Lube-Tech
136 ppm Cu, average 85 ppm Cu at 336 hours across all formulations). The increase in dissolved copper over time follows a modified Arrhenius behaviour. Copper strip ratings at 336 hours range from 1a to 3a. The lowest corrosion being Formula D, containing only Mo-AMIDE.
Figure 2: Dissolved copper by ICP (Extended D130 @ 160°C).
A visual comparison of the copper strips over the course of two weeks [Figure 3] demonstrates a minimal amount of corrosion on the bare copper. There is an inherent amount of baseline corrosion due to other componentry, as noted in the appearance of Formula 00. The singular addition of Mo-DTC (A) and Mo-AMIDE (B) contributes little beyond that.
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.151 page 4
It was somewhat unexpected that the singular top-treat of B-AMIDE (C) increased corrosion, since many borates are actually employed for their anti-corrosion properties. This detriment is easily mitigated, through binary and ternary combinations of the borate with the two molybdate additives.
Electrical conductivity All formulations, fresh and aged, yield electrical conductivities in a range similar to current EV specific fluid technology [Figure 4]. The conductivities with respect to temperature follow no specific trend when measured in fresh oil, other than the expected result that conductivity increases with temperature. This increase is a known property with most fluids and is most likely a direct result of reduced viscosity with the higher temperatures. A lower viscosity allows for easier flow of material and correspondingly, an easier flow of electrons.
The electrical conductivity of the fluids after oxidative ageing presents a less random behaviour than fresh oil. In general, the conductivities are higher than the respective fresh oil measurements. The viscosity changes in these oils are extremely minimal relative to the fresh oil, therefore, the observed conductivity changes are most likely the results of oxidative changes in the oils, with the increased polarity of the oxidative products driving the increase in conductivity.
Figure 3: Visual appearance of Cu Strips (Extended D130 @ 160°C).
From the aged oil data, none of the molybdenum or boron based additives are working as antioxidants, as all show an increase in conductivity above baseline oil 0. That being said, most combinations of the additives do show a greater resistance to oxidation than formulas using only the individual additives. Of particular note are Formula F, which is comprised of B-AMIDE and Mo-DTC, and Formula I, which is comprised of B-AMIDE, Mo-DTC, and Mo-AMIDE. In terms of conductivity, these two formulas demonstrated the least amount of oxidative degradation relative to baseline.
30 LUBE MAGAZINE NO.180 APRIL 2024
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