Additives
Anti-Wear and Anti-Oxidants: Zinc dithiophosphate, containing P and Zn in roughly equal proportions, is the most common anti-wear/anti-oxidant compound found in motor lubes and many gear lubes. Thus, we routinely investigate for its presence. There are several types of zinc dithiophosphates, with each having its own favorable properties for particular applications.
Zinc dithiophosphate is an additive that provides multifunction capability. In the anti-oxidant role it can break the oxidation chain of a lubricant; in the anti-wear role it chemically "plates" out on such components as cams and lifters, or gears and serves as a lubricant in the event that metal too metal contact takes place.
In as much as some ZN and P plate out, a decrease in these elements might be expected, but make-up lube, as with all additives, tends to restore the level, and maintain equilibrium. It is possible to find lubes that have P without Zn, used as an anti-wear agent.
Anti-Wear Properties: These materials are similar in scope to EP agents. Some plate or coat whi1e some combine chemically with metal surfaces, particularly ferrous (iron or steel), to form a protective coating, necessary in the event that the lube film is interrupted.
Anti-Oxidants: There are anti-oxidants for fuels and lubricants, and most of them are non-metallic. Oxidation is a general term used to describe the combining process with oxygen that a lubricant tends to do. This, in turn, forms undesirable compounds that are far less suitable as lubricants. A number of metals, most notably copper, tend to catalyze oxidation. Some types of antioxidants, therefore, react chemically with the offending metal to nullify its catalytic effect. Another way to inhibit oxidation is to break the chemical chain by sacrificing the anti-oxidant. This type of compound has a great affinity for oxygen when it appears in oxidation products, and combine with it to form harmless compounds while simultaneously stopping the oxidation chain.
