Potentiometric sensors for high temperature liquids

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 DHERES Cedex
(France) E-mail Jacques.Fouletier_at_lepmi.inpg.fr
Véronique GHETTA LPSC, IN2P3-CNRS, 53 Avenue des
Martyrs, 38026 GRENOBLE Cedex (France) E-mail
Veronique.Ghetta_at_lpsc.in2p3.fr
MATGEN-IV International Advanced School on
Materials for Generation-IV Nuclear
Reactors Cargèse, Corsica, September 24 - October
6, 2007
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
Part 2
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
(-) 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
What is diffusion potential?
Is there only a flux of matter?
8
Errors due to the porous membrane
(2) Electrochemical Diffusion - Liquid Junction
9
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
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
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
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
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
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
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
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 (200C - 1600C) - time life
required - stability domain of the
electrolytes - corrosion - reference electrode
Sodium Copper Steel Glass
Temperature (C) 400 1150 1650 1500
Rate of T changes (K.min-1) 5 50 5000 50
CO (ppm) 0.5 - 50 1 - 1000 1 - 2000
Time of operation 10 000 h 100 h 5 s 50 h
SE material ThO2 - Y2O3 (cub.) ZrO2 - CaO (cub.) ZrO2 - MgO (cub.-mon.) ZrO2 - Y2O3 (cub.)
21
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
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
Oxygen monitoring in molten sodium (3)
28
Oxygen monitoring in molten lead and lead-bismuth
(1)
Main challenge measurement at low temperatures
(lt 400C)
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 / YSZ or Air / Pt / YSZ J. Konys,
H. Muscher, Z. Vo?, O. Wedemeyer, J. Nucl. Mat.,
296 (2001) 289
29
Oxygen monitoring in molten lead and lead-bismuth
(2)
Measurement of oxygen activity in saturated
molten lead (335C lt T lt 530C)
V. Ghetta et al.
30
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
Oxygen monitoring in molten lead and lead-bismuth
(5)
Theoretical Faraday law
Theoretical Nerst law
32
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
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
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
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)
Fe3C / Fe / Na2CO3 - Li2CO3 / (( C
))Na or Graphite / Fe / Na2CO3 - Li2CO3 / (( C
))Na
Hobdell et al.
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
Carbon monitoring in molten sodium (3)
42
Thank you for your attention
43
Errors due to the measuring electrode
BUFFER CAPACITY OF A GAS
Buffer capacity number of moles of acid (or
base) inducing ?pH 1
44
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
A pressure less than 10-23 bar, is it possible?
He O2
P gt 10-7 bar
P lt 10-7 bar two situations
He O2 traces of CO, CO2, H2, H2O
He O2 CO, CO2 H2, H2O
P lt 10-7 bar
P lt 10-7 bar
Easy oxygen monitoring