A viable path to more environmentally friendly magnets has been demonstrated by materials scientists. These magnets are an iron-nickel alloy found in meteorites.
Many core green technologies, such as wind turbines and electric cars, are built on the power of high-performance magnets.
What is Tetrataenite?
But mining the rare earth components of these devices can have a significant negative impact on the environment. As a result, scientists are looking for alternatives to rare earth magnets, and tetrataenite, an iron-nickel alloy with a tetragonal crystal structure, is one of the leading candidates.
Tetrataenite typically forms in meteorites through extremely slow cooling over thousands of years, but a new study has discovered a way to create this magnet in the lab in just a few seconds. While the process has yet to produce a useful magnet, the researchers hope that further research will improve the magnetic properties of "cosmic magnets" and shed light on how they are created.
Tetrataenite meteorite specimens were first discovered in the 1980s. Iron and nickel, two common elements, are combined in a simple tetragonal configuration with magnetic moments inclined in one direction to form this magnetic material.
High performance magnets need this property called uniaxial magnetic anisotropy.
Tetrataenite has therefore attracted the attention of scientists looking for substitutes for rare earth magnets.
The problem is that the meteorite-based method of producing tetrataenite requires extremely slow cooling rates (less than 0,01 K per year). In most cases, trying to cool the iron-nickel components faster results in a cubic crystal structure rather than the required tetragonal structure.
Tetrataenite has been created by scientists in small quantities in the laboratory, but only under extremely harsh conditions such as neutron irradiation.
Lindsay Greer, Yurii Ivanov and colleagues at Cambridge University have now discovered a technique for rapidly forming this metal in ordinary environments. According to the researchers, the element phosphorus, a component of the meteorites that make up the tetrataenite, was a secret kept from them.
According to Greer, it is known that phosphorus accelerates diffusion in meteoritic compositions. However, no one has yet investigated the potential effect of phosphorus on tetrataenite production in vitro.
Ivanov claims that the presence of phosphorus is necessary to enable tetrataenite synthesis without the use of processes such as neutron irradiation.
Tetrataenite was not the study team's initial target. Instead, they wanted to learn more about the mechanical properties of the normally disordered, glass-like Fe-Ni-PB alloys. Alloy components were heated to 1123 K and then rapidly cooled as part of the team's standard casting process.
Solidified samples had a pattern of twigs known as dendrites. After analyzing these properties with x-ray diffraction and transmission electron microscopy, the researchers were shocked to discover the chemically organized structure of tetrataenite. Scientists discovered that phosphorus is responsible for speeding up the arrangement of materials by changing the ratio of elements in alloy components.
The findings showed that tetrataenite could form at cooling rates 100 billion times faster than meteorites live.
Tetrataenite is intriguingly produced, but Trinity College Dublin magnet expert Michael Coey questions whether this material meets basic magnet energy requirements. Because tetragonally ordered Fe-Ni alloys are produced using a new melt casting technique, Coey predicts the work will have an impact on the direction of future research on tetrataenite. However, I do not think that these alloys can replace rare earth elements in any permanent magnet application.
Greer and Ivanov agree that the minimum currently available data on the magnetic properties of tetrataenite indicates a potential incompatibility with high-performance neodymium-based magnets. But optimizing the tetrataenite casting process could improve the material's magnetic properties, making it a viable option, according to the researchers. According to Greer, more permanent magnet materials are beneficial as they allow for better balancing of factors such as magnetic performance and environmental impact. “Using rare earth magnets in a one-on-one trade is not necessarily the goal.”
For now, the team has shown how to create one piece of tetrataenite, but they claim that future work will focus on how to assemble large numbers of pieces into a bulk magnet. Greer explains, “To use an analogy, we've shown that we can make a brick—a piece of tetrataenite—but we haven't yet made a house—a magnet.
This work could have implications for astrophysics research as well as materials science as scientists reevaluate how long it takes for tetrataenite to form in a meteorite and how fast it cools in this space environment.
Günceleme: 26/11/2022 17:10