SILICON – The Miracle of Advanced Technology _ PART I

The technology development means exactly advanced knowledge in Material Science Engineering. And the exponential development of the advanced technology we have today is only possibe because of 2 elements with extraordinary powerful and amazing properties, namely: SILICON and CARBON.

I would say it loud and clear: Internet, Computers, Artificial Intelligence, Nanotechnology, Bio-Technology, Medicine and the entire Digital Technology is just not possilbe without these 2 elements. Silicon and Carbon both are there since the existence of Earth and they are both abundent. Their properties were just not discovered by humans earlier. Yet in the last 100 years the interest for these 2 elements has exponentially increased. Myself I had the opportunity to study them for my engineering and master degree in material science and after graduation I continued to work with both. Hence, I wish to share some interesting facts I learnd about these two miracles of science. So I will start with SILICON.

In nature, the SILICON is only found in compounds, so you would be more familiar with its various oxides – which include flint, sand, rock crystal, quartz, agate, amethyst & opal – and silicates, which include granite, asbestos, feldspar, mica & clay. The silicon in these compounds was originally formed by nuclear fusion inside dying stars before being ejected when the stars collapsed into a supernova. Silicon is the most abundant element in Earth’s crust after Oxygen accounting of 28% by mass. Over 90% of Earth’s crust consist of silicate materials. The most predominant being the compound formed from Oxygen and Silicon named silicon dioxide SiO2 which is nothing but exactly Sand. This crystalyne structure of sand is also known as Quartz. A quartz crystal is just a regular arrangement of these SiO2 molecules, in the same way that an ice crystal is a regular arrangement of H2O molecules or iron is a regular arrangement of iron atoms.

You most probably have already noticed that quartz and therefore sand have different colors. The reason for this is the precence of impurities between the SiO2 moleules. But HOW THE TINY IMPURITIES DEFINE COLORS IN QUARZ?

Irradiation gives the color of quartz. In case of pure quartz irradiation will cause electrons to be ejected from some of the oxygen atoms. Soon after the electrons will return immediately, and the crystal is colorless or white. Yet The addition of Al atoms to the SiO2 structure (about 1 Al atom for every 10.000 Si atoms) results in a change of color in the crystal. Like that we get Black Quartz.

Irradiation of Quartz

If Al3+ replaces the Si4+ ion in the SiO2 framework to maintain electrical neutrality of the crystal, a proton (H+) could be present. If irradiation ejects an electron from an oxygen atom near the aluminum ion, the electron can be trapped by the proton. The whole (AlO4)5- entity creates a “hole” color centre, being converted to (AlO4)4- . The hydrogen atom does not absorb light. (AlO4)4-) absorbs light to produce the gray-to-brown-to-black color of smoky quartz.

Black Quartz

The same happens if other impurities are replacing the Si4+ ion , different color can occur by irradiation by adding atoms of iron (Fe) , titan (Ti), manganese (Mn), phosphates and other elements are present in the structure. Hence we have a big variety of quartz colors. The main once are like these shown below:

Heating up quartz gives the SiO2 molecules energy and they vibrate, but until they reach a certain temperature they won’t have enough energy to break the bonds that hold them to their neighbors. This is the essence of being a solid. If you keep heating them, though, their vibrations will eventually reach a critical value – their melting point – at which they have enough energy to break those bonds and jump around chaotically, becoming liquid SiO2.

H2O molecules do the same thing when ice crystals are melted, becoming liquid water. But there is one very important difference between the two.

The difference is that when the liquid water is cooled again as we all know, crystals reform with ease and create ice again. It is almost impossible to stop this happening, in fact: from the ice that jams up your freezer compartment to the snow that covers mountains, all are made from liquid water that has refrozen into ice crystals. It is the symmetrical pattern of these H2O molecules that accounts for the delicate patterns of snow flakes. You can melt and freeze water repeatedly and the crystals will reform.

Ice Crystals

With SiO2 things are different. When this liquid cools down, the SiO2 molecules find it very difficult to form a crystal again. It’s almost as if they can’t quite remember how to do it: which molecule goes where, who should be next to whom appears to be a difficult problem for the SiO2 molecules. As the liquid gets cooler, the SiO2 molecules have less and less energy, reducing their ability to move around, which compounds the problem: it gets even harder for them to get to the right position in the crystal structure. The result is a solid material that has the molecular structure of a chaotic liquid: a GLASS. Since failing to form a crystal is all you need to do to make glass, you’d have thought it would be rather easy. But it’s not.

Light a fire on sands of a desert and, with a lot of wind to fan the flames, you may be able to get it hot enough for the sand to start to melt and become a translucent sticky liquid. When this liquid cools, it hardens and indeed becomes glass. But glass made this way will most certainly be full of bits of sand that didn’t melt. It will be brown and flaky and will soon fall apart, becoming part of the desert again.

There are 2 problems with this approach.

The 1st is that most sand doesn’t contain the right combination of minerals to make good glass: the brown colour is a dreaded sign in chemistry,  a clue that you have a mixture of impurities. It is the same with paints: random combinations of colours don’t yield pure results; instead you get brownish-grey colours. While some additives, so called ‘fluxes’, such as sodium carbonate, will encourage the formation of glass, most will not. Unfortunately, despite being mainly quartz, sand is also made up of whatever the wind blows in its direction.

The 2nd problem is that even if the sand has the right chemical composition, the temperatures needed to melt it are around 1200°C, much hotter than any normal fire, which tends to be in the region of 700-800°C. A lightning bolt will do the job, though. When one of these strikes the desert it creates temperatures in excess of 10,000°C which are easily high enough to melt the sand, creating shafts of glass called fulgurites. These glass staffs of charred matter look uncannily like the images of thunderbolts that the gods of thunder, such as the Norse god Thor, was said to hurl in anger. The word itself comes from the Latin fulgur, which means thunderbolt. They are surprisingly light, and this is because they are hollow. Although rough on the outside, inside is a smooth, hollow tube, formed when the lighting bolt vaporizes the sand it first encounters. As the heat conducts outwards from this entry hole, it melts the sand into a smooth coating for the tube. Further out the temperatures are only high enough to fuse together the sand particles, making their edges rather rough. The colours of fulgurites reflect the composition of the sand in which they are formed, varying from grey-black to translucent if created in a quartz desert. They can be up to 15 meters long and are fragile, since much of their bulk is made of lightly fused sand.

Until recently, they were thought of only as strange curiosities. However, because they trap bubbles of air inside themselves when they form, ancient fulgurites provide scientists studying global warming with a handy record of the desert climates of previous eras.

In one part of the Libyan desert, there is an area of exceptionally pure white sand, comprised almost entirely of quartz. Search this part of the desert and you may find a rare form of glass that looks nothing like a scruffy fulgurite but which has instead the jewel-like clarity of modern glass. A piece of this desert glass forms the centrepiece of a decorative scarab found on the mummified body of Tutankhamun. We know that this desert glass was not made by the ancient Egyptians because it has recently been established that it is 26 million years old. The only glass we know like it is Trinitite glass, the glass formed at the site of the Trinity nuclear bomb test in 1945 at White Sands, New Mexico.

Given that there was no nuclear bomb in the Libyan desert 26 milion years ago, the current theory is that the extremely high temperatures that would have been needed to create such optically pure glass must have been produced by the high-energy impact of a meteor.

So without the help of meteor strikes and nuclear explosions, how do you make the kind of glass that we would recognize in our windows, spectacles and drinking glasses?

Although the Egyptians and the Greeks made advances in glass making, it was the Romans who really brought glass into everyday life. It was they who discovered the beneficial effects of ‘flux’, in their case a mineral fertilizer called natron, which is a naturally occurring form of sodium carbonate. With it, the Romans were able to make transparent glass at a much lower temperature than would be needed to melt pure quartz. In the few locations where the right raw materials and fuel for the high-temperature furnaces were available, they manufactured glass in bulk and then transported it throughout the Roman  empire using their vast trading infrastructure, supplying it to local craftsmen who would turn it into functional objects. None of this was revolutionary, it had been done before, but by making it cheaper, according to Pliny*, they put it within the reach of the ordinary citizens.

*(Pliny the Elder (23AD-79AD) was a Roman writer and naturalist who, in his book Natural History, includes an alleged account of the of the discovery of glass. According to Pliny, the discovery of glass occurred when Phoenicians, who had anchored their boats on the shores of Palestine, set about to cook dinner on the beach. They were unable to find rocks on which to set their cooking pots so they used nitrum (believed by some to be saltpeter) from their ship’s cargo. When the nitrum and sand melted in the heat of the cooking fire the result was glass).

The Roman love of glass as a material is perhaps best demonstrated by their imaginative new uses for it. For instance they invented the glass window. Before the Romans, windows were open to the wind (the word means ‘wind eye’), and although these might have wooden shutters or cloth curtains to keep out excessive wind and rain, the idea that a transparent material might be able to provide complete protection was revolutionary. Admittedly their glass windows were small and fused together with lead, because they did not have the technology to make large panes of glass, but they started our obsession for architectural uses of glass, which is still growing today.

TO BE CONTINUED… (See the Part II of The Silicon Story in the next post)

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