WS2 nanoadditized lubricant for applications affected by hydrogen embrittlement

Abstract

Hydrogen is one of the cleanest available vehicle fuels but its small atomic size allows it to diffuse readily through the lattice of solid materials, which can cause catastrophic failure in high strength steels. Metal embrittlement has been identified as a major consequence of hydrogen uptake and represents an extra challenge for lubricated tribological parts in fuel cell vehicles, hydrogen compressors, storage tanks, dispensers and wind turbines that are normally subjected to high stresses. This study has found WS₂ nanoparticles as an effective additive candidate to impede the permeation of hydrogen into rolling element bearings at high temperatures and pressures. Compared to the pure polyalphaolefin (PAO) base oil, WS₂ nanoadditized oil reduced the concentration of permeated hydrogen in the bearing steel and led to controlled wear and smoother tracks. These effects are attributed to the formation of a chemical tribofilm on the wear track which reduces hydrogen embrittlement and extends the life of steel through several mechanisms: (1) its continuous generation impedes formation of nascent catalytic surfaces during rubbing and thus prevents the decomposition of oil/water molecules and generation of atomic hydrogen; (2) acts as a physical barrier to hydrogen permeation through the wear track; (3) the low coefficient of diffusion of hydrogen through the tungsten compounds found in the tribofilm further reduces hydrogen permeation; (4) some of the atomic hydrogen is used up in redox reactions during the formation of the tribofilm and (5) the tribofilm reduces the total amount of water in the steel formed by the reaction of hydrogen atoms with oxides and thus extends the fatigue life. WS₂ nanoadditized lubricants can lead to improved profitability and sustainability of the emerging renewable energy industry.