Measurements and influence of water content in silicone oil

The precise measurement of water in silicone oils is difficult owing to the reaction of water with siloxane to give silanols. In this paper we report kinetic and equilibrium measurements of water and silanol content in 50-cSt silicone oils from different manufacturers. By using different techniques we show that the oils contain free and bounded water whose total amount varies linearly with relative humidity. The silanol content was also deduced and is never less than 80–150 ppm in dry oil; it increases non-linearly with RH. The influence of water and silanols on several electrical properties of silicone oil is also discussed.