Metal Story: Magnesium (Mg) – A Fighter Against Fatigue
The search for the notorious “philosopher’s stone” was the biggest headache of “researchers” in medieval alchemic laboratories. The “stone” was to help them obtain gold from baser metals.
The search proceeded in various directions. Some asserted that lead, heated up to the point when it would release the “red lion” (i.e. up to melting point) and then boiled in tart grape alcohol, was the best raw material for the production of “the philosopher’s stone”, others thought that it was animal urine, while still others insisted that the truth was in water.
At the end of the 18th century a British alchemist, who was evidently a representative of the third group, boiled some mineral spring water near the town of Epsom, but instead of the “philosopher’s stone”, obtained a salt with a bitter taste and a laxative effect. A few years afterwards it was found that when this salt interacted with the “permanent alkali” (as soda and potash were called in those times), it formed a white friable and light powder which was exactly the same as the one produced by roasting a mineral discovered near the town of Magnesion in Greece. Because of this similarity Epsom salt was named white magnesia.
In 1808 Sir Humphry Davy, the well-known English scientist, analyzed white magnesia and obtained a new element which he named magnesium. The celebrations on the occasion of the discovery were not accompanied by fireworks because people then did not know that the new-born element possessed excellent pyrotechnical properties.
Magnesium is a very light silvery-white metal having only a fifth of the weight of copper and a 4.5th of the weight of iron. Even the “winged” aluminium is one and a half times heavier than magnesium. Its melting point is comparatively low, just 650° C, but it is quite difficult to melt magnesium under ordinary circumstances: heated in the air to a temperature of 550° C it bursts into a flare and bums up immediately with a blinding bright flame (this property is widely used in pyrotechnics). To ignite magnesium it is enough to hold a burning match to it, while in the atmosphere of chlorine it will flare up even at room temperature. While burning, magnesium emits large quantities of ultraviolet rays and heat: four grams of this “fuel” is sufficient to bring a glass of ice-cold water to a boil.
In the open air magnesium soon becomes dull, as oxidation film forms on its surface fast. This film, however, is a reliable protection against further oxidation.
Magnesium is very aggressive, easily depriving most elements of oxygen and chlorine. But while it effectively resists the action of some acids, soda, caustic alkalies, gasoline, kerosene and mineral oils, it is powerless against seawater and dissolves in it. It shows practically no reaction with cold water, but rapidly forces hydrogen out of hot water.
The earth’s crust is rich in magnesium (more than 2.3 per cent). Only six of its “colleagues” in the Mendeleyev Table are found in nature in greater quantities.
Scientists believe that the lower layers of the earth’s mantle contain particularly large amounts of this element. Magnesium is found in the composition of nearly 200 known minerals. One of them is quite extraordinary: it can be folded as a handkerchief, used as wrapping paper, or tom to shreads.
Some 20 years ago a unique specimen of this mineral was found in the Soviet Far East. Miners of a polymetal ore mine discovered a small cave and in it, hanging from the ceiling, there was something that ‘coked like a greyish-white “curtain” doubled in the middle. It was about a metre and a half long and a metre wide and to the touch felt like suede, soft and elastic. The lightness of the “fabric” was fantastic.
The unusual find was sent to Moscow. A chemical analysis showed that it consisted mainly of aluminosilicate of magnesium and was in fact the mineral Palygorskite of the asbestos group which was first discovered by Academician Fersman in the twenties of this century in the Palygorsk deposit in the Ural Mountains. For its unusual properties this mineral is often referred to as “mountain leather”. The leather” found in the Far East and now on display in the Mineralogical Museum of the USSR Academy of Sciences is remarkable in that it is the biggest in size ever discovered in the world.
Magnesite, dolomite and camallite are the principal industrially important raw materials for magnesium production.
Two processes are employed to produce magnesium: the electrothermal and electrolytic processes. The first is when magnesium oxide is reduced by any reducing agent — carbon, aluminium, etc. This process is quite simple and has been in increasingly wider use lately. But still the second, electrolytic, process remains the main one in magnesium production today. It consists in electrolysis of fused magnesium salts, mainly chlorides, yielding a very pure metal which contains more than 99.99 per cent of magnesium.
But not only the earth’s mantle is rich in this metal. The “blue chests” of the seas and oceans are a storehouse of practically inexhaustible and constantly replenished reserves of it. A mere cubic metre of seawater contains nearly 4 kilograms of magnesium. In all, over 6.10^16 tons of this metal is dissolved in the waters of the seas and oceans. Even people far removed from mathematics will not find it hard to perceive the magnitude of this figure. But still, here is an example to illustrate: since the beginning of its chronology, mankind has lived a little more than 60 thousand million seconds (6.10^10). Even if mankind had begun to use seawater to produce magnesium from the very first days of our era, it would have to turn out one million tons of this metal every second to have exhausted its reserves by now.
But Neptune should not worry for his wealth: even during the Second World War when magnesium production from sea water was at its peak it did not exceed 80000 tons a year (not a second!). The method by which magnesium is extracted from water is quite simple. Seawater is mixed in great tanks with lime milk prepared from sea shells. This mixture, called “magnesium milk”, is then turned into magnesium chloride. After that magnesium is separated from chlorine by electrolysis. Not long ago the Japanese firm Kurita Kogio designed a plant for the comprehensive utilization of seawater. According to estimates, the processing of four million litres of sea water will yield 108 tons of table salt, 2.2 tons of Glauber salt, 16.7 tons of chlorine and 15.9 tons of magnesium. Besides that, the plant will turn out three million litres of drinkine water and a large amount of brine for the production of caustic soda.
The water of salt lakes can also serve as a source of magnesium if it contains magnesium chloride (known as natural brine).
In the Soviet Union such “storehouses” of magnesium are found in the Crimea (the lakes Saki and Sasyk-Ivash), in the Volga area (Lake Elton) and in other regions.
So much for magnesium production. But what about the utilization of this element and its compounds?
Its light weight could make magnesium an excellent structural material. But unfortunately, pure magnesium is soft and wobbly. Therefore, engineers have to make do with alloys of magnesium with other metals. Its alloys with aluminium, zinc and manganese are in especially extensive use. Each of the components of this partnership plays its own role in improving the general properties of this metal: aluminium and zinc build up its strength and manganese increases its corrosion resistance. And magnesium? Magnesium makes the alloys light. Parts made of magnesium alloys are 20 to 30 per cent lighter than aluminium parts and 50 to 75 per cent lighter than cast-iron or steel parts. Such alloys are “offered jobs” more and more often in the automobile and textile industries and in printing.
Magnesium alloys have many other partners that increase their refractoriness and ductility and decrease their oxidizability. Among them are lithium, beryllium, calcium, cerium, cadmium and titanium. But there are also some enemies: iron, silicon and nickel impair the mechanical properties of magnesibm alloys and reduce their corrosion resistance.
Magnesium alloys are widely used in the aircraft industry. Back in 1935 Soviet aircraft designers built the Sergo Ordzhonikidze plane which contained almost 80 per cent of magnesium alloys. The plane passed all tests without a hitch and was in service for a long time under rigorous conditions.
Magnesium alloys are indispensable in the manufacture of rockets, nuclear reactors, engine parts, petroleum and oil tanks, railway car frames, buses, passenger cars, wheels, oil pumps, rock hammers, pneumatic drills, still and movie cameras and binoculars. And this list of instruments, parts, and subassemblies is far from complete.
Magnesium is also important to metallurgy where it is used as a reducing agent in the production of a number of metals, including vanadium, chromium, titanium and zirconium. Introduced as a modifier into molten iron, magnesium improves its structural and mechanical properties. Castings made of magnesium-modified cast-iron have successfully replaced steel forgings. Apart from that, magnesium helps to deoxidize steel and alloys (it reduces the content of oxygen, which is in this case a harmful impurity).
It is known that common electron valves begin to function normally only after they heat up to 800° C. Every time a radio or TV set is switched on some time passes before there is any sound or sight. To remove this shortcoming Polish scientists have suggested that the cathodes should be coated with magnesium oxide. The new valves begin to work as soon as the TV or radio set is turned on.
The ability of magnesium (in the form of powder, wire or ribbon) to burn with a dazzling white flame is made a wide use of in military technology for the manufacture of signal and other flares, tracer bullets and shells and incendiary bombs. Until recently the magnesium flare was indispensable in photography. “One, two, three! Now!” and a magnesium powder flare would light up the faces of those who wished their images to go down to posterity. But not any more: powerful electric lamps have forced magnesium out of this job.
Not that it hurts magnesium in any way: it has many and much more important things to do. It takes part in the great work of storing solar energy. It is a component of chlorophyl, the great wizard which absorbs solar energy and turns carbon dioxide and water into complex organic substances (sugar, starch, etc.) essential for the nutrition of man and animals. The process of formation of organic substances — photosynthesis (from the Greek “photos” meaning “light”) “is accompanied by expiration of oxygen from the leaves. There would be no life without chlorophyl and there would be no chlorophyl without magnesium, for it makes up two per cent of it. Is this much? Judge for yourself. The total amount of magnesium in the chlorophyl of plants alone is something like 100000 million tons. Apart from the plants magnesium is present in the composition of practically all living organisms, human being included. For example, if one’s weight is 60 kilograms, about 25 grams of it is magnesium.
Several years ago researchers at the University of Minnesota in the USA found that the more magnesium an egg shell contained the stronger it was. This meant that by changing the feed of laying hens it would be possible to make the egg shell harder. The meaning of this discovery to agriculture is illustrated by the following figures: the annual loss due to breakage in Minnesota alone is over one million dollars.
Magnesium finds an extensive application in medicine. We have already mentioned Epsom salts (magnesium salt of sulphuric acid or magnesium sulphate) which is an effective laxative. Pure magnesium oxide ’roasted magnesium) is used to treat high gastric acidity, heartburn and acid poisoning. Magnesium peroxide is a well-known desinfecting agent used for gastric disorders.
According to statistics, spasms of the blood vessels are far less common in inhabitants of northerly regions. It is general knowledge that intravenous and intramuscular injections of certain solutions of magnesium salts ease spasms and convulsions. Some fruits and vegetables (particularly apricots, pears and cauliflower) are a good source of magnesium helping to store the necessary quantity of this element in the organism. In regions where the diet is richer in magnesium, say in Asia, atherosclerosis and other heart diseases are less common than in Europe or the United States.
In Hungary it has been established experimentally that a deficiency of magnesium in the organism enhances predisposition to myocardial infarctions. One group of dogs was given feed which was rich in magnesium salts and the other was kept on a magnesium-deficient ration. By the end of the experiment the second group had suffered myocardial infarctions.
The incidence of heart disorders is much higher among nervous, easily excitable persons. This is explained by the fact that at the moment of excitation the magnesium of the organism “bums up”.
In the opinion of French biologists, magnesium is to help medicine to fight fatigue, the scourge of our time. Their experiments have demonstrated that the blood of tired people contains less magnesium than that of people who are physically fit, and it is a fact that even the slightest deviation of the normal “magnesium curve” produces a harmful effect.
It was also established by French biologists not long ago that some elements influence the sex of progeny. It appears that an excess of potassium in the mother’s food results in her offspring being mostly male, but if her food is rich in calcium and magnesium her offspring will predominantly be female. Probably the time is not far off when physicians will be prescribing special menus for mothers to guarantee the birth of a boy or girl “on order”. But it will first have to be found if these elements have this effect on the human organism: the observation just described has so far applied to … cows.
Medicine is not the only field where magnesium compounds are in extensive use. For example, magnesium oxide is used in rubber industry and also in the production of cement and refractory brick. Recently a Canadian firm developed a process for manufacturing a new refractory material (newcon), stable to the effect of slags, characterized by great strength and low porosity. High-purity magnesium compound is the basic component of the new refractory. Magnesium peroxide is used for bleaching fabrics (novozon). Magnesium sulphate finds application in the textile and paper industries as a mordant in dyeing. The water solution of magnesium chloride is the basis for the production of magnesium cement, xylolith and other synthetic materials. Magnesium carbonate is used for the making of heat-insulating materials.
Organic chemistry is yet another vast field for the activities of magnesium. In powder form magnesium is used to dehydrate important organic substances, such as alcohol and aniline. A significant role belongs to organomagnesium compounds tin them the atom of magnesium is bonded directly to the atom of carbon). These substances, particularly alkylmagnesium halides (Grignard reagent), with halogens (chlorine, bromine or iodine) included in their composition, are widely used in synthetic chemistry. The importance of these compounds is proved by the fact that the French chemist Victor Grignard was awarded the 1912 Nobel Prize for the discovery of alkylmagnesium halides and for related work in developing the synthesis of organic compounds.
Thus it is clear that the role of magnesium in nature and in the national economy is vast Still it is probably too early to say that this element has accomplished everything that it could. For example, not long ago magnesium alloys, from which parts of the rock-sampling automatic drilling rig on board the Iuna-24 space probe were made, “visited” the Moon where they “took part” in the “mining” of lunar rock. The rig had to meet strict demands. First it had to be light: on a lengthy journey every excess kilogram of load means additional fuel expenditure; second, the parts absolutely had to be strong: no sense sending them on such an important trip, unless there was certainty that they would not let down at a crucial moment. And obviously the working moments on the Moon could well turn out really crucial.
The designers of the rock-sampling automatic drilling rig settled for the superlight and strong titanium and magnesium alloys. Before sending the drill on its space journey scientists subjected it to a severe test on earth, making it drill different kinds of rock, including very hard mountain rock. The test was first conducted under normal climatic conditions and then in a big pressure-chamber where deep vacuum was created or the temperature was raised or lowered to imitate lunar temperatures of up to plus 110° C in the daytime and minus 120° C at night. The tests were successful, as was the subsequent flight of the automatic station which brought lunar rock to earth.
Source: Tales About Metals, S. Venetsky