Research Article Influence of Sonication on the Stability and ...bath sonicator ( Figure (c) ) increased with time, reecting the formation of agglomerates (with hydrodynamic radii

Research ArticleInfluence of Sonication on the Stability and ThermalProperties of Al2O3 Nanofluids

Monir Noroozi1 Shahidan Radiman1 and Azmi Zakaria2

1School of Applied Physics Faculty of Science and Technology Universiti Kebangsaan Malaysia (UKM) 43600 BangiSelangor Malaysia2Department of Physics Faculty of Science Universiti Putra Malaysia (UPM) 43400 Serdang Selangor Malaysia

Correspondence should be addressed to Monir Noroozi monirnoroozigmailcom

Received 2 September 2014 Revised 11 November 2014 Accepted 11 November 2014 Published 11 December 2014

Academic Editor WilliamW Yu

Copyright copy 2014 Monir Noroozi et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Nanofluids containing Al2O3nanoparticles (either 11 or 30 nm in size) dispersed in distilled water at low concentrations (0125ndash

05 wt) were prepared using two different ultrasonic devices (a probe and a bath sonicator) as the dispersant The effect of theultrasonic system on the stability and thermal diffusivity of the nanofluids was investigated Thermal diffusivity measurementswere conducted using a photopyroelectric technique The dispersion characteristics and morphology of the nanoparticles as wellas the optical absorption properties of the nanofluids were studied using photon cross correlation spectroscopy with a Nanophoxanalyzer transmission electronmicroscopy and ultraviolet-visible spectroscopy At higher particle concentration there was greaterenhancement of the thermal diffusivity of the nanofluids resulting from sonication Moreover greater stability and enhancementof thermal diffusivity were obtained by sonicating the nanofluids with the higher power probe sonicator prior to measurement

1 Introduction

The thermal properties of nanofluids play a vital role in thedevelopment of high-performance heat-transfer devices [1]Metal oxide nanofluids have attracted great interest in variousareas of nanotechnology from biological and biomedicalapplications to a new class of heat-transfer fluids becauseof their higher thermal conductivity than the correspondingbase fluids [2ndash6]The size and particle size distribution (PSD)of nanoparticles (NPs) in nanofluids critically affect theirthermal properties because dispersed NPs in a liquid tend toagglomerate and settle [7] This problem can be eliminatedby reducing the size and heterogeneity of the NPs Severalmethods have been developed to stabilize nanofluids towardsNP aggregation for example using electrostatic repulsion [8]or steric stabilization [9] Physical dispersion of a powder ina liquid can be achieved by ultrasonic irradiation to achievea homogeneous nanofluid with small-sized particles [10]The effect of ultrasonic irradiation on nanofluid formationdepends on the time temperature frequency and powerof the sonicator [11 12] Acoustic cavitation induced bysonication results in strong shear forces that can break up

agglomerates [13] In general acoustic cavitation in liquidscan improve diffusion rates producing highly concentratedand uniform dispersions of micrometer- or nanometer-sized materials in base fluids [14 15] Nanofluids have beenprepared in many studies demonstrating the potential usesof ultrasound baths [16ndash18] In contrast to the lower-intensitybath-type sonicators higher intensity ultrasound probes aretypically used to create suspensions and emulsions as wellas in biomedical applications [19ndash22] Although sonication isa useful technique to assist the dispersion and stabilizationof nanofluids the influence of the type of ultrasound system(ie probe or bath) on the synthesismechanismof nanofluidsis not clear Moreover there are very few reports dealingwith the effects of sonication on the thermal properties ofnanofluids

Numerous experimental investigations have been carriedout to measure the effect of NPs in base fluids on thethermal properties of nanofluids [23] Although the thermalconductivity of nanofluids has beenwidely studied in the pastfew years little work has been done to determine the mostsuitable thermal parameters of nanofluids [24ndash27] Thermaldiffusivity is defined as the thermal conductivity divided by

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2014 Article ID 612417 10 pageshttpdxdoiorg1011552014612417

2 Journal of Nanomaterials

the specific heat and density In general thermal diffusivityis measured more easily and accurately than the thermalconductivity The two other relevant properties are densityand specific heat which either are known values or caneasily be measured The photopyroelectric (PPE) techniqueusing a pyroelectric (PE) sensor in thermal contact with thesample [28 29] has been used as a powerful technique formeasuring the thermal diffusivity of liquids with very highprecision and resolution [30] The major advantage of thistechnique is the fixed noise bandwidth that improves theprecision and sensitivity of the system as well as eliminatingthe requirement for instrumental transfer function normal-ization A PPE experiment is relatively simple to design andthe materials that can be investigated vary from weakly tostrongly absorbing materials

In this paper the effects of sonication type on the stabilityand thermal properties of Al

2O3NPs of two different sizes (11

and 30 nm) dispersed in distilledwater (DW)were examinedThe thermal diffusivity enhancement of the Al

2O3nanofluid

was found to be both size and concentration dependent andwasmuch greater when the ultrasonic probe was used insteadof the bath Stabilization mechanisms of the nanofluids wereanalyzed by photon cross correlation spectroscopy trans-mission electron microscopy (TEM) and ultraviolet-visible(UV-vis) spectroscopyThermal diffusivitymeasurements forthe nanofluids and base fluid were obtained using the PPEtechnique

2 Materials and Methods

21 Preparation of Nanofluids Al2O3nanopowders of two

sizes size A (11 nm) and size B (30 nm) with 99 purity(Nanostructured and Amorphous Materials Inc) were usedin this study In each nanofluid sample NPs (0125 025or 05 wt) were dissolved in DW and magnetically stirredvigorously until a clear solution was observed after about1 h Two different ultrasonic systems were chosen to dispersethe NPs in the base fluid namely a probe-type sonicator(VCX 500 25 kHz 500W) and a bath-type sonicator (Power-sonic UB-405 40KHz 350W) The total amount of energydelivered to the sample was constant for both sonicators Allnanofluid samples were prepared by a two-step method inwhich the NPs were first produced and then dispersed in thebase fluids

The probe sonicator is expected to deliver a higher power(500W) to the suspension than the ultrasonic bath (350W)because the probe is directly immersed in the suspensionIn contrast to bath sonication that was performed at roomtemperature the probe sonicator operates at higher ampli-tudes and is more effective at inducing cavitation and causingheating Therefore for experiments using the ultrasonicprobe the nanofluid was placed in a separate container filledwith ice to prevent evaporation of the fluid caused by theelevated temperature

During sonication of a suspension traditional character-ization techniques such as TEM cannot be used to investigatethe particle size For this reason a Nanophox particle sizeanalyzer (Sympatec GmbH D-38678) was used to investigate

the particle size and distribution of aggregates in the nanoflu-ids This equipment is based on the principle of dynamiclight scattering where PSDrsquos of the NPs are measured fromtheir velocity owing to Brownian motion using the Einstein-Stokes equation [31] After each round of sonication themean particle size and size distributions of the NPs weredeterminedAll samples containing theAl

2O3nanofluidwere

diluted to very low concentrations formeasurement andweretransferred to rectangular glass cells by pipette The preparedsamples were also characterized using UV-vis absorptionspectrometer (UV-1650 PC Shimadzu) over the range of200ndash700 nm The morphology of the alumina clusters wascharacterized by TEM (H-7100 Hitachi Tokyo Japan)

22 Photopyroelectric Technique Set-Up The details of theexperimental set-up for thermal diffusivity measurements inliquid samples can be found elsewhere [32] The nanofluidsample was placed in the volume cell between two parallelwalls a metallic thin foil (50120583m thick) acted as a PE gener-ator and a 52120583m PVDF film (MSI DT1-028KL) acted as aPE detector A 200mWCWDPSS (MGL 150(10)) modulatedlaser beam impinged on the black painted external face ofthe thin metal foil and converted it to a thermal wave ThePVDF film was fixed with silicon glue to a Perspex substrateIn the cell the thermal wave propagates across the liquidand reaches the PE detector which generates a PE signalproportional to the intensity of the thermal wave The signalgenerated was sent to a lock-in amplifier (SR530) to increasethe PE amplitude To measure the thermal diffusivity in thistechnique the sample the PE detector and the backing mustbe in a thermally thick configuration To gain information ofthe sample near the surface [33] it is important to choosethe optimal frequency for thermophysical measurements ofnanofluids At frequencies below 7Hz the effect of reducedthermal thickness becomes obvious At very high frequenciesthe signal is very small and independent of frequencyTherefore the frequency range between 7 and 36Hzwas usedfor the frequency scanThe thermal diffusivitymeasurementswere performed at room temperature (asymp20∘C)Thenoise levelin the present set-up was about 75120583V LabVIEW softwareinstalled on a PC was used to capture the amplitude andphase data which were analyzed using Origin 8 A schematicof the experimental apparatus is shown in Figure 1

The PE signal 119878(119891) decreases exponentially with increas-ing modulation of the frequency and can be expressed asfollows [34]

119878 (119891) = 1198780exp(minus (1 + 119894) 119871

120583) (1)

ln 1003816100381610038161003816119878 (119891)1003816100381610038161003816 = ln100381610038161003816100381611987801003816100381610038161003816 minus119871

120583(2)

where 119878(119891) is the complex PE signal 1198780is a complex constant

and 119891 is the modulation frequency The thermal diffusionlength of sample is 120583 = (120572120587119891)12 In the thermally thickregime of the liquid sample when 119871 ≫ 120583 [35] thePE signal is determined by the thickness 119871 and thermaldiffusivity of the sample 120572 From the slope of the linear part

Journal of Nanomaterials 3

Backing

PC

PVDF

Glass window

Nanofluid sample

Chopper

Foil

Lock-in amplifier

Laser

Figure 1 Schematic side-view of the photopyroelectric technique

Samples A Samples B

(1) (2) (3) (4)

Figure 2 05 wt Al2O3nanofluids 30 days after formulation right

to left are nanofluids prepared from NPs of sizes A and B using thebath (numbers 1 and 3) and probe (numbers 2 and 4) sonicators

of the logarithmic amplitude versus (119891)12 plot the thermaldiffusivity 120572 = 1205871198712(ln |119878|radic119891)2 can be calculated A carefulcalibration of the PPE set-up was carried out by measuringthe thermal diffusivity ofDWas a reference prior to the actualmeasurements

3 Results and Discussion

31 Characterization and Stability of Nanoparticles Thevisual effect of the two sonication systems on Al

2O3NPs of

two sizes (A 11 nm B 30 nm) prepared as 05 wt nanofluidsover a 30-day observation period can be seen in Figure 2Nanofluids of NPs of sizes A and B prepared using the probesonicator were observed to be more stable as shown inFigure 2 (numbers 2 and 4)

The larger NPs had a tendency to sediment It can be seenin Figure 2 (number 3) that the greatest amount of sedimentwas attained in the nanofluid comprising size BNPs preparedusing the bath sonicatorThe stability of the nanofluids is sizedependent and it has been found that samples prepared underhigher intensity sonication are more stable [22]

The Al2O3NPs were dispersed in DW using either the

bath or the probe sonicators The hydrodynamic diameterand PSD of the Al

2O3in the nanofluids were measured three

times at 15min intervals The dispersions and results of theparticle size analysis of these samples are shown in Figure 3It can be seen that the PSDrsquos for sample A (11 nm) dispersed inDW using the bath and probe sonicators were in the range of91ndash109 nm (Figure 3(a)) and 65ndash71 nm (Figure 3(b)) respec-tively For sample B (30 nm) dispersed using the bath andprobe sonicators the PSDrsquos were in the range of 83ndash113 nm(Figure 3(c)) and 66ndash905 nm (Figure 3(d)) respectivelyThiscan be ascribed to the fact that the clusters were only slightlybroken up by the bath sonicator in contrast to the probesonicator which broke these up effectivelyThe smallestmeanhydrodynamic particle diameter was recorded for sampleA under probe sonication (Figure 3(b)) With decreasingparticle size the stability of the nanofluids under probesonication increases as shown in Figures 3(b) and 2 (number2) However in all cases the measured particle sizes werelarger than the nominal particle sizes claimed by the vendorThis indicates that the NPs agglomerated in DW and that theagglomerates were not completely broken up by sonicationThe mean of the PSD of the sample dispersed with thebath sonicator (Figure 3(c)) increased with time reflectingthe formation of agglomerates (with hydrodynamic radiilarger than 100 nm) which are usually observed in unstablesolutions In contrast the size distribution of the sampledispersed with the probe sonicator (Figure 3(d)) exhibiteda significant shift to smaller particle sizes because of thebreakup of clusters during sonication The small discrepancyclose to the baseline arises from a few small agglomerates inthe nanofluid Therefore the suspension remained relativelymonodisperse throughout the experiment The observednarrow size dispersion of the NPs in Figures 3(b) and 3(d)indicates the remarkably high efficiency of treatment with apowerful ultrasonic probe

Additionally the differences in the mean particle sizeobserved for dispersion with the different sonicators canprovide information about the stability and the degree ofdispersion of the nanofluids [25ndash27] In Figure 4 it can beobserved that for the nanofluid comprising NPs of size Aunder probe sonication there was no significant change inthemean particle size for the threemeasurements (65 68 and71 nm) Moreover the PSDrsquos were narrow indicating betterdispersion compared with the other nanofluids examined It


00

05

10

15

20

25

30

35

40

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(a)

00

05

10

15

20

25

30

35

40

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(b)

00

05

10

15

20

25

30

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(c)

00

05

10

15

20

25

30

35

40

45

50

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(d)

Figure 3 PSDrsquos determined using the Nanophox analyzer of Al2O3particles in the nanofluids after three measurements at 15min intervals

for NPs of sizes A ((a) and (b)) and B ((c) and (d)) prepared using the bath ((a) and (c)) and probe ((b) and (d)) sonicators PDS just aftersonication (◻) after 15min (I) and after 30min (Δ)

can be seen that even in the best-dispersed nanofluid theparticlemean size is seven times the nominal NP size (11 nm)This means that particles in the suspensions aggregate toform large nanoclusters even after ultrasonic treatment Touse the Nanophox analyzer with high resolution all Al

2O3

nanofluids were diluted to very low concentrations webelieve that the mean diameter and the relative PSD inthe Nanophox analyzer are valid for comparisons betweenpowders and dispersion processes [31]

To compare the effect of ultrasonic irradiation on thePSD the synthesized Al

2O3nanofluids were analyzed by

TEM Both powders used in the present work consisted ofloose agglomerates with sizes greater than 1120583m as shown inFigures 5(a) and 5(b) Figures 5(c) and 5(d) show the TEM

images of the synthesized Al2O3nanofluids A (11 nm) and B

(30 nm) respectively after treatment with the bath sonicatorUltrasonic irradiation promotes dispersion of theNPs inDWThe bath sonicator effectively reduced the particle size tobelow 200 nm From the TEM images in Figures 5(a)ndash5(d)it can be seen that the Al

2O3NPs are well distributed The

TEM images in Figures 5(e) and 5(f) show themorphology ofthe synthesized Al

2O3nanofluids A and B respectively after

dispersion using the probe sonicatorTheTEM images of theNPs show that the probe sonicator

effectively reduced the particle size to below 100 nm andthat the NPs formed isolated clusters in a stable suspensionComparing the TEM images for the different sonicators itcan be seen that the bath sonicator (Figures 5(c) and 5(d)) was


1 2 3

60

80

100

120

Part

icle

mea

ns d

iam

eter

(nm

)

Measurement time

A (bath)A (probe)

B (bath)B (probe)

Figure 4 Evolution of the mean particle size for three measure-ments at 15min intervals for NPs of sizes A and B prepared usingthe bath and probe sonicators

almost ineffective in reducing the particle size whereas theprobe sonicator was highly effective (Figures 5(e) and 5(f))As previously mentioned in all nanofluids the measuredparticle sizes were larger than the nominal particle sizesclaimed by the vendor This indicates that the oxide NPsagglomerated in DW through cohesive forces These hardaggregates cannot be broken down into individual NPs underthese operating conditions or even at very high input energylevels [22] Comparison of the size information obtained byTEM and from the Nanophox analyzer suggests that TEMprovides an average diameter of the dry particles whereas theNanophox analyzer provides an intensity-weighted averagediameter that is always larger than the average diameterbecause of the hydrodynamic layer on the particles [31]

The measurement of optical absorbance is useful forunderstanding the dispersion behavior of particles in liquidmedia Figure 6 shows the UV-vis absorption spectra ofthe Al

2O3NPs prepared in DW without and with the use

of the bath and probe sonicators for particle dispersionThe optical spectra of the original Al

2O3nanofluid (ie with-

out sonication) as a reference exhibit strong absorption in theUV range (between 200 and 300 nm) and low absorption athigher wavelengths this is consistent with previous reports[36] The spectral characteristics of the Al

2O3nanofluids

prepared using the bath and probe sonicators are similarhowever there is a slight difference in the absorption edgesThe sonicated samples show strong absorption below 300 nmand a blue shift of the absorption edge compared with theAl2O3nanofluid without sonication which can be attributed

to the reduction in particle size during sonication Theabsorption of Al

2O3particles increases after treatment with

the probe sonicator the difference in the absorption spectra

between the two samples (A and B) may be attributed toan increased quantity of Al

2O3NPs assembled in the fluid

[36] According to the Beer-Lambert law there is a linearrelationship between absorbance and concentration thus ahigher concentration of NPs leads to a higher absorbancevalue A higher NP concentration results in a more stablesuspension as was evident from the TEM and Nanophoxresults shown in Figures 5(e) 5(f) 3(b) and 3(d) Fornanofluidswith poor stability the absorptionwas lowbecauseof particle agglomeration [37] This spectral change indicatesthat NP agglomeration is considerably reduced when theprobe sonicator is used

32 Enhancement of Thermal Diffusivity Figure 7(a) showsthat the amplitude of the PE signal in the sample attenuatesrapidly to zero with increasing frequency The PE signal 119878(119891)decreases exponentially with increasing modulation of thefrequency in the thermally thick regime of the liquid sample[33] At frequencies below 7Hz the effect of reduced thermalthickness becomes apparent at very high frequencies theanomalous signal is very small and independent of frequencyTherefore the frequency range between 7 and 30Hz wasused for the frequency scan which is shown in Figure 7(b)In this figure the acquired PE signal is plotted as theln(amplitude) of the PE signal as a function of 11989112 In theuseful frequency range the curves are linear The thermaldiffusivity was calculated from the slope of the linear part ofthe ln(amplitude) of the signal curves

Before measuring thermal diffusivity of the nanofluidsthe PPE set-up was tested with DW as the base fluidThe recorded 120572 value was (1431 plusmn 0030) times 10minus3 cm2swhich differs by less than 2 from the values reported inthe literature [31] The thermal diffusivity results for theAl2O3nanofluids prepared using the different sonication

techniques at different concentrations of NPs of sizes Aand B are summarized in Tables 1 and 2 respectively Allvalues reported are the average of five measurements foreach sample and the standard deviation was calculated asan estimation of the uncertainty The results show that thethermal diffusivity of the Al

2O3nanofluids is higher than that

of DW [12]The thermal diffusivity of the nanofluids is shown in

Figure 8 as a function of NP concentration for the twodifferent sized NPs and sonication systems It is clear that inall nanofluids the thermal diffusivity increases gradually asthe Al

2O3is dispersed in the DWMoreover in all nanofluids

a high NP concentration significantly increased the thermaldiffusivity [24 25] as shown in Figure 8 and Tables 1 and 2

Figure 8(a) shows that the thermal diffusivity enhance-ment was greater for the smaller-sized NPs This is becausesmaller particles have higher effective surface area to volumeratios [38] Thus smaller particles helped form a stablenanofluid and the probe sonicator had a substantial effecton the thermal diffusivity At a given particle concentrationthe thermal diffusivity enhancement was greater for theprobe than the bath sonicator This is because the higherpower probe sonicator can effectively break large particlesgenerating a larger NP surface area and thus increasing the


100nm

(a)

100nm

(b)

100nm

(c)

100nm

(d)

100nm

(e)

100nm

(f)

Figure 5 TEM images of Al2O3NPs prepared in DWwithout ((a) and (b)) and with ((c) and (d)) the bath sonicator and ((e) and (f)) probe

sonicators for NPs of sizes A ((a) (c) and (e)) and B ((b) (d) and (f))

thermal diffusivity The beneficial effect of using the probesonicator on the thermal diffusivity of Al

2O3nanofluids

is more pronounced at a high particle concentration andsmall particle size For example the greatest enhancementof thermal diffusivity of 6 was achieved for the probesonicator with NPs of size A at a concentration of 05 wt

The smallest enhancement was asymp1 for NPs of size B at0125 wt with the bath sonicator These results are possiblyattributable to the rapid particle clustering at a high con-centration which necessitates using a more powerful soni-cation tool to break up large agglomerates into smaller-sizedparticles


200 300 400 500 600 700 800

00

05

10

15

20

25

Probe sonicating

Abs

(au

)

Wavelength (nm)

Before sonication

Bath sonicating

Figure 6 The UV-vis absorption spectra of the Al2O3NPs prepared in DW without and with the bath- and probe-type sonicators for

dispersion of the particles

5 10 15 20 25 30 35

0000

0001

0002

0003

0004

0005

0006

0007

Am

plitu

de (m

v)

f (Hz)

(a)

30 35 40 45 50 55 60

ln(a

mpl

itude

)

minus50

minus55

minus60

minus65

minus70

minus75

f12 (Hz)

(b)

Figure 7 (a) Amplitude of the PE signal as a function of the chopping frequency 119891 and (b) ln(amplitude) of the PE signal as a function ofthe square root of the chopping frequency and its fitting (2) for one of the samples

Table 1 Thermal diffusivity of Al2O3 nanofluids NPs type A (11 nm) prepared by using different sonication techniques at different NPsconcentrations

ConcentrationBath sonication Probe sonication

Thermal diffusivity(cm2s) times 10minus3

Thermal diffusivityenhancement



0125 1476 plusmn 0002 31 1482 plusmn 0004 35025 1483 plusmn 0003 35 1494 plusmn 0002 4305 1492 plusmn 0004 42 1515 plusmn 0003 58


01 02 03 04 05147

148

149

150

151

152

Bath sonicatingProbe sonicating

Concentration (wt)

Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(a)

01 02 03 04 05

144

146

148

150

152

Concentration (wt)Bath sonicatingProbe sonicating

Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(b)

01 02 03 04 05 06

144

146

148

150

152

Concentration (wt)11nm50nm

Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(c)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(d)

Figure 8 Several sets of data on the thermal diffusivity of Al2O3nanofluids as a function of NPs concentrations ((a)-(b)) using different

sonication techniques for two different NPs sizes types (a) A and (b) B and ((c)-(d)) for two NPs sizes (c) bath sonicator and (d) probesonicator

4 Conclusion

In this work Al2O3nanofluids were prepared using bath

and probe sonicators The influences of sonication typeand NP size and concentration on the thermal diffusivityenhancement of the nanofluids were analyzed using the

PPE technique As expected the enhancement in thermaldiffusivity was dependent on the power of the sonicationdevice Moreover the thermal diffusivity enhancement wasgreater with a decreased smaller particle size Compared withthe bath sonicator use of the more powerful probe sonicatorresulted in a greater thermal diffusivity enhancement and


Table 2 Thermal diffusivity of Al2O3 nanofluids NPs type B (30 nm) prepared by using different sonication techniques at different NPsconcentrations

ConcentrationBath Probe






stability of the nanofluids The beneficial effect of usingthe probe sonicator on the thermal diffusivity is more pro-nounced at a high particle concentration and smaller particlesize reaching about 6 at a particle concentration of about05 wt The thermal diffusivity measurements obtained bythis technique for the Al

2O3nanofluids at the different

concentrations and particles sizes studied are similar to thoseof nanofluids reported in the literature by other techniques

Conflict of Interests

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

Acknowledgments

The authors are grateful to the Ministry of Science Tech-nology and Innovation for supporting this work under theResearch University Grant Scheme no 05-02-12-1878RUThefinancial support from the Universiti Kebangsaan Malaysia(UKM) with Project code DIP-2012-32 is acknowledged

References

[1] S Kakac and A Pramuanjaroenkij ldquoReview of convective heattransfer enhancement with nanofluidsrdquo International Journal ofHeat and Mass Transfer vol 52 no 13-14 pp 3187ndash3196 2009

[2] S Ozerinc S Kakac and A G YazIcIoglu ldquoEnhanced thermalconductivity of nanofluids a state-of-the-art reviewrdquoMicroflu-idics and Nanofluidics vol 8 no 2 pp 145ndash170 2010

[3] C Kleinstreuer and Y Feng ldquoExperimental and theoreticalstudies of nanofluid thermal conductivity enhancement areviewrdquoNanoscale Research Letters vol 6 no 1 article 229 2011

[4] J A Eastman S U S Choi S Li W Yu and L J ThompsonldquoAnomalously increased effective thermal conductivities ofethylene glycol-based nanofluids containing copper nanoparti-clesrdquo Applied Physics Letters vol 78 no 6 pp 718ndash720 2001

[5] W Yu D M France J L Routbort and S U S Choi ldquoReviewand comparison of nanofluid thermal conductivity and heattransfer enhancementsrdquo Heat Transfer Engineering vol 29 no5 pp 432ndash460 2008

[6] P Keblinski S R Phillpot S U S Choi and J A EastmanldquoMechanisms of heat flow in suspensions of nano-sized particles(nanofluids)rdquo International Journal of Heat and Mass Transfervol 45 no 4 pp 855ndash863 2001

[7] LWang and J Fan ldquoNanofluids research key issuesrdquoNanoscaleResearch Letters vol 5 no 8 pp 1241ndash1252 2010

[8] SThomas andC B Panicker Sobhan ldquoA reviewof experimentalinvestigations on thermal phenomena in nanofluidsrdquoNanoscaleResearch Letters vol 6 article 377 2011

[9] J M Mason U B Hagemann and K M Arndt ldquoRoleof hydrophobic and electrostatic interactions in coiled coilstability and specificityrdquo Biochemistry vol 48 no 43 pp 10380ndash10388 2009

[10] E K Goharshadi and H Azizi-Toupkanloo ldquoSilver colloidnanoparticles ultrasound-assisted synthesis electrical and rhe-ological propertiesrdquo Powder Technology vol 237 pp 97ndash1012013

[11] C Ying Z Zhaoying and Z Ganghua ldquoEffects of different tis-sue loads on high power ultrasonic surgery scalpelrdquoUltrasoundin Medicine amp Biology vol 32 no 3 pp 415ndash420 2006

[12] L P Fallavena F H F Antunes J S Alves et al ldquoUltrasoundtechnology and molecular sieves improve the thermodynam-ically controlled esterification of butyric acid mediated byimmobilized lipase from Rhizomucor mieheirdquo RSC Advancesvol 4 no 17 pp 8675ndash8681 2014

[13] E-Q Xia X-X Ai S-Y Zang T-T Guan X-R Xu and H-BLi ldquoUltrasound-assisted extraction of phillyrin from ForsythiasuspensardquoUltrasonics Sonochemistry vol 18 no 2 pp 549ndash5522011

[14] S Sun H Zeng D B Robinson et al ldquoMonodisperse MFe2O4

(M = Fe Co Mn) nanoparticlesrdquo Journal of the AmericanChemical Society vol 126 no 1 pp 273ndash279 2004

[15] J Park K An Y Hwang et al ldquoUltra-large-scale syntheses ofmonodisperse nanocrystalsrdquoNatureMaterials vol 3 no 12 pp891ndash895 2004

[16] M C Horrillo J Gutierrez L Ares et al ldquoThe influence of thetin-oxide deposition technique on the sensitivity toCOrdquo Sensorsand Actuators B Chemical vol 25 no 1ndash3 pp 507ndash511 1995

[17] K C Grabar R G Freeman M B Hommer and M J NatanldquoPreparation and characterization of Au colloid monolayersrdquoAnalytical Chemistry vol 67 no 4 pp 735ndash743 1995

[18] E Levashov V Kurbatkina and Z Alexandr ldquoImprovedmechanical and tribological properties of metal-matrix com-posites dispersion-strengthened by nanoparticlesrdquo Materialsvol 3 no 1 pp 97ndash109 2010

[19] D Sun Z Y Zhou Y H Liu and W Z Shen ldquoDevelopmentand application of ultrasonic surgical instrumentsrdquo IEEE Trans-actions on Biomedical Engineering vol 44 no 6 pp 462ndash4671997

[20] Y Zou C Xie G Fan Z Gu and Y Han ldquoOptimizationof ultrasound-assisted extraction of melanin from Auriculariaauricula fruit bodiesrdquo Innovative Food Science and EmergingTechnologies vol 11 no 4 pp 611ndash615 2010

[21] F Chemat and M K Khan ldquoApplications of ultrasound in foodtechnology processing preservation and extractionrdquoUltrason-ics Sonochemistry vol 18 no 4 pp 813ndash835 2011


[22] W J Parak D Gerion T Pellegrino et al ldquoBiological applica-tions of colloidal nanocrystalsrdquo Nanotechnology vol 14 no 7pp R15ndashR27 2003

[23] X Zhang H Gu and M Fujii ldquoEffective thermal conductivityand thermal diffusivity of nanofluids containing spherical andcylindrical nanoparticlesrdquo Experimental Thermal and FluidScience vol 31 no 6 pp 593ndash599 2007

[24] X Zhang H Gu and M Fujii ldquoExperimental study onthe effective thermal conductivity and thermal diffusivity ofnanofluidsrdquo International Journal of Thermophysics vol 27 no2 pp 569ndash580 2006

[25] R G Fuentes J A P Rojas J L J Perez and J F S RamirezldquoStudy of thermal diffusivity of nanofluids with bimetallic NPswith Au (core)Ag (shell) structurerdquo Applied Surface Sciencevol 255 no 3 pp 781ndash783 2008

[26] S M S Murshed K C Leong and C Yang ldquoDeterminationof the effective thermal diffusivity of nanofluids by the doublehot-wire techniquerdquo Journal of Physics D Applied Physics vol39 no 24 pp 5316ndash5322 2006


[28] D Dadarlat C Neamtu V Tosa and M Streza ldquoAccurate pho-topyroelectric calorimetry applied to isotopic liquid mixturesrdquoActa Chimica Slovenica vol 54 no 1 pp 149ndash153 2007

[29] D Dadarlat C Neamtu M Streza et al ldquoHigh accuracyphotopyroelectric investigation of dynamic thermal parame-ters of Fe

3O4and CoFe

2O4magnetic nanofluidsrdquo Journal of

Nanoparticle Research vol 10 no 8 pp 1329ndash1336 2008[30] M Noroozi B Z Azmi and M M Moksin ldquoThe reliability

of optical fiber-TWRC technique in liquids thermal diffusivitymeasurementrdquo Infrared Physics amp Technology vol 53 no 3 pp193ndash196 2010

[31] J B Falabella T J Cho D C Ripple V A Hackley and M JTarlov ldquoCharacterization of gold nanoparticles modified withsingle-stranded DNA using analytical ultracentrifugation anddynamic light scatteringrdquo Langmuir vol 26 no 15 pp 12740ndash12747 2010

[32] J Ordonez-Miranda and J J Alvarado-Gil ldquoInfrared emissivitydetermination using a thermal-wave resonant cavity com-parison between the length- and frequency-scan approachesrdquoInternational Journal of Thermal Sciences vol 74 pp 208ndash2132013

[33] J Shen and A Mandelis ldquoThermal-wave resonator cavityrdquoReview of Scientific Instruments vol 66 no 10 pp 4999ndash50051995

[34] G Pan and AMandelis ldquoMeasurements of the thermodynamicequation of state via the pressure dependence of thermophysicalproperties of air by a thermal-wave resonant cavityrdquo Review ofScientific Instruments vol 69 no 8 pp 2918ndash2923 1998

[35] B Z Azmi M Noroozi Z A Sulaiman Z A Wahab and MM Moksin ldquoThermal wave interferometry of gas-liquid usingoptical fibre thermal wave resonator cavity techniquerdquo Journalof Physics Conference Series vol 214 no 1 Article ID 0120662010

[36] K Yatsui T Yukawa C Grigoriu M Hirai andW Jiang ldquoSyn-thesis of ultrafine 120574-Al

2O3powders by pulsed laser ablationrdquo

Journal of Nanoparticle Research vol 2 no 1 pp 75ndash83 2000[37] I L Liu P Shen and S Y Chen ldquoH+- and Al2+-codoped Al

2O3

nanoparticles with spinel-type related structures by pulsed laserablation in waterrdquoThe Journal of Physical Chemistry C vol 114no 17 pp 7751ndash7757 2010

[38] G A Lopez-Munoz J A Balderas-Lopez J Ortega-LopezJ A Pescador-Rojas and J S Salazar ldquoThermal diffusivitymeasurement for urchin-like gold nanofluids with differentsolvents sizes and concentrationsshapesrdquo Nanoscale ResearchLetters vol 7 no 1 article 667 2012

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


the specific heat and density In general thermal diffusivityis measured more easily and accurately than the thermalconductivity The two other relevant properties are densityand specific heat which either are known values or caneasily be measured The photopyroelectric (PPE) techniqueusing a pyroelectric (PE) sensor in thermal contact with thesample [28 29] has been used as a powerful technique formeasuring the thermal diffusivity of liquids with very highprecision and resolution [30] The major advantage of thistechnique is the fixed noise bandwidth that improves theprecision and sensitivity of the system as well as eliminatingthe requirement for instrumental transfer function normal-ization A PPE experiment is relatively simple to design andthe materials that can be investigated vary from weakly tostrongly absorbing materials

In this paper the effects of sonication type on the stabilityand thermal properties of Al

2O3NPs of two different sizes (11

and 30 nm) dispersed in distilledwater (DW)were examinedThe thermal diffusivity enhancement of the Al

2O3nanofluid

was found to be both size and concentration dependent andwasmuch greater when the ultrasonic probe was used insteadof the bath Stabilization mechanisms of the nanofluids wereanalyzed by photon cross correlation spectroscopy trans-mission electron microscopy (TEM) and ultraviolet-visible(UV-vis) spectroscopyThermal diffusivitymeasurements forthe nanofluids and base fluid were obtained using the PPEtechnique

2 Materials and Methods

21 Preparation of Nanofluids Al2O3nanopowders of two

sizes size A (11 nm) and size B (30 nm) with 99 purity(Nanostructured and Amorphous Materials Inc) were usedin this study In each nanofluid sample NPs (0125 025or 05 wt) were dissolved in DW and magnetically stirredvigorously until a clear solution was observed after about1 h Two different ultrasonic systems were chosen to dispersethe NPs in the base fluid namely a probe-type sonicator(VCX 500 25 kHz 500W) and a bath-type sonicator (Power-sonic UB-405 40KHz 350W) The total amount of energydelivered to the sample was constant for both sonicators Allnanofluid samples were prepared by a two-step method inwhich the NPs were first produced and then dispersed in thebase fluids

The probe sonicator is expected to deliver a higher power(500W) to the suspension than the ultrasonic bath (350W)because the probe is directly immersed in the suspensionIn contrast to bath sonication that was performed at roomtemperature the probe sonicator operates at higher ampli-tudes and is more effective at inducing cavitation and causingheating Therefore for experiments using the ultrasonicprobe the nanofluid was placed in a separate container filledwith ice to prevent evaporation of the fluid caused by theelevated temperature

During sonication of a suspension traditional character-ization techniques such as TEM cannot be used to investigatethe particle size For this reason a Nanophox particle sizeanalyzer (Sympatec GmbH D-38678) was used to investigate

the particle size and distribution of aggregates in the nanoflu-ids This equipment is based on the principle of dynamiclight scattering where PSDrsquos of the NPs are measured fromtheir velocity owing to Brownian motion using the Einstein-Stokes equation [31] After each round of sonication themean particle size and size distributions of the NPs weredeterminedAll samples containing theAl

2O3nanofluidwere

diluted to very low concentrations formeasurement andweretransferred to rectangular glass cells by pipette The preparedsamples were also characterized using UV-vis absorptionspectrometer (UV-1650 PC Shimadzu) over the range of200ndash700 nm The morphology of the alumina clusters wascharacterized by TEM (H-7100 Hitachi Tokyo Japan)

22 Photopyroelectric Technique Set-Up The details of theexperimental set-up for thermal diffusivity measurements inliquid samples can be found elsewhere [32] The nanofluidsample was placed in the volume cell between two parallelwalls a metallic thin foil (50120583m thick) acted as a PE gener-ator and a 52120583m PVDF film (MSI DT1-028KL) acted as aPE detector A 200mWCWDPSS (MGL 150(10)) modulatedlaser beam impinged on the black painted external face ofthe thin metal foil and converted it to a thermal wave ThePVDF film was fixed with silicon glue to a Perspex substrateIn the cell the thermal wave propagates across the liquidand reaches the PE detector which generates a PE signalproportional to the intensity of the thermal wave The signalgenerated was sent to a lock-in amplifier (SR530) to increasethe PE amplitude To measure the thermal diffusivity in thistechnique the sample the PE detector and the backing mustbe in a thermally thick configuration To gain information ofthe sample near the surface [33] it is important to choosethe optimal frequency for thermophysical measurements ofnanofluids At frequencies below 7Hz the effect of reducedthermal thickness becomes obvious At very high frequenciesthe signal is very small and independent of frequencyTherefore the frequency range between 7 and 36Hzwas usedfor the frequency scanThe thermal diffusivitymeasurementswere performed at room temperature (asymp20∘C)Thenoise levelin the present set-up was about 75120583V LabVIEW softwareinstalled on a PC was used to capture the amplitude andphase data which were analyzed using Origin 8 A schematicof the experimental apparatus is shown in Figure 1

The PE signal 119878(119891) decreases exponentially with increas-ing modulation of the frequency and can be expressed asfollows [34]

119878 (119891) = 1198780exp(minus (1 + 119894) 119871

120583) (1)

ln 1003816100381610038161003816119878 (119891)1003816100381610038161003816 = ln100381610038161003816100381611987801003816100381610038161003816 minus119871

120583(2)

where 119878(119891) is the complex PE signal 1198780is a complex constant

and 119891 is the modulation frequency The thermal diffusionlength of sample is 120583 = (120572120587119891)12 In the thermally thickregime of the liquid sample when 119871 ≫ 120583 [35] thePE signal is determined by the thickness 119871 and thermaldiffusivity of the sample 120572 From the slope of the linear part


Backing

PC

PVDF

Glass window

Nanofluid sample

Chopper

Foil

Lock-in amplifier

Laser


Samples A Samples B

(1) (2) (3) (4)






2O3NPs of









00

05

10

15

20

25

30

35

40

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(a)

00

05

10

15

20

25

30

35

40

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(b)

00

05

10

15

20

25

30

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(c)

00

05

10

15

20

25

30

35

40

45

50

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(d)




2O3













1 2 3

60

80

100

120

Part

icle

mea

ns d

iam

eter

(nm

)

Measurement time

A (bath)A (probe)

B (bath)B (probe)








2O3nanofluids


















100nm

(a)

100nm

(b)

100nm

(c)

100nm

(d)

100nm

(e)

100nm

(f)




2O3nanofluids




200 300 400 500 600 700 800

00

05

10

15

20

25

Probe sonicating

Abs

(au

)

Wavelength (nm)

Before sonication

Bath sonicating



5 10 15 20 25 30 35

0000

0001

0002

0003

0004

0005

0006

0007

Am

plitu

de (m

v)

f (Hz)

(a)

30 35 40 45 50 55 60

ln(a

mpl

itude

)

minus50

minus55

minus60

minus65

minus70

minus75

f12 (Hz)

(b)










01 02 03 04 05147

148

149

150

151

152


Concentration (wt)

Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(a)

01 02 03 04 05

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(b)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(c)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(d)



4 Conclusion

















Acknowledgments


References
































3O4and CoFe












2O3










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Backing

PC

PVDF

Glass window

Nanofluid sample

Chopper

Foil

Lock-in amplifier

Laser


Samples A Samples B

(1) (2) (3) (4)






2O3NPs of









00

05

10

15

20

25

30

35

40

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(a)

00

05

10

15

20

25

30

35

40

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(b)

00

05

10

15

20

25

30

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(c)

00

05

10

15

20

25

30

35

40

45

50

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(d)




2O3













1 2 3

60

80

100

120

Part

icle

mea

ns d

iam

eter

(nm

)

Measurement time

A (bath)A (probe)

B (bath)B (probe)








2O3nanofluids


















100nm

(a)

100nm

(b)

100nm

(c)

100nm

(d)

100nm

(e)

100nm

(f)




2O3nanofluids




200 300 400 500 600 700 800

00

05

10

15

20

25

Probe sonicating

Abs

(au

)

Wavelength (nm)

Before sonication

Bath sonicating



5 10 15 20 25 30 35

0000

0001

0002

0003

0004

0005

0006

0007

Am

plitu

de (m

v)

f (Hz)

(a)

30 35 40 45 50 55 60

ln(a

mpl

itude

)

minus50

minus55

minus60

minus65

minus70

minus75

f12 (Hz)

(b)










01 02 03 04 05147

148

149

150

151

152


Concentration (wt)

Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(a)

01 02 03 04 05

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(b)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(c)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(d)



4 Conclusion

















Acknowledgments


References
































3O4and CoFe












2O3










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




00

05

10

15

20

25

30

35

40

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(a)

00

05

10

15

20

25

30

35

40

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(b)

00

05

10

15

20

25

30

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(c)

00

05

10

15

20

25

30

35

40

45

50

01 1 10 100 1000 10000

Particle size (nm)

Den

sity

distr

ibut

ionq3lowast

(d)




2O3













1 2 3

60

80

100

120

Part

icle

mea

ns d

iam

eter

(nm

)

Measurement time

A (bath)A (probe)

B (bath)B (probe)








2O3nanofluids


















100nm

(a)

100nm

(b)

100nm

(c)

100nm

(d)

100nm

(e)

100nm

(f)




2O3nanofluids




200 300 400 500 600 700 800

00

05

10

15

20

25

Probe sonicating

Abs

(au

)

Wavelength (nm)

Before sonication

Bath sonicating



5 10 15 20 25 30 35

0000

0001

0002

0003

0004

0005

0006

0007

Am

plitu

de (m

v)

f (Hz)

(a)

30 35 40 45 50 55 60

ln(a

mpl

itude

)

minus50

minus55

minus60

minus65

minus70

minus75

f12 (Hz)

(b)










01 02 03 04 05147

148

149

150

151

152


Concentration (wt)

Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(a)

01 02 03 04 05

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(b)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(c)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(d)



4 Conclusion

















Acknowledgments


References
































3O4and CoFe












2O3










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




1 2 3

60

80

100

120

Part

icle

mea

ns d

iam

eter

(nm

)

Measurement time

A (bath)A (probe)

B (bath)B (probe)








2O3nanofluids


















100nm

(a)

100nm

(b)

100nm

(c)

100nm

(d)

100nm

(e)

100nm

(f)




2O3nanofluids




200 300 400 500 600 700 800

00

05

10

15

20

25

Probe sonicating

Abs

(au

)

Wavelength (nm)

Before sonication

Bath sonicating



5 10 15 20 25 30 35

0000

0001

0002

0003

0004

0005

0006

0007

Am

plitu

de (m

v)

f (Hz)

(a)

30 35 40 45 50 55 60

ln(a

mpl

itude

)

minus50

minus55

minus60

minus65

minus70

minus75

f12 (Hz)

(b)










01 02 03 04 05147

148

149

150

151

152


Concentration (wt)

Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(a)

01 02 03 04 05

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(b)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(c)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(d)



4 Conclusion

















Acknowledgments


References
































3O4and CoFe












2O3










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




100nm

(a)

100nm

(b)

100nm

(c)

100nm

(d)

100nm

(e)

100nm

(f)




2O3nanofluids




200 300 400 500 600 700 800

00

05

10

15

20

25

Probe sonicating

Abs

(au

)

Wavelength (nm)

Before sonication

Bath sonicating



5 10 15 20 25 30 35

0000

0001

0002

0003

0004

0005

0006

0007

Am

plitu

de (m

v)

f (Hz)

(a)

30 35 40 45 50 55 60

ln(a

mpl

itude

)

minus50

minus55

minus60

minus65

minus70

minus75

f12 (Hz)

(b)










01 02 03 04 05147

148

149

150

151

152


Concentration (wt)

Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(a)

01 02 03 04 05

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(b)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(c)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(d)



4 Conclusion

















Acknowledgments


References
































3O4and CoFe












2O3










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




200 300 400 500 600 700 800

00

05

10

15

20

25

Probe sonicating

Abs

(au

)

Wavelength (nm)

Before sonication

Bath sonicating



5 10 15 20 25 30 35

0000

0001

0002

0003

0004

0005

0006

0007

Am

plitu

de (m

v)

f (Hz)

(a)

30 35 40 45 50 55 60

ln(a

mpl

itude

)

minus50

minus55

minus60

minus65

minus70

minus75

f12 (Hz)

(b)










01 02 03 04 05147

148

149

150

151

152


Concentration (wt)

Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(a)

01 02 03 04 05

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(b)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(c)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(d)



4 Conclusion

















Acknowledgments


References
































3O4and CoFe












2O3










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




01 02 03 04 05147

148

149

150

151

152


Concentration (wt)

Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(a)

01 02 03 04 05

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(b)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(c)

01 02 03 04 05 06

144

146

148

150

152


Ther

mal

diff

usiv

ity (1

0minus3

cm2s

)

(d)



4 Conclusion

















Acknowledgments


References
































3O4and CoFe












2O3










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















Acknowledgments


References
































3O4and CoFe












2O3










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials












3O4and CoFe












2O3










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



Documents

Research Article Influence of Sonication on the Stability and ...bath sonicator ( Figure (c) ) increased with time, reecting the formation of agglomerates (with hydrodynamic radii