Unearthing Exceptional Materials: Investigating Earth and Space for Heat-Resistant Marvels

Scientists from the University of Virginia and Arizona State University, who have received funding from the U.S. Department of Defense, are examining rocks and minerals for their potential to create materials that are highly heat-resistant and robust.Credit: SciTechDaily.com

The U.S. Department of Defense is financing a collaborative research project that aims to use natural minerals and rocks to invent innovative heat-resistant materials, prioritizing efficiency in utilizing scarce earth elements and sustainability.

The most robust, heat-resistant materials ever created might have been overlooked.

The U.S. Department of Defense is looking to understand if the secrets of next-generation high-temperature materials can be found in minerals and rocks from Earth and beyond. To this end, the DOD granted $6.25 million to a team led by Elizabeth J. Opila from the University of Virginia and other team members from Arizona State University as part of the Multidisciplinary University Research Initiative, or MURI.

MURI, which is quite competitive, provides funding for fundamental scientific research that the DOD believes could lead to revolutionary discoveries in areas of its interest through insights from multiple fields.

Opila mentions that high-temperature materials are currently in high demand due to advancements in energy production, hypersonics, and innovations like additive manufacturing in the industry. The excitement lies in exploring new combinations of different elements and geologically and planetarily-inspired materials.

Opila states that despite the complexity of minerals and rocks compared to the compounds that materials scientists usually utilize, this complexity brings potential for this project.

Part of Professor Elizabeth J. Opila’s team is postdoctoral researcher Sandamal Witharamage. This team is developing innovative high-temperature materials inspired from planetary and geological influence under the Department of Defense Multidisciplinary University Research Initiative grant. Credit: University of Virginia School of Engineering and Applied Science

Opila said that geologists focus on the formation of the Earth and the location of different substances. The aim is to use this knowledge in practical applications.

Researchers aim to mimic nature's use of mineral compositions, temperature, pressure, and their rapid changes to create synthetic materials. This project aims to significantly expand the resources and methods for creating high-temperature materials and surpass anything that has been developed by humans or nature.

The Army Research Office is recognizing the need for enhanced refractory materials, materials that can withstand intense heat or corrosive conditions, and has called for proposals on Emergent Refractory Behaviors in Earth and Extraterrestrial Materials. Opila’s team intends to design, fabricate, test, and describe various new materials designed to outperform current ceramics, alloys, and coatings used in high-temperature conditions, such as a 3,000-degree Fahrenheit jet engine.

Opila, a former NASA scientist, specializes in corrosion-resistant and heat-resistant materials. Collaborating with her are experts in geology, materials science, and computational modelling from UVA’s School of Engineering and Applied Science and ASU’s Schools of Engineering of Matter, Transport and Energy; Molecular Sciences; and Earth and Space Exploration.

Opila's team at UVA includes Patrick E. Hopkins, the Whitney Stone Professor of Engineering in mechanical and aerospace engineering, and Bi-Cheng Zhou, assistant professor of materials science and engineering.

Hopkins' ExSiTE lab specializes in using laser-based techniques to measure thermal properties of materials, which will be crucial in characterizing the materials developed by the team.

Zhou, a computational modeller known for inventing variations on the CALPHAD method to expand its capabilities, along with another computational modelling specialist ASU's Qijun Hong, will leverage their expertise to expedite the discovery of promising "recipes" which experimental labs at both universities can test.

ASU’s labs are directed by Alexandra Navrotsky, a widely recognized interdisciplinary expert in thermodynamics and director of the Navrotsky Eyring Center for Materials of the Universe, and Hongwu Xu, a mineralogist and materials chemist and professor at ASU’s schools of Molecular Sciences and Earth and Space Exploration.

The teams will make and analyze prospective recipes — often exchanging samples for testing, Opila said, with her lab bringing extreme heat, while the ASU labs apply intense pressure as well as high-temperature testing.

Synthesis of test samples traditionally starts with an element in powder form, said UVA Ph.D. student Pádraigín Stack, which is chemically altered to isolate a target material, or a component of a target.

The new composition, which has been diluted, heated, and dried back to a powder, is then sintered, a process applying enough heat and pressure to form a dense puck of material. Thin slices from the puck, called coupons, provide the samples researchers will subject to various tests — for example, exposing it to steam at high velocities in Opila’s lab or, at ASU, applying geological-like pressures with a diamond anvil.

In addition to these traditional synthesis methods, the team will try approaches inspired by planetary or geological phenomena, such as hydrothermal synthesis, which occurs in heated water at elevated pressures. Since water is abundant in Earth’s hot, pressurized interior, hydrothermal processes are associated with, for example, the formation of minerals containing rare earth elements — critical components for many renewable energy applications.

In the lab, hydrothermal synthesis involves forming crystals in a hot water-based solution in a closed vessel such that gaseous molecules moving atop the liquid exert high vapor pressure within the system.

One focus of the MURI project is utilizing rare earth elements. Many rare earth elements are already used in conventional high-temperature materials, such as environmental barrier coatings in aviation and hypersonic flight, as well as batteries, LED devices and other increasingly in-demand products — but at a steep cost. While not actually rare, separating the elements from soil and rock requires dozens of steps, most of them polluting.

“All these rare earth oxides that we’re going to use are in minerals right now,” Opila said. “Somebody mines them and then they have to separate them all. For example, ytterbium and lutetium are neighbors on the periodic table. They are so chemically similar, it takes 66 steps involving many chemicals resulting in nasty waste products.”

The separation problem led Opila to ask a question at the heart of another project she and her students are working on that’s related to the MURI: “What if you take a mineral made of elements you want straight out of the ground but not separate them, just clean it up a bit and make your material from that?”

They’re experimenting with xenotime, a common mineral, to improve environmental barrier coatings, or EBCs, which protect jet engine parts from hazards like high-velocity steam and desert sand. Ingested sand can melt into glass and react with the underlying alloy if it infiltrates the coating.

“We know certain minerals are stable because we can find them in the ground,” Stack said. “You don’t find metallic iron in the ground, you find iron oxide because iron oxide is what’s stable. Let’s explore why something is stable, or if it has other useful properties, and use that knowledge to make something better.”