Wood made stronger after impregnation with iron mineral

Humans have been building with wood since time immemorial. Although it’s not as sturdy as concrete or steel, it’s more sustainable, and scientists are working on improving its properties so that it might displace those materials in some applications. One group of researchers have shown they can make wood stronger by infusing it with an iron mineral, but scaling up that hardness may present a challenge (ACS Appl. Mater. Interfaces, 2025, DOI: 10.1021/acsami.4c22384).

While enhanced wood is unlikely to replace steel or concrete, it may bring added durability to items currently built from wood, says Vivian Merk, an assistant professor of ocean and mechanical engineering at Florida Atlantic University who led the research with colleagues from FAU and the University of Miami. The process, she says, is environmentally friendly, using basic chemicals and water in a reaction that takes place at room temperature.

Trees consist of a honeycomb structure of hollow cells; the arrangement allows water and nutrients to flow through the tree while making the wood very strong for its weight. In the new study, the researchers took oak and imbued its cell walls with iron hydroxide. That increased the Young’s modulus of the cells—a measure of how much force is required to deform a material—by 160% and the hardness by 27%. When they tried bending a piece of treated wood, however, its performance was about the same as an untreated piece.

“On the nano and micro scale,” the team found significant reinforcement, Merk says. “But on the macro scale, it was not as drastic as we would hope for.” The difference seems to arise, she says, because the added material reinforces the cell walls, but the chemical process weakens the connections between the cells.

The researchers began with pieces of American red oak purchased from the Home Depot and cut into small cubes. The team chose oak because it is a so-called ring-porous hardwood, popular for building furniture and wine casks, and the thick cell walls made their work easier. They soaked the wood in a solution of iron nitrate and water. They then applied potassium hydroxide to cause crystals of iron hydroxide to precipitate in the pores. The iron hydroxide, a mineral commonly found in nature that’s similar to rust or magnetite, strengthened the cell walls while increasing the weight of the wood by less than 3%.

Merk says she’d like to explore changing the concentration of the hydroxide or tweaking the processing to see if that might improve the material even more. Lauri Rautkari, an associate professor of wood material science at Aalto University, calls the work “scientifically interesting.” He adds that, from an industrial perspective, it would be interesting to see what the main application would be.