Electrochimica Acta 46 (2001) 3851 – 3857 Characterization of deposits by direct observation and by electrochemical methods on a conductive transparent electrode. Application to biofilm and scale deposit under cathodic protection H. Cachet a , T. El Moustafid b , D. Herbert-Guillou a,b , D. Festy b , S. Touzain c , B. Tribollet a, * a UPR 15 du CNRS, Physique des Liquides et Electrochimie, 4 Place Jussieu, 75252 Paris Cedex 05, France b Laboratoire Materiaux Marins, IFREMER Centre de Brest, BP 70, 29280 Plouzane, France c LEMMA, Uniersite de La Rochelle, 17042 La Rochelle Cedex 1, France Received 31 May 2000; received in revised form 30 November 2000 Abstract A new device is proposed where the electrode is a transparent electrode in modified SnO 2 . With this new electrode the reduction of oxygen occurs in a way similar to a gold electrode. Simultaneously the oxygen current is recorded versus time and picture of the interface itself is taken with a digital camera through the electrode. An image analysis is performed to determine the coated area and the number of objects by surface unit. Under cathodic protection, the reduction of oxygen induces an increase of the interfacial pH and then formation of scale deposit. The usual chronoamperometric analysis was completed by an in situ observation of the scale deposit. In natural water the biofilm development was studied by electrochemical method to determine the biofilm thickness and this analysis is completed by a direct observation through the electrode. A good correlation between the two techniques was found. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Scale deposit; Biofilm; Chronoamperometry; Image analysis www.elsevier.com/locate/electacta 1. Introduction Combining different methods to analyze the same phenomenon is a usual way to increase our knowledge. Direct observation with optical microscopy or with SEM has been used since a long time in parallel with electrochemical measurements. The main difficulty for the analysis is due to the fact that the optical observa- tion is generally ex situ for an ordinary electrode polar- ized in a usual electrochemical cell and the electrochemical measurements are in situ. To avoid this problem it is necessary to do the optical observation and the electrochemical measurement simultaneously. Recently Orazem et al. [1,2] developed an impinging jet system and the fact that the electrode is stationary allows the use of in situ video microscopy; with this device it was possible to follow the growth of layers as corrosion products and to perform at the same time, the usual electrochemical measurements. The natural deposits coming from the water as scale deposit or biofilm are often studied with inert electrodes such as gold or platinum. The structure of these de- * Corresponding author. Tel.: +33-1-4427-4170; fax: +33- 1-4427-4074. E-mail address: bt@ccr.jussieu.fr (B. Tribollet). 0013-4686/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0013-4686(01)00672-7