Opera divas can shatter glass with an aria. But Alfred University scientist William LaCourse says sound waves can strengthen glass, too. His process could lead to superstrong windows and durable, lightweight bottles at a reasonable cost.
LaCourse's research began humbly: He exposed glass to everything from Madonna to Chinese classical music before settling on higher frequencies supplied by an ultrasonic horn--which is inaudible to the human ear.
The sound waves speed up a well-established but slow process of strengthening glass chemically. In LaCourse's method, a piece of glass is heated to around 850F in a liquid containing potassium nitrate and then bathed in ultrasound. The energy of the ultrasound waves accelerates the leaching of sodium ions from the glass. Each sodium ion is replaced by a larger potassium ion. The bulk of the potassium ions force microscopic cracks in the glass to close. LaCourse is working with Viracon Inc., an Owatonna (Minn.) glass fabricator, to scale up the technology for larger pieces of glass. Without sound waves, chemical strengthening has been so time-consuming and expensive that it is used only for special applications where strength is exceptionally important, such as in cockpit windows.