Measuring water content in hydrocarbons can be done a number of different ways, but few of them apply well to grease samples. This month's Editor's Choice paper investigates the use of three different dielectric cells (parallel plate, coaxial and interdigitated fringe) to estimate water content in greases. The results are very promising using calcium sulfonate complex greases, with further work required to determine suitability with different thickener technologies that are less hydrophilic, and different additive technologies. Should the technology work well on other greases, the technology could be considered for online monitoring.

A simple and inexpensive corrosion sensor was manufactured to study the corrosion rate of new and water-contaminated lubricating grease using a galvanic cell. A galvanic charge was developed between electroless nickel immersion gold (ENIG) and zinc, manufactured by selectively plating on a custom manufactured interdigitated printed circuit board. This article shows the methodology in using this concept for any application that may require quantifying the corrosivity of a liquid or semisolid that could be applied to the surface of the sensor. Water contamination is a problem in many grease-lubricated machine components, so a sensor concept was developed and a correlation between water content and the corrosion rate is shown. This method could be used to precisely study the corrosion rate of aged or contaminated lubricants and could potentially be used as a cheap and simple way to estimate water contamination in grease. To the best of the authors' knowledge, this sensor concept has not been used in industry or the literature.

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Machine maintenance is important for improving machine uptime and reliability, and for reducing costs. Grease is used in most rolling element bearings, and one common failure criterion is water contamination, so developing a sensor that can detect water content automatically without human input could be a useful endeavor. The temperature dependence on the dielectric properties of water-contaminated grease is investigated in this article with computer logged instrumentation. This method has been termed dielectric thermoscopy (DT). Several off-the-shelf (two lithium, one lithium complex, and two calcium sulfonate complex) and one unadditivized lithium grease are tested with varying amounts of water contamination from 0% to approximately 5%. Another grease is tested with small increments of added water from 0% to 0.97% to test the resolution of the measurement. The purpose is to use the capacitance temperature slope (termed dielectric thermoscopy) to show correlations to the water content of the grease sample and investigate whether any grease types will pose problems in the measurement. A small, custom-made fringe field capacitance sensor with an integrated temperature sensor has been used for this characterization, and data are logged automatically with laboratory equipment and a personal computer (PC). A useable and positive correlation to water content and the DT measurement of roughly 0.5 pF per 10 C and percentage of water was found, although it was found that some greases have different behavior than others.