Silicon as a pure element is almost never found in nature. It is, however, the second most common element in Earth's crust. In nature, it is commonly found as silicon dioxide (quartz), but can also be found bonded with many other elements. Its common usage is for the production of plastics, in which case silicon dioxide is usually bonded with hydrogen, oxygen and carbon. In the cases in which silicon is used for plastics, it is called silicone.
The Production of Pure Silicon
Pure silicon is produced by heating silicon dioxide along with carbon in an arc furnace at around 1900 degrees Celsius. The heat causes the oxygen in the silicon dioxide to split from the silicon and bond with the carbon. Hence, the outputs of this process are pure silicon, carbon monoxide and carbon dioxide.
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The Production of Crystalline Silicon
Crystalline silicon is mainly used as a semiconductor, which is a high-demand usage. Hence, a very cheap and fast method of producing silicon is used by semiconductor producers. This method is known as the Czochralski process. In this process, a thin rod tipped with a seed crystal is dipped in pure, molten silicon. The seed crystal is allowed to grow into silicon, then is removed. This method creates relatively large crystals with decent purity, which is why it is nearly the only method used for producing silicon for the semiconductor industry.