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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