Thermodynamics and Phase Diagram of the Ni-Sb-Sn System Ratikanta Mishra & Herbert Ipser Department of Inorganic Chemistry / Materials Chemistry, University of Vienna, Austria
Traditional Solder Materials As examples: Sn-Pb (62/38 wt.%) 327.5 C 183 C 232 C High-lead solders (up to 90 % Pb) for high-temperature soldering (90/10) eutectic (38/ 62) Pb Sn
Search is on for possible lead-free alloys with melting point between 250 and 400 C. It is now widely agreed that there is no drop-in replacement for the standard tin-lead solders Sn-Sb alloys with additional alloying elements Ag, Cu, Ni can be a possible candidate for new hightemperature solders. The present work deals with the phase diagram and thermodynamic studies Ni-Sb-Sn system
Overview Thermal analysis of Sn-rich corner Phase Diagram Ni-Sb Sb-Sn Sn system at 900 C Thermodynamics of Ni-Sb Sb-Sn Sn system
Thermal analysis of Sn-rich corner Samples : 20 Ni: 0-25 at % Sb: 0 to 25 at % Sn: 95-75 at % Heat Treatment: 3h 7d 12h RT 1050 C 1050 C 200 C 21d quench 200 C 200 C RT Isothermal sections at 200C. DTA XRD EPMA High resolution microscope Isopleths Scheil diagram Liquidus projection
EPMA & XRD Results
DTA results of 80% Sn alloys At % Sb Invariant Temperature ( C) Other Temperature ( C) 0 232.5, -- ---, 800 2.5 232.5, 243 --, 793 5 233, 243 --, 775 7.5 233, 242, 249 248, 743 10 232, 243, 250 263, 684 12.5 233, 244, 251 282, 635 15.0 233, 243, 251 285, 539 17.5 232.5, 243, 252 286, 388 Isopleth for 80 % at Sn 200 C
DTA results of 85% Sn alloys At % Sb Invariant Temperature ( C) Other Temperatur e ( C) 0 231.5, --, -- --, 780 2.5 231.5, 243, -- --, 743 5 232, 244, -- 249, 713 7.5 233, 242, 250 295, 634 10 232, 243, 251 319, 517 12.5 233, 242, 252 --. 344 Isopleth for 85 % at Sn 200 C
Experimental Results: Scheil Diagram Sn-rich corner
Liquidus projection
Phase diagram Ni-Sb-Sn system at 900 Samples : 30 Heat Treatment: RT RT 3h 1050 C 3h 1050 C 7d 2h 1050 C RT Grinding & pelleting 96h 6h 2weeks quenching 1050K 900 C 900 C RT Samples were analyzed by (XRD and EPMA)
XRD data Ni3Sn2-NiSb tie line a ( A) 4.16 4.12 4.08 4.04 4.00 3.96 3.92 (c) (a) 0.0 0.2 0.4 0.6 0.8 1.0 Mole frac. NiSb 5.26 5.24 5.22 5.20 5.18 5.16 5.14 c ( A) c/ /a 1.31 1.30 1.29 1.28 1.27 c/a plot Ni 3 Sn 2 phase as a function of composition 0.0 0.2 0.4 0.6 0.8 1.0 Mole frac. NiSb
Phase diagram Ni-Sb-Sn system at 900 C L1 2 The liquidus phase boundary is being determined by DTA
Thermodynamic Investigation of Ni-Sb-Sn Sn system by Isopiestic Vapor Pressure Method
pure Sb p Sb (T R ) Isopiestic Vapor Pressure Measurement Of Ni-Sn-Sb Sb system Ni-Sn alloys Before equilibration Conditions for Ni-Sn-Sb system fulfilled: pure Sb p Sb (T R ) After equilibration Temp. Reservoir, T R (T S > T R ) pni, p Sn << p Sb an alloy NixSn y Sb z p Sb (T S ) In equilibrium: p Sb (T S ) = p Sb (T R )
Quartz seal Isopiestic Apparatus Ni 3 Sn Quartz outer tube Ni-Sb-Sn alloy Ni 3 Sn 2 Ni 3 Sn 4 (up to 36 crucibles 12 each) Quartz crucible Quartz thermo-well Quartz crucible holder Quartz spacer Quartz reservoir Sb
Two-zone furnace for equilibration S-type thermocouple Stepper motor arrangement for controlled raising of thermocouple Two zone gradient furnace PC based DAS (Data acquisition system)
Furnace characteristics & Temperature profile Sample Temp. (K) 1300 Isopiestic apparatus 1250 1200 ~ 600 mm 1150 1100 1050 979 K 1000 height of the furnace 1200 mm 950 0 50 100 150 200 250 300 350 400 Distance (mm) Sample Temp. (K) 1300 1200 1100 1000 Tr= 979 K Tr=1090 K Tr=1017 K Tr=939 K Tr=1072 K 900 0 100 200 300 400 Distance (mm)
After equilibration quenching of the entire apparatus in cold water
Isopiestic equilibrium curves For Ni3Sn-Sb, Ni3Sn2-Sb and Ni3Sn4-Sb systems Ni 3 Sn-Sb system Ni 3 Sn 2 -Sb system 1350 1275 1200 Tr = 979 K Tr = 1090 K Tr = 939 K Tr = 1072 K 1400 1300 1200 Tr = 979 K Tr = 1090 K Tr= 1017 K Tr = 939 K Tr = 1072 K Ts (K) 1125 Ts, K 1100 1050 1000 975 0.4 0.5 0.6 0.7 0.8 0.9 1300 At. frac. Sb Tr=1017 K Tr= 939 K Tr = 1072 K 900 0.3 0.4 0.5 0.6 0.7 0.8 0.9 At. fraction Sb TS(K) 1200 1100 Ni 3 Sn 4 -Sb system 1000 0.3 0.4 0.5 0.6 0.7 0.8 0.9 At. Fraction Sb
lnp(sbx, Atm) l Vapour pressures antimony 10 0-10 -20-30 -40 Results Ni-Sb-SnSn System evaluation psb psb2 psb4-50 0.0 0.4 0.8 1.2 1.6 2.0 1000/T, K a ( T ) = Sb p = p + Sb, total S K = p p p Sb 2 Sb 4 2 Sb Sb p p 2 4 Sb o Sb ( T ( T S S ) ) a = Sb 4 p p Sb 0 Sb 4 4
Results Ni-Sn-Sb Sb System Partial enthalpies of antimony H Sb can be obtained from the slope of ln(a Sb ) vs. 1/T plot at a fixed Composition. Then the activities are converted into to one common temperature
Ln(a, Sb) 0.0-0.2-0.4-0.6 Results Ni3Sn2-SbSb System xsb=0.55 xsb=0.60 x Sb=0.65 xsb=0.70 XSb=0.75 xsb=0.80-0.8 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10000/T, K Natural logarithm of Sb activity vs. reciprocal temperature for selected compositions in the liquid phase as an example. Composition (At % Sb) ln 1 a P = H ( T ) R Partial Molar Enthalpy of Sb (kj/mol) 0.55 8.97 0.60 7.31 0.65 5.35 0.70 3.07 0.75 1.53 0.80 1.03 P Similar results were also obtained for Ni3Sn And Ni3Sn4 alloys
Integrated Gibbs-Helmholtz Equation: = 2 1 2 1 1 1 ) ( ln ) ( ln T T R H T a T a P P P Natural logarithm of the antimony activity as a function of composition for Ni 3 Sn 2 in the liquid phase at 1150 K; standard state: liquid Sb.
Summary The thermal analysis Sn-rich corner in the Ni-Sb-Sn System was carried out The diagram for 80 and 85 at Sb% isopleth was delineated The Scheil Diagram and the liquidus projections for Sn-rich corner of Ni-Sb-Sn system were determined. The phase diagram for ternary Ni-Sn-Sn system at 900 C is presented Thermochemical data on Ni-Sb-Sn system is being obtained by isopiestic method
Acknowledgements This research is part of the European Research Actions COST 531 and COST MP0602 Financial Support: Marie Curie Foundation (FP7-PEOPLE-IIF-2008, Project No. 234920) and the European Union (COST) for networking.
27