The chemical element titanium has the atomic number 22 and the symbol Ti. Titanium, a silver-coloured, low-density and high-strength transition metal, is resistant to corrosion in seawater, aqua regia, and chlorine, and can be formed by reduction of oxide, the only form found in nature.
William Gregor discovered titanium in 1791 in Cornwall, Great Britain. Martin Heinrich Klaproth named the metal after the Titans of Greek mythology. The element is found in almost all living organisms, as well as in bodies of water, rocks, and soil. It is mostly found in the minerals rutile and ilmenite, which are widely distributed in the Earth's crust and lithosphere.
The Kroll and Hunter procedures are used to separate the metal from the main mineral ores. The most common material, titanium dioxide, is a much-loved photocatalyst and is used in the manufacture of white pigments. Other substances include titanium trichloride (TiCl3), which is used as a catalyst in the production of polypropylene, and titanium tetrachloride (TiCl4), a component of smoke screens and catalysts.
Aerospace (jet engines, missiles and spacecraft), military, industrial processes (chemicals and petrochemicals, desalination plants, pulp and paper), automotive, agriculture (farming), medical prosthetics, orthopedic implants, dental and endodontic instruments and files, Titanium can be alloyed with iron, aluminum, vanadium and molybdenum, among other elements, for use in dental implants, sports equipment, jewelry, mobile phones and other applications.
The metal has two of its most valuable properties, corrosion resistance, and the highest strength-to-density ratio of any metallic element. Titanium is less dense than some steels, but just as strong in its unalloyed form. There are five naturally occurring isotopes of this element, between 46Ti and 50Ti, with 48Ti being the most common (73,8%). This element has two allotropic forms.
Physical Properties of Titanium
Titanium is a metal known for its high strength-to-weight ratio. It is a strong, lightweight metal that is metallic-white in color, highly ductile and shiny. It is valuable as a refractory metal due to its relatively high melting point (1,668 °C). It is paramagnetic compared to other metals and has relatively low electrical and thermal conductivity. Titanium becomes superconducting when cooled below its critical temperature of 0,49 K.
The final tensile strength of commercially pure (99,2% pure) titanium grades is approximately 434 MPa, comparable to the strength of ordinary, low-grade steel alloys, but less dense. Despite being 60% denser than aluminum, titanium is twice as strong as the most commonly used 6061-T6 aluminum alloy. The tensile strength of some titanium alloys, such as Beta C, can exceed 1.400 MPa. However, titanium weakens at temperatures exceeding 430 °C.
Titanium is non-magnetic, a poor conductor of heat and electricity, and is not as hard as some heat-treated steel grades. Machining requires safety precautions, as the material may be excreted in bile if sharp tools and correct cooling techniques are not used. Similar to steel structures, titanium structures have a fatigue limit that provides durability in certain applications.
The metal has a hexagonal form as a dimorphic allotrope and transforms into a body-centered cubic (lattice) form at 882 °C. When heated to this transition temperature, the specific heat of the form increases significantly, but then decreases rapidly and remains relatively constant for the form regardless of temperature.
Chemical Properties of Titanium
The surface of titanium metal and its alloys, like those of aluminum and magnesium, instantly oxidizes when exposed to air, forming a thin, non-porous passivation layer that protects the bulk metal from further oxidation or corrosion. This protective layer is initially only 1-2 nm thick, but gradually thickens over four years, reaching a thickness of 25 nm. This layer gives titanium an almost platinum-level corrosion resistance.
Most organic acids, chloride solutions, and diluted sulfuric and hydrochloric acids can all be used to attack titanium without damaging it. However, concentrated acids corrode titanium. Titanium is a highly reactive metal that burns in normal air at temperatures lower than its melting point, as evidenced by its negative redox potential. Only vacuum or an inert atmosphere can cause melting. It mixes with chlorine at 550°C. Besides absorbing hydrogen, it also interacts with other halogens.
Titanium combines readily with oxygen to form titanium dioxide at 1.200 °C in air and 610 °C in pure oxygen. Titanium, one of the few elements that burns in pure nitrogen gas, reacts at 800 °C to form titanium nitride, a brittle material. Titanium sublimation pumps are made from titanium evaporated from filaments due to its high reactivity with oxygen, nitrogen and many other gases. Titanium bonds chemically to these gases, acting as a scavenger for these gases. In ultra-high vacuum systems, such pumps create incredibly low pressures at low cost.
Günceleme: 04/02/2023 16:40
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