Scientific Events

In this presentation the formation of spinel (MgAl₂O₄) by reaction between periclase (MgO) and corundum (Al₂O₃) is addressed. The reaction MgO + Al₂O₃ => MgAl₂O₄ may be regarded as a model case for diffusive phase transformations in oxide systems. All phases involved are moderately to highly refractory and have applications in ceramics. Above about 800°C, periclase and corundum react to form a layer of polycrystalline spinel at their interface. A pronounced dichotomy of the internal microstructure and texture of the spinel layer reveals the original position of the periclase-corundum interface. This reflects the direction and extent of the necessary Mg²⁺ and Al³⁺ transfer across the spinel layer and allows to quantify the underlying diffusion process. Systematic deviations of the Mg/Al ratio of the spinel from local equilibrium values at the spinel-periclase and the spinel-corundum interface are due to a finite mobility of the two reaction interfaces. The resistance against interface motion arises from dislocation climb at the periclase-spinel interface, which is complemented by the formation of Schottky defects in the reactant periclase. In contrast, the corundum-spinel interface moves by the glide of partial dislocations. This is energetically less expensive than the dislocation climb at the periclase-spinel interface and allows for comparatively rapid approximation of local equilibrium. [more]

The extraction and processing of resources are directly linked to 50% of all human-induced climate impacts and 90% of biodiversity losses (Bruno Oberle et al., 2019). Promoting resource efficiency is therefore recognised worldwide as a solution approach to counteract this rapid development. The circular economy (CE) approach brings new dynamism to the discussion of the well-known concept of resource efficiency (van Ewijk, 2018; Weizsäcker et al., 1997). Both approaches aim to reduce resource use and thus prevent tremendous environmental impacts. For example, the CE is thought to be crucial for reaching climate neutrality by 2050 as well as decoupling of economic growth and resource use (European Commission, 2020). Studies estimate that eco-design, waste prevention and reuse may result in up to EUR 600 billions of savings for businesses in Europe (Kalmykova et al., 2018). The metal industry is of high importance in this discussion as metal production is responsible for 8% of the global energy expenditure (UNEP 2013). Steel production alone is responsible for a quarter of all industrial GHG emissions (Allwood et al., 2011; Ito et al., 2020). However, the metal industry and especially the steel industry can look back on a long history of recycling as a core principle of the CE resulting in great resource savings. Nevertheless, there are major doubts as to whether future steel production can be covered entirely by secondary material. This is due to the dependency of the recycling infrastructure on primary metallurgy, the limits of recycling and the low degree of circularity of steel (Haas et al., 2015; Pauliuk, Wang, et al., 2013; Steger et al., 2018; Xylia et al., 2018). In the presentation, the challenges of resource use in general as well as the possible strategies of the Circular Economy are presented and their applicability for the field of metals, in particular steel, is discussed. To illustrate this, project examples will be presented in which, on the one hand, the CE strategies of re-purposing/re-manufacturing and, on the other hand, a technical approach of sorting by specific type for recyling will be illustrated. [more]