Investigation of Micro-Tribological Behavior of MS2 Nanotubes
It is well known that metal dichalcogenides MS2 (M=Mo, W, Nb, Ta, TiS, Zr ,Hf, S=S, Se) have lamellar structure, the bonds of adjacent lamellae are weak van der Waals interactions and inter-lamellar are strong covalent interactions. The structures make adjacent lamellae easy to slip and it shows low friction coefficient during friction process. MS2 are often used as solid lubricants in high/low temperature, heave load and vacuum, in which oil is failure. WS2 has better high temperature properties than MoS2, although little natural WS2 mineral has been deposited, and people must synthesize it by chemical means, so its price is nearly 5 times expensive than that of MoS2. Until now little study is made comparing with MoS2. Furthermore the research papers about tribological behavior of NbS2, TaS2, TiS2, ZrS2, HfS2 are not seen. In this study the thermal decomposition method is used to produce fullerene-like MS2 nanotubes. The morphology, microstructure and tribological behavior of MS2 nanotubes are investigated by means of SEM, TEM, XRD and AFM. The results show that the diameter of MoS2, WS2 and NbS2 nanotube is less than 100nm, and the length is more than 2μm. The MoS2, WS2 nanotube has lower friction coefficient than MoS2 powder tested by AFM using Si3N4 probe. Similar results are also found for NbS2 nanotube. The macroscopic friction test for pin on disc tester shows nearly the same results. TEM image shows that MS2 nanotubes have rolling debris between two antagonist surfaces, and MoS2 powder only has flattened debris. It may be the fullerene structure brings the chemical stability and lead low friction.
Chunli BAI, Sishen XIE, Xing ZHU
C. S. Li et al., "Investigation of Micro-Tribological Behavior of MS2 Nanotubes", Solid State Phenomena, Vols. 121-123, pp. 785-788, 2007