Riassunto analitico
The impact of friction and wear in terms of energy consumption, CO2 emissions, and raw material waste are on a global scale. About the 23% (119 EJ) of the world’s total energy consumption is due to friction and wear through tribological contacts. In particular about 20% (103 EJ) of it is spent to overcome the friction between moving components with the remaining 3% (16 EJ) spent for the rectification of worn parts and spare equipment due to wear and wear-related failures.
These huge costs triggered a massive research activity in this field, in order to find methods and materials able to save both energy and raw materials. In particular 2D layered materials have increasingly attracted attention as thin coatings to reduce the wear and friction between solid interfaces in place of standard fluid lubricants. Among them, transition metal dichalcogenides, like molybdenum disulfide, and carbon-based layered materials, like graphite and DLC (Diamond like Carbon), demonstrated to be highly effective in friction and wear control. More recently phosphorene, i.e. a single layer of black phosphorus, has been been proposed as a new solid lubricant, thanks to its layered structure and the capability of phosphorus atoms to reduce friction and adhesion in iron/steel contacts. Indeed phosphorus is key element in lubricant additives used in high-performance engine oils. However the lubricating properties of phosphorene as coating, together with its applicability, are still relatively unknown compared to other layered materials.
Within this master thesis the tribological properties of phosphorene are studied computationally ab initio then compared to those of graphene. In particular, ab initio molecular dynamics is exploited to investigate the sliding behaviour of these two layered materials within a dynamic regime. Calculations are performed with a tribological system composed of three layers, in which one layer is stacked between the others two which are set in relative motion with constant velocity. Different loads are applied to the external layers and two different orientations of the inner layer are considered. Our group has, in fact, shown that structural superlubricity can be obtained for a perpendicular interlayer orientation in a previous work based on the static calculation of the potential energy surface. The aim here is to verify that the lubricity is maintained in dynamic conditions, by means of the calculation of the kinetic friction coefficient for different layer orientations. In the second part of the work, the effect of water intercalation between phosphorene layers is investigated. The tribochemistry of a water-intercalated phosphorene interface is studied here for the first time by ab initio methods.
The present work provides new insights into the tribological properties of phosphorene in different environments, and thanks to the comparison with graphene increase the knowledge about the possible application of this layered material as solid lubricant.
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