What are the Physical Foundations and Basic Challenges in Sustainable Metallurgy ?

This lecture gives a short introduction in the fields of sustainable metals and metallurgy, a domain also referred to as green metallurgy. Engineering materials and particularly metallic alloys have enabled technological progress over five millenia. Metallic materials have a historic and enduring importance in our society. They have paved the path of human civilization with load-bearing and functional 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 as well as hard and soft magnetism. The high and accelerating demand for load-bearing (structural) and functional metallic 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 metallic materials, specifically steel, aluminium, nickel and titanium, require a lot of energy when extracted and manufactured and these processes emit large amounts of greenhouse gases and pollution. The huge success of metallic products and industries also means that they have an important role in addressing the current 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 CO2-equivalent emissions (4.4 gigatons of carbon dioxide equivalent, Gt CO2eq) when counting only steels and aluminium alloys (the largest fraction of metal use by volume).
This lecture presents the main backgrounds and some of the basic physical and chemical foundations for improving the direct sustainability of structural metals, in areas including reduced-carbon-dioxide intense primary production, low-energy metallurgical synthesis, recycling, scrap-compatible alloy design, contaminant tolerance of alloys and improved alloy longevity. The lecture is also concerned with the effectiveness and technological readiness (TRL) of individual measures in Sustainable Metallurgy and also works on novel materials that enable improved energy efficiency through their reduced mass, higher thermal stability and better mechanical properties than currently available alloys.
Further reading:
Strategies for improving the sustainability of structural metals, Nature, vol. 575, pages 64–74 (2019)
© Dierk Raabe

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