Thermal Stability of Tin Nanopowder Prof. RNDr. Jan Vřešťál, DrSc., Doc. RNDr. Jiří Pinkas,...

Thermal Stability of Tin Thermal Stability of Tin NanopowderNanopowder

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

CALPHAD methodCALPHAD method

f

PhPhtot GwG

...... G G G G surfmagEid0Ph GGyi

Phii

-- Gibbs energies of pure components in different structures ( oGiPh)

-- Mixing terms (Gid, GE) and special terms (Gmag, Gsurf…)

Gsurf is of crucial importance in nanoscaleInput data for CALPHAD method

Solution: Minimization of Gtot (closed system, p,T – konst.)Output: Phase diagram (phase stability regions) – programs - TC

It is supposed, it is valid for r

>3nm ( > 1000 atoms)

Gibbs energy of surface: GGibbs energy of surface: Gsurfsurf

Gibbs energy of surface of 1 mol of substance: Gsurf = S.n. = (3Mr /) (1/r) (spherical particles, n = (rM/r)3)

Equilibrium at T: Gliq – Gsol = 0 Gbulk

liq +Gsurfliq – (Gbulk

sol +Gsurfsol)= 0

(Gbulkliq – Gbulk

sol) = Hm - SmT

(Gsurfliq – Gsurf

sol) = 3Mr (1/r) [( /) liquid - ( /) solid ]

Example: Calculation of T: (1/rliquid=0)

T = Tm - 3Mr (Tm/ Hm) (-1/rsolid) [( /) liquid - ( /) solid ]

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

Influence of substrate on the melting Influence of substrate on the melting temperature of nanoparticlestemperature 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)

DSC - nano Sn, atmosphere N2, 4NSigma-Aldrich: Tin nanosize activated powder 99.7 %, Average particle size: 100nm, Ord.No:57,688-3

exo

DSC - nano Sn, atmosphere N2 + 5%H2

(T,onset = 210 oC)

DSC - nano Sn, atmosphere Ar, 5NDSC - nano Sn, atmosphere Ar, 5N

Run 1Run 1

Run 2,3

DSC - bulk Sn, atmosphere Ar, 5NDSC - bulk Sn, atmosphere Ar, 5N

Run 1

Run 2,3

Nanoparticles of tin before heatingNanoparticles of tin before heating

100 nm

DistributionDistribution of particle of particle size before size before heating heating

0 40 80 120 160 200D ia m e te r o f p a rtic le s / n m

0

40

80

120

N p

art

icle

s

0 40 80 120 160 200D ia m e te r o f p a rtic le s / n m

0

20000

40000

60000

80000

100000

V o

f pa

rtic

les

/ .1

0-3

nm

3

N particlesV particles / .10-3 nm3

Diameter of particles / nm Diameter of particles / nm

Nanoparticles of tin after heatingNanoparticles of tin after heating

100 nm

DistributionDistribution of particle of particle size size after heatingafter heating

0 20 40 60 80 100 120

0

100

200

300

400

N partic les

D iam eter o f partic les / nm

0 20 40 60 80 100 120

0

20000

40000

60000

V of partic les / .10 -3 nm 3

D iam eter of partic les / nm

DSC - nano Sn, atmosphere Ar, 5NDSC - nano Sn, atmosphere Ar, 5N(repeated)(repeated)

Run 1Run 1

Run 2,3

powdered sample after heating in all cases

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