Behaviour of Ruthenium in high temperature oxidising conditions

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Behaviour of Ruthenium in high temperature
oxidising conditions
SAFIR interim seminar 20. - 21.1.2005

• Ulrika Backman Ari Auvinen Jorma Jokiniemi
• Maija Lipponen Riitta Zilliacus

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Objective

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

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Experimental facility
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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.

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Experimental matrix
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RuO2 - deposition profile and gas temperature
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SEM images of ceramic tube wall
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TEM image and SAD pattern of RuO2 particle
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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 800C.
• Deposition by thermophoresis at furnace outlet.
• Deposition by decomposition of RuO4 on steel at
  150-200C.
• Deposition decreased by increased furnace
  temperature (faster quench), by seed particles
  and by decreased O2 and RuO3 partial pressures.

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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

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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.

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