Solubility Study in Ag-Cu Binary System Prepared By Ball Milling Process

Transcription

1 Int. J. Nanosc. Nanotechnol., Vol. 8, No. 2, June 2012, pp Solublty Study n Ag-Cu Bnary System Prepared By Ball llng Process S... Shafe *, E. Salah, S. A. Tayeb Fard aterals and Energy Research Center (ERC) (*) Correspondng author: smm_shafee@yahoo.com (Receved:18 ar and Accepted: 23 June 2012) Abstract: Sold solutons of Ag-Cu were prepared va ball mllng process, for about 5-30 h. The Cu-20at%Ag and Cu- 3.64at%Ag composton were nvestgated by X-ray dffracton technque. It was realzed that the sold solublty level could be ncreased by ncreasng the ntal solute content n the mxture. In addton, shfts n peak postons of slver and copper were observed wth mllng tme. The dssoluton volume was estmated by thermodynamc relatons and was compared wth the measured values usng X-ray dffracton technque and t was observed that the measured and calculated volumes agreed well. The fnal dssoluton volume of ltters was calculated by thermodynamc relatonshp. Keywords: copper, slver, sold soluton, mechancal alloyng. 1. INTRODUCTION echancal alloyng process has become a wdely used technque to form powder materals and to synthesze a large range of none-equlbrum phases, from amorphous materals to nanocrystallne phases, to extended sold solutons [1-3]. Sold solublty extensons have been acheved n many alloy systems by non-equlbrum processng methods such as RSP and vapor deposton. Smlarly, mechancally alloyed powders also exhbt extenson of equlbrum sold solublty lmts. In addton to syntheszng stable (equlbrum) sold solutons, t has also been possble to synthesze metastable (non-equlbrum) supersaturated sold solutons by mechancal alloyng startng from blended elemental powders n several bnary and hgher order systems [4-10]. etastable alloys are of great nterest due to ther novel structure, propertes, and applcatons compared to ther equlbrum counter parts. In the present study, the effect of combnaton on sold soluton formaton n Ag-Cu system va mechancal alloyng process was nvestgated. 2- EXPERIENTAL PROCEDURE Cu (ERCK Art No ) and Ag (ALDRICH Art No ) powders were used as startng materals. The powder mxture of Cu-20at%Ag and Cu-3.64at%Ag and hardened steel balls were placed n stanless steel vals hermetcally sealed and mlled n a planetary ball mll. The weght rato of the powders to the balls (BPR) was kept at 1:15 for all experments. Handlng of powders and mllng process were performed under protecton of pure argon gas atmosphere. The vals were rotated at 300 rpm. The mechancally alloyed powders were characterzed by X-ray dffracton method usng CuKa radaton. Average gran szes of Cu and Ag phases were estmated by the peak broadenng of the X-ray dffracton patterns by usng Wlamson Hall method base on the formula (1) [12]. 105

2 Fgure 1: X-ray dffracton pattern of (a): as receved Ag and Cu powders (b): Cu-20 at.%ag (c): Cu-3.64at.% Ag at dfferent mllng tmes 5, 15 and 30 h Fgure 2: The average gran sze of Ag vs. mllng tme 0.9λ bcosq = + 2ηsn q (1) d Where η s stran n lattce, λ s wave length, θ s Bragg angle, b s full-wdth at halfmaxmum (FWH) of the Bragg peaks and d s gran sze. 3- RESULT AND DISCUSSION Increasng the mllng tme of pure slver and copper powders gave rse to the broadenng of the X-ray dffracton peaks and reducng the ntensty of certan peak such as the one at (111). These were due to the formaton of nanometer-sze coherent 106 Shafe, et al.

3 dffracton domans and the accumulaton of lattce defects. However, the peak postons of slver and copper hardly changed wth mllng tme. When aforementoned mechancal mxtures were mlled, local mutual dssoluton processes formed a new face-centered cubc (fcc) phase wth ts (111) peak postoned between the (111) reflectons of Ag and Cu, as shown n Fgure 1. A shft n the dffracton peaks of Cu towards lower angles was the result of an ncrease n lattce constant whch consequently referred to the dssoluton of Ag nto Cu. In contrast a shft n the dffracton peak of Ag towards upper angles suggested a decrease n lattce constant due to dssoluton of Cu nto Ag owng to smaller atomc radus of Cu. It s worth notng that the atomc rad of Cu and Ag are nm and nm, respectvely. The average gran szes of Ag phase n both mxtures were estmated by the peak broadenng of X-ray dffracton peaks and the Wllamson Hall method as shown n Fgure 2. Fgure 4: Dssoluton volume percent accompanyng the formaton of Cu-20%atAg sold soluton 4- THERODYNAICAL INVESTIGATION Gbbs free energy of a soluton may be wrtten as follow [11]: G = RT( X ln a + X ln a ) (eq.1) A A B B Where G s the change n the molar Gbbs free energy by the soluton, x A and xb are the mole fracton of A and B n the soluton, R and T are unversal gas constant and temperature, respectvely and the a denotes actvty. Also: a = X. γ (eq.2) A A A Where γ s the actvty coeffcent. For the component : G = RT ln a (eq.3) Fgure 3: Lattce parameter changes of Cu vs. mllng tmes Fgure 3 depcts the changes n the lattce parameter of Cu as a functon of mllng tme for both mxtures. The quantty s desgnated as G, the partal molar Gbbs free energy of the soluton of. The general thermodynamc relatonshp for the state propertes of a system s applcable to the partal molar propertes of components of a system. Thus, for the component present n a soluton: G P T, Comp = V And for the pure component : (eq.4) Internatonal Journal of Nanoscence and Nanotechnology 107

4 G P 0 T, Comp = V 0 (eq.5) The partal molar volume change accompanyng the formaton of a soluton ( ) s defned as: V G P T, comp = V When x s not a functon of pressure, then: ln γ p T, comp V = RT (eq.6) (eq.7) Fgure 5: Scannng electron mcroscopy (SE) and Cu dot maps of Cu-20 at.%ag powder mlled for 5 h a) BS and b) SE 15h c) BS and d) SE 30h e) BS and f) SE 108 Shafe, et al.

5 In the present study, the dssoluton volume calculated from the thermodynamc relatons was n a good agreement wth the one measured usng the X-ray dffracton. In ths way, shft peak shows change of lattce parameter and volume due to dffuson. In the other hand, the fnal dssoluton volume was calculated usng equaton 7. For calculatng the temperature value, equaton 8 was used. The fnal dssoluton volume was measured to be ltters usng equaton 7. A complete dssoluton was acheved after 30h of mllng, as shown n Fgure 4. Dbal T = T(1 + ) (eq.8) D chm (T =573K, P=1.2atm), T s effectve temperature for alloyng, whch s equvalent to a rse n the temperature of the system to (> T= ambent temperature). Furthermore, t was proposed that T s related to T through the followng relatonshp. Where, Dbal and D chm are the ballstc and chemcal nter dffuson coeffcents, respectvely. It may be ponted out that D chm s exponentally related wth temperature, whle D bal s consdered to be temperature ndependent [13]. Fgure 5 shows SE mages and the Cu dot maps of Cu-20 at. %Ag powder after mllng for dfferent duratons. 5- CONCLUSIONS echancal alloyng process was performed n the Ag-Cu system. It was shown that the sold solublty level rose by ncreasng the ntal solute content n a powder mxture. The shfts n the poston of peaks n the X-ray dffracton patterns were utlzed to determned changes n the lattce parameter values and calculated the sold solublty levels. The fnal dssoluton volume calculated by thermodynamc relatonshps was ltters. Ths calculated volume was n a good agreement wth the one measured by the X-ray dffracton method. The results suggested that XRD patterns could be a relable method n quantfyng the phase transformaton thermodynamcs of sold phases subjected to mechancal alloyng. REFERENCES 1. Koch, C. C., aterals scence and technology, Vol. 15, (1991), p a, E., Atzmon,., ater. Chem. Phys, Vol. 39, (1995), p Shngu, P. H., Ishhara, K. N., ater. Trans. Jap Inst. etals, Vol. 36, (1995), p Suryanarayana, C., Prog ater Sc., Vol. 46, (2001), p Huang, J. Y., Jang, J. Z., Yasuda, H., or, H., Phys Rev B, Vol. 58. (1998), p Duwez, P., Wllens, R. H., Klement, W., Jr. J. Appl. Phys, Vol. 31, (1960), p Benjamn, J. S., etall. Trans, Vol. 1, (1970), p Zghal, S., Twesten, R. Wu, F., Bellon, P., Acta ater, Vol 50, (2002), p Najafabad, R., Srolovtz, D. J., a, E., Atzmon,., J. Appl. Phys, Vol. 74, (1993), p Johnson, W. L., Prog. ater. Sc, Vol. 30, (1986), p Gaskell, D. R., Introducton to Thermodynamcs of aterals. 2 nd ed Cullty, B. D., Stoock, S. R., Elements of X-ray Dffracton. 3 rd ed Pab, S. K., Das, D., ahapatra, T. K., anna, I., Actaater, Vol. 46, (1998), p Internatonal Journal of Nanoscence and Nanotechnology 109

6 110 Shafe, et al.