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Home / Metal Story: Cobalt (Co)

Metal Story: Cobalt (Co)

날짜 게시 됨: 30/ 05/ 2018 - 포스터: VTRiT


Metal Story: Cobalt (Co) – The Charge of the Guns of Peace

It is said that the well-known 16th century chemist and doctor Paracelsus liked to demonstrate a trick which was invariably successful. He would first show his audience a painting of a winter landscape — snow-covered trees and hills. After letting them admire it as long as they pleased, he would turn winter into summer before their very eyes: the trees would cover with foliage and the white hills would disappear beneath new green grass.

Was it a miracle? But we know that there are no miracles in this world. The magician in that experiment was chemistry. At room temperature a solution of cobalt chloride containing a quantity of nickel or iron chloride is colourless. But if it is used to draw something, then warmed up even a little bit after it is dry, it becomes beautiful green in colour. It was this kind of a solution that Paracelsus had applied to his magic canvas. At a certain moment the scientist, unobserved by the people in the audience, would light a candle behind the canvas and the amazing change of season would set in.

True, Paracelsus himself could not say what was the exact chemical composition of his paints: neither cobalt nor nickel were known to science yet. Meanwhile cobalt compounds had been in use as pigments for several centuries by then. Even 5 000 years ago a blue cobalt pigment was known in ceramics and glass making, while in China it was used in the manufacture of the famous blue china. Ancient Egyptians covered earthen pots with a blue cobalt-containing glaze. In King Tutankhamen’s tomb archaeologists found glass stained blue with salts of cobalt. Glass of the same origin was also discovered in excavation sites in ancient Assyria and Babylonia.

It seems that the secret of preparation of cobalt paints had been lost somewhere at the beginning of our era, since the blue glass dating to that period made by masters in Byzantine, Alexandria and Rome had no cobalt and the blue colour which was achieved by introduction of copper was clearly inferior to the ancient blue pigment.

The “separation” of glass from cobalt lasted for a long time: it was only in the Middle Ages that glass-makers in Venice began to turn out the wonderful blue glass which had soon won popularity in many countries. And it was again cobalt to which the glass owed its fame.

The Venetian craftsmen vigilantly guarded the secret of their glass which was of unsurpassed beauty. To reduce the possibility of any “information leak”, in the 1 8th century the government of Venice transferred all glass factories to the small island of Murano which no outsider was permitted to visit. Neither were the glass-makers themselves allowed to leave the island without permission of the authorities. Still there was one Giorgio Belerino, an apprentice, who managed to flee from the island and make it as far as Germany. There he opened his own glass-shop. The shop did not last long, though. One day a fire “occurred”, the shop burned down and the fugitive owner was found stabbed with a dagger.

According to surviving 17th century documents, in Russia there was a great demand for the expensive, very stable and rich cobalt paint which was called “golubets” (in Russian the word “goluboy” means “blue’ . This paint was used for the wall paintings in the Faceted Hall, the Armoury, the Archangel Michael and the Dormition Cathedrals in the Kremlin and in other magnificent edifices of that period.

The expensiveness of cobalt paints was to be explained by the very small production of cobalt ores. True, it would be more correct to say that industry simply had no idea of cobalt ores, since no sizable accumulations of this element exist in nature. Cobalt only accompanies in fairly small amounts such elements as arsenic, copper, bismuth and some others. That was why miners in medieval Saxony had not suspected that their mountains were rich in rock containing an unknown metal. Every now and then they would come across a mysterious ore that possessed the outward characteristics of silver ore, but they invariably failed in all their attempts to produce silver from it. Furthermore, when that ore was roasted it released poisonous gases that were extremely troublesome to the miners. Finally they did learn how to distinguish between genuine silver ore and its deceptive replica. They began to call it “cobold” after the mountain spirit whose “adobe” the ore was.

In 1735 the Swedish chemist G. Brandt analyzed some ores of Saxony, including the notorious “cobold”, and on the basis of the material he obtained, gave a dissertation proving that the ores contained a then unknown metal. Brandt named the new metal after the ore “cobold”. Had this discovery been made in our days, the teletypes would have spread the news throughout the world immediately. But no such thing was possible in the 18th century, and for years the Swedish chemist’s dissertation was known only to a select few. Even thirty years after that some scientists, among them Leman in St. Petersburg, believed “cobold” to be a mixture of copper, iron and some “special earth”.

It was only at the end of the 18th century that the efforts of many scientists, including the Russian chemist G. .1. Guess, brought about the confirmation and formalization of Brandt’s discovery, and the metal he had found was given the name that we have always used —cobalt.

By that time the closest chemical relative of cobalt, nickel, had already been discovered. These metals often went together in nature and it was for good reason that scientists had to face the question of how to separate them and obtain each in pure form.

The answer to that most complicated chemical problem was found quite unexpectedly by … a veterinary doctor Charles Askin. This is how it happened. The veterinarian devoted all his free time to his hobby, metallurgy. In 1834 he became interested in nickel and its alloys. Askin attempted to extract nickel from ore. But unfortunately (or rather fortunately) the ore with which he was working also had cobalt in it. Askin did not know what to do about cobalt and turned for advice to Benson, the owner of a local chemical plant. As it turned out, Benson was in need of cobalt which he used in the manufacture of ceramics. But Benson did not know any way of separating the two metals. After some thinking the researchers decided to try chlorinated lime and made a careful calculation of the amount they would need. Each set to work separately.

Benson had enough chlorinated lime. He measured out the necessary quantity, tried it on the ore, but luck was not with him: his solution contained a deposit of the oxides of both metals.

Meanwhile Askin had discovered that the chlorinated lime at his disposal was only half of the calculated amount. “This is my hard luck ” Askin must have thought to himself. Nevertheless, he decided to go on with the experiment. But as they say, every cloud has a silver lining. To Askin’s amazement and joy, the experiment which had seemed so unpromising, gave the desired result: cobalt had precipitated in the form of oxide and nickel, for which there had not been enough chlorinated lime, had almost wholly remained in solution. Subsequently Askin’s method was somewhat improved and has been widely used in industry ever since to separate chemically- related metals.

Cobalt’s sphere of action had remained extremely limited until the beginning of the 20th century. Metallurgists, for example, who treat cobalt with such respect today, had a very vague idea about its properties. A book published in 1912 by Ye. Pro on the metallurgy of nonferrous metals asserted that until now metallic cobalt has not presented any interest from the standpoint of industry. There were attempts to introduce cobalt in iron and prepare special steels, but the latter have still found no application,”

The esteemed author was mistaken. Even five years before his book was published the Heynes firm had produced new alloys characterized by great hardness and intended for metalworking. One of the best of the new alloys which were named stellites (from the Latin “stella” star) contained more than 50 per cent of cobalt. After that the production of hard alloys was steadily growing, with cobalt playing an important role in them.

Soviet scientists and engineers developed the super-hard pobedit, an alloy which was superior to foreign analogous alloys. Apart from tungsten carbide, it also contained cobalt.

In 1917 the Japanese scientists Honda and Takati obtained a patent for a steel which contained from 20 to 60 per cent of cobalt and possessed high magnetic properties. The need in this steel which came to be known as Japanese, was great. The end of the 19th and the beginning of the 20th centuries were characterized by a virtual intrusion of magnetic materials in industry, hence the acute magnetic steel “hunger”.

Of the three ferromagnetic metals — iron, nickel and cobalt — cobalt possesses the highest Curie point, i. e. the temperature at which a metal ceases to be magnetic. Whereas for nickel the Curie point is as low as 358°C and for iron it is 770°C, for cobalt it is 1 130°C. Since magnets have to work in most varied conditions, very high temperatures included, cobalt was destined to become the principal component of magnetic steels.

Hardly had cobalt steel been developed, than it became the focus of attention of military and industrial bosses who had rightly guessed that they could have their own (alas, not at all harmless) use for its special properties. Even during the Civil War in Russia (1918-1920) sailors and Red Army men came across unusual mines on which minesweepers of the Northern Dvina Flotilla got blown up, never having even touched them. When divers managed to get hold of one of those sinister “toys” and defuse it was found that it was magnetic. The principle on which it operated was that as soon as the steel hull of a ship turned up in the magnetic field of the mine it was immediately detonated and the ship sank.

On the eve of the Second World War the production of cobalt steels used for the manufacture of magnetic mines had gone up considerably in Nazi Germany. Goebbels’ propaganda asserted that in precision, sensitivity and speed of reaction the German mines were “superior to the nervous system of many higher beings brought forth by the Creator”. Indeed, when the Germans had managed to mine the coast of England and the mouths of the Thames and other principal rivers from the air, the damage done to the British Fleet by the magnetic mines was heavy. But every poison has its antidote. Only two weeks after Germany’s treacherous attack on the Soviet Union, M. I. Ivanov, military engineer 3rd rank, working near Ochakov on the Black Sea defused the first German magnetic mine.

A remarkable incident took place at an ore mine in the Urals also during the war. Cobalt of which no one had suspected was discovered in old tailing heaps of an ore dressing factory which had been processing copper ore for many years by then. Within a short period of time a process of cobalt extraction was developed and the defence industry was supplied with a most valuable metal mined from “barren” rock.

During the war cobalt began to be included in heat-resistant steels and alloys from which parts of aircraft engines are made, missiles, high-pressure steam boilers and turbocompressor and gas turbine blades. One of those alloys is vitallium which contains up to 65 per cent of cobalt. But the short supply of cobalt and its high price are the factors holding back what would have been even a more extensive application of it in metallurgy.

There are spheres, however, where cobalt successfully replaces platinum which is an even more expensive metal and the yearly production of which is easily loaded onto one truck. Electrolytic metallurgy cannot do without insoluble anodes i.e. anodes that will not react with the electrolyte. Platinum is a very good metal there, but it is too expensive. The question of replacing platinum with a cheaper metal has intrigued scientists for a long time. A meticulous search has enabled them to develop an alloy which is in no way inferior to platinum, and moreover, is even better in its ability to withstand aggressive acids. This alloy contains up to 75 per cent of cobalt.

In some cases a combination of cobalt with platinum is used. The British firm Mulard has created a magnetic alloy of these metals which has high corrosion resistance and easily yields to machining. It is used in miniature magnetic parts for electric watches, hearing aids and data units.

An alloy of cobalt and chromium has been proved an excellent material for dental fixtures. It is twice as strong as gold and much cheaper, naturally.

So far we have been discussing ordinary cobalt, but it must be said that since 1934 when the outstanding French scientists Frederic and Irene Joliot-Curie discovered the phenomenon of artificial radioactivity, science and engineering have shown a lively interest in the radioactive isotopes of various elements, including cobalt. Of the 12 isotopes of this element cobalt-60 has found the widest application. Its rays have a high penetrating ability. In power of radiation 17 grams of radioactive cobalt are equivalent to one kilogram of radium, nature’s most powerful source of radiation. This is why when this isotope is produced, stored and transported (just as in the case of other isotopes) the strictest safety measures are taken to protect people from the lethal rays.

After ordinary metallic cobalt is turned into radioactive cobalt it is “bottled up” like a genie in special containers resembling common milk cans. In these containers coated with a layer of lead, cobalt-60 is taken by special vehicles to the place of its future work. But what if the vehicle gets into a road accident, will it mean that the ampule with cobalt will break and threaten human lives? No, this is out of the question. True, there is no automobile that can be guaranteed against an accident. But even if it does happen, the “can” will remain intact: it is subjected to the severest tests before it is allowed to receive its deathly charge. Such cans are dropped from a height of 5 metres onto concrete slabs, placed in thermochambers and put through other such trials. It is only then that they are allowed to carry the little ampule. These and other measures reliably protect people who work with radioactive sources.

Radioactive cobalt has many “professions”. Most widely used in industry, for example, is flaw detection by gamma rays, that is, control over the quality of production by means of gamma-radiography. The gamma source in it is cobalt-60. This method involving relatively inexpensive and compact equipment makes it possible easily to detect cracks, pores, airholes, and flaws in massive casts, weld seams, units and components situated in places difficult of access. The fact that the gamma rays are distributed by the source evenly in all directions enables the operator to inspect a large number of objects simultaneously and those shaped like cylinders, simultaneously along the entire perimeter.

Gamma rays have enabled Egyptologists to clear up one mystery which has intrigued them for a long time now. Some of them asserted that Tutankhamen’s mask was made from a solid piece of gold, while others argued that it consisted from several gold parts. They decided to use a cobalt gun — a special installation “charged” with cobalt-60. It was established that the mask indeed consisted of several parts, but that their fit was so prefect it was absolutely impossible to detect the joints.

Radioactive cobalt is used to control the level of molten metal in smelting furnaces and the level of the charge in blast furnaces and bunkers, as well as to maintain the level of liquid steel in the crystallizers of continuous-pouring installations.

There is a special instrument to measure the thickness of skin-plating of hulls, walls of pipes, steam boilers, etc. which cannot be reached from the inside by standard instruments.

The so-called labeled atoms, i. e. radioactive isotopes of a number of elements, including cobalt, find extensive use in the study of technological processes and operating conditions of various equipment.

For the first time in world experience scientists and engineers in the Soviet Union have built a commercial radiation-and-chemical reactor in which the source of gamma rays is also furnished by cobalt- 60.

Along with the modern methods of treatment of various substances — super-high pressures, ultra-sound, laser radiation and plasma treatment — radiation methods are being introduced in industry on a large scale, making it possible to significantly improve the quality of many materials. For example, radiovulcanized tires, have a 10-15-per-cent longer service life, while the fabric for school uniforms into which polystyrene molecules have been “grafted” by means of radiation is twice as durable. Even gems become more beautiful after “radio treatment”: the diamond irradiated by fast neutrons acquires a blue tinge, slow neutrons make it green while the cobalt-60 rays give it a soft bluish-green colour. Radioactive cobalt is also employed in agriculture to determine the earth’s moisture content, estimate the water reserves of snow, irradiate seeds before sowing, etc.

Not long ago French scientists disco- vered that radioactive cobalt could be effectively used to capture … lightning. A small addition of the isotope to the material from which the lightning rod is made causes gamma rays to ionize considerable volumes of the air around it. The electrical discharges in the atmosphere are then attracted to the radioactive lightning rod as though by a magnet. The rod “collects” lightning within a radius of several hundred metres.

Today radioactive cobalt is the doctor’s reliable aide in the battle for people’s lives. Grains of the isotope cobalt-60 placed in medical “guns” bombard internal malignant growths without doing any harm to the organism, but damaging the fast-growing sick cells, halting their activity and thus eliminating the foci of the sinister disease.

In the underground storage rooms of the USSR Isotope organization there are kept dozens of containers, big and small, with cobalt, strontium, cesium and other radioactive substances. When time comes they are sent to hospitals and clinics, factories and research institutions where atoms are used for peace.

Source: Tales About Metals, S. Venetsky


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