While lumber certainly has many desirable qualities as a building material, it typically has to be pressure-treated with eco-unfriendly chemicals to keep from rotting. With that problem in mind, US scientists are working on a greener alternative – giving the wood a shot of metal oxide.
Led by Asst. Prof. Mark Losego, a team at Georgia Tech is taking advantage of an existing technique known as atomic layer deposition. Although typically used in the manufacturing of electronics, in this case the technology is being utilized to deposit an ultra-thin protective coating of metal oxide throughout the entire cellular structure of pieces of lumber.
The process involves placing the wood in a low-pressure airtight chamber, then introducing a metal oxide gas. The gas molecules proceed to permeate the wood – they travel throughout it, using its interconnected pores as an internal pathway. As those molecules do so, they react with the wood, forming a metal oxide coating on its inner structure.
Although that coating is only a few atoms thick, it’s highly effective at keeping the lumber from absorbing water, even when the wood is submerged. As a result, and possibly also due to other effects of the treatment, the lumber is much more resistant to mold growth over time. And as an added bonus, the treated wood is also less thermally-conductive than regular lumber, allowing it to better insulate buildings against heat loss.
In lab tests, the researchers infused 1-inch (25-mm) lengths of pine 2 x 4’s with three types of metal oxide: titanium oxide, aluminum oxide and zinc oxide. It was found that the titanium oxide was the most effective at keeping the wood from absorbing water – an untreated piece of 2 x 4 absorbed three times as much.
Along with its versatility and renewability, one of wood’s other selling points as a building material is the fact that once it is discarded, it biodegrades. More research still needs to be conducted concerning how the metal oxide treatment will affect the lumber in that regard, although Losego believes it likely shouldn’t be a problem.
“We are actually actively studying biodegradation of these sorts of materials right now,” he tells us. “The ‘coating’ is nominally only an atom or a few atoms thick, so the expectation is that it wouldn’t have that much of an effect on biodegradation, however, I can’t say that with 100-percent certainty.”