Primary vs Secondary ZDDP

[RDY4WAR]

First post. Been lurking the site for years and finally joined.

I've been researching this for a little while. I know a little about their function, that primary has a slower consumption rate but harder to activate, and secondary is the opposite. What I'm hoping to find out is the difference in molecular structure that distinguishes one from the other. Also, in what applications is each one used?

Is one found in gas oil and other in diesel oil?

Does one brand use one over the other?

Do specialty oils (break-in, racing, etc...) use one over the other?

Is primary even found in engine oil? (doesn't sound like it would be favorable)

 

[1JZ_E46]

I know that not all zddp is created the same. For example, Driven Racing Oils’ racing tier of oils uses zddp that is designed to rapidly deplete (i.e. sacrifice itself) for maximum wear protection.

 

[SilverFusion2010]

Basically the ZDDP molecules that are mixed in oil (primary) are large molecules. ZDDP has an interesting property by which with heat and friction new species of ZDDP are formed (secondary). These are what adhere to metal surfaces and provide boundary layer protection.

That’s the short version. MolaKule or one of our other chemist can delve into the specific details.

 

[Gokhan]

Originally Posted By: RDY4WAR
First post. Been lurking the site for years and finally joined.

I've been researching this for a little while. I know a little about their function, that primary has a slower consumption rate but harder to activate, and secondary is the opposite. What I'm hoping to find out is the difference in molecular structure that distinguishes one from the other. Also, in what applications is each one used?

Is one found in gas oil and other in diesel oil?

Does one brand use one over the other?

Do specialty oils (break-in, racing, etc...) use one over the other?

Is primary even found in engine oil? (doesn't sound like it would be favorable)

Here is the structure of the ZDDP, with the four R's being the alkyl groups. Alkyl groups are simple C - H - C - H chains such as methyl (1 C), ethyl (2 C's), propyl (3 C's), butyl (4 C's), ... ZDDP alkyl chains are characterized by how many carbon atoms are in the chain (it could be anywhere from a few to more than a dozen) and if the carbon atom that attaches to the ZDDP molecule is primary or secondary. Carbon atoms make four bonds. Primary carbon atom means that only one of the bonds is another carbon (the remaining being two hydrogen atoms and the ZDDP molecule); secondary carbon atom means two of the bonds are other carbon atoms (the remaining being one hydrogen and the ZDDP molecule), and tertiary carbon atom means three of the bonds are other carbon atoms (the remaining being the ZDDP molecule). Bonds to primary carbon atoms are more stable than bonds to secondary carbon atoms, which are in turn more stable than bonds to tertiary carbons atoms, as hydrogen bonds are more difficult (require more energy) to break than carbon bonds.

There are also ZDDP's that use aryl groups (aromatic carbon rings) instead of alkyl groups (carbon chains).

These are some additional compounds used instead of ZDDP:

ZDDP's are classified according to the number of carbon atoms in the alkyl chain and whether the bonding carbon is primary, secondary, or tertiary. You can have a mix as well, as there are four alkyl chains and some can be primary while others can be secondary. There can also be a different number of carbon atoms in each of the four alkyl chains.

Regarding the antiwear ability, there is no clear answer. Some say secondary ZDDP is better. However, this paper found that primary ZDDP with 8-carbon alkyl chains (P8 ZDDP) was best when used in combination with dinuclear moly DTC. So, there is no clear answer in regard to which ZDDP is better in terms of antiwear ability. It's complicated.

(Link) Influence of the alkyl group of zinc dialkyldithiophosphate on the frictional characteristics of molybdenum dialkyldithiocarbamate under sliding conditions
Masayoshi Murakia ^a and Hisayuki Wadab ^b
^a Department of Mechanical Engineering, Shonan Institute of Technology, 1-1-25 Tsujido Nishikaigan, Fujisawa, Kanagawa 251-8511, Japan
^b Lubricants Research Laboratory, Nippon Mitsubishi Oil Corporation, 8 Chidori-cho, Naka-ku, Yokohama 231-0815, Japan

The article studies three different types of ZDDP (two primary and one secondary) along with dinuclear moly for various moly concentrations. The optimal Mo concentration could be as little as 200 ppm or as high as 700 ppm, depending on the type of ZDDP. Also, different ZDDP types lead to different minimum friction coefficient (and antiwear properties, which may get better or worse as friction gets lowered). They found that primary-8-carbon-alkyl-chain ZDDP was best in terms of friction reduction because its better temperature stability and slower decomposition and activation resulted in more molybdenum atoms being embedded in the antiwear film while this film formed, increasing the effectiveness of moly. So, it's not necessarily true that a faster-decomposing secondary ZDDP provides better antiwear. When the synergistic effect of other antiwear/extreme pressure/friction modifier (AW/EP/FM) additives are considered, primary ZDDP could be better, as it competes less with other additives due to its slower decomposition and activation resulting from its better temperature stability.

 

[RDY4WAR]

That is a good read. I have a much better understanding of this now.

Is any specific type of ZDDP preferred for specialty oils such as break-in oil, racing oil, etc...?

 

[SonofJoe]

I'm taking a bit of break from BITOG but I'll comment on this post.

In the context of ZDDP, the words 'primary' & 'secondary' refer to the types of alcohols used to react with Phosphorus Pentasulphide (P2S5) to form what is commonly referred to a 'thio-acid'. You make ZDDP by simply neutralising thio-acid with Zinc Oxide (ZnO).

Perhaps the first thing to say is you very rarely get 'pure' primary ZDDPs used in engine oils. Industrial applications yes, but motor oils no. What you tend to see used are so-called 'mixed' & 'secondary' ZDDPs. In this context, 'mixed' means that a combination of both primary & secondary alcohols are used to react with P2S5. There are reasons to do this. First primary alcohols are relatively cheap while secondary alcohols help with additive solubility.

Matching individual ZDDPs to individual applications is a very tricky business for the simple reason that ZDDP impacts on so many aspects of oil performance. A ZDDP that might be optimum for wear might be rubbish on Teost so there's usually a need for compromise. Personally, I tended to opt for the cheapest & lightest ZDDP I had in my armoury for all applications and would only ever move away from it if I hit a brick wall (which, I never did but might today if I was still formulating oils).

Hope that helps...

 

[RDY4WAR]

It does help a lot. Thank you.

It has me curious about how each one may get used, and how well one individual ZDDP may work with another. The original thought that lead me down this quest was a lot of talk about flat tappet cams and ZDDP which always included someone praising a specific brand of oil supplement for ZDDP. My thoughts are how do we know the ZDDP in that bottle of goo is useful for the application? What if it doesn't play well with the ZDDP and other additives already in the oil? What if the extra ZDDP is a fast consumption type and it's gone within 500 miles? We don't know.

I guess the main question is about oils designed specifically for older engines with flat tappet cams, like Amsoil Z-Rod, would have a different (better?) ZDDP type usage than the common option of Rotella diesel oil or adding a bottle of gôo to API-SN gas oil. Does the flat lifter and cam environment want a different individual ZDDP than the rod and main bearings or the distributor gear? It has me curious.

I've always preferred using an oil dedicated for the task, but haven't had a good argument for why.

I think I have a much better understanding of it now. My curiosity is spiked now though about ZDDP and it's relationship with moly. Those graphs above are interesting. I like oils with good amounts of moly. Is it possible to have too much of a good thing when it comes to moly? I'm not sure now.

 

[Tom NJ]

Great to see you back SonofJoe! Hope you hang around.

 

[SonofJoe]

You're asking a lot of good questions but I suspect, no one, not even seasoned industry specialists, can give you the detailed answers you're seeking.

That said, from the top...

Regarding, flat tappet cams, the mixed, light ZDDPs that existed way back when flat tappets were the norm are still around today. They haven't really changed that much. The thing that's different today is the AMOUNT of ZDDP you're allowed to put in PCMO, which because of concerns about catalyst poisoning, is significantly lower than is was say in the 1970s. You're not quite as restricted on ZDDP in HDDO which is why I guess you like Rotella. Same applies to Amsoil who 'do their own thing' with oils.

As regards fast vs slow consuming ZDDPs, these are terms I don't recognise or TBH have ever come across. In theory, ZDDP reacts with metal surfaces only to get scraped off and replenished. It suggests a mechanism of 'consumption' but I never saw anything which suggested this was what was happening in reality. Typically, you might see a very linear build-up of Iron in the oil during a 100 hour engine test, which suggests wear rates are uniform with time. You do very occasionally see wear rates rocket up in the last few hours of a test but this is invariably due to acid attack, brought on by exhaustion of TBN & AO and not because of anything to do with ZDDP depletion.

Regarding what different ZDDPs do, perhaps it's worthwhile saying that whilst, in theory, there are an infinite number of ZDDPs, the reality is that only a handful exist in commercial form and used in engine oils, with all the different AddCos making essentially the same stuff. Once you realise just how eye wateringly expensive, and how 'rule bound' oil development programs are, you can understand why ZDDPs have to be severely rationalised this way. Typically an AddCo will focus on a light mixed primary/secondary ZDDP (for cheapness & to minimise ZDDP treat for a given level of Phos in oil), light full secondary & heavy full secondary (where Phosphorus Volatility specs apply). That's usually it!!

As often as not, whether you use mixed or secondary ZDDPs is just down to what an individual formulator 'believes'. Personally I like 'cheap' and developed a fact-based rational based around 'cheap is good or good enough'. However, I've worked with people (invariably idiots!) who given a choice between something cheap and something expensive, will ALWAYS opt for the more expensive component!

I like Moly and yes it works nicely alongside ZDDP. However you need to get your head around why people use Moly in oils because it's not always obvious. I pioneered the use of Moly in my old outfit but as an ANTIOXIDANT, not as an additive for antiwear. Did it help on wear? Probably but I was never that bothered about it because ZDDP was doing everything I needed to do on that front.

Apologies for such verbose answers. Again, hope it helps...

 

[RDY4WAR]

SonofJoe,

I am really liking your answers. Please, feel free to share any knowledge you want. I'm a blank page waiting to written on.


Regarding the reduced amounts of ZDDP... I've heard and read that high amounts of calcium conflict with ZDDP as far as surface aggression goes that calcium will scrub the ZDDP off. I've also heard that some calcium works with ZDDP for friction reduction. I'm not sure what to believe there. If high amounts of calcium (3,000+ ppm) or other detergents inhibit ZDDP from doing it's job effectively, could the 800 ppm limit sufficient if it didn't have to fight the detergents?

My attraction to moly has been for friction reduction. I like the idea of reduced friction for mog in the daily driver and free'd up power in the drag car. I'm not a fan of Rotella or any diesel oil in gas engines. I just see a lot of people using it. Perhaps its harmless in a gas engine. For me, when there's good quality gas oils out there that have sufficient ZDDP like Amsoil Z-Rod, Valvoline VR1, Joe Gibbs Driven, Schaeffer's, Red Line, etc..., I don't see a reason to use diesel oil.

Any knowledge you're willing to share in this area, I am all ears.

 

[SonofJoe]

I personally wouldn't say high levels of over based metallic detergents, be they Calcium or Magnesium based, would ever meaningfully interfere with the surface action of ZDDP. Very occasionally you might see ZDDP 'complex' with uncapped ashless dispersant but even with this, I doubt it impacts on ZDDPs ability to form a protective, sacrificial film. Remember the film only forms at points of high pressure and/or temperature (eg a cam tip) which causes ZDDP in the oil to breakdown to the very reactive Phos & Sulphur species which react with metal.

I have however seen certain ester base oils screw up wear control & I've always been somewhat 'anti-ester' ever since (sorry TomNJ!).

Moly has many fine qualities. However, unless you're using it around the 1000ppm Mo level, I doubt it will contribute that much to mpg reduction and at that high a treat, it's simply not cost effective (the Moly costs more than the value of the fuel you save). If you genuinely want to improve fuel economy, use a thin oil & drive a small, lightweight car with a very gentle right foot. I drive a 1.0 L N/A Suzuki Celerio which weighs in at an anorexic 835 kg (1837 lbs), runs on 0W20 & typically pootles around at a sedate 55 mph. I get really grumpy if I get less that 72 mpg Imperial (approx 60 mpg US).

I honestly wouldn't know where to start recommending an oil for a drag racer. Such an engine regime is just too far removed from what the lubricant industry develops for everyday vehicles!

 

[RDY4WAR]

Thanks for the insight.

The mpg is a bit of an uphill battle. It's a 2002 Tahoe 5.3L that tows the Camaro to the track. The longest haul with it is a 515 mile haul one way to a race in Kentucky each year. That's about 8 hours each way cruising down the highway with a 5500 lbs load. It has 231k miles, currently running Amsoil Signature Series 5w-30 and has no issues making the drive each year so far. I just can't help but think I could be doing something more. I know mpg is going to stink regardless of oil used. I just want this thing to live another 230k more.

The drag car is a Camaro with a 355ci LT1. It runs for less than 3 minutes from leaving the lanes to the burnout to coming back to the pits. The oil temps are usually 175-180°F max after the pass. I run Amsoil Dominator 5w-20 but have considered switching to Mobil 1 Racing 0w-30 based on a VOA posted on here.

Would you say a PAO/mPAO vs group III base oil would have a greater impact on friction than a couple hundred ppm of moly change?

 

[Gokhan]

Effects of structure of zinc dialkyldithiophosphates on tribological properties of tetrahedral amorphous carbon film under boundary lubrication
Hikaru Okubo (a), SeiyaWatanabe (a), Chiharu Tadokoro (b), and ShinyaSasaki (b)
(a) Graduate School, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo 125-8585, Japan
(b) Tokyo University of Science, Japan
February 26, 2016
(Link)

This excellent paper studies different ZDDP types for DLC/DLC (ta-C/ta-C [tetrahedral amorphous carbon film]) contacts and steel/steel contacts.

In Figure 1 note the difference between primary and secondary ZDDP in the first figure. In primary ZDDP the attaching carbon has only one carbon neighbor (carbon bond). In secondary ZDDP the attaching carbon has two carbon neighbors (carbon bonds).

Its interesting that primary ZDDP results in less friction but more wear while secondary ZDDP results in less wear but more friction. Figure 19 explains how.

In Tables 2 & 3 and Figures 11 & 12, X-ray photoelectron spectroscopy (XPS) results show the concentration of various atoms as a function of depth in the ZDDP film (depth profile of the atoms in the ZDDP film). Etching time is proportional to the depth in the ZDDP film, with t = 0 corresponding to the surface layer and the depth increases as t increases.

A lot of info to absorb!

 

[bunnspecial]

Gokhan,

Do you know if ZDDPs in motor oil will exhibit roughly the same 31-P NMR δ as show for what(presumably) is a "pure" ZDDP sample?

If so, I'm booking some NMR time tomorrow(or realistically probably next week) and and do P-31 NMR on a some oil.

In addition, did they specify a solvent? I'm guessing CDCl3 would probably work fine, but wanted to double check in case it was something different/exotic.

 

[JAG]

Cool thread. Thanks to all who added information. Dispersants make up more of the additive package than any other type of additive in motor oils. The following thesis paper shows how dispersants hinder ZDDP. https://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=5104&context=etd

 

[dblshock]

Oy vey!...do I really want to learn all this? just give a bottle of 0/40 Edge so I can get on with the next problem.

 

[RDY4WAR]

I've never been able to simply accept something for what it is. I have to know why or how. I'm also stuck at home for several weeks healing a broken back so I have A LOT of time on my hands.

 

[Gokhan]

Originally Posted by RDY4WAR
I've never been able to simply accept something for what it is. I have to know why or how. I'm also stuck at home for several weeks healing a broken back so I have A LOT of time on my hands.

Wow, get well soon!

Here is some more info by the Russian Oil Mafia (Oil-Club Russia). I have no idea how these guys get a hold of these things.

But then if they can get into private email servers...

HIGH PRODUCTION VOLUME (HPV)
CHEMICAL CHALLENGE PROGRAM
For
ZINC DIALKYLDITHIOPHOSPHATE CATEGORY
Prepared by
The American Chemistry Council
Petroleum Additives Panel
Health, Environmental, and Regulatory Task Group
April 19, 2005
(Link)

Secondary alkyl groups in the structure drawings in Pages 2 - 5 are the ones where the vertex (carbon) attached to the oxygen has a branch sticking from it (meaning it neighbors a second carbon through that branch). If there is no branch on the vertex next to the oxygen, it's a primary alkyl group. For example, the first and third ZDDP structures have four secondary alkyls; the second ZDDP structure has for primary alkyls, and the fourth ZDDP structure has two primary alkyls and two secondary alkyls (mixed primary and secondary).

 

[Gokhan]

Originally Posted by bunnspecial
Gokhan,

Do you know if ZDDPs in motor oil will exhibit roughly the same 31-P NMR δ as show for what(presumably) is a "pure" ZDDP sample?

If so, I'm booking some NMR time tomorrow(or realistically probably next week) and and do P-31 NMR on a some oil.

In addition, did they specify a solvent? I'm guessing CDCl3 would probably work fine, but wanted to double check in case it was something different/exotic.

I messaged you with more details.

It says SecC3- C6 ZnDTP in PAO4 over the figure; so, it's secondary C3 - C6 ZDDP in KV100 = 4 cSt PAO.

It's interesting that the study found that when you go from secondary to primary and also from shorter to longer alkyl chains, wear increases, friction decreases, and basic-ZDDP ratio increases, neutral-ZDDP ratio decreases.

So, for wear protection, neutral secondary ZDDP with the shortest alkyl chains is best. This is because it's the least stable type of ZDDP, therefore forming the ZDDP films fast and well while it decomposes and reacts with the friction surfaces. Since it produces thicker and rougher films than more stable primary and/or longer-chain ZDDP, the wear is less but the friction is more. (Again, the neutral-ZDDP ratio increases and the basic-ZDDP ratio decreases when you go from primary to secondary and/or longer-chain to shorter-chain ZDDP.)

Here are the structures of neutral and basic ZDDP:

 

[SonofJoe]

Originally Posted by RDY4WAR
I've never been able to simply accept something for what it is. I have to know why or how. I'm also stuck at home for several weeks healing a broken back so I have A LOT of time on my hands.


Sorry to hear about your back. Hope the recovery goes well.

Regarding your comment about 'needing to know how & why', I suspect you would make a first rate lubricant researcher but a terrible oil formulator!

I used to know one of the guys mentioned in the R&D papers cited above & we worked together on stuff from time to time. He was a really nice guy, extremely personable, highly cooperative & far more intelligent than me. The quality of his work was always top notch & he's published a lot of industry papers.

That said, I would have to say that in all the time I knew him, his impact on COMMERCIAL oil development was virtually zero (as in zip, nada, nichts, rien!).

The people that control commercial oil development are generally known as 'formulators'. These are the people that design oils to pass the big engine test programs that allow an oil to be labelled up as SN/A3/B4/MB this/VW that/BMW the other. The skill set you need to do this successfully is truly vast! You have to be part-chemist, part-chemical engineer, part-mechanical engineer, part -statistician, part-salesman plus being a pretty slick cost-accountant. Focussing on one specific aspect of oil design (eg ZDDP/Ashless interaction) is a luxury you can ill afford because you have to simultaneously juggle hundreds of variables in your head, anyone of which can individually cause a program to come to a juddering, embarrassing & expensive halt! To be a good oil formulator, you need to be comfortable with 'ambiguity' and accept that there will never be enough time or money to understand what you're doing!

Hope that helps...