Stories About Chemistry
95. Union of Carbon and Silicon
There are two elements in nature which can claim a special position. The first is carbon. It is the basis of all animate things. Its claim is valid primarily because carbon atoms are capable of combining strongly with one another to form chain-like compounds:
The second is silicon. It is the basis of all inorganic nature. But silicon atoms cannot form such long chains as carbon atoms, and besides the number of silicon compounds found in nature is smaller than the number of carbon compounds, though they are much more numerous than the compounds of any other chemical element.
Scientists decided to “correct” this shortcoming of silicon. Indeed, silicon is tetravalent just like carbon. True, the bond between carbon atoms is much stronger than that between silicon atoms, but silicon makes up for this by being less active.
Now if we could obtain compounds similar to organic compounds but with silicon instead of carbon, what wonderful properties they might possess!
At the beginning the scientists were unlucky. True enough, they proved that silicon could form compounds in which its atoms alternate with oxygen atoms:
but these compounds were not stable.
They scored their first success when they decided to combine silicon atoms with carbon atoms. Such compounds, which have become known as organosilicon compounds or silicones, indeed have a number of unique properties. Various resins have been made on the basis of silicones, and from them plastics can be obtained which can resist high temperatures over long periods.
Elastomers, based on organosilicon polymers possess very valuable qualities, one of which is heat resistance. Some grades of silicone rubber are stable up to 350°C. Now imagine a tyre cover made of such a rubber.
Silicone rubbers do not swell at all in organic solvents. They are now used for making various kinds of hose for fuel transport lines.
Some silicone liquids and resins hardly change their viscosity over a wide range of temperatures. This made them eligible as lubricants. Owing to their low volatility and high boiling point silicone liquids have found extensive usage in high-vacuum pumps.
Organosilicon compounds are water-repellant and this valuable property is utilized in the manufacture of water-repellant fabrics. But that is not all. Water is said to wear away stone. Tests made at important construction projects have shown that it is useful to impregnate structural materials with various organosilicon liquids.
Strong heat-resistant enamels have been developed recently, based on silicones. Copper or iron plates coated with such enamels can withstand several hours’ heating at 800°C.
And this is only the beginning of the peculiar union of carbon and silicon. But this “dual” union no longer satisfies chemists. They have set themselves the task of introducing other elements into the molecules of organosilicon compounds, such as aluminium, titanium, or boron. This problem has also been successfully solved and has resulted in an absolutely new class of substances known as polyorganometallosiloxanes. The chains of these polymers may consist of different kinds of links: silicon-oxygen-aluminium, silicon-oxygen-titanium, silicon-oxygen-boron, etc. Such substances melt at temperatures of 500-600°C, competing in this respect with many metals and alloys.
There was a flash report not so long ago that Japanese scientists had allegedly succeeded in creating a polymeric material which could resist heating to 2000°C. Maybe this was an error, but even so it was not far from reality. For the term “heat-resistant polymers” will soon go down in the long list of up-to-date engineering materials.