Summary
In this commentary paper, a model entitled “Materials Tetrahedron” is critiqued, and an alternative format the “Materials Square Pyramid” is proposed. The Materials Tetrahedron has incorporated at its four vertices the elements of processing, structure, properties, and performance. The problem with model's perspective is that it does not address the entire life cycle of the material; that is, sustainability issues are ignored because a systems perspective to materials usage is absent. In the proposed Materials Square Pyramid, the four pillars of Materials Tetrahedron, processing, structure, properties, and performance now occupy the four triangular faces of the square pyramid, their importance and their interrelationships are retained, but now these four pillars rest on a base that requires that sustainability and criticality issues be considered.
In the proposal, the author focuses on metals, a key component in the world of materials, and the entire life cycle of a metal in a product is considered from a sustainable perspective to modern society’s use of metals. This type of cycle is labeled as an anthropogenic cycle. It has been described as the “quantitative characterization of the flows of a specific material into, within, and from a given system”. By examining the Materials Tetrahedron in the context of the life cycle of a metal in the anthroposphere, it is observed that it addresses only the middle portion of the life cycle, namely, the fabrication and manufacturing and the use component of the life cycle. It also omits the beginning and end of the life cycle, namely, production of the metal and the disposal or recycling of the metal at end-of-life. The incorporation of a sustainability component into the Materials Polyhedron ensures that the entire life cycle of the metal is considered, and the incorporation of the criticality component into the materials polyhedron addresses the issues of supply and demand challenges for the metal in question.
Drawing from the field of industrial ecology, the utility of the Materials Tetrahedron versus that of the Materials Square Pyramid is compared using three examples: lead solder, cobalt in lithium ion batteries, and rare earth elements in permanent magnets. Lead solder was used in the electronics industry and other industries for many decades. but it was eventually abandoned by the electronics industry because it posed a serious hazard to human health and the environment. Although the use of the materials tetrahedron supported 60/40 tin–lead solder, the use of the materials square pyramid would raise a red flag, because criticality considerations in the environmental implications’ domain are factored into the analysis of the suitability of this metal alloy.
Lithium cobalt oxide, LiCoO2, is the original intercalation cathode material used in Li-ion batteries from 1991. Now, however, the goal is to eliminate the use of cobalt as much as possible because “cobalt is a limited and expensive component”. Use of the materials square pyramid would highlight the issues of supply risk and vulnerability to supply risk, whereas the materials tetrahedron does not.
The promotion of electric vehicles in the marketplace has led to concerns on the part of the automakers about the availability and cost of metals such as lithium, cobalt, and the rare earth elements (REEs). Vehicles' electric motors depend on permanent magnets that are composed of REEs and more specifically neodymium in the form of Nd2Fe14B. Fearing that the availability of REEs will decrease and their cost will increase, many automakers have already eliminated its use of terbium (Tb) and dysprosium (Dy), used to improve the heat resistance of the neodymium magnets, and are reducing the amount of neodymium in their magnets by replacing it with low-cost lanthanum and cerium. The author considers that this event reflects the use of the concepts of criticality and substitutability in their choice of magnets, concepts incorporated in the materials square pyramid but not the materials tetrahedron.
The author argues that the use of Materials Square Pyramid provides a proactive approach to metals selection that requires us to consider the entire life cycle of the metal and better allows us to anticipate problems and challenges. This is aligned with the shift of the chemical industry from pollution control to pollution prevention.
Relevance for Complex Systems Knowledge
The paper deals with systems thinking and sustainable development.
The author connects systems thinking with the life cycle of the material which requires the consideration of various sustainability issues (e.g. whether the current rates of metal consumption are sustainable).
