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Description
Friction and wear cause a quarter of losses of the global energy production. A well-known practical approach to reduce friction is to introduce another substance, called lubricant, to the contact surfaces. A variety of lubricants, both liquid and solid, are available on the market; the global lubricants market size was estimated at $128.5 billion in 2018.
However, friction reduction in some specific conditions may still be a challenge. For example, providing lubrication in oxidative environments at high temperatures, which is essential for certain technological applications, such as cutting tools. Traditional lubricants, both liquid and solid, are unsuitable for the task due to their lack of oxidation resistance.
A possible solution of the problem – a hard and oxidation-resistant coating (TiN, Si3N4, and others), containing a dopant that would, upon operation, diffuse to the surface of the coating and provide lubrication. Vanadium is a popular choice as such a dopant; in the operation conditions (above 700ºC, humid air) it is known to form oxides on the surface, which in turn melt, providing liquid lubrication. However, the exact mechanisms of oxidation and the effects of conditions on the resulting VxOy phases are not entirely clear.
We are studying the process of vanadium oxidation computationally, using the reactive molecular dynamics within Reactive Force Field (ReaxFF) approach. ReaxFF is an empirical potential, that is shown to be capable of performing at the Density Functional Theory (DFT) based methods level of accuracy, while consuming significantly less computational resources. ReaxFF enables nanosecond-long simulations for tens of thousands of atoms at the same computational cost, as hundreds of picoseconds for hundreds of atoms in DFT.
We develop a suitable ReaxFF parameterization and apply it to the oxidation simulations. We find vanadium pentoxide, V2O5, to be the predominant outcome of the oxidation. We study the effects of oxygen pressure, load, temperature and humidity on the oxidation rate and reaction outcome.
