Tagged: reliability

Understanding Oxidation: The Basis for Antioxidant Use

When speaking about antioxidants, the first thing that comes to mind is oxidation. This is the primary reason that antioxidants exist: to reduce oxidation. But what is oxidation, and why should there be antioxidants?

Oxidation occurs in everything in life (not just finished lubricants). We see oxidation regularly when we leave certain fruits exposed to the atmosphere (think about cut pears or apples). After being in the elements for some time, they are no longer fresh and have degraded slightly.

A similar reaction occurs during the oxidation of finished lubricants. Greg Livingstone provides an excellent summary of the oxidation process in his article, “Varnish, Deposits in Bearings, Causes, Consequences, and Cures.” The oxidation degradation pathway begins with initiation, where free radicals are formed in the presence of heat, wear metals, water, and oxygen as shown in Figure 1.

Understanding Oxidation The Basis for Antioxidant Use

Afterward, during propagation, the free radicals form hydroperoxides, which can create oxidation by-products (Alkoxy radicals), eventually leading to high molecular weight oxygenated by-products.

During this process, the free radicals can also react with primary antioxidants, or the hydroperoxides can react with secondary antioxidants to slow these reactions. However, they will still form the high molecular weight oxygenated by-products once depleted.

Next in the termination phase is polymerization and agglomeration, followed by the physical and chemical changes to the lubricant. It must be noted that there are various stages to oxidation, and typically, when we see sludge or varnish, oxidation has already occurred.

Figure 1: Summary of the oxidation process.

When oxidation occurs, the oil quickly loses its antioxidants; they can no longer protect the oil. As such, the oil begins to undergo physical changes where sludge and varnish appear, and viscosity usually increases. These oils also experience a rise in acid production after these reactions occur.

Now that we have a better understanding of oxidation, whereby the antioxidants are deployed to help reduce the oxidation rate, we can dive deeper into the world of antioxidants and how they can help fight against oxidation for the finished lubricant.

Find out more in the full article, "Antioxidants in Lubricants: Essential or Excessive?" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd.

Lubricant Degradation

Determining the Root Causes of Oxidation in Lubricants

Finally, we’ve arrived at the point where we can effectively determine the root cause. It is critical that the analyst understands oxidation and has knowledge of the evidence needed before embarking on the root cause journey. As noted in the first part of this article, the question we should ask is, “How could?”.

We hypothesize that oxidation is occurring. In a complete root cause analysis, we should hypothesize the occurrence of all the degradation mechanisms and eliminate them with evidence-based data.

There are two main ways in which oxidation can occur either through the presence of oxygen and temperature over the normal operating temperature of the system or if there is a less-than-adequate presence of antioxidants.

Determining the Root Causes of Oxidation in Lubricants

If we follow our line of questioning with the presence of oxygen and temperature and again ask, “How could?” we can get two primary responses. Either there was an air leak in the system, or the system was being pushed beyond its operating limits.

If we further investigate the air leak into the system, we ask, “How could it?” again. There are two main ways: either there are damaged components, or a less-than-adequate system design allows air to enter the system.

If we follow the pathway of investigating “how could” the system be pushed beyond its operating limits, then we can come up with two hypotheses. Either an increase in production was required, or there was a malfunction of the components, which caused strain on the other components.

Both of these hypotheses are physical and can be investigated further, but we will focus on the lubricant aspect of this article. Hence, we will follow the questioning surrounding the less-than-adequate presence of antioxidants.

We begin with the question, “How could we have a less-than-adequate presence of antioxidants?”. From the information gathered in this article, we know this can result from free radicals or less than adequate lubricant specifications.

We will investigate the “Presence of free radicals” first.

“How could we have the presence of free radicals?” Free radicals can emerge as a result of chemical reactions.

“How could these chemical reactions produce free radicals?” There are two main ways in which this can occur. Either the lubricant got contaminated, which introduced catalysts for these chemical reactions, or adverse operating conditions gave rise to these chemical reactions.

Then, we must ask again, “How could we have contamination?” Contamination can occur if leaks are getting into a closed lubrication system or if there is ingress of foreign material from the environment.

Our line of questioning continues when we ask, “How could we have leaks in a closed lubrication system?”. These can result from damaged components or seals allowing leaks into the system or if the system is less than adequately designed.

These are physical attributes of the system, so we will go back to investigating the lubricant aspect.

This is where we get to ask our famous question, “How could we have ingress of foreign material from the environment?”. Ideally, this can be classified in three ways;

There are openings which are allowing materials to enter the system or
Wrong lubricant was placed in the system or
Contaminated lubricant was placed in the system

Let’s investigate all three aspects, starting with the openings allowing foreign material to enter the system. There are two main ways in which this can occur. Either the openings were not closed after use, or the safety latches malfunctioned.

Suppose the openings were not closed after use. In that case, there is a possibility that there were less than adequate inspections to verify that these were closed after use or a less than adequate procedure for the task being completed which required the opening of the hatch.

On the other hand, if the safety latches malfunctioned, this could result from less than adequate checks to verify the functioning of the safety latches.

In these cases, the root causes are not the physical elements but rather the systemic reasons for these procedures not being adequately performed.

Now we investigate the second central hypothesis, “How could the wrong lubricant be placed in the system?” While there are many ways in which this can occur, we have narrowed it down to two main areas.

Either there were less than adequate checks to verify that the technician received the correct lubricant, or there were less than adequate procedures to dispatch the correct lubricant from the warehouse. We will not go further into these two as they are now systemic causes that must be addressed.

Onto the third hypothesis of “How could a contaminated lubricant be placed in the system?”. There are two main avenues for this to occur. Either there were improper storage and handling procedures, or there needed to be more adequate procedures to verify the cleanliness of the lubricant before entering the system.

The other hypothesis stemming from the “less than the adequate presence of antioxidants” is having “less than adequate lubricant specifications.” Let’s investigate this one a bit further.

“How could we have a less than adequate lubricant specification?” Typically, this can result from the lubricant not being blended properly or less than adequate antioxidant levels, which were inappropriate to protect the lubricant.

Now, the line of questioning changes to “Why?” as we have gone past the physical element and some decision-making was involved in this hypothesis. We must ask, “Why wasn’t the lubricant blended properly?”

This can result from less than adequate procedures to ensure the quality of the lubricant by the supplier or less than sufficient checks for the proper blending mix being processed.

These are factors one should consider when receiving any lubricant from their supplier.

On the other hand, if we follow the line of questioning of “How could there be a less than adequate antioxidant level to protect the lubricant?” we can come up with the following.

Either the operating environment caused the antioxidants to be depleted at a higher rate. This would be as a result of a harsh but normal operating environment. In this case, we may be unable to make those environmental changes (without the OEM’s consent).

Or the antioxidants used were not suited to the operating conditions. This is where the line of questioning again shifts to “Why were they not suited?”. This could result from inadequate information in choosing the right lubricant suited for the system.

What Is the Real Root Cause of Oxidation?

From the logic tree that we have created, we can see that there is no sole root cause for oxidation. It can stem from various causes, including physical, human, and even systemic roots. The main takeaway from this exercise is to acknowledge that root causes are not limited to physical causes, such as leaks in the system.

Instead, the actual root causes can be linked to systemic areas of concern where there may not have been enough information to guide the analyst in choosing the most ideally suited lubricant for the application. There are also root causes related to the lubricant not being appropriately blended.

It is critical to thoroughly investigate the real root causes when the lubricant becomes degraded to avoid being stuck in the loop of constantly experiencing degradation.

For more info on other methods, check out the book Bob Latino, and I authored called “Lubrication Degradation – Getting Into the Root Causes,” published by CRC Press.

References:

Ameye, Jo, Dave Wooton, and Greg Livingstone. 2015. Antioxidant Monitoring as Part of a Lubricant Diagnostics – A Luxury or Necessity. Rosenheim, Germany. February 2015.

Latino, Bob, Sanya Mathura. 2021. Lubrication Degradation – Getting into the Root Causes. CRC Press, Taylor & Francis.

Find out more in the full article, "Here's a more comprehensive approach to revealing oxidation root causes" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd.

Lubricant Degradation

How do I know if Oxidation is occurring?

What Evidence is needed to prove that oxidation has occurred / is occurring?

However, understanding the oxidation process is just one part of the puzzle. When performing an investigation, we also need to know what factors or characteristics should be present. Additionally, we need to prove that their presence confirms our hypothesis of whether or not oxidation is occurring. This is where the line of evidence-based questioning plays a significant role.

When oxidation occurs, it is usual to see the presence of aldehydes, ketones, hydroperoxides, and even carboxylic acids. These can be confirmed using the FTIR (Fourier Transform Infrared test).

Typically, one will also find some deposits in the system. These deposits can be further characterized and tested to determine their nature using FTIR. Their presence, however, may be confirmed using the MPC (Membrane Path Colorimetry, ASTMD7843) test.

Identifying the presence of the deposits and/or the compounds listed above can lead to the conclusion that oxidation has occurred.

Another critical characteristic of oxidation is the depletion of antioxidants. This can be easily identified by utilizing the RULER® (Remaining Useful Life Evaluation Routine) test. This test quantifies the remaining antioxidants in the oil and gives the value for the amines and phenols (which is very important, especially in synergistic mixtures).

As such, one can detect the trend in the depletion of antioxidants and implement measures to prevent this before they become depleted.

The main tests to assist in determining the presence of Oxidation include:

RULER (Remaining Useful Life Evaluation Routine) levels less than 25% compared to new oil. This value represents the level of antioxidants in the oil. Hence, low levels indicate that the antioxidants are decreasing, possibly due to oxidation. This test can accurately give information on whether oxidation is currently occurring in the oil before deposits are formed.

An increase in acid number indicates the presence of acids resulting from oxidation. However, it must be noted that this change in acid number only occurs after oxidation has taken place. Hence this test is not a good indicator to determine if oxidation is occurring; instead, it is more definitive in letting us know that oxidation has already occurred.

Rapid color changes – darkening of the oil due to the deposits being present. While color is not the best indicator, in some instances, the darkening of the oil can provide a bystander to ask whether something is occurring in the oil. It is not a definitive test for the presence of oxidation.

FTIR test (Fourier Transform Infrared) for the presence of insolubles formed during the oxidation reaction. This can accurately determine the presence of any compound to assist us in determining whether oxidation is occurring.

MPC (Membrane Patch Colorimetry) levels outside the normal range (above 20). This lets us know that insoluble deposits are present in the oil. One must note that there may be instances where the deposits might not appear in the MPC test. As such, this should not be a standalone test to determine the presence of deposits.

RPVOT (Rotating Pressure Vessel Oxidation Test) levels are less than 25% compared to new oil (this is the warning limit). This is the industry standard, but this test does not have a high repeatability value in that if the same test were performed on identical samples, the values would be different. Additionally, the value (reported in minutes) is not easily translated into the environment of the components.

These tests provide us with the evidence we need to determine the presence of oxidation when performing the root cause analysis on the component’s failure.

Lubricant Degradation

How Can Oxidation Occur in Lubricants?

Typically, when an oil undergoes degradation, the first culprit to be blamed is oxidation. We often hear that the oil has oxidized, producing varnish, leading to its degradation. While this simple statement may seem plausible, it is not the only way oil can degrade.

If an oil has undergone oxidation, the real question we should be asking is not how much varnish has been produced but what caused the oxidation in the first place?

In this article, we will explore the various ways in which an oil can degrade via oxidation. However, as you know from previous articles, other degradation methods exist.

How Can Oxidation Occur?

Before diving further into the root cause of oxidation, one must first fully understand how oxidation occurs. When truly investigating a root cause for a failure, we should start with the question “How could?” rather than “Why?”.

This line of questioning heavily influences the answers. The “How could?” responses stem from a more evidence-based approach.

On the contrary, if we question “Why?” this is more opinionated and can mislead the investigation towards a biased opinion rather than the facts.

This leads us to the main question, “How can oxidation occur?”.

According to Ameye, Wooton, and Livingstone, 2015, oxidation occurs when there is any reaction in which electrons are transferred from one molecule. Ideally, in oxidation, during the initiation phase, free radicals are formed, which in turn produce more free radicals.

A free radical is a molecular fragment with one or more unpaired electrons which are accessible and can easily react with other hydrocarbons, as explained by Ameye, Wooton, and Livingstone, 2015.

After the initiation phase, which has the free radicals, the propagation phase follows, in which the antioxidants react with these free radicals to make them more stable. This is part of the reaction in which there is usually a drastic depletion of antioxidants or where the oil becomes sacrificial.

The antioxidants act as a barrier to protect the base oil from oxidizing. However, they can no longer protect the base oil once they become depleted. This leads to the termination phase, where the remaining free radicals attack the base oil.

As a result, this gives rise to the condensation phase, where we begin to physically notice the changes in the oil’s viscosity and the presence of insoluble by-products. These are the deposits that are known are lube oil varnish to some but can further be defined by their chemical composition.

Understanding how oxidation occurs can assist us in determining the root cause when an oil degrades. It allows us to identify the different stages to further help us determine if it is indeed oxidation that is occurring or not.

Lubricant Degradation

The Influence of Lubricant Selection on Degradation

Guidelines should always be followed when selecting a lubricant for a particular application. OEMs will have specific criteria ranges for specialty applications that must be satisfied. Some general guidelines which should be considered can be summarized in the table below based on the listed mechanisms above.

Based on the three listed mechanisms above, one can identify that choosing a lubricant can impact the type of degradation which occurs during its lifetime. As such, when selecting lubricants, it is critical to note their applications and the conditions they will endure.

Having a history of lubricant failures for particular equipment can also assist in this regard by informing users of past failure trends. Therefore, when selecting a lubricant, operators can be more mindful of the properties which should not be compromised during the selection process.

The process of troubleshooting degradation in lubricants has been covered in detail in the book, “Lubrication Degradation – Getting Into the Root Causes” by Bob Latino and myself, published by CRC Press, Taylor and Francis.

Find out more in the full article, "How lubricant selection impacts degradation and machine failure" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd.

Lubricant Degradation

Which Degradation Mechanism Is Affected?

My previous article published in Precision Lubrication covered six degradation mechanisms: oxidation, thermal degradation, microdieseling, electrostatic spark discharge, additive depletion, and contamination.

Upon further investigation, there are only three mechanisms where selecting the correct lubricant will impact the degradation mode. These are; oxidation, microdieseling, and electrostatic spark discharge. The properties of the lubricant can easily influence each of these degradation mechanisms.

When selecting a lubricant, especially for rotating equipment, one of the critical areas of importance is the performance of the antioxidants. When formulated, oils must be balanced to protect the components in various aspects.

Thus, some oils that boast a high level of antioxidants may suffer from low levels of antiwear, or these increased levels can react with other components to reduce the performance of the oil. During oxidation, antioxidants are depleted at an accelerated rate which can lead to lube oil varnish. Hence, the choice of lubricant can influence this degradation mechanism.

A good trending test, in this case, would be the RULER test to accurately quantify and trend the remaining useful antioxidants for the oil. This test can easily distinguish and quantify the type of antioxidant rather than providing an estimate of the oxidation, as with the RPVOT test.

It has been noted that oils with an RPVOT of more than 1000 mins have a low reproducibility value which can mislead users during trending of lubricant degradation. Corrosion inhibitors, not just antioxidants, have also influenced the RPVOT values. Thus, there are better tests for monitoring the presence of antioxidants and helping operators to detect the onset of possible lube oil varnish.

On the other hand, during microdieseling, entrained air can lead to pitting the equipment’s internals and eventually the production of sludge or tars depending on whether the entrained air experiences a high or low implosion pressure.

If bubbles become entrained in the lubricant and do not rise to the surface, this can directly result from the lubricant’s antifoaming property. The antifoaming property is essential when selecting an oil, especially for gearboxes. Typically, OEMs will have recommendations for their components that should be followed.

Another degradation mechanism that can be influenced by lubricant selection is electrostatic spark discharge. This mechanism occurs when the lubricant accumulates static electricity after passing through tight clearances. These then discharge at the filters or other components inside the equipment, providing sharp points or ideal areas to allow static discharge.

This is frequently seen in hydraulic oils due to the very tight clearances within the equipment. If fluid conductivity is above 100 pS/m, the risk of static being produced is reduced. Some OEMs also provide particular values the lubricant should meet for this property.

Lubricant Degradation

Has the Lubricant Failed the Equipment, or Has the Equipment Failed the Lubricant?

Many lubrication engineers are faced with finding the most appropriate lubricant for an application. Therefore, they are tasked with selecting the “right” lubricant; subsequently, their decision can influence several outcomes.

A lot of the positive results are in the realm of extending the life of the oil, providing better energy efficiency, and even saving costs associated with downtime. However, can the choice of an “incorrect” lubricant impact its degradation process or lead to the presence of lube oil varnish?

Has the Lubricant Failed the Equipment, or Has the Equipment Failed the Lubricant?

Lubricants provide many different functions. These can range from moving heat or contaminants away from the components, minimizing wear and friction, improving efficiency, providing information about the status of the lubricant, or even transmitting power, as is the case with hydraulic oils.

There has been the time aged question of whether a lubricant fails the equipment or the equipment has failed the lubricant. If a deeper dive is performed into this question, one can deduce that lubricants are engineered to withstand particular conditions.

Once those conditions are met, lubricants can perform their intended functions. However, if the conditions exceed the tolerances of the lubricant, then one will notice a faster degradation. In this case, the environment and its conditions have failed the lubricant.

On the other hand, lubricants are designed to be sacrificial and are used up while in service. Hence, it is normal to see additives’ values deplete when trending oil analysis values, especially for turbine oils. Quite notably, additives responsible for antiwear or extreme pressure will decrease over time as they protect the components.

For this instance, the lubricant would have been performing its function until it could no longer do so or has reached its end of life. The conditions in the environment cannot be blamed for the lubricant failing. This is the nature of the lubricant.

Lubricant condition monitoring lets analysts detect whether a lubricant is undergoing degradation and can even help determine some areas where it has begun to fail. For instance, if the RULER® test can quantify the remaining antioxidants in an oil. Analysts can easily interpret its results to determine if the process of oxidation is occurring within that lubricant.

Similarly, an FTIR test can detect whether contaminants are present in the lubricant or if the additive packages have become severely depleted. These tests all aid in allowing analysts to successfully determine whether or not a lubricant is performing at its full functional capacity.

Oil Properties

What are the types of Lubricant Additives?

There are many types of lubricant additives, and various formulations exist from different suppliers. In this section, we will cover the most common additives found in finished lubricants.

Pour Point Depressants

All liquids have a particular temperature at which they can effectively flow. The liquid’s viscosity and current temperature determine how quickly it moves. As the name implies, this type of additive can assist in lowering the temperature at which the lubricant flows¹.

What are the types of Lubricant Additives

VI Improvers

This should not be confused with Pour Point Depressants. Viscosity Index Improvers are also known as Viscosity Modifiers². They assist the lubricant in increasing its viscosity at higher temperatures, allowing lubricants to operate in wider temperature ranges.

Friction Modifiers

When two surfaces rub against each other, friction is formed. Depending on the type and extent of friction, some surfaces can experience welding and even adhesive wear. This is where friction modifiers can help by reducing frictional forces associated with stick-slip oscillations and noises.

Defoamants (Antifoam)

Some lubricants succumb to foam being created in their systems. When foam is made, it significantly impacts the functions of the lubricant and can lead to excessive wear due to lack of lubrication (they disrupt the surface of the lubricant), cavitation (due to the presence of air bubbles), and even increased oxidation (due to presence of air trapped in the system). Foam can also affect the ability of a liquid to transfer heat or cool. Defoamants or antifoam additives reduce the amount of foam being produced.

Oxidation Inhibitors (Antioxidants)

Oxidation occurs in most lubricants. During the oxidation process, free radicals emerge, propagating to form alkyl or peroxy-radicals and hydroperoxides, which eventually react with others to form oxidation by-products. During the propagation phase, antioxidants are usually deployed to neutralize the free radicals or decompose the hydroperoxides³. As such, these additives are sacrificial in nature, as they protect the base oil from oxidation by being depleted.

There are many types of antioxidants, including phenolics and aromatic nitrogen compounds, hindered phenols, aromatic amines, zinc dithiophosphates, and a couple of others.

Rust and Corrosion Inhibitors

If oxygen and water are present at a location containing iron, then rust can be formed. Corrosion affects the non-ferrous metals in the presence of acids in the lubricant¹. Most pieces of equipment succumb to rust and corrosion quite easily, so these inhibitors were developed to mitigate these effects by forming protective layers on the surfaces of the equipment.

Detergents and Dispersants

These two often get confused as they usually work together to prevent deposits from accumulating in the oils. Detergents neutralize deposit precursors (especially in engine oils), while dispersants suspend the potential sludge or varnish-forming materials⁴.

Antiwear Additives

Antiwear additives reduce friction and wear, especially during boundary lubrication conditions. They are designed to reduce wear when the system is exposed to moderate stress².

Extreme Pressure Additives

Extreme Pressure additives are usually confused with antiwear additives, or the names are used interchangeably. However, extreme pressure additives begin to work when the system experiences high stress and try to prevent the welding of moving parts, unlike antiwear additives, which work when the system experiences moderate stress.

Find out more in the full article, "Lubricant Additives: A Comprehensive Guide" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd.

Oil Properties

Why Do We Need Lubricant Additives?

Lubricants keep the world turning. Once something moves, a lubricant should be present to reduce friction or wear between the surfaces. But what makes lubricants so unique in our industry? Is it just the base oil?

No, this is where the power of lubricant additives truly shines, an area many overlook.

Why Do We Need Lubricant Additives?

Before getting into the world of additives, let’s step back to the basics: why are they needed? A lubricant is composed of base oil and additives. Depending on the type of oil, different ratios of additives will be used for the various applications. Additionally, each Lubricant OEM will have its unique formula for its lubricant.

To simplify this, we can think of making a cup of tea. The first thing we need is some hot water in a cup. This can be our base oil. It can be used on its own (some people drink hot water or use it for other purposes), but if we want to make a cup of tea, we must add stuff.

Depending on the purpose for which you’re drinking the tea, you may choose a particular flavor. Perhaps peppermint for improved digestion or to help improve your concentration or chamomile to keep you calm.

These flavors can represent the various types of oils: gear oils, turbine oils, or motor oils. Different blends are suited for different applications.

Now, while we’ve added the tea bag to the hot water (and some people can drink tea like this), others need to add sweetener or milk. These are the additives to the base oil (hot water).

Depending on the preference of the person drinking the tea, there will be varying amounts of sweetener (honey, stevia, or sugar) and varying amounts of milk (regular, low-fat, oat, dairy-free). The combinations are endless!

The same can be said of additives in finished lubricants. Depending on the type of oil (tea flavor, think gear or turbine oil) and its application (the person drinking the tea, with dietary preferences of being dairy-free or sugar-free), the combination of lubricant additives and their ratios will differ. The percentage of additives can vary from 0.001 to 30% based on the type of oil.

Additives have three main functions in a finished lubricant. They can;

Enhance – improve some of the properties of the base oil
Suppress – reduce some of the characteristics of the base oil
Add new properties – introduce new features to the base oil

The finished lubricant will have properties from the base oil and additives combined.

Find out more in the full article, "Lubricant Additives: A Comprehensive Guide" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd.

Oil Properties

What is the Difference Between Antiwear and Extreme Pressure Additives?

The terms antiwear additives and extreme pressure additives are often used interchangeably, suggesting that they provide the same functions in a lubricant. This is not exactly true. While there are many similarities in how they function, both additives have distinct functions in protecting lubricants.

Both are film-forming additives (Bruce, 2012). Their functions are to reduce wear between two contacting surfaces or reduce friction to lower the heat produced between the two rubbing surfaces.

They can also be classified as boundary additives that can be temperature-dependent (EP additives) or non-temperature-dependent (Antiwear additives). They both function to mitigate against wear, which is usually caused during boundary lubrication where higher speeds, loads, or temperatures can cause contact with the asperities.

The Difference Between Antiwear and Extreme Pressure Additives

One of the significant differences, as noted by Mang & Dresel, 2007 is that antiwear additives are designed to reduce wear when the system is exposed to moderate stress. On the other hand, EP additives are much more reactive. These are used when the system’s stress is very high to prevent the welding of moving parts.

According to (Bruce, 2012), there are four main groups of commercially available EP additives based on the structures containing phosphorus, sulphur, chlorine, and overbased sulfonates. He explains that the phosphorus, sulphur, and chlorine-containing EP additives are activated by heat over a range of temperatures.

For instance, chlorine-containing EP additives are usually activated between 180-240°C, phosphorus-containing additives are activated at higher temperatures, and sulphur-containing additives operate at 600-1,000°C.

On the other hand, overbased sulfonates contain a colloidal carbonate that reacts with iron to form a thin-film barrier layer between tribocontacts. This protects the surface from direct contact and welding.

As we can see, antiwear and EP additives protect the surfaces between which the lubricant exists. However, they are activated differently and subsequently perform two different functions.

Antiwear additives protect against wear and are not temperature dependent, while EP additives are activated by high stress to prevent the welding of moving parts.

Both functions are essential to protecting the system from additional wear and ensuring it remains operational.

References

Bloch, H. (2009). Practical lubrication for industrial facilities, Second edition. Lilburn: Fairmont Press Inc.

Bruce, R. W. (2012). Handbook of Lubrication and Tribology, Volume II, Theory and Design, Second Edition. Boca Raton: CRC Press Taylor and Francis Group.

Coyle, C. L., Greaney, M. A., Stiefel, E. I., Francis, J. N., & Beltzer, M. (1991, Feb 26). United States of America Patent No. 4,995,996.

Mang, T., & Dresel, W. (2007). Lubricants and Lubrication, Second, Completely Revised and Extended Edition. Weinheim: WILEY-VCH Verlag GmbH & Co. KGaA.

Mortier, R. M., Fox, M. F., & Orszulik, S. T. (2010). Chemistry and Technology of Lubricants, Third Edition. (C. Bovington, Ed.) Dordrecht Heidelberg: Springer Science+Business Media B.V. doi:10.1023/b105569_3

Pirro, D. M., Webster, M., & Daschner, E. (2016). ExxonMobil, Lubrication Fundamentals, Third Edition, Revised and Explained. USA: CRC Press Taylor and Francis Group.

Zhang, J., & Spikes, H. (2016). On the Mechanism of ZDDP Antiwear Film Formation. Tribol Lett, pp. 1–2.

Find out more in the full article, "Antiwear Additives: Types, Mechanisms, and Applications" featured in Precision Lubrication Magazine by Sanya Mathura, CEO & Founder of Strategic Reliability Solutions Ltd.