Researchers at Akita University have succeeded in developing a method to produce high-purity silicon by combining rice husks and used diatomite, the university has announced.
High-purity silicon, also known as “silicon metal,” is mainly used for making semiconductors and solar power batteries, and Japan relies on imports from China for over half of its silicon metal supplies. The researchers hope the new method will allow low-cost, domestic mass production of silicon metal, as rice husks and diatomite are abundantly available waste materials.
Current manufacturing methods use coke and silica rock as ingredients and require large amounts of electricity, says Akita University instructor Hideki Murakami, who was involved with the research. He says nearly all coke and silica rock has to be imported, with 90 percent of those imports coming from China. Additionally, in recent years the prices of coke and silica rock have risen greatly.
Diatomite is sediment found in the ocean, created from the fossilized husks of diatoms, a type of phytoplankton. Diatomite is mainly composed of silicon dioxide, and is known for its high absorbency, water and heat retention. One of its uses is as a filter medium, for example in the production of beer.
In place of silica rock, the researchers used diatomite that had been thrown out as industrial waste, and in place of coke they used rice husks. Because diatomite and rice husks have properties that make them easily react to one another, the researchers were able to hold down electricity use when combining them and succeed in creating silicon metal of over 99 percent purity.
Although semiconductors require a yet higher level of purity, the researchers say the silicon metal they created is pure enough for use in solar power batteries or for synthesizing substitutes for petroleum-based materials like polyethylene.
According to Murakami, because both rice husks and diatomite are cheap waste materials, based on current night-time electricity rates, the new manufacturing process would allow creating silicon metal at about half the price of importing from China.
“From there, how much could be saved would depend on how far one could keep down transport and personnel costs. Within fiscal 2011 we want to get a definite cost estimate and see the process put into commercial use,” said Murakami.
