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Abstract

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

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Abstract

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  1. PRIMARY pH SENSOR DEVELOPMENT FOR HIGH TEMPERATURE AQUEOUS ENVIRONMENTSW Zhang and E A CharlesCorrosion 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, AgO2, 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 (AgO2) and H2 (Pt) electrodes showed reasonable agreement with calculated pH from a solution chemistry method. 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 Experimental and results YSZ (AgO2) vs H2(Pt) cell potential experimental data compared with thermodynamic calculated data YSZ (HgHgO) 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 Section of Refreshed autoclave showing electrode positions Yellow : Calculated Red and Blue : Measured 0.01 M H3BO3 + 0.01 M LiOH 0.01 M H3BO3 + 0.001 M LiOH 0.01 M H3BO3 + 0.0001 M LiOH T /°C Future work Conclusions • The modified thermodynamic approach can be applied to • a variety of internal elements. • (2) The YSZ (AgO2 ) pH sensor is a primary pH sensor. • Good agreement between measured pH from two pH electrodes • with calculated pH from a solution chemistry method is observed • (1) We are now modifying the Ag/AgCl reference electrode to enable it to work at temperatures above 300°C. • 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). 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. T(°K)

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