How is silicone made anyway?


With over 3000 different silicone products, WACKER is one of the world’s largest manufacturers. Hard to believe that all of these different applications come from the same metalloid: silicon. A quarter of the earth’s crust consists of the element silicon. But not in pure form: silicon is primarily found combined with oxygen in the form of quartz. The chemical name for quartz is silicon dioxide. How do we turn this into pure silicon? At WACKER, we do this inhouse at the company’s silicon plant in Holla, Norway. Quartz is transported to Holla by ship. The quartz is then melted with coal in a large furnace at temperatures of up to 1800 degrees. The carbon removes the two oxygen atoms from the silicon dioxide. What remains is liquid metallurgical-grade silicon. After it has cooled, it is broken into handy pieces. Before further processing, the silicon is finely ground. Silicon from Holla is then sent to WACKER’s Burghausen and Nünchritz sites… …to be manufactured into silicone. In addition to silicon, silicone synthesis also requires methanol. Methanol reacts with hydrogen chloride to form gaseous chloromethane. Before it encounters chloromethane, the silicon is ground into particles one millimeter in size. From there it goes to the fluidized-bed reactor to undergo the Müller-Rochow process. At roughly 300°C, the blend of chloromethane and silicon granules behaves like a boiling liquid. Ideal conditions for the two substances to react and form a crude silane mixture. This mixture is distilled to separate it into various chlorosilane versions. Depending on the desired downstream product, the chlorosilanes undergo various synthesis routes. Difunctional chlorosilanes are converted to long polysiloxane chains… …via hydrolysis and polycondensation. In this form they can be used directly as silicone fluid for applications such as cosmetics or textiles. Polysiloxane chains can also be used as the starting material for silicone rubber. Silicone rubber, in turn, can be used to produce a virtually inexhaustible range of rubber-like products, such as gaskets, diving masks or baking molds. Trifunctional chlorosilanes undergo hydrolysis and catalytic condensation to produce… …three-dimensional silicone-resin networks. These can find use in such fields as building protection. The advantage of silicone treatment is… that it renders construction materials water-repellent and breathable at the same time. This is because the silicone-resin network has a fine structure… …that allows moisture to exit yet prevents water from penetrating into a given material. And last but not least, WACKER uses tetrafunctional chlorosilanes as the raw material… …to manufacture pyrogenic silica. Pyrogenic silica is made by burning a crude silane mixture under a stream of hydrogen and air. Small molecules continually fuse together, forming aggregates… …which are ultimately bound together as agglomerates, which are deposited from the flame like ash. The step from quartz to the manifold variety of WACKER silicone products… …involves many synthesis routes. WACKER continuously looks to optimize its products and processes to meet future market demands. Silicones are indispensable in every walk of life. Constant development of silicones will continue to impact tomorrow’s future.

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