Kein Folientitel

1
Einleitung
Hochdruck-Kristallographie und Synthese 28.
August 2003
Reaktionskinetik der Disproportionierung von SnO
unter Druck
Hubertus Giefers
Universität Paderborn Department Physik AG
Wortmann
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Survey

• The system tin oxide
• The disproportionation of SnO at ambient pressure
• set up
• analysis of the spectra
• The disproportionation of SnO under pressure
• Summary
• Acknowledgement

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1. The system tin and tin oxide
Sn
SnO
Sn2O3
SnO2
thermodyn. stable
thermodyn. metastable
thermodyn. metastable
thermodyn. stable
7.31 g/cm³
6.4 g/cm³
7.03 g/cm³
5.9 g/cm³
0 - 10 GPa bct Sn-I 10 - 45 GPa bct Sn-II 45 -
gt120 GPa bcc Sn-III
two low pressure phases tetragonal and
orthorhombic
under hydrostatic pressure tetragonal a-PbO at
least to 60 GPa under nonhydrostatic
compression orthorhombic splitting
triclinic structure a phase transition at ca.
9 GPa to unkown structure
high pressure phase (gt10 GPa) fcc
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1. The system tin and tin oxyde under pressure
our high pressure study on SnO to 50
GPa tetragonal orth. splitting z(Sn) was
determined with EXAFS Sn2O3 to 30
GPa triclinic, unkown SnO2 to 50 GPa tetragonal,
orthorhomic, cubic
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2. Disproportionation of SnO at ambient pressure
SnO is metastable and disproportionates to the 2
stable materials SnO2 and Sn at elevated
temperatures.
SnO
T gt ca. 250 C
Sn2O3 Sn
SnO2 Sn
Depending on temperature and also on the
synthesis condition of SnO, the metastable
compound Sn2O3 is formed in the
disproportionation reaction, which decomposes to
SnO2 and Sn at higher temperature.
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2. Disproportionation of SnO at ambient pressure
The disproportionation of SnO was studied ex situ
and in situ with Energy Dispersive X-Ray
Diffraction (EDXRD) at beamline F3 at
HASYLAB/DESY in Hamburg.
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2. Disproportionation of SnO at ambient pressure
?heating band
? Al foil
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2. Disproportionation of SnO at ambient pressure
Sample environment
0.2 mm
irradiated SnO at 131 C 0 GPa after 15 h
Gasket
SnO
decomposed SnO (shape of SR beam)
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2. Disproportionation of SnO at ambient pressure
We analysed the normalized diffraction line
intensities of the 3 samples SnO, Sn2O3 and
SnO2. Sn was liquid or showed no
reproducible line intensities.
We used the fluoreszence lines of Sn to normalize
the bragg peaks. This is an advantage of EDXRD.
A time resolution of 100 s was achieved.
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2. Disproportionation of SnO at ambient pressure
At high T (gt370 C) the reaction is dominated by
thermal disproportionation. Sn2O3 is produced.
At low T (lt 250 C) SnO decomposes due to the
synchrotron radiation(!) to nanocrystalline SnO2
and Sn. No Sn2O3 is produced.
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2. Disproportionation of SnO at ambient pressure
Sharp-Hancock plot of the reaction progress a
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2. Disproportionation of SnO at ambient pressure
Arrhenius k A exp(-EA/RT)

• up to ca. 275 C the
• in situ reaction is radiation induced
• above 370 C the in situ reaction
• is mainly thermal induced

activation energy EA radiation induced range
27(2) kJ/mol thermal induced range 225(32)
kJ/mol
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2. Disproportionation of SnO at ambient pressure

• at beamline F3 it is possible to do angle
  dispersive XRD (ADXRD)
• the CCD camera is from GeoForschungsZentrum
  Potsdam
• with a time resolution of 150 s per frame
• - one test measurement was carried out at ambient
  pressure in the HP cell

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2. Disproportionation of SnO at ambient pressure
ADXRD kinetic study on the disproportionation of
SnO with 2 different SnO samples in the HP cell
at 434 C
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3. Disproportionation of SnO at high pressure
Reaction kinetics under pressure

• - high pressure cell made of a Ti-alloy
• - temperatures up to 500 C can be reached
• temperature at sample position was
• calibrated by the melting points of Pb, Sn, Zn
• diamond flats of 1 mm and 0.5 mm were
• used
• - pressures of 20 GPa were reached
• NaCl or MgO for pressure determination
• (Au was alloyed with Sn)
• - lN2 as pressure transmitting medium

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3. Disproportionation of SnO at high pressure
some examples under pressure
under pressure - no nanocrystalline SnO2 and Sn
at low T - no radiation induced
disproportionation - no production of Sn2O3 under
pressure due to the low crystallographic density
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3. Disproportionation of SnO at high pressure
Sharp-Hancock plot of
m reaction exponent k reaction
rate a reaction progress
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3. Disproportionation of SnO at high pressure
reaction exponent m diffusion m
0.5 phase-boundary 1 nucleation and growth 2

• the reaction kinetic
• changes strongly under
• pressure
• - the reaction exponent m
• is very low at 3 GPa
• in the measured p,T range
• the reaction exponent m
• is T independent

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3. Disproportionation of SnO at high pressure
The reaction rate k of the disproportionation of
SnO depends on the phase of metallic Sn (liquid,
Sn-I, Sn-II).
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4. Summary

• EDXRD provides a tool to study reaction kinetics
  in situ
• even at high pressure
• results are
• reaction rates k and reaction mechanism m
  (nucleation, growth)
• the existence of intermediate products or not
  (Sn2O3)
• the formation of high pressure phases at lower
  pressure (here SnO2-fcc)

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5. Acknowledgement

• - Felix Porsch EDXRD Messungen
• - H.-D. Niggemeier ex situ Proben
• Ulrich Ponkratz ADXRD Messungen