Wear Metals and Additive Elements Analysis in Used Lubricating Oils Using ICP-OES

Lubricating oils are used in very difficult conditions in engines reaching high temperatures and varying pressure conditions in contact with many metallic parts. The lubricating function of the oil can be modified according to the amount and the nature of the metals present. The analysis of used oil is an effective tool to ensure the control of the lubricating function of the oil. Moreover, monitoring the wear metals content can be used as a diagnostic to schedule preventive maintenance. In fact, preventive maintenance will reduce the cost directly linked to materials and parts but also due to down-time. Any harm or damage that may result from an engine failure may also be avoided.

The robustness of ICP-OES and its ability to handle organic solvents and to analyze many elements make this technique the best choice to perform such diagnostics. A simple dilution of the sampled oil in an organic solvent, as kerosene, has to be done so no tedious sample preparation is necessary and the analysis is performed within a few minutes.

According to the metals content and to the trends observed by the elemental monitoring, faulty parts and lubricating power decrease can be identified for preventive maintenance. The standard method ASTM D5185, describing the analysis of 22 elements, is suitable for the analysis of the additive elements as well as the wear metals in used lubricating oils. Wear metals analysed and their potential origins are given in Table 1
while additive elements and their role are given in Table 2. Some elements are used as both additives and wear metals. Monitoring their content is then crucial as a decreasing or an increasing value will induce different actions.