Pressure-induced exfoliation of inorganic fullerene-like WS2 particles in a Hertzian contact.

Nanoparticles are potential additives for the improvement of lubricant properties, because of the structural modifications they undergo under high pressures in mechanical contacts. The behavior of inorganic fullerene-like WS₂ nanoparticles (IF-WS₂) under high isotropic pressures of up to 20 GPa generated in a diamond anvil cell was studied and compared to the response of the lamellar 2H phase of WS₂. The same materials were then subjected to static uniaxial pressures in a Hertzian contact in the GPa range. The evolution of the particles as a function of pressure was studied by in situ Raman spectroscopy and transmission electron microscopy at the end of the test. Data analysis shows that IF-WS₂ particles resist high hydrostatic pressures well, but they are totally exfoliated by uniaxial compression in a Hertzian contact under low pressure. These results explain the excellent tribological properties at ambient temperature of IF-WS₂ nanolubricant that have previously been attributed to the nested nanospheres during the friction process but whose origin had not been clearly identified. [ABSTRACT FROM AUTHOR]