a spinel shell isformed on the surface of zeolite As a consequence the zeoliteacts as nanostructured transportmediumOn the other handaccording to Table 2 the values of the surface area suggest thefollowing aspects in the zeolite with 25 to 5 of SiO

2(NPs)the nanoparticles are being introduced inside the poresand among spaces of the mineral leading to a decrease in

the surface area However in the case of enriched zeolite with75 10 and 125 of SiO

2(NPs) the surface area increases Itmeans that the nanoparticles are agglomerated on the surfaceof zeolite because the pores are full of themThis is the reasonof a higher amount of dross in the molten aluminumwith 7510 and 125 of SiO

2(NPs) in comparison with that of the 25and 5

33 Magnesium Removal by Injection of Zeolite without andwith 119878119894119874

2(119873119875119904) Figure 5 shows the reduction of the Mg

content in the alloy as a function of the injection time Asit is seen in this figure when pure zeolite (without SiO

2(NPs))is injected the final content of Mg in the alloy after 70minof injection is 07 wt- of Mg The best result was obtainedwhen zeolite + 25 SiO

2(NPs) was injected In this case theMg content in the alloy was 01 wt- after only 47min ofinjection which is in agreement with the standard and thefinalMg content after 70min of injection reaches 00002wt- Similar effects occur when zeolite + 5 SiO

2(NPs) is used(52min of injection to reach 01 wt- of Mg) By contrastthe Mg removal decreases when zeolite enriched with 75to 125 of SiO

2(NPs) is used In these cases the target of01 wt- of Mg is not reached even by injection for 70min


Table 2 Measurements of surface area of zeolite without and with amorphous SiO2(NPs)

Material Mg(end) (wt-) 119882(oxidized material) (kg) 120578 () Area surface (m2g) Pore size (nm)Zeolite 05007 1210 6875 2209 15Zeolite 25 SiO2(NPs) 00002 0058 9998 2098 12Zeolite 5 SiO2(NPs) 00101 1100 9925 1847 13Zeolite 75 SiO2(NPs) 00500 1130 9837 2188 145Zeolite 10 SiO2(NPs) 01040 1600 9687 2294 17Zeolite 125 SiO2(NPs) 01090 1860 9318 2598 195Mg(end) final Mg content in the alloy

60Time (min)

Mg

(wt

)

Zeolite

7050403020100

12

08

06

04

02

00

10

16

14

18

Zeo + 25 SiO2(NPs)

Zeo + 75 SiO2(NPs)

Zeo + 125 SiO2(NPs)Zeo + 5 SiO2(NPs)

Zeo + 10 SiO2(NPs)

Figure 5 Mg removal from the alloy as a function of injection timeusing zeolite and zeolite with different percentages of SiO

2(NPs)

Comparatively the SiO2(NPs) enriched zeolite increases the

efficiency of the chemical reaction to remove Mg due to thesize and amorphous nature of the SiO

2(NPs)This suggests thatthe nanoparticles improve the surface energy of the zeoliteand its amorphous nature becomes as chemical catalyst Itshould be noted that the initial content of Mg in this researchwork is considerably high (16 wt- Mg) with regard to thatin other reports in the literature [4 10] that starts from 1wt- of Mg using enriched zeolites with different percentages ofSiO2as bulk Likewise removal times over 60min in order

to reach 01 wt- of Mg in the alloy are as shown by Munoz-Arroyo et al [11] This means that the Mg removal methodusing nanoparticles improves the efficiency of the process anddecreases the removal time Besides the power consumptioncan be lower in the process of Mg removal

34 Characterization of Reaction Products during the Mag-nesium Removal by Injection The slags were analyzed byX-ray diffraction in order to found the products of thereaction between the enriched zeolite with SiO

2(NPs) and theelements of the molten bath (Figure 6) The XRD patterns ofthe slags show peaks corresponding to spinel clinoptilolitepericlase anorthite and so forth Elements such as aluminum

0 10 20 30 40 50 60 70 80 90

Inte

nsity

(au

)A

AA A

CSE

C C H E H C H EE H

C H H P S E E HE

AA AC C E C

C SHP C E P E CS EE S E S E S

AH

N

AN E A

ANW W

P E NC C E C C C

C

W P EA E S

C

A

AA A

CC C CE E ES E

C EC

C SP

P SC C CC S E P E

A

A ACC

C C C E CC

S E CC

E CE

S S E P P

PEC

C

A

C C E E

E

E

E

E N E

2120579 (deg)

Z + 25 SiO2(NPs)

Z + 75 SiO2(NPs)

Z + 125 SiO2(NPs)

Z + 5 SiO2(NPs)

Z + 10 SiO2(NPs)

A = aluminum = AlS = silicon = Si

P = periclase = MgO

E = spinel = MgAl2O4

C = clinoptilolite = Ca816Si36 O

H = anorthite = Ca(Al2Si2O8)

N = nantroquite = CuClW = wurtzite = AlN

H2O)21872middot(

Figure 6 X-ray diffraction patterns of slags from the process wherezeolite is with nanoparticles of SiO

2

and silicon were also detected and belong to the aluminumalloy It is noticeable that in the slag from the zeolite with75 SiO

2(NPs) were identified wurtzite and nantroquite It ispostulated that both compounds are formed from impuritiesof the base magnesium alloy that was used to adjust thecontent of magnesium in the Al-Si alloy

The metallic specimens obtained during injection wereanalyzed by scanning electron microscopy to understandthe kinetics of the magnesium removal As can be seen inFigure 7(a) a particular specimen that shows a semireactedparticle of zeolite obtained in the samples treated withenriched zeolite with 5 nanoparticles injected for 20minwas found According to the corresponding EDX spectrathe chemical composition of the shell is approaching thestoichiometry of spinel Meanwhile the center of the particlebelongs to the chemical compositions of zeolite as shown inFigures 7(b) and 7(c) During the magnesium removal the


(c)(b)

(a)

Al

MgO

200100

(b)

Cu CaK

Si

Al

MgNa

O

400300200100

(c)

Figure 7 (a) Image of backscattered electron for a semireacted particle of enriched zeolite with 5 of SiO2nanoparticles obtained after 20

minutes of injection EDX of (b) shell and (c) center of particle

reaction products form a shell on the surface of enrichedzeolite with SiO

2(NPs) Hence the reaction rate is slow dueto the nature of the process a shell of reaction products isformed on the particles andmakes the mass transfer difficult

On this viewpoint it is postulated that the formationof a stable shell on the surface will be quickly formed asa stable diffusive barrier among dissolved Mg in the liquidbath of aluminum and shell on the zeolite (spinel) thatreduces the removal kinetics Finally when nanoparticles arein contact among them they tend to reduce their free energyreducing their surface energy Then at high temperatureinside the molten bath the nanoparticles coalesce (sinteringof the nanoparticles) reducing substantially the reactionarea This is the reason why the efficiency of magnesiumremoval decreases and a higher amount of dross in themoltenaluminum with 75 10 and 125 of SiO

2(NPs) is formed

4 Conclusions

Theuse of mineral zeolite enriched with 25 wt- of SiO2(NPs)

provided higher Mg removal from the molten alloy thanthat obtained using pure zeolite The kinetics of magnesiumremoval decreases as the percentage of SiO

2(NPs) increasespromoting the formation of a dross rich in intermetalliccompounds

The density high surface area and feasibility of ionexchange of the enriched particles allow better powder-liquidcontact improving the process kinetics

The methodology presented in this study is feasible to beapplied on an industrial scale

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgment

The authors wish to express their gratitude to the NationalCouncil of Science andTechnology (CONACyT) for support-ing the development of the postdoctoral fellow of R Munoz-Arroyo

References

[1] A Abedi M Shahmiri B A Esgandari and B Nami ldquoMicro-structural evolution during partial remelting ofAl-Si alloys con-taining different amounts of magnesiumrdquo Journal of MaterialsScience amp Technology vol 29 no 10 pp 971ndash978 2013

[2] MVoncina PMrvarM Petric and JMedved ldquoMicrostructureand grain refining performance of Ce on A380 alloyrdquo Journal ofMining and Metallurgy Section B Metallurgy vol 48 no 2 pp265ndash272 2012

[3] H Murat Lus ldquoEffect of casting parameters on the microstruc-ture andmechanical properties of squeeze cast A380 aluminumdie cast alloyrdquo Kovove Materialy vol 50 no 4 pp 243ndash2502012

[4] Y Wang H-T Li and Z Fan ldquoOxidation of aluminium alloymelts and inoculation by oxide particlesrdquo Transactions of theIndian Institute of Metals vol 65 no 6 pp 653ndash661 2012

[5] E A Vieira J R De Oliveira G F Alves D C R Espinosa andJ A S Tenorio ldquoUse of chlorine to remove magnesium frommolten aluminumrdquo Materials Transactions vol 53 no 3 pp477ndash482 2012

[6] V D Neff and P B Cochran ldquoPanel of Aluminum ProcessingrdquoLight Metals USA vol 1993 pp 1053ndash1060 1993

[7] T Lehner P J Koros and V Ramachandran InternationalSymposium on Injection in Process Metallurgy vol 1-2 TheMinerals Metals amp Materials Society Warrendale Pa USA1991

[8] R Munoz J C Escobedo H M Hernandez et al ldquoMagnesiumremoval frommolten aluminumalloys using zeolite and zeolite-silica mixturesrdquo Archives of Metallurgy and Materials Sciencevol 53 pp 965ndash968 2008

[9] J C Escobedo J F Hernandez S Escobedo et al ldquoEstudiocinetico de la eliminacion de magnesio en las aleaciones dealuminio mediante la inyeccion de polvos de sılicerdquo Revista deMetalurgia vol 39 no 3 pp 172ndash182 2003

[10] J C Escobedo A Flores V J F Hernandez et al ldquoRemovalof magnesium aluminum alloys using the method of reagentinjection powdersrdquo in Light Metals pp 885ndash891 TSM 2003

[11] R Munoz-Arroyo J C Escobedo-Bocardo H M Hernandez-Garcıa et al ldquoEstudio del mecanismo de eliminacion de mag-nesio de aleaciones Al-Si en estado lıquido mediante inyeccionde minerales base sılicerdquo Revista de Metalurgia vol 46 no 4pp 1988ndash4222 2010

[12] M-L Chen L Kang J Yang L Yang andH Gao ldquoMicrostruc-ture and mechanical properties of reinforced cast aluminum


bronze by modified Nano-SiC powderrdquo Foundry vol 57 no 4pp 330ndash333 2008

[13] J-W Li M-L Chen H Gao and Y-H Zhao ldquoStructures andproperties of cast irons reinforced by trace addition of modifiedSiC nanopowdersrdquo Chinese Journal of Chemical Physics vol 20no 6 pp 625ndash631 2007

[14] N T X Huynh V van Hoang and H Zung ldquoEvolution ofstructure of SiO

2nanoparticles upon cooling from the meltrdquo

PMC Physics B vol 1 article 16 2008[15] R Carmona-Munoz H M Hdz-Garcıa R Munoz-Arroyo

et al ldquoMagnesium removal from aluminum molten alloysusing silica based minerals and waste from coal-fired power(cenospheres)rdquo Chemical Technology An Indian Journal vol 8no 4 pp 115ndash120 2013

[16] H Tomokazu and S Hidekazu ldquoRemoval of magnesium frommolten aluminium scrap by compound-separation methodwith shirasurdquoMaterials Transactions vol 51 no 5 pp 838ndash8432010

Submit your manuscripts athttpwwwhindawicom

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MaterialsJournal of


Nano

materials


Journal ofNanomaterials


literature establish the effect of SiO2on the Mg removal as

presented by Munoz et al [8] and Escobedo et al [9] whichis performed according to the following

Mg(l) + 2Al(l) + 2SiO2(s) 997888rarr MgAl

2O4(spinel) + 2Si(s)

Δ119866∘

750∘C = minus37709 kJ

(1)

However silica requires supplementary processes for itsconcentration resulting in additional costs Additionally thekinetics of the Mg removal using silica is relatively slow[10] However in recent studies Munoz et al [8 11] havedemonstrated the feasibility of Mg removal from aluminummolten alloys by injecting zeolite (containing more than50wt- of SiO

2) and silica using an inert carrier gas

On the other hand nanotechnology has been applied infoundry processes to improve mechanical properties of somematerials according to studies in Al alloy treatment withnano-SiC powders in order to improve toughness [12] Liet al [13] improved the tensile strength and toughness aswell as wear resistance with the addition of SiC nanopow-ders in the performance of traditional cast iron Thereforethe nanotechnology may be used for removing undesirableelements during the adjustment of the final chemical alloyscomposition Zeolite with its high porosity is ideal to beimpregnated with amorphous SiO

2(NPrsquos) Further amorphousSiO2(NPrsquos) can act as chemical catalyst to remove magnesiumof molten aluminum improving the efficiency of the processDue to the fact that the surface structural defects (ieundercoordinated units) strongly increase with decreasingnanoparticle size diffusion of atomic species to the surface ofnanoparticles significantly increases as suggested by Huynhet al [14] and Carmona-Munoz et al [15] Therefore suchconsiderations are appropriate for impregnating the porousinner part of zeolite It is noteworthy that the nanoparticlescan increase the surface area of zeolite to reduce the time ofmagnesium removal from molten aluminum alloys

The aim of this work was the study of the Mg removalfrom a molten aluminum alloy by using mixtures of zeoliteand amorphous SiO

2(NPs) asMg remover agentsThe capacityof Mg agents was evaluated by comparing its effect with thatcorresponding to the pure zeolite

2 Experimental Procedure

21 Raw Materials and Characterization of Zeolites withoutAmorphous 1198781198941198742(NPs) The mineral zeolite was crushed in aball mill and classified obtaining powders with an averageparticle size smaller than 150 120583m The chemical composi-tion of the minerals was determined by atomic absorptionspectroscopy inductively coupled plasma atomic emissionspectroscopy and gravimetric method Amorphous SiO2(NPs)(Aldrich 9999) with size smaller than 10 nm were selectedfor this work These nanoparticles were characterized byTEM

22 Impregnation and Characterization of Zeolites with Amor-phous 119878119894119874

2(119873119875119904) The impregnation of zeolite with amor-

phous SiO2(NPs) was reached mixing the selected amount of

nanoparticles (25 5 75 10 or 125 wt-) with zeolite for30min in ethanol and drying the mixture in a furnace at80∘C for 12 h Samples of the enriched zeolites were analyzedby TEM and SEM and their surface area was measured byAutosorb 1-C using liquid nitrogen adsorption

23 Selection of the Al Alloy and Mg Removal by InjectionThe selected alloy was the A-332 aluminum base alloy (Al-1164Si-0338Fe-205Cu-16Mg-154Ni) An induction electricfurnace equipped with a silicon carbide crucible of 12 kg ofcapacity and temperature control was used to melt and holdthe alloy Injection equipment with devices to measure andcontrol the gas and powder flows was used to introducethe powder mixtures into the melt The injection lance(internal diameter of 698mm) was made of graphite andcovered externally with refractory material The selectedparameters for the submerged powder injection experimentswere argon (ultrahigh purity) flow of 44 Lmin powderflow of 162 gmin mass of aluminum alloy of 8 kg andaluminum alloy treatment temperature of 750∘C The lancewas submerged at the 85 of the depth of the melt Thevariable in the experiments was the composition of thepowder mixtures zeolite-SiO

2(NPs) to be injected (0 25 575 10 or 125 wt- of SiO

2(NPs)) The mass of the powdersto be injected was calculated considering the SiO

2as the

solid reagent and spinel and silicon as products accordingto the chemical reaction (1) For each experiment samplesof the melt were obtained every 10min and the produceddross (oxidized material) was collected at the end of theexperiment The solidified samples were analyzed by sparkatomic emission spectrometry to determine their chemicalcompositions and a sample of the dross was analyzed byXRDFinally the quantity of dross was weighted and the efficiencyof process was calculated with

120578 () =Mg(start) minusMg

(end)

Mg(start)

lowast 100 (2)

where 120578() is efficiencyMg(start) is initialMg content (wt-)

and Mg(end) is final Mg content (wt-)

24 Characterization of Reaction Products byDRX and SEMofSamples after the Magnesium Removal by Injection In orderto determine the reaction products of slags formed duringthe injection of enriched zeolite with different percentages ofSiO2(NPs) the samples were characterized by X-ray diffraction

(XRD) In the case of semireacted particles founded inthe metallic samples these samples were characterized andanalyzed by SEM and EDX respectively

3 Results and Discussions

31 RawMaterials Characterization Figure 1(a) shows a SEMimage of a particle of pure zeolite (irregular morphology)Two zones can be observed (1) a clear zone (labeled LZ)corresponding to the Carlsbad twins and (2) a dark zone(labeled DZ) containing mainly Si and O and Al Ca Na andK traces (classical chemical composition of Feldsparrsquos group)


O

Al

KNa Ca

Si

K

Si

AlO

100 200 300LZ

DZ

LZ

200100 300 400DZ

(a)

(b)










(a)

(b)







2(NPs) on the


Si

O

C

200100


1120583m

200nm

(a)

1120583m

(b)























60Time (min)

Mg

(wt

)

Zeolite

7050403020100

12

08

06

04

02

00

10

16

14

18

Zeo + 25 SiO2(NPs)

Zeo + 75 SiO2(NPs)


Zeo + 10 SiO2(NPs)


2(NPs)







0 10 20 30 40 50 60 70 80 90

Inte

nsity

(au

)A

AA A

CSE

C C H E H C H EE H

C H H P S E E HE

AA AC C E C


AH

N

AN E A

ANW W

P E NC C E C C C

C

W P EA E S

C

A

AA A

CC C CE E ES E

C EC

C SP

P SC C CC S E P E

A

A ACC

C C C E CC

S E CC

E CE

S S E P P

PEC

C

A

C C E E

E

E

E

E N E

2120579 (deg)

Z + 25 SiO2(NPs)

Z + 75 SiO2(NPs)

Z + 125 SiO2(NPs)

Z + 5 SiO2(NPs)

Z + 10 SiO2(NPs)


P = periclase = MgO





H2O)21872middot(


2





(c)(b)

(a)

Al

MgO

200100

(b)

Cu CaK

Si

Al

MgNa

O

400300200100

(c)






2(NPs) is formed

4 Conclusions








Acknowledgment


References




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




O

Al

KNa Ca

Si

K

Si

AlO

100 200 300LZ

DZ

LZ

200100 300 400DZ

(a)

(b)










(a)

(b)







2(NPs) on the


Si

O

C

200100


1120583m

200nm

(a)

1120583m

(b)























60Time (min)

Mg

(wt

)

Zeolite

7050403020100

12

08

06

04

02

00

10

16

14

18

Zeo + 25 SiO2(NPs)

Zeo + 75 SiO2(NPs)


Zeo + 10 SiO2(NPs)


2(NPs)







0 10 20 30 40 50 60 70 80 90

Inte

nsity

(au

)A

AA A

CSE

C C H E H C H EE H

C H H P S E E HE

AA AC C E C


AH

N

AN E A

ANW W

P E NC C E C C C

C

W P EA E S

C

A

AA A

CC C CE E ES E

C EC

C SP

P SC C CC S E P E

A

A ACC

C C C E CC

S E CC

E CE

S S E P P

PEC

C

A

C C E E

E

E

E

E N E

2120579 (deg)

Z + 25 SiO2(NPs)

Z + 75 SiO2(NPs)

Z + 125 SiO2(NPs)

Z + 5 SiO2(NPs)

Z + 10 SiO2(NPs)


P = periclase = MgO





H2O)21872middot(


2





(c)(b)

(a)

Al

MgO

200100

(b)

Cu CaK

Si

Al

MgNa

O

400300200100

(c)






2(NPs) is formed

4 Conclusions








Acknowledgment


References




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Si

O

C

200100


1120583m

200nm

(a)

1120583m

(b)























60Time (min)

Mg

(wt

)

Zeolite

7050403020100

12

08

06

04

02

00

10

16

14

18

Zeo + 25 SiO2(NPs)

Zeo + 75 SiO2(NPs)


Zeo + 10 SiO2(NPs)


2(NPs)







0 10 20 30 40 50 60 70 80 90

Inte

nsity

(au

)A

AA A

CSE

C C H E H C H EE H

C H H P S E E HE

AA AC C E C


AH

N

AN E A

ANW W

P E NC C E C C C

C

W P EA E S

C

A

AA A

CC C CE E ES E

C EC

C SP

P SC C CC S E P E

A

A ACC

C C C E CC

S E CC

E CE

S S E P P

PEC

C

A

C C E E

E

E

E

E N E

2120579 (deg)

Z + 25 SiO2(NPs)

Z + 75 SiO2(NPs)

Z + 125 SiO2(NPs)

Z + 5 SiO2(NPs)

Z + 10 SiO2(NPs)


P = periclase = MgO





H2O)21872middot(


2





(c)(b)

(a)

Al

MgO

200100

(b)

Cu CaK

Si

Al

MgNa

O

400300200100

(c)






2(NPs) is formed

4 Conclusions








Acknowledgment


References




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






60Time (min)

Mg

(wt

)

Zeolite

7050403020100

12

08

06

04

02

00

10

16

14

18

Zeo + 25 SiO2(NPs)

Zeo + 75 SiO2(NPs)


Zeo + 10 SiO2(NPs)


2(NPs)







0 10 20 30 40 50 60 70 80 90

Inte

nsity

(au

)A

AA A

CSE

C C H E H C H EE H

C H H P S E E HE

AA AC C E C


AH

N

AN E A

ANW W

P E NC C E C C C

C

W P EA E S

C

A

AA A

CC C CE E ES E

C EC

C SP

P SC C CC S E P E

A

A ACC

C C C E CC

S E CC

E CE

S S E P P

PEC

C

A

C C E E

E

E

E

E N E

2120579 (deg)

Z + 25 SiO2(NPs)

Z + 75 SiO2(NPs)

Z + 125 SiO2(NPs)

Z + 5 SiO2(NPs)

Z + 10 SiO2(NPs)


P = periclase = MgO





H2O)21872middot(


2





(c)(b)

(a)

Al

MgO

200100

(b)

Cu CaK

Si

Al

MgNa

O

400300200100

(c)






2(NPs) is formed

4 Conclusions








Acknowledgment


References




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(c)(b)

(a)

Al

MgO

200100

(b)

Cu CaK

Si

Al

MgNa

O

400300200100

(c)






2(NPs) is formed

4 Conclusions








Acknowledgment


References




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials


















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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