PRODUCTS & SERVICES
Passivation pathways eFluids provide a solution to prevent copper corrosion, which preserves vital component integrity Increasingly, electric and hybrid vehicle lubricants must offer conventional wear protection for steel gears and bearings while also effectively cooling coppercontaining e-motors, power electronics and potentially even battery modules. Fluid chemistries impact metals differently, in seen and unseen ways, so a deep understanding of surface chemistry is essential. Afton Chemical presents how conventional lubricants contribute to copper corrosion and how eFluid formulation can protect copper to preserve vital component integrity. In the presence of oxygen, copper surfaces form oxides. These may look green or black, as seen on church roofs. Discoloration is not a failure mode per se, so understanding the processes at a molecular level is key. If copper can be passivated with a protective, insoluble layer, visual appearance may be less relevant. However, when the surface layer formed is a soluble copper compound, this promotes leaching and removal of copper from the surface. Copper leaching is often caused by the traditional lubrication needs of steel gears and bearings.
Unprotected copper can suff er from corrosion including leaching. This can be prevented by the formation of stable layers
Oxygen reacts with steel surfaces to form a thin iron oxide layer. Extreme pressure (EP) melts iron oxide, allowing molten material to transfer from one surface to another, causing scuffing wear. Conventional EP additives contain sulfur, which competes with oxygen to create an iron sulfide layer that is more desirable: its higher melting point prevents scuffing. Active sulfur in conventional lubricants also reacts with copper. Copper sulfide also forms a layer on the surface, but this may not offer protection against copper gradually leaching into the lubricant. The copper sulfide may also become more brittle or mechanically different, flake off and weaken the affected components. Another failure mode can occur when electrical current flows
Discoloration of copper on a roof, showing continued stability over time
110 // July 2022 // www.electrichybridvehicletechnology.com
Sulphur is used traditionally to protect metal contact points, with phosphorous delivering protective surface films
through copper components or when copper components have electric potential differences. Copper ions can be leached out, resulting in positively charged copper ions migrating through the lubricant towards the negatively charged electrode. These copper particles may form copper-rich, branching needle-like electrodeposits known as dendrites, that can create unwanted circuits and cause component failure or even fires. Factors known to affect dendrite formation include distance between electrodes, voltage levels and lubricant composition including conventional EP additives. Passivating copper prevents it from reacting or behaving undesirably. Afton Chemical has an extensive history in this area and has been continuing to develop new technology accompanied by relevant testing. Preventing leaching can include utilizing chemistries that sequester or protect some of the active sulfur, stopping it from degrading and
reacting with copper but still allowing a protective EP film to form on gears and bearings. Other options involve creating a non-soluble film over copper components to protect them from sulfur. Some films alter the copper’s appearance, but still prevent leaching or stripping of copper from the surface. Further pathways include innovative new chemistries that don’t employ active sulfur, forming hard, protective films that still protect gears and bearings under EP conditions. New in-house tests also allow Afton to evaluate how different eFluids help reduce dendrite formation and improve component performance. Detailed molecular understanding, application knowledge and relevant testing jointly determine the best copper passivation pathways for EV performance and reliability. FREE READER INQUIRY SERVICE To learn more about Afton Chemical, visit: www.magupdate.co.uk/PEHV