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June 2002

News about Science, Technology and Engineering at Iowa State University

Inquiries at the interface
In an effort to better understand how materials form, scientists at the U.S. Department of Energy's Ames Laboratory at Iowa State University are investigating properties that exist in metals at the interface between liquid and solid phases during solidification. The work may one day allow scientists to tailor microstructural development, providing the basis for new and improved materials.

Ames Laboratory scientists Rohit Trivedi, Ralph Napolitano and James Morris have shown that there are many subtle variations in microscopic properties near the liquid-solid interface as the solid is "freezing out." Small variations depend upon which crystal face is in contact with the liquid. Different faces (orientations) give slightly different values for properties such as free energy, mobility and stiffness (surface tension). These properties play key roles in how a metal's microstructure evolves during solidification.

Innovative experimental techniques developed by Trivedi, a distinguished professor of materials science and engineering, and Napolitano provided the first reliable measurements of the minuscule variations in free energy at the liquid-solid interface. Morris's complementary calculations represent the first (and so far only) effort to theoretically predict the variation in interfacial free energy for aluminum.

"By revealing the essential physical behavior of liquid-solid interfaces, these critical experiments are facilitating significant advancement in the theoretical prediction of microstructures," Napolitano said. For more information, contact Napolitano, (515) 294-9101; Trivedi, (515) 294-5869; James Morris, (515) 294-8872; or Saren Johnston, Ames Lab Public Affairs, (515) 294-3474.

Researchers create organic compounds without solvents
Researchers at the U.S. Department of Energy's Ames Laboratory at Iowa State University have found a way to combine organic materials in solid state without the use of solvents. The solvent-free process means that environmentally harmful solvents, such as benzene, dichloromethane and others, could be removed from many of the chemical processes used to produce millions of consumer and industrial products.

Organic materials have stable molecular crystal structures that usually keep them from reacting when they're in a solid state. Solvents break down these crystal structures so the dissolved materials can be combined to form new compounds. But the process leaves behind a contaminated solvent that often can't be reused, creating disposal problems. "Most of these solvents pose serious risks to health and the environment and are costly to decontaminate and remove," said Ames Lab senior scientist Vitalij Pecharsky.

The Ames Lab discovery, announced in the June issue of the Journal of the American Chemical Society, uses high-energy ball-milling, a well-known process for producing and modifying metal alloys. Materials to be processed are placed in a hardened steel vial along with steel balls. The vial is vigorously shaken and the mechanical energy transferred into the system alters the crystallinity of the solids and provides mass transfer, eventually combining the materials into new compounds.

To test their theory, Pecharsky and Ames Lab colleagues Viktor Balema, Jerzy Wiench, and Marek Pruski turned to well-known and well-documented chemical transformations of organophosphorus compounds. The "Wittig reaction" was used to transform phosphorus ylides and aldehydes, or ketones, into unsaturated hydrocarbons -- building blocks in the preparation of numerous organic materials and pharmaceuticals.

Nearly all of the discovered transformations, previously performed exclusively in a solution, were found to be exceptionally efficient and selective in the solid state. Furthermore, they can be carried out consecutively, or as "one-pot" processes, when components required for performing several different processes are ball-milled together in the same vial.

"Remarkably, a 'one-pot' Wittig-type reaction between phosphines, organic halogenides, aldehydes or ketones, and a base is impossible in a solution, but has been successfully carried out in a mill without a solvent," said Pecharsky. For more information, contact Pecharsky, (515) 294-8220, or Kerry Gibson, Ames Lab Public Affairs, (515) 294-1405.

Food inspection device wins a technology transfer award
A food safety inspection device, developed at Iowa State University, has won a national award. Jake Petrich, Iowa State professor of chemistry; Mark Rasmussen, assistant professor of animal science and research microbiologist for the USDA's National Animal Disease Center in Ames; and Tom Casey, also of the USDA NADC, received a Technology Transfer Award from the Federal Laboratory Consortium.

The group developed a spectroscopic technology for detecting fecal contaminants on animal carcasses. The device is a non-contact spectroscopic apparatus that stimulates fluorescent emission from meat in order to inspect for markers of food-borne pathogens, specifically feces. The technology has proven more effective than visual inspection methods because it removes subjectivity from the process and can detect contamination on almost any size cut of meat. For more information contact Petrich, (515) 294-9422; Rasmussen, (515) 663-7350; or Bridget Bailey, ISU News Service, (515) 294-6881.


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