Phase Diagram Evaluations: Section II The Ag-Bi (Silver-Bismuth) System L Karakaya Middle East Technical University and W.T. Thompson Royal Military College of Canada Equ i l ib r ium D iagram The equilibrium condensed phases of the Ag-Bi system under atmospheric pressure are a liquid, L, and two solids, (Ag) and (cd3i). The system is a eutectic type with very little solid solu- bility in the Ag-rich solid and no detectable solubility in the Bi- rich solid. The assessed Ag-Bi phase diagram is shown in Fig. 1 and is very similar to [Hansen], [76Pre], and [76Zim]. The liquidus has been determined by thermal analysis [1894Hey, 1897Hey, 06Pet] over the entire composition range. In addition, Ag-liquidus determinations were made by equili- bration of liquid alloys with solid (Ag) followed by melt analy- sis [56Kle, 62Natl. The comparison with the liquidus proposed in this evaluation is shown in Fig. 2. The measured Bi-liquidus [1894Hey] is lower than the as- sessed diagram by -4 ~ for pure Bi, [1894Hey] reported a melting point of 267.87 ~ compared with the accepted value of 271.442 ~ [Melt]. This evaluation accepts the freezing point depression of [1894Hey] but adjusts the temperatures upward to coincide with the accepted melting point. The solid solubility of Bi in (Ag) was estimated to be -3 at.% on the basis of X-ray work [31Bro]. Lattice parameter measurements of alloys at the temperature extremes of 200 and 259 ~ yielded solubilities of 0.312 and 0.784 at.% B i, re- spectively [40Chi]. More extensive studies of Bi solubility involving both micrographic and lattice parameter measure- ments between 266 and 900 ~ were conducted by [46Rau]. Bi solubility in (Ag) was studied by thermoelectric power and lattice parameter measurements over the temperature range 300 to 900 ~ [75Gla, 83Ako]. Recently, electron probe mi- croanalysis (EPMA) of the Ag-rich phase quenched from 650 to 925 ~ in the two-phase region was reported [88Sch]. The solidus and solvus lines for the Ag side recommended in this evaluation are compared with all of the foregoing reported data in Fig. 3. The solidus line through the data points is based mainly on estimated thermodynamic data for the Ag solid so- lution. This is discussed in the "Thermodynamics" section. The projected solubility of Bi at 30 ~ is 0.004 at.%. On this basis, it appears that the solubility of 0.16 at.% reported by thermoelectric power measurement by [67Poi] at 30 ~ is ex- cessive. A systematic determination of Ag solubility in (ctBi) was not found in the literature. Negligible solubility was reported in electrodeposited alloys [50Rau]. The eutectic was reported to be at 262 ~ and 94.95 at.% Bi by [48Haj] and at 262.5 ~ and 95.05 at.% Bi by [62Nat]. The lat- ter value is accepted in this assessment. Metastab le Phases Supersaturated metastable (Ag) alloys can be prepared. One- phase electrodeposited alloys with up to 2.2 at.% Bi at 25 ~ were reported by [76Fer]. The same author claims up to 4.4 at.% Bi solubility can be obtained by quenching liquid alloys with more than 80 at.% Ag. [82Zho] obtained 2.25 at.% Bi solubility on rapid cooling of eutectic liquid. A metastable hexagonal ~-phase containing 12 to 16 at.% Bi was reported by [76Fer]. The same author reported that it de- composed exothermally (in the order of 1 kJ/g-atom) in the range 100 to 120 ~ Ahexagonal phase with similar lattice pa- rameters to those of [76Fer] was obtained by [76Pre] on rapid cooling of liquid alloys with more than 20 at.% Bi. In addition, [76Pre] reported a Bi-rich orthorhombic metastable phase with more than 85 at.% Bi when alloys with more than 50 at.% Bi were quenched. A phase with the formulation AgBi 2 was obtained at the Ag-Bi interface by subjecting alloys to pressures of-4000 kPa [66Mat]. Table 1 Ag-Bi Crystal Structure Data Composition, Pearson Space Strukturbericht Phase at.% Bi symbol group designation Prototype Reference (Ag) .............................................. 0 to 2.76 (cr, Bi) ............................................. 100 (~Bi) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 Metastable phases AgBi 2 ............................................ 66.67 ~-phase .......................................... 12 to 16 cF4 Fm'3m A 1 Cu [Kingl ] hR2 R'3m A7 txAs [Kingl] (a) C2/m . . . . . . [67Bru] mC4 C21m ... I~Bi [Ivlassalski2] . . . . . . . . . [66Mat] ibi . . . . . . . . . t76Fe,l (a) Monoclinic, high-pressure allotropic form of Bi at 26 kbar; 4 atoms/cell [67Bru]. Ca) Hexagonal [76Fer]. Journal of Phase Equilibria Vol. 14 No. 4 1993 525 Sect ion H: Phase D iagram Eva luat ions 0 i000 961.93'C 10 20 30 40 Weight 5O Percent B ismuth 60 70 80 90 lO0 o Q) c~ E-- 8oo i 600 400- Z00--p,--r---- 0 Ag 0 1000 L 961.93"C L 262.5"C 10 20 30 40 50 60 70 Atormc Percent B ismuth 80 Atomic Percent B ismuth ao 30 40 8o 60 70 95.05 (Bi)-- 9o 80 90 271.442"C I00 Bl 100 P E Z--, 800- 600- 400- Fig. 1 ~ 1.9 200- 0 10 Ag Assessed Ag-Bi phase diagram. 262.5~ 20 30 40 50 60 70 80 Weight Percent Btsmuth 97"3 4 (Bi 90 100 Bi Crystal Structures and Lattice Parameters Crystal structures are given in Table 1. Lattice parameters are listed in Table 2. Lattice parameters of electrodeposited meta- stable Ag-rich solid solutions and the metastable hexagonal ~- phase are also included in this table. Thermodynamics Sufficient data in the form of activities and enthalpies of mix- ing for the melt phase are available to permit a computation of the phase diagram when these data are combined with the Gibbs energies of melting for Ag [88Kar] and Bi [84Cha]. 526 Journal of Phase Equilibria Vol. 14 No. 4 1993 Phase Diagrnm Evaluat ions: Sect ion II 0 I000 I 961.93"C 800- o t~ 600- E o 400- 80 30 40 Weight Percent B i smuth 50 60 70 80 1897Hey �9 1894Hey [] 56Kle �9 62Nat - - -Ca lcu la ted L 90 I00 aOo_~L ~ r 0 . 9 9 262.5*C 0 10 20 30 40 50 60 70 AE Atomle Percent B ismuth Fig. 2 Comparison of experimental data with computed and assessed Ag Uquidus. 80 90 271.442"C I00 Bl E-- Weight Percent B i smuth o 10 800- 600 - I A40Chi I �9 62Nat I Q46~u 400 I �9 93Ako , ~ / 0 . 9 9 262.5"C ' ' " . . . . . . i . . . . . . . . . ~ . . . . . . . . . = . . . . . . . . . ~ . . . . . . . . J . . . . . . . . . i . . . . . . . . . r . . . . . . . . . i . . . . . . . . . . . . . . . . . . 2O0 0 Ag 1 2 3 4 5 6 7 Atomic Percent B i smuth 8 9 10 Fig. 3 Solid solubility of Bi in (Ag). Thermodynamic properties of Ag-Bi liquid alloys have been measured calorimetrically [30Kaw, 56Kle, 68Ita, 70Cas], electrochemically [61Gre, 63Ray, 71Pra], and by a vapor pressure method [63Ald]. Analytical expressions for com- Journal of Phase Equilibria Vol. 14 No. 4 1993 527 Sect ion H: Phase Diagram Evaluat ions ?SO0 - -Ca lc �9 S6Kle 70Cas e 0 0 61Gre 0.2 04 0.6 0.~ Atomic Fraction of B~auth Fig. 4 Enthalpy of mixing for liquid Ag-Bi alloys. Used in the com- putation of the phase diagram and compared with measured data. �9 �9 O o Q o 0 0.2 n.~ 0.6 0.8 I Atomic Fractlon of B1s~th Fig. 5 Activities of liquid Ag and Biin the Ag-Bi system. Calculated from Table 3 for I(X)0 K and compared with experimental data. Table 2 Ag-Bi Lattice Parameter Data Composition, Lattice parameters, nm Phase at.% Bi b c Comment Reference Ag ................................................ 0 0.40861 . . . . . . . . . [Kingl ] 0 0.40782 . . . . . . . . . [40Chi] 0 0.40857 . . . . . . . . [Massalski2] 0.260 0.40805 . . . . . . 259 ~ (a) [40Chi] 0.312 0.40809 . . . . . . 259 ~ (a) [40Chi] 0.521 0.40832 . . . . . . 259 ~ (a) [40Chi] 0.521 0.40833 . . . . . 250 ~ (a) [40Chi] 0.3 0.4089 . . . . . . Metastable [76Fer] 0.4 0.4090 . . . . . . Metastable [76Fer] 0.5 0.4091 . . . . . . Metastable [76Fer] 0.7 0.4093 . . . . . . Metastable [76Fer] 0.8 0.4094 ... Metastable [76Fer] 0.9 0.4095 ... Metastable [76Fer] 1.1 0.4097 . . . . . . Metastable [76Fer] 1.3 0.4099 . . . . . . Metastable [76Fer] 1.5 0.4101 . . . . . . Metastable [76Fer] 1.6 0.4102 . . . . . . Metastable [76Fer] 1.7 0.4103 . . . . . . Metastable [76Fer] 1.8 0.4104 . . . . . . Metastable [76Fer] 1.9 0.4105 . . . . . Metastable [76Fer] 2.2 0.4109 . . . . . . Metastable [76Fer] c(Bi ............................................... 100 0.47460 . . . . . . c~ = 57.23 ~ [Kingl , Massalski2] [3Bi Co) ........................................... 100 0.6674 0.6117 0.3304 [3 = 110.33 ~ [67Bru, Massalski2] q-phase .......................................... 12 to 16 0.2998 0.4849 Metastable [76Pre] (a) Anneal ing temperature. Co) High-pressure allolropic form of Bi stable at 26 kbar. position and temperature dependence of excess Gibbs energy were developed from these data in such a way as to provide reasonable agreement with the phase diagram, in particular the Ag liquidus (emphasizing the data of [62Nat]). The resul- tant equation is given in Table 3. The enthalpy of mixing ex- tracted from the excess Gibbs energy equation is compared with the experimental data in Fig. 4. The data of [30Kaw] were rejected because of large discrepancies with all other data. The activities (also derived from the excess Gibbs en- ergy equation in Table 3) are shown in relation to the scatter of experimental measurements in Fig. 5. A simple thermodynamic treatment was applied to handle the limited solid solubility in the ((xAg) phase. The limiting partial excess Gibbs energy of Bi (with respect to pure solid cfl3i) may be expressed by: G~ = 31 500 - 20.6T(K) J/g-atom 528 Journal of Phase Equilibria Vol. 14 No. 4 1993 Phase D iagrnm Eva luat ions : Sect ion 11 Table 3 Ag-Bi Thermodynamic Properties Standard Gibbs energies with respect to the liquid G~ = 0 J/g-atom G~ = 0 J/g-atom G~ = -1218.86 - 90.7247T- 0.4799 x 10-273 + 13.74TINT- 266 500/T J/g-atom G~ rhombohedral)=-13 642.5 - 17.238T- 10.048 • 10-37 2` -0.665 x 10-673 + 7.167TINT+ 831 800/T J/g-atom Thermodynamic properties of the liquid phase AH(L) = (10 500 - 4700XAg - 5500X2Ag) XAgXBI J/g-atom SeX(L) = (3.9 - 4Xgg + 6~Ag)XAgXBI J/g-atom- K Thermodynamic properties of the (Ag) phase (0 < XBi < 0.03) AH(Ag) = 31 500XB, J/g-atom SeX(Ag) = 20.6XBI J/g-atom.K This equation yielded the solidus and solvus lines shown in Fig. 3. This figure shows the relation of the computation to experi- mental data. The excess Gibbs energy was found to agree with data reported from Knudsen effusion studies at 1000 K [88Sch]. The effort to model thermodynamically the phases in the Ag- Bi system in such a way as to yield the measured Ag liquidus was successfully demonstrated that the measured thermody- namic properties for the melt phase are basically correct. How- ever, the computed Ag liquidus does not reproduce [62Nat], in whose precise work we can find no fault. The comparison is shown in Fig. 2. Therefore, in the evaluated diagram, we retain the direct Ag liquidus measurements of [62Nat] together with our calculated Ag solidus and solvus since this seems to offer a reasonable representation of the scatter of measurements for these phase boundaries. Addendnm The Ag-Bi system, contributed by R.P. Elliott and F.A. Shunk, was published in the Bulletin of Alloy Phase Diagrams, 1(2), 62-64 (1980). The present evaluation supersedes that earlier publication. Ci ted References 1894I-Iey: C.T. Heycock and EH. Neville, 'The Freezing Point of Triple Alloys," J. Chem. Soc., 65, 65-76 (1894). (Equi Diagram; Experimen- t ) 1897I-Iey: C.T. Heycock and EH. Neville, "Complete Freezing Point Curves of Binary Alloys Containing Silver or Copper Together with Another Metal," Philos. Trans. R. Soc. (London) A, 189, 25-69 (1897). (Equi Diagram; Experimental; #) 06Pet: G.I. Petrenko, "Alloying of Silver with Bismuth," Z. Anorg. Chem., 50, 136-139 (1906) in German. (Equi Diagram; Experimen- t ) 30Kaw: M. Kawakami, "A Further Investigation of the Heat of Mixture in Molten Metals," Sci. Rep. Tokohu Imp. Univ., 19, 521-549 (1930). (Thermo; Experimental) 31Bro: S.T. Broderick and W.E Ehret,"X-Ray Studyofthe Alloys of Ag with Bi, Sb, and As (I)," J. Phys. Chem., 35, 2627-2636 (1931). (Equi Diagram; Experimental) 40Chi: H.H. Chiswik and R. Hultgren,"An X-Ray Study of the Alloys of Silver with Lead, Bismuth and Thallium," Trans. AIME, 137, 442-446 (1940). (Equi Diagram, Crys Structure;Experimental) 46Rau: E. Raub and A. Engel, "Reverse Saturation Curves in the Sepa- ration of Mixed Crystals from Melts," Metallforschung I, 76-81 (1946) in German. (Equi Diagram; Experimental) 48Haj: O. Hajicek,'q3inary Alloys Containing aEutectic, Hu~ Listy, 3, 265-270 (1948) in Polish. (Equi Diagram; Theory) 50Rau: E. Raub and A. Engel, "Structure of Galvanic Alloy Depositions III. Copper-l_e, ad and Silver-Bismuth Alloys" Z. MetaUkd., 41,485- 491 (1950) in German. (EquiDiagram; Experimental) 56Kle: O J. Klepp a,"Th e Thermodynamic Properties o f the Moderately Dilute Liquid Solutions of Copper, Silver and Gold in Thallium, Lead and Bismuth," J. Phys. Chem., 60, 446-452 (1956). (Equi Diagram, Thermo; Experimental; #) 60Gre: Z. Gregorczyk,"Thermodynamic Characteristics of Liquid Ag- Bi Mixtures," Roczniki Chemii, 34, 621-634 (1960) in Polish. (Thermo; Experimental) 61Gre: Z. Gregorczyk,"I'hermodynamic Characteristics of LiquidAg- Bi Mixtures. II," Roczniki Chemii, 35, 307-316 (1961) in Polish. (Thermo; Experimental) *62Nat: M.W. Nathans and M. Leider, "Studies on Bismuth Alloys. I. Liquidus Curves of the Bismuth-Copper, Bismuth-Silver, and Bis- muth-Gold Systerns," J. Phys. Chem, 66, 2012-2015 (1962). (Equi Diagram, Thermo; Experimental; #) 63Aid: A.T. Aldred and J.N. Pratt, "Vapour Pressure of Liquid Silver + Bismuth Alloys," Trans. Faraday Soc., 59, 673-678 (1963). (Thermo; Experimental) 63Ray: J.B. Raynor,'q'hermodynamics of Silver-Bismuth Alloys,"Ber. Bunsenges., 67, 629-632 (1963). (Thermo; Experimental;#) 66Mat: B.T. Matthias, A. Jayaraman, T.H. Geballe, K. Andres, and E. Corenzwit, "Many More Superconducting Bismuth Phases," Phys. Rev. LetL, 17, 640-643 (1966). (Meta Phases, Crys Structure; Experi- mental) 67Bru: RaM. Brugger, R.B. Bennion, and T.G. Warlton, "Crystal Struc- ture of Bi-ll at 26 kbar," Phys. Lett. A, 24, 714-717 (1967). (Crys Structure; Experimental) 67Po!: D.D. Pollock, "Solubility Limits of Some Silver-Rich Binary Solid Solutions Near Room Temperature," Trans. AIME, 239, 1768- 1770 (1967). (Equi Diagram; Experimental) 68Ira: K. Itagaki and A. Yazawa, "Measurements of Heats of Mixing in Liquid Silver Binary AUoys,"J. Jpn. Inst. MeL, 32,1294-1300(1968) in Japanese. (Thermo; Experimental; #) 70Cas: R. Castanet, Y. Claire, M. Gilbert, and M. Laffitte, "Entropies of Formation of Silver and (Group) B Metal Liquid Alloys," Rev. InL Hautes Temp. Refract., 7, 51-60 (1970) in French. (Thermo; Experi- mental) 71Pra: H.N. Prasad, "I'hermodynamic Investigations in Bismuth-Sil- ver System Using Solid Electrolyte," Banaras Met., 4, 62-64 ( 1971). (Thermo; Experimental) 75Gla: B.M. Glazov and R.A. Akopyan, "Determination of the Retro- grade Solidus in the Ag-Pb and Ag-Bi Systems," Izv. Akad. Nauk SSSR, Met., 1, 162-165 (1975) in Russian. (Equi Diagram; Experi- mental; #) 76Fer: R. Ferro, R. Marazza, R. Capelli, G. Rambaldi, and E Baffi, "Some Metastable Alloys in the Silver-Bismuth System," J. Less- Common Met., 46, 45-50 (1976). (Meta Phases, Crys Structure; Ex- perimental) 76Pre: B. Predel and H. Bankstahl, "Metastable Phases in the Silver- Bismuth System"Z MetaUkd, 67, 793-799 (1976) in German. (Equi Diagram, MetaPhases; Experimental; #) Journal of Phase Equilibria Vol. 14 No. 4 1993 529 Sect ion H: Phase Diagram Evaluat ions 76Zbn: B. Zimmermann, E-T. Henig, and H.L. Lukas,'q'he System Ag- Bi-TI, Calculated from the Optimized Binary Boundary Systems,"Z Metallkd., 67, 815-820 (1976) in German. (Equi Diagram; Compila- tion;#) 82Zho: X. Zhou, J. Jin, Y. Ning, and Z. Zhao, "Metastable Extension of Solid Solubility of Certain Simple Metals or Metalloids in Ag,"Acta Metall. Sin., 18, 534-539 (1982) in Chinese. (Meta Phases; Experi- mental) 83Ako: R.A. Akopyan, S.Kli. Mamedova, and E.R. Kerimov, "A Study of the Retrograde Solidus Curves in the Systems Ag-Pb and Ag-Bi," Izv. V U.Z. Tsvet~ Metall., 6, 83-86 (1983) in Russian. (EquiDiagram; Experimental; #) 84Cha: DJ. Chakrabarti and D.E. Laughlin, "The Bi-Cu (Bismuth- Copper) System," Bull. Alloy Phase Diagrams, 5, 148-155 (1984). (Thermo; Compilation) 88Kar: I. Karakaya and W.T. Thompson, 'The Ag-Pd (Silver-Palla- dium) System," Bull, Alloy Phase Diagrams, 9, 237-243 (1988). (Thermo; Compilation) 88Seh: D. Schmid, V. Behrens, and Th. Hehenkamp, "Thermody- namic Investigations of Solid Silver-Arsenic and -Bismuth Al- loys," Acta Metall., 36, 621-625 (1988). (Equi Diagram, Thermo; Experimental) *Indicates key paper. #Indicates presence of aphase diagram. Ag-Bi evaluation contributed by I. Karakaya, Department of Metallurgical Engineering, Middle East Technical University, Ankara, Turkey 06531 and W.T. Thompson, Department of Chemistry and Chemical Engineering, Royal Military College of Canada, Kingston, Ontario K7K 5L0. This work was sup- ported by a grant from ASM International. Literature searched through 1990. Dr. Thompson is the Alloy Phase Diagram Program Co-Category Editor for binary silver alloys. The thermodynamic computation of the phase diagram was performed with the Facility for the Analysis of Chemical Thermodynamics (F*A*C*T) codeveloped by the senior author. 530 Journal of Phase Equil ibria Vol. 14 No. 4 1993