(2010) hapçı effect of electrolysis parameters on the morphologies of copper powder obtained in a

8162019 (2010) Hapccedilı Effect of Electrolysis Parameters on the Morphologies of Copper Powder Obtained in A

httpslidepdfcomreaderfull2010-hapci-effect-of-electrolysis-parameters-on-the-morphologies-of-copper 17

Effect of electrolysis parameters on the morphologies of copper powder obtained in arotating cylinder electrode cell

Goumlkhan Orhan Goumlkccedile Hapccedilı

Istanbul University Faculty of Engineering Metallurgical and Materials Engineering Department 34320 Istanbul Turkey

a b s t r a c ta r t i c l e i n f o

Article history

Received 27 July 2009

Received in revised form 1 March 2010Accepted 1 March 2010

Available online 6 March 2010

Keywords

Electrolytic copper powder

Apparent density

Rotating cylinder electrode (RCE)

Electrodeposition

In this paper electrolysis method was used to produce copper powder particulates The effects of parametric

values such as current density concentration of copper ions electrolyte temperature and rotation speed of

cathode on the morphologies and on the apparent densities of copper powders were examined These

parameters were evaluated by the current ef 1047297ciency of hydrogen evolution In addition scanning electron

microscopy (SEM) was used for analyzing the morphology of the copper powders It was found that the

increasing of the current density or the electrolyte temperature decreased the size of the powder particles

promoting their morphology into dendritic structure In contrast the increase of copper ion concentration or

rotation speed of cathode also increased the size of the particles resulting in a cauli1047298ower-like morphology

All powder particles obtained were consisted of agglomerated copper grains The most important difference

was the size and the shape of the copper grains which were notably in1047298uenced by the electrolysis

parameters The apparent density values of copper powders were found to be suitable for many powder

metallurgical applications Attempts were also made in the later part of the paper to determine optimum

process parameters for the production of electrolytic copper powders

copy 2010 Elsevier BV All rights reserved

1 Introduction

Copperpowder takes up themost signi1047297cant portion of thepowdermetallurgy than any other metal powder Due to their excellentelectrical and thermal conductivities it has many applications such asself-lubricating bearings electrical and electronic components andseveral mechanical parts in different industrial areas [12]

The shape size and other physical properties of metal powdersstrongly depend on the manufacturing technique Copper powderscan be produced by a number of methods There are four maincommercially available methods electrochemical reduction of

copper oxide chemical precipitation and atomization [1ndash4] In thiswork electrolysiswas used to produce copper powders Theproposedmethod is environmentally friendly and enables working in a closed-circuit It is also an economical processing method with a low capitalinvestment and operational cost Since this method enables the

production of metal powder with high purity it has the advantages of good green strength andlow oxygencontent compared with theotheralternative powder production technologies Another signi1047297cant

feature of this method is that it allows production of powders witha wide range of density (04ndash40 g cmminus3) [5]

Many investigators [6ndash13] studied the electrodeposition of copperpowders from acid sulphate solutions by potentiostatic or galvano-

static methods They investigated the morphologies of copper

deposits obtained at overpotentials belonging to the plateau of thediffusion limiting current density and larger overpotentials Accordingto their results the morphologies and the properties of copper

powders are strongly dependent on the parameters such as amongstothers overpotential the quantity of evolved hydrogen [6ndash8] currentdensity [910] concentrations of copper ions [11] and H2SO4 [12] andtemperature of the solution [13] For example powder particles were

either dendritic (if particles are formed with a quantity of evolvedhydrogen below the critical value for the change of hydrodynamicconditions) or cauli1047298ower-like (if they were formedwith a quantity of evolved hydrogen above critical value) [6ndash8]

Increase in mass transport for an electrochemical process can beachieved by modifying either the solution parameters (concentrationdiffusion coef 1047297cient viscosity etc) or physical and geometricalparameters of the electrode (surface area ratio of area to volumeand increasing the relative motion between electrode and electro-

lyte) However gas evolution strongly promotes mass transfer at anelectrode According to Popov [67] the average current ef 1047297ciency of hydrogen evolution of 30 is suf 1047297cient to change the hydrodynamic

conditions in the near-electrode layerThe mass transport to an inner RCE in turbulent 1047298ow may be

described by dimensionless empirical correlations of the form [14]

Sh = K Rea

Sc b

eth1THORN

where the Sherwood Reynolds and Schmidt numbers (Sh Re and Screspectively) describe mass transport 1047298uid 1047298ow and transport

Powder Technology 201 (2010) 57ndash63

Corresponding author

E-mail address gorhanistanbuledutr (G Orhan)

0032-5910$ ndash see front matter copy 2010 Elsevier BV All rights reserved

doi101016jpowtec201003003

Contents lists available at ScienceDirect

Powder Technology

j o u r n a l h o m e p a g e w w w e l s ev i e r c o m l o c a t e p ow t e c



properties of the electrolyte respectively The constants ldquoK rdquo and ldquoardquo

values for b =0356 vary with the surface type and Re number Gabe

et al obtained the value a =07 on a smooth cylinder and observedthat ldquoardquo changes to 092 as the electrode surface becomes rougher(often powder deposits) The value of K is 0079 for both of themLimiting current density which is the minimum current density for

the formation of powder on the RCE through dimensionlessparameters can be given by the following Eq (2) [14]

iL = 0079 z F c U 092

d008

υ0564

D0644

eth2THORN

where z is the number of electrons (valence number) involved in a

redox process F is the Faradays constant (C molminus1) c is theconcentration (mol cmminus3) U is the electrode peripheral velocity(cm sminus1) d is the cylinder electrode diameter (cm) D is the diffusioncoef 1047297cient (cm2 sminus1) and ν is the kinematic viscosity (cm2 sminus1)

An electrolytic metal powder represents disperse electrodepositsremoved from the electrode by tapping or some such similar mannerIn the potentiostatic systems disperse deposits of copper are obtainedat overpotentials on theplateau of thelimitingcurrent density as well

as at higherones (atthe endof this plateau)Copper electrodepositionprocess occurs simultaneously with the hydrogen evolution reaction

In galvanostatic systems electrodeposit of copper has thetendency to form powders when current densities larger than the

limiting diffusion current density are used (or overpotentials outsidethe plateau of the limiting diffusion current density) [46715] Alsothe increasing of the overpotential (current density) leads to theformation of a more dispersed deposit characterized by the decreased

particle size [15]An electrolytic metal powder consists of particles These particles

may have various forms and sizes And each of these particles exhibitmore or less the same characteristics as if they are deposited under

identical conditions as long as the removal process of deposits fromthe electrode is identical The most important properties of a metalpowder are the speci1047297c surface area the apparent density the1047298owability the particle grain size and distribution [2] These prop-erties called decisive properties characterize the behaviour of a metal

powder The morphologies of the copper powder particles correlatedwith the apparent density and 1047298owability have been reported by

Pavlovic et al [16] and Popov et al [1718] It can be seen from theseinvestigations that the more dendritic the structure of the powderparticles is the lower the apparent density of the copper powdersAlso Popov et al [18] have proposed a method for the determination

of the critical apparent density which permits the free 1047298ow of electrodeposited copper powder

The aim of this study is to produce copper powders from acidsulphate solutions by means of electrolysis with the use of a RCE that

provides faster ionic movement due to the convective diffusion at theelectrodendashelectrolyte interface and to optimise the production pa-rameters The effect of current density concentration of copper ionselectrolyte temperature and rotation speed of the cathode which

affect the limiting current density on process data and themorphologies of copper powders as well as on the apparent densitieswere investigated

2 Experimental

In all experiments electrodeposition of the copper powders ontocylindrical cathode was performed in a laboratory scale electrolysiscell with a rotating cylinder cathode (RCE) A stainless steel cathode

(Oslash20times50 mm) and lead anode were utilized The total electrolytevolume was 1250 mL

Anolyte and catholyte were separated by a diaphragm in the cellIn the 1047297rst section electrolysis is carried out and in the second section

the 1047297ltration is performed for preventing metal powders produced

from clogging solution circulation pumps One of the most important

technological problems faced in the electrolysis is the continuity of process due to the change in the cathode size In the designed cell the

metal powder produced is removed from the cathode surface by ascraper which is added back to the solution and then 1047297ltered Thusthe cathode size is kept constant and the continuity problem is solvedIt is important to note that the cathode-scraper was positioned at a

distance of 1 mm from the surface of the cathodeIn all experiments electrolytic copper powder was galvanostati-

cally deposited from the following solutions

5gL1Cu

2thornthorn 150 5gL

1H2SO4 ethSolutionITHORN

10gL1Cu

2thornthorn 150 5gL

1H2SO4 ethSolutionIITHORN

20gL1Cu

2thornthorn 150 5gL

1H2SO4 ethSolutionIIITHORN

Distilled water and analytical grade chemicals were used for thepreparation of solutions for the electrodeposition process Electrolytewas pumped from the second section (1047297ltration part) to the 1047297rst

section where the electrolysis was carried out (electrolyte circulationrate 1 dm3min)

The copper powder was deposited galvanostatically at the currentdensity values of 200 250 and 300 mA cmminus2 while values of 30 and

60plusmn 05 degC were selected as the electrolysis temperature The cathoderotation speed values of 140 550 and 1100 rpm were used Followingthe electrolysis the obtained powder was washed several times withthe distilledwater After being washedwith waterin order to prevent

oxidation the powder was rinsed with ethanol and dried at 95 degC inan oven under vacuum

The powder particles were characterized by using a scanningelectron microscope (model JEOL JSM 5600) Copper analysis of the

obtained powder was carried out at ICP (Spectro Ciros Vision)According to these results the current ef 1047297ciencies were calculatedbased on Faradays law The apparent densities were measured by a

2 cm3 minimized Arnold meter

3 Results and discussion

31 Current density

The effect of current density on the morphology of electrolyticcopper powder and on the properties of the copper powder wasinvestigated at current density values of 200 250 and 300 mA cmminus2

The results obtained from Solution II areshownin Fig1 These powderparticles were electrodeposited under the standard conditions withthe electrolyte temperature of 30 degC with the cathode rotation speedof 140 rpm

It can beseen from Fig 1a and b that thepowder particlesobtainedat 200 mA cmminus2 are sponge-like These particles actually have acauli1047298ower-like structure The agglomerates of globular copper grainsbecome the dominant form of the powder morphology electrode-

posited at this current density It is important to note that dendriticmorphology was not formed at 200 mA cmminus2 SEM investigation of these powders showed the presence of new nucleation sites over theexisting enlarged grains which resulted in noticeable differences in

the grain size distributionFig 1c and d shows the morphologies of copper powder obtained at

a current density of 250 mA cmminus2 The change in the morphologyfrom cauli1047298ower-like to dendrites is clearly seen at this current level

The branches seen on higher magni1047297cation (Fig 1d) constitute thedendritic character of these particles It can be concluded from Fig 1a

and c that increasing the current density from 200 mA cmminus2

to

58 G Orhan G Hapccedil ı Powder Technology 201 (2010) 57 ndash63



250 mA cmminus2 leads to the increase of dispersion The copper powderparticlesobtained at 300 mA cmminus2 areshownin Fig1eandfAtthe 1047297rstsight the morphology of this copper powder is similar to themorphology of copper powder obtained at 250 mA cmminus2 ie it has a

dendritic structure and more dispersed deposit due to the increased

current density (Fig 1c and e) Meanwhile it may be seen from Fig 1f that the shape of the powder particles is completely different at thiscurrent density The powder particles are highly branched (primarysecondary etc) dendrites which consisted of corncob-like elements

However there is a noticeable difference in their sizes It is known that

Fig 1 SEM photomicrographs of copper powder particles obtained from Solution II at different current densities (andashb) 200 (cndashd) 250 and (endashf) 300 mA cmminus2

(magni1047297cations a c e times1000 and b d f times5000 respectively at 140 rpm and 30 degC)

59G Orhan G Hapccedil ı Powder Technology 201 (2010) 57 ndash63



the electrodeposition process which led to the formation of the highlybranched dendritic particles was controlled by the diffusion of ions to

the electrode surface rather than electron transfer control [71215]According to Popov [15] the deposits obtained at low current

densities consist of a low number of nuclei However with theincreasing of current density the numberof growth sites increase and

the grain size of the deposit decreases This is in good agreement withthe fact that dendrites obtained at low current density (Fig 1c and d)

were less branched and denser than that of obtained at a highercurrent density (Fig 1e and f) The increase of dispersion and thedecrease of grain size of copper powders with the current densityincrease are the result of the increased nucleation rate

The results obtained at these current densities can be explained as

follows As expected when the deposition time is lower than theinduction time for dendritic growth the morphology of copperpowder (obtained at 200 mA cmminus2) becomes similar to one obtainedat lower current densities This is due to the increasedlimiting current

density with the use of a RCE which improved hydrodynamicconditions The current ef 1047297ciency for the hydrogen evolution at200 mA cmminus2 was zero and it was relatively low for 250 and300 mA cmminus2 with values of 2 and 4 respectively

Following these 1047297ndings it now becomes easy to correlate theproperties of thepowder with the current density The decrease in thesize of the grains with the increasing of current density leads to anincrease in the speci1047297c surface area of the powder It is known that the

increase in the speci1047297c surface area of a powder means a decrease inthe apparent density [616] The apparent densities of powdersobtained at 200 and 250 mA cmminus2 are 125 and 115 g cmminus3respectively A decrease in apparent density with the increasing of

current density was observed as expected Although the apparentdensity values at 300 mA cmminus2 were expected to be lower due to thesize of copper grains the apparent density value of 150 g cmminus3 wasobtained at this current density which was believed to be as a result of

the particle shape In this case it can be assumed that the apparentdensity depends on both the shape and the grain size of the powderparticles

32 Concentration of copper ion

The effects of copper ion concentration parameter on the mor-phology of electrolytic copper powders were examined in Solutions I II and III For all solutions the values of current density electrolytetemperature and rotation speed of the cathode were kept constant at

200 mA cmminus2 30 degC and 140 rpm respectively The morphologies of copper powder particles obtained from Solutions I and III are depictedin Fig 2 The comparison of the effect of different current densities ata lower concentration of copper ion on the morphology of copper

powder is shown in Fig 3As may be seen from Fig 2a that the copper powder particles

obtained from Solution III have a denser deposit and are consisted of agglomerated copper grains The shape of these grains can be

characterized as being ldquocoarserdquo Interestingly dendrites were notformed in Solution III at 200 mA cmminus2 It was noticed that the mor-phologies of copper powder at a higher copper ion concentrationvalue of 20 g L minus1 were similar to those obtained at lower current

densities just before the beginning of the dendritic growth despiteworking at a higher current density than the limiting current densityIt can be clearly seen from Fig 1b that the copper powder is consistedof agglomerated copper grains which are substantially smaller than

that of obtained in Solution III In addition the dispersion of copperpowders increased with the decreasing of the concentration of copperion from 20 to 10 g L minus1 The morphology of copper powders shown inFigs 2b and 3a was obtained from Solution I Branched dendrites

formed in Solution I where globular elements constitute the branchesIt is important to note that the size of the individual coppergrains was

considerably small The agglomerated copper particles remain as the

main characteristics of powders obtained from Solutions II and III at acurrent density value of 200 mA cmminus2 However lower concentra-

tions of Cu ions (Solution I ) at 200 mA cmminus2 led to the formation of dendritic structure Both types of powder particles are brancheddendrites which consisted of agglomerated copper grains The shapeof the individual copper grains is globular (Fig 3) The morphology of

copper powder obtained at 300 mA cmminus2 is similar to the oneobtained at 200 mA cmminus2 probably because of the hydrogen evo-lution values which are close to each other (294 and 218 respec-

tively) The most important difference is actually in the size of grainsTheestimated average size of coppergrains from Fig 3a isabout10plusmn02 μ m while it is about 500plusmn150 nm from Fig 3b The nucleationrate and the grain size are dependent upon on the current density sothe grain size is considerably decreased at 300 mA cmminus2

The different morphologies of copper powders were obtained fromsolutions with different concentrations of Cu ions This effect can beexplained in terms of the limiting current density which is the min-imum current density for the formation of powder According to

Eq (2) the limiting current density increases with the increasing of concentration of Cu ions For this reason the current ef 1047297ciency valuesof copper powders produced in a RCE cell ranging from 706 to 100are dependent on the concentration of Cu ions and current density

Under constant conditions the apparent densities of copper

powders obtained from Solutions I II and III were 077 125 and

Fig 2 SEM photomicrographs of copper powder particles obtained at a current

density of 200 mA cmminus2 from different solutions (a) Solution III and (b) Solution I

(magni1047297cation times1000 at 140 rpm and 30 degC)




250 g cmminus3 respectively Decreasing of the concentration of copper

ion leads to a decrease in the size of the copper grains Thedecrease inthe size of the grains led to an increase in the speci1047297c surface area An

increase in the speci1047297c surface area of a powder resulted in a decreasein the apparent density

33 Rotation speed of the cathode

In order to determine theeffect of rotation speed of the cathode onthe morphology of electrolytic copper powders and the production

data experiments were carried out at the cathode rotation speedvalues of 140 550 and 1100 rpm while the current density and theelectrolyte temperature values were kept constant at 200 mA cmminus2

and 30 degC in Solution I respectively as the reference conditions The

morphologies of the copper powders are given in Figs 2b and 4It may be seen from Fig 4a that the powder particles obtained at

550 rpm are sponge-like The morphology of copper powders ob-tained at this rotation speed of the cathode was similar to that of

obtained at 140 rpm Both types of powder particles were brancheddendrites and branches were consisted of the agglomerated coppergrains (see Figs 2b and 4a) The most important difference was thesize of growing grains which was considerably small at 140 rpm Also

increasing of the rotation speed of the cathode from 140 rpm to550 rpm led to a decrease in the dispersion of the deposit On the

other hand dendritic structures were not formed at the rotation

speed of 1100 rpm (Fig 4b) The growth of the powder particles wasin one direction and agglomerated copper grains were seen clearlyCopper powders obtained at 1100 rpm were nearly compact and had

a more dense structure with respect to the copper powders obtainedat a lower rotation speed of the cathode It can also be noticed that thesize of coppergrains increased with theincreasing of rotation speed of the cathode from 140 to 1100 rpm The same effect can also be clearly

seen at a higher current density value of 300 mA cmminus2 (see Figs 3band 5) Fig 5 shows the morphology of copper powder particlesobtained from Solution I at 300 mA cmminus2 and 1100 rpm The increase

in the size of the grainswiththe increasingof rotation speed leads to adecrease in the speci1047297c surface area of the powder and consequentlyto an increase in the apparent density Under constant experimentalconditions (200 mA cmminus2 30 degC and Solution I ) the apparentdensities of powders obtained at 140 550 and 1100 rpm were 077

110 and 210 g cmminus3 respectively as expectedThe morphologies of copper powders obtained primarily depend

on the limiting current density According to Eq (2) the increase of the rotation speed of the cathode led to an increase of the limiting

current density The increase of the convective diffusion at theelectrodendashelectrolyte interface with the mechanical stirring led to thedecrease of the diffusion layer thickness and consequently results inan increase of limiting diffusion current density The increase of the

limiting current density led to the formation of copper powders at a

current density which is effectively lower than the speci1047297ed one It is

Fig 3 SEM photomicrographs of copper powder particles obtained from Solution I at

current densities of (a) 200 and (b) 300 mA cmminus2 (magni1047297cation times5000 at 140 rpm

and 30 degC)

Fig 4 SEM photomicrographs of copper powder particles obtained at different

rotation speeds of the cathode (a) 550 and (b) 1100 rpm (magni1047297cation times750 at

200 mA cmminus2 Solution I and 30 degC)




known that the formation of dendritic structures is a main char-acteristic of electrodeposition at the limiting current density andbelonging to the plateau of the limiting current density Therefore the

time needed to initiate dendritic growth (ie the induction time)depends on the current density of the electrodeposition The increasein current density led to the decrease of time needed for the initiationof the dendritic growth Hence dendritic structures were not formed

at a rotation speed of the cathode of 1100 rpm The morphologies of copper powders obtained at the rotation speed of 1100 rpm becomesimilar to those obtained at some lower current densities before theinitiation of the dendritic growth The morphology obtained as well as

the quantity of hydrogen evolution is dependent upon the limitingcurrent density which increasedwith the increasing of rotation speed

At lower Cu ions concentration values as in Solution I which waseasily reached at the limiting current density the current ef 1047297ciency of

hydrogen evolution at 140 550 and 1100 rpm was 218 72 and 0respectively Simultaneously the current ef 1047297ciency of hydrogenevolution at 140 rpm was 294 while it was 17 at 1100 rpm and

at a higher current density (300 mA cmminus2) It is known that thehydrogen evolution affects the hydrodynamic conditions inside theelectrochemical cell [6712] On the other hand the mass transportcontrol at a RCE is imposed by the rotation speed of cylindrical

cathode ie an increase of rotation speed leads to an increase of Reynolds number and consequently to an increase of the limitingcurrent density In this case the change of morphology of copper canbe ascribed to the cathode rotation

34 Electrolyte temperature

The morphologies of electrolytic copper powder particulates ob-tained from Solution II at the current density values of 200 mA cmminus2

and at the cathode rotation speed of 140 rpm are shown in Figs 1a band 6a b It is clearly seen from both 1047297gures that temperature has a

strong effect on the morphology of the copper powder particles SEMimages of the copper powder particles obtained from Solution II at60 degC are given in Fig 6 They have a dendritic structure with manybranches (Fig 6a) similar to the appearance of degenerated dendrites

Thestructure of these dendritesis consistedof irregularcopper grainsCareful analysis showed that the size of copper grains that formeddendrites obtained at 60 degC were considerably smaller than thoseobtained at 30 degC (Fig 6b) Copper dendrites were formed instead of

cauli1047298ower-like forms at 60 degC which is actually due to the increasingtemperature value from 30 to 60 degC This is in accordance with the

position of a current density (overpotential) of 200 mA cmminus2

which

is within the limiting current density plateau Also the morphology of copper powders obtained at thetemperature value of 60 degC wasfoundto be similar to that of obtained at 30 degC and 250 mA cmminus2 (see Fig 1c

and d) The apparent density values of powders obtained at 30 degC and60 degC under the same experimental conditions were measured as 125and 095 g cmminus3 respectively They are in good agreement with themorphologies of copper powders

At lower concentrations of Cu ions in Solution I the morphologiesof copper powder did not change with the increasing of temperaturefrom 30 degC (Fig 3a) to 60 degC (Fig 7) as compared to the higher

concentration of copper ions in Solution II On the other hand theshape of the copper dendrites was changed The morphology of copper powders obtained from Solution I at the processing conditionsof 60 degC 200 mA cmminus2 and 140 rpm is shown in Fig 7 It can be seenfrom Fig 7 that degenerated dendrites were formed

In the experiments where the electrolyte temperature value was30 degC the average current ef 1047297ciency of the hydrogen evolution waszero in Solution II while at 60 degC the average current ef 1047297ciency of thehydrogen evolution was considerably low with a value of 75 On the

other hand the average current ef 1047297ciency of hydrogen evolutionobtained from Solution I at 30 degC was found to be about 218When the temperature was increased to 60 degC the average currentef 1047297ciency of the hydrogen evolution also increased to 35 in the same

solution According to Popov [6] the average current ef 1047297ciency of

hydrogen evolution of 30 was suf 1047297cient to cause the mixing of the

Fig 5 SEM photomicrographs of copper powder particles obtained at a rotation

speed of the cathode of 1100 rpm and at a current density of 300 mA cmminus2

(magni1047297cation times5000 Solution I and 30 degC)

Fig 6 SEM photomicrographs of copper powder particles obtained from Solution II at a

temperature of 60 degC (magni1047297cations a) times1000 and b)times5000 at 200 mA cmminus2 and

140 rpm)




solution in the near-electrode layer while decreasing the diffusionlayer thickness and increasing the limiting diffusion current density

Due to the change in the hydrodynamic conditions the cauli1047298

ower-like shape of the powder particles formed Contrary to this concept

dendritic particles were formed from Solution I when the currentef 1047297ciency of hydrogen evolution was 35 The obtained morphologiescan be explained by the use of a RCE which enables a good control of mass transport conditions

As a result it may be noticed that for a higher concentration of Cuions the increasing of temperature affects the morphology of copperpowder On the other hand the increase in temperature does not lead

to any change of the morphology of copper powder at the lowerconcentration of Cu ions

4 Conclusions

Copper powder particles formed by the electrolysis method usinga RCE cell under different conditions were analyzed by means of SEMtechnique It was found that the structure of the powder particulates

are dependent upon the electrolysis parameterssuch as concentrationof used electrolyte current density rotation speed of the cylindricalcathode and the electrolyte temperature The effects of these pa-rameters were determined by the limiting current density phenom-

enon In all cases changes in morphologies of copper powders areascribed to the change of limiting current density which is dependenton the mass transport conditions at RCE cells

The morphologies of copper powders were found to be den-

dritic at the current density values of 250 and 300 mA cmminus2 and incauli1047298ower-like form at the current density value of 200 mA cmminus2

under the same working conditions in Solution II Dendritic struc-tures were also formed at the current density values of 200 and

300 mA cmminus2 in Solution I while electrodeposition from Solution III with a current density value of 200 mA cmminus2 did not form anydendritic morphology In the current study it was shown that theshape of copper dendritesis dependent on the applied current density

as well as the Cu ions concentration of electrolyte Dendrites were notformed at high cathode rotation speeds for example at 1100 rpmDendrites were only formed at the lower rotation speeds of thecathode (for example at 140 and 550 rpm) and at lower Cu ions

concentration values as in the case of Solution I In this case thechange in the hydrodynamic conditions of the RCE cell caused by themechanical stirring was the main reason for the change of morphol-ogies of copper powders

Two types of particle morphologies were formed from Solution II depending upon the temperature increase On the other hand at a

lower concentration of Cu ions any increase in temperature did notlead to a changein thestructure of the powderparticulates havingthe

dendritic formDepending on the electrolysis conditions the current ef 1047297ciency for

copper powder production by the electrolysis method in a rotatingcylindrical cathode cell variedin therangebetween 65 and100 with

an energy consumption range between 272 and 420 kWh kgminus1 CuThe apparent density values of copper powder also changed with

respect to their morphologies The smaller the dendritic structure of powder particulates the lower the apparent density of copperpowder Therefore the apparent densities of copper powders can becontrolled by changing the electrolysis parameters Depending on theelectrolysis conditions the apparent densities of copper powders

were measured to be withinthe range between 077 and 250 g cmminus3

Acknowledgements

This work is a part of research project supported by the Scienti1047297cand Technological Research Council of Turkey (TUBITAK project No

105M137) The authors would like to thank TUBITAK for 1047297nancialsupport

References

[1] A Agrawal S Kumari D Bagchi VB Kumar D Pandey Hydrogen reduction of copper bleed solution from an Indian copper smelter for producing high puritycopper powders Hydrometallurgy 84 (2006) 218ndash224

[2] PW Lee WB Eisen BL Ferguson RM German R Iacocca D Madan HSanderow YT Hardbound 9th Edition ASM Metals Handbook PowderMetallurgy vol 7 ASM International Ohio 1998

[3] JL Everhart Copper and Copper Alloy Powder Metallurgy Properties and Applica-tions 2007 httpwwwcopperorgresourcesproperties129_6homepagehtml

[4] MG Pavlović KI Popov Metal Powder Production by Electrolysis 2005 httpelectrochemcwrueduencyclart-p04-metalpowderhtm

[5] MG Pavlović JL Pavlović ID Doroslovački ND Nikolić The effect of benzoicacid on the corrosion and stabilisation of electrodeposited copper powderHydrometallurgy 73 (2004) 155ndash162

[6] ND Nikolić LjJ Pavlović MG Pavlović KI Popov Morphologies of electro-chemicallyformed copper powder particles and theirdependenceon the quantity

of evolved hydrogen Powder Technology 185 (2008) 195ndash201[7] ND Nikolić KI Popov LjJ Pavlović MG Pavlović The effect of hydrogen

codeposition on the morphology of copper electrodeposits I The concept of effective overpotential Journal of Electroanalytical Chemistry 588 (2006) 88ndash98

[8] ND Nikolić KI Popov LjJ Pavlović MG Pavlović Morphologies of copperdeposits obtained by the electrodeposition at high overpotentials Surface ampCoatings Technology 201 (2006) 560ndash566

[9] R Walker SJ Duncan The morphology and properties of electrodeposited copperpowder Surface Technology 23 (1984) 301ndash321

[10] A Agrawal S Kumari D Bagchi V Kumar BD Pandey Recovery of copperpowder from copper bleed electrolyte of an Indian copper smelter by electrolysisMinerals Engineering 20 (2007) 95ndash97

[11] ND Nikolić KI Popov LjJ Pavlović MG Pavlović Determination of criticalconditions for the formation of electrodeposited copper structures suitable forelectrodes in electrochemical devices Sensors 7 (2007) 1ndash15

[12] ND Nikolić G Branković MG Pavlović KI Popov The effect of hydrogen co-deposition on the morphology of copper electrodeposits II Correlation betweenthe properties of electrolytic solutions and the quantity of evolved hydrogen

Journal of Electroanalytical Chemistry 621 (2008) 13ndash

21[13] ND Nikolić LjJ Pavlović MG Pavlović KI Popov Effect of temperature on theelectrodeposition of disperse copper deposits Journal of the Serbian ChemicalSociety 72 (12) (2007) 1369ndash1387

[14] DR Gabe GD Wilcox J Gonzalez-Garcia FC Walsh The rotating cylinderelectrode its continued development and application Journal of AppliedElectrochemistry 28 (1998) 759ndash780

[15] KI Popov SS Djokić BN Grgur Fundamental aspects of electrometallurgyKluwer AcademicPlenum Publishers New York 2002

[16] MG Pavlović LjJ Pavlović ER Ivanović V Radmilović KI Popov The effect of particle structure on apparent density of electrolytic copper powder Journal of the Serbian Chemical Society 66 (2001) 923ndash933

[17] KI Popov SB Krstić MČ Obradović MG Pavlović LjJ Pavlović ER IvanovićThe effect of the particle shape and structure on the 1047298owability of electrolyticcopper powder III A model of the surface of a representative particle of 1047298owingcopper powder electrodeposited by reversing current Journal of the SerbianChemical Society 69 (1) (2004) 43ndash51

[18] KI Popov SB Krstić MG Pavlović The critical apparent density for the free 1047298owof copperpowder Journal of theSerbian Chemical Society 68 (6)(2003) 511ndash513

Fig 7 SEM photomicrograph of copper powder particles obtained from Solution I at a

temperature of 60 degC (magni1047297cation times5000 at 200 mA cmminus2 and 140 rpm)




properties of the electrolyte respectively The constants ldquoK rdquo and ldquoardquo

values for b =0356 vary with the surface type and Re number Gabe

et al obtained the value a =07 on a smooth cylinder and observedthat ldquoardquo changes to 092 as the electrode surface becomes rougher(often powder deposits) The value of K is 0079 for both of themLimiting current density which is the minimum current density for

the formation of powder on the RCE through dimensionlessparameters can be given by the following Eq (2) [14]

iL = 0079 z F c U 092

d008

υ0564

D0644

eth2THORN

where z is the number of electrons (valence number) involved in a

redox process F is the Faradays constant (C molminus1) c is theconcentration (mol cmminus3) U is the electrode peripheral velocity(cm sminus1) d is the cylinder electrode diameter (cm) D is the diffusioncoef 1047297cient (cm2 sminus1) and ν is the kinematic viscosity (cm2 sminus1)

An electrolytic metal powder represents disperse electrodepositsremoved from the electrode by tapping or some such similar mannerIn the potentiostatic systems disperse deposits of copper are obtainedat overpotentials on theplateau of thelimitingcurrent density as well

as at higherones (atthe endof this plateau)Copper electrodepositionprocess occurs simultaneously with the hydrogen evolution reaction

In galvanostatic systems electrodeposit of copper has thetendency to form powders when current densities larger than the

limiting diffusion current density are used (or overpotentials outsidethe plateau of the limiting diffusion current density) [46715] Alsothe increasing of the overpotential (current density) leads to theformation of a more dispersed deposit characterized by the decreased

particle size [15]An electrolytic metal powder consists of particles These particles

may have various forms and sizes And each of these particles exhibitmore or less the same characteristics as if they are deposited under

identical conditions as long as the removal process of deposits fromthe electrode is identical The most important properties of a metalpowder are the speci1047297c surface area the apparent density the1047298owability the particle grain size and distribution [2] These prop-erties called decisive properties characterize the behaviour of a metal

powder The morphologies of the copper powder particles correlatedwith the apparent density and 1047298owability have been reported by

Pavlovic et al [16] and Popov et al [1718] It can be seen from theseinvestigations that the more dendritic the structure of the powderparticles is the lower the apparent density of the copper powdersAlso Popov et al [18] have proposed a method for the determination

of the critical apparent density which permits the free 1047298ow of electrodeposited copper powder

The aim of this study is to produce copper powders from acidsulphate solutions by means of electrolysis with the use of a RCE that

provides faster ionic movement due to the convective diffusion at theelectrodendashelectrolyte interface and to optimise the production pa-rameters The effect of current density concentration of copper ionselectrolyte temperature and rotation speed of the cathode which

affect the limiting current density on process data and themorphologies of copper powders as well as on the apparent densitieswere investigated

2 Experimental

In all experiments electrodeposition of the copper powders ontocylindrical cathode was performed in a laboratory scale electrolysiscell with a rotating cylinder cathode (RCE) A stainless steel cathode

(Oslash20times50 mm) and lead anode were utilized The total electrolytevolume was 1250 mL

Anolyte and catholyte were separated by a diaphragm in the cellIn the 1047297rst section electrolysis is carried out and in the second section

the 1047297ltration is performed for preventing metal powders produced

from clogging solution circulation pumps One of the most important

technological problems faced in the electrolysis is the continuity of process due to the change in the cathode size In the designed cell the

metal powder produced is removed from the cathode surface by ascraper which is added back to the solution and then 1047297ltered Thusthe cathode size is kept constant and the continuity problem is solvedIt is important to note that the cathode-scraper was positioned at a

distance of 1 mm from the surface of the cathodeIn all experiments electrolytic copper powder was galvanostati-

cally deposited from the following solutions

5gL1Cu

2thornthorn 150 5gL

1H2SO4 ethSolutionITHORN

10gL1Cu

2thornthorn 150 5gL

1H2SO4 ethSolutionIITHORN

20gL1Cu

2thornthorn 150 5gL

1H2SO4 ethSolutionIIITHORN

Distilled water and analytical grade chemicals were used for thepreparation of solutions for the electrodeposition process Electrolytewas pumped from the second section (1047297ltration part) to the 1047297rst

section where the electrolysis was carried out (electrolyte circulationrate 1 dm3min)

The copper powder was deposited galvanostatically at the currentdensity values of 200 250 and 300 mA cmminus2 while values of 30 and

60plusmn 05 degC were selected as the electrolysis temperature The cathoderotation speed values of 140 550 and 1100 rpm were used Followingthe electrolysis the obtained powder was washed several times withthe distilledwater After being washedwith waterin order to prevent

oxidation the powder was rinsed with ethanol and dried at 95 degC inan oven under vacuum

The powder particles were characterized by using a scanningelectron microscope (model JEOL JSM 5600) Copper analysis of the

obtained powder was carried out at ICP (Spectro Ciros Vision)According to these results the current ef 1047297ciencies were calculatedbased on Faradays law The apparent densities were measured by a

2 cm3 minimized Arnold meter

3 Results and discussion

31 Current density

The effect of current density on the morphology of electrolyticcopper powder and on the properties of the copper powder wasinvestigated at current density values of 200 250 and 300 mA cmminus2

The results obtained from Solution II areshownin Fig1 These powderparticles were electrodeposited under the standard conditions withthe electrolyte temperature of 30 degC with the cathode rotation speedof 140 rpm

It can beseen from Fig 1a and b that thepowder particlesobtainedat 200 mA cmminus2 are sponge-like These particles actually have acauli1047298ower-like structure The agglomerates of globular copper grainsbecome the dominant form of the powder morphology electrode-

posited at this current density It is important to note that dendriticmorphology was not formed at 200 mA cmminus2 SEM investigation of these powders showed the presence of new nucleation sites over theexisting enlarged grains which resulted in noticeable differences in

the grain size distributionFig 1c and d shows the morphologies of copper powder obtained at

a current density of 250 mA cmminus2 The change in the morphologyfrom cauli1047298ower-like to dendrites is clearly seen at this current level

The branches seen on higher magni1047297cation (Fig 1d) constitute thedendritic character of these particles It can be concluded from Fig 1a

and c that increasing the current density from 200 mA cmminus2

to








































































and 30 degC)






















which














140 rpm)










4 Conclusions

















Acknowledgements



References






























































































and 30 degC)






















which














140 rpm)










4 Conclusions

















Acknowledgements



References









































which














140 rpm)










4 Conclusions

















Acknowledgements



References
































4 Conclusions

















Acknowledgements



References
























(2010) hapçı effect of electrolysis parameters on the morphologies of copper powder obtained in a

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