KEY CONCEPTS
• Lithium-based greases are the great all-rounders and account for around 50% of all grease sold globally.
• Fluctuations in the price and availability of lithium hydroxide monohydrate have led grease manufacturers and their customers to consider alternatives.
• An alternative thickener system with similar flexibility to be used across a wide range of applications has yet to be identified.
Many articles, blogs and podcasts have been devoted to the rising demand for lithium from battery manufacturers, the resultant declining fraction of the lithium hydroxide market held by grease manufacturing and, therefore, the fluctuations in availability and price for the manufacture of lithium-based greases. Many focus on likely replacements from a wide variety of alternative thickeners,¹ considering the applications in which a particular alternative thickener type could substitute for one with a lithium-based thickener, and the potential additivation required to address some of the performance detriments.

The problem for formulators, lubrication engineers and sales staff when suggesting alternatives is that lithium greases are the “great all-rounders,” whereby a single customer can use the same grease or family of greases in multiple applications, so minimizing the chances of serious contamination if the wrong grease is applied. Lithium greases are often cheaper than alternatives and, therefore, more widely available and better understood.

So, rather than another article about replacing lithium, this article is a primer for those new to the industry (and hopefully a reminder for those more experienced) of the strengths of the individual grease types and their logical use in certain applications.

The basics
Greases—more accurately lubricating greases—are semi-solids consisting of a lubricating oil (synthetic, mineral or natural base fluid, plus additives) mixed with a thickener system. The thickener helps to retain the base oil and additives in the lubricated part, while releasing the oil and additives during operation. 

The thickener may be a metal soap, derived from lithium, sodium, calcium or aluminum or non-soap derived from a different chemical reaction, such as so-called calcium sulfonate or polyurea greases. A further sub-class of non-soap thickener covers dispersions of solids in oil: clays, silica or organic polymers, such as polytetrafluoroethylene (PTFE). Most tribological function comes from the oil and associated additives, the thickener’s main role being to retain the lubricating oil in the contact, for example in a bearing or an open gear (see Figures 1 and 2). 


Figure 1. A greased bearing.


Figure 2. Grease on an open gear of a rotary cement kiln. Figure courtesy of Carl Bechem GmbH.

Under shear, the viscosity of the fluid usually decreases rapidly and approaches that of the base oil, such that many greases are sold with a viscosity for the grease itself (on the NLGI scale²) and reference to the viscosity of the base oil included in the product name. A grease intended for high-load/low-speed applications requires a more viscous base oil than one intended for high-speed applications, for example, but they could have the same NLGI consistency (see Figure 3).


Figure 3. Lubricating greases are often sold with some reference to the base oil viscosity. Figure courtesy of Shell.

Manufacturing processes differ with the grease type. However, for most common greases, manufacture requires a chemical reaction to produce the thickener in situ, which is followed by addition of the additives. This makes grease manufacture significantly different from the mixing processes that are required to produce most liquid lubricants.

According to the annual NLGI Lubricating Grease Production Survey Report,³ the dominant grease types are lithium soap, lithium complex, anhydrous calcium and urea, which together accounted for over 80% of production in 2023. There are many other types of thickener, each with their unique properties. “The NLGI survey covers 12 thickener types representing the majority of global manufacturing volume,” says STLE member Gary Dudley, president of GKD Consulting & Services, which took over management of the survey on behalf of NLGI in 2024.

A lubricating grease should maintain its consistency over its working life, releasing the oil to provide lubrication during operation, while also preventing oil leakage from the contact. The ability of the grease to do this is tested by its worked penetration, oil separation and dropping point. There is a common misinterpretation that dropping point is an indication of the maximum working temperature for a grease. “Dropping point [is the temperature] at which the thickener is no longer able to support the grease matrix. Maximum upper working temperature is well below the dropping point,” says STLE member Dennis Eijdenberg, technical support manager at Axel Christiernsson.

As most greases are used in open or semi-open applications, some applications also bring the grease into contact with water, so water wash out, water resistance and corrosion resistance are also commonly tested and reported. Other tests regarding oxidative stability and wear prevention are influenced more by the additives than the thickener. 

Many other tests are dictated by the application, where resistance may be required to one or more of extremes or variation in temperature, load or humidity. Greases may also face environments where contamination of the grease is highly likely, such as mining, agriculture or on-deck equipment on ships, or where the grease could be a contaminant if it was released, such as food and pharmaceutical manufacture or release (accidental or intended) into water or onto land.

Lithium greases
The most common grease thickener type globally (but not in North America) is in decline, accounting for 38% of all grease sales by weight in 2023, but having been 50% of the market as recently as 2020.³ While several factors may have introduced short-term perturbations of recent annual data, the trend can be measured back for many years. 

The saponification reaction to produce lithium greases is usually between lithium hydroxide monohydrate and 12-hydroxystearic acid, or 12-HSA, producing one equivalent of water for every equivalent of the lithium 12-hydroxystearate (12-HS) salt. The lithium hydroxide is often added as an aqueous solution. This, and the water of reaction, must be removed, so the temperature of the mixture is raised to around 200°C to aid in removal of the water and finish the grease reaction. 

Lithium greases may also be produced by reacting lithium hydroxide with less refined raw materials, such as hydrogenated castor oil fatty acid (HCOFA) or hydrogenated castor oil (HCO). HCOFA is roughly a 9:1 mix of 12-HSA and stearic acid (same chain length, but no hydroxyl group). HCO is another traditional raw material, which also liberates glycerol on saponification. Glycerol has some benefits for a grease, but is difficult to remove, due to its boiling point of 290°C. 

So far, so chemically simple, but it’s what happens as the solid lithium 12-HS salt crystallizes that lends lithium grease its unique properties. The lithium soap thickener forms a matrix of fibers that can hold the lubricating oil in situ (see Figure 4). Such structures were imaged by scanning electron microscopy and reported as early as 1947. Generally, the more rapid the cooling rate, the shorter the fibers and the more mobile the grease. A further step called milling or homogenization is usually used. This is typically a higher shear process that gives the grease its smooth appearance and improves the structural stability of the grease.


Figure 4. Scanning electron micrograph of a lithium 12-hydroxystearate grease thickener network. Figure courtesy of Hodapp, A., Conrad, A., Hochstein, B., Jacob, K.-H. and Willenbacher, N. (2022), “Effect of base oil and thickener on texture and flow of lubricating greases: Insights from bulk rheometry, optical microrheology and electron microscopy,” Lubricants, 10 (4): 55, https://doi.org/10.3390/lubricants10040055.

As stated previously, lithium greases are the great all-rounders, which can see them used in almost every application around a workshop or factory. “For most applications simple lithium soap-thickened greases are sufficiently shear stable and water repellent,” according to Tim-Oliver Mattern, global market manager – steel at Carl Bechem GmbH. They are also relatively cheap, due to the relatively low cost of raw materials and relatively simple manufacturing process. 

“Lithium greases have no intrinsic disadvantages,” says Andy Waynick, technical editor of NLGI Spokesman, with many years of experience in grease R&D. As such, “lithium grease can be seen as a jack of all trades but a master of none,” according to Eijdenberg. 

However, lithium thickener technology “does not provide much in the way of intrinsic functional properties such as extreme pressure (EP)/antiwear (AW), oxidation inhibition, corrosion inhibition and water resistance,” warns Waynick. “For applications where maintaining true grease rheology is required, performance is limited to moderate elevated temperatures due to the thickener losing its ability to maintain such rheology as the temperature approaches the dropping point.” However, as they are compatible with all common lubricant base oils, similar additive chemistry to liquid (industrial) lubricants can be applied to enhance performance. “Nearly all commonly identified performance areas can be improved by correct use of additives,” says Waynick. 

But that performance improvement may not be sufficient for many applications. “When enhanced performance is required in more demanding applications, mixed soaps, lithium complex greases or other thickener types will have to be used, according to the required aspects and lubrication challenges,” says Eijdenberg. So, while lithium greases are the great all-rounders, there is room for improvement in almost every aspect of grease application. From the outset there was significant R&D output of both scientific papers and patents identifying methods by which grease performance could be improved (see Figure 5).


Figure 5. A comparison of grease thickener properties drawn from many sources.

Lithium complex greases
Comparatively much more popular in North America than simple lithium soap-based greases, lithium complex greases have enhanced thermal and shear stability. “In operational terms, this … offers the potential for extended product application versatility and in-service durability,” says Eijdenberg.

Most lithium complex greases are formed by adding dibasic acids (usually carbon chains with an acid group at each end) to the lithium hydroxide reaction mixture. According to Waynick, the reaction products are not “complexes” in the chemical term, as there are no atomic scale interactions between the separate ingredients. Rather, they are mixtures of thickeners. “So much of the properties of lithium complex greases is about co-crystallization of the simple lithium soap component and the other component used to make the lithium complex thickener in the manufacturing process,” he continues. Many hours of process development have been devoted at many different grease manufacturing plants to optimizing conditions for a given grease reactor.

“Lithium complex thickeners can be seen like small pore, industrial sponges,” says Eijdenberg. By contrast, simple soap lithium thickeners are analogous to bath sponges, that usually have large pores and release almost all absorbed liquid quickly and with little applied force. “Lithium complex thickeners release their oil more gradually under pressure, are harder to tear apart and are able to operate over a wider temperature range.”

Boron-containing compounds—usually boric acid or organic derivatives—can also be used to raise the dropping point of lithium greases. However, their mode of action is through chemical reaction with the Li-12 HS, unlike the organic diacids described previously. Boron reacts with hydroxyl groups on the 12-HS chains, forming a chemical bridge between the organic moieties.

Boron brings additional functionality to the grease beyond an increased dropping point. Depending on the boron compound used in manufacture, the resulting grease could have enhanced wear or oxidation resistance or rust inhibition relative to complex greases manufactured using different boron compounds. 
Borated lithium complex greases are usually manufactured using 12-HSA, not HCO. “The liberated glycerol will react preferentially [with the boron compound], preventing the cross-linking reactions that raise the dropping points,” explains Waynick.

While lithium complex thickeners are more shear and temperature stable, there are potential drawbacks. “The significantly higher amount of ionic lithium in the overall grease (relative to simple lithium soap), can [require] higher levels of certain performance additives to achieve the same boost in performance,” says Waynick. For the same reason, the cost of lithium complex greases will be significantly higher than simple lithium soap greases. 

There are several grease experts, mainly in Europe, who consider that the use of lithium complex greases for many applications in North America is not justified on technical grounds, as simple lithium soaps or anhydrous calcium greases are more than fit for the required lubrication tasks.

Lithium-calcium greases
Also referred to as calcium-lithium greases, these mixed simple soap thickener systems—produced by adding calcium hydroxide to the saponification process—will have their own category in the 2024 NLGI Survey, to be published in mid-2025. Previously, manufacturers have chosen to collect production volumes into either the lithium or calcium categories. 

According to Eijdenberg, “Calcium-lithium is often used as the platform from which to develop grease targeting those applications exposed to more harsh, heavy-duty operating conditions where high loads, slow speeds and water and dirt may be prevalent. Typically, increased base oil viscosities are applied, sometimes in combination with polymers and specific other additives to enhance adhesiveness and protection against corrosion, water ingress as well as water wash out.” Applications include marine and dredging operations, wheel bearings in agricultural and forestry equipment and a wide range of applications in forestry, mining agriculture and cement production, such as chassis components, slew rings, plain bearings and bushes, pivot pins, connectors and couplings.

Anhydrous calcium greases
The third highest volume of global manufacture, anhydrous calcium thickeners are also based on soaps—in this case, the reaction of an inorganic calcium salt with 12-HSA and/or HCO. “Anhydrous calcium greases are water repellent, have a high load carrying capacity and are cost efficient,” says Mattern. However, according to Waynick, “the measurable level of intrinsic corrosion protection and water resistance imparted by the thickener is typically not enough to pass the most commonly used corrosion (rust) prevention and water resistance tests.” So, some additivation is still necessary.

Anhydrous calcium greases are the thickener type with the fastest global volume growth but beware statistics! “The majority of growth [in manufactured volume] seen with anhydrous calcium greases is limited to the Chinese market,” says Dudley. “Typically, the choice to move to an anhydrous calcium grease these days is based on cost relative to a lithium grease and not performance.” Indeed, production of anhydrous greases has stalled or fallen back in North America and Europe and—reflecting the geographical variation in grease markets—anhydrous calcium greases hardly feature in Japan.³

On the positive side, “Anhydrous calcium thickeners are approved for use in incidental food contact (H1). Furthermore, they are approved for use in environmentally sensitive applications, making them ideal for use in (total) loss applications in marine, agriculture, forestry or rail,” according to Eijdenberg. The raw materials for manufacturing the anhydrous calcium thickener are on the Lubricant Substance Classification list (LuSC-list) in Europe,⁴ which identifies components and packages approved for use in lubricant formulations intended to be submitted for European Ecolabel certification.

With very good low-temperature and low-speed performance and very good water resistance, the applications are similar to lithium-calcium greases. The hydrophobic nature of the thickener leads to a wide range of uses in marine applications including on deck equipment and cargo doors, as well as applications in agriculture, forestry, off-road applications and rail.

Urea greases
Called “polyurea greases” by many, these grease thickeners suffer from another chemical misnomer, in that the thickeners are oligomers, not polymers. “Most of the urea greases available on the global market are diurea [or] tetraurea with longer molecular chains. Real polyurea thickeners with even longer molecular chains are a brand-new development and are currently just introduced to the market,” says Frank Reichmann, technology manager bearings at Carl Bechem GmbH. Unlike all other greases covered by the NLGI survey, urea greases are metal free. 

Invented in the 1950s,⁵ most urea greases are manufactured using highly toxic reagents—particularly the di-isocyanates. The good news is that the grease thickeners themselves are non-toxic. Indeed, some are even approved for incidental food contact. The search has been on for many years to find less dangerous precursors that are also cost effective. The costs of health and safety mitigations tend to keep the price of these greases high, and their availability limited to a relatively small number of manufacturers.

Urea greases have many performance strengths. “They are water repellent, have high load carrying capacity, chemically resistant, have a very high dropping point and can be customized for various applications,” says Reichmann.

“Polyurea greases can generally be divided into shear stable and shear unstable versions, usually dictated by the type of isocyanate and amines used in manufacturing. The shear stable versions display … high temperature resistance, a high degree of mechanical stability and very good antioxidative behavior,” says Eijdenberg. Shear unstable urea thickeners can amongst others be found in non-demanding agricultural applications.

“The ability to customize a polyurea’s performance based on the raw materials used is a unique feature that allows you to tailor [these] greases to a range of different of applications,” says Dudley. “These include the high-temperature and high-speed properties for electric motor applications, while adjusting shear properties for use in constant velocity joints (CVJs).” However, the wide variety of possible chemistry means that some urea thickeners aren’t compatible with each other, nor with most of the soap-thickened greases in the market.

“Urea-based thickener greases respond very well to antioxidants,” says Waynick. “Depending on how the urea-based thickener is made, the thickener may itself provide significant oxidation inhibition properties, something that other well-established traditional thickener systems do not provide.”

There is a strong regional bias in markets whereby urea greases command roughly 10% of the global manufacturing volume, but 30% of the volume in Japan. According to Dudley, “Initially, demand was driven by the automotive markets need for use in CVJs. But now they are recognized as superior greases for high-temperature/high-speed bearing applications. Generally, the market recognized that the higher cost does justify the investment for longer equipment and grease life.” 

Waynick agrees about demanding applications, “Urea-based greases have established themselves as the gold standard for certain high temperature applications such as high-speed, high-temperature electric motor bearings, CVJs and automotive wheel bearings.” 

Per Reichmann, “in a steel mill, urea greases are found in high-temperature applications like strand guide rolls in continuous casters and roller table rolls near furnace exits. Ester-based urea greases with low-noise properties are nowadays applied in high-speed applications such like drive trains of electric vehicles.”

Calcium sulfonate greases
Calcium sulfonate greases are a unique class of greases in terms of their manufacturing route, as they start from one of the most common lubricant detergents: highly overbased calcium alkylbenzene sulfonates. Whereas the detergent is a clear and bright Newtonian fluid, addition of small amounts of water and another non-aqueous material converts the mixture to a semi-solid. At the chemical level the calcium carbonate core of overbased detergent micelle is converted from amorphous (structure cannot be detected by X-ray crystallography) in the detergent to calcite, which has a lamellar structure.⁶

“In terms of providing intrinsic functionality, calcium sulfonate greases are easily the best of all the commonly used traditional grease thickener systems,” says Waynick.

They are “water absorbing, with high load carrying capacity, provide very good corrosion protection and have a very high dropping point,” says Mattern. “This sees them deployed in heavy-duty applications in earth moving equipment, excavators, work roll bearings in hot strip mills and pellet presses.”

Calcium alkylbenzene sulfonates are excellent rust inhibitors at low concentrations, so it is little surprise that the greases derived from them have excellent rust inhibition. “Calcium sulfonate greases provide good water resistance without the use of additives,” according to Waynick. “They can often be found in extremely wet applications, including where the lubricated part is submerged underwater. Also, various rust preventative applications requiring protection for very long times without relubrication are often well served by calcium sulfonate greases,” such as mining and construction equipment.

When first introduced, they had very poor low temperature pumpability, due to the relatively high level of the overbased calcium sulfonate in the thickener. This restricted the applications in which they could be used. These issues have been largely overcome by compositional and manufacturing process modifications, but the resulting calcium sulfonate complex greases have many components and complex manufacturing processes.⁷ This is seen by some as a significant barrier to their widespread adoption at the levels of market penetration currently enjoyed by lithium-based greases.

As calcite has a lamellar structure similar to graphite or molybdenum disulfide, the calcium sulfonate complex thickener system also has inherent load carrying capacity, so greases require less or no additivation for AW and EP applications. However, due to their relatively low oil separation, they are not well suited for high-speed applications. “If properly formulated and manufactured, calcium sulfonate-based thickener systems can be used in NSF H1 greases,” says Waynick. 

And there is more, according to Eijdenberg. “Calcium sulfonate complex thickeners are considered multi-complex thickeners, also referred to as functional thickeners, where the incorporation of additives into the soap structure instead of dissolving them in the base oil, significantly increases the lubricating characteristics of the final product. The product also adheres well to surfaces and forms a barrier toward dust and dirt. The technology is the prime choice for wet, dirty and highly loaded conditions, especially at low speed and medium to high temperatures, as found for example in high demanding steel mill applications.”

Aluminum-based greases
Aluminum-based greases are another soap-based grease. The majority of aluminum-based greases in the market are classed as complex greases. They are usually derived from a roughly 1:1:1 mixture of an aluminum source, a long chain acid and a short chain acid. Statistically, this means that each aluminum ion, which has three positive charges, is usually bound to one of each acid and a hydroxyl group. “Aluminum complex greases can be made with relative ease due to the clean and facile thickener formation reactions. They can be made in virtually all available base oils,” says Waynick.

Aluminum complex thickeners impart good tackiness, according to Mattern. “They provide a common base for open gear lubricants and have a low hardening tendency.” They are often deployed in the food processing industry, where they are able to function in high temperature applications.

But they have an Achilles’ heel, according to Waynick. “Aluminum complex greases have extremely poor shear stability at higher temperatures [and] will typically fail much more quickly on high temperature bearing life tests such as ASTM D3336 when compared to a polyurea or lithium complex grease.” These two problems have limited aluminum complex greases in high temperature applications where either sealed-for-life or very infrequent relubrication is required. 

Aluminum complex greases are used in steel mill and mining applications where frequent relubrication is possible, although calcium sulfonate complex greases have been gaining ground in such applications.

According to Eijdenberg, aluminum complex greases are also still used in extreme heavy loaded, slow moving open gears application, for example in mining. “The thickener here typically does not contribute much to the lubricating qualities of the product, and heavy-duty open gear aluminum complex greases are usually combined with a high level of solid additives content and a very high viscosity base oil blend, making pumpability and spray ability challenging,” he says.

Clay-based thickeners
Fine clays, particularly bentonite, have been used in grease making for centuries. When treated with reactive organic compounds and/or polar activators, they can behave as thickeners. “The use of clay as a gelling agent results in a grease that can be used at very high temperatures up to 200°C, as it does not melt or flow,” says Eijdenberg. “However, the absence of a fibrous matrix structure limits the mechanical stability of clay-based greases, and compatibility with other thickeners generally is limited, so this thickener comes with quite some challenges as well.”

One of the unique properties of clay greases is their ability to reversibly flex their consistency with the shearing forces they experience. “When properly made clay greases are sheared under low shearing forces, they will soften. If they are subsequently sheared under higher shearing forces, they will harden back up,” says Waynick. 

Clay greases flow well at low temperatures. However, the structure is not resistant to high shear, limiting applications in many areas. The unique chemistry also restricts the use of common lubricants additives. “Many of the most commonly used corrosion inhibitors will de-gel organo-clay greases,” says Waynick. In a parallel with aluminum complex greases, many oil-soluble EP/AW additives are not suitable for organo-clay greases, as their interaction with the thickener interferes with their surface activity. This can usually be compensated using dispersed solid additives to provide such protection.

While organo-clay greases have their niches, widespread use is highly unlikely due to their incompatibility with other greases. Dedicated kettles or a strict cleaning regime are required in a grease manufacturing plant. Alternatively, clay greases are purchased from a third party. Incompatibility in use requires careful flushing of equipment if greases are changed. Combined with some of the disadvantages stated above, it is a commonly held view that the market share is likely to decline further in the upcoming years.

Hydrated calcium greases
Often claimed to be the earliest patented greases, hydrated calcium greases (cup greases) are usually manufactured from lime (calcium hydroxide) and tallow. According to E. N. Klemgard in his 1937 book “Lubricating Greases: Their Manufacture and Use”:⁸ 

“It is probable that the beginning of our present art of cup grease manufacture can be found in the Partridge patent of 1835⁹ which refers to a ‘composition paste — as an antifriction, applicable to the bearings of wheels and machinery.’” 

The 1835 patent pre-dates the American petroleum industry by around 25 years, so almost certainly pre-dates the use of mineral oil in liquid lubricants.¹⁰ Nowadays they account for only around 2% of global production, with lower market share in Europe and North America.

The weakness is the poor high temperature performance, as loosely bound water, which stabilizes the grease matrix, evaporates above around 70°C. Cup greases are still used in marine applications such as stern-tube lubrication due to their high level of water resistance, but the increasing popularity and wider availability of anhydrous calcium thickened greases will render hydrated calcium greases outdated and obsolete.

What’s likely in the future?
Although recent price fluctuations have resulted in increased interest in potential alternative lubricating grease thickener systems, no one is forecasting that lithium-based greases are going to disappear soon. “It is very likely that lithium-based greases will continue to contribute a significant wedge in the world grease production pie chart,” says Waynick. 

R&D focus appears to be on optimization of raw materials without compromising properties, or addressing new requirements, such as sustainability. The search for an “all-purpose” thickener system that can match those based on lithium is probably lower priority than the development of specialized products for specific high demanding applications.
 
REFERENCES
1. Sosa, Y. (2024), “An update on lithium base greases” TLT, 80 (12), pp. 30-36. Available at www.stle.org/files/TLTArchives/2024/12_December/Cover_Story.aspx.
2. ASTM D4950-22. “Standard Classification and Specification for Automotive Service Greases,” ASTM International, West Conshohocken, Pa., USA. 
3. B. Farrington and D. H. Birdsall, Oil Gas J. 45, No. 46, 268–70275–9 (1947). Farrington, B. B. and Birdsall, D. H., “An electron microscope study of lubricating grease,” NLGI Spokesman, 11, p. 4, (1947).
4. https://ec.europa.eu/environment/ecolabel/documents/LuSC-list%20vs%2010012022.pdf 
5. Swakon, E. A. and Brannen, C. G. (June 14, 1955), U.S. Patents 2,710,839, 2,710,840, 2,710,841 to Standard Oil Company of Chicago.
6. McMillen, R. L. (March 22, 1966), U.S. Patent 3,242,079 to Lubrizol Corporation.
7. Muir, R. and Blokhuis, L. (Dec. 24, 1985), U.S. Patent 4,560,489 to Witco Corporation.
8. Klemgard, E. N. (1937), Lubricating Greases: Their Manufacture and Use, Reinhold Publishing Corporation, NY, USA, https://archive.org/stream/in.ernet.dli.2015.84129/2015.84129.Lubricating-Greases-Their-Manufacture-And-Use_djvu.txt.
9. British Patent 6945, Dec. 7, 1835.
10. https://mil-comm.com/lubricants/the-ultimate-historical-timeline-of-mechanical-lubrication/