Petrified wood yields super ceramics

National laboratory develops ultra-strong, heat-tolerant carbon alloys.

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Materials scientists at the Pacific Northwest National Laboratory (PNNL), Richland, Wash., have developed a chemical process, now available for licensing, that transforms wood into ceramics. These lab-created petrified woods are reportedly stronger than steel, withstand high temperatures and have a high surface area, like that of carbon. These materials offer another advantage — they are made from natural biological materials, which are abundant, renewable and easy on the environment. Scientists say the materials could be used as catalysts and filters, as well as for cutting tools, abrasives and coatings.

The wood is first soaked in acid, then infused with a source of either titanium or silicon, and is finally baked in an argon-filled furnace at 1,400°C. The silica and titanium take up permanent residence in the cellulose with the carbon to form the ceramics silicon carbide (SiC) and titanium carbide (TiC).

“The newly formed silicon carbide or titanium carbide exactly duplicates the intricate hierarchical cellulose structure of the wood,” says Eric Lund, commercialization manager for PNNL. “It also is possible to create the ‘negative’ of the wood structure by adjusting the initial acid treatment of the wood.”

“The ability to convert a natural material into an inorganic ceramic while maintaining the shape of the natural material is unprecedented,” Lund says. Previous techniques involved using ethane or methane-gas reactions, but the resulting materials could not retain their shape. Because the PNNL materials retain the crystalline form of the wood, they maintain their shape, or macrostructure, as well as their porosity, or microstructure. This structure gives the silicon carbide and titanium carbide their strength.

The intricate network of microchannels and pores in plant matter provides enormous surface area that is maintained in the new materials. Because these new ceramics can also withstand temperatures of at least 1,400°C, they are ideal for high-temperature catalysis processes.

“One gram of either material flattened has enough porosity to cover a football field: a feature that should make the materials invaluable as catalysts in industrial chemical separations, or as filters for pollutants from gaseous effluents,” says PNNL scientist Yongsoon Shin.

The new materials also offer possibilities for the cutting tools industry, where they could be used to form templates into which metal could be infused, resulting in stronger, harder blades, rotors and other cutting tools.

To form tougher and longer-lasting abrasives, wood flour could be infused with silicon and titanium, says Shin.

Fermentation boosts mannitol yields
A chemist at the U.S. Department of Agriculture’s Agricultural Research Service (ARS), Washington, D.C., has found a biobased method for making mannitol by feeding high-fructose corn syrup to the bacterial species Lactobacillus intermedius in a deep-tank fermentor. The bacteria convert 72% of the syrup into mannitol in several hours. ARS chemist Badal Saha’s technique can produce mannitol from fructose, as well as sucrose and other sugars.

Mannitol is a sweet, minty-tasting alcohol that is used as a base for chewable antacids and vitamins. It also has pharmaceutical and medical uses as an osmotic diuretic and as a hypertension treatment.
Manufacturers traditionally produce mannitol by high-pressure catalytic hydrogenation of a 50-50 mixture of fructose and glucose. Besides producing chemical wastes, the process converts only about 25% of the sugars to mannitol.

Saha is collaborating with zuChem Inc., Chicago, to scale-up and refine the approach.

New polymer defies convention
A team of chemical engineers at Virginia Commonwealth University, Richmond, Va., has developed a polymer that is hydrophilic when dry, and hydrophobic when wet — the opposite of most materials.
“This discovery runs counter to intuition,” says Kenneth J. Wynne, professor of chemical engineering at the university. “Water-induced hydrophobic surfaces may lead to applications for many things, including the testing of bodily fluids, switching devices, drag-reducing coatings and many others.

“Sometimes an engineer wants to guide the flow, or turn off tiny streams of fluid, such as blood, in a test tube, and this kind of phenomenon could be useful in creating channels for that purpose.”

Wynne and graduate student Umit Makal were working to create antimicrobial coatings by incorporating a molecule called hydantoin into fluorine-containing polymer chains. Makal was testing the behavior of water on one of these coatings and observed that the water drops were spreading, wetting the surface.
“After we took the drop off and put it back again, it started hating the water,” Makal says. “The surface became water repellent where the original drop of water had been.”

Wynne and Makal concluded that the change was caused by a rearrangement of the polymer side chain, which exposed the hydrophobic, fluorine-containing groups to the surface and made them repel water. “The process can be reversed by drying the surface,” Wynne says.

The polymer has not yet been optimized for either its performance or economics. However, several companies have expressed interest in the material, and one will be performing tests.

Ethanol capacity shows spirited growth
Northstar Ethanol LLC started up in May an ethanol plant near Lake Crystal, Minn., that will process more than 17.5 million bushels of corn and produce 50 million gallons of ethanol and 150,000 tons of distillers grains annually.

Nationwide, 85 ethanol plants have the annual capacity to produce over 3.8 billion gallons. Sixteen ethanol plants are under construction with a combined annual capacity of nearly 780 million gallons, according to the Renewable Fuels Association, Washington, D.C.

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