Ag/AgCl ion-selective electrodes in neutral and alkaline environments containing interfering ions

Abstract

Chloride ingress can lead to serious degradation of various materials and structures. Continuous measurements of local chloride concentrations is thus of uttermost importance for laboratory research, monitoring of structures, and predictions of the residual life span for the most common building materials. This work investigates the applicability of Ag/AgCl ion-selective electrodes for the non-destructive continuous measurement of local chloride concentrations in concrete and stone when exposed to chloride-bearing environments such as seawater. The work studies the stability of Ag/AgCl ion-selective electrodes in neutral and alkaline solutions and the sensitivity to the main interfering ions coming from the environment and from the material itself. The results indicate negligible interference from fluoride, sulfate, and hydroxyl but considerable from bromide and sulfide. In chloride-free alkaline solutions, Ag/ AgCl ion-selective electrodes are not stable over time, but-upon chloride arrival-they permit again reliable measurements of the chloride concentration. The results concerning interference are discussed by taking into account typical exposure environments and it is concluded that the ion-selective electrodes can satisfactorily be used to monitor chloride concentrations in built structures made out of concrete or stone.

Challenges and opportunities in corrosion of steel in concrete

“…A number of sensors have been developed over the past years to measure durability-relevant parameters on engineering structures. This includes embeddable reference electrodes [115], sensors for chloride concentrations [116][117][118][119] and pH values [120][121][122] of the concrete pore solution, and sensors for the measurement of concrete resistivity or galvanic currents [123].…”

Korrosionsmonitoring von Stahlbetonbauwerken

“…In Abhängigkeit von der individuellen Fragestellung stehen für verschiedene Teilprozesse sowohl während der Einleitungs‐ als auch während der Schädigungsphase unterschiedliche mögliche Messprinzipien zur Verfügung. Die Veränderung des Chloridgehalts im Beton während der Einleitungsphase lässt sich baupraktisch mit ionenselektiven Elektroden bis heute nicht mit ausreichend hoher Zuverlässigkeit bestimmen. Allerdings findet ein Chlorideintrag in den Beton grundsätzlich nur bei einem gleichzeitigen Feuchteeintrag statt, sodass z.…”

PH-monitoring in mortar with thermally-oxidized iridium electrodes

“…One hour after the mortar prisms (with the embedded IrO x sensors) were cast, another 2.5 cm thick mortar layer with an embedded Ag/AgCl ion-selective electrode was cast on top of the previous samples. This match-cast part contained 4% of admixed chlorides by weight of cement to ensure that the Ag/AgCl electrode exhibits a stable potential [21] and thus could serve as internal reference electrode. The distance between the IrO x sensor embedded at "depth 2" (Fig.…”

“…where E Ag/AgCl ISE is the potential of the Ag/AgCl ISE internal reference electrode [21]. The diffusion potential E diffusion was calculated with the Henderson equation as described elsewhere [25].…”