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Stories About Chemistry

INDEX

Chemistry Spreads Wide

92. Diamonds Once More

A raw, unfaced diamond is the champion of �all the minerals, materials, etc� in hardness. Modern engineering would have a hard time without diamonds.

A faced and ground diamond becomes a brilliant, which has no equal among gems. Greyish-blue diamonds are especially prized by jewellers They occur �once in a blue moon� and this makes then price truly fantastic. But after all, gem diamonds are not so very important. If only there were more ordinary diamonds, so that we should not have to worry over every tiny crystal!

Alas, there are very few diamond deposits on Earth, and still less rich ones. One of them is in South Africa and it still gives up to ninety per cent of the world�s diamond production outside of the Soviet Union. In this country a very large diamond-bearing region was discovered about ten years ago in Yakutia, and now diamonds are produced there on an industrial scale. The formation of natural diamonds required extraordinary conditions, namely, immense temperatures and pressures. Diamonds were born in the deeper layers of the Earth�s crust. At places diamond-bearing melts subsequently broke out on to the surface and froze, but this happened very rarely.

But can�t we get along without nature�s help? Can�t man make diamonds himself?

The history of science knows of numerous attempts to produce diamonds artificially (By the way, one of the first �fortune seekers� was Henri Moissan, the first to isolate fluorine in the free state). Not one of them was successful. Either the method was fundamentally wrong, or the experimenters did not have at their disposal equipment which could withstand the combination of exceedingly high temperatures and pressures.

Only in the middle fifties of this century did modern engineering finally find the key to the problem of producing artificial diamonds. As might have beer expected, the starting material was graphite. It was subjected simultaneously to a pressure of 100 thousand atmospheres and a temperature of about three thousand degrees. Now diamonds are produced in many countries of the world.

But in this case chemists could only rejoice together with everybody else. They played but a minor part, most of the credit for this accomplishment being due to the physicists. However, the chemists scored in another way, having helped substantially to perfect diamonds. To perfect diamonds? Can anything be more ideal than diamond? Its crystal structure is the most perfect in the world of crystals It is the ideal geometric arrangement of carbon atoms in diamond crystals that makes them so hard.

Diamonds cannot be made any harder, but a substance harder than diamond can be made. Chemists have created the starting material for producing such a substance. There is a chemical compound of boron and nitrogen called boron nitride. It is nothing much to look at, but what puts one on the alert is its crystal structure, which is the same as that of graphite. That is why boron nitride has long been known as �white graphite.� True, nobody has ever tried to make pencil of it...

Chemists found a cheap way to synthesize boron nitride. Physicists put it to severe tests involving hundreds of thousands of atmospheres and thousands of degrees... The logic they followed was quite simple. Since �black� graphite could be changed into diamond, why could not a substance similar to diamond be obtained from its �white� counterpart?

The result was borazon, a substance that exceeds diamond in hardness It leaves scratches on smooth diamond faces, and can withstand higher temperatures: it is not so easy to burn borazon.

Borazon is still too expensive. It will take some effort to bring its price down. But the most important part has already been done. Man has again proved more capable than nature.

...It was reported not long ago that Japanese scientists have succeeded in preparing a substance considerably harder than diamond. They subjected magnesium silicate (a compound consisting of magnesium, silicon, and oxygen) to a pressure of 150 tons per square centimetre. For obvious reasons the details of the synthesis are not advertised. The newborn �king of hardness� has no name as yet. But that does not matter. What does matter is that unquestionably diamond, which has for centuries headed the list of the hardest substances, will in the near future be far from the top of this list.