The ubiquitous use of chromium and its derivatives as corrosion preventative compounds accelerated rapidly after the second industrial revolution, with such compounds now integral to modern society.
However, the detrimental impact of chromium compounds on the environment and human health has prompted the need to revisit the majority of current industrial corrosion protection measures. This review retraces the origins of chromium replacement motivations, introducing the various legislative actions aimed at diminishing the use of chromium compounds, and critically reviews alternative corrosion preventative technologies developed in the recent decades to now. The review (click here to download) is intended for a broad audience in order to provide a concise update to an increasingly timely issue.
Introduction
Chromium compounds have been a staple of consumerist society for over a century, with applications ranging from wood treatments to corrosion prevention.1 It has been documented since the 1920’s that hexavalent chromium is carcinogenic in nature, after multiple studies noted an increase in the incidence of nasal and lung cancer amongst industrial workers in direct contact with Cr6+ compounds.2,3,4 A number of studies were collated and reported by the World Health Organization (WHO) in 1972 and 1980, which adjudicated the carcinogenic nature of chromium compounds based upon independent investigations around the world.1,5 Despite the obvious dangers, it was not until 1980 that the toxic nature of hexavalent chromium was officially documented in the annual report on carcinogens established by the US Department of Health and Human Service (HHS).6 Hexavalent chromium is now known to induce irreversible health damage including nose, throat, eye and skin irritation, but most notably, significantly increases an individual’s risk of lung cancer.3,4,7 In addition, chromates have also been documented to induce genotoxicity on aquatic and botanic life through soil and water contamination, owing to poor waste management and disposal maintenance.8,9,10,11
In response the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) was developed in 2006. REACH is a European (E.U.) legislation that obligates companies to identify, manage and register the risks associated with listed dangerous substances when production or consumption levels exceed 1 ton per year.12 Consequently, chromium compound usage is now restricted unless granted exclusive authorization from the European Chemical Agency (ECHA).12 Although companies continue to use hexavalent chromium in numerous industrial formulations, the present period of so-called “respite” has a non-negligible economic impact on companies, as the total cost associated with this authorization is estimated at €1.5 M.13 Furthermore, this authorization is only valid for a limited time, with an imminent sunset date set for January 2019.14 In the wake of legislative shift, albeit no global legislative shift to date, many metal finishing industries are now compelled to seek safe, environmentally friendly alternatives to chromate compounds.
Although extensive research has been underway since the 1980s to date, hexavalent chromium remains the benchmark corrosion preventative compound in essentially all industries. For instance, corrosion protection of metallic components in aeronautical applications continues to rely on hexavalent chromium compounds. In one example that confronts the present industrial status quo, it was stated that environmental and health concerns drove the use of a non-chromated (i.e., non Cr6+ containing) primer on the F-22 aircraft (produced by Lockheed Marin), resulting in inadequate corrosion protection.15 Thereafter the F-22 program switched to a chromated primer. Interestingly, the F-35 (Joint Strike Fighter) under present day development has also opted to use a non-chromated primer that has—interestingly—never been tested on an aircraft in a corrosive operating environment (albeit that the F-35 program cost is estimated at US$1.508 trillion.16 This is just one scenario that highlights the implications of inevitable eradication of chromates from the market, and the lack of viable (demonstrated) substitutes incites the need for unorthodox approaches and for revision of previously disregarded alternatives, in the hope of creating a future that promises engineering quality whilst also ensuring user safety and social responsibility.
