many advanced engineering applications, like clean-energy production, communications or computing, use emergent technologies that utilize numerous chemical elements. as a result, a much greater proportion of metals in the periodic table are economically significant than in past centuries. technology-critical elements are those elements for which a striking acceleration in usage has emerged, relative to past consumption. the tce concept is related to the degree to which an element is seen to be critical. criticality is related to scarcity, which, in turn, is related to any imbalance between supply and demand. various attempts at the assessment of this criticality have taken place over recent years.