Titanium is a chemical element in group 4 of the periodic table with the symbol “Ti”. A silver-grey metal with the atomic number 22 and the atomic weight 47.867, Titanium is light-weight, strong and corrosive-resistant.
Titanium has a strength similar to steel, although less dense, and is often used as an alloy form in the aeronautical and aerospace industry on aircraft and rockets because it can endure extreme temperatures.
The common use of titanium is in the form of Titanium Dioxide (TiO2), which is used as a bright white pigment in paints, enamels, papers and art materials. Titanium Dioxide increases the whiteness, reflectivity and opaqueness of paints and enamels.
Manufacturers combine a specific ratio of titanium mixed with other metals such as aluminium, iron and molybdenum to make titanium alloys for enhanced properties. ASTM international’s grading classification for titanium alloys ranges from grade 1 being the softest and most ductile, to grade 38 being extremely hard with a very high tensile strength.
Titanium is the 9th most abundant element found in the Earth’s crust, constituting 0.44% of the total crust. Two common minerals through which titanium is extracted are ilmenite and rutile.
Properties of Titanium
Along with strength and high corrosion resistance, titanium possesses various other qualities.
• Titanium melting point is 1668°C.
• On the Mohs scale of hardness it is 6.5
• It has a boiling point of 3287°C.
• Titanium has a density of 4.54 g/cm³.
• The transformation temperature for changing phase is 882°C.
• The atomic weight of titanium is 47.88.
• The percentage of titanium metal in the Earth’s crust is 0.44%.
• The strength of titanium is twice that of steel and three times that of aluminium.
• There are 26 recognised isotopes of titanium. Ti-48 is the most commonly found.
• Titanium is light-weight
• Titanium has outstanding resistance against corrosion, especially against seawater and salt water.
• It has low thermal expansion and there is only minor dimension alteration when exposed to heat.
• It is flexible in nature and the modulus of elasticity is 116 GPa.
• Its tensile strength has a value of 220 MPa.
• The value of shear modulus is 43.0 GPa.
• The hardness level of titanium on the Vickers scale is 60.
• The Poisson’s ratio is 0.34
• Titanium’s thermal conductivity value is 17 W/mK.
Applications of Titanium
Titanium is used in various fields where high tensile strength, durability, fuel efficiency and corrosion resistance are required. Some properties are similar to that of steel and aluminium. It is lightweight compared to steel but has the same strength. In comparison with aluminium, titanium is heavier and stronger.
Use of Titanium in the Aerospace Industry
Titanium alloys are widely used in the aerospace industry in rotors, compression blades, hydraulic system parts, landing gear, missiles, aircraft exhaust vents and naval ships.
The grade 5 platinum alloy (Ti-6Al-4V) constitutes 50% of titanium use in aircraft, from engines to window frames. It is made up of 6% Aluminium and 4% Vanadium.
Its major characteristics include corrosion resistance, heat tolerance, light-weightiness and strength. It is called the “workhouse” of titanium alloys. Its major applications are:
• Jet engine rotating parts. Titanium-made fan blades increase efficiency and reduce noise.
• Airframe manufacture to reduce weight and increase performance.
Use of Titanium in the Biomedical Field
Grade 23 titanium alloy (Ti-6Al-4V ELI) is also called surgical titanium, because of its biocompatible nature. It is widely used in medical sciences as a body implant because it is not harmful to the human body and has great inertness. Because of its flexibility, it can be moulded into coils, wires, strands and tubes. Its basic properties are high corrosion resistance, high strength, low modulus, flexibility, light-weightiness and excellent strength.
Some of the uses of titanium alloys in the biomedical industry are as follows:
- Orthopaedic surgeons use titanium alloys for artificial hip and knee joints, bone plates, screws for fixing fractures, cardiac prostheses and pacemakers.
- In dentistry, pure titanium grades and a titanium alloy (grade 5) are used for dental implants, crowns, bridges, dentures and screws to implant prostheses.
- Titanium coatings are used to enhance the performance of medical devices, and to reduce wear and damage.
- Medical components such as surgical tweezers, forceps, scissors, needles, pins, rods and implantation plates are nowadays made up of titanium.
Use of Titanium in the Jewellery Industry
Due to its lightweight and less dense properties, titanium is considered a comfortable metal with respect to wearability.
Titanium is hypoallergenic and resistant to corrosion, therefore titanium rings can be worn by people with allergies to other metals, hence its popularity for piercings and body jewellery.
Titanium has become very fashionable for men’s wedding bands, in particular black titanium wedding rings.
Titanium wristwatches from brands such as Seiko, Farer, Tissot, Breitling, Longines, and the Titanium Apple Watch 6 are highly sought after due to the metal’s advantageous properties.
Black titanium is created using a specific grade of Titanium which when heated produces a black coating. However, over time this black coating will scratch off.
Contrary to popular belief, titanium rings can be easily cut off with a ring cutter in a hospital emergency.
What kind of Titanium is used in Jewellery?
The alloys used in titanium jewellery constitute 6% Aluminium, 4% Vanadium, 0.25% iron and 0.2% oxygen along with titanium. These alloys are stronger than pure titanium.
Advantages of Titanium Jewellery
- Cheaper than gold and platinum, as both are rare elements, whereas titanium is found in abundance.
- It will not tarnish
- It is very light
- Can be coloured electrolytically, a process known as anodising. This is often seen with body jewellery for piercings.
Disadvantages of Titanium Jewellery
- So strong that rings are difficult to resize or adjust.
- Due to this jewellers find it a hard metal to deal with and therefore the cost of labour may be high.
- Over time it may dull or leave a satin patina.
- Black titanium rings will not stay black forever, the coating will scratch off.
Working with Titanium for Jewellery Making
Manipulating Titanium to make jewellery with is labour-intensive and quite hard, and therefore most jewellers will work with sheets, rods or tubes in their original state as they cannot be cast or soldered.
- Titanium can be cut with saw blades, but make sure to always use beeswax or some form of lubricant.
- Titanium can be filed using regular Vallorbe steel files, but clean these regularly to avoid the teeth becoming clogged.
- Titanium can be drilled using tungsten carbide drill bits at high speeds
- Titanium can be carved using tungsten carbide burrs, a popular choice for leaving iridescent marks after anodising.
Polishing Titanium Jewellery
On the Mohs scale of hardness, it is 6.5 so Titanium jewellery will scratch, and will eventually leave a satin finish, but this can be very easily polished.
Polishers used for similar hard white metals such as Platinum are also used for polishing titanium. These are often impregnated with a diamond abrasive or a ceramic bond.
- Diapol diamond polishers: diamond impregnated. Unmounted in various shapes and sizes
- Diatwist Single: diamond grit radial polishing twist discs
- Diamond Polishing Paste: paste in ready-to-use syringes in various micron sizes
- Rubber Silicone Polishers: ceramic bonded abrasives mounted, in various shapes and sizes
- Dialux Polishing Compounds: Green/Vert and Grey/Gris blocks
- Diamond abrasive polishing cloths: can be cut and glued or used as is
- Airflex Heat-free polishing wheels: cool-running open pore abrasives
- EVE Chrom Plus: Silicone carbide abrasives.
- Green Soft Wheels: Use the green soft wheel as a final polish after the EVE Chrom Plus.
Use of Titanium in the Electronic Industry
- Titanium hybrid circuit boards are more efficient than traditional circuit boards.
- Titanium circuits are used in a variety of applications for flow measurement, fluid pressure and temperature measurement.
- Widely used in hard disk drives.
Aluminium was previously used in electronics but it is now replaced by titanium because of its huge advantages. It minimises the interference in data processing, has the ability to endure heat during the coating process and the purity of titanium increases the disk capacity.
Use of Titanium in the Automotive Industry
The use of titanium in the automobile industry has grown exponentially since the abundance of racing car markets and franchises have increased. Because of its properties such as corrosion resistance, durability, strength, flexibility and titanium melting point, titanium became a choice metal, mainly for use in engine parts of vehicles.
• Connecting rods
• Valves and valve retainers
• Wrist pins
• Rocker arms
• Exhaust systems
• Bodywork frames
Other Titanium Applications
• Titanium thin wall tubing In power plants
• Chemical processing industries use titanium to increase equipment life.
• Titanium pipes are used in the petroleum industry.
• Because of its strength and high ballistic ratio, titanium is used for the use of making armour.
• Eyeglass frames
• Fishing rods
• Sports equipment: golf clubs, tennis rackets, skis, snooker and pool cue shafts, baseball bats.
• Outdoor gear: Walking poles and Ice Picks
• Motorsports and bicycles.
• Titanium Dioxide contains bright white pigment and reflective properties -frequently in paints, paper plastics, rubbers, the textile industry, and ceramics.
Advantages and Disadvantages of Titanium
Like all other metals and chemical elements, titanium has some advantages and disadvantages.
- The most common advantage of titanium is its strength. It is one of the strongest and most durable metals on Earth. It has the highest strength-to-density ratio in the periodic table.
- Does Titanium Rust? Titanium has a natural resistance against corrosion and rust even in hard water and harsh weather. Unlike other metals, titanium doesn’t oxidise and holds its position for years.
- Titanium metal is very difficult to cast, because of its toughness and strength and titanium melting point.
- Titanium is usually expensive as compared to other types of metals like steel, aluminium and iron, as titanium is rarer than these metals.
- High-cost machinery is required to process.
Titanium is obtained through several ores residing in the Earth’s crust such as rutile, ilmenite and Leucoxene, using the open pit method.
Workable titanium deposits are spread worldwide, mainly in Australia, the United States, Canada, South Africa, Sierra Leone, Ukraine, Malaysia, Russia, Norway and many other regions on the globe.
Common mineral rutile contains 95% Titanium Dioxide, ilmenite contains 50 to 60% TiO2 and Leucoxene contains some iron deposits.
Titanium minerals form in alluvial and volcanic formations. Rutile mineral deposits are depleting and hard to find, so ilmenite deposits are often mined.
Production of Titanium
Titanium metal from raw minerals, is produced through the Kroll process. This technology is globally used to extract titanium from ores. This process includes many steps such as extraction, purification, sponge production, alloy formation and shaping.
At the manufacturing site, mineral ores like rutile and ilmenite are processed. Rutile can be used naturally, whereas ilmenite is processed to remove iron and obtain 85% titanium dioxide. As a result of a chemical reaction, impure titanium tetrachloride (TiCl4) and carbon monoxide (CO) are obtained.
The obtained metal is put into distillation tanks and heated to remove impurities, using fractional distillation and precipitation. Metal chlorides of iron, silicon, vanadium and magnesium are separated from the concentrate.
Purified Titanium tetrachloride is shifted into a stainless-steel vessel reactor. After adding magnesium, the vessel is heated at about 1,100°C. To remove air and prevent contamination with oxygen and chlorine, Argon is pumped inside. As a result, liquid magnesium chloride and pure titanium solid are obtained.
Through boring, titanium solid is taken out from the reactor and then reacted with water and hydrochloric acid to remove excess magnesium chloride remains. The remaining element is in the form of a porous metal called sponge.
To make an alloy, pure titanium metal is mixed with various elements and scrap metals. The used ratio of sponge to alloys is determined in the laboratory before the procedure is done. After mixing, everything is pressed into a disc-like form and welded together to create a titanium electrode.
The electrode is then put into a vacuum arc furnace, where it is melted. In this copper container, an arc is used to melt the sponge and form it into an ingot. All of the extra air is removed from the container using argon. The ingot is then reheated and melted a couple of times to create a commercially acceptable ingot and shipped to goods manufacturers where it is crushed and formed.
Recycling of by-products
During pure titanium manufacturing, magnesium chloride is obtained, which is recycled in a recycling cell just after it is produced. In this cell, firstly, magnesium metal is separated out and then chlorine gas is produced. Both of these are reused in the production of titanium.
Global Titanium Reserves
Ilmenite and rutile are the two most important sources of titanium. According to the United States Geological Survey (USGS), ilmenite constitutes 92% of the global titanium. The total reserves of titanium all over the world are 750 million tons.
China has 20 million tonnes of reserves, which is almost 29% of the world's total, and is the leading country in ilmenite mineral production. Australia accounts for 24 million tonnes of rutile reserves, which is 50% of the total world’s reserves. It is the leading country having rutile minerals in abundance.
The leading countries having titanium minerals were South Africa, Australia, the US, China, Canada and India.
History of Titanium
In 1791, a geologist named William Gregor discovered an unknown mineral whilst studying black sand in Cornwall, then in 1795, a chemist named Martin Heinrich Klaproth from Germany, rediscovered it in the element rutile, in Hungary. He understood that the mineral contained the oxide of the previously discovered mineral in 1791 and named it “Titanium” after the “Titans” from Greek mythology.
Pure titanium metal was first invented by Matthew A. Hunter in 1910, by heating Titanium Tetrachloride (TiCl4) with sodium under high temperature. This was then known as the Hunter process.
In 1932, William Justin Kroll reduced Titanium Tetrachloride with calcium, magnesium and sodium and named this method the Kroll process.
Then in 1960, titanium metal was used in the Cold War by the Soviet Union for military and submarine components. After that, titanium and titanium alloys have been widely used for many purposes throughout the world.
Types of Titanium Alloys
Titanium is present in two types of crystallographic forms. Pure titanium or unalloyed titanium, at room temperature, has a hexagonal closed-packed crystal type form known as the alpha (α) phase. When the same crystal is heated up to 883°C, it transforms into a body-centred cubic structure called the beta (β) phase. The experimentation of these crystallographic structures by adding different alloys in a thermochemical process led to the production of various alloys with different properties. The major classification of titanium alloys based on their phases are α alloys, β alloys and α +β alloys.
Alpha alloys contain metals such as aluminium and tin. These metals have α-stabilizing agents that perform their duty by inhibiting change at the phase transition temperature.
Alpha alloys have a higher creep resistance than beta alloys and are therefore preferable to be used in high-temperature appliances and machinery. Unlike beta alloys, alpha alloys miss the ductile-to-brittle phase, making them ideal for cryogenic applications.
The properties of alpha alloys include intermediate strength, toughness and weldability. Alpha alloys cannot be strengthened by heating.
Alpha Beta Alloys
Alpha and beta alloys are composed of a mixture of alpha and beta phases, having 10-50% of the beta phase achieved at room temperature. The most common alpha-beta alloy is Ti-6Al-4V, which is difficult to form even in forged conditions. Other alpha-beta alloys usually have good formability. The general characteristics of these alloys can be controlled through heat treatment that is used for identifying and adjusting the amount of beta phase present in them. The process involves using a solution treatment and heating it up to 480-650°C, tempering thus the alpha crystal, alpha and beta mixing with each other properly.
The third class is beta alloys. When transition or β-stabilizing elements are added to titanium, all types of beta alloys can be manufactured. These elements contain vanadium, niobium and molybdenum. These elements decrease the transition temperature of α to β phase, thus producing a body-centred cubic (bcc) β phase. They tend to show outstanding forgeability on a wider range of forge temperatures, as compared to α alloys.
Some useful properties of beta alloys are their hardenability and readiness for high temperatures. Beta alloys are more cold workable than the alpha-beta alloys, and can be strengthened through heat.
Some β alloys have powerful corrosion resistance to commercially pure grades. Common thermal treatment includes solution treatment along with heating at temperatures of 450°C to 650°C. Finely spread α particles are obtained in the retained β particles, through this treatment.
This major classification is further divided into ASTM International grades. Pure titanium grades are 1, 2, 3 and 4. Titanium alloys are graded 5, 7, 11, 12 and 23. Grade 5 titanium or Ti-6AL-4V is the most frequently used alloy all over the world due to its many benefits. It is widely used in the aerospace and automotive industries, medical sciences and chemical processing factories.
Titanium is a metal having outstanding properties with many applications. The use of titanium as a substitute for aluminium, steel or iron is unlikely due to cost, the high energy consumption and the high-cost machinery to process it. Because of these disadvantages, titanium cannot be considered as a future substitute metal, but where high strength, corrosion-resistant and flexible metal are required, Titanium will continue to be desirable.