Content area
Full Text
But maximizing their performance depends on formulating the proper lubricant and monitoring it during use.
DEMANDS PLACED ON LUBRICANTS TO PROVIDE SUPERIOR PERFORMANCE under more stressful operating environments over longer periods of time are increasing. This means that the function that antioxidants perform to protect lubricants is continuing to increase in importance.
With the implementation of two new engine oil specifications, as was discussed in a previous TLT article,1 antioxidants will continue to play an important role in automotive lubricants. But antioxidants also are an important additive used in industrial lubricants.
This article furnishes an update on the use of antioxidants in industrial lubricants that includes discussions about critical lubricant applications, how to select antioxidants, assessing antioxidant performance and future trends.
Input on developments with antioxidants has been obtained from representatives at the following companies: BASF, Chemtura, Fluitec Industries, King Industries, Polnox, Rhein Chemie and Vanderbilt Chemical.
FUNCTION OF ANTIOXIDANTS
Oxidation is a multistep process involving a three-step radical process that if left unchecked will eventually lead to the total breakdown of the components in the lubricant. In the first step of the radical process, known as initiation, an external factor such as heat, severe pressure or the presence of a metal will trigger the formation of a free radical (or unpaired electron) that is derived from one of the organic components found in the lubricant. Either a bond inside the organic species between two atoms is broken to form the radical or an electron is subtracted from a molecule by an oxidized metal.
The free radical formed is a highly reactive species that can react with oxygen to form a hydroperoxide radical in the second step of the radical process. This is known as propagation because the additional radicals formed accelerate the decomposition of the lubricant. The hydroperoxide radicals formed engage in a third step, known as the multiplying step, leading to the formation of additional radicals.
Dr. Michael König, senior manager application for Rhein Chemie Rheinau GmbH in Mannheim, Germany, says, "A second aspect of propagation is that the peroxides formed can further react to form additional radicals in a branching and multiplying process. By continuous breaking of bonds, smaller or even volatile molecules are generated." A schematic showing initiation, propagation and...