Ice’s Secrets Hold Promise for Green Projects

Charles T. Troy, charlie.troy@laurin.com

LIVERMORE, Calif. – In a development that could have an impact on two vital areas – water purification and fuel cell design – researchers at Sandia National Laboratories have imaged ice a few nanometers thick as it forms bulk ice, a task heretofore considered impossible.

Sandia’s Konrad Thürmer images ice.

They accomplished this trick by employing a scanning tunneling microscope (STM), a device that should not work with ice because it relies on conducting current, which runs contrary to ice’s insulating property. But using an STM to image ice successfully is precisely what Sandia physicists Norm Bartelt and Konrad Thürmer did.

According to Bartelt, the interaction between water and solids plays a role in the design of fuel cells and water purification systems.

Ice cubes or snowflakes?

The work at Sandia seeks to answer one of ice’s mysteries: Snow-flakes form in a classic six-sided symmetrical shape but, at low temperatures, ice grows in a cubic form. What the researchers found was that, when an ice film is extremely thin, measuring an average of about 1 nm thick, the water molecules form small, tabular islands of crystalline ice.

Images reveal that ice grows faster around screw dislocations leading growth spirals (labeled “S”), where cubic ice is being produced.

Once the thickness reaches 4 or 5 nm, the ice islands join together and start to form a continuous film.

The researchers are not finished. Future plans include putting salts on an ice crystal to see how they change the crystal’s growth and depositing molecules that react with water, such as atomic oxygen, to determine the exact point on the surface where water dissociates.