Scandiumis achemical elementwith symbolScandatomic number21. A silvery-white metallictransition metal, it has historically been sometimes classified as arare earth element, together withyttriumand thelanthanoids. It was discovered in 1879 by spectral analysis of themineralseuxeniteandgadolinitefromScandinavia.Scandium is present in most of the deposits of rare earth anduraniumcompounds, but it is extracted from these ores in only a few mines worldwide. Because of the low availability and the difficulties in the preparation of metallic scandium, which was first done in 1937, it took until the 1970s before applications for scandium were developed. The positive effects of scandium onaluminiumalloyswere discovered in the 1970s, and its use in such alloys remains its only major application. The global trade of the pure metal is around a hundred pounds a year on average.[3]The properties of scandium compounds are intermediate between those ofaluminiumand yttrium. Adiagonal relationshipexists between the behavior ofmagnesiumand scandium, just as there is betweenberylliumand aluminium. In the chemical compounds of the elements shown as group 3, above, the predominantoxidation stateis +3.Properties[edit]Chemical characteristics of the element[edit]Scandium is a soft metal with a silvery appearance. It develops a slightly yellowish or pinkish cast whenoxidizedby air. It is susceptible to weathering and dissolves slowly in most diluteacids. It does not react with a 1:1 mixture ofnitric acid(HNO3) and 48%hydrofluoric acid(HF), possibly due to the formation of an impermeablepassive layer. Scandium turnings ignite in air with a brilliant yellow flame to formscandium(III) oxide.[4]Isotopes[edit]Main article:Isotopes of scandiumScandium exists naturally exclusively as theisotope45Sc, which has anuclear spinof 7/2. Thirteenradioisotopeshave been characterized with the most stable being46Sc with ahalf-lifeof 83.8days,47Sc with a half-life of 3.35days, and48Sc with a half-life of 43.7hours. All of the remainingradioactiveisotopes have half-lives that are less than 4hours, and the majority of these have half-lives that are less than 2minutes. This element also has fivemeta stateswith the most stable being44mSc (t= 58.6h).[5]The isotopes of scandium range from36Sc to60Sc. The primarydecay modeat masses lower than the only stable isotope,45Sc, iselectron capture, and the primary mode at masses above it isbeta emission. The primarydecay productsat atomic weights below45Sc arecalciumisotopes and the primary products from higher atomic weights aretitaniumisotopes.[5]Occurrence[edit]In terms ofearth's crust, scandium is not particularly rare. Estimates vary from 18 to 25ppm, which is comparable to the abundance ofcobalt(2030ppm). Scandium is only the 50th most common element on earth (35th most abundant in the crust), but it is the 23rd most common element in theSun.[6]However, scandium is distributed sparsely and occurs in trace amounts in manyminerals.[7]Rare minerals from Scandinavia[8]andMadagascar[9]such asthortveitite,euxenite, andgadoliniteare the only known concentrated sources of this element. Thortveitite can contain up to 45% of scandium in the form ofscandium(III) oxide.[8]The stable form of scandium is created insupernovasvia ther-process.[10]Production[edit]World production of scandium is in the order of 2 tonnes per year in the form ofscandium oxide. The primary production is 400kg while the rest is from stockpiles ofRussiagenerated during theCold War. In 2003, only three mines produced scandium: the uranium andironmines inZhovti VodyinUkraine, the rare earth mines inBayan Obo,Chinaand the apatite mines in theKola peninsula,Russia. In each case, scandium is a byproduct from the extraction of other elements[11]and is sold as scandium oxide.The production of metallic scandium is in the order of 10kg per year.[11][12]The oxide is converted toscandium fluorideandreducedwith metalliccalcium.MadagascarandIveland-Evjeregion inNorwayhave the only deposits of minerals with high scandium content,thortveitite(Sc,Y)2(Si2O7) andkolbeckiteScPO42H2O, but these are not being exploited.[12]The absence of reliable, secure, stable and long term production has limited commercial applications of scandium. Despite this low level of use, scandium offers significant benefits. Particularly promising is the strengthening of aluminium alloys with as little as 0.5% scandium. Scandium-stabilized zirconia enjoys a growing market demand for use as a high efficiencyelectrolyteinsolid oxide fuel cells.Compounds[edit]See also categories:Scandium compoundsandScandium mineralsThe chemistry is almost completely dominated by the trivalent ion, Sc3+. The radii of M3+ions in the table below indicate that in terms of chemical properties, scandium ions are more similar to those of yttrium than to those of aluminium. In part for this similarity, scandium is often classified as a lanthanide-like element.Ionic radii (pm)

AlScYLaLu

53.574.590.0103.286.1

Oxides and hydroxides[edit]The oxideSc2O3and the hydroxide Sc(OH)3areamphoteric:[13]Sc(OH)3+ 3 OH Sc(OH)36Sc(OH)3+ 3 H++ 3 H2O [Sc(H2O)6]3+The - and - forms of scandium oxide hydroxide (ScO(OH)), are isostructural with theiraluminium oxide hydroxidecounterparts.[14]Solutions of Sc3+in water are acidic because ofhydrolysis.Halides and pseudohalides[edit]ThehalidesScX3(X =Cl, Br, I) are very soluble in water, but ScF3is insoluble. In all four halides the scandium is 6-coordinated. The halides areLewis acids; for example, ScF3dissolves a solution containing excess fluoride to form [ScF6]3. The coordination number 6 is typical of Sc(III). In the larger Y3+and La3+ions,coordination numbersof 8 and 9 are common.Scandium(III) triflateis sometimes used as aLewis acidcatalyst inorganic chemistry.Organic derivatives[edit]Main article:Organoscandium chemistryScandium forms a series of organometallic compounds withcyclopentadienylligands (Cp), similar to the behavior of the lanthanides. One example is the chlorine-bridged dimer, [ScCp2Cl]2and related derivatives ofpentamethylcyclopentadienylligands.[15]Uncommon oxidation states[edit]Compounds that feature scandium in the oxidation state other than +3 are rare but well characterized. The blue-black compound CsScCl3is one of the simplest. This material adopts a sheet-like structure that exhibits extensive bonding between the scandium(II) centers.[16]Scandium hydrideis not well understood, although it appears not to be asaline hydrideof Sc(II).[2]As is observed for most elements, a diatomic scandium hydride has been observed spectroscopically at high temperatures in the gas phase.[1]Scandium borides and carbides arenon-stoichiometric, as is typical for neighboring elements.[17]History[edit]Dmitri Mendeleev, creator of theperiodic table, predicted the existence of an elementekaboron, with anatomic massbetween 40 and 48 in 1869.Lars Fredrik Nilsonand his teamdetected this elementin the mineralseuxeniteandgadolinite. Nilson prepared 2grams ofscandium oxideof high purity.[18][19]He named the element scandium, from theLatinScandiameaning "Scandinavia". Nilson was apparently unaware of Mendeleev's prediction, butPer Teodor Cleverecognized the correspondence and notified Mendeleev.[20]Metallic scandium was produced for the first time in 1937 byelectrolysisof aeutecticmixture, at 700800C, ofpotassium,lithium, andscandium chlorides.[21]The first pound of 99% pure scandium metal was produced in 1960. The use for aluminium alloys began in 1971, following a US patent.[22]Aluminium-scandium alloys were also developed in theUSSR.[23]Laser crystals of gadolinium-scandium-gallium garnet (GSGG) were used in strategic defense applications developed in theStrategic Defense Initiative(SDI) in the 1980s and the 1990s.[24][25]Applications[edit]

Parts of theMiG-29are made from Al-Sc alloy.[26]The addition of scandium to aluminium limits the excessive grain growth that occurs in the heat-affected zone of welded aluminium components. This has two beneficial effects: the precipitated Al3Sc forms smaller crystals than are formed in otheraluminium alloys[26]and the volume of precipitate-free zones that normally exist at the grain boundaries of age-hardening aluminium alloys is reduced.[26]Both of these effects increase the usefulness of the alloy.[why?]However,titanium alloys, which are similar in lightness and strength, are cheaper and much more widely used.[27]The main application of scandium by weight is in aluminium-scandium alloys for minor aerospace industry components. These alloys contain between 0.1% and 0.5% of scandium. They were used in the Russian military aircraft, specifically theMiG-21andMiG-29.[26]Some items of sports equipment, which rely on high performance materials, have been made with scandium-aluminium alloys, includingbaseball bats,[28]andbicycle[29]frames and components.Lacrosse sticksare also made with scandium. The American firearm manufacturing companySmith & Wessonproduces revolvers with frames composed of scandium alloy and cylinders of titanium or carbon steel.[30][31]Dentists use Erbium, chromium: yttrium-scandium-gallium garnet (Er,Cr:YSGG) lasers for cavity preparation and in endodontics.[32]Approximately 20kg (as Sc2O3) of scandium is used annually in theUnited Statesto make high-intensity discharge lamps.[33]Scandium iodide, along withsodium iodide, when added to a modified form ofmercury-vapor lamp, produces a form ofmetal halide lamp. This lamp is a white light source with highcolor rendering indexthat sufficiently resembles sunlight to allow good color-reproduction withTVcameras.[34]About 80kg of scandium is used in metal halide lamps/light bulbs globally per year. The first scandium-based metal halide lamps were patented byGeneral Electricand initially made in North America, although they are now produced in all major industrialized countries. Theradioactive isotope46Sc is used inoil refineriesas a tracing agent.[33]Scandium triflateis a catalyticLewis acidused inorganic chemistry.[35]Health and safety[edit]Elemental scandium is considered non-toxic and little animal testing of scandium compounds has been done.[36]Themedian lethal dose(LD50) levels for scandium(III) chloride for rats have been determined as 4mg/kg forintraperitonealand 755mg/kg for oral administration.[37]In the light of these results compounds of scandium should be handled as

Titaniumis achemical elementwith the symbolTiandatomic number22. It is a lustroustransition metalwith a silver color, low density and high strength. It is highly resistant tocorrosioninsea water,aqua regiaandchlorine.Titanium was discovered inCornwall,Great Britain, byWilliam Gregorin 1791 and named byMartin Heinrich Klaprothfor theTitansofGreek mythology. The element occurs within a number ofmineraldeposits, principallyrutileandilmenite, which are widely distributed in theEarth's crustandlithosphere, and it is found in almost all living things, rocks, water bodies, and soils.[2]The metal is extracted from its principal mineral ores via theKroll process[3]or theHunter process. Its most common compound,titanium dioxide, is a popularphotocatalystand is used in the manufacture of white pigments.[4]Other compounds includetitanium tetrachloride(TiCl4), a component ofsmoke screensandcatalysts; andtitanium trichloride(TiCl3), which is used as a catalyst in the production ofpolypropylene.[2]Titanium can bealloyedwithiron,aluminium,vanadium,molybdenum, among other elements, to produce strong lightweight alloys for aerospace (jet engines,missiles, andspacecraft), military, industrial process (chemicals and petro-chemicals,desalination plants, pulp, and paper), automotive, agri-food, medicalprostheses, orthopedicimplants, dental and endodontic instruments and files,dental implants, sporting goods, jewelry,mobile phones, and other applications.[2]The two most useful properties of the metal are corrosion resistance and the highest strength-to-weight ratio of any metal.[5]In its unalloyed condition, titanium is as strong as somesteels, but 45%

Physical properties[edit]Ametallicelement, titanium is recognized for its high strength-to-weight ratio.[7]It is a strong metal with lowdensitythat is quiteductile(especially in anoxygen-free environment),[2]lustrous, and metallic-white incolor.[9]The relatively high melting point (more than 1,650C or 3,000F) makes it useful as arefractory metal. It isparamagneticand has fairly lowelectricalandthermal conductivity.[2]Commercial (99.2% pure)gradesof titanium haveultimate tensile strengthof about 63,000psi(434MPa), equal to that of common, low-grade steel alloys, but are 45% lighter. Titanium is 60% more dense than aluminium, but more than twice as strong[6]as the most commonly used 6061-T6 aluminium alloy. Certain titanium alloys (e.g., Beta C) achieve tensile strengths of over 200,000 psi (1,400MPa).[10]However, titanium loses strength when heated above430 C(806F).[11]Titanium is fairly hard (although not as hard as some grades of heat-treated steel), non-magnetic and a poor conductor of heat and electricity. Machining requires precautions, as the material will soften andgallif sharp tools and proper cooling methods are not used. Like those made from steel, titanium structures have afatigue limitwhich guarantees longevity in some applications.[9]Titanium alloys have lower specific stiffnesses than in many other structural materials such as aluminium alloys andcarbon fiber.The metal is a dimorphicallotropewhose hexagonal alpha form changes into a body-centered cubic (lattice) form at882 C(1,620F).[11]Thespecific heatof the alpha form increases dramatically as it is heated to this transition temperature but then falls and remains fairly constant for the form regardless of temperature.[11]Similar to zirconium and hafnium, an additional omega phase exists, which is thermodynamically stable at high pressures, but is metastable at ambient pressures. This phase is usually hexagonal (ideal) or trigonal (distorted) and can be viewed as being due to a soft longitudinal acousticphononof the phase causing collapse of(111) planesof atoms.[12]Chemical properties[edit]

ThePourbaix diagramfor titanium in pure water, perchloric acid or sodium hydroxide[13]Likealuminiumandmagnesiummetal surfaces, titanium metal and its alloysoxidizeimmediately upon exposure to air. Nitrogen acts similarly to give a coating of the nitride. Titanium readily reacts with oxygen at1,200 C(2,190F)in air, and at610 C(1,130F)in pure oxygen, formingtitanium dioxide.[7]It is, however, slow to react with water and air, as it forms apassiveand oxide coating that protects the bulk metal from further oxidation.[2]When it first forms, this protective layer is only 12nmthick but continues to slowly grow; reaching a thickness of 25nm in four years.[14]Related to its tendency to form a passivating layer, titanium exhibits excellent resistance to corrosion. It is almost as resistant asplatinum, capable of withstanding attack by dilutesulfuricandhydrochloric acidsas well as chloride solutions, and most organic acids.[3]However, it is attacked by concentrated acids.[15]As indicated by its negative redox potential, titanium is thermodynamically a very reactive metal. One indication is that the metal burns before it melting point is reached. Melting is only possible in an inert atmosphere or in a vacuum. At550 C(1,022F), it combines with chlorine.[3]It also reacts with the other halogens and absorbs hydrogen.[4]Titanium is one of the few elements that burns in pure nitrogen gas, reacting at800 C(1,470F)to formtitanium nitride, which causes embrittlement.[16]Because of its high reactivity toward oxygen, nitrogen and many other gases,titanium filamentsare applied intitanium sublimation pumpsas scavengers for these gases. Such pumps are inexpensive and reliable devices for producing extremely low pressures inultra-high vacuumsystems.Occurrence[edit]2011 production of rutile and ilmenite[17]

Countrythousandtonnes% of total

Australia130019.4

South Africa116017.3

Canada70010.4

India5748.6

Mozambique5167.7

China5007.5

Vietnam4907.3

Ukraine3575.3

World6700100

Titanium is always bonded to other elements in nature. It is the ninth-mostabundantelement in theEarth's crust (0.63% bymass)[18]and the seventh-most abundant metal. It is present in mostigneous rocksand insedimentsderived from them (as well as in living things and natural bodies of water).[2][3]Of the 801 types of igneous rocks analyzed by theUnited States Geological Survey, 784 contained titanium. Its proportion in soils is approximately 0.5 to 1.5%.[18]It is widely distributed and occurs primarily in themineralsanatase,brookite,ilmenite,perovskite,rutileandtitanite(sphene).[14]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 these minerals have been mined in 2011, respectively.[17]Significant titanium-bearing ilmenite deposits exist in westernAustralia,Canada,China,India,Mozambique,New Zealand,Norway,UkraineandSouth Africa.[14]About 186,000 tonnes of titanium metal sponge were produced in 2011, mostly in China (60,000 t), Japan (56,000 t), Russia (40,000 t), United States (32,000 t) and Kazakhstan (20,700 t). Total reserves of titanium are estimated to exceed 600 million tonnes.[17]Titanium is contained inmeteoritesand has been detected in thesunand inM-typestars;[3]the coolest type of star with a surface temperature of3,200 C(5,790F).[19]Rocksbrought back from themoonduring theApollo 17mission are composed of 12.1% TiO2.[3]It is also found incoalash,plants, and even thehumanbody.Isotopes[edit]Main article:Isotopes of titaniumNaturally occurring titanium is composed of 5 stableisotopes:46Ti,47Ti,48Ti,49Ti, and50Ti, with48Ti being the most abundant (73.8%natural abundance). Elevenradioisotopeshave been characterized, with the most stable being44Ti with ahalf-lifeof 63 years,45Ti with a half-life of 184.8 minutes,51Ti with a half-life of 5.76 minutes, and52Ti with a half-life of 1.7 minutes. All of the remainingradioactiveisotopes have half-lives that are less than 33 seconds and the majority of these have half-lives that are less than half a second.[8]The isotopes of titanium range inatomic weightfrom 39.99u(40Ti) to 57.966 u (58Ti). The primarydecay modebefore the most abundant stable isotope,48Ti, iselectron captureand the primary mode after isbeta emission. The primarydecay productsbefore48Ti are element 21 (scandium) isotopes and the primary products after are element 23 (vanadium) isotopes.[8]Titanium becomes radioactive upon bombardment withdeuterons, emitting mainlypositronsand hardgamma rays.[3]Compounds[edit]See also categories:Titanium compoundsandTitanium minerals

TiN-coateddrillbitThe +4oxidation statedominates titanium chemistry,[20]but compounds in the +3oxidation stateare also common.[21]Commonly, titanium adopts anoctahedral coordination geometryin its complexes, but tetrahedral TiCl4is a notable exception. Because of the high oxidation state of Ti(IV), titanium(IV) compounds exhibit a high degree ofcovalent bonding.Oxides, sulfides, and alkoxides[edit]The most important oxide is TiO2, which exists in three importantpolymorphs,anatase,brookite, andrutile. All of these are white diamagnetic solids, although mineral samples can appear dark (seerutile). The adopt polymeric structures in which Ti is surrounded by sixoxideligands that link to other Ti centers.Titanatesusually refers to compounds made from titanium dioxide, as representedbarium titanate(BaTiO3), which is produced synthetically. With aperovskitestructure, this material exhibitspiezoelectricproperties and is used as a transducer in the interconversion ofsoundandelectricity.[7]Many minerals are titanates, e.g.illmenite(FeTiO3).Star sapphiresandrubiesget theirasterism(star-forming shine) from the presence of titanium dioxide impurities.[14]Thealkoxidesof titanium(IV) are useful compounds that convert to the dioxide. They are volatile, colourless compounds that are sensitive to water.Titanium ethoxide, with the molecular formula Ti4(OEt)16, reacts with water to deposit solid TiO2via thesol-gel process.Titanium isopropoxideis used in the synthesis of chiral organic compounds via theSharpless epoxidation.Titanium forms a variety of sulfides, but onlyTiS2has attracted significant interest. It adopts a layered structure and was used as a cathode in early generation oflithium batteries. Since Ti(IV) is a"hard cation", the sulfides of titanium are unstable in the presence of moisture, tending to hydrolyze to the oxide and hydrogen sulfide.Nitrides, carbides[edit]Titanium nitride(TiN), having a hardness equivalent tosapphireandcarborundum(9.0 on theMohs Scale),[22]is often used to coat cutting tools, such asdrill bits.[23]It also finds use as a gold-colored decorative finish, and as abarrier metalinsemiconductor fabrication.[24]Titanium carbide, which is also very hard, is found in high-temperature cutting tools and coatings).Halides[edit]Titanium tetrachloride(titanium(IV) chloride, TiCl4[25]) is a colorless volatile liquid (commercial samples are yellowish) that in air hydrolyzes with spectacular emissoin of white clouds. Via theKroll process, TiCl4is produced in the conversion of titanium ores to titanium dioxide, e.g., for use in white paint.[26]It is widely used inorganic chemistryas aLewis acid, for example in theMukaiyama aldol condensation.[27]In thevan Arkel process,titanium tetraiodide(TiI4) is generated in the production of high purity titanium metal.

Titanium(III) compounds are characteristically violet, illustrated by this aqueous solution oftitanium trichloride.Titanium(III) and titanium(II) also form stable chlorides. A notable example istitanium(III) chloride(TiCl3), which is used as acatalystfor production ofpolyolefins(seeZiegler-Natta catalyst) and a reducingagentin organic chemistry.Organometallic complexes[edit]Main article:Organotitanium chemistryOwing to the important role of titanium compounds as polymerization catalyst, compounds with Ti-C bonds have been intensively studied. The most common organotitanium complex istitanocene dichloride((C5H5)2TiCl2). Related compounds includeTebbe's reagentandPetasis reagent. Titanium forms carbonyl complexes, e.g.(C5H5)2Ti(CO)2.[28]History[edit]

Martin Heinrich Klaprothnamed titanium for theTitansofGreek mythology.Titanium wasdiscoveredincludedin amineralinCornwall,Great Britain, in 1791 by theclergymanand amateur geologistWilliam Gregor, then vicar ofCreedparish.[29]He recognized the presence of a new element in ilmenite[4]when he found black sand by a stream in the nearbyparishofManaccanand noticed the sand was attracted by amagnet.[29]Analysis of the sand 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.[18]Gregor, realizing that the unidentified oxide contained a metal that did not match the properties of any known element, reported his findings to theRoyal Geological Society of Cornwalland in the German science journalCrell's Annalen.[29]Around the same time,Franz-Joseph Mller von Reichensteinproduced a similar substance, but could not identify it.[4]The oxide was independently rediscovered in 1795 byPrussianchemistMartin Heinrich Klaprothin rutile from Boinik (German name of unknown place) village ofHungary(Now inSlovakia).[29]Klaproth found that it contained a new element and named it for theTitansofGreek mythology.[19]After hearing about Gregor's earlier discovery, he obtained a sample ofmanaccaniteand confirmed it contained titanium.The processes required to extract titanium from its various ores are laborious and costly; it is not possible to reduce the ore in the normal manner, by heating in the presence ofcarbon, as that producestitanium carbide.[29]Pure metallic titanium (99.9%) was first prepared in 1910 byMatthew A. HunteratRensselaer Polytechnic Instituteby heating TiCl4withsodiumat 700800C in theHunter process.[3]Titanium metal was not used outside the laboratory until 1932 whenWilliam Justin Krollproved that it could be produced by reducingtitanium tetrachloride(TiCl4) withcalcium.[30]Eight years later he refined this process by usingmagnesiumand evensodiumin what became known as theKroll process.[30]Although research continues into more efficient and cheaper processes (e.g.,FFC Cambridge), the Kroll process is still used for commercial production.[3][4]

Titanium sponge, made by theKroll processTitanium of very high purity was made in small quantities whenAnton Eduard van ArkelandJan Hendrik de Boerdiscovered the iodide, orcrystal bar, process in 1925, by reacting with iodine and decomposing the formed vapors over a hot filament to pure metal.[31]In the 1950s and 1960s theSoviet Unionpioneered the use of titanium in military and submarine applications (Alfa ClassandMike Class)[32]as part of programs related to the Cold War.[33]Starting in the early 1950s, titanium began to be used extensively for military aviation purposes, particularly in high-performance jets, starting with aircraft such as theF100 Super SabreandLockheed A-12.In the USA, theDepartment of Defenserealized the strategic importance of the metal[34]and supported early efforts of commercialization.[35]Throughout the period of theCold War, titanium was considered astrategic materialby the U.S. government, and a large stockpile of titanium sponge was maintained by theDefense National Stockpile Center, which was finally depleted in the 2000s.[36]According to 2006 data, the world's largest producer, Russian-basedVSMPO-Avisma, was estimated to account for about 29% of the world market share.[37]As of 2009, titanium sponge metal was produced in six countries: China, Japan, Russia, Kazakhstan, USA and Ukraine (in order of output).[38]In 2006, the U.S. Defense Agency awarded $5.7 million to a two-company consortium to develop a new process for making titanium metalpowder. Under heat and pressure, the powder can be used to create strong, lightweight items ranging from armor plating to components for the aerospace, transport, and chemical processing industries.[39]Production and fabrication[edit]

Titanium (mineral concentrate)The processing of titanium metal occurs in 4 major steps:[40]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.Because the metal reacts with oxygen at high temperatures it cannot be produced byreductionof its dioxide.[9]Titanium metal is therefore produced commercially by theKroll process, a complex and expensivebatch process. (The relatively high market value of titanium is mainly due to its processing, which sacrifices another expensive metal, magnesium.[41]) In the Kroll process, the oxide is first converted to chloride through carbochlorination, wherebychlorinegas is passed over red-hot rutile or ilmenite in the presence of carbon to makeTiCl4. This is condensed and purified byfractional distillationand thenreducedwith 800C moltenmagnesiumin anargonatmosphere.[7]A more recently developed method, theFFC Cambridge process,[42][43]may eventually replace the Kroll process. This method uses titanium dioxide powder (which is a refined form of rutile) as feedstock to make the end product which is either a powder or sponge. If mixed oxide powders are used, the product is an alloy manufactured at a much lower cost than the conventional multi-step melting process. The FFC Cambridge process may render titanium a less rare and expensive material for theaerospaceindustry and the luxury goods market, and could be seen in many products currently manufactured using aluminium and specialist grades of steel.Common titaniumalloysare made by reduction. For example, cuprotitanium (rutile withcopperadded is reduced), ferrocarbon titanium (ilmenite reduced withcokein an electric furnace), and manganotitanium (rutile with manganese or manganese oxides) are reduced.[44]2 FeTiO3+ 7 Cl2+ 6 C 2 TiCl4+ 2 FeCl3+ 6 CO (900C)TiCl4+ 2 Mg 2 MgCl2+ Ti (1100C)About 50gradesof titanium and titanium alloys are designated and currently used, although only a couple of dozen are readily available commercially.[45]TheASTM Internationalrecognizes 31 Grades of titanium metal and alloys, of which Grades 1 through 4 are commercially pure (unalloyed). These four are distinguished by their varying degrees of tensile strength, as a function ofoxygencontent, with Grade 1 being the most ductile (lowest tensile strength with an oxygen content of 0.18%), and Grade 4 the least (highest tensile strength with an oxygen content of 0.40%).[14]The remaining grades are alloys, each designed for specific purposes, be it ductility, strength, hardness, electrical resistivity,creepresistance, resistance to corrosion from specific media, or a combination thereof.[46]Thegradescovered by ASTM and other 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.[47]In terms of fabrication, allweldingof titanium must be done in an inert atmosphere ofargonorheliumin order to shield it from contamination with atmospheric gases such as oxygen,nitrogen, orhydrogen.[11]Contamination will cause a variety of conditions, such asembrittlement, which will reduce the integrity of the assembly welds and lead to joint failure. Commercially pure flat product (sheet, plate) can be formed readily, but processing must take into account the fact that the metal has a "memory" and tends to spring back. This is especially true of certain high-strength alloys.[48][49]Titanium cannot besolderedwithout first pre-platingit in a metal that issolderable.[50]The metal can be machined using the same equipment and via the same processes asstainless steel.[11]Applications[edit]

A titanium cylinder, "Grade 2" qualityTitanium is used insteelas an alloying element (ferro-titanium) to reducegrain sizeand as a deoxidizer, and instainless steelto reduce carbon content.[2]Titanium is often alloyed with aluminium (to refine grain size),vanadium,copper(to harden),iron,manganese,molybdenum, and with other metals.[51]Applications for titanium mill products (sheet, plate, bar, wire, forgings, castings) can be found in industrial, aerospace, recreational, and emerging markets. Powdered titanium is used inpyrotechnicsas a source of bright-burning particles.Pigments, additives and coatings[edit]

Titanium dioxideis the most commonly used compound of titaniumAbout 95% of titanium ore extracted from the Earth is destined for refinement intotitanium dioxide(TiO2), an intensely white permanentpigmentused inpaints,paper,toothpaste, andplastics.[17]It is also used incement, ingemstones, as an optical opacifier inpaper,[52]and a strengthening agent in graphite composite fishing rods and golf clubs.TiO2powder is chemically inert, resists fading in sunlight, and is very opaque: this allows it to impart a pure and brilliant white color to the brown or gray chemicals that form the majority of household plastics.[4]In nature, this compound is found in themineralsanatase,brookite, and rutile.[2]Paint made with titanium dioxide does well in severe temperatures, and stands up to marine environments.[4]Pure titanium dioxide has a very highindex of refractionand anoptical dispersionhigher thandiamond.[3]In addition to being a very important pigment, titanium dioxide is also used insunscreensdue to its ability to protect skin by itself.[9]Recently, titanium oxide has been put to use in air purifiers (as a filter coating), or in film used to coat windows on buildings so that when titanium oxide becomes exposed toUV light(either solar or artificial) and moisture in the air, reactive redox species like hydroxyl radicals are produced so that they can purify the air or keep window surfaces clean.[53]Aerospace and marine[edit]Due to their hightensile strengthto density ratio,[7]high corrosion resistance,[3]fatigue resistance, high crack resistance,[54]and ability to withstand moderately high temperatures withoutcreeping, titaniumalloysare used inaircraft,armor plating,navalships,spacecraft, andmissiles.[3][4]For these applicationstitanium alloyedwith aluminium, zirconium, nickel,[55]vanadium, and other elements is used for a variety of components including critical structural parts, fire walls,landing gear, exhaust ducts (helicopters), and hydraulic systems. In fact, about two thirds of all titanium metal produced is used in aircraft engines and frames.[56]TheSR-71 "Blackbird"was one of the first aircraft to make extensive use of titanium within its structure, paving the way for its use in modern military and commercial aircraft. An estimated 59 metric tons (130,000 pounds) are used in theBoeing 777, 45 in theBoeing 747, 18 in theBoeing 737, 32 in theAirbus A340, 18 in theAirbus A330, and 12 in theAirbus A320. TheAirbus A380may use 77 metric tons, including about 11 tons in the engines.[57]In engine applications, titanium is used for rotors, compressor blades, hydraulic system components, andnacelles. Thetitanium 6AL-4Valloy accounts for almost 50% of all alloys used in aircraft applications.[58]Due to its high corrosion resistance tosea water, titanium is used to make propeller shafts and rigging and in theheat exchangersofdesalination plants;[3]in heater-chillers for salt wateraquariums, fishing line and leader, and for divers' knives. Titanium is used to manufacture the housings and other components of ocean-deployed surveillance and monitoring devices for scientific and military use. The formerSoviet Uniondeveloped techniques for makingsubmarineswith hulls of titanium alloys.[59]Techniques were developed in the Soviet Union to forge titanium in huge vacuum tubes.[55]Industrial[edit]

High-purity (99.999%) titanium with visiblecrystallitesWelded 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 downhole andnickelhydrometallurgyapplications due to their high strength (e. g.: titanium Beta C alloy), corrosion resistance, or combination of both. Thepulp and paperindustry uses titanium in process equipment exposed to corrosive media such as sodium hypochlorite or wet chlorine gas (in the bleachery).[60]Other applications include:ultrasonic welding,wave soldering,[61]andsputteringtargets.[62]Titanium tetrachloride(TiCl4), a colorless liquid, is important as an intermediate in the process of making TiO2and is also used to produce theZiegler-Nattacatalyst, and is used to iridizeglassand because it fumes strongly in moist air it is also used to make smoke screens.[9]Consumer and architectural[edit]Titanium metal is used in automotive applications, particularly in automobile or motorcycle racing, where weight reduction is critical while maintaining high strength and rigidity.[63]The metal is generally too expensive to make it marketable to the general consumer market, other than high-end products, particularly for the racing/performance market. Late modelCorvetteshave been available with titanium exhausts.[64]Titanium is used in many sporting goods:tennis rackets,golf clubs,lacrossestick shafts;cricket, hockey, lacrosse, and football helmet grills; andbicycleframes and components. Although not a mainstream material for bicycle production, titanium bikes have been used by race teams andadventure cyclists.[65]Titanium alloys are also used inspectacleframes.[66]This results in a rather expensive, but highly durable and long lasting frame which is light in weight and causes no skin allergies. Manybackpackersuse titanium equipment, including cookware, eating utensils, lanterns, and tent stakes.[66]Though slightly more expensive than traditional steel or aluminium alternatives, these titanium products can be significantly lighter without compromising strength. Titanium is also favored for use byfarriers, since it is lighter and more durable than steel when formed intohorseshoes.[66]Titanium has occasionally been used in architectural applications: the 40 m (131foot) memorial toYuri Gagarin, the first man to travel in space, inMoscow, is made of titanium for the metal's attractive color and association with rocketry.[67]TheGuggenheim Museum Bilbaoand theCerritos Millennium Librarywere the first buildings in Europe and North America, respectively, to be sheathed in titanium panels.[56]Other construction uses of titanium sheathing include the Frederic C. Hamilton Building inDenver,Colorado[68]and the 107 m (350foot)Monument to the Conquerors of SpaceinMoscow.[69]Because of its superior strength and light weight when compared to other metals traditionally used in firearms (steel,stainless steel, and aluminium), and advances in metalworking techniques, the use of titanium has become more widespread in the manufacture of firearms. Primary uses includepistolframes andrevolvercylinders. For these same reasons, it is also used in the body of laptop computers (for example, inApple's PowerBook line).[70]Some upmarket categories of tools made to be lightweight and corrosion-resistant, such as shovels and flashlights, are made of titanium or titanium alloys as well.Jewelry[edit]Because of its durability, titanium has become more popular for designer jewelry (particularly,titanium rings).[66]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 alsoalloyed with goldto produce an alloy that can be marketed as24-caratgold, as the 1% of alloyed Ti is insufficient to require a lesser mark. The resulting alloy is roughly the hardness of 14-carat gold and thus is more durable than a pure 24-carat gold item would be.[71]Titanium's durability, light weight, dent- and corrosion resistance makes it useful in the production ofwatchcases.[66]Some artists work with titanium to produce artworks such as sculptures, decorative objects and furniture.[72]The inertness and ability to be attractively colored makes titanium a popular metal for use inbody piercing.[73]Titanium may beanodizedto produce various colors, which varies the thickness of the surface oxide layer and causesinterference fringes.[74]Medical[edit]Because it isbiocompatible(it is non-toxic and is not rejected by the body), titanium is used in a gamut of medical applications including surgical implements and implants, such as hip balls and sockets (joint replacement) that can stay in place for up to 20 years.[29]The titanium is often alloyed with about 4% aluminium[75]or 6% Al and 4% vanadium.Titanium has the inherent ability toosseointegrate, enabling use indental implantsthat can remain in place for over 30 years. This property is also useful fororthopedic implantapplications.[29]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.[76]Since titanium is non-ferromagnetic, patients with titanium implants can be safely examined withmagnetic resonance imaging(convenient for long-term implants). Preparing titanium for implantation in the body involves subjecting it to a high-temperatureplasmaarc which removes the surface atoms, exposing fresh titanium that is instantly oxidized.[29]Titanium is also used for thesurgical instrumentsused inimage-guided surgery, as well as wheelchairs, crutches, and any other products where high strength and low weight are desirable.