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Corrosion of copper conductors in mineral oil insulated power transformers is a well-known problem in electrical power management and distribution worldwide. Recently, some corrosive compounds containing sulfur (e.g. DBDS, dibenzyl disulfide) have been identified to play an important role in this process. A common strategy to limit corrosion, either as precaution or remedy, is the addition of a passivator (Irgamet 39™, I39™) in the oil, with a recommended concentration of 100 ppm to protect the surface of conductors from chemical attack from corrosive oil components. In this study, samples of naturally non-corrosive oil with different concentrations of I39™ are used to treat copper surfaces that are aged under inert atmosphere and analyzed with X-ray Photoelectron (XPS) to assess directly the effective amount of passivator covering the surface of metal and its dependence on the original concentration in oil. The main aim is, therefore, to determine the effect of the concentration of I39™ originally in oil on the effective surface coverage of copper conductors to observe its distribution and to verify the recommended passivator concentration to be used.

This paper presents a very compact and low power consumption mixed mode circuit for voice signal processing. A re-configurable ADC/DAC stage was implemented both in analog and digital blocks, taking advantage of the half-duplex operation and thus reducing the total area and consumption. The circuit was designed in a 0.18/spl mu/m digital CMOS process supplied at 1.8/3.3 V. The presented circuit and architectural design techniques reduce the area down to 0.42mm/sup 2/ and the power consumption to 0.94mA in D-to-A mode and 0.88mA in A-to-D mode, while featuring 8 Ohm speaker driving delivering 70mW and all the necessary microphone interface and bias including a 0 to 42 dB gain control. The measured THD is 0.015% and the dynamic range is 71.2dB in D-to-A mode, while A-to-D mode the THD is 0.004% and the dynamic range is 74dB.