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September 1, 2004
The Production of Metallic Nanopowders is Scaled Up
Chemical Engineering, Sept. 1, 2004
By Gerald Ondrey, PhD
Last month, QuantumSphere, Inc. (Costa Mesa, Calif.; edlinks. che.com/3646-531) opened a new facility to make nanometer-sized powders of metal, boosting the firm’s production capacity tenfold to 2,500 lb/month of nanoaluminum (n-Al) and nanonickel (n-Ni). “The customer demand for QuantumSphere’s products far exceeded our aggressive expectations,” says CEO Kevin Maloney.
QuantumSphere claims to have a two-year lead over competitors because its vapor-condensation process is able to control the particle size and the thickness of the particle’s outer oxide layer. As a result, the nanopowders show improved performance when used in propellants, munitions and other pyrolytic applications, says Maloney. For example, the average size of n-Al can range from 20 to 80 nm, with an Al 2 O 3 coating independently controlled to be from 1.5 to 10 nm. When used in solid propellants increases the burning rate by a factor of 100 compared to using micron-sized Al powder. This can improve the thrust of rockets or the filling time of airbags, he says.
To make n-Al, Al wire (1199 alloy) is continuously fed into a vacuum chamber where it is melted and vaporized by an intermetallic resistance element that is electrically heated to about 1,850°C. Al vapor is quenched by a controlled, laminar flow of an inert gas into liquid droplets, which subsequently solidify into nanospheres. Oxygen is dosed downstream to form the oxide shell before the n-Al is collected in a combination of a cyclone and a barrier filter. The product is scraped from the filter and removed from the vacuum chamber via an N 2 -inerted airlock, and conveyed to the packaging facility. The process is completely automated, and computer control of the metal flux, chamber pressure, temperature and gas flow enables powders to be made with the desired particle size, size distribution and oxide-layer thickness. Although nanopowders cost about 100 times more than conventional powders, only one-half to one-quarter of the material is needed for a typical application. “More importantly, the nanopowders allow things to happen that were not possible before,” says Maloney.