**Author details**

bearing, it is heat treated in the presence of a carbon or nitrogen source. The resulting surfaces have little oxide or hydroxide present but a surface dominated by carbides or nitrides. It is unknown if phosphate ester additives will form a lubricious film on these surfaces. The nonheat-treated steels have been shown to react; however, heat-treated steals are currently under study [18]. The interaction of antioxidants, esters, and phosphate esters in the presence of

**Figure 11.** Structure of surface films formed by the reaction of phosphate esters with a steel bearing surface.

Metal ion deactivators are incorporated into lubricants to react with metal ions typically formed from the action of naturally occurring acids on the metallic parts of the lubrication system. The metal ions are of concern because of their catalytic effects, principally the tendency

In aviation lubricants, the primary metal ion deactivator is benzotriazole. It is thought that benzotriazole reacts with metal atoms at the surface and in solution. On the surface, benzo‐ triazole forms a passive layer that prevents further reaction at the metal surface. Dissolved metal ions react with the benzotriazole to form a complex, which reduces the reactivity of the soluble metal ion. An added benefit of benzotriazole as an additive is that it also acts as an

In the quest for higher-performance turbine engines, a number of changes are under devel‐ opment. Possibly the most significant is the development of harder and more corrosionresistant metal alloys such as Pyrowear and CSS22, among others, hard coatings such as TiC, and low-density silicone nitride–bearing materials. These materials are designed for high load

various carbides has been shown to increase reactivity [19].

of copper ions to form a gummy copper mercaptide gel.

**6.5. Metal atom deactivators**

50 Recent Progress in Some Aircraft Technologies

antioxidant [20].

**7. Future developments**

David W. Johnson\*

Address all correspondence to: djohnson1@udayton.edu

Department of Chemistry, University of Dayton, Dayton, Ohio, USA
