Nanopowders may be extremely tiny in size, but their role is getting bigger in powder-based processing innovations. In various applications such as catalysis, coatings, cosmetics, electronics, sensors and drug delivery, these particles, which are only about 1-100 nanometers in size (a nanometer is one-billionth of a meter), are delivering advantages over current materials and becoming increasingly important.

Providing controlled functionality and greater reactivity, such powders at the nanoscale represent the direction in which powder-based processing is heading. Indeed, processing improvements have long centered on decreasing particle size and advancing particle uniformity. Now, with newly developed powder production and synthesis methods, the market may soon see even better particle capabilities and even tinier particles.

One such groundbreaking method is Xerox's emulsion aggregation (EA) process, which forms 1-15 micron particles from smaller nanometer-sized particles. Reinventing toner production, the technology may also be applied in biotech, personal hygiene and related areas, the company says.

Pat Burns, manager of the composite and nanostructure materials area at the Xerox Research Centre of Canada in Ontario, explains that the company developed this new technology to produce tinier toner particles in a cost-effective manufacturing process. "The smaller particle size will give you improved image resolution, and you'll end up using about 40% less toner on a page," says Burns. "We wanted to control structure—to be able to put different things inside, put wax particles inside, not on the surface."

The environmentally friendly EA process provides the company maximum control over the manner in which the particles form, letting researchers manipulate temperature, time and stirring and influence particle size and shape. This method allows magnetite, colorants and other materials to be added inside the particles and layered structures to be developed.

Xerox has already launched a toner product based on the new process in Spain and intends to introduce it in the United States as well. The technology is currently available to those who want to license it for biomedical, personal hygiene and other applications.

Another promising powder processing method is laser vaporization, which is being refined by researchers at Virginia Commonwealth University (VCU). According to Dr. Samy El-Shall, a VCU professor of physical chemistry, nanoparticles of specified sizes can be formed by processes utilizing laser vaporization.

With this method, researchers can exert control over composition as well. "When (we) vaporize, we don't want (the metal atoms) to diffuse," he explains. "We want them to condense under our conditions before they go away from each other. So, in this case, you form new particles from the condensation of these atoms, and these new particles will not be just iron, just aluminum and just nickel—they will contain three atoms in the composition we desire."

One possible application for these nanopowders is catalysis, says El-Shall. A silica platinum made up of nanosized particles exhibited "very strong catalytic activity for hydrolyzation reaction," he notes. Even though these nanoparticle-based catalysts are heterogeneous, he says, they perform as well as homogeneous catalysts—at times even better—because of the particles' diminutive size.

And even more applications are now possible because of a recent nanopowder breakthrough by El-Shall and other VCU researchers. Using the laser vaporization process, they were able to form a new class of metallic and related types of nanoparticle fibers and filaments.

"Using a process that produces ultra-pure nanoparticles with laser vaporization and controlled condensation and then applying an electric field, we have shown that several classes of metallic and semiconductor nanoparticles can be assembled into chains and filaments that retain their unique properties," says El-Shall. "This holds great promise for the development of novel functional materials and for the engineering of a wide variety of nanodevices and sensors."

As a result, stronger plastics, integrating nanoparticle filaments inside polymer chains, may be developed, says El-Shall. Also, researchers are currently looking into using the nanoparticles as catalysts to expel carbon monoxide from air. Moreover, they are considering utilizing the tiny powders as a "smart dust" that senses chemical and biological warfare agents and environmental pollutants.

Ongoing nanopowder research is not only focusing on new processes but on a proven one as well—fluidization—commonly used in many powder processes within the chemical, petrochemical and pharmaceutical industries, but on micron-scale particles.

With the aim of better understanding nanoparticle behavior within fluidized beds, researchers at the Illinois Institute of Technology (IIT) in Chicago and the New Jersey Institute of Technology in Newark are manipulating factors on the reactor, including gravitational force. "At the end of this project, we hope that scientists and engineers who want to use reactors based on nanoparticles (can benefit from) tools for design and calculations," says Dr. Hamid Arastoopour, professor and chairman of IIT's chemical and environmental engineering department.

During the four-year project, which is under a National Science Foundation (NSF) grant, researchers hope to create a computer simulation to help design systems using nanosized particles. Getting a better grasp of nanoparticle fluidization will improve the production of nanocomposites with customized properties for catalyst and other applications.

Several small companies are also pursuing nanopowder research. For example, Tetronics Ltd. of England has been producing nanopowders for over 15 years, focusing primarily on applying thermal plasmas either as a clean heat source or in material processing. Meanwhile, Nanopowder Enterprises Inc. of New Jersey is eyeing the coatings area, using nanopowders to make harder, scratch-resistant products.

Nanopowder Enterprises is also working on other nanopowder applications, including "nano-additives" for coolants, which could potentially reduce the size of cooling equipment. And ultimately, the company wants "to be a nanomaterials provider," says Dr. Ganesh Skandan, chief operating officer, which would entail selling products directly to the end user.

Indeed, nanopowders represent the present and future of powder-based processing. And as their importance in innovations grows, more companies and academic institutions will surely take note of these tiny wonders.

Source: Cover Story: How Small Can You Go?
Kathie Canning
Chemical Processing, April 11, 2003
http://www.chemicalprocessing.com/Web_First/CP.nsf/ArticleID/CBOH-5LHMA4