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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...

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To assure auxiliary propulsion of diesel submarines, DCN developed an anaerobic (atmosphere independant) system called MESMA. It is an electrical energy production using a turbo generator supplied by a heating system in which the hot gases are produced by combustion of fuel (gasoil) and oxygen stored on board of the submarine.One injects in the combustion chamber to cool gases a part of condensates of these same gases. The medium concentrates itself in aggressive species, mainly sulphurous species coming from gasoil, and three types of corrosion risks must be taken into account : -Molten salt corrosion of the combustion chamber (salts in solution in the diesel oil and recirculated condensates and which become molten salts during the combustion and the evaporation in the flame), -high temperature oxidation and scaling in the hot parts, under the action of the combustion gases, -corrosion by the hot acidic condensates (until temperatures of the order of 250°C).Corrosion resistance in combustion gas condensates appeared to be the critical point. Subsequently, a study was performed to search for the materials resistant to this type of corrosion, taking also into account the other materials features determining their possibility of use (resistance to the other types of aggression, high temperature characteristics, weldability…).Considering the gasoil used and the process, the representative conditions to perform tests were defined and the main tests consisted in exposure of samples with examination of surfaces and electrochemical tests at 250°C. They have been completed by tests at 80°C to verify that there was not inversion of material behaviour at intermediate temperatures.A large number of materials were tested : austenitic, duplex and ferritic stainless steels, nickel and cobalt alloys, unalloyed titanium and zirconium. The first tests, that mainly involved NiCr22Mo9Nb4 nickel alloy used by DCN in other applications, quickly highlighted selective corrosion of nickel, displayed by nickel enrichment corrosion products and resulting in localised corrosion taking the shape of pits or cracks. The risk of corrosion varies little with the concentration of sulphuric acid, but increases as the medium is made more oxidising. The nitric acid at these temperatures seems to behave in particular like an extremely powerful oxidant even at low concentrations.The following tests reinforced this result and showed that there is a direct relation between the corrosion resistance of an alloy in this medium and its concentration in nickel and in cobalt, except for the titanium that doesn't contain any of these two elements but is sensitive to pitting. The highest resistance alloys are those having high chromium content and limited nickel content, i.e. superferritic, duplex and austenitic stainless steels, as well as the zirconium. Electrochemical tests confirmed the good behaviour of stainless steels and zirconium, their steady passivation on a large domain of potential permitting to assure their corrosion resistance even though