Top of the Metals

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Once the “top of the metals” is found, it is soon in a great boom in science and technology. After the most refractory metal tungsten discovered, the first incandescent light bulbs came out in 1910, becoming a landmark that human conquered the darkness. In 1947, when titanium metal with the highest specific strength (the ratio of the strength and weight) was refined more, the aircraft that flew twice or three times faster than the speed of sound soon appeared in the sky, then the spacecraft appeared to explore the mysteries of the universe. So, it is quite interesting to discuss these top metals and their superior characteristics.

The lightest metal—- lithium

Lithium is the lightest metal in nature, with volume only of 0.543g/cm3. It floats when is thrown into the water. If an aircraft is made of lithium, just two people can carry it away. Lithium is a silvery-white metal and chemically active, so it widely used in industrial production and daily life. Especially not long ago, lithium has been applied in the atomic energy industry. It is well-known that hydrogen bombs are powerful. However, the hydrogen of hydrogen bombs is the deuterium that is once heavier than ordinary hydrogen, or the tritium that is twice heavier than ordinary hydrogen. Lithium can produce not only tritium, but also lithium hydride, lithium deuteride and tritide lithium. On June 17, 1967, China successfully exploded the first hydrogen bomb, which was made of the lithium hydride and lithium deuteride. It is calculated that explosive force of 1kg of lithium deuteride equals to 50,000 tons of TNT.

The heaviest metal—- osmium

Osmium is the heaviest metal in nature. Existing in osmiridium, osmium is a gray-blue metal, hard and brittle, with the volume of 22.48g/cm3 and 41.35 times heavier than lithium in the same volume. Osmium-iridium alloy is very wearable, so it can make fountain pen’s nibs, but also watches or bearings of precious instruments.

The highest melting point metal—-tungsten

Tungsten is known for the highest melting point of 3,410°C, with the volume more than 19g/cm3 as well as high hardness. Surprisingly, the metal with high melting point and hardness has a rarely good plasticity, which means that 1kg of tungsten rod can be pulled into more than 300km of filaments. This filament still has some strength and high luminous efficiency as well as long service life at the temperature of 3,000°C, so it is excellent material to produce various bulb filaments. Tungsten is most used to make tungsten steel. The strength of tools made by tungsten steel is several times or dozens of times stronger than that of tools made by ordinary steel. The barrel with tungsten steel can still maintain good flexibility and mechanical strength during continuous shooting even if it is too hot with friction.

The lowest melting point and the softest solid metal—-cesium

Cesium melts when it is at the temperature of 28.5°C. It will soon melt into liquid on the hands. It is softer than paraffin, so can be freely cut into various shapes. As photoelectric effect is particularly good, and able to turn light signal into an electrical signal, it becomes a major photographic material for the production of photoelectric cells, film, television and fax.

The greatest special strength metal—-titanium

Titanium metal powder is an important additive for powder metallurgy and alloys. Tensile strength of many new-type titanium alloys is over 1,000kg/mm2. Titanium can withstand not only high temperatures above 500°C, but also low temperatures less than minus 100°C. Thus, titanium and titanium alloys are indispensable materials for the manufacture of aircrafts, rockets, missiles and submarines. For a supersonic long-range interceptor, titanium content accounts for 95% of its total weight. Currently, there is more than half of titanium used to make airframes and main parts of jet engines all around the world. So, titanium is known as “space metal”.

The hardest metal—- chromium

As the hardest metal in nature, chrome is silvery white and chemically stable, which almost does not rust in water and air. Its main purpose is to make alloys and refine stainless steel. The advent of stainless steel is considered as one of the greatest inventions in the 20th century, with epoch-making significance. It has promoted the development of medical treatment, instrument and defense industry, as well as food processing, textile printing and dyeing, tobacco production and liquor-making industry.

The strongest corrosion resistance metal—- niobium

Niobium’s surface will not rust in air for more than ten years. British chemist Hatchett firstly discovered niobium element in 1801. But pure niobium metal was obtained until 1929. Niobium has strong corrosion resistance, with snow-white luster and hard texture. A niobium is firstly put into hot concentrated nitric acid for two months, and then moved to the aqua regia which can melt gold and platinum for six days and nights, finally, the niobium has no change. In addition, it has been widely used to manufacture a variety of acid-resistant equipment in the chemical industry. As for niobium metal powder, an important application is used to produce capacitors.

The rarest metal—- rhenium

Rhenium is the world’s rarest metal. In 1925, two German scientists Noddack and Tucker found rhenium by X-ray in platinum ore for the first time. World production of rhenium is only 3g by the year of 1930, while only 10 tons currently. How rare it is! But why it is so rare? Because rhenium reserves is very few in the earth’s crust. Rhenium content in molybdenite is e tancehigh, but only for the ten thousandth. Although rhenium is rare, the role is huge. It is hard and silvery-white metal, melting point up to 3,180°C, with great specific gravity about twice than that of iron. It is not only chemically stable but also corrosion resistant to acid, alkali and salt. In the metallurgical industry, rhenium can improve performance and structure of alloys as an alloying additive. Generally, pure tungsten and pure molybdenum at a lower temperature will become as brittle as glass that they are difficult to process, so their applications are greatly restricted. But, adding the right amount of rhenium to make tungsten-molybdenum alloy or molybdenum-rhenium alloy, the alloys will have good plasticity so that they can be processed into a variety of structural materials, but also can maintain “three highs” —- high hardness, high strength and high temperature resistance at the same time. Many parts of the U.S. spacecraft are made of this kind of rhenium alloy. In addition, rhenium has high hardness and mechanical strength, high electrical resistance and other electrical properties. For example, a rhenium alloy wire thinner than hair can withstand 7kg of gravity; electrical contactors of general electrical equipments sometimes damage a few days and nights, while electrical contactors made by rhenium can be used several months or even several years; ordinary tungsten filament coated with rhenium can prolong the service life of 10 times.