1. Thermal Stability of Tin Nanopowder Prof. RNDr. Jan Vřešťál, DrSc., Doc. RNDr. Jiří Pinkas, Ph.D., Masaryk university Brno, Czech Republic RNDr. Aleš Kroupa, CSc., Institute of Physics of Materials AS CR Brno, Czech Republic

3. CALPHAD method CALPHAD method - - Gibbs energies of pure components in different structures ( o G i Ph ) - - Mixing terms (G id, G E ) and special terms (G mag, G surf …) Gsurf is of crucial importance in nanoscale Input data for CALPHAD method Solution: Minimization of G tot (closed system, p,T – konst.) Output: Phase diagram (phase stability regions) – programs - TC It is supposed, it is valid for r  >3nm (  > 1000 atoms)

4. Gibbs energy of surface: G surf Gibbs energy of surface of 1 mol of substance: G surf = S.n.  = (3M r  /  ) (1/r) (spherical particles, n = (r M /r) 3 ) Equilibrium at T: G liq – G sol = 0 G bulk liq +G surf liq – (G bulk sol +G surf sol )= 0 (G bulk liq – G bulk sol ) =  H m -  S m T (G surf liq – G surf sol ) = 3M r (1/r) [(  /  ) liquid - (  /  ) solid ] Example: Calculation of T : (1/r liquid =0) T = T m - 3M r (T m /  H m ) (-1/r solid ) [(  /  ) liquid - (  /  ) solid ]

5. Dick K. et al., JACS 124 (10), 2312-2317 (2002), Au Crosses: Calculation - Estimation – Au (Buffat, Borel): (  /  ) liquid = 0,74/17300=4,28.10-5 (  /  ) solid = 0,90/19000=4,74.10-5 Au

6. Influence of substrate on the melting temperature of nanoparticles a) Graphite substrate b) Tungsten substrate Role of substrate only when it shows good wettability 31 (2007) 105-111 Melting temperature of gold nanoparticles (r>5nm)

7. DSC - nano Sn, atmosphere N 2, 4N Sigma-Aldrich: Tin nanosize activated powder 99.7 %, Average particle size: 100nm, Ord.No:57,688-3 Ord.No:57,688-3 exo

8. DSC - nano Sn, atmosphere N2 + 5%H2 (T,onset = 210 o C)

9. DSC - nano Sn, atmosphere Ar, 5N Run 1 Run 2,3

10. DSC - bulk Sn, atmosphere Ar, 5N Run 1 Run 2,3

11. Nanoparticles of tin before heating 100 nm

12. Distribution of particle size before heating N particles V particles /.10 -3 nm 3 Diameter of particles / nm

13. Nanoparticles of tin after heating 100 nm

14. Distribution of particle size after heating

15. DSC - nano Sn, atmosphere Ar, 5N (repeated) Run 1 Run 2,3 powdered sample after heating in all cases

16. Summary - - Simple considerations taking into account surface energy in phase equilibrium calculations were presented - - Literature examples confirming these theoretical results are shown, complemented by own preliminary experimental results - Challenge to exploit these results in industrial practice is raised (e.g.soldering at very low temperatures); - Problem of surface oxidation of Sn nanoparticles should be solved