Zinc has been a key component in almost all types of lubricating oil for decades. It's primarily used as an anti-wear agent or as an antioxidant.
Zinc-based additives used in oils are sacrificial, and are thus depleted as they do their job. However, it's not simply the metal zinc added to the oil that performs this function. There is a chemical reaction between zinc oxides and an organic thiophosphoric acid that produces an effective resultant known as zinc dialkyldithiophosphate (ZDDP).
Zinc-based hydraulic oil is widely used as it offers a number of benefits. Under boundary conditions, a sacrificial layer of anti-wear additive (typically zinc-based) is established on the load-bearing surface of machine components to help protect against the results of friction.
Another advantage of ZDDP is that it able to perform several key functions at once. Without ZDDP, multiple additives are needed and often at higher concentrations and cost than zinc dialkyldithiophosphate.
Zinc oxide is used in the chemical industry for its own properties, such as it's anti UV properties, or to increase the viscosity of a material, or as a component of a more complex catalyst system to induce a range of organic chemical reactions.
A number of zinc-based chemicals use zinc oxide as part of their manufacturing process, and these chemicals are then used in the manufacture of other materials such as paint, plastic and rubber.
