Influences of hydrogen and trace moisture content on the friction of silicone rubber

In recent years, the utilisation of hydrogen energy has gained importance in order to achieve carbon neutrality. This utilisation requires the establishment of technologies for the safe use of hydrogen, and the role of sealing materials is essential. Examples of sealing materials used in hydrogen include piston rings used in reciprocating compressors as dynamic seals and O-rings that are subjected to repeated loads of high-pressure hydrogen as static seals. These sealing products are subjected to sliding in hydrogen when in use. Unexpected high friction causes excessive elastic deformation and possibly induces serious mechanical failure of O-rings. For this reason, research has recently been carried out to lay the foundations for frictional properties in hydrogen (1)(2). In this study, the effect of hydrogen on the friction mechanism between silicone rubber and SUS316L was investigated. The rubber was molded in the shape of a hemisphere. Reciprocating friction tests were performed with a pin-on-disk apparatus in air, hydrogen and gases bubbled in water to vary the amount of water content at atmospheric pressure. The friction coefficient of the friction test in hydrogen was higher than that in air. Futhermore, the friction coefficient of the friction test in wet hydrogen (water content = 30~300 ppm) was higher than that in relatively dry hydrogen (water content = 4~7 ppm). These results suggested that gas atmosphere and water content of gas had an influence on the friction between rubber and SUS316L. To elucidate the friction mechanism, the surfaces of the rubber and SUS316L after testing were analyzed using optical microscopy, SEM/EDS and FT-IR. (1) Sawae Y et al. Friction and wear of PTFE composites with different filler in high purity hydrogen gas, 157 (2021) 106884. (2) Theiler G et al. Influence of counterface and environment on the tribological behaviour of polymer materials, 93 (2021) 106912.