In this paper, a new corrosion sensor based on a quartz crystal microbalance is presented. A 50 m thick disk of solid metal is glued directly on the surface of a 2 MHz AT-cut quartz crystal. An electronic oscillator designed for highly damped quartz resonators allows the resonance frequency of the quartz-glue sample system to be followed. Simultaneous electrochemical measurements are possible as the metal sample can be polarized. The mass sensitivity of this electrochemical quartz crystal microbalance was determined by carrying out a copper electrodeposition directly on the sample surface. The potentiostatic dissolution of 304 stainless steel in 1 M HCl is discussed in this paper. The mass loss during potentiostatic dissolution was measured by the frequency shift of the microbalance sensor and compared to the mass loss calculated from Faraday's law. A very good agreement was found as both results had a relative difference lower than 5%.Quartz crystal microbalance ͑QCM͒ is a widespread technique to study mass changes of thin films in various media including liquids. In particular, it has been proposed as a measurement tool for the determination of corrosion rates of metals and for the study of the influence of inhibitors. 1-3 So far, QCM measurements have been limited only to electrodeposited or evaporated metals, whose chemical reactivity, in most cases, is known to be different from that of solid metals. 4 The feasibility of direct QCM measurements on these materials was already demonstrated. 5 In this paper, a novel corrosion sensor based on the QCM is described. This novel microbalance can be used to determine the corrosion rates of solid metals and alloys with a high accuracy, since a foil of the studied metal is directly glued on the crystal. Moreover, simultaneous electrochemical measurements are possible as the metal sample can be polarized. Thus, this sensor is an electrochemical quartz crystal microbalance ͑EQCM͒ for solid materials. In this paper, the feasibility was demonstrated for the dissolution of 304 stainless steel in HCl medium. ExperimentalThe experimental setup included a homemade QCM and a threeelectrode electrochemical measurement system. The probe of the QCM consisted of a quartz crystal on which the studied metal sample was glued on one of its electrodes. A data acquisition system simultaneously recorded the potential, current, and frequency of the probe.Probe.-The piezoelectric transducer was a 2 MHz AT-cut quartz crystal 14 mm in diam ͑CQE, France͒. This frequency was lower than that of common QCMs to allow the crystal to oscillate with much higher loads. The crystal was coated with gold electrodes of 5 mm diam by the manufacturer. An underlayer of chromium provided gold adhesion to the crystal. Gold was chemically removed from the electrode disk on the side where the sample was to be glued in order to improve the adhesion of the metal sample.The metal sample was a disk cut out from a foil of 304 stainless steel ͑Goodfellow, U.K.͒. The disk was 50 m thick and had a 5 mm diam. The glue us...
This paper describes a driving circuit for an electrochemical quartz crystal microbalance (EQCM) adapted to a wide range of applications. The oscillator is a Miller-type parallel oscillator using an operational transconductance amplifier (OTA). A theoretical study of the oscillating circuit led to the analytical expression of the microbalance frequency as well as to an overestimation of the error on the mass measurement. The reliability of the EQCM was then experimentally verified through electrochemical copper deposition and dissolution. The limit of operation of the EQCM was also investigated, both analytically and experimentally. This work shows that parallel oscillators using few electronic components allow a very reliable EQCM to be obtained for mass measurements on metallic films, even if they are highly damped.
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