Uniform Dispersion of Multiwalled Carbon Nanotubes in Copper Matrix

8/9/2019 Uniform Dispersion of Multiwalled Carbon Nanotubes in Copper Matrix

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Hindawi Publishing CorporationInternational Journal o Manu acturing EngineeringVolume , Article ID , pageshttp://dx.doi.org/ . / /

Research ArticleUniform Dispersion of Multiwalled Carbon Nanotubesin Copper Matrix Nanocomposites Using Metal InjectionMolding Technique

Ali Samer Muhsan, 1 Faiz Ahmad, 1 Norani M. Mohamed, 2

Puteri Sri Melor Megat Yusoff, 1 and Muhammad Rafi Raza 3

Mechanical Engineering Department, Universiti eknologi PE RONAS (U P), Bandar Seri Iskandar, ronoh, Perak Darul Ridzuan, Malaysia

Centre of Innovative Nanostructures and Nanodevices (COINN), U P, Bandar Seri Iskandar, ronoh,Perak Darul Ridzuan, MalaysiaDepartment of Mechanical & Materials Engineering, Universiti Kebangsaan, UKM Bangi,Selangor Darul Ehsan, Malaysia

Correspondence should be addressed to Faiz Ahmad; [email protected]

Received March ; Accepted August

Academic Editors: A. Lockamy and B.-K. Min

Copyright Ali Samer Muhsan et al. Tis 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 properly

cited.Tis work presents a novel abrication approach o multiwalled carbon nanotubes (MWN s) rein orced copper (Cu) matrixnanocomposites. A combination o nanoscale dispersion o unctionalized MWN s in low viscose media o dissolved paraffin waxunder sonication treatment ollowed by metal injection molding (MIM) technique was adopted. MWN s contents were varied

rom to vol.%. In ormation about the degree o puri cation and unctionalization processes, evidences on the existence o theunctional groups, effect o sonication time on the treated MWN s, and microstructural analysis o the abricated Cu/MWN s

nanocomposites were determined using EM, EDX, FESEM, and Raman spectroscopy analysis. Te results showed that theimpurities o the pristine MWN s such as Fe, Ni catalyst, and the amorphous carbon have been signi cantly removed aferpuri cation process. Meanwhile, FESEM and EM observations showed high stability o MWN s at elevated temperatures anduni orm dispersion o MWN s in Cu matrix at different volume ractions and sintering temperatures ( , & C). Teexperimentally measured thermal conductivities o Cu/MWN s nanocomposites showed remarkable increase ( . % higher thansintered pure Cu) with addition o vol.% MWN s, and slight decrease below the value o sintered Cu at and vol.% MWN s.

1. Introduction

With continued demand or high-per ormance electronicdevices with low cost, small size andmore efficient electronicsystems, thermal challenges became a serious concern inelectronicpackaging design[ ]. More transistorsmeans moreheat is generated within these systems. High-operating tem-perature decreases the overall reliability or even permanently damages the entire electronic system [ ]. Tere ore, a new thermal management solution is required to provide cost-effective means o dissipating heat rom next generationmicroelectronic devices [ ]. In response to these criticalneeds, high-per ormance heat sink nanocomposite made

o copper rein orced by multiwalled carbon nanotubes isproposed.

Te superior physical, mechanical, and thermal prop-erties o MWN s have led it to have very high impact ondevelopingnew generations o nanocompositematerialswithenhanced unctionality and wide range o applications [ ].However, incorporation o MWN s in metal matrix has itsown barriers and difficulties that might destroy the desiredproperties o MWN s [ ].

Meanwhile, dispersion o MWN s in metal matrixnanocomposites is known as the most difficult challengein abricating MWN s based metal matrix nanocomposite.


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International Journal o Manu acturing Engineering

Tis can be attributed to the ollowing actors: ( ) theincompatibility in phases between metalmatrix andMWN s;( ) the large difference in density; ( ) bundling and tanglingphenomenon o MWN s that occurs due to the high sur acearea o MWN s associated with van der Waal orcesbetweenindividual MWN s. Experimentally, most o the previous

works showed decrease in the physical properties o MWN sbased nanocomposites mostly due to the MWN s clusteringphenomenon [ ].

Tere ore, several techniques have been suggested toimprove the dispersion o MWN s. Un ortunately, most o these techniques were limited to polymer nanocomposites,while only ew researchers have ocused on improvingMWN s dispersion in metal matrix nanocomposite. Even so,their results did not meet their expectations. For example,Chu et al. [ ] studied the effect o incorporating differ-ent amounts o MWN s in Cu matrix using ball millingmixing technique on thermal conductivity. Tey ound thatthere was no enhancement in the thermal conductivity andthey proposed that this behaviour was probably due to therandom orientation o MWN s, the existence o inter acialthermal resistance between MWN s and copper particlesassociated with low phase contrast ratio o MWN s tocopper, as well as the poor dispersion o MWN s in thecopper matrix. Similar results were reported by Kim et al. [ ]afer rein orcing Cu with nickel-coated single-walled carbonnanotubes (SWN s). Tey suggested that the existence o grain boundaries and de ects in the polycrystals o thecomposite, resulting in lower thermalconductivity comparedto the matrix. Cho et al. [ ] used a combination o wet mix-ing process accelerated by hetroaggregation method usingacid-treated MWN s ollowed by Spark Plasma Sinteringtechnique. Teir results, however, showed no enhancementin thermal conductivity with MWN s contents higher than

vol.%. On the other hand, some researchers have carriedoutunctionalization process on MWN s to enhance the disper-

sion o the puri ed MWN s andcreate sidewalls groupssuchasCOOHthathave thepotentialto bind MWN s to themetalmatrix[ ].For example,Kim etal. [ ] reported theobser- vation o enhanced mechanical properties o MWN /Cunanocomposites using a molecular mixing technique. Tey also observedoxygenatomsat the inter acebetweenMWN sandCu matrixandproposedthat these oxygen moleculeshada positive effect on the inter acial strength.

Tere ore, this study aims to develop a new dispersingtechnique o multiwalled carbon nanotubes rein orced cop-per matrix nanocomposites that ensures a homogeneous dis-persion o MWN s in Cu matrix. Tis technique is basically a multilevel mixing approach o nanoscale dispersion o the

unctionalized MWN s in Cu/MWN s eedstock ollowedby MIM process.

2. Experimental Methods

. . Materials. CommercialCupowderparticleswith diame-terranging o m were purchased rom Sandvik Osprey L D, UK. Multiwalled carbon nanotubes with diameter o

nm and m in length were purchased rom Shen-zhen Nano- echnologies Port Co., Ltd., China. Te purity o MWN s was % with ash content o . wt.%.

. . Nanoscale Dispersion Process. In this method, MWN swere rst puri ed and unctionalized using concentratedacids with the assist o heating and sonication process.MWN s were immersed in an acid solution o H 2 SO4 ( %)and HNO 3 ( %) in a ratio o : or different sonicationtimes ( . , . and h) under temperature o C. Func-tionalization has been applied to enhance the dispersion o puri ed MWN s and create sidewalls groups that have thepotential to bind MWN s to the Cu matrix.

Afer MWN s being puri ed and unctionalized inconcentrated acids under sonication treatment, MWN swere washed by distilled water and dried at C or h.MWN s were mixed again with low viscous liquid mediao dissolved paraffin wax (PW) diluted in heptane solventalong with magnetic stirring. Tiswas ollowed by sonication

agitation process to ensure uni orm dispersion o MWN sin PW solution. Te dried MWN s/PW mixture was thenmixed with the other components o the binder system(Polyethylene, PE; Stearic Acid, SA) in Z-blade mixer at

C. Tis step provided a high-viscous liquid media withhigh shear orces that allowed MWN s to be mixed properly by dispersing the MWN s clusters with uni orm dispersioninto themoltenbinder system. Te copperpowderwasaddedgradually during the mixing process to orm Cu-MWN s-Binder eedstock as illustrated in Figure .

. . Metal Injection Molding Process. Metal injection mold-ing (MIM) technique involves our main stages: eedstock preparation; injection molding o the prepared eedstock;binder removal or debinding process (solvent and thermaldebinding) to get a shaped porous metallic part; sinteringprocess in which thedebindedsamples are condensedto ormpure or composite metallic products [ ]. In this technique,the prepared eedstock in the previous stage was granulatedto small pieces to be plasticized in a heated barrel o injectionmolding machine, and, then, a controlled volume o themolten eedstock is injected rom the plasticator underpressure into a closed mould, with solidi cation beginningon the moulds cavity wall to get the desired shape. Teinjection moulded samples are called green samples. ocompletely remove the binder rom the green samples, two

consecutive processes o solvent and thermal debinding wereapplied. Afer the binder is being totally removed, sinteringprocess under Argon atmosphere with different sinteringtemperature o , and C was carriedoutas shownin Figure .

3. Results and Discussion

. . EM and EDX Analysis. Figure shows the transmissionelectron micrograph ( EM) o MWN s be ore (a) and afer(b) puri cation process. It can be seen that the impuritieso the pristine MWN s, such as Fe, Ni catalyst, and theamorphous carbon have been success ully removed afer the


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Z-blademixers

(PW + PE + SA + CN s + Cu)

Ultrasonication at Deionized water PW + heptane + CN s + magneticstirring +

Feedstock preparation

H2SO4 + NHO 3solution

CN s ltered andwashed by deionized

water

Pristine CN

CONH

COOH-unctionalized

Dried (PW + CN s)

or 24 hrs.

70C or 2.75 hours

Dried at 120C

ultrasonication at 85C

F : Nanoscale dispersion process o MWN s in Paraffin Wax (PW).

Injection molding o CN s/Cu eedstock Molded CN s/Cu green samples Solvent debinding process (heptane)

Termal debinding and sintering process Sintered samples o CN s/Cu

Molded CN s/Cu (green samples)

F : Metal injection process o MWN s/Cu nanocomposites.

puri cation and sonication process. Tese results were ur-ther proved by Energy dispersive X-ray spectroscopy (EDX)and Raman microscope inspection. EDX results ( able )show that Fe catalyst was completely eliminated and Ni wasreduced signi cantly afer acid treatment. However, longertime o sonication treatment may result in aggressive oxida-tion o the MWN sur ace that can degrade the MWN s.Tere ore, in order to test the effect o sonication process on

the MWN s structure, different sonication hours o . , . ,and were applied. Te results revealed that the sonicationtime o . h was recorded as the optimal parameter.

. . Raman Spectroscopy and SEM Characterization estsof Functionalized MWN s. Raman spectroscopy revealednecessary in ormation on the evolution o MWN s aferchemical or physical treatment [ ]. Figure illustrates the


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100 nm

(a)

100 nm

(b)

F : EM images o (a) Pristine MWN s and (b) Puri ed MWN s with sonication treatment or . h.

Raman spectra o pristine MWN s (Raw MWN s), acidtreated MWN s with sonication time o . , . and h.Te D/G ratio represents the de ect density in graphiticstructures. As clearly shown in Figure , there were twopeaks at cm1 (D band) and the other at cm1 (Gband). By the comparison o the D/ G ratios o these spectra,it could be seen that this ratio was varied as sonicationtime increased. Te pristine MWN s had the lowest D/ Gratios o . . Te D / G ratios gradually increased to . ,

. , and . o the MWN s treated under sonicationprocess o . , . , and hours, respectively. Te amounto de ects apparently increased in MWN s afer unctional-ization process, especially the one afer hours o sonication

treatment. Tese results were urther con rmed by FESEMcharacterization, as shown in Figure . Tis Figure includesour FESEM images which corresponding to (a) the pristine

MWN s, (b) acid treated MWN s ( unctionalized MWN s)with sonication process o . , (c) . , and (d) hours.Although EDX inspection test showed higher impuritiesremoval at h sonication treatment ( able ), Figure (d)revealed that clear damages were occurred on the MWN sstructure afer hours o sonication treatment. Tere ore,based on these results, the sonication treatment time chosenwas . hours.

. . Microstructural Analysis of Cu/MWN s Nanocomposites.Figure shows the FESEM images o Cu/MWN s nanocom-posites demonstrating the quality o MWN s dispersion inCumatrixatdifferent abrication stages. Figures (a) and (b)illustrate the FESEM o Cu/MWN s green (be ore debindingprocess) and sintered parts, respectively. Tese parts were

abricated without utilizing the newly developed technique,and they are presented here or comparison purposes. Itclearly showed that MWN s were agglomerated between theCu particles and ormed porosities rather than enhancingthe inter acial bonding. Figures (c) and (d) represent thegreen andbrown (thermal debinded) Cu/MWN s parts aferapplyingthe new dispersion technique. Figures (e), ( ),and

(g) show the ractured sur aces o the sintered Cu/MWN s

: EDX results o acid treated MWN s under differentSonication Hours.

Element Weight% Atomic%. h Sonication treatment

C . .O . .Fe . .Ni . .

. h Sonication treatmentC . .O . .Fe

S . .Ni . .

h Sonication treatmentC . .O . .Fe S . .Ni . .

parts at different sintering temperature ( , , andC, resp.). Figure (h) presents a EM nanograph, which

in turn illustrates the incorporation o the individual MWNinto theCu particles. It revealed that themechanicaldamagesin MWN s structure were very ew. It also showed a goodinter acial bonding at Cu/MWN s inter ace.

In general, we can clearly note that MWN s dispersionhas been signi cantly improved afer utilizing the new technique o nanoscale dispersion. Tis can be attributed

rst to the unctionalization process that provides COOHgroups on the outer sur aces o the MWN s. In addition,sonication process generates energy in different orms onthe MWN s clusters, these energies are oscillating zones o high temperature with extremely rapid heating and coolingrates; alternating impulses o veryhighpressure; ormationo


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Sonicated or 5 h

D band G bandG band

Sonicated or 2.75 h

Sonicated or 0.5 h

Pristine CN s

Raman shif (1/cm)

I n t e n s i t y ( % )

200

180

160

140

120

100

80

60

40

20

0500 1000 1500 2000 2500 3000

F : Raman spectra o raw MWN s and unctionalized MWN s using a mixture o H2 SO4 : NHO3 ( : ) under different sonicationsdwell time.

200 nm

(a)

200 nm

(b)

200 nm

(c)

200 nm

(d)

F : FESEM images o raw and unctionalized MWN s. (a) pristine MWN s, (b) sonication treatment or . hour, (c) treated or .

hours and (d) treated or hours.

microbubbles throughout the liquidmediumo MWN s thatgrowth and collapse on the MWN s sur aces. Tese energiesare sufficient to push the individual MWN apart andovercome the van der Waal orces between MWN s, whichis considered as the main reason o the MWN s clusteringphenomenon [ ]. Meanwhile, MIM technique providedhigh-shear orces rom thebindersystemcomponents during

eedstockpreparation thatdisperse andex oliate the MWN sclusters into the Cu matrix homogeneously. Tis indicatesthat nanoscale dispersion method combined with MIM

technique is a very effective method or achieving uni ormdistribution o MWN s in metal matrix nanocomposites.

. . Relative Density. Figure shows the effect o sinteringtemperatureon the relativedensity o MWN s/Cu nanocom-posites at different dwell time and MWN s vol.%. At Csinteringtemperature anddwelltime o min, themeasuredrelative densities were about . %, . %, . %, and %

or pure copper, , , and vol.% MWN s, respectively. Ingeneral, the relativedensitieso MWN s/Cunanocomposites


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10 m

(a)

20 m 5 m

CN s clusters

(b)

10 m

(c)

2 m 500 m

CN s implantedin Cu particles

(d)

2 m 20 m

(e)

1 m20 m

( )

2 m 20 m

(g)

100 nm400 nm

Cuparticle

CN s

(h)

F : FESEM micrographo sinteredCu- vol.% MWN s nanocomposites.(a) and(b) are theFESEMo Cu/MWN s green and sinteredparts, respectively, be ore applying the new dispersion technique, (c) and (d) represent the green and brown samples o Cu/MWN s sinteredat and C, respectively, both are afer applying the new dispersion technique. Images (e), ( ) and (g) show the ractured sur aces o the sintered Cu/MWN s parts at , and C, respectively. (h) EM nano-graph showing good bonding at the inter ace between

unctionalized MWN s and Cu particles.


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60 70 80 90 100 110 12088

90

92

94

96

98

100

Pure Cu1 vol.% cN s

5 vol.% cN s10 vol.% cN s

R e l a t i v e d e n s i t y ( % )

Sintering time (min)

Sintering temperature: 1050 C

F : Relative densities o MWN s/Cu nanocomposites.

0 25 50 75 100 125160180

200220240260280300320340360380400

Sintered CuCu-1 vol.% MWN s

Cu-5 vol.% MWN sCu-10 vol.% MWN s

T e r m a l c o n d u c t i v i t y ( W / m K )

emperature ( C)

Sintering temperature =

Dwell time = 2 hrs

1050 C

F : Termal conductivities o MWN s/Cu composites as aunction o MWN s volume raction with two different measuring

temperatures ( and C).

were lower than the pure Cu matrix due to accumulation o

MWN s at the grain boundaries o the Cu matrix, which isthebasiso theporescreation.Tese accumulations increasedby increase the MWN s volume raction. Similar behaviourwas observed at min and min dwell times. However,it can also be noted that there is an increasing in all relativedensities results as the dwell time increased regardless atwhich sintering temperature were they abricated.

. . Termal Conductivity Measurement. Termal conduc-tivities o MWCN s/Cu composites were measured usingNE ZSCH model LFA NanoFlash apparatus (LFA ,Netzsch, Germany). Figure demonstrates the thermalconductivities o MWN s/Cu nanocomposites as a unction

o MWN s volume raction with two different measuringtemperatures ( and C). Te MWN s/Cu thermalconductivities were measured in direction perpendicular tothe injection molding axis and it showed varied values asMWN s content increased. Te highest value was recordedat Cu- vol.% MWN s ( . W/mK) sintered at C

or minutes. Tis value corresponds to an increase o W/mK ( . %) over that o the sintered copper (Cumatrix). It is worth mentioning that the sintered copper pow-der with polycystic structure has lower thermal conductivity ( W/mK) than the monocrystal copper ( W/mK), andthis most probably is due to the existence o grain boundary and de ects in polycrystals [ ]. It can also be seen thatthermal conductivities o sintered copper and Cu- vol.%MWN s were slightly decreased by increasing the measuringtemperature rom to C due to the ree electronsthat dissipate their kinetic energy to atoms as a result o increased collision [ ]. Reversely, at high MWN s con-tent (higher than vol.% MWN s), thermal conductivities

showed an increase as the measuring temperature increased.Whereas, thermal conductivity o Cu- vol.% MWN s wasrelatively increased rom . to . W/mK by increasingthe measuring temperature rom to C, respectively.Similar conduct was noted at Cu/ vol. MWN s. Tis canbe attributed to the consistency o high MWN s thermalconductivity at elevated temperature. However, by increasingMWN s content more than vol.%, the measured thermalconductivities o the composites showed deviation comparedto the estimated values which were obtained by the rule o mixture (RM), and became even lower than that o the sin-tered copper. Some researchers have reported similar behav-ior showing that thermal conductivity o Cu/CN s nanocom-

posite increased with low CN s content and then decreasedas CN s content increased [ ]. For instance, Chu andcoworkers [ ] have abricated Cu/CN s nanocompositesusing a novelparticlescompositingmethod ollowed byspark plasma sintering. Tey reported that the addition o CN sshowed no enhancement in the overall thermal conductivity o the abricated nanocomposites. Tey suggested that thepresence o an inter acial thermal resistance is believed to bethe main reason o why the measured thermal conductivitiesare being degraded ( W/mK). Tey also attributed theseunexpected results to the ollowing actors: low wettability between CN s and Cu matrix, nonhomogeneity or bundlingo CN s, porosity and incomplete consolidation processing.Likewise, Kim et al. [ ] have reported same underper or-mance thermal conductivity o Nick-coated SWCN s/Cu( W/mK). Yamanakaet al. [ ] proposed that the decreasein thermal conductivity is mostly due to the difficulty indispersing clustered CN s with an increase in CN s content.Other similar results were published by Cho and coworker[ ]. Tey used a combination o a wet mixing processaccelerated by hetroaggregation method using acid-treatedCN s ollowed by SPS consolidation technique. Tey notedthat the highest record thermal conductivity was at vol.%CN s ( . W/mK). Teir results, however, showed noenhancement in thermal conductivity with CN s contentshigher than vol.% CN s. Tere ore, our novel technique


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o using unctionalized CN s associate with ultrasonicationprocess ollowed by MIM method perhaps is the ultimatetechnology in abrication o CN s/MM nanocomposites.Tis is due to its ability in combining two or more ingredientmaterials that are not compatible at molten state and difficultto be abricated via conventional techniques. It also ensures a

gooddispersion o CN s in metal matrices by providing highshear orces during mixing process ( eedstock preparation).

4. Conclusions

For the rst time, uni orm dispersion o multiwalled carbonnanotube rein orced copper matrix nanocomposites wassuccess ully achieved. Te newly developed approach o nanoscale dispersion ollowed by MIM abrication techniquewas proved to be effective in ex oliating the MWN s clustersand homogeneously distribute the individual MWN in Cumatrix. Nanoscale dispersion process provided a unctionalgroup on the top sur ace o MWN s, which signi cantly

enhanced the solubility o MWN s in the liquid media o dissolvedparaffinwax. Tese results were veri ed using EDX,EM, FESEM, and Raman spectroscope analysis method.

EDX and Raman Spectroscope provided sufficient in orma-tion on the quality o the puri cation and unctionalizationprocess. In addition, it explained the effects o sonicationtreatment on the MWN s structure. EM and FESEMimages showed high stability o MWN s in Cumatrix athighsinteringtemperature. Italso demonstrateda good adherencebetween dispersed MWN s and Cu particles. Te measuredthermal conductivities showed remarkable increase o %with addition o vol.% MWN s, and slight decrease at and vol.% MWN s compared to the value o pure sintered

Cu. Tere ore, MIM is considered to be the most promisingtechnique or orming and abricating high per ormanceheat sink nanocomposites with high precision in shape, high volume production and cost much lower than the traditionalmethods.

Conflict of Interests

Te authors declare that they have no con ict o interests inthis research.

Acknowledgments

Te authors would like to thank the Universiti eknologiPE RONAS or providing unds and laboratory acilities tosupport this project.

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Uniform Dispersion of Multiwalled Carbon Nanotubes in Copper Matrix

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