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Introduction to Titanium
Date: 2015-12-31 09:19:35 Hits: 300In 1791 William Gregor the British reverend, mineralogist, and chemist discovered titanium. He examined the magnetic sand from the local river, Helford, in the Menachan Valley in Cornwall, England, and isolated “black sand”, now known as “ilmenite”. By removing the iron with a magnet and treating the sand with hydrochloric acid he produced the impure oxide of a new element. He named it “mechanite”, after the location. Four years later, the Berlin chemist Martin Heinrich Klaproth independently isolated titanium oxide from a Hungarian mineral, now known as “rutile”. Greek mythology provided him a new name from the children of Uranos and Gaia, the titans. The titans were utterly hated by their father and so detained in captivity by him in the earth’s crust, similar to the hard to extract ore – hence he named it Titanium.
It took more than 100 years before Matthew Albert Hunter from Rensselaer Polytechnic Institute in Troy, N.Y., was able to isolate the metal in 1910 by heating titanium tetrachloride (TiCl4) with sodium in a steel bomb. Finally, Wilhelm Justin Kroll from Luxembourg is recognized as father of the titanium industry. In 1932 he produced significant quantities of titanium by combining TiCl4 with calcium. At the beginning of World War II he fled to the United States. At the U.S. Bureau of Mines he demonstrated that titanium could be extracted commercially by reducing TiCl4 by changing the reducing agent from calcium to magnesium. Today this is still the most widely used method and is known as the “Kroll process”. After the Second World War, titanium-based alloys were soon considered key materials for aircraft engines. In 1948 the DuPont Company was the first to produce titanium commercially. Today aerospace is still the prime consumer of titanium and its alloys, but other markets such as architecture, chemical processing, medicine, power generation, marine and offshore, sports and leisure, and transportation are gaining increased acceptance.
Titanium is not actually a rare substance as it ranks as the ninth most plentiful element and the fourth most abundant structural metal in the Earth’s crust exceeded only by aluminum, iron, and magnesium. Unfortunately, it is seldom found in high concentrations and never found in a pure state. Thus, the difficulty in processing the metal makes it expensive. Even today it is produced only in a batch process, and no continuous process exists as for other structural metals. Titanium usually occurs in mineral sands containing ilmenite (FeTiO3), found in the Ilmen mountains of Russia, or rutile (TiO2), from the beach sands in Australia, India, and Mexico. Titanium dioxide is a very versatile white pigment used in paint, paper, and plastic, and consumes most of world production. Besides Russia, Australia, India, and Mexico, workable mineral deposits include sites in the United States, Canada, South Africa, Sierra Leone, Ukraine, Norway, and Malaysia. Of all the 112 chemical elements in the periodic system known today, about 85% are metals or metalloids. There are various ways to classify the metals, such as ferrous or nonferrous metals, ingot or sintered metals, light or heavy metals. Titanium is classified as a nonferrous and light metal.
The properties of metals are essentially based on the metallic bonding of the atoms in the crystal lattice. This means that the free, mobile valence electrons in the lattice result in classic “metallic” properties such as electrical conductivity, plastic deformation by atomic slip in crystal lattices, and alloying by incorporation of impurity atoms into the crystal lattice with the consequence of increased hardness and strength as well as reduced ductility.
Metals vary substantially in weight. At 0.5g/cm3 Lithium has the lowest density while Osmium and Iridium are the heaviest metals with a density of 22.5g/cm3. The separation point between light and heavy metals is 5g/cm3. Therefore, Titanium with a density of 4.51g/cm3 is the heaviest light metal. Although twice as heavy as the classic light metal – aluminum – it has only about half the specific weight of iron or nickel.
Titanium alloys primarily stand out due to two properties: high specific strength and excellent corrosion resistance. This also explains their preferential use in the aerospace sector, the chemical industry, medical engineering, and the leisure sector. Only at temperatures below 300 centigrade degree do carbon fiber reinforced plastics have a higher specific strength than titanium alloys. At higher temperatures the specific strength of titanium alloys is particularly attractive. However, the maximum application temperature is limited by their oxidation behavior. Since titanium aluminides partly overcome this disadvantage, they have become the subject of intense alloy development efforts. While conventional elevated temperature titanium alloys are used only up to temperatures slightly above 500 centigrade degree, TiAl-based alloys directly compete with well-established high temperature steels and Ni-base superalloys.
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