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Materials Chemistry and Physics 106 (2007) 134–141

Effect of lead content on the dezincification behaviour of leaded brass inneutral and acidified 3.5% NaCl solution

Satendra Kumar a, T.S.N. Sankara Narayanan a,∗, A. Manimaran b, M. Suresh Kumar b,1

a National Metallurgical Laboratory, Madras Centre CSIR Complex, Taramani, Chennai 600113, Indiab Sri Ramakrisna Mission Vidhyalaya College of Arts and Science, Coimbatore 641020, India

Received 8 November 2006; received in revised form 16 May 2007; accepted 21 May 2007

bstract

The corrosion behaviour of leaded brasses with 2, 2.4, 2.8, and 4.85 wt.% of lead in both neutral (pH 6.5) and acidified (pH 3.0) 3.5% NaCl solutionas studied. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), current–time transient, and accelerated leaching studiesere employed to assess the corrosion behaviour. The study reveals that the lead content of the alloy has a pronounced influence on the extentf corrosion attack in neutral and acidified 3.5% NaCl solutions at potentials closer to and anodic to Ecorr. Scanning electron micrographs (SEM)how the existence of lead as a separate phase in leaded brass before subjecting it to corrosion and the formation of hexagonal platelets or flowerhaped crystals on selected areas after corrosion. The structural separation of lead from the rest of the alloy forms galvanic cells and decreases theorrosion resistance of leaded brasses in neutral 3.5% NaCl solution at potentials closer to Ecorr. In contrast, at potentials anodic to Ecorr in neutral.5% NaCl solution and in acidified 3.5% NaCl solution, precipitation of lead based compounds on the surface of leaded brass decreases the extentf corrosion attack and causes a deviation from the typical dezincification behaviour. The precipitation of lead based compounds induces passivity

f the leaded brasses, which is evident in the anodic segments of the polarization curves obtained for acidified 3.5% NaCl solution. This studyoncludes that increase in lead content of leaded brass alloys could provide an improvement in their corrosion resistance only under conditionshere compounds of lead gets precipitated on the surface and induces passivity. 2007 Elsevier B.V. All rights reserved.

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eywords: Alloys; Electrochemical techniques; Electron microscopy; Corrosio

. Introduction

Brass possesses an attractive combination of properties,amely, good corrosion resistance, good machinability, highhermal and electrical conductivity and better resistance toiofouling. Hence, it finds extensive use in water distributionystems, water treatment units, condensers, heat exchangers inil, chemical and petrochemical industries, and in processinglants used for electricity generation and desalination [1–4].any alloying elements were added to brass to improve its char-

cteristic properties. Alloying with lead enables an improvementn the machinability of brass. The benefits of alloying a smallercentage of lead in brass have been realized in the form of

∗ Corresponding author. Tel.: +91 44 2254 2077; fax: +91 44 2254 1027.E-mail address: tsnsn@rediffmail.com (T.S.N.S. Narayanan).

1 Present address: Biomolecular Engineering Lab, Department of Chemicalngineering, National Taiwan University of Science and Technology, Taipei06, Taiwan, ROC.

bplawlmu1

254-0584/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.matchemphys.2007.05.030

mproved tool life and reduction in cutting forces, which offeronsiderable savings in power consumption [5]. However, theoxicity of lead is a major concern with the use of leaded brass.un and Barsoum [6] have reported that even light abrading of

he surface of leaded brass could result in spontaneous growthf lead whiskers and hillocks, which might easily disperse inhe atmosphere and could cause serious health problems for theeople, who are dealing with leaded brass on a daily basis. Deal-oying of the constituent elements is the main mode failure wheneaded brass comes in contact with aqueous solutions. Leadedrass fixtures are found to be an important source of lead inotable water [7–12]. It has been reported that the amount ofead leached from leaded brasses frequently exceeds 50 mg l−1,nd the prominent spikes of lead in water, could be associatedith dislodging of corrosion products [7,13–15]. Leaching of

ead in tap water causes serious health problems ranging fromental retardation in children to hypertension and renal fail-

re [12,16–20]. The World Health Organization has suggested0 mg l−1 as the permissible limit of lead in potable water [21]

stry and Physics 106 (2007) 134–141 135

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otedoettToappipsurtlapadlBthcotovcon

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Table 1Chemical composition of the leaded brasses used in the present study

Alloy nomenclature %Cu %Zn %Pb %Sn %Fe %Ni %Al

LB1 58.80 37.73 2.02 0.22 0.20 0.54 0.09LB2 58.20 38.54 2.43 0.36 0.17 0.30 –LL

sTp2dpaScrscao(co1iBiaa(

3

3N

The potentiodynamic polarization curves of leaded brasses(LB1–LB4) in neutral 3.5% NaCl solution (pH 6.5) are shownin Fig. 1. The corrosion potential (Ecorr) and corrosion currentdensity (icorr) are given in Table 2. The Ecorr of LB1 is around

S. Kumar et al. / Materials Chemi

hereas a lower level of 5 mg l−1 has been proposed by the USnvironmental Protection Agency [22,23]. The toxicity of leadas warranted the development of aluminum bronzes and bis-uth containing brasses that have <0.25 wt.% lead for drinkingater applications [24]. Kim et al. [25] have reported that thoughnleaded bismuth containing brasses exhibit an improvementn corrosion resistance with increase in bismuth content of thelloy, they are more susceptible for dezincification compared toeaded brass due to the increased amount of the �-phase causedy alloying of bismuth. Moreover, bismuth containing brass iseported to be highly susceptible for stress-induced dezincifi-ation and its stress corrosion cracking resistance in Mattson’solution is relatively lower than that of leaded brass [26]. Dueo these limitations, the large scale use of bismuth containingrasses compared to leaded brasses becomes uncertain.

The dependence of corrosion of leaded brasses on the pHf the medium, presence of natural organic matter, concen-ration of anions such as, sulphate, chloride, orthophosphate,tc. has already been established [7–10,27,28]. However, theependence of the extent of corrosion attack of leaded brassn the lead content of the alloy is not fully understood. Thelectrochemical behaviour of leaded brass with lead content inhe range of 1–3.4 wt.% in neutral chloride and sulphate solu-ions was investigated by Badawy and his co-workers [29–32].he results of their study show that increase in lead contentf brass from 1 to 3.4 wt.% increases the corrosion resistancend improves the stability of the alloy in both chloride and sul-hate media. The improvement in stability is attributed to theassive film formation. From metallurgical perspective, lead isnsoluble in copper or copper–zinc alloys and it forms micro-articles dispersed in the alloy [33]. Korshin et al. [27] havehown the presence of discrete islets of lead in leaded brasssing back-scattered electron imaging (BEI). Further, using X-ay photoelectron spectroscopy (XPS), they have confirmed thathese islets contain high amounts of lead, whereas little or noead could be detected on the adjacent surface. Since lead existss a separate pure phase on the surface of leaded brass, the leadhase and the rest of the alloy could form a galvanic couple andccelerate the rate of oxidation of lead. The increased rate of oxi-ation of the surface lead, evidenced by the higher percentage ofead in the total leached metal is reported by Korshin et al. [27].ased on the observations made using secondary ion mass spec-

rometry (SIMS) and scanning electron microscopy (SEM) theyave confirmed that accumulation of substantial amounts of leadorrosion products occurs simultaneously with dezincificationf the near-surface metal. Hence, it is imperative to understandhe dependence of the lead content on the corrosion behaviourf leaded brass and, under what conditions the lead could pro-ide an improvement in corrosion resistance or otherwise. In thisontext, the present work aims to study the corrosion behaviourf leaded brasses with 2, 2.4, 2.8, and 4.85 wt.% of lead in botheutral and acidified 3.5% NaCl solution.

. Experimental details

Four leaded brasses with a lead content of 2, 2.4, 2.8 and 4.85 wt.% ofead, designated as LB1, LB2, LB3 and LB4, respectively, were used in this

Fn

B3 58.38 38.36 2.83 0.08 0.20 0.05 0.23B4 63.04 30.33 4.85 0.81 0.23 0.65 0.90

tudy. The chemical composition of these leaded brasses is given in Table 1.he samples used for electrochemical studies were cut from a 2 mm thick sheet,olished using 60 grit silicon carbide paper followed by 220, 400, 600, 1/0,/0, 3/0 and 4/0 grades of emery paper, degreased with acetone and rinsed witheionized water. The electrochemical measurements were performed using aotentiostat/galvanostat/frequency response analyzer (ACM instruments, UK)nd a flat cell. A 3.5% NaCl solution was used as the electrolyte medium.tudies were conducted both in neutral (pH 6.5) as well as in acidic (pH 3.0)onditions. The pH of the solution was adjusted with the addition of hydrochlo-ic acid. Only 1 cm2 of the leaded brass electrode was exposed to the electrolyteolution. A graphite rod and saturated calomel electrode (SCE) served as theounter and reference electrodes, respectively. All experiments were performedt 27 ± 1 ◦C. Potentiodynamic polarization studies were conducted at a scan ratef 100 mV min−1. The corrosion potential (Ecorr) and corrosion current densityicorr) were determined using the Tafel extrapolation method. Electrochemi-al impedance spectroscopic (EIS) studies of the leaded brasses were carriedut at their respective open circuit potentials in the frequency range between0,000 and 0.01 Hz. The charge transfer resistance (Rct) and double layer capac-tance (Cdl) were determined from the Nyquist plots after fitting the data usingoukamp software. The current–time transients were recorded at three different

mpressed potentials, namely, −250 mV, −100 mV and 0 mV versus SCE. Themount of copper and zinc ions leached out from the alloy at these potentialsfter 2 h of immersion were analyzed using atomic absorption spectrophotometerAAS) (GBC-Avanta).

. Results

.1. Corrosion behaviour of leaded brasses in neutral 3.5%aCl solution

ig. 1. Potentiodynamic polarization curve of leaded brasses (LB1–LB4) ineutral 3.5% NaCl solution (pH 6.5).

136 S. Kumar et al. / Materials Chemistry and Physics 106 (2007) 134–141

Tabl

e2

Cor

rosi

onbe

havi

our

ofle

aded

bras

ses

inne

utra

l3.5

%N

aCls

olut

ion

eval

uate

dby

pote

ntio

dyna

mic

pola

riza

tion,

elec

troc

hem

ical

impe

danc

esp

ectr

osco

py,c

urre

nt–t

ime

tran

sien

tstu

dies

and

the

exte

ntof

leac

hing

ofco

pper

and

zinc

atdi

ffer

enti

mpr

esse

dpo

tent

ials

Allo

yus

edC

orro

sion

pote

ntia

lE

corr

(mV

)

Cor

rosi

oncu

rren

tden

sity

i cor

r(�

Acm

−2)

Cha

rge

tran

sfer

resi

stan

ce(R

ct)

(�cm

−2)

Dou

ble

laye

rca

paci

tanc

e(C

dl)

(F)

Stea

dyst

ate

curr

entd

ensi

ty(m

Acm

−2)

atdi

ffer

enti

mpr

esse

dpo

tent

ials

aE

xten

tof

leac

hing

ofC

uan

dZ

nat

diff

eren

tim

pres

sed

pote

ntia

lsa

−100

mV

0m

V−2

50m

V−1

00m

V0

mV

Cu

(mg)

Zn

(mg)

Cu

(mg)

Zn

(mg)

Cu

(mg)

Zn

(mg)

LB

1−2

328.

4329

591.

47×

10−4

1.75

4.32

0.00

10.

018

0.21

0.39

1.81

0.39

LB

2−2

408.

7024

041.

59×

10−4

1.70

4.22

0.00

60.

022

0.26

0.31

1.87

0.38

LB

3−2

5611

.00

2106

2.50

×10

−41.

554.

100.

008

0.02

50.

340.

282.

110.

37L

B4

−264

21.7

448

15.

06×

10−4

1.45

3.60

0.01

30.

028

0.52

0.26

2.51

0.37

aPo

tent

ialv

alue

sin

mV

vs.S

CE

.

Fa

−w4attw4

3acsT(tvfistdt

eSbateoLasibttoo

ig. 2. Nyquist plot of leaded brasses (LB1–LB4) in neutral 3.5% NaCl solutiont their respective open circuit potentials.

232 mV (versus SCE) and there is a cathodic shift in the Ecorrhen the lead content of the brass is increased from 2.02 to.85 wt.%. There is not much variation in the icorr of LB1, LB2nd LB3 and they are of the order of 8–11 �A cm−2. However,here is a significant change in the icorr of LB4 compared tohe rest of the alloys. The icorr increased from 8 to 22 �A cm−2

ith the increase in the lead content of the brass from 2.02 to.85 wt.%.

The Nyquist plots of leaded brasses (LB1–LB4), in neutral.5% NaCl solution at their respective open circuit potentials,re shown in Fig. 2. The shape of the curves, in general, indi-ates a semicircle followed by a diffusion tail. The size of theemicircle decreases with increase in lead content of the alloy.he charge transfer resistance (Rct) and double layer capacitance

Cdl) are given in Table 2. Though there is not much variation inhe icorr of LB1, LB2 and LB3, the Rct values of these brasses,iz., 2959, 2404 and 2106 � cm−2, respectively, indicate suf-cient variation to distinguish their corrosion resistance. Theignificant change in the corrosion resistance of LB4 comparedo the other three alloys is also evident in EIS studies. The Rctecreased from 2959 to 481 � cm−2 when the lead content ofhe brass is increased from 2.02 to 4.85 wt.%.

Current–time transient studies were performed at three differ-nt potentials, namely, −250 mV, −100 mV and 0 mV (versusCE). The former one is closer to the Ecorr of these leadedrasses in neutral 3.5% NaCl solution whereas the latter two arenodic to the Ecorr. There is not much variation in current–timeransients of all the four leaded brasses at −250 mV and theyxhibit a reasonable variation in the steady state current densitynly at higher anodic potentials. The current–time transients ofB1–LB4 in neutral 3.5% NaCl solution at −100 and 0 mVre shown in Fig. 3(a and b), respectively. The average steadytate current density values obtained at these potentials are givenn Table 2. The average steady state current density of leadedrasses at −100 and 0 mV is decreased when the lead content of

he alloy is increased from 2.02 to 4.85 wt.%. This indicates aotally different trend on the dependence of corrosion resistancef leaded brasses on the lead content of the alloy, than the onebserved in potentiodynamic polarization and EIS studies.

S. Kumar et al. / Materials Chemistry and Physics 106 (2007) 134–141 137

F(

b−oitd−fcoitctrs

33

(

Fa

idptidoiaw4atrctaatc(coapwrw(

3asl

ig. 3. Current–time transient of leaded brasses in neutral 3.5% NaCl solutiona) at −100 mV and (b) at 0 mV (potentials in mV vs. SCE).

To get a better insight on this phenomenon, the leadedrass alloys were kept at three different impressed potentials of250 mV, −100 mV and 0 mV versus SCE for 2 h. The extent

f copper and zinc ions leached out at these potentials are givenn Table 2. At −250 mV, the extent of leaching of zinc is higherhan that of copper for all the four leaded brasses, a typicalezincification behaviour expected for such alloys. However, at100 mV, the typical dezincification behaviour is observed only

or LB1 and LB2 whereas for the other two leaded brasses, theopper content is higher than zinc. A comparison of the amountf copper and zinc ions leached in to the solution at this potentialndicates an increase in copper and decrease in zinc concentra-ion with increase in lead content of the brass. At 0 mV, the zincontent of all the four leaded brasses is significantly lower thanhat of copper. It is interesting to note that the amount of zincemains almost constant whereas the amount of copper increasesteadily with increase in lead content of the alloy.

.2. Corrosion behaviour of leaded brasses in acidified

.5% NaCl solution

The potentiodynamic polarization curves of leaded brassesLB1–LB4) in acidified 3.5% NaCl solution (pH 3.0) are shown

tfot

ig. 4. Potentiodynamic polarization curve of leaded brasses (LB1–LB4) incidified 3.5% NaCl solution (pH 3.0).

n Fig. 4. The corrosion potential (Ecorr) and corrosion currentensity (icorr) are given in Table 3. It is obvious to expect aronounced cathodic shift in Ecorr and a significant increase inhe icorr of all the four leaded brasses following the decreasen pH of the medium from 6.5 to 3.0. However, the depen-ence of corrosion resistance with the lead content of the alloybserved in neutral 3.5% NaCl solution is also evident in acid-fied 3.5% NaCl solution. The Ecorr of LB1 (2.02 wt.% Pb) isround −430 mV (versus SCE) and it exhibits a cathodic shiftith further increase in lead content of the brass from 2.02 to.85 wt.%. There is only a slight variation in the icorr of LB1, LB2nd LB3 and they are in the order of 22–34 �A cm−2. However,here is a significant change in the icorr of LB4 compared to theest. The icorr increased from 22 to 103 �A cm−2 when the leadontent of the brass is increased from 2.02 to 4.85 wt.%. Fromhe Ecorr and icorr values it appears that the nature of corrosionttack of these leaded brasses is quite similar in both neutral andcidified 3.5% NaCl, with the extent of attack being higher inhe acidified medium. However, a comparison of the polarizationurves of these leaded brasses in neutral and acidified 3.5% NaClFigs. 1 and 4) reveals some interesting features other than theathodic shift in Ecorr and increase in icorr. The anodic segmentf the polarization curves of all the four leaded brasses exhibitsctive–passive transitions in the acidified medium (Fig. 4). Theassive range and the passive current density (ipass) increasesith increase in lead content of the alloy. For LB1 the passive

ange and ipass is about 65 mV and 62 �A cm−2, respectively,hereas they are around 200 mV and 307 �A cm−2 for LB4

Table 3).The Nyquist plots of leaded brasses (LB1–LB4), in acidified

.5% NaCl solution, at their respective open circuit potentials,re shown in Fig. 5. It is evident that LB1 and LB2 exhibit aemicircle followed by a Warburg diffusion tail whereas only ainear portion is observed for LB3 and LB4. The appearance ofhe semicircle followed by a Warburg diffusion tail suggests dif-

usion controlled process whereas the linear portion is indicativef the capacitive behaviour. Among LB1 and LB2, the size ofhe semicircle is higher for LB2. The charge transfer resistance

138 S. Kumar et al. / Materials Chemistry and Physics 106 (2007) 134–141

Tabl

e3

Cor

rosi

onbe

havi

our

ofle

aded

bras

ses

inac

idifi

ed3.

5%N

aCls

olut

ion

(pH

3.0)

eval

uate

dby

pote

ntio

dyna

mic

pola

riza

tion,

elec

troc

hem

ical

impe

danc

esp

ectr

osco

py,c

urre

nt–t

ime

tran

sien

tstu

dies

and

the

exte

ntof

leac

hing

ofco

pper

and

zinc

atdi

ffer

enti

mpr

esse

dpo

tent

ials

Allo

yus

edC

orro

sion

pote

ntia

la

Eco

rr(m

V)

Cor

rosi

oncu

rren

tden

sity

i cor

r(�

Acm

−2)

Pass

ive

rang

e(m

V)

Pass

ivat

ion

curr

ent

dens

ity(i

pass

)(�

Acm

−2)

Cha

rge

tran

sfer

resi

stan

ce(R

ct)

(�cm

−2)

Dou

ble

laye

rca

paci

tanc

e(C

dl)

(F)

Stea

dyst

ate

curr

entd

ensi

ty(m

Acm

−2)

atdi

ffer

enti

mpr

esse

dpo

tent

ials

aE

xten

tof

leac

hing

ofC

uan

dZ

nat

diff

eren

tim

pres

sed

pote

ntia

lsa

−100

mV

0m

V−2

50m

V−1

00m

V0

mV

Cu

(mg)

Zn

(mg)

Cu

(mg)

Zn

(mg)

Cu

(mg)

Zn

(mg)

LB

1−4

3021

.67

6562

407

1.62

×10

−31.

804.

400.

250.

130.

940.

322.

400.

39L

B2

−482

26.2

290

9110

763.

68×

10−3

1.75

4.25

0.21

0.07

0.92

0.32

2.25

0.38

LB

3−5

0434

.34

160

105

1483

4.79

×10

−31.

664.

150.

190.

060.

910.

312.

170.

39L

B4

−513

103.

0020

030

717

361.

84×

10−3

1.36

3.90

0.14

0.04

0.78

0.26

1.58

0.36

aPo

tent

ialv

alue

sin

mV

vs.S

CE

.

Ft

(TdRtsiaasio

3avalE

−adtLtttZIci

4

bi

ig. 5. Nyquist plot of leaded brasses (LB1–LB4) in acidified 3.5% NaCl solu-ion at their respective open circuit potentials.

Rct) and double layer capacitance (Cdl) are given in Table 3.he Rct values of leaded brasses indicate sufficient variation toistinguish their corrosion resistance in acidified medium. Thect increased from 407 to 1736 � cm2 when the lead content of

he alloy is increased from 2.02 to 4.85 wt.%. Though a cathodichift in Ecorr (−430 to −513 mV) and a significant increase incorr (22–103 �A cm2) with the increase in lead content of thelloy is observed in polarization study, the Rct values of theselloys suggest a reversal in trend. However, the increase in pas-ivation range with increase in lead content of the alloy observedn polarization study supports the observed trend in Rct valuesf these alloys.

The current–time transients of leaded brasses in acidified.5% NaCl solution at −100 and 0 mV are shown in Fig. 6(and b), respectively. The average steady state current densityalues obtained at these potentials are given in Table 3. Theverage steady state current density decreases with increase inead content of the alloy and supports the results obtained byIS studies.

The extent of copper and zinc ions leached out at −250 mV,100 mV and 0 mV (versus SCE) after 2 h of immersion in

cidified 3.5% NaCl solution are given in Table 3. The typicalezincification behaviour is not observed in any of the alloys athese potentials. The applied potentials are anodic to the Ecorr ofB1–LB4 in acidified 3.5% NaCl solution. Hence, it is obvious

o expect a significant dissolution of both copper and zinc fromhese alloys. However, at all these potentials, the copper con-ent is higher than zinc and there is a significant decrease in then/Cu ratio when the potential is increased from −250 to 0 mV.

t is interesting to note that the amount of zinc remains almostonstant whereas the amount of copper decreases steadily withncrease in lead content of the alloy at −100 and 0 mV.

. Discussion

Potentiodynamic polarization and EIS studies of leadedrasses in neutral 3.5% NaCl solution reveal a cathodic shiftn Ecorr, an increase in icorr and a decrease in Rct with increase

S. Kumar et al. / Materials Chemistry and Physics 106 (2007) 134–141 139

F(

iittkmiinldutiptftpacHl

Fc

ta

nH0ec−fHdtm+aooa(ootdsiafiiuicw

ig. 6. Current–time transient of leaded brasses in acidified 3.5% NaCl solution:a) at −100 mV and (b) at 0 mV (potentials in mV vs. SCE).

n lead content from 2.02 to 4.85 wt.%. The results of our studyndicate a different trend on the dependence of corrosion resis-ance of leaded brass with the lead content of the alloy comparedo that reported by Badawy and his co-workers [28–32]. It is wellnown that lead is insoluble in Cu or Cu–Zn alloys and formsicro-particles dispersed in the alloy [33]. In order to get a better

nsight, the surface of LB4 (4.85 wt.% lead) before subjectingt to corrosion is assessed using SEM (Fig. 7). The presence ofumerous white spots suggests the presence of discrete islets ofead. Korshin et al. [27] have also observed the presence of suchiscrete islets of lead in leaded brass with 2.5–3.7 wt.% of lead,sing BEI. Using XPS, they have confirmed that these islets con-ain high amounts of lead, whereas the surface adjacent to theslets contains little or no lead [27]. If lead could form a separatehase due to its insolubility in the brass alloy, then the struc-ural separation of the lead phase and the rest of the alloy wouldorm a galvanic couple. Since the standard electrode potential ofhe Pb2+/Pb couple (E0 = −0.126 V) lies between the standardotentials of the Zn2+/Zn and Cu2+/Cu couples (E0 = −0.762

nd +0.342 V, respectively), the formation of such a galvanicouple would increase the rate of corrosion of leaded brasses.ence, the observed increase in corrosion rate with increase in

ead content from 2.02 to 4.85 wt.% could be attributed due to

baat

ig. 7. SEM image of the surface of LB4 (4.85 wt.% Pb) before subjecting it toorrosion (white spots indicate the presence of discrete islets of lead).

he structural separation of the lead phase from the rest of thelloy and the formation of galvanic cells between them.

The current–time transients of all the four leaded brasses ineutral 3.5% NaCl solution did not vary much at −250 mV.owever, their average steady state current density at −100 andmV decreased with increase in lead content of the alloy. Thextent of leaching of zinc is higher than that of copper (typi-al dezincification behaviour) for all the four leaded brasses at250 mV whereas a reversal in trend is observed at −100 mV

or LB3 and LB4 and for all the four leaded brasses at 0 mV.eidersbach and Verink [34] proposed that the mechanism ofezincification of �-brass is dependent on the applied poten-ial. In the potential range of −0.9 V to 0 V (versus SHE), the

echanism involves preferential dissolution of zinc; at 0.0 to0.2 V, the alloy dissolves with re-deposition of copper, whilet potentials above +0.2 V, both copper and zinc dissolve with-ut re-deposition of copper [34–36]. Obviously, the dependencef mechanism of dezincification on the applied potential is alsopplicable for leaded brass. Since the Ecorr of leaded brassesLB1–LB4) in neutral 3.5% NaCl solution lies in the rangef −232 to −264 mV, the typical dezincification behaviour isbserved at −250 mV. However, at −100 and 0 mV, as the poten-ial is much anodic to the Ecorr of leaded brasses, pronouncedissolution of both copper and zinc is observed. The decrease inteady state current density at −100 and 0 mV and the decreasen Zn/Cu ratio observed at −100 mV for LB3 and LB4 and forll the four leaded brasses at 0 mV suggest the formation of sur-ace film involving compounds of lead. In order to get a betternsight on this phenomenon, the surfaces of LB1 and LB4, aftermmersion in neutral 3.5% NaCl solution for 2 h, were assessedsing SEM (Fig. 8(a and b), respectively). The surface featuresndicate the formation of hexagonal platelets or flower shapedrystals on selected areas. Similar type of hexagonal thin platesas also observed by Korshin et al. [27] on the surface of leadedrass from organic-free water. Based on the similarity in shape

nd morphology of the crystals that form on the surfaces of leadnd lead–tin solder in organic-free water, they have suggestedhat the hexagonal crystals formed on the surface of leaded brass

140 S. Kumar et al. / Materials Chemistry and Physics 106 (2007) 134–141

F3

iiuotacsial

sitHofiTcbih

F3

ciT0tctztLcfitt3apt

ig. 8. SEM image of the surface of leaded brass after immersion in neutral.5% NaCl solution (pH 6.5) for 2 h: (a) LB1 and (b) LB4.

s hydrocerussite (Pb3(OH)2(CO3)2). Since the electrolyte usedn the present study contains chloride ions, the corrosion prod-cts formed on the surface of leaded brass should also containther lead compounds besides hydrocerussite. Since the forma-ion of such compounds on LB1 and LB4 are evident at selectedreas, it could be presumed that they are formed on or near theorroding lead islets. Hence, it is evident that the decrease inteady state current density at −100 and 0 mV and the decreasen Zn/Cu ratio observed at −100 mV for LB3 and LB4 and forll the four leaded brasses at 0 mV is due to the precipitation ofead compounds on the surface of leaded brass.

Polarization studies of leaded brasses in acidified 3.5% NaClolution (pH 3.0) indicate a cathodic shift in Ecorr and an increasen icorr with increase in lead content from 2.02 to 4.85 wt.%, arend similar to that observed in neutral 3.5% NaCl solution.owever, the active-passive transitions in the anodic segmentsf the polarization curves of all the four leaded brasses in acidi-ed 3.5% NaCl solution indicates the formation of a passive film.he dependence of the passivation range and ipass on the lead

ontent of the alloy strongly supports the involvement of leadased compounds in such films. The increase in Rct with increasen lead content of alloy further supports this view. Badawy andis co-workers [28–32] have also attributed the improvement in

NtRc

ig. 9. SEM image of the surface of leaded brass after immersion in acidified.5% NaCl solution (pH 3.0) for 2 h: (a) LB1 and (b) LB4.

orrosion resistance of leaded brasses observed with the increasen lead content of the alloy, to the increase in passivity of the film.he decrease in average steady state current density at −100 andmV with increase in lead content of the alloy supports the view

hat the surface film that form on leaded brasses could possesompounds of lead. The deviation from the typical dezincifica-ion behaviour and the pronounced dissolution of copper andinc observed in the potential range from −250 to 0 mV is dueo the fact that these potentials are much anodic to the Ecorr ofB1–LB4 in acidic 3.5% NaCl solution. However, the signifi-ant decrease in the Zn/Cu ratio when the potential is increasedrom −250 to 0 mV and the decrease in copper content withncrease in lead content of the alloy could be due to the precipi-ation of lead based compounds. In order to get a better insight,he surfaces of the LB1 and LB4 after immersion in acidified.5% NaCl (pH 3.0) for 2 h were assessed by SEM (Fig. 9(and b)). Fig. 9 makes evident of the formation of hexagonallatelets or flower shaped crystals on selected areas, similar tohat observed on the surface of leaded brasses in neutral 3.5%

aCl solution. Hence, the passivation behaviour observed in

he anodic segment of the polarization curve and, the increase inct, decrease in steady state current density with increase in leadontent of the alloy and, the decrease in Zn/Cu ratio observed

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S. Kumar et al. / Materials Chemi

t −100 and 0 mV, are due to the precipitation of lead basedompounds on the surface of leaded brass.

. Conclusions

In neutral 3.5% NaCl solution, the leaded brasses indicatecathodic shift in Ecorr, an increase in icorr and a decrease inct with increase in lead content from 2.02 to 4.85 wt.%. How-ver, the average steady state current density at −100 and 0 mVecreases with an increase in lead content of the alloy. The typ-cal dezincification behaviour is observed for all the four leadedrasses only at −250 mV whereas a reversal in trend is observedt −100 mV for LB3 and LB4 and for all the four leaded brassest 0 mV. In acidified 3.5% NaCl solution, the active–passive tran-ition observed in the anodic segment of the polarization curvesndicates passivation of the surface of the leaded brass. The pas-ive range, passive current density (ipass) and Rct increases withncrease in lead content of the alloy from 2.02 to 4.85 wt.%. Theverage steady state current density measured at −100 and 0 mVs found to decrease with increase in lead content of the alloy.he typical dezincification behaviour is not observed in acidi-ed 3.5% NaCl solution since the applied potentials are morenodic to the Ecorr of leaded brasses in this medium. The copperontent is higher than zinc and there is a significant decreasen the Zn/Cu ratio when the potential is increased from −250o 0 mV. Scanning electron micrographs show the existence ofead as a separate phase in leaded brass before subjecting it toorrosion and the formation of hexagonal platelets or flowerhaped crystals on selected areas after corrosion. The structuraleparation of lead from the rest of the alloy leads to the forma-ion of galvanic cells and decreases the corrosion resistance ofeaded brasses in neutral 3.5% NaCl solution at potentials closero Ecorr. At potentials anodic to Ecorr in neutral 3.5% NaCl solu-ion and in acidified 3.5% NaCl solution, precipitation of leadased compounds on the surface of leaded brass decreases thextent of corrosion attack and causes a deviation from the typ-cal dezincification behaviour. The precipitation of lead basedompounds induces passivity of the leaded brasses in acidified.5% NaCl solution. This study concludes that increase in leadontent of the leaded brasses could provide an improvementn corrosion resistance only under conditions where com-ounds of lead gets precipitated on the surface and inducesassivity.

cknowledgements

The authors express their sincere thanks to Prof. S.P.ehrotra, Director, National Metallurgical Laboratory (NML),

amshedpur, and Dr. S. Srikanth, Scientist-in-charge, NML

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nd Physics 106 (2007) 134–141 141

adras Centre, for their constant support and encouragemento carry out this work. The authors thank the Director, NML, foriving permission to publish this work.

eferences

[1] H.C. Shih, R.J. Tzou, J. Electrochem. Soc. 138 (1991) 958.[2] M.I. Abbas, Br. Corros. J. 26 (1991) 273.[3] H.M. Shalaby, A. Al-Hashem, M. Lowther, J. Al-Besharah (Eds.), Indus-

trial Corrosion and Corrosion Control Technology, Kuwait Institute forScientific Research, Kuwait, 1996.

[4] G. Quartarone, G. Moretti, T. Bellomi, Corrosion 54 (1998) 606.[5] N. Gane, Philos. Mag. A 43 (1981) 545.[6] Z.M. Sun, M.W. Barsoum, J. Mater. Res. 20 (5) (2005) 1087.[7] M.R. Schock, C.H. Ne, J. Am. Water Works Assoc. 80 (1988) 47.[8] M.C. Gardels, T.J. Sorg, J. Am. Water Works Assoc. 81 (1989) 101.[9] R.G. Lee, W.C. Becker, D.W. Collins, J. Am. Water Works Assoc. 81 (1989)

52.10] E.R. Samuels, J.C. Meranger, Water Res. 18 (1984) 75.11] J.L. Paige, B.S. Covino Jr., Corrosion 48 (1992) 1040.12] R.P. Maas, S.C. Patch, A.F.W. Parker, J. Environ. Health 65 (1) (2002) 9.13] H. Buchler, M. Turpe, Werkstoffe und Korrosion 48 (1997) 813.14] N.H. Lin, A. Torrents, A.P. Davis, M. Zeinali, F.A. Taylor, J. Environ. Sci.

Health: Part A 32 (1997) 865.15] P. Grandjean, Environ. Res. 17 (2) (1978) 303.16] M.J. Ellenhorn, D.G. Barceloux, Medical Toxicology, Elsevier, New York,

1988, p. 1030.17] P. James, M.D. Keogh, Hazardous Materials Toxicology, Williams &

Wilkins, Baltimore, MD, 1992, p. 834.18] A.L. Jadhav, S.V. Kala, Q. Liu, Toxic Substance Mechanisms 14 (1995)

27.19] H.L. Needleman, J.A. Riess, M.J. Tobin, G.E. Biesecker, J.B. Greenhouse,

J. Am. Med. Assoc. 275 (1996) 363.20] J.A. Staessen, H. Roels, R. Fagard, J. Am. Med. Assoc. 275 (1996) 1563.21] World Health Organization, Revision of the WHO Guidelines for Drinking

Water Quality, World Health Organization, Geneva, 1993.22] S. Reiber, J. Am. Water Works Assoc. 83 (1991) 83.23] N.F. Gray, Drinking Water Quality: Problems and Solutions, John Wiley

and Sons, Chichester, 1994.24] S.B. Jung, J. Jpn. Copper Brass Res. Assoc. 33 (1994) 132.25] J.-G. Kim, S.-B. Jung, O.-H. Kwon, Corrosion 57 (4) (2001) 291.26] S.-J. You, Y.-S. Choi, J.-G. Kim, H.-J. Oh, C.-S. Chi, Mater. Sci. Eng. A345

(2003) 207.27] G.V. Korshin, J.F. Ferguson, A.N. Lancaster, Corros. Sci. 42 (2000) 53.28] W.A. Badawy, F.M. Al-Kharafi, Corros. Prevention Control 46 (6) (1999)

149.29] S.S. El-Egamy, A.S. El-Azab, W.A. Badawy, Corrosion 50 (1994) 468.30] W.A. Badawy, S.S. El-Egamy, A.S. El-Azab, Corros. Sci. 37 (1995) 1969.31] R.M. El-Sherif, K.M. Ismail, W.A. Badawy, Electrochim. Acta 49 (2004)

5139.32] K.M. Ismail, R.M. El-Sherif, W.A. Badawy, Electrochim. Acta 49 (2004)

5151.

34] R.H. Heidersbach, E.D. Verink, Corrosion 28 (1972) 397.35] E.D. Verink, R.H. Heidersbach, ASTM STP-516, ASTM, Philadelphia,

1972, p. 303.36] J.Y. Zou, D.H. Wu, W.C. Qiu, Electrochim. Acta 42 (1997) 1733.