Nano-iron turns red oak into lightweight steel rival

A Florida Atlantic University team infused red oak with ferrihydrite nanoparticles, boosting cell-wall strength without adding bulk or sacrificing flexibility. The one-pot, low-cost process nudged wood toward construction-grade strength, reportedly with only a “small amount of extra weight,” according to mechanical tests spanning AFM to full-beam bending.

Working with colleagues at the University of Miami and Oak Ridge National Laboratory, the researchers aimed to see if adding these extremely hard minerals at the nanoscale could fortify the wood cell walls effectively and sustainably. As published in ACS Applied Materials and Interfaces, the team led by Vivian Merk, Ph.D. created these iron-based minerals (specifically ferrihydrite, an iron oxyhydroxide) through a straightforward chemical process that mixes ferric nitrate with potassium hydroxide directly within the wood structure.

Mechanical testing highlights the technique’s potential: nanoscale stiffness surged by about 260% and hardness by 127%, yet the wood gained only a small amount of extra mass/weight. This targeted strengthening occurs within the cell walls. Consequently, despite these nanoscale improvements, the overall macroscopic failure behaviour remained largely unchanged, likely due to impaired adhesion between cells.

The study reveals a distinction between strengthening the components and strengthening the whole structure. While nanoindentation and AFM confirmed significant hardening and stiffening within the ferrihydrite-infused secondary cell walls, the overall fracture behavior in bending tests remained largely unchanged. The researchers propose that the “harsh chemical conditions” necessary for the in situ mineral deposition might simultaneously impair the adhesion between wood cells. In turn, that potentially would offset the nanoscale gains when the material is stressed macroscopically, they reasoned.