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PRIMARY pH SENSOR DEVELOPMENT FOR HIGH TEMPERATURE AQUEOUS ENVIRONMENTS W Zhang and E A Charles Corrosion Research Group, Herschel Building, University of Newcastle Upon Tyne, NE1 7RU. Abstract - PowerPoint PPT PresentationTRANSCRIPT
PRIMARY pH SENSOR DEVELOPMENT FOR HIGH TEMPERATURE PRIMARY pH SENSOR DEVELOPMENT FOR HIGH TEMPERATURE AQUEOUS ENVIRONMENTSAQUEOUS ENVIRONMENTS
W Zhang and E A CharlesW Zhang and E A CharlesCorrosion Research Group, Herschel Building, University of Newcastle Upon Tyne, NE1 7RUCorrosion Research Group, Herschel Building, University of Newcastle Upon Tyne, NE1 7RU
Abstract
A yttria stablised zirconia (YSZ) thimble has been used with a silver powder/dry air internal element, AgO2, to prepare a pH sensor. A
modified thermodynamic approach is proposed to calculate the YSZ pH sensor potential, identify the YSZ pH sensor as a primary pH
sensor and to determine solution pH at high temperatures. The pH sensor has been tested over the temperature range 150 to 300°C in
several solutions. Measured pH values using YSZ (AgO2) and H2 (Pt) electrodes showed reasonable agreement with calculated pH
from a solution chemistry method.
P latinum E lectrode
W ater In le t
Autoclave Body (Inconel 600)
Ag/AgC lR eference E lectrode
W ater O utle t
YSZ pH Sensor
PTFE W asherSeal N ut'O ' R ing Seal
YSZ pH Sensor
Thermodynamic Calculations
1. Niedrach, Macdonald et al. based on 2. Danielson et al., Macdonald et al. based on 3. W Zhang and E A Charles based on
00 nFEG
2
ln0OPRTG
Section of Refreshed autoclave showing electrodepositions
Experimental and results
YSZ (HgHgO) vs H2(Pt) cell potential experimental data compared with thermodynamic calculated data
YSZ (AgO2) vs H2(Pt) cell potential experimental data compared with thermodynamic calculated data
Measured pH using YSZ electrodes in comparison with calculated pH from a solution chemistry method
6
6.5
7
7.5
8
8.5
9
9.5
10
150 200 250 300
pH
0.01 M H3BO3 + 0.0001 M LiOH
0.01 M H3BO3 + 0.001 M LiOH
0.01 M H3BO3 + 0.01 M LiOH
T(°K)
T /°C
(1) The modified thermodynamic approach can be applied to
a variety of internal elements.
(2) The YSZ (AgO2 ) pH sensor is a primary pH sensor.
(3) Good agreement between measured pH from two pH electrodes
with calculated pH from a solution chemistry method is observed
Conclusions(1) We are now modifying the Ag/AgCl reference electrode to enable it to work at temperatures
above 300°C.(2) We are also modifying the autoclave for refreshed solution tests up to 400°C.(3) We would like to find a YSZ junction composition and structure that would allow the pH
sensor to operate from room temperature upwards ( currently the YSZ has too high an impedance below 100°C).
Future work
Key reference: (1) L.W.Niedrach, J.Electrochem.Soc. 127(1980)2122, (2) M.J.Danielson, O.H.Koski and J.Myers, J.Electrochem.Soc., 132(1985)296, (3) D.D.Macdonald, S. Hettiarachchi
and S.J.Lenhart, J. Solut.Chem.17(1988)719, (4) D.D.Macdonald and L.B.Kriksunov, J. Electrochim.Acta, 47 (2001) 775, (5) W.Zhang and E.A.Charles, J.Appl. Electrochem. 33 (2003)1025.
Yellow : Calculated Red and Blue : Measured