New Nano Step Makes Purifying Silicon Cheap

by Kathy S. on November 3, 2015

New Nano Step Makes Purifying Silicon CheapWhile Silicon is the second most abundant element on earth, it’s usually not refined enough naturally for integrated circuits and solar cells. Silicon can be purified, but it’s expensive, dirty and not optimized for battery electrodes, thermoelectrics and solar cells. Now scientists from Nanjing University and Stanford University have developed a simple and inexpensive method to get 99.999 percent pure silicon from bulk ferrosilicon.

Nearly photovoltaic grade silicon starts with bulk silicon, which is milled to a nanoscale powder and purified with a strong mix of acids. The acids strip away oxygen and metal impurities, converting the material from 84 percent silicon by weight to 99.999 percent. This acid etching method has been around since WWII, but the method never received high purity because the particles have only just now been reduced to nano size. For this reason, a more expensive process for producing high purity—99.9999999—became the standard.

The new, inexpensive method isn’t this pure, which means it isn’t pure enough for today’s integrated circuits; however, it can achieve the level of purity needed for thermoelectric devices and battery electrodes. The process for making silicon that’s 99.999 percent pure or “five nines” costs about $1 per kilogram.

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