In the 21st century, we are dealing with several severe environmental issues like pollution, global warming and fast depletion of natural resources. These are directly linked to the global energy consumption. Out of many things happening in our daily life, friction and wear are major occurring phenomena that we are dealing with. They contribute to 23% of the global energy consumption. Friction accounts for 20% and wear and wear related failures contribute to 3% of this 23%.1 Whether it be cars, household appliances, industrial machinery, pumps etc., each one of them experience some kind of friction and wear when metals’ parts inside them slide against each other. This leads to energy losses. Science behind interacting surfaces, i.e., tribology plays a significant role in our life. Nano-lubricants have proved to be the next generation alternatives to conventional lubricants like engine oil, mineral oil, vegetable oil etc. They have led to substantial reduction in friction and wear behaviour of these conventional oils. Several studies have been carried out in literature with different additives such as carbon-based materials like graphene, Single Wall Carbon Nanotubes (SWCNT), Multiwall Carbon Nanotubes (MWCNT), Graphitic Carbon Nitrides (g-CN), Reduced Graphene Oxide (r-GO) etc.
Carbon based materials can be easily processed and are being used for versatile applications as they readily combine with other carbon-based materials or non-carbon-based materials forming strong bonds. These materials have astonishing and remarkable characteristics such as high hardness, high density, high strength and physical, chemical, electrical and thermal properties. These material properties can be easily tailored and have shown promising results in various energy applications.
Nanocarbon is no-doubt a wonder material for tribological applications. In a step to reduce the energy losses, our lab has developed many novel energies conserving carbon-based nano-lubricants and nano-coolants. Solar exfoliated graphene dispersed engine oil results in 80% reduction in friction and 33% reduction in wear compared to the base oil.2 Nitrogen doped rGO based nano-oils results in a decrease of 25% in coefficient of friction in comparison with base oil. This nano-oil was tested in induced draft fans in thermal power plant (NTPC) and have remarkably decreased the power consumption.3 MWCNT based nanofluids also been used for direct absorption solar thermal energy, significantly enhanced the heat transfer and solar absorption properties, thereby improving the overall efficiency of the machinery. Results revealed that solar energy can be harvested more efficiently in Direct Absorber Solar Collectors with these nanofluids. This is not the case for conventional solar collectors.4 Graphene wrapped MWCNT dispersed in de-ionized water and ethylene glycol displayed improved thermal conductivity compared to pristine carbon nanomaterial.5 Functionalized hybrid nanostructure of MWCNT and hydrogen exfoliated graphene based nanofluids improved the thermal transport properties, suggesting the use of these nanofluids for coolant applications.6 Iron nanoparticles infused CNT dispersed in gear box oil, vegetable oil and engine oil results in a substantial reduction in friction.7,8 These nano-lubricants form a protective film in between the sliding surfaces preventing severe wear damage by transfer of additive residues on to the sliding surface and thereby forming strong bonds with the surface. Functionalization and tuning of material properties have led to the design of environmentally friendly and non-toxic nano-lubricants and nano-coolants. These works have indeed helped researchers to develop newer materials and subsequently helped to improve the efficiency and performance of the devices and machinery by reducing the energy consumption and losses.
Another added advantage of the lubricants is that they can be used as coolants and termed as cooling lubricants. Simultaneously, they transfer heat generated at the interacting sliding surfaces to the surroundings for heat dissipation thereby avoiding overheating. These nano-oils can be circulated in and around the industrial machinery like pumps, transformers, radiators, automotive etc. Anti-corrosion additives are highly beneficial for significantly improving the energy efficiency.
Reduction in friction and wear can considerably contribute to lowering the emission of greenhouse gases thereby combating climate change. Current trend is that the industries are moving towards the use of energy conserving lubricants. They are implementing various specifications and testing procedures to improve fuel efficiency. This in turn helps to economize the energy consumption thereby reducing the operational cost, lifespan, maintenance, repair of the machinery. Development of newer energy conserving lubricant for other base oils is the need of the hour in order to achieve significant reduction in global energy consumption and meet the sustainability goals for greener future.
Shubhang Srivastava is an interdisciplinary Ph.D. scholar at IIT Madras in the Department of Physics and Metallurgical and Materials Engineering. He did his Master’s in Energy Science and Technology from Ulm University, Germany. His research interests are nano-lubricants, nano-coolants and supercapacitors.
Prof. Sundara Ramaprabhu After completing Ph.D. in Physics from Indian Institute of Technology Madras, Chennai, Dr. S. Ramaprabhu worked at Darmstadt, Germany for 2 years as Alexander von Humboldt-Stiftung Fellow and for 5 years at University of Geneva, Switzerland. He is a DAAD Fellow, Visiting Fellow to Germany, South Korea and Japan. He is a member of American Chemical Society and Member of Electrochemical Society. His research areas are Nanotechnology, Hydrogen Energy Technology, Fuel Cell Technology. He has guided 45 Ph.D. students and developed 10 technologies. He has published in 420 International journals of repute and has 53 patents. He has delivered 210 invited talks in International and National Conferences.
