Wear limits the lifespan of many mechanical devices with moving parts. To reduce wear, lubricants are frequently enriched with additives that form protective pads on rubbing surfaces. With first-principles molecular dynamics simulations of pads derived from commercial additives, namely zinc-phosphates, we unravel the molecular origin of how anti-wear pads can form and function. These effects originate from pressure-induced changes in the coordination number of atoms acting as cross-linking agents, in this case zinc, to form chemically connected networks. The proposed mechanism explains a diverse body of experiments and promises to prove useful in the rational design of anti-wear additives that operate on a wider range of surface materials with reduced environmental side-effects.

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