Greenhouse gas emission reduction targets have increased demand for clean energy technologies, and the growth required for these technologies has led to concern over material availability and criticality. Critical materials are defined as having risks associated with them such as supply gaps or price volatility. Existing metrics for criticality determination are narrowly focused on physical scarcity of single materials, whereas many critical materials are byproducts of large, complex, interconnected material systems. Industrial ecology borrows methods from ecology to study complex material and energy flows, which can be used for a systems-perspective analysis. In this work, critical rare earth material systems are likened to food webs and analyzed using ecological network metrics and metrics borrowed from network analysis. This study considers food web metrics—partner diversity, connectance, specialization asymmetry, vulnerability, extinction slope, niche overlap, weighted betweenness, normalized degree, interaction push-pull, cluster coefficient, Shannon’s diversity, interaction evenness, and d’—best suited for describing systemic criticality in metal or mineral use systems. These metrics were applied to 10 rare earth elements and their end uses for China, Japan, and the United States from 1995-2007 as a case study to determine if ecologically inspired metrics could provide improved criticality assessment. Metrics address three system levels: 1) network, 2) group, and 3) individual elements/products. It was determined that some metrics highlight instances where rare earth systems are becoming more specialized making them vulnerable to supply risks. Application of ecological network metrics to material systems has advantages for criticality assessments, and future work should consider additional systems and the interactions between the various metrics to better understand these systems and lessons available from a systems-perspective.
Library of Congress Subject Headings
Clean energy industries--Materials; Rare earths; Business logistics
Sustainable Systems (MS)
Department, Program, or Center
Hubler, Berlyn Jo, "Ecologically Inspired Metrics for Rare Earth Element Critical Material Systems" (2016). Thesis. Rochester Institute of Technology. Accessed from
RIT – Main Campus