A comparative analysis of adsorption of six normal-alkanes (C N H 2N+2 , N = 4, 6, 8, 10, 12, 16) on Fe(110), FeO(110), and Fe 2 O 3 (0001) was carried out using classical molecular dynamics (MD) simulation. A realistic model system for adsorbed alkanes was employed using the COMPASS force field (FF), while the appropriate relaxed surfaces and an effective interfacial potential were obtained from ab initio calculations. The results show that butane molecules orient randomly on Fe(110) and Fe 2 O 3 (0001) surfaces, but they preferentially orient in the (010) direction on FeO (110) at low temperature. Additionally, alkanes adsorb physically on Fe(110), FeO(110), and Fe 2 O 3 (0001), in the following decreasing order Fe(110) > FeO(110) > Fe 2 O 3 (0001). The adsorption energies per saturated carbon site decrease with an increase of molecular chain length, and this propensity is similar for different surface potentials. In contrast, the saturated carbon density is insensitive to the surface potentials and shows an increasing trend for short alkane chains, but it remains steady for longer chains.

No abstract

No abstract

No abstract

No abstract

No abstract

The tribological behaviors of three types of sodium phosphates (sodium ortho-, pyro-, and metaphosphate) with different chain lengths are evaluated using the ball-on-disk tribometer at 800 °C. The tribological results show that all three sodium phosphates can reduce friction by approximately 45−65% and wear rate by 80−90%, and, among these, shorter-chainlength phosphate shows a lower friction and wear. XPS spectra indicate a phosphate glassy film consisting of Na, Fe, P, and O elements formed on the tribostressed area. The tribochemistry of tribosurface investigated by XPS and XANES reveals that NaPO 3 and Na 4 P 2 O 7 react with oxide wear debris to produce mixed short-chain Na/Fe polyphosphate in the tribostressed area, leading to a severe depolymerization for NaPO 3 and a slight polymerization for Na 4 P 2 O 7 . However, little polymerization/ depolymerization was found for crystalline sodium orthophosphate.

No abstract