Green Nano Tribology

Si-wei Zhang, past chairman of the Chinese Tribology Institution, coined the term 'Green Tribology' and launched it as an international concept in June 2009.

Green tribology is the science and technology of the tribological aspects of ecological balance and of environmental and biological impacts. Its main objectives are the saving of energy and materials and the enhancement of the environment and the quality of life (Peter Jost 2009, [2]).












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Fig. 5.2 From the macro- to the nanoscale. New types of microscopy allow for visualization and active interaction on very small scales, and therefore open up whole new domains for science and technology, e.g. nanotribology. © 2010 Springer 1281

We need green tribology because of the current pressures on energy, materials and food [58]. A focus on tribology might give breathing space while fuller solutions to environmental problems are being addressed [2]. Tribology must fall into line with the major politics of world environment and energy. Economic benefits derived from the application of tribology for the UK comprise £8-10 billion, out of which 60-70% would be energy related, all this largely from existing and applied research (innovation) [2].

Tribology covers all length scales. In this chapter, we concentrate on nano-tribology (length scale some 10-9 nm). New types of microscopy now allow access to the nanocosmos, not just to view, but to interact (Fig. 5.2). This opens up completely new opportunities.

Nanotribology deals with nanosurfaces, nanoagents and nanoprocesses. For green nanosurfaces, points such as nanostructured surfaces, hierarchical surfaces, material selection, coated materials and monomolecular lubricant layers need to be addressed. The importance of nanosurfaces regarding Green Nanotribology is in the medium range. Of very high importance for Green Nanotribology are nano-agents. Points to address here are physical and chemical properties, the effect on the environment and biology, and the changes of the properties during the tribo-process. Regarding green nanoprocesses, the importance of points to address is in the medium to low range. Points to address comprise energy efficiency, the share between process relevant energy, destructive energy and waste and reusable energy as well as the effectiveness of reusing process energy [21].

In going green, tribology can benefit from a look at biology. Recently, biology has changed from being a highly descriptive science to a science that can be understood by engineers and researchers coming from the hard sciences, in terms of concepts, ideas, languages and approaches [24, 26]. In former times, tribology as well as biology used to be very descriptive. Inter- and transdisciplinary connections between the two fields were nearly impossible because of limited causal knowledge and limited causal relationships in both fields. This has changed. Today, we have increased causal knowledge [29] in both fields and therefore a promising area of overlap between tribology and biology [25, 30]. Causal knowledge indicates the fact that we know the relevant natural laws and can therefore construct explanations and forecasts. In biology, this is very often the case in physiology: We get cold feet when the vessels contract, because according to the laws of physics (fluid mechanics) less blood flows through these vessels (Drack, 2011, personal communication).

Biomimetics, the field that deals with knowledge transfer from biology to engineering and the arts, is a booming science that attracts more and more researchers, papers and attention [5, 48, 83]. Otto Schmitt [69], the inventor of the Schmitt trigger coined this field in 1982. One of the interesting aspects of such an interdisciplinary science as biomimetics is the variety of the publication channels. The author of this chapter for example has long been working in the field of bioinspired nanotribology and has published in journals as diverse as the Polish Botanical Journal (touching on the tribology of photosynthetic microorganisms with rigid parts in relative motion on the nanoscale) [78], Nano Today, elaborating on the tribology of biological hinges and interlocking devices, natural switchable adhesives and self-repairing molecules [22], the Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology (touching on hinges and interlocking devices in microorganisms, [23]) and Tribology [25], proposing new ways of scientific publishing and accessing human knowledge inspired by transdisciplinary approaches regarding nanotribology. Biological best practice systems regarding nanotribology are functional and—in many cases— beautiful (Fig. 5.3).

Turning nanotribology green implies more than just the usage of sustainable additives [21]. Tribology is a systems science; therefore also the environment and the development with time have to be accounted for.

Nanoagents in tribology are additives, products of the additives and byproducts that appear in the system after the technological application. Reaction products (which can be harmful) have to be either chemically inert after use or are fed back to the system for further usage (waste-to-wealth concept). Not-used nanoagents need to be either inert or fed back to the reaction. Potentially harmful byproducts that have nothing to do with the initial nanoagent need to be either neutralized or re-used. Biomimetic tribological nanotechnology might help to turn nanotribology green, but it cannot be stated often enough that biomimetics does not automatically yield sustainable or even just green products [29].

Green control of friction, wear and lubrication on the nanoscale can be achieved by taking into consideration environmental aspects of nanoscale lubrication layers, environmental aspects of nanotechnological surface modification techniques and

Fig. 5.3 This fossil diatom Solium exsculptum lived 45 millions of years ago on the island of Mors in Denmark. Scanning electron microscopy reveals unbroken diatom shells, with elaborate linking structures, and various micromechanical, incl. tribological, optimizations. © F. Hinz, Alfred Wegener Institute Bremerhaven, Germany. Image reproduced with permission

Fig. 5.3 This fossil diatom Solium exsculptum lived 45 millions of years ago on the island of Mors in Denmark. Scanning electron microscopy reveals unbroken diatom shells, with elaborate linking structures, and various micromechanical, incl. tribological, optimizations. © F. Hinz, Alfred Wegener Institute Bremerhaven, Germany. Image reproduced with permission nanotribological aspects of green applications such as artificial photosynthesis. Questions that need to be addressed in turning nanotribology green are for example [21]:

• Do the processes get greener with the envisaged nanotribology (e.g. better coatings, less wear, less stiction)?

• Do the processes turn worse because of chemical reactions?

• Is the envisaged Green Nanotribology only pseudo-green, and in reality the negative impact on the environment/biology is only translated to other layers?

The usage of new technologies, materials and devices might increase advantages, but generates new problems. Exact eco-balance calculations need to be performed to prevent pseudo-green approaches. Biodiesel for example might be greener in the production than conventional products, yet still has technical concerns when used at concentrations greater than 5% [16].

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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