Lets learn about Tribotronics and Tribocatalysis

Tribotronics

Tribotronics is a term coined by The Division of Machine Elements at Lulea University of Technology. Tribotronics in simple terms means developing an active tribological system or converting a passive tribological system into an active one. Tribotronics is still a concept and requires a lot of research and development before it can be brought into practical applications.

Tribotronics can be referred to as an advanced tool/method of predictive maintenance. Predictive maintenance involves regular monitoring of indicators of machine condition, which provides the data which can be used to predict when maintenance should be performed. Tribotronics is an integration of Tribology and Electronics. It employs a sensor that monitors the tribological parameters of a system in real-time that helps in determining the actual state of the system.

A Tribotronic system consists of four main components:

1. Sensors: Extracts tribological data about the condition of the system and transmits it to the central processing unit.
2. Central processing unit (CPU): Tribological data received from various sensors is processed by software’s in real time and a solution to the problem in the form of output is sent to actuators.
3. Actuators: Implements the solution received from central processing unit
4. Computer: Allows the user to view and control the adjustments or solutions made by the Trbotronic system.

In order to understand the working of Tribotronic system, consider a piston sliding against cylinder wall. The sensors will look for friction or wear loss (which can be in the form of material loss or weight loss) at the interface of piston and cylinder wall contact. This data is picked up by sensors and processed by a CPU. Depending on the results, the CPU can actuate lubricant injectors using tribo-actuators to dispense lubricant at the interface to reduce friction or wear. The CPU can calculate quantity and quality of lubricant required for the particular interface in order to maintain existing lubrication regime and also can re-introduce additives in case of additive depletion in a lubricant.

A more practical example has been referred by Sergei Glavatskih and Erik Hoglund in their paper “Tribotronics—Towards active tribology”. The authors depicts the use of a micro-heater which acts as a tribo-actuator for providing “on-demand” lubrication in space applications when friction between tribo-contacts increases.

A Tribotronic system helps in reducing inspection costs as causes/conditions leading to failure are predicted earlier via electronic sensors and systems. The technology focuses on automated sensors and data processing units which helps in reducing labor costs. Failure of machine components reduces which leads to decrease in equipment cost and down time.

Tribotronics is the future of maintenance. Proper data on friction and wear of mechanical components will help in improving the life and reliability of the entire machine. Further research and development can help in decreasing tribological failures in machines.

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Tribocatalysis

Tribocatalysis is a subsection of tribochemistry dealing with the changes of catalytic properties of solids due to the effect of mechanical energy. A catalyst decreases the activation energy (Ea) required to initiate the reaction process. Tribocatalysis also lowers the activation energy, and lowers it even more than regular catalysis. The tribocatalytic process does not need heat to initiate the reactions while the regular heterogeneous catalytic process needs an elevated temperature of at least 200◦C.

Tribocatalytic enhancement types

There are two types of tribocatalytic enhancement of chemical reactions:

1. One is when the catalytic reaction is enhanced by friction. The catalyst is activated by the mechanical energy associated with mechanical treatment. This mechanism is called tribo-activated catalytic reaction.
2. On the other hand, when the tribochemical reaction is enhanced by the existence of catalyst. The wear particles can be a catalyst because their elemental size is as small as commonly used catalyst. The mechanism is called catalysed tribochemical reaction.

Tribocatalysis and NIRAM approach

In catalytic processes, relatively small energy is input to the system to promote reaction, which is common in three catalytic systems – Tribocatalysis, photocatalysis, and electrocatalysis. In tribocatalytic reactions the source of low energy is the low energy electron emission, which is one process of the NIRAM approach.

The negative-ion-radical action mechanism (NIRAM) approach was proposed by Kajdas (Bhushan and Kajdas, 2001; Kajdas, 1985a, 1985b, 1987 and 1994). The NIRAM approach considers several processes: (a) emission process and creation of positively-charged sites, generally on tops of asperities; (b) action of the emitted electrons with some additives causing formation of reactive negative ions and free radicals; (c) reaction of negative ions with activated metal surfaces, and other reactions, e.g., free radical reactions, forming tribofilm.

The NIRAM approach was proposed in order to explain the mechanism of tribochemical reactions. Reactions are said to be initiated by low-energy electrons (exoelectrons) emitted under boundary friction conditions. Emitted electrons interact with molecules in the contact area, which then dissociate forming a negative ion and a radical or a negative ion radical. Emitted low-energy electrons can initiate tribochemical reactions, which govern tribology processes by forming AW films.

The detailed mechanisms of tribocatalysis have not been elucidated as much as those of photocatalysis or electrocatalysis, because in tribocatalysis many physical and chemical processes take place at the same time and they are interrelated to each other. In addition, chemical compounds formed during the wear process may act as catalysts, although it is difficult to characterize the real function of such catalysts.

Examples of tribocatalytic reactions – Oxidation of carbon monoxide

When palladium was rubbed against aluminum oxide in an atmosphere of carbon monoxide and oxygen, carbon dioxide is produced. When sliding commenced, the pressure of carbon monoxide and oxygen started to decrease; on the other hand, that of carbon dioxide increased. This means that the synthesis reaction of carbon dioxide is enhanced by the rubbing of palladium catalyst against aluminium oxide.

Tribocatalysis provides an alternative approach for forming lubricants lubricants with conventional EP additives

A new approach to extreme pressure lubrication has been developed through the use of tribocatalysis. Under severe operating conditions, a nanocoating containing a catalyst based on a transition metal facilitates the in-situ conversion of a lubricant base oil to form a tribofilm containing amorphous carbon species. The tribofilm demonstrates superior reductions in coefficient of friction and wear.

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References according to indivisual topics

1. Glavatskih, Sergei, and Erik Höglund. “Tribotronics – Towards Active Tribology.” Tribology International 41.9-10 (2008): 934-39, https://doi.org/10.1016/j.triboint.2007.03.001.
2. Adachi K, Kato K. Reliable design of space system in tribology viewpoint. In: 22nd international symposium on space technology and science, 2000, p. 593–8.
3. Adachi K, et al. Micro-system of lubrication with in-situ tribocoating for space mechanisms. In: International tribology conference, Kobe 2005
4. Liu, Ying, Simiao Niu, and Zhong Lin Wang. “Theory of Tribotronics.” Advanced Electronic Materials 1.9 (2015): 1500124
5. Kajdas, C., and K. Hiratsuka. “Tribochemistry, Tribocatalysis, and the Negative-ion-radical Action Mechanism.” Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 223.6 (2009): 827-48. – Main source of above article
6. Pawlak, Z. “Chapter 5: Surface Tribochemistry and Activated Processes.” Tribochemistry of Lubricating Oils. Amsterdam: Elsevier, 2003. 183-84
7. “Definition of Catalyst.” Chemistry Dictionary. Web. 23 Jan. 2017. http://www.chemicool.com/definition/catalyst.html
8. Tribocatalysis: A new extreme pressure lubrication approach. Dr. Neil Canter (Contributing editor), TLT Magazine – An STLE Publication, October 2016