Researchers find new ways to make metal oxides
4 Apr 2001
Scientists at the US Department of Energy's Brookhaven National Laboratory have recently developed a novel way of making metal oxides. This class of compounds, which includes magnesium oxide and zinc oxide, is commonly used in catalysts and cosmetics, and is also important to the growing field of nanotechnology.
The new method for making metal oxides, patented by Brookhaven Senior Chemist John Larese and retired Brookhaven Chemist Walter Kunnmann, avoids some of the problems of traditional methods, 'and allows greater control of the particle size and chemical composition of the product,' says Larese.
One key difference: The traditional method requires processing a molten metal at high temperature; the newly patented method entirely avoids the dangers and difficulties of working with the liquid phase.
Instead of directly transforming the solid metal to its liquid state, 'we combine the metal with graphite in a vessel and heat it to form an intermediate compound, a metal carbide,' says Larese. Then the scientists apply more heat to decompose the metal carbide. The metal gets released as a vapour, which can then be oxidized to form a pure metal oxide powder.
Because the heat can be added in a controlled fashion, the scientists can vary the vapour density. The more dense the vapour, the larger the particles they produce. The result is the ability to produce metal oxide powders with uniform particle sizes anywhere from 5 to 500 nanometers.
The method also allows the scientists to add other elements such as chromium, iron, copper, and nickel to make more complex particles. These additives, or 'dopants,' can alter the electrical, optical, and magnetic properties of the final product, so they can be tailored for a variety of uses.
'For example, adding chromium as a dopant to magnesium oxide has resulted in a material that breaks apart certain nitrogen oxides one hundred times better than commercially available magnesium oxide,' Larese says. This reaction is important in smokestack scrubbers that aim to prevent nitrogen oxide pollutants from getting into the atmosphere.
In addition, learning how to deposit metal clusters and molecules of various sizes on the surface of tiny powder particles may have applications in many other areas of materials science where scientists are trying to manipulate the physical properties of materials by creating or controlling nanoscale structures.
The work was funded by the US Department of Energy.
