Sustainable materials Research Papers - Academia.edu (original) (raw)

Metallic materials have enabled technological progress over thousands of years. The accelerated demand for structural (that is, load-bearing) alloys in key sectors such as energy, construction, safety and transportation is resulting in predicted production growth rates of up to 200 per cent until 2050. Yet most of these materials require a lot of energy when extracted and manufactured and these processes emit large amounts of greenhouse gases and pollution. Here we review methods of improving the direct sustainability of structural metals, in areas including reduced-carbon-dioxide primary production, recycling, scrap-compatible alloy design, contaminant tolerance of alloys and improved alloy longevity. We discuss the effectiveness and technological readiness of individual measures and also show how novel structural materials enable improved energy efficiency through their reduced mass, higher thermal stability and better mechanical properties than currently available alloys. Structural metallic materials have a historic and enduring importance in our society. They have paved the path of human civilization with load-bearing applications that can be used under the harshest environmental conditions, from the Bronze Age onwards. Only metallic materials encompass such diverse features as strength, hardness, workability, damage tolerance, joinability, ductility and toughness, often combined with functional properties such as corrosion resistance, thermal and electric conductivity and magnetism. This versatility comes with a vast understanding of thermo-mechanical processing of metals (accrued over millennia of metals use), which in turn enable numerous production , manufacturing, design, repair and recycling pathways. Benefit and environmental impact of metallic alloys Metals have enabled multiple applications in the fields of energy conversion , transportation, construction, communication, health, safety and infrastructure. Examples over the millennia have been agricultural tools, manufacturing machinery, energy conversion engines and reinforcements in huge concrete-based infrastructures. Recent applications include structural alloys for weight reduction combined with high strength and toughness in the transportation sector 1-4 , efficient turbines operating at higher temperatures for power plants and air traffic 5,6 , components for safe nuclear and fusion power and disposal 7 , targeted endurance or corrosive dissolution of biomedical implants 8 , embrittlement-resistant infrastructures for hydrogen-based industries 9 or reusable spacecraft 10. Metallurgical alloys and products boost innovation and economic growth: the global market for metals is about 3,000 billion euros per year 11,12. The success of the structural metals industry also means that it has an undisputable role in addressing our environmental crisis. The availability of metals (most of the elements used in structural alloys are among the most abundant), efficient mass producibility, low price and amenability to large-scale industrial production (from extraction to the metal alloy) and manufacturing (downstream operations after solidification) have become a substantial environmental burden: worldwide production of metals leads to a total energy consumption of about 53 exajoules (10 18 J) (8% of the global energy used) and almost 30% of industrial CO 2-equivalent emissions (4.4 gigatons of carbon dioxide equivalent, Gt CO 2 eq) when counting only steels and aluminium alloys (the largest fraction of metal use by volume) 13 ; see Table 1. Although the production volumes of nickel and titanium are much smaller, they have an eminent role in aerospace and biomedical materials and nickel is primarily used as an alloying element in stainless steel (accounting for two-thirds of nickel's uses). The worldwide annual production in terms of mass, energy and CO 2 is presented in Table 1, with metal lost in manufacturing for these four key structural metals (where nickel use in stainless steel is the focus). Mining and production of these materials have a huge impact in terms of resource use, emissions and waste generation, and this impact continues to grow, because of trends around urbanization, electrification and digitization (in 1950 less than 30% of the population lived in cities but this number is projected to exceed 60% by 2025). In addition, there are substantial byproducts of both industries that cause considerable environmental damage when not managed properly in perpetuity (losses throughout the supply chain are shown in Fig. 1 along with the quantities of material recovered as scrap). The two largest material groups (steel and aluminium) alone create huge mining and extraction byproducts, namely, 2,400 million tons (Mt) per year of tailings