Effect of high-pressure hydrogen exposure on wear of polytetrafluoroethylene sliding against stainless steel

Abstract

Mechanical components in hydrogen energy systems, such as a fuel cell vehicle and related infrastructures, will operate in high-purity hydrogen. Especially, some seals and valves in fuel cell vehicles should articulate against metal counterface within a pressurized hydrogen gas. However, the effect of high-pressure hydrogen gas on tribological behaviour of materials used in sliding surfaces has not been identified yet. In this study, unfilled polytetrafluoroethylene (PTFE) pins and 316L austenitic stainless-steel discs were exposed to high-pressure hydrogen gas and then the chemical and physical changes in their surface and the tribological characteristics were investigated. The results of an X-ray photoelectron spectrometer analysis of the exposed stainless-steel surface indicated that metal oxides in the passive surface layer of stainless steel can be reduced significantly during the high-pressure hydrogen exposure. Increased metal contents of the stainless surface resulted in enhanced metal fluoride formation and subsequent development of a PTFE transfer film. Consequently, the exposed PTFE specimens showed lower specific wear rate when compared to the unexposed specimen.

Influences of Trace Water in a Hydrogen Environment on the Tribological Properties of Pure Iron

“…Over the past several years, the authors' research group has studied the influences of a hydrogen environment on tribological properties of various materials [1][2][3][4][5][6][7][8]. The studies were motivated by the significance of hydrogen as an energy carrier and the necessity for overcoming its congenital defect, i.e., low energy density in terms of volume.…”

A Review on Applicability, Limitations, and Improvements of Polymeric Materials in High-Pressure Hydrogen Gas Atmospheres

“…The XPS spectra revealed some differences in chemical compositions in both transfer films and the stainless-steel counterpart surfaces after tests. Using the same test set-up and methodology, Nakashima et al [127,128] examined the wear and friction behavior of PTFE in high-pressure hydrogen (40 MPa) to identify the effect of humidity in gaseous hydrogen [127] and higher hydrogen pressure with longer duration. [128] They observed a lower wear rate for tested unfilled PTFE grades with a higher humidity content in the high-pressure hydrogen.…”

“…Using the same test set-up and methodology, Nakashima et al [127,128] examined the wear and friction behavior of PTFE in high-pressure hydrogen (40 MPa) to identify the effect of humidity in gaseous hydrogen [127] and higher hydrogen pressure with longer duration. [128] They observed a lower wear rate for tested unfilled PTFE grades with a higher humidity content in the high-pressure hydrogen. [127] A lower wear behavior in high-pressure hydrogen exposed PTFE was monitored compared with tests in air.…”

“…Hence, they conclude that in high-pressure hydrogen exposed conditions, steel counterparts do not form protective metal oxide layers and the pure metal composite is exposed to the active PTFE radicals, which form metal fluoride stable bonds as a transfer film and this transfer film hinders the subsequent wear due to the relative motion. [128] Theiler et al conducted tribology tests on PI [129] and PEEK [130] grades in hydrogen gas conditions (up to 0.1 MPa) to identify the influence on tribological properties by exposure to hydrogen. They also assumed no chemical reaction of PI or PEEK matrix in high-pressure hydrogen, however, they found tribologically induced reactions on the fresh metal surface of the counterpart and surface of PI and PEEK in the presence of hydrogen.…”

Tribological characteristics of polyimide composites in hydrogen environment

“…Tribological investigations of polymers and polymer composites in hydrogen gas or liquid are rare, but get growing interest due to the increasing number of hydrogen projects. Since early work carried out by the NASA [4], research has been predominantly made at the Hydrogenius Research Center in Japan [5][6][7] and at BAM [8][9][10][11][12]. Author's previous benchmark of composites in liquid hydrogen (LH 2 ) showed that generally graphite filled polymers have beneficial friction behavior [11] in this condition.…”