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Potentiometric sensors for high temperature liquids PART 2

ML 4-1 & ML 4-2. Potentiometric sensors for high temperature liquids PART 2. Jacques FOULETIER Grenoble University, LEPMI, ENSEEG, BP 75, 38402 SAINT MARTIN D’HERES Cedex (France) E-mail: Jacques.Fouletier@lepmi.inpg.fr Véronique GHETTA

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Potentiometric sensors for high temperature liquids PART 2

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  1. ML 4-1 & ML 4-2 Potentiometric sensors for high temperature liquids PART 2 Jacques FOULETIER Grenoble University, LEPMI, ENSEEG, BP 75, 38402 SAINT MARTIN D’HERES Cedex (France) E-mail: Jacques.Fouletier@lepmi.inpg.fr Véronique GHETTA LPSC, IN2P3-CNRS, 53 Avenue des Martyrs, 38026 GRENOBLE Cedex (France) E-mail: Veronique.Ghetta@lpsc.in2p3.fr MATGEN-IV: International Advanced School on Materials for Generation-IV Nuclear Reactors Cargèse, Corsica, September 24 - October 6, 2007

  2. Part 2 Sources of errors in potentiometric cells: - Errors ascribed to the reference electrode - reversibility - reactivity - Errors due to the porous membrane - concentration modification - diffusion potential - Errors due to the solid electrolyte membrane - partial electronic conductivity - interferences - Errors due to the measuring electrode - buffer capacity - mixed potential Case studies: - Oxide ion activity in molten chlorides - Oxidation potential in molten fluorides - Monitoring of oxygen, hydrogen and carbon in molten metals (Pb, Na)

  3. Sources of errors in potentiometric cells

  4. - Errors ascribed to the reference electrode(s) - reversibility - reactivity - Errors due to the porous membrane - concentration modification - diffusion potential Errors due to the solid electrolyte membrane - partial electronic conductivity - interferences - Errors due to the measuring electrode - buffer capacity - mixed potential (-) Pt / Ag / AgCl / NaCl - KCl / Porous / NaCl - KCl - Na2O / YSZ / Pt, O2 (+) membrane Sources of errors in potentiometric cells:

  5. Errors ascribed to the reference electrode (1) • Types of reference electrodes: • • 2nd kind electrodes: Ag/AgCl/Cl-, Ni/NiO/YSZ • • Gas electrodes: O2/Pt/YSZ, Cl2/Cg/Cl- • Requirements: • Easy to handle • Long term stability (oxidation, miscibility within the electrolyte, etc.) • No partial reduction of the electrolyte, inducing electronic conductivity • Known thermodynamic data (calibration often necessary), • advantage of air or pure oxygen reference electrode • Reversibility (low sensitivity to perturbations)

  6. Errors due to the porous membrane (1) Porous plugs or frits are used to prevent mixing of the contents of the various compartments in a manner analogous to aqueous bridges. Glue cap Porous alumina tube (5 % porosity) Platinum wire Ag LiCl-KCl + AgCl 0.75 mol.kg-1 • concentrations modification of the • analyzed medium • contamination of the reference salt • - diffusion potential Flux of matter through the porous membrane

  7. Ionic membrane: protonic conductor Non-porous mixed conductor Porous membrane u(H+) u(H+) H+ HCl C1 HCl C1 HCl C1 HCl C2 HCl C2 HCl C2 u(Cl-) u(Cl-) f2 Jmatter Jmatter f1 Jmatter Porous membrane Porous membrane C1 > C2 C1 > C2 C1 > C2 u(H+) > u(Cl-) u(H+) > u(Cl-) What is “diffusion potential”? Is there only a flux of matter?

  8. Liquid Junction J(H+) J(H+) HCl C1 HCl C2 u(H+) HCl C1 HCl C2 -+ -+ -+ -+ HCl C1 HCl C2 J(Cl-) u(Cl-) f2 f1 J(Cl-) E Transitory State SPACE CHARGE Porous membrane Stationary State J(H+) = J(Cl-) C1 > C2 u(H+) > u(Cl-) Junction Potential Ej = f2 -f1 Electric field E Errors due to the porous membrane (2): Electrochemical Diffusion - Liquid Junction

  9. Porous membrane Concentrated solvent salt + diluted solute Concentrated solvent salt E ~ 0 Errors due to the porous membrane (2’): Electrochemical Diffusion - Liquid Junction When the solvent salt is the same in both compartments and the concentrations of solutes are low (less than 0.1 molal), the liquid junction potentials across the compartment separator is at most one or two mV and can be neglected.

  10. Errors due to the solid electrolyte membrane (1) - partial electronic conductivity - interferences Errors due to mixed conductivity of the electrolyte Two situations: - one or both interfaces are outside the electrolytic domain Examples: oxygen monitoring in molten steel or molten sodium - both interfaces are within the electrolytic domain (the electronic transport number is smaller than 1%) Errors due to interferences at the electrolyte interface(s) - exchange of particles Examples: exchange H+/Li+(pH electrode), K+/Na+

  11. Temperature Oxygen dissolved in liquid sodium Oxygen dissolved in liquid steel Log PO2 Domain of predominant ionic conduction (99%) • use of YDT instead of YSZ for oxygen analysis in molten sodium • use of YSZ (or CSZ) in molten steel: correction required E measured = Ethx ti Patterson diagram Errors due to the solid electrolyte membrane (2) 1. One or both interfaces are outside the electrolytic domain Case of oxygen monitoring in molten steel and sodium

  12. (1) - E (V) (2) (3) 0.3 0.2 T = 1600°C Liquid steel Oxygen concentration gradient at the liquid steel-electrolyte interface 0.1 0 Steel 100 200 10 2 0 50 500 1000 2000 CSZ Oxygen content (ppm) (% O) interface (% O) bulk p(O2) J (O ) 2 2 Mo/MoO Errors due to the solid electrolyte membrane (3) 1. One or both interfaces are outside the electrolytic domain (1) Nernst (2) Correction of the ionic transport number (3) Diffusion polarization correction

  13. O2- e- SOLID SOLID METAL METAL J(O2) ELECTROLYTE ELECTROLYTE J sp O2 (P1) O2 (P2) a J J a des des J J ads ads P P1 > P2 P GAS GAS Equilibrium conditions Stationary state J = J J + J = J ads des sp ads des measured activity= oxygen pressure measured activity oxygen pressure Errors due to the solid electrolyte membrane (4) 2. Both interfaces are inside the electrolytic domain Partial electronic conductivity within the electrolyte e- flux Compensated by an identical ionic flux Electroneutrality Consequence: oxygen semipermeability flux through the electrolyte without external current

  14. bulk C ibulk surf theor meas C isurf solution Examples: NASICON (Na3Zr2Si2PO12) -Alumina (NaAl11O17) Potassium cation Exchange Li+, Na+, K+, as a function of the size of the channel Errors due to the solid electrolyte membrane (6) Interference When a solid electrolyte is in contact with an active species, it can penetrate into the the bulk by exchange followed by diffusion: iSE + jsol jSE + isol i j SE Solution Empirical equations for the Galvani potential have been developed

  15. pH sensor Errors due to the solid electrolyte membrane (7) Interference Case of the glass electrode Protons do not penetrate into the membrane (their mobility is very low). The interfering phenomenon is a surface reaction with the formation of a gel which can be viewed as a thin protonic membrane

  16. Errors due to the measuring electrode Main source of error: • The analyzed solutions are often complex and the cell e.m.f. is not • a thermodynamic voltage but a mixed potential This mixed potential can be due to impurities within the analyzed medium or can be observed after a long term exposition due to deposition of impurities on the measuring electrode.

  17. M  M++ e- 1/2 O2 + 2 e-  O2- E Ired E1 Iox I At the mixed potential, Em, Ioxidation = Ireduction Em (2) reduction oxidation E2 (1) Mixed potential: generally, the voltage takes an intermediate value (E2 < Em < E1) Mixed potential If there is more than one redox couple in the analyzed system (solution or gas), the voltage is not a thermodynamic potential. It the case of a M+/M in a solution saturated with oxygen. The following reactions take place:

  18. Exhaust gases composition Lambda sensor Variation of the emf vs. A/F ratio Mixed-potential type oxygen sensor

  19. Menasina beach • Case studies: • Oxide ion activity in molten chlorides • Oxidation potential in molten fluorides • - Monitoring of oxygen, hydrogen and carbon in molten metals (Pb, Na)

  20. Media conditions: Solid electrolyte measurements in melts Main difficulties: - thermal shock - wide temperature range (200°C - 1600°C) - time life required - stability domain of the electrolytes - corrosion - reference electrode

  21. Air E Seal Ref 1 ((O2-)) Ref.2/M M/Ref.1 YSZ Pt Pt(+) YSZ ERef2 YSZ E Pt Emea. Pt(-) ERef1 ((O )) 2- Melt M/MOx Pd/PdO, Ni/NiO, etc. Oxide ion activity in molten chlorides (1) (-) Pt/Ag/AgCl/NaCl-KCl/Pyrex/NaCl-KCl-Na2O/YSZ/Pt,O2 (+) Ref.1 Ref.2 Sensing membrane Zirconia sensor B. Tremillon, G. Picard, Proc. 1st Intern. Symp. on Molten Salt Chem. and Techn. Kyoto (1983), p. 93.

  22. Theor. Slope: 72 mV/u. p(O2-) LiCl-KCl-ZnCl2 T = 723 K -270 ZnO E(mV) / Ag -280 -290 -300 Li2O -310 -320 -log(O2-) 1,8 1,4 1 Oxide ion activity in molten chlorides (2) Ref / O2- / YSZ / Pt, O2 Measurement of oxide solubility in molten chlorides J. Shenin-King, PhD Thesis, Paris 6, 1994

  23. The Dolmen of Paomia Monitoring of oxygen, hydrogen and carbon in molten metals (Na, Pb)

  24. Monitoring of oxygen

  25. Oxygen monitoring in molten sodium (1) Brookhaven National Lab., USA, 1972 Interatom, Germany, 1975 Berkeley Nuclear Lab., UK, 1982 Harwell, UK, 1983 Nuclear Research Institute, Czechoslovakia, 1984 Oxygen meters have application to both primary and secondary circuits of a fast reactor. When used in a fast reactor primary coolant circuit they have to perform in high-radiation environment. The corrosion of metals and alloys increases with high oxygen concentration in sodium. Stability of the electrolytes (n-type or p-type electronic conductivity). Electrode reaction kinetics at low temperatures. YDT electrolyte J. Jung, J. Nuclear Mat., 56 (1975) 213. M.R. Hobdell, C.A. Smith, J. Nuclear Mat., 110 (1982) 125 R.G. Taylor, R. Thompson, J. Nuclear Mat., 115 (1983) 25. D. Jakes, J. Kral, J. Burda, M. Fresl, Solid State Ionics, 13 (1984) 165. H. Ullmann, K. Teske, Sensors and Actuators B, 4 (1991) 417.

  26. Oxygen monitoring in molten sodium (2) • Reference electrode Sn/SnO2 and In/In2O3. • Good performance over lifetimes exceeding 400 days. • Grain-boundary attack under high-oxygen sodium. • Tests under -radiation R.G. Taylor, R. Thompson, J. Nuclear Mat., 115 (1983) 25

  27. Thoria-yttria electrolyte soldered in a stainless steel tube. Electrolyte crucible (ThO2 - Y2O3 10-12 mol.%). Glass brazing. Glass brazing Temperature dependence of the saturation solubility in liquid sodium. Log CO = 5.64 ± 0.22 - (2120 ± 100)/T (CO in ppm) D. Jakes, J. Kral, J. Burda, M. Fresl, Solid State Ionics, 13 (1984) 165. D. Jakes, J. Sebkova, L. Kubicek, J. Nuclear Mat., 132 (1985) 88. H. Ullmann, K. Teske, Sensors and Actuators B, 4 (1991) 417. Oxygen monitoring in molten sodium (3)

  28. Reversibility of the electrode reactions YSZ electrolyte Reference electrode YSZ • Bi / Bi2O3 / YSZ J.L. Courouau, P. Deloffre, R. Adriano, J. Phys. IVFrance, 12 (2002) 141. J. L. Courouau, J. Nucl. Mat.,335 (2004) 254. Oxygen monitoring in molten lead and lead-bismuth (1) Main challenge: measurement at low temperatures (< 400°C) • Air / Pt / YSZ and Air / La0.7Sr0.3CoO3 / YSZ mixed conductor V. Ghetta, J. Fouletier, M. Hénault, A. Le Moulec, J. Phys. IV France,12 (2002) 123 • In / In2O3 / YSZor Air / Pt / YSZ J. Konys, H. Muscher, Z. Vo, O. Wedemeyer,J. Nucl. Mat.,296 (2001) 289

  29. -9.00 E(mV) Gas inlet Gas outlet -10.0 Air log (ao) -11.0 -12.0 ao LEAD -13.0 Oxygen sensor with air reference -14.0 550 300 350 400 450 500 T (Celsius) Oxygen monitoring in molten lead and lead-bismuth (2) Measurement of oxygen activity in saturated molten lead (335°C < T < 530°C) V. Ghetta et al.

  30. Coupling of an oxygen sensor with a zirconia pump I(mA) E(mV) Gas outlet Gas inlet I pump Air • Zirconia tube • Pt/Air internal electrodes • Zirconia tube • Pt/Air internal electrodes Air ao LEAD Oxygen pump The oxygen content in the bath is controlled by the oxygen pump The actual oxygen activity is measured with the oxygen sensor Oxygen sensor Oxygen monitoring in molten lead and lead-bismuth (4) V. Ghetta, F. Gamaoun, M. Hénault, A. Le Moulec, J. Fouletier, J. Nucl. Materials, 296 (2001) 295-300. V. Ghetta, J. Fouletier, M. Hénault, A. Le Moulec, J. Phys. IV France, 12 (2002) 123-140.

  31. Closed system I(mA) E(mV) 2 independent measurements Air Air ao SENSOR PUMP Oxygen monitoring in molten lead and lead-bismuth (5) Theoretical Nerst law Theoretical Faraday law

  32. -4 4.0 10 -4 3.0 10 nO variations (moles) -4 2.0 10 slope -4 1.0 10 T = 527 °C 0 0.0 10 0 10 20 30 40 50 60 70 80 Qcumulative (Coulomb) Oxygen monitoring in molten lead and lead-bismuth (6) Verification of the functioning of the set-up Theoretical straight line V. Ghetta et al.

  33. Monitoring of hydrogen

  34. Hydrogen monitoring in molten sodium (1) Na(H) / Fe / CaH2 - CaCl2 / Fe / Li, LiH Solid electrolyte Iron diffusion membrane Reference electrode C.A. Smith, CEGB Technical Disclosure Bulletin, 227 (1974). M.R. Hobdell, C.A. Smith, J. Nuclear Mat., 110 (1982) 125. T. Gnanasekaran, V. Ganesan, G. Periaswami, C.K. Mathews, H.U. Borgstedt, J. Nuclear Mat. 171 (1990) 198.

  35. Log pH2 -20 -30 -10 0 0 (Hi•) domain Log pO2 (h•) domain -10 Main specificity: Various conductivity domains as functions of temperature and atmospheres -20 T =600° -30 (VO••) domain -40 Hydrogen monitoring in molten metals (2) Use of protonic conductors: - Yb, Nd or Gd cerates (BaCeO3) - In doped zirconate (CaZrO3) Sensors for monitoring of hydrogen in Al (ca. 973 K), Cu (ca. 1423 K) or Zn (ca. 723 K) 400° 500° N. Kurita, N. Fukatsu, K. Ito, T. Ohashi J. Electrochem. Soc., 142 (1995) 1552. N. Fukatsu, N. Kurita, T. Yajima, K. Koide, T. Ohashi, J. Alloys and Compounds, 231 (1995) 706.

  36. Three limiting cases CaZr0.9In0.1O3- T=1473 K T=973 K T=773 K Condition of copper melting Condition of Al melting Condition of Na melting No direct contact between (Al) and the electrolyte Mixed conduction at low oxygen activities Protonic conductor Hydrogen monitoring in molten metals (3) N. Kurita, N. Fukatsu, K. Ito, T. Ohashi J. Electrochem. Soc., 142 (1995) 1552. N. Fukatsu, N. Kurita, Ionics, 11 (2005) 54.

  37. Sensor for liquid Al ((H))metal // Zirconate // Pt/gaz, fixed % H2 Measurement of the hydrogen activity in the gas phase equilibrated with the molten Al With Pb, Pb-Li (or Na ?) the electrolyte could be in contact with the melt metal. Hydrogen monitoring in molten metals (4)

  38. The greek church Monitoring of carbon

  39. Carbon monitoring in molten sodium (1) An optimum amount of carbon in austenitic and ferritic steels used as structural materials is essential for maintaining good mechanical properties during the life of the reactor. Owing to the solubility of carbon in molten sodium, according to the temperature, carburization or decarburization can take place. Moreover, accidental ingress of oil from pumps or contamination from carbon dioxide in air will lead to a build up of carbon activity in sodium. Carbide-chloride electrolytes: not successful Alkali molten carbonates M.R. Hobdell, C.A. Smith, J. Nuclear Mat., 110 (1982) 125. M.R. Hobdell, E.A. Trevillion, J.R. Gwyther, S.P. Tyfield, J. Electrochem. Soc.,129 (1982) 2746. S. Rajendran Pillai, C.K. Mattews, J. Nuclear Mat., 137 (1986) 107.

  40. Carbon monitoring in molten sodium (2) Hobdell et al. Fe3C / Fe / Na2CO3 - Li2CO3 / (( C ))Na or Graphite / Fe / Na2CO3 - Li2CO3 / (( C ))Na Rajendral Pillai Electrode reaction at both electrodes: CO32- + 4 e- = C + 3 O2- Main difficulties: - use of a permeable -iron membrane (equilibrium ?) - life time of the reference

  41. Fe3C/Fe/Na2CO3-Li2CO3/(( C ))Na Cgraphite/Fe/Na2CO3-Li2CO3/(( C ))Na Permeable thin Fe membranes E Ni capsule containing Cg Permeable thin Fe membrane E Fe3C Graphite Na2CO3-Li2CO3 Na2CO3-Li2CO3 Molten Na Molten Na S. Rajendran Pillai, C.K. Mattews, J. Nuclear Mat., 137 (1986) 107. M.R. Hobdell, C.A. Smith, J. Nuclear Mat., 110 (1982) 125. Discontinuous measurement Carbon monitoring in molten sodium (3)

  42. Thank you for your attention

  43. Buffer capacity of an acid/base mixture Titration of a weak acid Maximum buffer capacity Buffer capacity Errors due to the measuring electrode BUFFER CAPACITY OF A GAS Buffer capacity : number of moles of acid (or base) inducing ∆pH = ± 1

  44. He-O2 log d (mol.) - 2 800°C 900°C 1000°C - 4 CO2-CO-O2 Pressure domains of correct utilization of the sensor at 900°C - 6 - 8 4 8 12 16 0 - log pO2 (atm) PO (bar) 2 Oxygen pressure domain 1 <---------> 10-6 10-10 <---------------> 10-25 -5 -25 10 10 -15 1 -20 10 -10 10 10 He, Ar or N - O 2 2 mixtures CO - CO or H - H O 2 2 2 O partial vacuum - 2 Errors due to the measuring electrode (3) BUFFER CAPACITY: OXYGEN SENSORS : Buffer capacity of the gas Number of moles of oxygen for changing the chemical potential of 1 kJ/mole of gas

  45. Errors due to the measuring electrode Monitoring of the oxygen pressure down to 10-25 bar provided the gas exhibits a sufficient buffer capacity D PUMP SENSOR CO2 or Ar-H2 (5%) or H2 I E P(O2)

  46. No oxygen monitoring A pressure less than 10-23 bar, is it possible? He + O2 P > 10-7 bar P < 10-7 bar: two situations He + O2 + traces of CO, CO2, H2, H2O He + O2 CO, CO2+ H2, H2O P < 10-7 bar P < 10-7 bar Easy oxygen monitoring

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