ZDDP

Grumpy Bear · March 17

https://www.stle.org/files/TLTArchives/2019/09_September/Tech_Beat.aspx

https://link.springer.com/article/10.1007/s11249-025-01968-3

Edited March 17 by Grumpy Bear

customboss · March 17

14 minutes ago, Grumpy Bear said:

https://www.stle.org/files/TLTArchives/2019/09_September/Tech_Beat.aspx

https://link.springer.com/article/10.1007/s11249-025-01968-3

I have 3 VA Dr appointments today so wait for it.

Grumpy Bear · March 17

I'm slogging through these papers. Ouch! LOL

customboss · March 17

customboss · March 17

2 hours ago, Grumpy Bear said:

https://www.stle.org/files/TLTArchives/2019/09_September/Tech_Beat.aspx

https://link.springer.com/article/10.1007/s11249-025-01968-3

I got up early.

Briefing Document: Zinc Dialkyldithiophosphates (ZDDPs) in Lubricants

Subject: Review of Zinc Dialkyldithiophosphate (ZDDP) Additives in Lubricants

This briefing document summarizes the key themes and important information regarding Zinc Dialkyldithiophosphates (ZDDPs) as lubricant additives, based on the provided excerpts from "Mechanisms of ZDDP—An Update | Tribology Letters" and "Tech Beat". ZDDPs have been a cornerstone of lubricant technology for decades, providing crucial antiwear, extreme pressure, and antioxidant properties. However, environmental concerns and the evolution of engine technology have led to ongoing research into their mechanisms, limitations, interactions with other additives, and potential alternatives.

1. Overview and Historical Context:

ZDDPs have been widely used in automotive and industrial lubricants for approximately 75 years, since their initial development and patenting in the early to mid-1940s. Several organizations, including Union Oil Co. of California and Lubri-Zol Corporation (now The Lubrizol Corporation), played key roles in their development.
"One of the most widely used additives in automotive and industrial lubricants for the past 75 years has been zinc dialkyldithiophosphates (ZDDPs)." (Tech Beat)
ZDDPs are synthesized through a two-step process involving the reaction of an alcohol with phosphorus pentasulfide, followed by neutralization with zinc oxide.

2. Multifunctional Properties and Key Applications:

ZDDPs exhibit a range of beneficial properties, making them indispensable in many lubricant applications. These include:
Antiwear: Forming a protective boundary film on metal surfaces to prevent direct contact and reduce wear under high load and temperature conditions.
Extreme Pressure (EP): Protecting surfaces from scuffing and seizure under very high pressures.
Antioxidant: Acting as a peroxide decomposer, inhibiting the chain reaction that leads to lubricant oxidation.
"ZDDPs are one of the most widely used petroleum additives, providing both wear and oxidation protection. They are ubiquitous in engine oil products and also are featured in other application areas." (Ian Bell, Afton Chemical, Tech Beat)
Key application areas for ZDDPs include:
Engine oils (gasoline and diesel)
Hydraulic fluids (often as the main additive)
Gear oils
Greases
Rust and oxidation (R&O) oils
Turbine oils
Compressor oils
Metalworking fluids

3. Types and Molecular Structure:

The performance of ZDDPs is highly influenced by their molecular structure, specifically the alkyl (R) groups derived from the alcohols used in their synthesis.
The main classifications of ZDDPs based on alcohol type are:
Primary (straight chain): Generally exhibit greater thermal stability and less volatile phosphorus but potentially less effective antiwear action.
Secondary (branched): Typically show lower thermal stability and more volatile phosphorus but provide more effective antiwear performance and form tribofilms faster. "secondary ZDDPs usually form tribofilms much faster than primary ones and are also less thermally stable." (Mechanisms of ZDDP)
Alkyl aryl (aromatic): Have different stability and performance characteristics, with poorer hydrolytic stability.
Mixed: Combinations of primary and secondary alcohols to tailor performance.
Tertiary alkyl ZDDPs are thermally unstable and not used.
The zinc to phosphorus ratio is typically 1:1, and the sulfur to zinc or phosphorus ratio is 2:1.
ZDDPs exist in solution in equilibrium between monomeric and dimeric forms, especially at lower temperatures. Most commercial ZDDPs also contain a proportion of a basic form.

4. Mechanisms of Tribofilm Formation and Behavior:

ZDDPs form a protective tribofilm on rubbing metallic surfaces through a complex series of chemical reactions, influenced by factors like temperature, pressure, and shear stress (mechanochemistry). "When metallic surfaces are rubbed together in a ZDDP-containing oil or grease, the ZDDP reacts chemically to form a typically 50 to 150 nm thick film on the rubbing surfaces." (Mechanisms of ZDDP)
The tribofilm typically has a pad-like structure, consisting of thin metal sulfide at the substrate interface, overlain with thicker pads of primarily iron and zinc phosphate and polyphosphate, separated by valleys with negligible film.
The composition and mechanical properties of ZDDP tribofilms evolve during prolonged rubbing. The top layer, representing recently formed material, is often a thin layer of polyphosphate.
The rate of tribofilm formation increases exponentially with applied pressure and temperature, indicating mechanochemical control.
There is evidence of an initial rapid formation of a sulfur-rich layer (possibly iron sulfide or zinc/iron sulfate) at the substrate interface, which may precede the development of the phosphate-rich film.
The precise molecular reactions during tribofilm formation, including the potential transfer of alkyl groups from oxygen to sulfur, are still under investigation.

5. Characterization Methods:

Significant advancements have been made in techniques used to study ZDDP tribofilms, including:
Atomic Force Microscopy (AFM): To map film thickness, topography, friction, and mechanical properties at the nanoscale.
Spacer Layer Interferometry (SLIM): For in situ measurement and monitoring of tribofilm thickness in rolling-sliding contacts.
Scanning White Light Interferometry (SWLI): To measure surface topography and wear, with considerations for potential misinterpretations due to internal reflections.
Nanoindentation: To map the elastic modulus and hardness of tribofilms.
Focussed Ion Beam (FIB) milling: To prepare cross-sections of tribofilms for detailed analysis using Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), and Energy Dispersive X-ray Spectroscopy (EDX) to determine depth-wise composition.
Atom Probe Tomography (APT): A newer technique providing high-resolution 3D maps of elemental distribution within tribofilms.
X-ray Absorption Near Edge Structure (XANES) and X-ray Photoelectron Spectroscopy (XPS): To determine the chemical composition and bonding within the tribofilms, including variations with depth. In situ XANES under helium atmosphere has been used.

6. Undesirable Features and Regulatory Pressures:

ZDDPs contain phosphorus, sulfur, and zinc, which can have negative impacts on exhaust aftertreatment systems in vehicles:
Phosphorus and sulfur oxides can poison or coat catalyst surfaces.
Zinc-containing ash (sulfated ash) can block particulate filters.
This has led to progressively reduced permitted levels of phosphorus, sulfur, and metals in engine oils, driven by environmental regulations and engine oil specifications (e.g., GF-5 and GF-6).
The introduction of phosphorus retention limits in engine oil specifications aimed to minimize the amount of phosphorus entering the exhaust.
ZDDP is also aquatically toxic and can negatively impact the demulsibility performance of oils.
Some ZDDPs can be volatile, exacerbating the impact on aftertreatment devices.
The zinc content contributes to total ash, which is also under regulatory pressure.

7. Interactions with Other Lubricant Additives:

ZDDP performance is significantly affected by interactions with other species present in lubricants, including:
Overbased Detergents (Ca and Mg based): Can compete with ZDDP for surface adsorption, incorporate into the tribofilm (as calcium phosphate and CaCO3), affect polyphosphate chain length, influence thermal decomposition, and generally degrade antiwear performance. Magnesium detergents may be more detrimental than calcium-based ones.
Friction Modifiers (OFMs, polymeric FMs, MoDTC): Can have varied effects on ZDDP tribofilm formation and friction. Amine and amide-based OFMs can reduce boundary friction but may suppress or remove ZDDP films. MoDTC forms MoS2 on rubbed surfaces, even within ZDDP films, and the combination often exhibits synergistic friction reduction and wear protection. ZDDP may help protect MoS2 and facilitate its formation from sulfur-free Mo additives.
Dispersants (e.g., succinimide): Can interfere with ZDDP adsorption and tribofilm formation, potentially leading to the formation of thick iron sulfide layers instead of phosphate films.
Antioxidants: Supplementary antioxidants are increasingly used to compensate for reduced ZDDP concentrations.
EP Additives: High concentrations of ZDDP can compete with other EP additives for surface adsorption.
Borate Esters: Can synergistically increase the dropping point of lithium soap-based greases in the presence of ZDDP.

8. Influence of Contaminants:

Water: Increased water levels (from humidity or direct contamination, including from biofuel combustion) generally reduce tribofilm thickness, shorten polyphosphate chains, and increase wear rates. Hydrated ethanol can accelerate the removal of pre-formed tribofilms.
Engine Soot/Carbon Black: Can abrade ZDDP tribofilms, potentially leading to the formation of iron sulfide layers.

9. Behavior on Non-Ferrous Surfaces:

ZDDP behavior on non-ferrous metals like aluminum alloys and diamond-like carbon (DLC) coatings can differ significantly from that on steel.
Tribofilm formation on aluminum alloys can be patchy and influenced by the specific alloy composition.
On DLC coatings, ZDDP typically forms patchy films that are less durable and easily removed compared to those on steel. Pad-like structures similar to steel are primarily observed on DLCs containing tungsten inclusions. The sulfur distribution in films on DLC is also different, concentrating near the top surface.
Film formation rates can vary on different non-ferrous metals (e.g., faster on Ni-rich surfaces, slower on Cr- and Mo-rich surfaces).

10. Impact on Friction and Wear:

ZDDP tribofilm formation can lead to a progressive increase in friction at intermediate entrainment speeds in mixed rolling/sliding conditions due to the increasing surface roughness caused by the pad-like film structure. Friction correlates strongly with the lambda ratio (ratio of EHD film thickness to composite surface roughness).
Boundary friction coefficients can vary depending on the ZDDP alkyl structure.
ZDDP can promote micropitting in gears and rolling bearings by preventing the smoothing of surfaces during run-in due to rapid tribofilm formation, leading to high asperity stresses. Running-in without ZDDP prior to its introduction can mitigate this.
While ZDDP generally reduces wear, under very high loads in pure sliding contacts, it can sometimes increase wear compared to base oil alone, potentially due to delamination of sulfide particles.
Scuffing resistance is improved by ZDDP, provided a tribofilm is allowed to form under milder conditions before high sliding speeds are imposed. Scuffing can occur if the tribofilm becomes too thin (below ~5 nm) under severe conditions.
The assumption that thicker ZDDP tribofilms directly correlate with superior wear reduction is being challenged by studies showing other additives with thinner films exhibiting better wear performance. Wear control might also involve non-adherent particulate triboproducts.

11. Modeling of ZDDP Behavior:

Computer-based modeling has become increasingly important in understanding ZDDP behavior at both macro and molecular levels.
Macro-scale models aim to simulate tribofilm formation and removal by incorporating solid contact models, Arrhenius kinetics, diffusion, and film removal mechanisms due to asperity contact. SLIM data has been crucial for validating these models.
Molecular-scale modeling uses computational chemistry to study ZDDP adsorption, decomposition pathways, and interactions with surfaces and other molecules.

12. Outstanding Questions and Future Directions:

Key areas where understanding is still limited include:
The initial stages of ZDDP reaction with rubbing surfaces to form sulfides and the molecular mechanisms involved.
The influence of ZDDP molecular structure on this initial reaction, especially concerning film formation on non-ferrous surfaces.
The precise molecular reactions occurring during the entire tribofilm formation process.
The mechanisms by which ZDDP tribofilms eventually fail and lead to wear.
The evolution of tribofilms on actual rubbing parts in firing engines over extended periods.
Future research should focus on these areas, potentially utilizing in situ spectroscopic methods.
The future use of ZDDPs will likely be influenced by increasingly stringent environmental regulations, the push for improved fuel economy, and the growing use of non-ferrous materials and electric vehicles. While alternatives are being explored, ZDDP's excellent cost-performance and multifunctional properties suggest it will remain a significant lubricant additive for the foreseeable future, albeit potentially at reduced concentrations and with tailored chemistries.

Conclusion:

ZDDPs remain critical lubricant additives due to their versatile antiwear, EP, and antioxidant properties. However, concerns regarding their impact on exhaust aftertreatment systems and the environment have driven research into understanding their mechanisms, limitations, and interactions, as well as the development of alternative technologies. While the future may see a managed reduction in their use in some applications, particularly automotive, ZDDPs continue to offer a cost-effective and highly functional solution for a wide range of lubrication needs. Ongoing research is crucial for optimizing their use, mitigating their negative impacts, and potentially tailoring them for new material pairings and operating conditions.

customboss · March 17

9 minutes ago, customboss said:

"It is essential to understand the alternative antiwear technology employed for zinc-free systems. Is it MoDTC, MoDDP, an ash-free phosphorous or nitrogen-based polyamines? Nitrogen-based additives are complicated to trend as Nitrogen is not reported as part of an ICP panel. Therefore the presence of wear metals in the oil is a better indicator of wear performance."

customboss · March 17

https://precisionlubrication.com/articles/zinc-lubricant-additives/#:~:text=Zinc (also known as ZDDP,the lubricant formulator's best friend.

Grumpy Bear · March 18

Counter Point

In 1993 we saw the peak of ZDDP levels in API service class SH. 1200 Phosphorus 1600 Zinc + 2:1 Sulphur. Been on the decline ever since. Each new paper tells us this is a evil chemical that needs to die and regulation is trying very hard to do that. Pretty much all a given. Maybe even true and we would know if they ever come up with a test method to fret out the hypothesis.

Here's the thing. ZDDP secondary, still supports about 99% of all PCMO. It is the current and foreseeable reality and given the outlook for ICE's it may just be Custers last stand. We are stuck with it.. There is just no future for the industry to sink that kind of investment in a dying market. Sad and yet true.

These papers give us page after page of arguments telling us how it is harmful to man and machine and all the interactions of a bazillion types of which two are of any consequence at all. They lack REFERNCES in type and in concentration. To little is a motor killer. To much is a motor killer. All said without guardrails and references. Site interactions that NO ONE BLENDING is doing. It was only a test.... Yet these papers move the public image and give ammo to the marketers.

Look about long enough and you will find some consensus with the additive suppliers and major engine builders that 600 PPM is unworkable for any real length of time. WE are getting close. That some upper limit exist where in the chemical becomes corrosive culminating it corrosive WEAR. Fun fact: Break-in oils live in this arena and rely on that fact. 2800-3000 phosphorus and up. Also fun fact; 2,000 phos/ 2,260 Zinc is a pretty common Red Line Power Sports oil concentration. and no ones bearings are pitting out. Red Line has a formulation that incorporates this level of ZDDP AND has a weak acid TBN over 11 utilizing over 2400 ppm calcium! Dyson Analysis Jan 24 2003 (BITOG)

Now....was that so hard?

Once upon a time EVERY blender told you not to mix oils and to flush when changing. Chemical interactions and all. Now? Mix and match at will. "Compatible with all mineral and synthetic oils" is the usual moniker.

Let me distil this. What matters in this moment is WEAR and what is available. I can't use what I wish I had.

ZDDP has some trade offs. That's just a fact. It is also the most used and potent wear additive we have.

How to make best use of it....now there is a question worth its air.

Edited March 18 by Grumpy Bear

Grumpy Bear · March 20

Did we notice?

Wear and friction are independent of each other? ZDDP decreases wear but increases friction. Good trade Dumb Bear (Dances with Wolves).

Toyota 0W8 and 0W16 oils contain a very high amounts of Moly (over 700 ppm). Equal to the amount of zinc. That Toyota oil is made by Exxon/Mobil.

That the amount of Moly in Exxon/Mobil Toyota oil is higher than the concentrations in Red Line HP oils which are condemned by many as "over the top" or "over added"?

Reality is, that moly is doing the work of viscosity and coupled with Boron is the offset for lower concentrations of ZDDP.

That AN is used now as a replacement of POE to reduce the competition for polar additives with equivalent solvency at reduced cost but exchanges HTHS viscosity for the same 100C viscosity to do it? Bad trade Dumb Bear.

The the industry is more focused on energy (C.A.F.E.) credits and regulatory mandates than wear protection?

That you need to look out for your own interest because no one else is. :mad:

customboss · March 21

On 3/19/2025 at 10:36 PM, Grumpy Bear said:

Did we notice?

Wear and friction are independent of each other? ZDDP decreases wear but increases friction. Good trade Dumb Bear (Dances with Wolves).

Toyota 0W8 and 0W16 oils contain a very high amounts of Moly (over 700 ppm). Equal to the amount of zinc. That Toyota oil is made by Exxon/Mobil.

That the amount of Moly in Exxon/Mobil Toyota oil is higher than the concentrations in Red Line HP oils which are condemned by many as "over the top" or "over added"?

Reality is, that moly is doing the work of viscosity and coupled with Boron is the offset for lower concentrations of ZDDP.

That AN is used now as a replacement of POE to reduce the competition for polar additives with equivalent solvency at reduced cost but exchanges HTHS viscosity for the same 100C viscosity to do it? Bad trade Dumb Bear.

The the industry is more focused on energy (C.A.F.E.) credits and regulatory mandates than wear protection?

That you need to look out for your own interest because no one else is.

customboss · March 21

customboss · March 21

https://neol.world/neol-technology/

customboss · March 21

Is this the ZDDP replacement answer? Renewable Lubricants Inc. Was a company I did work for in early 2000's and they used a copper sulfonate additive combined with boron and antimony. Combined with High Oleic base stocks and GRP III and IV bases essentially as additives we outperformed most racing oils of the day.

NEOL maybe a game changer.

customboss · March 26

What is temperature of hydrogen release “welding”?
2000 C

What are normal temps in a V8 spark engine?

Can Hydrogen gases be released from alloys other than hard steel?
Yes.

customboss · March 26

On 3/21/2025 at 1:12 PM, customboss said:

Is this the ZDDP replacement answer? Renewable Lubricants Inc. Was a company I did work for in early 2000's and they used a copper sulfonate additive combined with boron and antimony. Combined with High Oleic base stocks and GRP III and IV bases essentially as additives we outperformed most racing oils of the day.

NEOL maybe a game changer.

Just watched this again with a few minutes to digest.

Very familiar with the 11.8 ISM Cummins DI TURBO engine as we used it for standardized valve train wear testing for HD engine oils. This is a total redesign since I departed Cummins. X12

Diesel engines have at least double the compression ratio of spark engines.

It’s designed to run on 10w30 HD lubricant.

300 hr test each 10w30 and 0w30

clean reference on left. Engine was fresh from factory