Silicon - the main pillar of today's technology

 Silicon - the main pillar of today's technology

Silicon is an element known (hopefully) to everyone, and rightfully so. It's the most abundant solid element by mass in the Earth's crust and the second most abundant one overall (after oxygen, with whom it more often than not occurs together). It doesn't exist in it's pure form in nature however and silica sand is the main source of it. Next time you walk on sand, sweep the floor or kick a rock, think about how weird the chemistry of silicon is.

Small chunks of elemental Si.

Big chunks of elemental Si (awesome!).

Why so? Because all that this beautiful, shiny, metallic element needs to become dirt is some oxygen. Sometimes a bit of aluminum, iron and magnesium too. The atmospheric oxidation actually happens on the surface of elemental silicon too, but the oxide layer is thin and covers the bulk of the material from further degradation.

The metalloid itself is pretty hard - not very, but enough to scratch some glass or tempered alloy steel. It has a metallic luster similiar to some of the less reactive metals, like rhenium (Re) or hafnium (Hf), but can be easily distinguished from them by the low density and deeply bluish tinge. When broken, it tends to turn into fine dust of sharp particles, so it's best to keep it as is. To get chunks of pure silicon is not all that expensive and an impressive sample can be acquired rather easily.

The popularity and availablity of elemental silicon was caused mainly by, in spite of Wolfgang Pauli's himself words, an outstanding rise of semiconductor industry. This is not a subject that needs much explanation.

Silicon chips.

Silicon diodes.

Silicon has the property of being a semiconductor, meaning it's neither a conductor, nor an insulator. It has a band gap between it's valence and conduction bands that allows electrons to flow in a controlled manner, as opposed to metals. To work as intended, silicon needs to be doped with other elements, like boron group or nitrogen group elements, which increase the number of positive carriers of electricity - holes, and negative ones - electrons respectively. Such doped material can be used in manufacturing of so called p-n junctions, essential for the production of diodes, transistors and hundreds of other components.

Semiconductor grade silicon is produced in the form of large monocrystalline slugs using the Polish chemist and material expert's Jan Czochralski's method. The slugs are then sliced into thin wafers and polished to prepare for further steps, resulting in the manufacturing of etched electronic chips in on the surface of the silicon.

Not a silicon wafer - it's actually GaAs.

I don't own an actual silicon wafer, but just for the informativeness sake, I'm showing a semicondictor wafer I do own - a gallium arsenide one. A silicon wafer would look identical, apart usually from the diameter though, as larger wafers are available.

Electronics aren't the only industrial use for silicon and it's compounds. It is used in a huge spectrum of materials, ranging by... softness? There are all sorts of silicon-based rubbers, with a distinctive silicon-oxygen-silicon chain, instead of the usual carbon-carbon-carbon one. The more interesting branch of silicon compounds might however be the hard ones - ceramics.

Silicon dioxide is a popular choice for all sorts of things, from sandpapers, to melting crucibles. It is also needed to create insulative layers in electronics, or simply, electrical insulators as seen on high voltage poles.

Pure SiO2.

SiC plate.

Silicon carbide, on the other hand is a material close to any materials engineer's heart, as it makes for a great, hard, durable and unreactive abrasive that is used in the versatile sanding disks needed for sample preparation. In it's solid form, SiC can be used in cutting inserts and even ballistic plates. Other interesting forms of silicon carbide are moissanite, which is a rare mineral similiar to diamond, and so called "whiskers" which are thin, long crystals of very high tensile strength, often implemented in tough corrundum based ceramics.

There is a lot to talk about when it comes to the element silicon. Maybe enough to someday return back to it and talk some more!