Hot-spot bubbles ease glassmaking.

Metallic glasses may blast off now that sonochemistry promises an easy way to make them. Also called amorphous metals, these glasses possess unusual electronic and magnetic properties but are tough to make because the molten metal must cool very quickly to prevent crystalization, says chemist Kenneth S. Suslick of the University of Illinois at Urbana-Champaign.

But Suslick and his colleagues have now made amorphous iron using utrasound. High-intensity pulses of sound cause bubbles to form, expand and then implode, creating short-lived hot spots that reach temperatures of about 5,200 kelvins, says Suslick. Their rapid cooling helps create metallic glasses.

By zapping solutions of powdered iron pentacarbonyl for three hours with ultrasound, the researchers made amorphous iron that assayed 96 percent pure by weight, they report in the Oct. 3 NATURE. Other methods yield no better than 80 percent.

The scientists also note that this amorphous iron worked better than crystalline iron powder as a catalytic agent in converting carbon monoxide and hydrogen to hydrocarbons. They suggest the larger surface area of the amorphous form enhances the chemical reactivity.