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Edited by B. L. Turner, Arizona State University, Tempe, AZ, and approved February 27, 2015 (received for review January 8, 2015)
Significance
In the past decade, sporadic shortages of metals and metalloids crucial to modern technology have inspired attempts to determine the relative “criticality” of various materials as a guide to materials scientists and product designers. The variety of methodologies that have been used for this purpose have (predictably) resulted in widely varying results, which are therefore of little use. In the present study, we develop a comprehensive, flexible, and transparent approach that we apply to 62 metals and metalloids. We find that the metals of most concern tend to be those with three characteristics: they are available largely or entirely as byproducts, they are used in small quantities for highly specialized applications, and they possess no effective substitutes.
Abstract
Imbalances between metal supply and demand, real or anticipated, have inspired the concept of metal criticality. We here characterize the criticality of 62 metals and metalloids in a 3D “criticality space” consisting of supply risk, environmental implications, and vulnerability to supply restriction. Contributing factors that lead to extreme values include high geopolitical concentration of primary production, lack of available suitable substitutes, and political instability. The results show that the limitations for many metals important in emerging electronics (e.g., gallium and selenium) are largely those related to supply risk; those of platinum group metals, gold, and mercury, to environmental implications; and steel alloying elements (e.g., chromium and niobium) as well as elements used in high-temperature alloys (e.g., tungsten and molybdenum), to vulnerability to supply restriction. The metals of most concern tend to be those available largely or entirely as byproducts, used in small quantities for highly specialized applications, and possessing no effective substitutes.
Footnotes
- ↵1To whom correspondence should be addressed. Email: thomas.graedel{at}yale.edu.
Author contributions: T.E.G. and B.K.R. designed research; T.E.G., E.M.H., N.T.N., P.N., and B.K.R. performed research; E.M.H., N.T.N., and P.N. analyzed data; and T.E.G., E.M.H., N.T.N., and B.K.R. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1500415112/-/DCSupplemental.
Criticality of metals and metalloids
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