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Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine.
Titanium was discovered in Cornwall, Great Britain, by William Gregor in and was named by Martin Heinrich Klaproth after the Titans of Greek mythology. The element occurs within a number of minerals, principally rutile and ilmenite, which are widely distributed in the Earth's crust and lithosphere; it is found in almost all living things, as well as bodies of water, rocks, and soils.[9] The metal is extracted from its principal mineral ores by the Kroll and Hunter processes.[10] The most common compound, titanium dioxide, is a popular photocatalyst and is used in the manufacture of white pigments.[11] Other compounds include titanium tetrachloride (TiCl4), a component of smoke screens and catalysts; and titanium trichloride (TiCl3), which is used as a catalyst in the production of polypropylene.[9]
Titanium can be alloyed with iron, aluminium, vanadium, and molybdenum, among other elements. The resulting titanium alloys are strong, lightweight, and versatile, with applications including aerospace (jet engines, missiles, and spacecraft), military, industrial processes (chemicals and petrochemicals, desalination plants, pulp, and paper), automotive, agriculture (farming), sporting goods, jewelry, and consumer electronics.[9] Titanium is also considered one of the most biocompatible metals, leading to a range of medical applications including prostheses, orthopedic implants, dental implants, and surgical instruments.[12]
The two most useful properties of the metal are corrosion resistance and strength-to-density ratio, the highest of any metallic element.[13] In its unalloyed condition, titanium is as strong as some steels, but less dense.[14] There are two allotropic forms[15] and five naturally occurring isotopes of this element, 46Ti through 50Ti, with 48Ti being the most abundant (73.8%).[16]
Characteristics
Physical properties
As a metal, titanium is recognized for its high strength-to-weight ratio.[15] It is a strong metal with low density that is quite ductile (especially in an oxygen-free environment),[9] lustrous, and metallic-white in color.[17] Due to its relatively high melting point (1,668 °C or 3,034 °F) it has sometimes been described as a refractory metal, but this is not the case.[18] It is paramagnetic and has fairly low electrical and thermal conductivity compared to other metals.[9] Titanium is superconducting when cooled below its critical temperature of 0.49 K.[19][20]
Commercially pure (99.2% pure) grades of titanium have ultimate tensile strength of about 434 MPa (63,000 psi), equal to that of common, low-grade steel alloys, but are less dense. Titanium is 60% denser than aluminium, but more than twice as strong[14] as the most commonly used -T6 aluminium alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of over 1,400 MPa (200,000 psi).[21] However, titanium loses strength when heated above 430 °C (806 °F).[22]
Titanium is not as hard as some grades of heat-treated steel; it is non-magnetic and a poor conductor of heat and electricity. Machining requires precautions, because the material can gall unless sharp tools and proper cooling methods are used. Like steel structures, those made from titanium have a fatigue limit that guarantees longevity in some applications.[17]
The metal is a dimorphic allotrope of an hexagonal α form that changes into a body-centered cubic (lattice) β form at 882 °C (1,620 °F).[22] The specific heat of the α form increases dramatically as it is heated to this transition temperature but then falls and remains fairly constant for the β form regardless of temperature.[22]
Chemical properties
Pourbaix diagram for titanium in pure water, perchloric acid, or sodium hydroxide[23]Like aluminium and magnesium, the surface of titanium metal and its alloys oxidize immediately upon exposure to air to form a thin non-porous passivation layer that protects the bulk metal from further oxidation or corrosion.[9] When it first forms, this protective layer is only 1&#;2 nm thick but it continues to grow slowly, reaching a thickness of 25 nm in four years.[24] This layer gives titanium excellent resistance to corrosion against oxidizing acids, but it will dissolve in dilute hydrofluoric acid, hot hydrochloric acid, and hot sulfuric acid.
Titanium is capable of withstanding attack by dilute sulfuric and hydrochloric acids at room temperature, chloride solutions, and most organic acids.[10] However, titanium is corroded by concentrated acids.[25] Titanium is a very reactive metal that burns in normal air at lower temperatures than the melting point. Melting is possible only in an inert atmosphere or vacuum. At 550 °C (1,022 °F), it combines with chlorine.[10] It also reacts with the other halogens and absorbs hydrogen.[11]
Titanium readily reacts with oxygen at 1,200 °C (2,190 °F) in air, and at 610 °C (1,130 °F) in pure oxygen, forming titanium dioxide.[15] Titanium is one of the few elements that burns in pure nitrogen gas, reacting at 800 °C (1,470 °F) to form titanium nitride, which causes embrittlement.[26] Because of its high reactivity with oxygen, nitrogen, and many other gases, titanium that is evaporated from filaments is the basis for titanium sublimation pumps, in which titanium serves as a scavenger for these gases by chemically binding to them. Such pumps inexpensively produce extremely low pressures in ultra-high vacuum systems.
Occurrence
Titanium is the ninth-most abundant element in Earth's crust (0.63% by mass)[27] and the seventh-most abundant metal. It is present as oxides in most igneous rocks, in sediments derived from them, in living things, and natural bodies of water.[9][10] Of the 801 types of igneous rocks analyzed by the United States Geological Survey, 784 contained titanium. Its proportion in soils is approximately 0.5&#;1.5%.[27]
Common titanium-containing minerals are anatase, brookite, ilmenite, perovskite, rutile, and titanite (sphene).[24] Akaogiite is an extremely rare mineral consisting of titanium dioxide. Of these minerals, only rutile and ilmenite have economic importance, yet even they are difficult to find in high concentrations. About 6.0 and 0.7 million tonnes of those minerals were mined in , respectively.[28] Significant titanium-bearing ilmenite deposits exist in Australia, Canada, China, India, Mozambique, New Zealand, Norway, Sierra Leone, South Africa, and Ukraine.[24] About 210,000 tonnes of titanium metal sponge were produced in , mostly in China (110,000 t), Japan (50,000 t), Russia (33,000 t) and Kazakhstan (15,000 t). Total reserves of anatase, ilmenite, and rutile are estimated to exceed 2 billion tonnes.[28]
production of titanium minerals and slag[28] Country thousandThe concentration of titanium is about 4 picomolar in the ocean. At 100 °C, the concentration of titanium in water is estimated to be less than 10&#;7 M at pH 7. The identity of titanium species in aqueous solution remains unknown because of its low solubility and the lack of sensitive spectroscopic methods, although only the 4+ oxidation state is stable in air. No evidence exists for a biological role, although rare organisms are known to accumulate high concentrations of titanium.[29]
Titanium is contained in meteorites, and it has been detected in the Sun and in M-type stars[10] (the coolest type) with a surface temperature of 3,200 °C (5,790 °F).[30] Rocks brought back from the Moon during the Apollo 17 mission are composed of 12.1% TiO2.[10] Native titanium (pure metallic) is very rare.[31]
Isotopes
Naturally occurring titanium is composed of five stable isotopes: 46Ti, 47Ti, 48Ti, 49Ti, and 50Ti, with 48Ti being the most abundant (73.8% natural abundance). At least 21 radioisotopes have been characterized, the most stable of which are 44Ti with a half-life of 63 years; 45Ti, 184.8 minutes; 51Ti, 5.76 minutes; and 52Ti, 1.7 minutes. All other radioactive isotopes have half-lives less than 33 seconds, with the majority less than half a second.[16]
The isotopes of titanium range in atomic weight from 39.002 u (39Ti) to 63.999 u (64Ti).[32] The primary decay mode for isotopes lighter than 46Ti is positron emission (with the exception of 44Ti which undergoes electron capture), leading to isotopes of scandium, and the primary mode for isotopes heavier than 50Ti is beta emission, leading to isotopes of vanadium.[16]
Titanium becomes radioactive upon bombardment with deuterons, emitting mainly positrons and hard gamma rays.[10]
Compounds
The +4 oxidation state dominates titanium chemistry,[33] but compounds in the +3 oxidation state are also numerous.[34] Commonly, titanium adopts an octahedral coordination geometry in its complexes,[35][36] but tetrahedral TiCl4 is a notable exception. Because of its high oxidation state, titanium(IV) compounds exhibit a high degree of covalent bonding.[33]
Oxides, sulfides, and alkoxides
The most important oxide is TiO2, which exists in three important polymorphs; anatase, brookite, and rutile. All three are white diamagnetic solids, although mineral samples can appear dark (see rutile). They adopt polymeric structures in which Ti is surrounded by six oxide ligands that link to other Ti centers.[37]
The term titanates usually refers to titanium(IV) compounds, as represented by barium titanate (BaTiO3). With a perovskite structure, this material exhibits piezoelectric properties and is used as a transducer in the interconversion of sound and electricity.[15] Many minerals are titanates, such as ilmenite (FeTiO3). Star sapphires and rubies get their asterism (star-forming shine) from the presence of titanium dioxide impurities.[24]
A variety of reduced oxides (suboxides) of titanium are known, mainly reduced stoichiometries of titanium dioxide obtained by atmospheric plasma spraying. Ti3O5, described as a Ti(IV)-Ti(III) species, is a purple semiconductor produced by reduction of TiO2 with hydrogen at high temperatures,[38] and is used industrially when surfaces need to be vapor-coated with titanium dioxide: it evaporates as pure TiO, whereas TiO2 evaporates as a mixture of oxides and deposits coatings with variable refractive index.[39] Also known is Ti2O3, with the corundum structure, and TiO, with the rock salt structure, although often nonstoichiometric.
The alkoxides of titanium(IV), prepared by treating TiCl4 with alcohols, are colorless compounds that convert to the dioxide on reaction with water. They are industrially useful for depositing solid TiO2 via the sol-gel process. Titanium isopropoxide is used in the synthesis of chiral organic compounds via the Sharpless epoxidation.[41]
Titanium forms a variety of sulfides, but only TiS2 has attracted significant interest. It adopts a layered structure and was used as a cathode in the development of lithium batteries. Because Ti(IV) is a "hard cation", the sulfides of titanium are unstable and tend to hydrolyze to the oxide with release of hydrogen sulfide.[42]
Nitrides and carbides
Titanium nitride (TiN) is a refractory solid exhibiting extreme hardness, thermal/electrical conductivity, and a high melting point.[43] TiN has a hardness equivalent to sapphire and carborundum (9.0 on the Mohs scale),[44] and is often used to coat cutting tools, such as drill bits.[45] It is also used as a gold-colored decorative finish and as a barrier layer in semiconductor fabrication.[46] Titanium carbide (TiC), which is also very hard, is found in cutting tools and coatings.[47]
Halides
Titanium(III) compounds are characteristically violet, illustrated by this aqueous solution of titanium trichloride.Titanium tetrachloride (titanium(IV) chloride, TiCl4[48]) is a colorless volatile liquid (commercial samples are yellowish) that, in air, hydrolyzes with spectacular emission of white clouds. Via the Kroll process, TiCl4 is used in the conversion of titanium ores to titanium metal. Titanium tetrachloride is also used to make titanium dioxide, e.g., for use in white paint.[49] It is widely used in organic chemistry as a Lewis acid, for example in the Mukaiyama aldol condensation.[50] In the van Arkel&#;de Boer process, titanium tetraiodide (TiI4) is generated in the production of high purity titanium metal.[51]
Titanium(III) and titanium(II) also form stable chlorides. A notable example is titanium(III) chloride (TiCl3), which is used as a catalyst for production of polyolefins (see Ziegler&#;Natta catalyst) and a reducing agent in organic chemistry.[52]
Organometallic complexes
Owing to the important role of titanium compounds as polymerization catalyst, compounds with Ti-C bonds have been intensively studied. The most common organotitanium complex is titanocene dichloride ((C5H5)2TiCl2). Related compounds include Tebbe's reagent and Petasis reagent. Titanium forms carbonyl complexes, e.g. (C5H5)2Ti(CO)2.[53]
Anticancer therapy studies
Following the success of platinum-based chemotherapy, titanium(IV) complexes were among the first non-platinum compounds to be tested for cancer treatment. The advantage of titanium compounds lies in their high efficacy and low toxicity in vivo.[54] In biological environments, hydrolysis leads to the safe and inert titanium dioxide. Despite these advantages the first candidate compounds failed clinical trials due to insufficient efficacy to toxicity ratios and formulation complications.[54] Further development resulted in the creation of potentially effective, selective, and stable titanium-based drugs.[54]
History
Titanium was discovered in by the clergyman and geologist William Gregor as an inclusion of a mineral in Cornwall, Great Britain.[55] Gregor recognized the presence of a new element in ilmenite[11] when he found black sand by a stream and noticed the sand was attracted by a magnet.[55] Analyzing the sand, he determined the presence of two metal oxides: iron oxide (explaining the attraction to the magnet) and 45.25% of a white metallic oxide he could not identify.[27] Realizing that the unidentified oxide contained a metal that did not match any known element, in Gregor reported his findings in both German and French science journals: Crell's Annalen and Observations et Mémoires sur la Physique.[55][56][57] He named this oxide manaccanite.[58]
Around the same time, Franz-Joseph Müller von Reichenstein produced a similar substance, but could not identify it.[11] The oxide was independently rediscovered in by Prussian chemist Martin Heinrich Klaproth in rutile from Boinik (the German name of Bajmócska), a village in Hungary (now Bojničky in Slovakia).[55][b] Klaproth found that it contained a new element and named it for the Titans of Greek mythology.[30] After hearing about Gregor's earlier discovery, he obtained a sample of manaccanite and confirmed that it contained titanium.[60]
The currently known processes for extracting titanium from its various ores are laborious and costly; it is not possible to reduce the ore by heating with carbon (as in iron smelting) because titanium combines with the carbon to produce titanium carbide.[55] Pure metallic titanium (99.9%) was first prepared in by Matthew A. Hunter at Rensselaer Polytechnic Institute by heating TiCl4 with sodium at 700&#;800 °C (1,292&#;1,472 °F) under great pressure[61] in a batch process known as the Hunter process.[10] Titanium metal was not used outside the laboratory until when William Justin Kroll produced it by reducing titanium tetrachloride (TiCl4) with calcium.[62] Eight years later he refined this process with magnesium and with sodium in what became known as the Kroll process.[62] Although research continues to seek cheaper and more efficient routes, such as the FFC Cambridge process, the Kroll process is still predominantly used for commercial production.[10][11]
Titanium "sponge", made by the Kroll processTitanium of very high purity was made in small quantities when Anton Eduard van Arkel and Jan Hendrik de Boer discovered the iodide process in , by reacting with iodine and decomposing the formed vapors over a hot filament to pure metal.[63]
In the s and s, the Soviet Union pioneered the use of titanium in military and submarine applications[61] (Alfa class and Mike class)[64] as part of programs related to the Cold War.[65] Starting in the early s, titanium came into use extensively in military aviation, particularly in high-performance jets, starting with aircraft such as the F-100 Super Sabre and Lockheed A-12 and SR-71.[66]
Throughout the Cold War period, titanium was considered a strategic material by the U.S. government, and a large stockpile of titanium sponge (a porous form of the pure metal) was maintained by the Defense National Stockpile Center, until the stockpile was dispersed in the s.[67] As of , the four leading producers of titanium sponge were China (52%), Japan (24%), Russia (16%) and Kazakhstan (7%).[28]
Production
Titanium (mineral concentrate) Basic titanium products: plate, tube, rods, and powderEconomic processes
The processing of titanium metal occurs in four major steps: reduction of titanium ore into "sponge", a porous form; melting of sponge, or sponge plus a master alloy to form an ingot; primary fabrication, where an ingot is converted into general mill products such as billet, bar, plate, sheet, strip, and tube; and secondary fabrication of finished shapes from mill products.[68]
Because it cannot be readily produced by reduction of titanium dioxide,[17] titanium metal is obtained by reduction of TiCl4 with magnesium metal in the Kroll process. The complexity of this batch production in the Kroll process explains the relatively high market value of titanium,[69] despite the Kroll process being less expensive than the Hunter process.[61] To produce the TiCl4 required by the Kroll process, the dioxide is subjected to carbothermic reduction in the presence of chlorine. In this process, the chlorine gas is passed over a red-hot mixture of rutile or ilmenite in the presence of carbon. After extensive purification by fractional distillation, the TiCl4 is reduced with 800 °C (1,470 °F) molten magnesium in an argon atmosphere.[15] Titanium metal can be further purified by the van Arkel&#;de Boer process, which involves thermal decomposition of titanium tetraiodide.
2 FeTiO 3 + 7 Cl 2 + 6 C &#; 900 o C 2 FeCl 3 + 2 TiCl 4 + 6 CO {\displaystyle {\ce {2FeTiO3 + 7Cl2 + 6C ->[900^oC] 2FeCl3 + 2TiCl4 + 6CO}}}
TiCl 4 + 2 Mg &#; o C Ti + 2 MgCl 2 {\displaystyle {\ce {TiCl4 + 2Mg ->[^oC] Ti + 2MgCl2}}}
Common titanium alloys are made by reduction. For example, cuprotitanium (rutile with copper added is reduced), ferrocarbon titanium (ilmenite reduced with coke in an electric furnace), and manganotitanium (rutile with manganese or manganese oxides) are reduced.[70]
About fifty grades of titanium alloys are designed and currently used, although only a couple of dozen are readily available commercially.[71] The ASTM International recognizes 31 grades of titanium metal and alloys, of which grades one through four are commercially pure (unalloyed). Those four vary in tensile strength as a function of oxygen content, with grade 1 being the most ductile (lowest tensile strength with an oxygen content of 0.18%), and grade 4 the least ductile (highest tensile strength with an oxygen content of 0.40%).[24] The remaining grades are alloys, each designed for specific properties of ductility, strength, hardness, electrical resistivity, creep resistance, specific corrosion resistance, and combinations thereof.[72]
In addition to the ASTM specifications, titanium alloys are also produced to meet aerospace and military specifications (SAE-AMS, MIL-T), ISO standards, and country-specific specifications, as well as proprietary end-user specifications for aerospace, military, medical, and industrial applications.[73]
Titanium powder is manufactured using a flow production process known as the Armstrong process[74] that is similar to the batch production Hunter process. A stream of titanium tetrachloride gas is added to a stream of molten sodium; the products (sodium chloride salt and titanium particles) is filtered from the extra sodium. Titanium is then separated from the salt by water washing. Both sodium and chlorine are recycled to produce and process more titanium tetrachloride.[75]
Pilot plants
Methods for electrolytic production of Ti metal from TiO2 using molten salt electrolytes have been researched and tested at laboratory and small pilot plant scales. The lead author of an impartial review published in considered his own process "ready for scaling up."[76] A review "discusses the electrochemical principles involved in the recovery of metals from aqueous solutions and fused salt electrolytes", with particular attention paid to titanium. While some metals can be refined by electrowinning at room temperature, "there is a strong chance of attack of the refractory lining by molten titanium."[77] Zhang et al concluded their Perspective on Thermochemical and Electrochemical Processes for Titanium Metal Production in that "Even though there are strong interests in the industry for finding a better method to produce Ti metal, and a large number of new concepts and improvements have been investigated at the laboratory or even at pilot plant scales, there is no new process to date that can replace the Kroll process commercially."[78]
Fabrication
Market price of TitaniumAll welding of titanium must be done in an inert atmosphere of argon or helium to shield it from contamination with atmospheric gases (oxygen, nitrogen, and hydrogen).[22] Contamination causes a variety of conditions, such as embrittlement, which reduce the integrity of the assembly welds and lead to joint failure.[79]
Titanium is very difficult to solder directly, and hence a solderable metal or alloy such as steel is coated on titanium prior to soldering.[80] Titanium metal can be machined with the same equipment and the same processes as stainless steel.[22]
Forming and forging
Commercially pure flat product (sheet, plate) can be formed readily, but processing must take into account of the tendency of the metal to springback. This is especially true of certain high-strength alloys.[81][82] Exposure to the oxygen in air at the elevated temperatures used in forging results in formation of a brittle oxygen-rich metallic surface layer called "alpha case" that worsens the fatigue properties, so it must be removed by milling, etching, or electrochemical treatment.[83]
Applications
A titanium cylinder of quality "grade 2"Titanium is used in steel as an alloying element (ferro-titanium) to reduce grain size and as a deoxidizer, and in stainless steel to reduce carbon content.[9] Titanium is often alloyed with aluminium (to refine grain size), vanadium, copper (to harden), iron, manganese, molybdenum, and other metals.[84] Titanium mill products (sheet, plate, bar, wire, forgings, castings) find application in industrial, aerospace, recreational, and emerging markets. Powdered titanium is used in pyrotechnics as a source of bright-burning particles.[85]
Pigments, additives, and coatings
Titanium dioxide is the most commonly used compound of titanium.About 95% of all titanium ore is destined for refinement into titanium dioxide (TiO
2), an intensely white permanent pigment used in paints, paper, toothpaste, and plastics.[28] It is also used in cement, in gemstones, and as an optical opacifier in paper.[86]
TiO
2 pigment is chemically inert, resists fading in sunlight, and is very opaque: it imparts a pure and brilliant white color to the brown or grey chemicals that form the majority of household plastics.[11] In nature, this compound is found in the minerals anatase, brookite, and rutile.[9] Paint made with titanium dioxide does well in severe temperatures and marine environments.[11] Pure titanium dioxide has a very high index of refraction and an optical dispersion higher than diamond.[10] Titanium dioxide is used in sunscreens because it reflects and absorbs UV light.[17]
Aerospace and marine
Lockheed A-12, first plane made of 93% titaniumBecause titanium alloys have high tensile strength to density ratio,[15] high corrosion resistance,[10] fatigue resistance, high crack resistance,[87] and ability to withstand moderately high temperatures without creeping, they are used in aircraft, armor plating, naval ships, spacecraft, and missiles.[10][11] For these applications, titanium is alloyed with aluminium, zirconium, nickel,[88] vanadium, and other elements to manufacture a variety of components including critical structural parts, landing gear, firewalls, exhaust ducts (helicopters), and hydraulic systems. In fact, about two thirds of all titanium metal produced is used in aircraft engines and frames.[89] The titanium 6AL-4V alloy accounts for almost 50% of all alloys used in aircraft applications.[90]
The Lockheed A-12 and the SR-71 "Blackbird" were two of the first aircraft frames where titanium was used, paving the way for much wider use in modern military and commercial aircraft. A large amount of titanium mill products are used in the production of many aircraft, such as (following values are amount of raw mill products used, only a fraction of this ends up in the finished aircraft): 116 metric tons are used in the Boeing 787, 77 in the Airbus A380, 59 in the Boeing 777, 45 in the Boeing 747, 32 in the Airbus A340, 18 in the Boeing 737, 18 in the Airbus A330, and 12 in the Airbus A320.[91] In aero engine applications, titanium is used for rotors, compressor blades, hydraulic system components, and nacelles.[92][93] An early use in jet engines was for the Orenda Iroquois in the s.[better source needed][94]
Because titanium is resistant to corrosion by sea water, it is used to make propeller shafts, rigging, heat exchangers in desalination plants,[10] heater-chillers for salt water aquariums, fishing line and leader, and divers' knives. Titanium is used in the housings and components of ocean-deployed surveillance and monitoring devices for science and military. The former Soviet Union developed techniques for making submarines with hulls of titanium alloys,[95] forging titanium in huge vacuum tubes.[88]
Industrial
Welded titanium pipe and process equipment (heat exchangers, tanks, process vessels, valves) are used in the chemical and petrochemical industries primarily for corrosion resistance. Specific alloys are used in oil and gas downhole applications and nickel hydrometallurgy for their high strength (e. g.: titanium beta C alloy), corrosion resistance, or both. The pulp and paper industry uses titanium in process equipment exposed to corrosive media, such as sodium hypochlorite or wet chlorine gas (in the bleachery).[96] Other applications include ultrasonic welding, wave soldering,[97] and sputtering targets.[98]
Titanium tetrachloride (TiCl4), a colorless liquid, is important as an intermediate in the process of making TiO2 and is also used to produce the Ziegler&#;Natta catalyst. Titanium tetrachloride is also used to iridize glass and, because it fumes strongly in moist air, it is used to make smoke screens.[17]
Consumer and architectural
Tweeter loudspeaker driver with a membrane with 25 mm diameter made from titanium; from a JBL TI loudspeaker box, c.&#;
Titanium metal is used in automotive applications, particularly in automobile and motorcycle racing where low weight and high strength and rigidity are critical.[99](p&#;141) The metal is generally too expensive for the general consumer market, though some late model Corvettes have been manufactured with titanium exhausts,[100] and a Corvette Z06's LT4 supercharged engine uses lightweight, solid titanium intake valves for greater strength and resistance to heat.[101]
Titanium is used in many sporting goods: tennis rackets, golf clubs, lacrosse stick shafts; cricket, hockey, lacrosse, and football helmet grills, and bicycle frames and components. Although not a mainstream material for bicycle production, titanium bikes have been used by racing teams and adventure cyclists.[102]
Titanium alloys are used in spectacle frames that are rather expensive but highly durable, long lasting, light weight, and cause no skin allergies. Titanium is a common material for backpacking cookware and eating utensils. Though more expensive than traditional steel or aluminium alternatives, titanium products can be significantly lighter without compromising strength. Titanium horseshoes are preferred to steel by farriers because they are lighter and more durable.[103]
Titanium has occasionally been used in architecture. The 42.5 m (139 ft) Monument to Yuri Gagarin, the first man to travel in space (), as well as the 110 m (360 ft) Monument to the Conquerors of Space on top of the Cosmonaut Museum in Moscow are made of titanium for the metal's attractive color and association with rocketry.[104][105] The Guggenheim Museum Bilbao and the Cerritos Millennium Library were the first buildings in Europe and North America, respectively, to be sheathed in titanium panels.[89] Titanium sheathing was used in the Frederic C. Hamilton Building in Denver, Colorado.[106]
Because of titanium's superior strength and light weight relative to other metals (steel, stainless steel, and aluminium), and because of recent advances in metalworking techniques, its use has become more widespread in the manufacture of firearms. Primary uses include pistol frames and revolver cylinders. For the same reasons, it is used in the body of some laptop computers (for example, in Apple's PowerBook G4).[107][108]
In , Apple launched the iPhone 15 Pro, which uses a titanium enclosure.[109]
Some upmarket lightweight and corrosion-resistant tools, such as shovels, knife handles and flashlights, are made of titanium or titanium alloys.[108]
Jewelry
Relation between voltage and color for anodized titaniumBecause of its durability, titanium has become more popular for designer jewelry (particularly, titanium rings).[103] Its inertness makes it a good choice for those with allergies or those who will be wearing the jewelry in environments such as swimming pools. Titanium is also alloyed with gold to produce an alloy that can be marketed as 24-karat gold because the 1% of alloyed Ti is insufficient to require a lesser mark. The resulting alloy is roughly the hardness of 14-karat gold and is more durable than pure 24-karat gold.[110]
Titanium's durability, light weight, and dent and corrosion resistance make it useful for watch cases.[103] Some artists work with titanium to produce sculptures, decorative objects and furniture.[111]
Titanium may be anodized to vary the thickness of the surface oxide layer, causing optical interference fringes and a variety of bright colors.[112] With this coloration and chemical inertness, titanium is a popular metal for body piercing.[113]
Titanium has a minor use in dedicated non-circulating coins and medals. In , Gibraltar released the world's first titanium coin for the millennium celebration.[114] The Gold Coast Titans, an Australian rugby league team, award a medal of pure titanium to their player of the year.[115]
Medical
Because titanium is biocompatible (non-toxic and not rejected by the body), it has many medical uses, including surgical implements and implants, such as hip balls and sockets (joint replacement) and dental implants that can stay in place for up to 20 years.[55] The titanium is often alloyed with about 4% aluminium or 6% Al and 4% vanadium.[116]
Medical screws and plate used to repair wrist fractures. Scale is in centimeters.Titanium has the inherent ability to osseointegrate, enabling use in dental implants that can last for over 30 years. This property is also useful for orthopedic implant applications.[55] These benefit from titanium's lower modulus of elasticity (Young's modulus) to more closely match that of the bone that such devices are intended to repair. As a result, skeletal loads are more evenly shared between bone and implant, leading to a lower incidence of bone degradation due to stress shielding and periprosthetic bone fractures, which occur at the boundaries of orthopedic implants. However, titanium alloys' stiffness is still more than twice that of bone, so adjacent bone bears a greatly reduced load and may deteriorate.[117][118]
Because titanium is non-ferromagnetic, patients with titanium implants can be safely examined with magnetic resonance imaging (convenient for long-term implants). Preparing titanium for implantation in the body involves subjecting it to a high-temperature plasma arc which removes the surface atoms, exposing fresh titanium that is instantly oxidized.[55]
Modern advancements in additive manufacturing techniques have increased potential for titanium use in orthopedic implant applications.[119] Complex implant scaffold designs can be 3D-printed using titanium alloys, which allows for more patient-specific applications and increased implant osseointegration.[120]
Titanium is used for the surgical instruments used in image-guided surgery, as well as wheelchairs, crutches, and any other products where high strength and low weight are desirable.[121]
Titanium dioxide nanoparticles are widely used in electronics and the delivery of pharmaceuticals and cosmetics.[122]
Nuclear waste storage
Because of its corrosion resistance, containers made of titanium have been studied for the long-term storage of nuclear waste. Containers lasting more than 100,000 years are thought possible with manufacturing conditions that minimize material defects.[123] A titanium "drip shield" could also be installed over containers of other types to enhance their longevity.[124]
Precautions
GIANT ANODE supply professional and honest service.
Titanium is non-toxic even in large doses and does not play any natural role inside the human body.[30] An estimated quantity of 0.8 milligrams of titanium is ingested by humans each day, but most passes through without being absorbed in the tissues.[30] It does, however, sometimes bio-accumulate in tissues that contain silica. One study indicates a possible connection between titanium and yellow nail syndrome.[125]
As a powder or in the form of metal shavings, titanium metal poses a significant fire hazard and, when heated in air, an explosion hazard.[126] Water and carbon dioxide are ineffective for extinguishing a titanium fire; Class D dry powder agents must be used instead.[11]
When used in the production or handling of chlorine, titanium should not be exposed to dry chlorine gas because it may result in a titanium&#;chlorine fire.[127]
Titanium can catch fire when a fresh, non-oxidized surface comes in contact with liquid oxygen.[128]
Function in plants
Nettles contain up to 80 parts per million of titanium.[30]An unknown mechanism in plants may use titanium to stimulate the production of carbohydrates and encourage growth. This may explain why most plants contain about 1 part per million (ppm) of titanium, food plants have about 2 ppm, and horsetail and nettle contain up to 80 ppm.[30]
See also
×
10&#;6/K, αc = 10.06×
10&#;6/K, and αaverage = αV/3 = 9.68×
10&#;6/K.The thermal expansion is anisotropic : the coefficients for each crystal axis are (at 20 °C): α/K, α/K, and α= α/3 =/K.
(p&#;244)
[By virtue of this I will derive the name for the present metallic substance &#; as happened similarly in the case of uranium &#; from mythology, namely from the first sons of the Earth, the Titans, and thus [I] name this new species of metal: "titanium"; ... ]
References
Bibliography
The earth contains a lot of titanium - it&#;s the ninth most abundant element in the earth&#;s crust. By mass, there&#;s more titanium in the earth&#;s crust than carbon by a factor of nearly 30, and more titanium than copper by a factor of nearly 100.
But despite its abundance, it's only recently that civilization has been able to use titanium as a metal (titanium dioxide has been in use somewhat longer as a paint pigment). Because titanium so readily bonds with oxygen and other elements, it doesn&#;t occur at all in metallic form in nature. One engineer described titanium as a &#;streetwalker," because it will pick up anything and everything. While copper has been used by civilization since BC, and iron since around BC, titanium wasn&#;t discovered until the late s, and wasn&#;t produced in metallic form until the late 19th century. As late as , there was no commercial production of titanium, and the metal only existed in tiny amounts in labs. But less than 10 years later, thousands of tons of it were being made a year. And 10 years after that, it formed the literal backbone of the most advanced aerospace technology on the planet.
As a report to the National Research Council notes, &#;the birth of a tonnage structural metal industry is an unusual event. Only three such births have occurred in the past 100 years [now closer to 150] &#; aluminum, magnesium, and titanium &#; and no new one is in prospect.&#; How did titanium go from totally unused to a critical aerospace technology? What does it tell us about technological development? Let&#;s take a look.
Titanium was first discovered in by William Gregor, an English clergyman and chemist who realized he couldn&#;t identify a metal contained in a white oxide mixed in with the black sands of Cornwall. In , Martin Klaproth, a Prussian chemist, was able to extract titanium from the mineral rutile. Because of the strong bond it formed with oxygen, Klaproth named the metal &#;titanium&#; after the Greek Titans.
Because titanium bonds so readily with other elements and contaminates so easily, it's extremely difficult to obtain in a pure state, and for the next hundred years titanium was mostly regarded as a laboratory curiosity. In the s, two Swedish scientists successfully produced 94% pure titanium metal, and in Matthew Hunter, a scientist at General Electric, developed a variant of their process to produce metallic titanium while searching for a material for improved lightbulb filaments.
But a commercially viable process for producing titanium wasn&#;t developed until the s. In William Kroll, a scientist from Luxembourg, began experimenting with titanium in his home lab, and developed a process to produce titanium by reacting titanium chloride (TiCl4) with magnesium under a vacuum. By , he had successfully produced 50 pounds of titanium metal, and successfully formed it into wires, rods, sheets, and plating. Kroll came to the US in to attempt to sell his process, but was unsuccessful.
Kroll&#;s samples of titanium metal in , via KrollThat same year, the US Bureau of Mines began to investigate titanium, in response to promising studies of its properties performed by the Philips Corporation (which had developed its own process for producing titanium). The Bureau of Mines concluded the Kroll process had the most potential as a commercial process and began to develop it. Its work was delayed by the war, but as early as the Bureau of Mines was making 15-pound batches of titanium in a plant that could make 100 pounds of titanium a week.
After the war, the Bureau&#;s work on titanium accelerated. By it had successfully scaled up Kroll&#;s process, and had produced two tons of titanium &#;sponge,&#; a porous, spongy metal created by the process, which is melted down to produce bars, sheets, wires, etc. A report on titanium&#;s properties commissioned by the Bureau concluded that titanium and its alloys had great potential engineering applications. Titanium was nearly as strong as stainless steel, but weighed 40% less. It was also incredibly corrosion-resistant, and maintained much more strength at elevated temperatures compared to aluminum. This made it potentially very useful for aerospace applications, where weight was at a premium and materials were often exposed to high temperatures.
The military had followed the progress of the Bureau&#;s development work, and interest in the metal was high after samples began to be investigated by Army, Navy, and Air Force labs. Titanium began to be called a &#;wonder metal&#;:
The metal gained numerous advocates within the military and industry. Early promoters visualized the use of titanium in naval vessels, armor plate, tanks, trucks, landing craft, aircraft structures, and airborne equipment. It was thought that it could possibly replace both aluminum and steel in the design of many defense applications. - Simcoe
In , titanium first began to be produced commercially, at a small DuPont plant that could produce 100 pounds of titanium a day. The first batches of titanium went to experimental use on military jets, such as the F-84 and the F-86. To try to kickstart the industry, the Air Force encouraged manufacturers to substitute steel with titanium, and the Army Ordnance Corporation placed an order for $1 million worth of titanium metal.
F-84, via wikipediaIn the press, titanium began to be called &#;the wonder metal," &#;the miracle metal," and the &#;Cinderella metal&#; (because it had been overlooked for so long). An executive for a company producing titanium noted that &#;Sensational magazine articles predicted that titanium would become the miracle metal-for spacecraft, &#;atomic furnaces,&#; airplanes of all kinds, submarines, railroad tracks, truck bodies, portable bridges&#; (Rowley ). Between and , more than two dozen companies announced plans to produce titanium.
But the nascent titanium industry struggled. In , the materials advisory board projected the need for 30,000 tons of titanium products, but actual shipments were just 75 tons, barely enough for research applications. Producers had assumed that the same equipment for melting, rolling, and shaping stainless steel could be used for titanium, but this turned out to be very difficult: titanium didn&#;t behave like steel, or like any other metal. Titanium was found &#;not to forge like any other material,&#; (DTIC ) and stamping it in presses damaged the stamping dies. A company that studied grinding titanium noted that &#;titanium grinds unlike steel. Anything you have learned concerning the effective grinding of steel does not apply in the case of titanium&#;. The first attempts to use titanium on commercial aircraft resulted in a sheet of metal so brittle it could be torn in half like a sheet of paper. Mills found that they often &#;produced more scrap than useful metal" (Simcoe ).
To support the budding industry, the US government stepped in. It funded the construction of several titanium sponge plants, and agreed to purchase any surplus titanium sponge production for the national stockpile. It offered rapid amortization of titanium production equipment for tax purposes, and demonstrated production techniques at the Bureau of Mines&#; pilot plant. The Army funded projects to develop better alloys, including one of 6% aluminum and 4% vanadium (Ti-6Al-4V) that remains the most popular alloy of titanium today, and is credited with saving the titanium industry. When it was found that rolling titanium into sheets consistently was difficult, in the Department of Defense initiated a program to develop sheet rolling of titanium, &#;one of the most comprehensive technical programs ever undertaken in metallurgy&#; (Simcoe ). Production problems were overcome, and titanium was increasingly used for aerospace applications. By , Pratt and Whitney had produced jet engines with titanium components, and the US industry was producing thousands of tons of titanium products a year.
In the late s, Lockheed won a contract to develop a high-speed, high altitude reconnaissance plane for the CIA. Because it was the 12th iteration of a design codenamed &#;Archangel," it became known as the A-12. To meet the unprecedented performance requirements (a cruising speed of Mach 3 and a cruising altitude of nearly 90,000 feet), Lockheed needed a metal that would retain its strength at the hundreds of degrees the exterior of the plane would reach. This ruled out aluminum, leaving either stainless steel or titanium. Ultimately, titanium alloy was selected for the A-12, as it would cut the gross weight of the plane nearly in half.
Titanium had never been used to such an extent on an aircraft, or anywhere else. Lockheed had worked with titanium on a small scale since but prior to the A-12 titanium had mostly been used for small components on jet engines. For several years, for instance, 50% of all titanium was used in the J-57 jet engine. But on the A-12, titanium would be used for nearly every part of the airplane &#; 93% of the gross weight of the A-12&#;s structure was titanium.
Building a plane out of titanium proved difficult. Initially Lockheed &#;had no idea how to extrude it, push it through into various shapes, or weld or rivet or drill it&#; (Rich ), and every production problem solved seemed to reveal two or three more. Titanium was found to be &#;totally incompatible&#; with chemicals like chlorine, fluorine, and cadmium. In one case, an engineer who marked a sheet of titanium using a pen with chlorine-based ink was shocked to see the ink etch away the metal like acid. Titanium bolts that were heated had their heads pop off, a problem that was eventually traced to cadmium-coated wrenches used to tighten them. Titanium welds made in the summer unexpectedly failed, due to (it was eventually realized) chlorine that the local utility added to the water during the summer to prevent algae growth.
When Lockheed tried to fabricate a portion of the forward fuselage, which had to be made from a novel &#;beta&#; titanium alloy, it found that the titanium was so brittle after heat treating that it would shatter if dropped on the floor. This was eventually resolved by replacing an acid-pickling process with one identical to that of Lockheed&#;s supplier, but not before scrapping thousands of titanium components. Of the first pieces fabricated from the beta titanium alloy, 95% were lost.
But over time, Lockheed overcame its production problems. In machining, for instance, drill bits initially needed to be replaced every ten holes, ten times as often as when drilling aluminum. In other machining operations, the rate of metal removal was just 5% of the rate when machining aluminum. To improve its machining, Lockheed developed new drill bits, cutting fluids, and cutting machinery, and learned the proper &#;feeds and speeds&#; for machining titanium (it was found, for instance, that small changes in cutting speed had a large effect on tool life). Over the course of the program, the rate of metal removal in machining was increased to &#;3 to 10 times the industry average&#; (Johnson ), and drill life was increased by more than a factor of 10.
The A-12 &#;practically spawned its own industrial base&#; (CIA ), and over the course of the program thousands of machinists, mechanics, fabricators, and other personnel were trained in how to work with titanium efficiently. As Lockheed gained production experience with titanium, it issued reports to the Air Force and to its vendors on production methods, and &#;set up training classes for machinists, a complete research facility for developing tools and procedures, and issued research contracts to competent outside vendors to develop improved equipment" (Johnson ).
The A-12 first flew in . 14 years later, its successor, the better-known SR-71, set an airspeed record of nearly miles per hour, which remains unbroken today.
While titanium manufacturing for aerospace was ramping up, a very different use of the metal was being discovered. In , Swedish medical researcher Per-Ingvar Brånemark was studying blood flow in healing bones. In one experiment studying the bone marrow of rabbits, Brånemark&#;s team implanted a tiny camera into rabbits legs, to watch the wound heal from the inside. When they later went to remove the camera, they found that the titanium camera casing had bonded with the bone.
At the time, it was thought that the body would eventually reject any foreign object implanted in it. Dr. Brånemark&#;s discovery that bone would bond directly with titanium (which he dubbed &#;osseointegration&#;) was radical, and had huge potential implications for medical implants. Brånemark quickly pivoted his research to study osseointegration, eventually receiving a grant from the US National Institutes of Health. Research on his own students (where he implanted a small piece of titanium in their arms) showed that titanium could be safely implanted in the body with no ill-effects.
Interestingly, during the course of this research, it was noticed that bone could conduct sound &#; a deaf patient was able to &#;hear&#; the ultrasonic vibrations used to check that the titanium had been implanted correctly. One of Brånemark&#;s students followed up on this discovery, and developed the first bone conduction implants to restore hearing in deaf people.
Brånemark&#;s team went on to develop titanium dental implants (which were often made from surplus aircraft-grade titanium) that lasted much longer than implants of other metals. Today, the Brånemark system of dental implants is still sold, and titanium is the most popular material for dental implants, as well as being used for other medical implants such as artificial hips.
You can get a sense of the development of the titanium industry by reading reports on industrial symposiums held in the s, 50s, and 60s.
The first symposium on titanium was held in , and was organized by the Navy to provide &#;a comprehensive review of the titanium research effort&#;. Several military organizations discussed their research programs, but most of the presentations were on topics such as physical properties of titanium and its various alloys, the crystal structure that resulted from different methods of fabrication, and methods of melting titanium sponge. The pages are full of pictures of laboratory setups, graphs of data on stress-strain relationships, phase diagrams, and magnified pictures of titanium microstructure. Nearly all the presentations are from either research labs or from companies trying to produce raw titanium &#;sponge&#; from ore.
In , another titanium symposium was held, this one sponsored by the Army&#;s Watertown Arsenal. By then, titanium was being manufactured in large quantities, and while the prior symposium had been focused on laboratory studies of titanium&#;s physical and chemical properties, the symposium was a &#;practical discussion of the properties, processing, machinability, and similar characteristics of titanium". While physical characteristics of titanium still took center stage, there was a practical slant to the discussions &#; how wide a sheet of titanium can be produced, how large an ingot of it can be made, how can it be forged, or pressed, or welded, and so on. Presentations were by titanium fabricators, but also by metalworking companies that had been experimenting with the metal.
Though by many of these companies had been working with titanium for years, there&#;s an air of uncertainty in many of the presentations, a distinct sense of &#;this is what we&#;ve learned so far, but there&#;s still much we don&#;t know.&#; A company that studied the effects of different working fluids when grinding titanium admitted that not enough was known about the chemistry at work to understand why different fluids had different effects. A company that studied surface treatments and polishing methods noted that &#;materials and methods for polishing titanium have not been definitively established," and that while &#;the most commonly used abrasives are not completely satisfactory," manufacturers were working on the problem, and &#;more efficient methods will no doubt be developed&#;. A company that studied cold-forming of titanium sheets described its own methods as &#;crude and undeveloped&#;.
In , another titanium symposium was held, this one sponsored by the Northrup Corporation. By this time, titanium had been used successfully for many years, and the purpose of this symposium was to &#;provide technical personnel of diversified disciplines with a working knowledge of titanium technology.&#; This time, the lion&#;s share of the presentations are by aerospace companies experienced in working with the metal, and the uncertain air that existed in the symposium is gone. A presenter on titanium&#;s corrosion resistance noted that &#;the corrosion resistance of titanium, unlike that of most metals, can be defined within rather simple limits." A presentation on forging noted that &#;titanium alloys are quite forgeable&#;The evidence which substantiates this statement is the large number of jet engine and missile components plus the growing lists of structural parts that have been produced in the last 10 years.&#; And a presentation on machining noted that &#;Fifteen years ago, titanium was considered to be very difficult to machine. Subsequent research and experience, however, have progressively improved this situation," the result of &#;gradual refinements in tool materials, machine tools, tool geometries, and cutting fluids&#;.
Thus, by the mid-s, titanium had become a mature engineering material. While there was still much to learn about titanium, the practical aspects of working with it and using it to solve engineering problems were well-understood, and it increasingly found use in aerospace and other industry applications. Following the A-12, for instance, military aircraft began to make extensive use of titanium in their structural frames. From military aircraft, titanium made its way into commercial aircraft. By , 46% of titanium was going towards commercial aircraft, compared to 37% to government aerospace projects.
What can we learn from the story of titanium?
For one, titanium is a government research success story. Titanium metal was essentially willed into existence by the US government, which searched for a promising production process, successfully scaled it up when it found one, and performed much of the initial research on titanium&#;s material properties, potential alloys, and manufacturing methods. Nearly all early demand for titanium was for government aerospace projects, and when the nascent industry struggled, the government stepped in to subsidize production. As a result, titanium achieved a level of production in 10 years that took aluminum and magnesium nearly 30.
The government&#;s support of the early industry was successful: shortly after the program was initiated in , the cost of titanium began to decline more steeply. Since then, titanium costs have fallen at an impressive 23% learning rate (ie: costs fall 23% every time cumulative production doubles), similar to the learning rate in solar PV production. When government subsidies were removed in the late s, the industry struggled, but cost declines continued. And from the initial government projects in military aerospace, titanium has spread into commercial aircraft, medical implants, industrial equipment, and other uses. Titanium is thus a successful case of the government jumpstarting an industry.
Via USGS dataBut titanium is also a story about the limits of this sort of jumpstarting. Despite its impressive learning rate, titanium remains an expensive, niche material. A report noted that titanium is five times as expensive as aluminum to refine and ten times as expensive as aluminum to turn into finished products. Despite initial expectations, titanium hasn&#;t widely displaced either aluminum or stainless steel, and is only used where its unique properties make its high cost worth it. The aerospace industry remains the largest user of titanium.
It's interesting to compare progress in titanium production with progress in solar photovoltaics. In both cases, the basic phenomenon (metallic titanium and producing electricity from sunlight) had been explored in the late s, but it wasn&#;t until mid-20th century technology breakthroughs (the Kroll process and the silicon PV cell) that they became practical. In both cases, the US government funded much of the initial development, and acted as the first customer (government satellites and government aerospace projects). Both have similar learning curve slopes, and both technologies gradually expanded outside of their initial markets as knowledge was gained and the costs of the technology fell. And in both cases, there were sky-high expectations for the &#;potentially world-changing technology&#; that neither initially lived up to.
But whereas titanium remains a relatively niche, expensive technology, solar PV is increasingly widely deployed, and seems poised to become the primary method of electric power production. In learning curve terms, while both titanium and solar PV have similar learning rates, the solar PV curve has stretched much farther. Between and today, cumulative titanium production has increased by perhaps a factor of 5-10 (cumulative US consumption of titanium sponge was about 250,000 tons in , and about 1.3 million tons in ). Cumulative solar PV production, on the other hand, has increased by a factor of more than 300,000. Though they have the same learning rate, solar PV has had many more doublings in production volume, and its costs have thus fallen much further.
Data via USGS and
LafondI can see at least two potential factors here. One is that solar PV production has seen a much greater level of government support than titanium production has. In addition to early government support in the s, solar PV also saw US and Japanese government investment in the s, and German government support in the s (via a generous feed-in tariff). Today, governments around the world support solar PV via feed in tariffs, tax credits, and renewable portfolio standards. Continued government subsidies have incentivized increased production, which has resulted in the costs of solar PV continuing to fall. Without that government support, the level of production of solar PV would have been much lower, and its march down the learning curve would have happened much more slowly.
Titanium, on the other hand, has seen much less government support. After subsidies were withdrawn in the late s, the titanium industry has been dependent on large government or commercial aerospace projects. If those fail to materialize (such as when Cold War strategy pivoted from bombers to missiles, or when supersonic commercial aircraft development was canceled), the industry has struggled. If government support of the industry had continued, perhaps it would be farther along on its learning curve.
The other potential factor is technical: while there are many potential process improvements to solar PV manufacturing, there may be substantially fewer potential improvements in titanium production. In the s, it was hoped/assumed that a better process for producing titanium sponge would come along to replace the Kroll process, which is a laborious and energy-intensive batch process that must be done in an inert atmosphere. But such a process has never materialized, and the Kroll process remains the primary method of refining titanium ore. Likewise, turning titanium sponge into metal is an energy and capital-intensive process, often requiring multiple rounds of melting the metal to achieve sufficient purity. This process has also changed little since the s.
Beyond the lack of process improvements, titanium is just fundamentally difficult and expensive to deal with. Turning titanium ingots into bars and sheets is a challenge due to titanium&#;s reactivity: it readily absorbs impurities, requiring &#;frequent surface removal and trimming to eliminate surface defects&#; which are &#;costly and involve significant yield loss.&#; Machining titanium is likewise fundamentally expensive. As one report notes:
The hardness that makes titanium so desirable also makes it more difficult to machine than traditional aluminum. This presents a challenge akin to that of machining high-strength steel. However, the process is complicated by titanium&#;s high reactivity and low thermal conductivity. It is highly reactive and tends to wear tools very quickly, especially at higher temperatures. The low thermal conductivity means that high temperatures can be generated easily in the course of machining. Consequently, titanium must be machined at lower tool speeds, slowing production.
If there are simply fewer potential process improvements in titanium production compared to solar PV, due to the lack of better refining processes and the various physical constraints dictated by its chemistry, there&#;s less room for costs to fall. With less room for costs to fall, titanium remains an expensive, niche material, which in turn keeps production volumes low.
Titanium is also a story about the importance of serendipity in scientific discovery and technology advancement. Titanium&#;s biocompatibility, and its usefulness for medical implants, was discovered purely by chance. Studying biocompatibility led to another chance discovery, that of bone conduction of sound. Both of these discoveries led to the development of important medical technology, implants and hearing aids.
Finally, titanium is also a story about the critical role that manufacturing plays in technology development. The knowledge required to turn titanium into a practical technology came from the research lab, but it also came from the factory floor. Using titanium meant understanding its chemical properties, but it also meant figuring out how to forge it, weld it, press it, turn it into fasteners, design parts effectively with it, designing tools to machine it, and a million other shop floor discoveries that came from actually building things with the metal. As one producer noted, &#;you cannot ship a customer a carload full of tensile properties, nor a box full of Charpy tests. You have to make something out of the material in order to use these marvelous characteristics.&#; (DTIC ). It's only after the enormous effort to build the all-titanium A-12, and the training of thousands of machinists, fabricators, engineers, and other workers to work with titanium, that we begin to see titanium being used in large amounts in military and commercial aircraft. This sort of practical knowledge &#; the learning that comes from actual production &#; is critical for technological progress. Technology consists of materials and machines and ideas, but they&#;re all stitched together by a collection of people that know how to do things. It&#;s by way of those people doing those things, and understanding them better and better, that new and better technology becomes possible.
Report of Symposium on Titanium,
Proceedings of the titanium symposium at Watertown Arsenal,
Titanium : Lectures given at Norair symposium
Johnson - Some Development Aspects of the YF-12A Interceptor
Johnson - Development of the Lockheed SR-71 Blackbird
Rich - Skunk Works: A personal memoir of my years at Lockheed
Donachie - Titanium: A technical guide
Titanium: Past, Present, and Future ()
Tylecote - History of metallurgy
Simcoe - The history of metals in America
Robarge - Archangel: CIA&#;s supersonic A-12 reconnaissance aircraft
Seong - Titanium: industrial base, price trends, and technology initiatives
Abkowitz - The emergence of the titanium industry
Kroll - How commercial titanium and zirconium were born
Titanium in aerospace applications ()
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