Simonetti made this custom ice machine by hand, combining things bought on Amazon like baking pans, griddles and spindles. It’s like a science kitchen set, but it does the job. That job is to tackle the two obstacles that prevent the formation crystal-clear ice: cracks and bubbles.
Cracks form because water expands as it solidifies. Water freezes from the outside, forming a solid ice shell with liquid core. As the core solidifies, it tends to expand against the shell, which causes a buildup of internal forces that leads to cracking.
To prevent this cracking, Simonetti has made a cylinder with a metal base and plastic sides. Simonetti puts the metal part he’s inspecting inside of the cylinder and fills it with water. He then chills the metal base, which causes the water to freeze from bottom to top. The water eventually solidifies around the metal part and expands to the open top of a cylinder, rather than the sides.
Bubbles are little trickier. Dissolved air exists in water. As water freezes, it expels the excess air. This excess air accumulates on the freeze front, or where the water is turning to ice, to form bubbles.
“In order to prevent this phenomenon, you need to simply reduce the concentration of air on top of the freeze front. To do that, we stir the water to have constant flow,” says Simonetti.
To create this constant flow, Simonetti uses a spindle. By keeping the water in motion, the excess air never accumulates and the bubbles never form.
The result is a metal part encased by a block of crystal-clear ice, rivaling even the clearest ice sculpture. Simonetti can send ultrasonic waves unimpeded through this block to measure the safety of a metal part. When he’s done, he simply puts the part under water and the ice melts right off.
Simonetti admits that ice is only one step forward in inspecting these critical-safety parts. Ice is a good coupling medium because it has similar properties to that of metal, but it’s still not exact.
“Ideally, if the coupling medium were made of the same material as the part, it would be perfect,” says Simonetti. “But that is not practical with something like liquid titanium. Experimentally, you couldn’t remove it.”
Simonetti is now experimenting with nanoparticles to create ice that more closely resembles the properties of a metal part. The idea is to freeze suspensions of nanoparticles into the water to make the ice denser, heavier and mechanically stronger.
Simonetti’s taking calls from many industries, including engineering firms, car manufacturers and the military. He thinks the publication has helped establish legitimacy in his cryoultrasonic approach, as well as limit skepticism. He, too, doubted the approach at first.
“It’s entirely new. Whenever you have something that is so novel, there are a lot of skeptics from the academic community,” he says. “When you freeze water, it looks terrible. You think, ‘This is not going to work.'”
Simonetti pulls the finished block of ice out of the freezer to inspect. The ice completely encases the metal part. As Simonetti holds up the ice, he can see right through it. It’s as clear as an ice sculpture of a swan and, somehow, just as impressive.