Voorhees and Genau

Peter Voorhees and Amber Genau



Space Station

International Space Station



NASA Research

NASA Glenn Research Center

Preventing gravity from keeping research down

 “Our two greatest problems are gravity and paperwork,” Wernher von Braun, one of the key figures in the space race, is credited as saying. “We can lick gravity, but sometimes the paperwork is overwhelming.”

Peter Voorhees, professor and chair of materials science and engineering, understands that sentiment better than most. Voorhees has spent more than 20 years working on a materials science experiment with NASA — one he started as a postdoctoral researcher in 1984. After creating quite a bit of paperwork documenting every nut, bolt, and screw back to its original source, he has seen his experiment defy gravity and make its way to the International Space Station.

Voorhees is the principal investigator on one of the two experiments that NASA’s Glenn Research Center sent on the space shuttle Endeavor’s August launch. The experiment, which NASA named Coarsening in Solid-Liquid Mixtures-2, is designed to learn more about the fundamental science that drives the coarsening process. Understanding that process is key to the science of making stronger, more predictable alloys.

Coarsening occurs in nearly every material composed of two crystals, and Voorhees points to Italian salad dressing as a classic demonstration of the process: After shaking the bottle of dressing, droplets of oil merge into larger droplets and eventually separate into a layer separate from the vinegar. The total surface area of two droplets is greater than one larger droplet, causing the droplets to continue to merge until they reach their lowest possible surface area. Coarsening of raindrops can occur in clouds and takes place in a wide variety of materials, such as the high-temperature alloys used in jet engine turbine blades and aluminum alloys used in bicycles. “Coarsening is used to tailor the mechanical properties of materials, but no one understands exactly how fast the process occurs,” says Voorhees. “From a materials standpoint, we want to know how fast this process occurs so that we can predict what’s going to happen to a product, which is especially important for products like a turbine blade.”

While coarsening occurs in a wide variety of materials, solid-liquid systems are ideal from an experimental standpoint. Unfortunately, when using these systems researchers have run into a key limitation on Earth: gravity. Just like ice in a glass of water, the solid particles float to the top of the sample. Working in the low-gravity conditions available in the International Space Station, researchers are able to study how the process works when the particles are evenly distributed throughout the liquid.

“We’re trying to study the fundamental forces that drive coarsening — the actual interactions between the particles,” says Amber Genau, a graduate student in Voorhees’s lab. “We want to get rid of all possible confounding factors, and gravity is the biggest one. Conducting this experiment in space allows us to better identify those driving factors.”

Genau and Voorhees prepared 20 samples of a lead-tin mixture to send on the shuttle Endeavor. Once the samples reached the International Space Station, astronauts placed furnaces holding the samples into the glove box of the station. The furnaces were specifically designed for this experiment and are isothermal to less than a hundredth of a degree. Once the lead-tin mixture melts, the remaining spherical tin particles are allowed to coarsen for a set amount of time before the samples are flushed with water to dramatically slow the coarsening process. In all, astronauts ran five cycles of the experiment to study the process over different lengths of time.

Another NASA shuttle will retrieve the samples from the International Space Station in February. The samples will be quickly returned to Voorhees’ lab for analysis. Using a serial sectioning process, researchers will remove thin layers from each sample and take digital images to create a series of images representing each layer of the sample. Researchers will use this data make a three-dimensional representation to compare to representations formed using coarsening theories.

“Once we analyze information about how fast the coarsening process occurs in space, we can test our theories and refine our models to make them more predictive,” Voorhees says. “This could help us in designing all kinds of materials — from steels to aluminum alloys.”

—Kyle Delaney