Although wood has many ideal building material qualities, it is often stresstreated with ecologically disadvantaged chemicals to prevent it from decaying. With this in mind, American scientists are working on a greener alternative to making wood metal oxides.
The Georgia Institute of Technology team, led by Associate Professor Mark Rosego, is using an existing technique called atomic layer deposition. Although commonly used to manufacture electronics, in this case the technology is used to deposit ultra-thin protective coatings of metal oxides in the entire honeycomb structure of wood.
The process involves placing wood in a low-pressure airtight chamber and then introducing metal oxide gas. Gas molecules continue to penetrate into wood, using interconnected holes as internal paths, which spread in wood. When these molecules do this, they react with wood to form a metal oxide coating on their internal structure.
Although the coating is only a few atoms thick, it can effectively prevent wood from absorbing water even if it is submerged. As a result, wood may also be more resistant to mold growth over time due to other effects of the treatment. In addition, treated wood is less thermally conductive than regular wood, allowing buildings to be better insulated from heat loss.
In laboratory tests, the researchers injected three types of metal oxides into pines, which were 1 inch long: titanium oxide, alumina oxide and zinc oxide. The study found that titanium oxide is most effective in preventing wood from absorbing water – untreated wood absorbs three times as much water as it does.
In addition to the versatility and renewable nature of wood, another selling point of wood as a building material is that it is biodegradable once discarded. More research is needed on how metal oxide treatment will affect wood in this regard, although Rosego believes this may not be a problem. “In fact, we are now actively looking at the biodegradation of these materials, ” he says. The ‘coating’ is nominally just one or several atoms thick, so it is expected that it will not have much effect on biodegradation, but I can’t be 100 percent sure of that. “
The team recently published a paper on the study in the journal Langmuir.