The Titanium Age: From Dream Metal to Practical Metal
With numerous kinds of metal being used in a multitude of applications, metal has become something people cannot live without.
Here, we will delve into the wonderful world of a specific kind of metal, the titanium.
History of Titanium
Man’s history with metal begins with the use of copper approximately 6000 years ago. Iron came into the fold about 4000 years ago, and aluminum entered the scene about 100 years from now. Titanium came a lot later, about 60 years ago.
In 1790, a British mineralogist named William Gregor discovered titanium when he was examining black sand from a stream nearby, and found an unidentifiable metallic oxide. But although Gregor is credited with the discovery, it was the German chemist by the name of Martin Heinrich Klaproth who gave the mysterious new chemical element its name, named after the Titans of Greek mythology.
It was difficult to produce titanium metal from the ore since it cannot be simply reduced using carbon. Although a number of chemists tried different methods, it wasn’t until about 100 years later in 1910 that a metallurgist named Matthew Hunter found a way to produce 99.9% pure titanium metal. His method, now known as Hunter Process, involved reducing titanium(IV) chloride (TiCl4) with sodium (Na). Then in 1946, Luxembourgish metallurgist William Justin Kroll successfully produced even purer titanium by reducing TiCl4 with magnesium in a method now called Kroll Process, which is the standard method of commercial titanium production today.
Characteristics of Titanium
Titanium is recognized for its lightness, high corrosion resistance and high strength-to-weight ratio. Compare titanium’s specific gravity (4.51) to carbon steel (7.9) and copper (8.9) and the difference is obvious. Strength-to-weight ratio is 6 times that of aluminum and twice that of carbon steel.
Additionally, titanium is harmless and biocompatible, non-magnetic, heat resistant and has high designability.
One misconception that people often have is that titanium is an all purpose metal. Titanium does have weaknesses, such as its high cost in production, low abrasion resistance and low heat / electrical conductivity.
The cost is especially an important factor. That is why The Japan Titanium Society continues research and development in finding new and better ways to produce titanium.
Applications of Titanium
Titanium is applied in a myriad of industries. At power and chemical plants, titanium is used in seawater desalination systems, condensers, turbine blades, desulfurization devices, heat exchangers, reaction tanks, piping, electrodes and tank trucks. In aerospace industries, it is used in aircrafts, engine components, rocket parts and fuel tanks. In automobiles, engine components and mufflers are often titanium. In architecture, titanium can be found being used in roofs, walls and floors of buildings, as well as monuments, bridge wires and handrails. In offshore engineering, boats, seismographs and riser pipes; in semiconductors, steppers, cooling plates and frames; in the medical field, artificial bones, root canals, heart valves, cardiac pacemakers, stent catheter and artery clips; in the food industry, heat exchangers and electrodes in food processors and water purifiers. Also sporting goods like golf clubs, tennis rackets, skis, bicycles, mountaineering and fencing equipment, as well as everyday goods like eyeglass frames, watches, digital cameras, cell phones, and kitchen wares use titanium materials. Titanium is also seen as an important factor in future renewable energy technologies such as tidal, geothermal power generation and ocean thermal energy conversion.
Amount of Titanium in Use
– Boeing 777: approx. 60t to 70t per aircraft
– Boeing 787: approx. 100t per aircraft
– 100 MW PWR nuclear power plant: approx. 200 to 250t
– 130,000t/day MSF seawater desalination plant: Approx. 1500t
– 100,000t/day Terephthalic acid plant: approx. 30 to 50t
Titanium is the fourth most abundant metallic element in the Earth’s crust after aluminium (Al), iron (Fe), and magnesium (Mg). There are two primary ores from which titanium is extracted from: Rutile, mostly consisting of titanium dioxide, and Ilmenite, which is a titanium-iron oxide mineral.
The ores are not found in Japan, and are primarily imported from countries like Australia, Canada and India. Titanium exists in the Earth’s crust as titanium dioxide (Ti02) and is reduced with magnesium in the Kroll process. Titanium produced from this method resembles a “sponge,” which is why it is called as such. The sponge then gets melted, forged and rolled into mill products.
1. From Ore to Titanium(IV) Chloride [TiO2＋2Cl2＋2C → TiCl4＋2CO]
The ore we use is usually rutile, which is heated with chlorine (Cl) and carbon (C) at a temperature of about 1000°C to 1100°C to produce the impure titanium(IV) chloride (TiCl4) as an intermediate. Because the temperature is so high, the impure titanium(IV) chloride is a gas, but is then cooled into a liquid. Pure titanium(IV) chloride is then separated by fractional distillation.
2. Reduced by Magnesium Into Sponge [TiCl4＋2Mg → Ti＋2MgCl2]
Liquid titanium(IV) chloride gets mixed in an argon gas atmosphere containing molten magnesium, which separates titanium and magnesium chloride and produces titanium sponge. The sponge gets crushed into pieces of 2 to 3 cm, which gets sealed in a barrel with argon gas. The magnesium chloride is separated into chlorine and magnesium, which is reused in the reduction process.
Titanium Mill Products
1. Making Ingots from Sponge
The 2 to 3 cm pieces of sponge gets compressed into compacts of 20 to 40 cm sizes. Then the compacts get gathered and welded into a rod, which gets thrown into a Vacuum Arc Remelting (VAR) furnace to cast into an ingot. In an Electron Beam Melting (EB) furnace, scraps of titanium can be recycled to make an ingot.
2. Ingots Processed into Mill Products
Ingots then get slabbed, forged and rolled into billets and slabs. Billets are further processed into wires, bars, mold materials or seamless pipes, while slabs get turned into plates, sheets, welded tubes, and rolled coils. This processing of slabs into mill products is the same as processing stainless steel.
Then the mill products like the bars and plates get turned into eyeglass frames, watches or golf clubs that we all use in our daily lives.
Titanium and Titanium Alloy Charts
|Type||Heat Treatment||Tensile Strength (Mpa)||0.2% Proof Stress (Mpa)||Stretch (%)||Features||Related Standards|
|JIS Gr. 1||Annealing||270～410||165～||27～||Formability||ASTM G1|
|JIS Gr. 2||Annealing||340～510||215～||23～||Versatile,
|JIS Gr. 3||Annealing||480～620||345～||18～||Moderate Strength||ASTM G3、AMS4900|
|JIS Gr. 4||Annealing||550～750||485～||15～||High Strength||ASTM G4、AMS4901、4921|