The Viability of pH Measurements in Supercritical Aqueous Systems

Abstract

The measurement of pH of aqueous systems at high temperature is becoming increasingly important because of the need to monitor the chemistry of nuclear power plant cooling water systems and the cycle chemistry of fossil-fueled power reactors. We have previously shown that the yttria-stabilized zirconia pH sensor can be used for accurate pH measurements of aqueous systems up to 320~ This paper describes the viability of pH measurement of aqueous systems up to and above the critical temperature of water.

Vent fluid chemistry of the Rainbow hydrothermal system (36°N, MAR): Phase equilibria and in situ pH controls on subseafloor alteration processes

“…For example, at 375°C, one unit change in pH will result in 0.129 V change for DE(V) T,P . It is important to emphasize that the YSZ-pH sensor is a primary pH electrode owing to the well defined thermodynamic properties of the internal E°H g/HgO reference electrode (Hettiarachchi et al, 1992;Ding and Seyfried, 1996;Macdonald et al, 2005) and, thus, requires no calibration once the electrochemical response has been established. This was done for the sensors used at Rainbow both before and during the cruise (Ding and Seyfried, 2007).…”

“…Seven AA cells power the system. Based on experimental calibrations (Hettiarachchi et al, 1992;Ding and Seyfried, 1996;Macdonald et al, 2005), the inherent uncertainties in pH from the sensor are on the order of ±0.02 pH units. As indicated earlier, however, uncertainties in Cl concentration can also contribute measurement error in pH data, although, the form of the Nernst equation mitigates the effect of this.…”

Electrochemistry at High Pressures: A Review

“…They carried out high quality potentiometric measurements (accuracy from 3 to 10 mV) using a flow-through technique along with a flow-through external pressure-balanced Ag/AgCl reference electrode (EPBRE) in which the electroactive element is maintained at room temperature via a non-isothermal electrolyte bridge [118] thereby overcoming the problem with the value of the thermal liquid junction potentials varying AE 150 mV depending on the nature of the electrolyte bridge and the thermal gradient across it. Other pH sensing electrodes that they have successfully developed include a tungsten oxide [122], glass electrodes for moderately high temperature (200 ± 250 8C) [119], and a YZS (yttrium-stabilized zirconia) pH sensitive membrane electrode [120,121] containing a Hg/HgO internal element fitted into an autoclave contained in a once through/recirculating flow loop that operates in a single-phase mode at both sub and supercritical temperatures (temperatures from 200 and 390 8C and pressure of 255 bar). They also developed Pd-Pt electrodes for measuring dissolved H 2 in supercritical media [123].…”

Electrochemical techniques for monitoring and controlling corrosion in water-cooled nuclear reactor systems

“…The YSZME with a cu/cuo internal element was initially used as a reference electrode by niedrach [32][33][34][35] for measuring corrosion potentials of stainless steel components in nuclear reactor coolant circuits. The work of Macdonald et al [36][37][38][39][40][41][42] and later by lvov and others [43] concentrated on exploring the thermodynamics of the YSZME, as noted above, because of its utility as a primary pH sensor (i.e., one that does not need to be calibrated). Since these initial studies, the YSZME with a ag/ o 2 internal element has been used to sense acidity in aqueous solutions at temperatures as high as 528°c using an external pressure balanced reference electrode (EPBRE) based on the ag/agcl, Kcl (sat), electroactive element [4,44,45].…”