Behaviour of Ruthenium in high temperature oxidising conditions

1. SAFIR interim seminar 20. - 21.1.2005 Behaviour of Ruthenium in high temperature oxidising conditions Ulrika Backman & Ari Auvinen & Jorma Jokiniemi & Maija Lipponen & Riitta Zilliacus

2. Objective Quantify the effect of • Oxygen partial pressure • Oxidation temperature • Tube material on ruthenium release, transport and speciation

3. Experimental facility

4. Methods • Solid RuO2 particles were collected on plane filters. • Gaseous RuO4 was trapped in 1M NaOH-water solution. • Filters and precipitates were analysed with INAA (detection limit 2g/sample). • NaOH solution was analysed using ICP-MS (detection limit 0.05g/l). • Deposition profile was measured using radiotracer technique (Ru103 -isotope) • RuO2 particle morphology was determined with TEM. • RuO2 particle crystallinity determined with SAD. • RuO2 deposit morphology was studied with SEM.

5. Experimental matrix

7. RuO2 - deposition profile and gas temperature

8. SEM images of ceramic tube wall

9. TEM image and SAD pattern of RuO2 particle {110} {101} <112>

10. Conclusions (1/2) • Ruthenium release • Released mainly as RuO3, 5% released as RuO4. • Approximately constant 9-11 mg/min in air flow at 1500 K. • Release rate decreases as O2 partial pressure decreases. • Release rate increases with oxidation temperature. • Ruthenium deposition • Very significant (65-88%). • Deposition by RuO3 to RuO2 reaction at 800°C. • Deposition by thermophoresis at furnace outlet. • Deposition by decomposition of RuO4 on steel at 150-200°C. • Deposition decreased by increased furnace temperature (faster quench), by seed particles and by decreased O2 and RuO3 partial pressures.

11. Conclusions (2/2) • Transport of gaseous ruthenium • In dry experiments with stainless steel tube: 0.1 - 0.2 % • Fraction was independent of release temperature, oxygen partial pressure and concentration of ruthenium • Probably due to the catalytic effect of the stainless steel tube surface on the decomposition of RuO4 to RuO2 • Using alumina tube: 5% • Comparable to the fraction given by thermodynamic equilibrium • RuO2 seems not have a strong catalysing effect on the decomposition of RuO4. • When atmosphere contained some water: 5 % • Most likely the water vapour passivated the stainless steel tube surface

12. Further experiments • The effect of water vapour on Ru release and speciation • With and wo. seed particles. • Variable steam partial pressure. • The effect of seed particles on Ru transport • In dry conditions. • Variable particle number concentration. • Time dependence of Ru release rate and speciation • Online experiments with radioactive ruthenium. • Catalytic decomposition of RuO4 by RuO2 • Experiments with and wo. filters doped with RuO2.