Faculty Profile: Ricardo Castro
Assistant Professor, Chemical Engineering and Materials Science
By Derrick Bang/Photo by Kevin Tong
Upon joining UC Davis in 2009, Professor Ricardo Castro immediately plunged into two distinct but related projects. The first, the development of nanocrystalline materials for radiation resistance, caught the attention of the U.S. Department of Energy's Office of Science, which awarded Castro an Early Career Research Program Award in spring 2011, including a grant of $762,935.
Castro's second project, involving an effort to control the behavior of nanoparticles under heat treatment, resulted in a National Science Foundation CAREER Award, also in spring 2011. This honor included a cash grant of $450,000. Both cash awards are intended to fund Castro's respective projects over five years.
Castro's goal with the first project is the design and development of radiation-resistant materials for structures — such as nuclear power plants — that must withstand extreme environments. The steel often used for such structures quickly starts to suffer from amorphization and loses its crystallinity (the degree of structural order in a solid); the metal becomes brittle and subject to breakage, and therefore must be repaired or replaced every few years. This is both expensive and time-consuming.
Castro is tackling this problem at the nano level. "Nanomaterials aren't just different because they're small; they have different properties because they are small."
Very small particles are collectively surrounded by a lot of surface interfaces. Consider a cylinder filled with tennis balls; now imagine that same cylinder filled with small marbles. The marbles collectively possess far greater surface area and interfaces.
"The interface offers a space for the defect to occur without compromising the crystallinity of the structure," Castro explains. "We're working on sustaining the process, and using it to make better materials. The idea is to create safety supports for the steel used in nuclear reactors, so it can improve the overall mechanical properties and radiation resistance in such structures."
Castro's second project, involving an effort to control the behavior of nanoparticles under heat treatment, resulted in a National Science Foundation CAREER Award from the Ceramics division. This honor, also presented earlier this year, included a cashgrant of $450,000. Both cash awards are intended to fund Castro's respective projects for five years.
"That should be enough time to deliver good results," he said, "although, when you start to dig in, you realize there are more and more questions."
The heat treatment of nanoparticles involves numerous unknowns. Getting a nanostructure material ready for use is a huge technological problem; it's easy for certain materials and nearly impossible for others. Tin oxide, for example, is an important material for gas sensors that are designed to detect sulfuroxides in industrial environments; such oxides are highly dangerous, because they form acid when exposed to water. Unfortunately, it's incredibly difficult to make tin oxide a nanograin structure in dense form ... and Castro wants to know why.
A finished dense material isn't merely a single chunk; it's composed of many tiny, nanosize grains. They're compacted to make the single part, via a treatment known as sintering (the welding together of small particles by applying heat below the melting point). The problem is that such particles are inclined to come together — to form interfaces — like adjacent drops of water, which absorb each other until only a few huge puddles remain. The goal, though, is to get the particles to "attach" without gobbling each other up. A finished part composed of a higher concentration of separate tiny particles offers greater surface area, which means better sensitivity to the gasses being detected by the sensor.
The recipient of a 2011 Young Investigator Award from the Society of Hispanic Professional Engineers (SHPE), Castro is energized by his proximity to the many other researchers across the UC Davis campus. "It's a highly scientific environment. I can go next door and talk high-level science to any of my colleagues, and get very good feedback. This makes my work better."
While working on his Ph.D. at Brazil's University of Sao Paulo, Ricardo Castro took advantage of a program that allowed him to further his research during a half-year stay in a foreign country. He selected the United States and came to UC Davis, which he deemed a good place for his research into the phase transitions of nanocrystalline aluminum: how to better understand — and control — the phase change from alpha aluminum, used for its structural properties, and gamma aluminum, which is essentially a catalyst.
After earning his doctorate, Castro became a professor at Brazil’s Centro Universitário da FEI. He put together a lab and, after a few years, began a three-way collaboration with researchers at UC Davis and the Universidad Nacional Autónoma de Mexico (UNAM), on the subject of nano-structure materials, and how best to understand ionic conductivity in ceramics.
Eventually, he was persuaded to join the UC Davis College of Engineering fulltime, which he did in 2009. "UC Davis is one of the greatest centers for research; its visibility is getting bigger and bigger."