CHAMPAIGN, Ill. -- When a liquid moves fast enough, gas bubbles will form and collapse. This process -- called cavitation -- is responsible for the pleasant babbling sound of streams and rivers, and for the stealth-defying sound of propellers on submarines. Chemists at the University of Illinois have discovered that in addition to making noise, high-velocity liquids also can drive chemical reactions.
"By colliding two streams of liquids together at a combined speed of 450 mph, we can break some of the strongest chemical bonds," said Kenneth Suslick, a U. of I. professor of chemical sciences. "With water, for example, the oxygen-hydrogen bond ruptures. The fragments can recombine to form hydrogen peroxide and other highly reactive intermediates that can destroy contaminants in the water."
Some contaminants can be destroyed directly by the implosive collapse of the bubbles. Other less volatile contaminants can be destroyed through secondary reactions with some of the fragments, such as free hydrogens and hydroxyl radicals -- both of which are extremely reactive. "This raises the possibility of using turbulent liquid jets as a simple way of purifying water contaminated with low levels of chemical waste," Suslick said.
The jets are made by pumping liquids at very high pressures through very small holes drilled in gemstones. "Only gems are hard enough to take the pressure without cracking or eroding," Suslick said. Currently, liquid jets are used industrially for making emulsions (such as cosmetic lotions) and for cutting extremely hard materials.
"The chemistry of turbulent liquids comes from 'hydrodynamic cavitation,'
which causes the formation, growth and implosive collapse of small gas bubbles
in the moving liquid," Suslick said. "This is very similar to
the effects of high-intensity ultrasound in a liquid, where the collapse
of sound-driven bubbles generates intense local heating, forming a hot spot
in the cold liquid
Contact: James Kloeppel, Physical Sciences Editor
University of Illinois at Urbana-Champaign