Transcript Kein Folientitel

Einleitung
Hochdruck-Kristallographie und Synthese
28. August 2003
Reaktionskinetik der Disproportionierung von
SnO unter Druck
Hubertus Giefers
Universität Paderborn
Department Physik
AG Wortmann
H. Giefers, Universität Paderborn
Survey
1. The system tin – oxide
2. The disproportionation of SnO at ambient pressure
- set up
- analysis of the spectra
3. The disproportionation of SnO under pressure
4. Summary
5. Acknowledgement
H. Giefers, Universität Paderborn
1. The system tin and tin oxide
Sn
SnO
Sn2O3
SnO2
thermodyn.
thermodyn.
thermodyn.
thermodyn.
stable
metastable
metastable
stable
7.31 g/cm³
6.4 g/cm³
5.9 g/cm³
7.03 g/cm³
0 - 10 GPa
bct Sn-I
under hydrostatic triclinic structure two low pressure
phases:
pressure tetragonal
tetragonal and
a-PbO
a
phase
10 - 45 GPa
orthorhombic
at least to 60 GPa
transition
bct Sn-II
at ca. 9 GPa
high pressure
under nonhydrostatic
to unkown
compression
45 - >120 GPa
phase (>10 GPa)
structure
orthorhombic
bcc Sn-III
fcc
splitting
H. Giefers, Universität Paderborn
1. The system tin and tin oxyde under pressure
1.00
Sn-I + Sn-II (bct)
SnO (st)
SnOx (triclinic)
SnO2 (st)
0.95
V/V0
0.90
our high pressure
study on:
SnO to 50 GPa
tetragonal + orth. splitting
z(Sn) was determined with
EXAFS
0.85
0.80
Sn2O3 to 30 GPa
0.75
triclinic, unkown
0.70
0.65
SnO2 to 50 GPa
0
5
10 15 20 25 30 35 40 45 50 55 tetragonal, orthorhomic,
p (GPa)
snoz_p.opj
cubic
H. Giefers, Universität Paderborn
2. Disproportionation of SnO at ambient pressure
SnO
Sn2O3 + Sn
T > ca. 250 °C
SnO is metastable and
disproportionates to the 2 stable
materials SnO2 and Sn at
elevated temperatures.
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.
H. Giefers, Universität Paderborn
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.
2Q
H. Giefers, Universität Paderborn
2. Disproportionation of SnO at ambient pressure
collimator ↓
←heating band
ceramic spacer →
↓ Al foil
HP cell →
←thermocouple
H. Giefers, Universität Paderborn
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)
H. Giefers, Universität Paderborn
2. Disproportionation of SnO at ambient pressure
SnO
T = 370 °C
Intensity
t = 42000
12000
15000
18000
21000
24000
27000
30000
33000
36000
39000
3000
6000
9000
300 sss
25
30
35
40
45
50
55
60
65
We analysed the
normalized diffraction
line intensities of the
3 samples SnO, Sn2O3
and SnO2. Sn was
liquid or showed no
reproducible
line intensities.
Energy (keV)
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.
H. Giefers, Universität Paderborn
2. Disproportionation of SnO at ambient pressure
At high T (>370 °C) the
reaction is dominated by
thermal disproportionation.
At low T (< 250 °C) SnO
decomposes due to the
synchrotron radiation(!) to
nanocrystalline SnO2 and Sn.
Sn2O3 is produced.
No Sn2O3 is produced.
1.2
1.2
0.8
0.6
0.4
0.2
0.0
SnO
SnO2
SnOx
1.0
Yield fraction
Yield fraction
T = 370 °C
T = 297 °C
1.0
0.8
0.6
0.4
0.2
0
5000
10000 15000 20000 25000 30000 35000
Time (s)
0.0
0
10000
20000
30000
40000
Time (s)
H. Giefers, Universität Paderborn
2. Disproportionation of SnO at ambient pressure
Sharp-Hancock plot of the reaction progress a
1.5
1.0
Avrami-Erofe'ev Plot
SnO
ln(-ln(1-a))
0.5
1.5
1.0
a = 0.2 .. 0.63
a from SnO
0.0
-0.5
-0.5
-1.0
-1.0
-1.5
-1.5
-2.0
-2.0
-2.5
-2.5
-3.0
-3.0
6.0
6.5
434
434
425
416
407
388
370
333
296
268
241
186
131
0.5
0.0
-3.5
5.5
in °C
a = 0.2 .. 0.63
a from SnO2+Sn2O3
7.0
7.5
8.0
8.5
ln( t(s) )
9.0
9.5 10.0 10.5 11.0
-3.5
5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0
ln( t(s) )
avramib.opj
H. Giefers, Universität Paderborn
2. Disproportionation of SnO at ambient pressure
Temperature (°C)
-4
Avrami-Erofe'ev
SnO, SnO2, Sn2O3
ln(-ln(1-a)) = C + m*ln(t)
mit C = m*ln(k)
a = 0.2 .. 0.63
m
300
250
200
0.01
radiation induced
thermal induced
-6
F0
F1
1E-3
EA,r = 25(7) kJ/mol
ln(Ar) = -6.0(2)
-8
EA,t = 166(19) kJ/mol
ln(At) = 21(3)
1E-4
-10
0.8
D2
D3
0.4
0
50
100
150
200
250
300
350
Temperature (°C)
-12
400
450
500
avramib.opj
- up to ca. 275 °C the
in situ reaction is radiation induced
- above 370 °C the in situ reaction
is mainly thermal induced
0.00016
1E-5
359 °C
0.00018
0.00020
0.00022
0.00024
1/RT (mol/J)
0.00026
avramib.opj
Arrhenius:
k = A exp(-EA/RT)
„activation energy EA“
radiation induced range : 27(2) kJ/mol
thermal induced range: 225(32) kJ/mol
H. Giefers, Universität Paderborn
-1
1.2
350
k (s )
A2 : Avrami-Erofe'ev
F0 : Reaktionskinetik 0. Ordnung
F1 : Reaktionskinetik 1. Ordnung
D2 : 2D Diffusion (Zylinder)
D3 : 3D Diffusion (Kugel)
1.6
400
a from SnO and Sn2O3 + SnO2
A2
-1
2.0
450
Disproportionation of SnO
ln( k(s ) )
2.4
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
t =1620
= 825
=1020
=1220
=1425
180 ss
615
H. Giefers, Universität Paderborn
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
yield fraction
1.0
0.8
SnO from
ChemPur
0.6
0.4
SnO
SnO2
0.2
0.0
yield fraction
1.0
0.8
SnO from
Aldrich
0.6
0.4
0.2
0.0
0
500
1000
time (s)
1500
2000
kinetik.opj
H. Giefers, Universität Paderborn
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
H. Giefers, Universität Paderborn
3. Disproportionation of SnO at high pressure
Yield fraction
some examples
under pressure
1.2
p = 5.8 GPa
T = 296 °C
p = 3.3 GPa
T = 296 °C
1.0
0.8
0.6
0.4
0.2
0.0
SnO
SnO2
0
2000
4000
Time (s)
0
2000
4000
Time (s)
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
H. Giefers, Universität Paderborn
3. Disproportionation of SnO at high pressure
Sharp-Hancock plot of a  1  e
  k t m
ln  ln 1  a   m  ln k   m  ln t 
1.0
p(GPa) / T(°C)
2.4/232
3.1/241
4.8/241
5.4/241
5.8/241
8.0/241
8.0/241
4.9/269
2.3/296
3.3/296
3.3/296
4.9/296
5.8/296
5.8/296
6.4/296
11.0/296
14.8/296
3.0/324
3.6/324
2.2/370
SnO2
0.5
ln(-ln(1-a))
0.0
-0.5
-1.0
-1.5
-2.0
5
6
7
8
9
10
m: reaction
exponent
k: reaction
rate
a: reaction
progress
11
ln(t (s))
H. Giefers, Universität Paderborn
3. Disproportionation of SnO at high pressure
reaction exponent m:
diffusion m ≈ 0.5
phase-boundary ≈ 1
nucleation and growth ≈ 2
1.8
m
425 °C
370 °C
324 °C
296 °C
269 °C
241 °C
232 °C
1.4
1.2
1.0
0.8
0.6
0.4
- in the measured p,T range
the reaction exponent m
is T independent
radiation
induced
m
- the reaction exponent m
is very low at 3 GPa
a = 1 - exp (-( k·t ) )
a = 0.2 .. 0.63
1.6
0.2
0.0
- the reaction kinetic
changes strongly under
pressure
0
2
4
6
8
10
12
14
16
p (GPa)
H. Giefers, Universität Paderborn
3. Disproportionation of SnO at high pressure
-5 liquid-Sn
1E-3
-6
-8
-9
-10
-11
Sn-II
Sn-I
425 °C
370 °C
324 °C
269 °C
232 °C
-12
-13
0
1E-4
k (s-1)
ln(k (s-1))
-7
2
4
6
8
10
400 °C
350 °C
296 °C
241 °C
open: ex situ
12
14
1E-5
16
p (GPa)
The reaction rate k of the disproportionation of SnO depends on
the phase of metallic Sn (liquid, Sn-I, Sn-II).
H. Giefers, Universität Paderborn
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)
H. Giefers, Universität Paderborn
5. Acknowledgement
- Felix Porsch: EDXRD Messungen
- H.-D. Niggemeier: ex situ Proben
-Ulrich Ponkratz: ADXRD Messungen
H. Giefers, Universität Paderborn