Materials science and engineering researchers at the University of California, Davis, and materials company Homerun Resources, Inc., have developed a groundbreaking one-step laser-pulse technique to purify raw silica sand to over 99.99% purity. The method is the first phase in a collaborative effort to create a pathway to a carbon-neutral process of deriving silicon from silica sand.

The project began when Subhash Risbud, Distinguished Professor emeritus of materials science and engineering at UC Davis, was connected via a mutual friend with Brian Leeners, CEO of Canada-based materials company Homerun Resources.

Leeners needed someone to investigate purifying the raw silica sand the company was mining in Bahia, Brazil, using lasers as a potentially environmentally friendly purification method.

Risbud, who has a rich history of researching glass, much of which is made from silica, had used lasers in previous studies with quantum dot nanostructures and was interested in pursuing Leeners' theory.

Arish Naim, a Ph.D. student in materials science and engineering, had recently come under Risbud's mentorship and was eager to take on the project, drawn to its clean energy aspect. Risbud, Naim and Leeners developed a proposal for Homerun Resources, with Naim taking the lead on the experiments.

From grains of sand

First, the raw silica sand is homogenized, meaning all the particles are made the same size so that the heat is uniform when it's applied to the sample. The sand is sealed in a vacuum and treated with lasers — at UC Davis, Naim uses the physics department's laser at the Crocker Nuclear Laboratory — pulsed every femtosecond for different time periods between two and 24 hours. (The exact specifications are currently under patent review.)

Naim had also attempted thermal and furnace treatments with varying results, but when she was doing calculations on the data from the laser experiment's X-ray fluorescence analysis, or XRF, she was stunned. After a couple of adjustments in the experimental parameters, the experiment resulted in over 99.99% purified silica.

"I turned to the person who does the XRF for me, and I was like, 'Do you think this looks like the right number?' He said, 'Yeah, I think this is the right number,'" Naim said. "I was like, 'Are you serious?' It was validating, it was exciting, it was all emotional. It was a remarkable day that I'll never forget."

Risbud said that silica at this level of purity has a wide range of applications. Silicon wafers, for instance, are used in semiconductor devices, solar cells, LEDs, communication systems and the sensors in smartphones and medical imaging.

Purified silica can also be converted to silicon carbide, which is becoming increasingly sought-after in the semiconductor industry to replace silicon chips. Its ability to operate under extreme conditions makes it practical for electric vehicles, medical sensors, space exploration and renewable energy systems.

Leeners, who has been part of research and development in tech and materials science for 30 years, was amazed and pleased at the fast and desired result.

"Things never happen quickly, and your dreams rarely get fulfilled 100%, so to have Subhash and Arish come back and say, 'Yeah, we did the first test, and we got five nines,' I was like, wow," he said. "We knew silica could achieve that, but we didn't know if the laser could do that."

A pathway to cleaner silicon

The team has goals to convert the purified silica into silicon carbide and then advance it to a high enough grade to use in anodes for lithium-ion batteries. Naim has spent the summer months at Lawrence Berkeley National Laboratory working on how to best go about the conversion to silicon carbide.   

"Purifying the silica was stage one," Naim said. "The end goal of this project is developing a value chain at the intersection of the battery and the mining industry to help in the clean energy transition in the U.S. This will be an advantage to the silicon industry, to the battery industry and to silicon metallurgy. It's a holistic project."

Using clean energy to purify raw silica and generate battery-grade silicon carbide was one of the reasons lasers were considered in the first place, as opposed to the typical techniques.

"The idea is you take sand, which has impurities in it," Risbud said. "You heat it, and the impurities leave by evaporation. The normal way of doing this is chemical, which means you put some acid on it, leach it, wash it or do any number of steps in mineralogy and materials science."

The dream, said Leeners, is to develop a fully green processing technique so those chemicals — which are relatively safe and self-contained in the purifying process — aren't even part of the equation.

"Theoretically you could have a solar energy generation facility creating the electricity that goes into the thermal processing done by lasers, which would then create silica that is recycled into creating more solar energy through silicon-based photovoltaics," he said. "It has the potential to be an elegant industrial cycle."

Powerful partnership

Naim and Risbud are working with Leeners on creating a similar pathway for taking silica quartz stone from British Columbia and graphite, from a sister company to Homerun, to battery anode silicon and graphite powders. The relationship between Homerun Resources and UC Davis has been positive and productive, and all three collaborators are excited to see the project through to fruition.

"We're completely reliant on the brain power of UC Davis in this process," said Leeners. "It's a really good team dynamic relative to brainstorming and being creative, and it's been an extremely rewarding, awesome endeavor that's going to continue."