Naphthenic acid corrosion is a major concern for the oil refinery business. W hile much is E. SLAVCHEVA now known about the phenomenon, it is still not completely understood because of the B. SHONEcomplex influences on corrosion of the type of acid and other constituents in the crude oil A. TURNBULL and the eVects of both temperature and fluid flow. A review of this form of corrosion has been undertaken with respect to the role of crude oil composition, temperature, fluid velocity, physical state (vapour or liquid), pressure, and materials of construction. Simple measures of corrosivity based on the total acid or neutralisation number are insuYcient. T he sulphur content of the crude is important but the extent to which the various sulphur containing compounds act as inhibitors or corrodents is not understood. T here is little knowledge also of the nature of films formed on the steel surfaces under operating conditions and the role of natural inhibitors that may be present in crudes requires more attention.

The paper reports on the deposition of iridium oxide thin films by dc reactive magnetron sputtering and their characterization by surface analysis methods (X-ray diffraction, scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy) and electrochemical techniques (cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic square waves). The sputtering process was investigated by applying the method of generic curves. An optimal combination of sputtering parameters has been established [40 standard cubic centimeters per minute (sccm) argon/8-12 sccm oxygen/40% effective pump power/100 W dc power/“cold” sputtering] that yields stable microporous amorphous films with a highly extended surface. These films have shown an excellent electrochemical reversibility in physiological saline solution with a “safe” potential range of −1.2 to 1.3 V vs. Ag/AgCl reference electrode, a charge delivery capacity of 90-95 mC/cm2, a constant impedance of 70-80 Ω in the frequency range of 100 kHz down to 0.5-1.0 Hz, and a quick response to bipolar current pulses with a safe charge per phase of 2 mC/cm2/ph. The demonstrated remarkable electrochemical characteristics combined with their established long-term mechanical stability and corrosion resistance allow one to recommend the use of sputtered iridium oxide films as an ideal electrode material for neural stimulation. © 2004 The Electrochemical Society. All rights reserved.

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