Understanding Magnetite: More Complex Than Anyone Thought
Just in case anyone’s New Year’s resolution involves continuing education, here is a much-anticipated guide to Fe3O4, magnetite, the lodestone, the most magnetic natural material on earth, and one with a bright future in science. We’ll never know exactly when humans first began to use magnetite as compasses but we do know that during the Han Dynasty, somewhere around 220 BCE, someone in China had figured it out. Around the same time, the first Chin emperor is said to have used a board with a South-pointing compass like the one shown below to convince his court that he had a divine right to rule. Magic and science are indistinguishable, sometimes.
But magnetite’s legend goes back even further: some historians date the legend of Magnes of Crete to 900 BCE. As the story has it, Magnes, an old shepherd, was climbing Mount Ida when his shoe nails and metal staff tip got stuck to the rock. The story crowned Magnes the discoverer of this wonder element, aptly named magnetite.
In modern times, magnetite provides about 40% of the world’s raw iron (magnetite is a ferrous oxide, technically a rust of iron, from which iron metals are extracted). But more applications are always being developed, and that leads to some exciting science.
A new future for magnetite
Today, scientists are interested in magnetite for a new set of reasons. In particular, a range of advanced materials applications lay ahead — depending on what we learn about magnetite’s structure and properties.
Up until very recently, for example, there was reason to believe that magnetite could be used for advanced electronics (thanks to its half-metal surface and other properties). That changed this month with a paper in Science laying out clear evidence that magnetite is better suited to catalytic applications.
A catalytic material speeds up a reaction without getting used up. It’s a process often used to speed up production of industrial materials, like ammonia, but it’s a process also useful in medicine.
Precious metals like gold and platinum are much sought-after for their catalytic function, but their costliness presents a challenge. To bring down costs, an ideal catalyst would maximize surface area, so all of the precious metal is helping at one time in reactions.
That’s where iron oxides come in — they’re already widely used in industry as they are relatively inexpensive and reactive. But, if they can be used to hold individual atoms of metal catalysts like gold, they could be used to maximize gold’s efficiency as a catalyst.
Solving a modelling mystery
Eamon McDermott, a Canadian theoretical chemistry PhD student at the Vienna University of Technology, and second author on the Science paper, says that scientists thought it was impossible to properly measure magnetite and metal oxides’ surfaces, which would make it difficult to understand how gold and other metals bonded to it.
But McDermott’s team showed that it was possible to model exactly how gold bonds to the metal oxide, which could help develop extremely efficient catalyst systems for industry and medicine — and help to properly measure the surfaces.
The paper shows that the often used model of magnetite’s surface is wrong.
McDermott and his collaborators altered the model in their research. Something else happened when they did this, a voltage change instigated a change in the surface pattern.
“This is completely not something that would just happen coincidentally,” McDermott said. This weirdness was a sign that their model worked:the physical structure wasn’t actually changing, but changes in electrons made it look like it was. With this information in hand, it was clear that the team’s new model worked. Moreover, it changes how magnetite is understood, opening up new doors to highly efficient catalysis.
It also means that other metal oxides could be modelled, opening up new doors for research. The lodestone of old has come a long way, but as with most things, there’s plenty more to be seen.
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