Extreme pressure antiwear additives

Extreme pressure antiwear additives are a type of chemical additive used in lubricants to reduce the rate of wear and tear on machinery. These additives form an extremely thin protective film on metal surfaces which reduce friction and resulting abrasion. They also provide some corrosion protection and deposit control.

The additives are of various types such as sulfonates, phosphates, halogenated compounds, chlorine-based compounds, phosphorus derivatives, and certain polymers.

The most common extreme pressure antiwear additives used in gear oils are:

1. Zinc Dialkyl Dithiophosphate (ZDDP): ZDDP is one of the most widely used EP additives due to its excellent antiwear and extreme pressure properties. It forms a protective film on metal surfaces, reducing friction, and preventing metal-to-metal contact under high-load and high-temperature conditions.
2. Sulfur-Phosphorus Compounds: These compounds, such as sulfurized fatty acid esters and sulfur-phosphorus esters, provide effective EP and antiwear performance. They react with metal surfaces to form a durable protective film that prevents wear and reduces friction in extreme pressure conditions.
3. Chlorinated Paraffin: Chlorinated paraffin compounds, such as chlorinated fatty acids and chlorinated hydrocarbons, have good extreme pressure and antiwear properties. They create a thin boundary layer of chloride on metal surfaces, reducing wear and friction in high-load applications.
4. Organic Sulfur Compounds: Organic sulfur compounds, such as sulfurized olefins and sulfurized alkylphenols, provide excellent EP and antiwear properties. They react with metal surfaces to form a chemically bonded film, reducing friction, and preventing wear in extreme pressure conditions.

These extreme pressure antiwear additives are often used in combination with other additives to provide a comprehensive additive package that meets the specific requirements of gear oils in different applications. The exact composition and concentration of these additives can vary depending on the specific gear oil formulation and the intended application.