UNIVERSITY PARK, PA. --- Researchers at Penn State's Applied Research Laboratory (ARL) have developed a faster, cheaper and cleaner method of producing ultrafine metal powders, such as silver used in solder, dental fillings, circuit boards, high-speed photographic film and a host of other applications.
Dr. Jogender Singh, ARL senior research associate and associate professor of materials science and engineering, led development of the process. He was recently honored with an R&D Magazine 100 award which recognizes 100 of the best new discoveries or inventions of the year.
Most recently, Singh says, his group has also shown that the new process can substitute for electroplating in some applications by depositing coatings or patterns on metal surfaces. In addition, he expects, eventually, to be able to use the process to produce carbon nanotubes, the invisible carbon wires recently discovered by others, that have stirred so much interest in the microelectronics industry.
Singh initially developed the new process for silver and nickel. Using a household blender, a laser and inexpensive reaction materials, he showed that he could produce ultrafine silver powder, 100 times finer than any now on the market. The silver powder is purer and more uniform too. In the invisible 1 to 100 nanometer range, the individual particles are smaller than the smallest bacteria or about the size of a small virus.
Singh makes the silver powder by putting silver nitrate, an inexpensive, colorless liquid used in pharmaceuticals, photography, and dyes, in the blender with a reducing agent at room temperature. Next, he whirls the mixture while irradiating it in bursts with the laser. As a laser burst hits the liquid, it creates a tiny "hot spot" where the silver nitrate and reducing agent can react. The result is a tiny particle of silver.
Singh can control the size and, to an extent, the shape of the particle by altering the laser energy, rotation speed and constituents of the reaction. He can make solid particles, porous particles, composite particles and even hollow nanotubes of an silver-nickel alloy. Unfortunately, he says, so far, the production rate of carbon nanotubes has been limited and uneconomical.
Singh notes that the new process can produce silver and nickel particles at a rate of .5 to 3 grams per minute, higher than any other technique now available, except grinding. Grinding, however, cannot make particles in the nanometer range.
By focusing the laser on a metal plate bathed in the reaction solution, the technique can be used to deposit silver or nickel in any desired pattern. The process could replace electroplating in some applications and potentially could be used to fabricate circuit boards or other super small microelectronics.
Extracting waste silver from spent photographic solutions is another possible application. Singh notes that the reaction materials used in the new process are environmentally friendly. Hydrazine, a carcinogen, is used in the commercial reactions most often used to produce silver powder currently.
Singh's co-inventors include his ARL associates, Eric Whitney and Paul Denney. The process is being patented and is available for licensing. Singh has published several articles on the work, most recently, "Nanoparticle Synthesis By A Novel Laser-Liquid-Solid Interaction Technique" in the Proceedings of the International Conference on Recent Advances in Metallurgical Process (Bangalore, India) and "A Novel Technique in Synthesis of Silver Nanoparticles By Laser-Liquid Interaction" in the current issue of the Journal of Materials Science.
Note: Contact Dr. Singh at (814) 863-4812 or firstname.lastname@example.org
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