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Intermetallics 45 (2014) 1e4

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Intermetallics

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Single phase synthesis of g-brass (Cu5Zn8) nanoparticles by electricarc discharge method and investigation of their orderedisordertransition temperature

Mansoor Farbod*, Alireza MohammadianPhysic Department, Shahid Chamran University, Ahvaz, Islamic Republic of Iran

a r t i c l e i n f o

Article history:Received 29 July 2013Received in revised form10 September 2013Accepted 21 September 2013Available online 12 October 2013

Keywords:A. Nanostructured intermetallicsB. Phase transformationB. Alloy designF. Diffraction

* Corresponding author. Tel./fax: þ98 6113331040.E-mail address: farbod_m@scu.ac.ir (M. Farbod).

0966-9795/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.intermet.2013.09.012

a b s t r a c t

Single phase g-brass (Cu5Zn8) nanoparticles were synthesized using the electric arc discharge method.The effect of various arc currents and pressures on the size and phase purity of the CueZn alloy wasstudied. The arc currents of 200, 300 and 400 A and chamber pressures of 1, 2 and 3 atm of Ar wereexamined. The samples were characterized using XRD and SEM measurements. The results showed thatthe spherical nanoparticles of Cu5Zn8 with a mean particle size of 21 nm were produced at a pressure of1 atm and an arc current of 300 A. Post annealing and quenching of the samples were used to investigatethe order disorder phase transformation temperature of Cu5Zn8 in the nanosized form. The XRD analysesshowed that the disorder phase starts at 400 �C and completes at 480 �C which is different from the bulkbrasses.

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1. Introduction

Alloys which are composed of a metal and one or more otherelements have often superior properties from than the constituents[1]. The properties of the alloys can be improved by their fabrica-tion in the nanosized form. Reducing the particle size is a newapproach to improve different properties of a material which hasbeen the subject of nanotechnology in recent years [2]. Nano alloyscan be recognized as a class of alloys with a particle size in thenanoscale [3]. The nano alloys, due to the quantum size and surfaceeffects, can have improved properties compared to the bulk alloys[4]. Also the nanoscale phase transitions have generated muchattention especially due to the size-dependence of material prop-erties and their impact on the performance of nanoscale devices[5]. Brass is an alloy of copper and zinc whose properties can bevaried depending on the weight percentages of copper and zinc.Brasses are widely used in many applications because of theirexcellent electrical and thermal conductivities, corrosion resistanceand non-magnetic properties [6].

By now, several fabrication methods have been used for thepreparation of brass nanoparticles including wire electrical explo-sion [7], mechanical alloying [8], laser ablation [9] and arc discharge

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[3]. In these methods always a mixture of different brass phasessuch as a, b, g and 3has been obtained [7e9]. The arc dischargemethod is a technique which has the potential to produce nano-particles by optimizing different parameters such as the arcdischarge current, the arc chamber atmosphere, the chamberpressure etc. [10].

Here we report the fabrication of single phase g-brass (Cu5Zn8)with the phase purity of more than 98%. The samples were char-acterized by SEM using a Leo, 1455 VP scanning electron micro-scope and XRD using a PW-1840 Philips diffractometer at roomtemperature utilizing Cu Ka radiation (wavelength of l ¼ 1.5418�A).The peak position and intensities were taken between 20 and 80�

with a velocity of 0.02�/s. In order to determine the orderedisordertransition temperature, first the samples were annealed at a certaintemperature and then quenched to room temperature.

2. Experimental

In order to fabricate CueZn alloy by arc discharge method, firstthe electrodes using pure Cu and Zn powders with a phase purity ofw99.99% and at a weight present of Cu (61%)-Zn (39%) were pre-pared. The powders were mixed and pressed into a bar shapedelectrode by pressing them using a mini-press. Cylindrical barswith diameter of 6 mm and different lengths (2e3 cm) were pre-pared under 410MPa pressure and used as both anode and cathode.The arc system was a home-made cylindrical and multi-port

Fig. 1. SEM image of Cu5Zn8 samples, formed at 1 atm of Ar and arc currents of a) 200,b) 300 and c) 400 A.

Table 1Mean particle size of the prepared nanoparticles at different conditions.

Pressure (atm.) Arc current (A) Mean particle size (nm)

1 200 330 (73 nm particles on them)1 300 211 400 215 (66 nm particles on them)2 200 1862 300 230 (34 nm particles on them)2 400 1753 200 1753 300 190 (26 nm particles on them)3 400 145 (35 nm particles on them)

M. Farbod, A. Mohammadian / Intermetallics 45 (2014) 1e42

stainless steel chamber [11]. The cathode was fixed but the anodecould continuously move to keep a constant distance of about1 mm between the electrodes. When the arc discharge is formed,an intensive evaporation of electrodes into the chamber environ-ment occurs and layer of product powders are deposited on theinner walls of the chamber. Due to the consumption of the anodeduring the arc formation, the anode was moved towards thecathode by a DC motor. Depending on the arc parameters, differentproducts were formed which were collected for characterization.

In order to find the optimum fabrication conditions for pro-ducing CueZn alloy nanoparticles, the experiments were per-formed at 1, 2 and 3 atm pressures of pure Ar under electricalcurrents of 200, 300 and 400 A. The formation of the arc either inoxygen or in air caused the production of ZnO as the main impurityphase.

It is known that brass is one of the simplest alloys exhibitingorderedisorder phenomena [12]. The orderedisorder transition forbrasses in the bulk form occurs at 454e468 �C [13]. To find whethersuch a transition and at what temperature occurs for g-brass innanoparticle form, the nanoparticles of Cu5Zn8 were annealed attemperatures of 400, 420, 440, 460, 480, 500 and 600 �C for 3 h inAr and then were quenched to room temperature. The phasetransition then was examined by XRD measurements.

3. Results and discussions

3.1. SEM analyses

Fig. 1 shows the SEM image of samples which were prepared at1 atm of Ar under arc currents of 200, 300 and 400 A. The meanparticle sizes of the prepared nanoparticles at different conditionsare listed in Table 1. As can be observed the particle size isdependent on the conditions and at 1 atm pressure and an arccurrent of 300 A the average size of the nanoparticles is about21 nm. Under these conditions the nanoparticles are spherical andthe particle size distribution is nearly uniform. For higher pressuresit seems that the size of the nanoparticles is not dependent on thearc current and the mean particle size is ranging between 145 and230 nm.

3.2. Sample’s phase identification

In order to identify the phase composition of the products, XRDpatterns of all samples were recorded. Fig. 2 shows the XRD pat-terns of the samples prepared at 1 atm pressure of Ar underdifferent currents of 200, 300, and 400 A. The samples preparedunder a current of 300 A, exhibit only reflections of Cu5Zn8 (JCPDS010710397) and there are only a very small traces of Cu (%61)-Zn (%39) and ZnO in the patterns.

The approximate percentage of the different phases was calcu-lated using the following relation [14].

xphaseð%Þ ¼P

IðxphaseÞA �100 x¼ Cu5Zn8;Cuð0:61ÞZnð0:39Þ;ZnO

A¼PIðCu5Zn8;Cuð0:61ÞZnð0:39Þ;ZnOÞ

where, I is the intensity of different peaks.The calculated phase percentages of the prepared nanoparticles

are listed in Table 2. One can observe, at all conditions, that Cu5Zn8is the major phase but a maximum phase purity of 98.8% was ob-tained for the samples prepared at 1 atm of Ar under a current of300 A. This is an interesting result because by other fabricationmethods a mixture of different phases including a, b, g, and 3hasbeen obtained. It is to be noticed that although the wt.% of Cu in theelectrodes was higher than that of Zn, the final product was Cu5Zn8

Fig. 2. XRD patterns of Cu5Zn8 nanoparticles produced under currents of 200, 300 and400 A at 1 atm pressure of Ar. Fig. 3. XRD pattern of Cu5Zn8 nanoparticles quenched from different temperatures.

M. Farbod, A. Mohammadian / Intermetallics 45 (2014) 1e4 3

with a higher wt.% of Zn. We found that some of the Cu powdermelts and drops during the arc formation and doesn’t participate inthe final product.

3.3. Nanoparticles phase transformation investigation

As it is known the order and disorder phases are distinguish bysuperstructure reflections. By transforming from the order to thedisorder phase, some peaks which are called superstructure linesdisappear in the XRD patterns [13]. Fig. 3 shows the XRD patterns ofCu5Zn8 nanoparticles after annealing at different temperatures andthen quenched to room temperature. By comparing the pattern ofthe quenched samples with that of the as prepared sample, one canobserve that by quenching from 400 �C, a small peak at 45.6� in thedisordered samples disappeared but a small peak of ZnO appears at34.4�. By increasing the quenching temperature up to 480 �C thepeaks at 37.90�, 52.52�, 64.56�, 34.99�, 48.01�, 71.95�, 73.81� and50.35� disappear and only 4 main peaks of Cu5Zn8 at 43.41�, 56.72�,62.97� and 79.48� remain.

By further increasing the quenching temperature no more peakdisappearance was observed which means that the disorder phaseis almost completed at 480 �C. By post annealing of the samples athigher temperatures, the trace of ZnO as the main impurity phaseappeared. At 500 �C and higher, a trace of Cu0.61Zn0.39 (a-brass) wasalso observed.

The lattice constant evolution of Cu5Zn8, which has cubicstructure, during the orderedisorder transition, was calculated byusing the XRD data. The results showed that by increasing the

Table 2Phase percentage of the prepared nanoparticles at different conditions.

Pressure (atm.) Arc current (A) Cu5Zn8 (%) Cu0.61Zn0.39 (%) ZnO (%)

1 200 94 3 31 300 99 0 11 400 99 0 12 200 87 9 42 300 97 2 12 400 92 4 43 200 90 6 43 300 92 6 23 400 93 4 3

quenching temperature and growing the disorder phase, the latticeconstant increased from 8.884 �A to a maximum of 9.004 �A whenthe sample was quenched from 500 �C. This means that the mi-crostructures and possibly other features are depended on the or-deredisorder transition.

4. Conclusions

Single phase g-brass (Cu5Zn8) nanoparticles were producedusing arc discharge method which is important in large scale pro-duction. XRD analysis showed that at all conditions, the majorityphase was Cu5Zn8 with a maximum phase purity of 98.8% wasobtained for the samples which were produced at 1 atm of Ar undercurrent of 300 A. The SEM results showed that the average particlesize under these conditions was 21 nm. The investigations alsoshowed that the disorder phase started to grow at 400 �C andalmost completes at 480 �C, different from the bulk brasses. Duringthis transition the lattice constant increased.

Acknowledgment

The authors acknowledge Shahid-Chamran University of Ahvazfor financial support of this work and Dr Ranjbar for his helps.

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