Einleitung

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

2. 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

3. 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 5.9 g/cm³ 7.03 g/cm³ 0 - 10 GPa bct Sn-I 10 - 45 GPa bct Sn-II 45 - >120 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 (>10 GPa) fcc

4. 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

5. 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 > 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.

6. 2Q 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.

7. collimator ↓ ceramic spacer → ←thermocouple HP cell → 2. Disproportionation of SnO at ambient pressure ←heating band ↓ Al foil

8. 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)

9. 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.

10. 2. Disproportionation of SnO at ambient pressure At high T (>370 °C) the reaction is dominated by thermal disproportionation. Sn2O3 is produced. At low T (< 250 °C) SnO decomposes due to the synchrotron radiation(!) to nanocrystalline SnO2 and Sn. No Sn2O3 is produced.

11. 2. Disproportionation of SnO at ambient pressure Sharp-Hancock plot of the reaction progress a

12. 2. Disproportionation of SnO at ambient pressure • up to ca. 275 °C the • in situ reaction is radiation induced • above 370 °C the in situ reaction • is mainly thermal induced Arrhenius: k = A exp(-EA/RT) „activation energy EA“ radiation induced range : 27(2) kJ/mol thermal induced range: 225(32) kJ/mol

13. t = 180 s t = 615 s t = 825 s t =1020 s t =1220 s t =1425 s t =1620 s 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

14. 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

15. 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

16. 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

17. 3. Disproportionation of SnO at high pressure Sharp-Hancock plot of m: reaction exponent k: reaction rate a: reaction progress

18. 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

19. 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).

20. 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)

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