title: Superlubricity behavior with phosphoric acid-water network induced by rubbing.
abstract: In present work, a superlubricity phenomenon of phosphoric acid (H(3)PO(4)) was found under ambient conditions. An ultralow friction coefficient of about 0.004 between glass/Si(3)N(4) and sapphire/sapphire tribopairs was obtained under the lubrication of a phosphoric acid aqueous solution (pH 1.5) at high contact pressure (the maximum pressure can reach about 1.65 GPa) after a running-in period of about 600 s. The experimental results indicate that the superlow friction state was very stable for more than 3 h. In such a state, solidlike films formed on the two sliding surfaces, which are hydrates of phosphoric acid with a hydrogen-bonded network according to the Raman spectrum. The superlubricity mechanism is mainly attributed to the hydrogen bond effect that forms a hydrated water layer with low shearing strength, and the dipole-dipole effects that form an interfacial Coulomb repulsion force also make some contributions to low friction. This work may help us to introduce a new approach to superlubricity and may lead to the wide application of superlubricity in future technological and biomedical areas.
authors.affiliation: State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
authors.forename: Jinjin
authors.initials: J
authors.lastname: Li
authors.forename: Chenhui
authors.initials: C
authors.lastname: Zhang
authors.forename: Jianbin
authors.initials: J
authors.lastname: Luo