Insights from the 24th International Colloquium Tribology

Advancements, Challenges, and Innovations in Lubricant Technologies

This year marked the 24th International Colloquium Tribology (TAE), which convened from January 23rd to 25th in its traditional location, Esslingen, Germany. Despite a slightly diminished attendance of approximately 300 participants compared to previous editions, the event maintained its international significance. The colloquium sustained its appeal to technical professionals from universities and technological centers, but experienced lower participation from lubricant blenders. Consequently, the discussions during the event leaned more towards academic perspectives, lacking input from lubricant blenders and original equipment manufacturers (OEMs). Simultaneously, as a lubricant ingredient supplier, it remained valuable to gain insights into the state-of-the-art developments, emerging trends in new technologies, and diverse methodologies and criteria for assessing various tribological behaviors. Sustainability, electric vehicles (EVs), and renewable energy emerged as prominent themes in the TAE discussions. On the networking front, uncertainties persisted due to geopolitical conflicts, a dearth of OEM specifications, environmental and chemical regulations, and a sluggish economic context compounded by high inflation rates.

One of the firsts articles of the TAE discusses the implementation of tribology and design principles to minimize carbon emissions and maximize return on investment in industry, aiming for a carbon-neutral approach. Tribology plays a crucial role in extending the service life of machinery, with wear resistance being a key factor during the design process. The shift from linear to elliptical economy models emphasizes the importance of leveraging existing knowledge in surface enhancement to promote longevity. Connected machinery, driven by machine learning and predictive maintenance practices, allows for proactive actions to prolong technical life, significantly reducing lifetime CO2 emissions. Design changes, such as modularization, become essential in the elliptical economy, providing flexibility, maintainability, and accommodating future upgrades. Low-friction solutions are prioritized to minimize energy consumption during the use phase, particularly in components like rolling bearings. The article concludes that despite existing technologies in tribology, economic viability and a lack of awareness among engineers hinder consistent application, emphasizing the need for a collective shift towards sustainability and shared costs across the life cycle value chain for effective adoption of tribological solutions.

Solvay introduced novel sulfur-free polymeric antiwear additives, denoting them as polymeric AW, distinguished by a remarkable 95% phosphorous content compared to traditional ZDDP (zinc dialkyldithiophosphate). The evaluation involved various 4-ball tests (ASTM D4172) to assess wear scar diameter, revealing comparable results to those achieved with ZDDP. The promotion of these polymeric additives is particularly targeted at electric vehicles (EVs). However, it is imperative to exercise critical scrutiny, advocating for additional testing to ascertain the complete substitution capacity of these additives for conventional AW additives. While 4-ball testing provides insights into point contact wear, it is essential to recognize the limitations of this methodology, as other configurations may exhibit more aggressive wear patterns. Additionally, ZDDP primarily acts as an extreme pressure additive, thereby contributing to reduced wear due to its capacity to mitigate extreme pressure. To establish a fair comparison, it is recommended to benchmark against pure antiwear additives prevalent in the market. Solvay's findings also indicated a reduction in conductivity relative to ZDDP, a logical outcome given the significant decrease in organometallics within the molecular structure.

Oleon and Cargill introduced their organic friction modifier technologies during their presentations. Oleon conducted a preliminary study comparing their polymeric ester structures with existing technologies, such as GMO (Glyceryl monooleate), MoDTC (Molybdenum di-thiocarbamate), amides, and polymerized glycerol esters. The focus of Cargill's presentation centered on the application of their technologies for Heavy-Duty Diesel Engine Oils (HDDEO) and the challenges posed by applications with hydrogen-fueled internal combustion engines, particularly in the presence of water. Both companies utilized the MTM tribometer to measure the coefficient of friction at different stages of the Stribek curve and supplemented their findings with images illustrating film-forming capacities. Notably, both presentations showcased tests conducted at temperatures exceeding 100 °C, steering away from discussions at lower temperatures where these technologies may exhibit reduced effectiveness due to their activation temperature, making them less suitable for industrial applications with operational temperatures below 100 °C.

In the segment dedicated to biobased additives, Solvay presented novel molecular structures derived from a two-step reaction process. The initial intermediate was synthesized through a decarboxylative ketonization reaction involving corresponding fatty acids (RCOOH). The resulting twin-tailed intermediate R-(C=O)-R could be further functionalized with amine/amide groups. Evaluation of these molecules was conducted using both the High-Frequency Reciprocating Rig (HFRR) and the 4-ball tribometer. Comparative analyses against conventional lubricating additives, such as GMO, MoDTC, and ZDDP, indicated that the presented chemical structures serve as promising alternatives based on their favorable wear and coefficient of friction results.

In the same section, King presented a water-emulsionable rust preventive concentrate characterized by effective multi-metal rust protection, even in challenging conditions like salt fog, high humidity, and salt atmosphere. The formulation demonstrated qualities of stable emulsions, low foam generation, ease of removal, and was noteworthy for being free of volatile organic compounds (VOC).

Regarding base oils, a limited number of presentations were conducted in this section. The University of Athens introduced a method for converting hydrocracker residues into a base oil closely aligned with Group II specifications, with the exception of its pour point value, which they sought to decrease through the application of PAMAs; however, the reduction was not sufficient. Additionally, two other presentations were centered on naphthenic (2–3 cSt @ 40 °C), specifically addressing very low viscosity naphthenic and their thermal stabilities.

Interesting and accurate way to describe the benefits of using esters within a formula, which are normally used as base oils due to their biodegradability and renewability potentials for EALs but not due to their unique and superior characteristics to enhance Group I to IV base oils, and therefore use less additives. Gemma Stephenson pointed that the utilization of esters can significantly enhance both the intrinsic and extrinsic properties of lubricants. Factors such as the choice of raw materials (petrochemical versus biobased), processing methods, and transportation practices play crucial roles in influencing the carbon footprint of a lubricant molecule. It is essential to note that even if a material is entirely biobased, its sustainability over the lifespan of an oil depends on its performance in use. Consequently, when assessing lubricants for specific applications, it is imperative to consider both intrinsic and extrinsic properties to make the most sustainable choice.

Another noteworthy aspect is the increasing significance of modeling as a tangible and valuable tool for predicting the performance of various molecules, along with assessing their bioactivity-toxicity.

These represent the most noteworthy insights from the 24th International Colloquium Tribology at the TAE. Over the span of three days, more than 100 presentations were condensed into sessions held in adequately equipped rooms.

Marc Alumà López
Lubricant BU Director, IQL

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