Titanium

Titanium is a chemical element with the symbol Ti and atomic number 22 with the Group of 4.Titanium is a lustrous, white metal when pure. Titanium minerals are quite common. The metal has a low density, good strength, is easily fabricated, and has excellent corrosion resistance. The metal burns in air and is the only element that burns in nitrogen. It is marvellous in fireworks.
Titanium is resistant to dilute sulphuric and hydrochloric acid, most organic acids, damp chlorine gas, and chloride solutions. Titanium metal is considered to be physiologically inert.
Titanium is present in meteorites and in the sun. Some lunar rocks contain high concentrations of the dioxide, TiO2. Titanium oxide bands are prominent in the spectra of M-type stars.

Basic information about and classifications of titanium.
   *Name: Titanium
   *Symbol: Ti
   *Atomic number: 22
   *Atomic weight: 47.867 (1)
   *Standard state: solid at 298 K
   *CAS Registry ID: 7440-32-6 Group in periodic table: 4
   *Group name: (none)
   *Period in periodic table: 4
   *Block in periodic table: d-block
   *Colour: silvery metallic
   *Classification: Metallic

   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 and gall if sharp tools and proper cooling methods are not used. Like those made from steel, titanium structures have a fatigue limit which guarantees longevity in some applications. Titanium alloys have lower specific stiffnesses than in many other structural materials such as aluminium alloys and carbon fiber.

   The metal is a dimorphic allotrope whose hexagonal alpha form changes into a body-centered cubic (lattice) β form at 882 °C (1,620 °F).The specific heat of the alpha 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.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 acoustic phonon of the β phase causing collapse of (111) planes of atoms.

       Titanium was discovered by William Gregor at 1791 in England. Origin of name: named after the "Titans", (the sons of the Earth goddess in Greek mythology).
Titanium was discovered by the Reverend William Gregor in 1791, who was interested in minerals. He recognized the presence of a new element, now known as titanium, in menachanite, a mineral named after Menaccan in Cornwall (England). Several years later, the element was rediscovered in the ore rutile by a German chemist, Klaproth.

The pure elemental metal was not made until 1910 by Matthew A. Hunter, who heated TiCl4 together with sodium in a steel bomb at 700-800°C.

Compounds:
The +4 oxidation state dominates titanium chemistry,but compounds in the +3 oxidation state are also common.Because of this high oxidation state, many titanium compounds have a high degree of covalent bonding.

Star sapphires and rubies get their asterism from the titanium dioxide impurities present in them.Titanates are compounds made with titanium dioxide. Barium titanate has piezoelectric properties, thus making it possible to use it as a transducer in the interconversion of sound and electricity.Esters of titanium are formed by the reaction of alcohols and titanium tetrachloride and are used to waterproof fabrics.

Titanium nitride (TiN), having a hardness equivalent to sapphire and carborundum (9.0 on the Mohs Scale), is often used to coat cutting tools, such as drill bits.It also finds use as a gold-colored decorative finish, and as a barrier metal in semiconductor fabrication.

Titanium tetrachloride (titanium(IV) chloride, TiCl4) is a colorless liquid which is used as an intermediate in the manufacture of titanium dioxide for paint.It is widely used in organic chemistry as a Lewis acid, for example in the Mukaiyama aldol condensation.Titanium also forms a lower chloride, titanium(III) chloride (TiCl3), which is used as a reducing agent.

Titanocene dichloride is an important catalyst for carbon-carbon bond formation. Titanium isopropoxide is used for Sharpless epoxidation. Other compounds include titanium bromide (used in metallurgy, superalloys, and high-temperature electrical wiring and coatings) and titanium carbide (found in high-temperature cutting tools and coatings).

Isolation:

      Isolation: titanium is readily available from commercial sources so preparation in the laboratory is not normally required. In industry, reduction of ores with carbon is not a useful option as intractable carbides are produced. The Kroll method is used on large scales and involves the action of chlorine and carbon upon ilmenite (TiFeO3) or rutile (TiO2). The resultant titanium tetrachloride, TiCl4, is separated from the iron trichloride, FeCl3, by fractional distillation. Finally TiCl4 is reduced to metallic titanium by reduction with magnesium, Mg. Air is excluded so as to prevent contamination of the product with oxygen or nitrogen.

                         2TiFeO3 + 7Cl2 + 6C (900°C) → 2TiCl4 + 2FeCl3 + 6CO
                           
                                         TiCl4 + 2Mg (1100°C) → 2MgCl2 + Ti

Excess magensium and magneium dichloride is removed from the product bytreatment with water and hydrochloric acid to leave a titanium "sponge". This can be melted under a helium or argon atmosphere to allow casting as bars.

Titanium Orbital Properties:

Ground state Electron Configuration:  [Ar].3d2.4s2
Shell structure: 2.8.10.2
Term symbol: 3F2
Pauling electronegativity: 1.54 (Pauling units)
First ionisation energy: 658.8 kJ mol-1
Second ionisation energy: 1309.8 kJ mol-1

Production & Frabrication:

                The processing of titanium metal occurs in 4 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.

Because the metal reacts with oxygen at high temperatures it cannot be produced by reduction of its dioxide.Titanium metal is therefore produced commercially by the Kroll process, a complex and expensive batch process. (The relatively high market value of titanium is mainly due to its processing, which sacrifices another expensive metal, magnesium.) In the Kroll process, the oxide is first converted to chloride through carbochlorination, whereby chlorine gas is passed over red-hot rutile or ilmenite in the presence of carbon to make TiCl4. This is condensed and purified by fractional distillation and then reduced with 800 °C molten magnesium in an argon atmosphere.

A more recently developed method, the FFC Cambridge process,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 the aerospace industry and the luxury goods market, and could be seen in many products currently manufactured using aluminium and specialist grades of steel.

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.

                  2 FeTiO3 + 7 Cl2 + 6 C → 2 TiCl4 + 2 FeCl3 + 6 CO (900 °C)
                                 TiCl4 + 2 Mg → 2 MgCl2 + Ti (1100 °C)

About 50 grades of titanium and titanium alloys are designated and currently used, although only a couple of dozen are readily available commercially.The ASTM International recognizes 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 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 (highest tensile strength with an oxygen content of 0.40%).The remaining grades are alloys, each designed for specific purposes, be it ductility, strength, hardness, electrical resistivity, creep resistance, resistance to corrosion from specific media, or a combination thereof.

The grades covered 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.

In terms of fabrication, all welding of titanium must be done in an inert atmosphere of argon or helium in order to shield it from contamination with atmospheric gases such as oxygen, nitrogen, or hydrogen. Contamination will cause a variety of conditions, such as embrittlement, 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.Titanium cannot be soldered without first pre-plating it in a metal that is solderable.The metal can be machined using the same equipment and via the same processes as stainless steel.

Titanium Properties:

           The atomic weight of titanium is 47.88. Titanium is lightweight, strong, corrosion resistant and abundant in nature. Titanium and its alloys possess tensile strengths from 30,000 psi to 200,000 psi (210-1380 MPa), which are equivalent to the strengths found in most of alloy steels.

Titanium is a low-density element (approximately 60% of the density of iron) that can be strengthened by alloying and deformation processing. Titanium is nonmagnetic and has good heat-transfer properties. Its coefficient of thermal expansion is somewhat lower than that of steels and less than half that of aluminum.

One of titanium’s useful properties is a high melting point of 3135°F (1725°C). This melting point is approximately 400°F above the melting point of steel and approximately 2000°F above that of aluminum.

Titanium can be passivated, and thereby exhibit a high degree of immunity to attack by most mineral acids and chlorides. Titanium is nontoxic and generally biologically compatible with human tissues and bones. The excellent corrosion resistance and biocompatibility coupled with strength make titanium and its alloys useful in chemical and petrochemical applications, marine environments, and biomaterial applications.

Titanium is not a good conductor of electricity. If the conductivity of copper is considered to be 100%, titanium would have a conductivity of 3.1%. From this it follows that titanium would not be used where good conductivity is a prime factor. For comparison, stainless steel has a conductivity of 3.5% and aluminum has a conductivity of 30%.

Electrical resistance is the opposition a material presents to the flow of electrons. Since titanium is a poor conductor, it follows that it is a fair resistor.


Applications:
  *Titanium alloys are used in aircraft (including helicopters), armor plating, naval ships, spacecraft and               missiles. Titanium alloys do not fatigue easily, are strong and are resistant to corrosion so they are perfect       for use in the above items.
  *Most titanium is converted to titanium oxide. This is the white pigment found in toothpaste, paint, paper         and some plastics. Cement and gemstones also contain titanium oxide. Fishing rods and golf clubs are also     made stronger through the use of titanium oxide.
  *Heat exchangers in desalination plants (which turn sea water into drinking water) are made from titanium        as it is resistant to corrosion in sea water.
  *Body piercings are generally made out of titanium. Titanium is perfect for this as it is easily colored and is       inert (will not react with other things).
  *Surgical instruments, wheelchairs and crutches are all made out of titanium for high strength and low               weight!
  *Dental implants are made with titanium. People with titanium dental implants can still go in an MRI                  machine!
  *Hip balls and joint replacements are made out of titanium and they can stay in place for around 20 years.
  *Many firearms (guns) are made from titanium as it is strong and lightweight.
  *The body of a laptop is often made from titanium.
  *Titanium is occasionally used in buildings.
Football helmet grills, tennis rackets, cricket helmets and bicycle frames are all made from titanium.



                                                                 Published by Ravindra.K(Mechanical Engineering)