Green tribology: principles, research areas and challenges

Michael Nosonovsky Bharat Bhushan () Articles on similar topics can be found in the following collections Receive free email alerts when new articles cite this article - sign up in the box at the top right-hand corner of the article or click here - Email alerting service I N T RO D U C T I O N Green tribology: principles, research areas and challenges B Y M ICHAEL N OSONOVSKY1 AND B HARAT B HUSHAN2,* 1College of Engineering and Applied Science, University of Wisconsin, Milwaukee, WI 53201, USA 2Nanoprobe Laboratory for Bio- and Nanotechnology and Biomimetics (NLBB), Ohio State University, 201 West 19th Avenue, Columbus, OH 43210-1142, USA In this introductory paper for the Theme Issue on green tribology, we discuss the concept of green tribology and its relation to other areas of tribology as well as other green disciplines, namely, green engineering and green chemistry. We formulate the 12 principles of green tribology: the minimization of (i) friction and (ii) wear, (iii) the reduction or complete elimination of lubrication, including self-lubrication, (iv) natural and (v) biodegradable lubrication, (vi) using sustainable chemistry and engineering principles, (vii) biomimetic approaches, (viii) surface texturing, (ix) environmental implications of coatings, (x) real-time monitoring, (xi) design for degradation, and (xii) sustainable energy applications. We further define three areas of green tribology: (i) biomimetics for tribological applications, (ii) environment-friendly lubrication, and (iii) the tribology of renewable-energy application. The integration of these areas remains a primary challenge for this novel area of research. We also discuss the challenges of green tribology and future directions of research. 1. Introduction Tribology (from the Greek word trbu tribo meaning to rub) is defined by the Oxford dictionary as the branch of science and technology concerned with interacting surfaces in relative motion and with associated matters (as friction, wear, lubrication and the design of bearings) (Oxford English Dictionary; http://grove.ufl.edu/wgsawyer/). The term was introduced and defined for the first time in 1966 by Prof. H. Peter Jost, then the chairman of a working group of lubrication engineers, in his published report for the UK Department of Education and Science (Jost 1966). It was reported that huge sums of money have been lost One contribution of 11 to a Theme Issue Green tribology. in the UK annually owing to the consequences of friction, wear and corrosion. As a result, several centres for tribology were created in many countries. Since then, the term has diffused into the international engineering field, and many specialists now claim to be tribologists. Typical tribological studies cover friction, wear, lubrication and adhesion, and involve the efforts of mechanical engineers, material scientists, chemists and physicists (Bhushan 1999, 2001, 2002). Since the emergence of the word tribology almost 50 years ago, many new areas of tribological studies have developed that are at the interface of various scientific disciplines, and various aspects of interacting surfaces in relative motion have been the focus of tribology. These areas include, for example, nanotribology, biotribology, the tribology of magnetic storage devices and microelectromechanical systems (MEMS)/nanoelectromechanical systems and adhesive contact (Bhushan & Gupta 1991; Bhushan 1996, 1999, 2000, 2001, 2002, 2008, 2010). The research in these areas is driven mostly by the advent of new technologies and new experimental techniques for surface characterization. Recently, the new concept of green tribology has been defined as the science and technology of the tribological aspects of ecological balance and of environmental and biological impacts. H. P. Jost (2009, unpublished data) elaborated on the need for green tribology and has mentioned that the influence of economic, market and financial triumphalisms have retarded tribology and could retard green tribology from being accepted as a not-unimportant factor in its field. . .. Therefore, by highlighting the economic benefits of tribology, tribology societies, groups and committees are likely to have a far greater impact on the makers of policies and the providers of funding than by only preaching the scientific logic. . . Tribology societies should highlight to the utmost the economic advantage of tribology. It is the language financial oriented policy makers and markets, as well as governments, understand. The specific field of green or environment-friendly tribology emphasizes the aspects of interacting surfaces in relative motion, which are of importance for energy or environmental sustainability or which have impact upon todays environment. This includes tribological technology that mimics living nature (biomimetic surfaces) and thus is expected to be environment friendly, the control of friction and wear, which is of importance for energy conservation and conversion, environmental aspects of lubrication and surface-modification techniques and tribological aspects of green applications, such as wind-power turbines, tidal turbines or solar panels (figure 1). It is clear that a number of tribological problems could be put under the umbrella of green tribology and are of mutual benefit to one another. Green tribology can be viewed in the broader context of two other green areas: green engineering and green chemistry. The US Environmental Protection Agency defines green engineering as the design, commercialization and use of processes and products that are technically and economically feasible while minimizing (i) generation of pollution at the source and (ii) risk to human health and the environment (US Environmental Protection Agency 2010). The three tiers of green engineering assessment in design involve: (i) process research and development, (ii) conceptual/preliminary design, and (iii) detailed design pollution prevention, process heat/energy integration and process mass integration (Allen & Shonnard 2001). Another related area is green chemistry, also known as sustainable chemistry, which is defined as the design of chemical products and processes that reduce or eliminate the use or generation of hazardous substances (US Environmental Protection Agency 2010). Green chemistry technologies provide a number of benefits, including reduced waste, eliminating costly end-of-the-pipe treatments, safer products, reduced use of energy and resources and improved competitiveness of chemical manufacturers and their customers. Green chemistry consists of chemicals and chemical processes designed to reduce or eliminate negative environmental impacts. The use and production of these chemicals may involve reduced waste products, non-toxic components and improved efficiency. Anastas & Warner (1998) formulated the 12 principles of green chemistry that provided a road map for chemists to implement green chemistry: (1) Preven (...truncated)