FOCUS: Wood – a new discovery

The bio-magnet

Apr 5, 2016 | AMANDA ARROYO
Wood can be magnetized. And an Empa team has figured out exactly how. Even if magnetic wood only lends itself to smaller applications, the first industrial partners have already expressed their interest.

Empa and ETH Zurich researcher Vivian Merk sits in her lab playing with a magnet. Not to while away the time; it’s her job. Nor is the magnet in her hand just any old magnet; it is made of wood and Merk magnetized it herself. “It’s a piece of cake,” says the researcher.
To magnetize a piece of wood, Merk soaks it in a highly acidic solution containing iron chloride salts. Once the liquid has penetrated deep into the wood, Merk places the sample in a strong alkaline solution. What happens next is referred to as a precipitation reaction. It suddenly starts “snowing” in the test tube – and this is precisely what takes place inside every wood cell, the lumen. The snowstorm begins on the cell’s interior wall. As the flakes are ferrous oxide nanoparticles, however, the snowflakes are almost black, not white. The magnetization is strongest along the grain because the wood cells are arranged lengthways and the most ferrous oxide particles are stored in this direction. The particles are enclosed in the wood, where they remain, even if the wood is washed for days on end.   
The magnetic particles come in two different forms – maghemite and magnetite. The brown-colored maghemite forms from the black-colored magnetite when it oxidizes in air. As a result, more imperfections develop in the crystal, which affects the color and explains why magnetizable wood is also very dark.
“Realistically, we’ll never treat an entire beam in a house,” says the researcher; “magnetic wood is more suited to smaller applications.” These might be toys or furniture, such as the magnetic board Merk is currently producing. Use in the automobile industry would also be conceivable to functionalize wood fittings in future. Not only would this have an interesting additional function; thanks to the dark color, it would also look very elegant.