Study of ZDDP tribofilm various temperatures and concentrations

[spiderbypass]

Seemed like interesting article regarding ZDDP synthesis and forming tribofilms at various temperatures… Came out in 2018-2019 so fairly recent… seemed straightforward enough to garnish some understanding and complicated enough to feel smarter reading it …

In situ synchrotron XAS study of the decomposition kinetics of ZDDP triboreactive interfaces

One of the major obstacles in replacing the widely used zinc dialkyldithiophosphate (ZDDP) antiwear additive with a more environmentally friendly one is the difficulty of time-resolving the surface species resulting from its decomposition mechanism under ...

www.ncbi.nlm.nih.gov

 

[Jetronic]

What I get from that is: make sure you have enough viscosity at cold starts as you could be stripping the phosphate layer quicker than it gets replaced.

 

[ZeeOSix]

What I get from that is: make sure you have enough viscosity at cold starts as you could be stripping the phosphate layer quicker than it gets replaced.

All motor oil is many times thicker when cold than when hot ... even 0W.

 

[Jetronic]

of course it is, was that even a question?

 

[ZeeOSix]

of course it is, was that even a question?

Then how does the "make sure you have enough viscosity at cold starts" come into play if all oil is thick at cold start-up?

 

[Jetronic]

The oils they use have no shear thinning, and it was already too thin to prevent the need of zddp. zddp you can't replace quick enough at low temps.

 

[RDY4WAR]

I have questions regarding this study. Feel free to call me out if these are answered in the article, and I happen to miss it.

1. How much ester was added to the PAO for solvency? The only thing it mentions about this is...

"a trace of ester oil to aid the solubility of ZDDP in PAO."

PAO has poor additive response, which is supposed to improve with the addition of ester but it takes a certain amount. I really wish they would've noted the concentration there in order to get a better picture of the additive response. I also wish this test was done with a group III base oil as well.

2. The ZDDP concentration was limited to 800 ppm phosphorus. This is good for common use oils, but they're testing tribofilm establishment. With common use, a tribofilm is already established and can hold its own until the oil gets warm to replenish it. The time you'd be trying to establish that tribofilm initially, and only time you'd use just secondary alkyl ZDDP, would be during break-in in which case a break-in oil would have much more ZDDP in the 2500-3500 ppm range. A break-in oil wouldn't be formulated with a PAO/POE base oil either. It just seems like a weird test to me, or maybe I'm looking too far into it and missing the point of the test. (highly possible)

 

[OVERKILL]

I have questions regarding this study. Feel free to call me out if these are answered in the article, and I happen to miss it.

1. How much ester was added to the PAO for solvency? The only thing it mentions about this is...



PAO has poor additive response, which is supposed to improve with the addition of ester but it takes a certain amount. I really wish they would've noted the concentration there in order to get a better picture of the additive response. I also wish this test was done with a group III base oil as well.

2. The ZDDP concentration was limited to 800 ppm phosphorus. This is good for common use oils, but they're testing tribofilm establishment. With common use, a tribofilm is already established and can hold its own until the oil gets warm to replenish it. The time you'd be trying to establish that tribofilm initially, and only time you'd use just secondary alkyl ZDDP, would be during break-in in which case a break-in oil would have much more ZDDP in the 2500-3500 ppm range. A break-in oil wouldn't be formulated with a PAO/POE base oil either. It just seems like a weird test to me, or maybe I'm looking too far into it and missing the point of the test. (highly possible)

I know the Mobil blending guide examples only show 2% POE added for that purpose, take that as you will, so I think that's an excellent question.

 

[MolaKule]

I have questions regarding this study. Feel free to call me out if these are answered in the article, and I happen to miss it.

1. How much ester was added to the PAO for solvency? ...

And unless I missed it, they never stated how they determined how much additional ester was needed for solvency, since ZDDP IS an ester as well.

While this article may have been somewhat of a step forward for X-ray absorption spectroscopy (XAS) studies, it seemed to drudge up more questions than it answered.

In formulating, how much ester and what type is needed depends greatly on the viscosity and type of the PAO. Generally speaking, higher viscosity PAO's need more, say TMP, to improve solvency and diesters may be needed to enhance seal swell.

In addition, so many of the other DI components in a balanced formulation are esters as well. What I have found is that by using a good ester-based dispersant, few additional esters are needed for either GroupIII or IV oils.

This peaked my interest as well so I added 5% of pure zddp (by volume) to pure 6 cSt Chevron PAO (95% by volume) and it solved just fine.

In a complex DI package with all of the other chemistry involved, I do not think a PAO based formulation has this exact evolution of ferrous phosphates and zinc sulfides as this article described.