Issue 51

P. Ferro et al., Frattura ed Integrità Strutturale, 51 (2020) 81-91; DOI: 10.3221/IGF-ESIS.51.07 82 Earths and Heavy Rare Earths, Baryte, Bismuth, Hafnium, Helium, Natural Rubber, Phosphorus, Scandium, Tantalum, and Vanadium. The CRMs list is updated every three years. As it can be observed from the above mentioned ‘black list’, CRMs are linked to clean technologies. They are irreplaceable in solar panels, wind turbines, electric vehicles, and energy-efficient lighting. Unfortunately, the criticality assessment related to raw materials is a very difficult task and there is not a recognized method to reach that goal in literature [2,3]. For example, in a recent paper, Hofmann et al. [4] showed that material scientists seem frequently not concerned with the criticality of raw materials so that they suggested to advance the implementation of the concept of materials criticality in materials research and development. An excellent review of the criticality concept, as well as the methodologies used in its assessment, was presented by Frenzel et al. [5]. In that work, the authors also discussed a number of risks present in global raw materials markets that are not captured by most criticality assessments and, finally, they proposed measures for the alleviation of such risks. In another recent paper, Tkaczyk et al. [6] present a multi-faceted and multi-national review of the essentials for the critical raw materials, Co, Nb, W, and rare earth elements (REEs). Such raw materials are relevant for emerging technologies and will thus continue to be of increasing major economic importance. That paper deals with also a ‘sustainability evaluation’ for each element, including essential data about markets, applications and recycling. Possibilities for substitution is finally summarized and analyzed. In recent studies, the European Commission's Joint Research Centre (JRC) showed that several green technologies could be at risk because of potential supply risks of certain metals [7–9]. In particular, electric vehicles are of particular criticism because their dependence on critical REEs used in NdFeB permanent magnets (PM). Because of its high energy density, NdFeB is expected to be used also in high-tech applications and energy-related devices such as generators in wind turbines [10]. For these reasons, the global demand for REEs is likely to be increasing in the coming years [10-13], despite they are evaluated as ‘critical materials’ [14-19]. Among the ‘mitigating strategies’ aimed to face this issue, both recycling and substitution are considered in literature. For instance, substitution was found more feasible in cases where it takes place at the product, component or technology level rather than the element level [20-22]. Many works in literature confirm the substitution as a good method to face the increasing challenge of CRMs supply risk [23-26]. The research framework programs (e.g. FP7 and H2020) provides financial support to relevant projects related to substitution of critical raw materials. Gkanas et al. [27] defined four advantages linked to CRMs substitution: flexibility in materials supply, cost saving, weaken monopoly power of suppliers and environmental benefits. In 2012, the European Parliament observed that ‘the majority of substitutes are currently in the research and development stage and market-ready solutions are rarely available’ [28]. Therefore, the substitution concept needs to broaden its scope to include, for instance, product design, changes to process, higher material efficiency and product replacement by new technology [29]. In this scenario, Pavel et al. studied the possibility to substitute rare earths used both in electric road transport applications [30] and wind turbines [31]. They firstly showed how, despite the benefits of climate change mitigation and from potential fuel savings, several barriers could hinder the widespread adoption of electric vehicles because a potential supply disruption of critical rare earths for magnet-based electric traction motors. They demonstrated how the potential supply risks associated with rare earths for electric road transport applications cannot be easily mitigated as there are no effective substitutes for the rare earths used in permanent magnets. The general feeling is that more effort is needed to develop new solutions and to search for even better alternatives. In another work, Rademaker et al. [32] showed that in the brief period waste flows from permanent magnets will remain small relative to the rapidly growing global rare earth elements demand. Therefore, during the next decade, recycling is unlikely to substantially contribute to global REE supply security. On the other hand, in the long term, waste flows will increase sharply and will meet a substantial part of the total demand for these metals. Future REE recycling efforts should, therefore, focus on the development of recycling technology and infrastructure. Perez et al. [33] provides an overview of the present status and outlook on technologies used to recover critical metals from solution, including precipitation, reduction, ion exchange, solvent extraction, electrochemical methods and adsorption onto novel, sustainable materials. They finally suggested key directions to tackle existing challenges in the field of resource recovery and improve the sustainability of future material cycling. Despite the different works present in literature aimed to assess the raw materials criticality and suggest mitigating actions such as recycling and substitution, methods aimed to help the designer to play out the necessary ‘mitigating actions’ required to reduce the criticality of industrial products are not yet developed. Literature studies are mainly focused on REEs substitution with particular reference to specific applications [34] while a systematic methodology for a generic critical material substitution in design is still absent. In the following, an overall indicator for raw material criticality assessment is first proposed. A systematic procedure for alloy substitution in a CRMs perspective is then developed and illustrated with an example.