Thermal Stability of Tin Nanopowder

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Thermal Stability of Tin Nanopowder

• Prof. RNDr. Jan Vretál, DrSc.,
• Doc. RNDr. Jirí Pinkas, Ph.D.,
• Masaryk university Brno,
• Czech Republic
• RNDr. Ale Kroupa, CSc.,
• Institute of Physics of Materials AS CR Brno,
• Czech Republic

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CALPHAD method

• - Gibbs energies of pure components in different
  structures ( oGiPh)
• - Mixing terms (Gid, GE) and special terms (Gmag,
  Gsurf)
• Gsurf is of crucial importance
  in nanoscale

Input data for CALPHAD method
It is supposed, it is valid for r ?gt3nm (? gt 1000
atoms)
Solution Minimization of Gtot (closed system,
p,T konst.) Output Phase diagram (phase
stability regions) programs - TC
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Gibbs energy of surface Gsurf

• 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
• Gbulkliq Gsurfliq (Gbulksol Gsurfsol) 0
• (Gbulkliq Gbulksol) ?Hm - ?SmT
• (Gsurfliq Gsurfsol) 3Mr (1/r) (? /?) liquid
  - (? /?) solid
• Example
• Calculation of T (1/rliquid0)
• T Tm - 3Mr (Tm/ ?Hm) (-1/rsolid) (? /?) liquid
  - (? /?) solid

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Au

• Dick K. et al., JACS 124 (10), 2312-2317 (2002),
  Au
• Crosses Calculation - Estimation Au (Buffat,
  Borel)
• (? /?) liquid 0,74/173004,28.10-5
  
• (? /?) solid 0,90/190004,74.10-5

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Influence of substrate on the melting temperature
of nanoparticles
31 (2007) 105-111
Melting temperature of gold nanoparticles (rgt5nm)

• Graphite substrate
• Tungsten substrate

Role of substrate only when it shows good
wettability
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DSC - nano Sn, atmosphere N2, 4N Sigma-Aldrich
Tin nanosize activated powder 99.7 , Average
particle size 100nm, Ord.No57,688-3
exo
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DSC - nano Sn, atmosphere N2 5H2(T,onset
210 oC)
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DSC - nano Sn, atmosphere Ar, 5N
Run 2,3
Run 1
Run 1
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DSC - bulk Sn, atmosphere Ar, 5N
Run 2,3
Run 1
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Nanoparticles of tin before heating
100 nm
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Distribution of particle size before heating
N particles
V particles / .10-3 nm3
Diameter of particles / nm
Diameter of particles / nm
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Nanoparticles of tin after heating
100 nm
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Distribution of particle size after heating
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DSC - nano Sn, atmosphere Ar, 5N(repeated)
powdered sample after heating in all cases
Run 2,3
Run 1
Run 1
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• 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