What is Titanium? – Its Alloys, Grades, and Properties

What is Titanium?

Titanium, with the symbol Ti and atomic number 22, is a chemical element or light silvery metal in Group 4 (IVB) of the periodic chart. It has a high melting point, tensile strength, and thermal and electrical conductivity qualities.

Although minor amounts of titanium are present in practically every rock, it is not found in considerable deposits. Titanium is a lustrous grey metal with high strength and low corrosion rate utilized in various applications. Titanium is employed in 80 percent of aerospace applications, while the remaining 20 percent is used in armor, medical hardware, and consumer items.

Titanium’s resistance to corrosion by water and chemical media is very impressive. This resistance is due to a thin coating of titanium dioxide (TiO₂) that accumulates on its surface, making these materials extremely difficult to penetrate.

Titanium has a low elasticity modulus. It means that titanium is extremely flexible and can be bent back into its original shape. Many current applications require memory alloys (alloys that can be bent while cold but return to their original shape when heated).

History of Titanium

After World War II, titanium metal in any form took off. Titanium was not separated as a metal until 1910 when American chemist Matthew Hunter created it by reducing titanium tetrachloride (TiCl4) with sodium (the Hunter technique).

Commercial manufacturing did not begin until the 1930s when William Justin Kroll demonstrated that titanium could be reduced from chloride using magnesium. To this day, the Kroll process is the most widely utilized commercial production method.

Titanium’s first major application was in military aircraft once a cost-effective manufacturing process was found. In the 1950s and 1960s, titanium alloys were used in Soviet and American military aircraft and submarines. Titanium alloys began to be employed by commercial aircraft builders in the early 1960s.

Swedish doctor, Per-Ingvar Branemark’s studies dating back to the 1950s showed that titanium triggers no negative immune response in humans, allowing the metal to integrate into our bodies in a process known as osseointegration.

Manufacturing Process of Titanium

A procedure known as the Kroll process is used to manufacture titanium metal. There are five stages to this process. The first stage is extraction, the second is purification, the third is sponge manufacture, the fourth is alloy creation, and the fifth is forming and shaping.

1. Extraction

The extraction of titanium ores is the first step in the Kroll process. Mines supply the titanium ores to the producer. Ilmenite, rutile, and other titanium minerals can be found in these ores. Rutile is most commonly used in its natural state.

On the other hand, Ilmenite requires processing, which is the first stage in removing the iron so that the residual portion contains 85 percent titanium dioxide. These ores are cooked to 900 °C in a fluidized bed reactor with chlorine and carbon.

The chemical reaction occurs, resulting in the formation of impure titanium tetrachloride and carbon monoxide as a by-product. Because titanium dioxide is not yet pure after removing iron, contaminants are present in TiCl4.

2. Purification

This process involves heating the TiCl₄ in a huge distillation tank. Fractional distillation and precipitation procedures separate the impurities present in this step. All contaminants, including vanadium, silicon, magnesium, zirconium, and iron, are removed using these two processes.

3. Sponge Formation

Sponge formation is the third stage of the Kroll process. The refined titanium tetrachloride is poured into a stainless-steel reactor vessel in liquid form at this stage. The magnesium is added to the vessel and heated to 1100 °C, where the magnesium reacts with chlorine to generate magnesium chloride.

Because there’s a risk that oxygen and nitrogen are present in the air, argon gas is injected into the vessel to eliminate it, preventing any oxygen and nitrogen reactions.

Because titanium has a far greater melting point than steel, the titanium left in the vessel is not pure and solid. This titanium solid is then bored out of the vessel and treated with a solution of water and hydrochloric acid. It is done to get rid of any extra magnesium or magnesium chloride. The titanium obtained at the end of this cycle is sponge form, hence the name sponge formation.

4. Alloy Creation

In a consumable-electrode arc furnace, the pure titanium sponge is combined with other alloys and scrap metals to make usable alloys in the fourth stage. The bulk is crushed and welded to form a sponge electrode after melting and mixing all needed metals in the required proportions.

This sponge electrode is melted in a vacuum arc furnace to prepare ingots. For economically acceptable ingots, these ingots are routinely melted several times.

5. Forming and Shaping:

The ingots are retrieved from the furnace, tested for flaws, and then sent out to be employed to produce titanium alloy items in the final stage of the Kroll process.

Welding, casting, forging, powder metallurgy, and other procedures shape the ingots into the finished product. The product’s specifications determine everything.

Compounds of Titanium

1. Titanium Oxide

Titanium oxide (TiO₂), the most important oxide, exists in three solid crystalline forms: rutile, anatase, and brookite. Rutile is the most frequently naturally occurring type, and it is used as a pigment in the chemical industry. Ti is coupled to six oxygen atoms octahedrally and destroys the octahedral environment in others. 

Ti₂O₃, a violet-colored Ti (III) oxide with a structural type comparable to –Al₂O₃. TiO is produced by heating TiO₂ with metallic titanium in a cubic crystalline form similar to sodium chloride. However, it is frequently non-stoichiometric, having one-sixth empty sites for both ions. It functions as a metal conductor.

2. Titanium Disulfide

Titanium disulfide (TiS₂) is the most important sulfide chemical, formed by sulfur atoms in a layer structure and used as an electrode in lithium battery development.

3. Halides

TiCl4, a colorless and volatile liquid, is the most common halide of titanium. Yellowish titanium tetrachloride is used in industry and tends to hydrolyze in the air, resulting in beautiful white clouds.

The extraction of titanium metal from its ores also uses titanium tetrachloride. Its purpose is to produce titanium dioxide, used in white paints. Lewis acids made of titanium halides are commonly used. 

The Van Arkel procedure produces titanium tetraiodide, TiI4, another titanium halide, as high purity titanium metal. Stable halides of titanium (III) and titanium (II) can also be formed. Titanium trichloride and titanium dichloride are two examples. These chemicals are employed in the manufacture of polyolefins as a catalyst. 

4. Organometallic Complexes

Titanocene-dichloride (C₅H₅)₂TiCl₂ is the most well-known organometallic compound of titanium. For polymerization catalysts, titanium organometallic complexes are extensively researched. Petasis reagent and Tebbe’s reagent are two other organometallic titanium complexes.

Alloys of Titanium

1. Alpha Alloys

In order to boost the hardness and tensile strength of commercially pure titanium, it is alloyed with small amounts of oxygen. A variety of economically pure titanium grades with strength values ranging from 290 to 740 MPa can be produced by modifying the amounts added. 

Although minor amounts of beta phase are possible if the impurity levels of beta stabilizers such as iron are significant, these materials are nominally completely alpha in structure. While the alpha alloys cannot be heat-treated to increase strength, adding 2.5 percent copper to titanium produces a material that responds to solution treatment and ageing in the same way that aluminum-copper alloys do.

2. Alpha-Beta Alloys

Vanadium, molybdenum, iron, and chromium stabilize the beta phase, and numerous alpha-beta alloys have been developed. These are typically medium to high-strength materials with tensile strengths between 620 and 1250 MPa and creep resistance between 350 and 400°C. Low and high cycle fatigue, as well as fracture toughness, is becoming increasingly significant design features. 

Thermomechanical and heat treatment techniques have been devised to ensure that the alloys give the best mechanical qualities for varied purposes. At temperatures exceeding 450°C, alloys near alpha are used for maximum creep resistance. They offer sufficient creep strength at temperatures up to 600°C.

 3. Beta Alloys

The other form of titanium material is beta alloys. All-beta alloys can be created when enough beta-stabilizing elements are added to titanium. These materials have been around for a long time, but their appeal has recently grown. They’re easier to harden than alpha-beta alloys, and some have superior corrosion resistance than commercially pure grades. 

There are international and national specifications for titanium materials used in aerospace, but none for materials used in non-aerospace applications. In this field, the ASTM collection of specifications is widely used.

Grades of Titanium

Grade 1

It is the most malleable and soft of these grades. It is the most formable, corrosion-resistant, and impact-resistant material available.

Grade 2

Because of its versatility and ubiquitous availability, Grade 2 titanium is the “workhorse” of the commercially pure titanium industry. It has many of the same properties as Grade 1 titanium but is slightly more durable. Both are resistant to corrosion.

Grade 3

It is the least common commercially pure titanium grade, yet that does not diminish its worth. Grade 3 is stronger than Grades 1 and 2, has similar flexibility, and is slightly less formable than its predecessors but has higher mechanical properties.

Grade 4

The most powerful of the four commercially pure titanium grades are Grade 4. It’s also noted for its high formability and weldability and remarkable corrosion resistance.

Grade 5

Grade 5 titanium, also known as Ti 6Al-4V, is the most widely used of all titanium alloys and is renowned as the “workhorse” of titanium alloys. It is responsible for 50% of all titanium consumption on the planet. The strength of Ti 6Al-4V can be increased through heat treatment. 

This alloy is desirable because of its great strength at a low weight, practical formability, and high corrosion resistance. Due to its adaptability, Ti 6AI-4V is the ideal alloy for application in various industries, including aerospace, medical, marine, and chemical processing.

Grade 7

Mechanically and physically, Grade 7 is equivalent to Grade 2. However, it is an alloy because it contains the interstitial element palladium. Grade 7 titanium alloy is the most corrosion-resistant, with excellent weldability and fabricability. The grade is used in chemical processes and industrial equipment components.

Grade 11

Grade 11 is almost identical to Grade 1, except that a small quantity of palladium has been added to improve corrosion resistance, converting it to an alloy. Other advantages include optimal ductility, cold formability, functional strength, impact toughness, and exceptional weldability.

Grade 12

The high-quality weldability of Grade 12 titanium earns it an “excellent” rating. It’s a tough alloy that can withstand extreme temperatures. Grade 12 titanium has the same characteristics as stainless steel from the 300 series. This alloy can be hot or cold formed using a press brake, hydro press, stretch, or the drop hammer method.

Grade 23

Grade 23, commonly known as Ti 6AL-4V ELI, is a pure Ti 6Al-4V. It’s possible to make coils, strands, wires, and flat wires. It’s the finest choice for any application requiring high strength, lightweight, excellent corrosion resistance, and high toughness. It is more damage-resistant than other alloys.

Ti 5Al-2.5Sn

Ti 5Al-2.5Sn is a non-heat treatable alloy with excellent welding and stability qualities. Temperature stability, strength, corrosion resistance, and creep resistance are excellent. Creep is a word that refers to the process of plastic straining over time at high temperatures.

Properties of Titanium

• At Standard Temperature and Pressure, it is found as solid.
• Titanium has a standard atomic weight of 47.867. 
• Titanium has a boiling point of 3287 °C. 
• It has a shiny silvery grey-white look. It has a melting point of 1668 °C. 
• The crystal structure is hexagonal and close-packed (hcp). 
• It has an electronegativity of 1.54 on the Pauling scale. 
• It is light in weight. It weighs 4.506 grams per cubic meter.
• It’s a beautiful transition metal with a lot of strength. 
• It is corrosion-resistant. Dilute sulfuric acid and hydrochloric acid do not damage it. 
• Among all metallic elements, it possesses the highest strength-to-density ratio.
• It has a lower electrical and thermal conductivity than other metals and is paramagnetic. 
• It is non-magnetic and ductile. 
• There are numerous isotopes in it. The isotopes ⁴⁶Ti, ⁴⁷Ti, ⁴⁸Ti, ⁴⁹Ti, and ⁵⁰Ti are stable and exist naturally. Although the most prevalent isotope of titanium, ⁴⁸Ti, is its main isotope
• Titanium interacts with oxygen in the air at a temperature of 1200 °C. 

                           Ti + O₂ 1200°C = TiO2 

• Water reaction – Titanium reacts relatively slowly with water.

                            Ti + 2H₂O = TiO₂ + 2H₂O 

• When exposed to pure nitrogen gas, titanium reacts with nitrogen to generate titanium nitride. The reaction takes place at 800 °C. 

                             2Ti + N2 = TiN

Uses of Titanium

• Titanium (IV) complexes were the first non-platinum compounds researched for cancer treatment in medicine due to their excellent efficiency and low biological toxicity.
• These alloys are employed in various chemical and industrial applications, including the storage of alkaline solutions, chlorine compounds, wet and other hostile chemicals, and the manufacture of rails, railway wheels, and excels.
• Manganese, chromium, iron, molybdenum, aluminum, vanadium, and tin alloys have lightweight and mechanical strength advantages. It is mostly employed in the aerospace and missile industries.
• Smelting or rutile with iron and coke in an electric furnace produces ferrotitanium, which is used as a scavenger in the steel industry to remove oxygen and nitrogen from steel.
• Because of its remarkable covering power, titanium oxide (TiO₂) is widely employed as a white pigment in chemistry. It is manufactured using the same method as metal extraction.

Conclusion

Titanium is a bright grey metal with high strength and low corrosion rate. Due to its high melting and boiling temperatures, it is a particularly useful metal for its refractory qualities. Oxides, sulfides, alkoxides, nitrides, carbides, and other titanium metal compounds exist.

Due to its exceptional strength, titanium metal and alloys are used in various industries, including medical, aerospace, and automotive. Some titanium compounds may have negative health and environmental consequences.

References:

1. The Properties, Characteristics and Uses of Titanium Metal. (2019, October 31). ThoughtCo; www.thoughtco.com. https://www.thoughtco.com/metal-profile-titanium-2340158
2. Pappas, S., & @Live Science. (2017, October 3). Facts About Titanium | Live Science. Livescience.Com; www.livescience.com. https://www.livescience.com/29103-titanium.html
3. Hong, K. (2021, January 5). “I am Titanium” | Element | Periodic Table | ChemTalk. ChemTalk; chemistrytalk.org. https://chemistrytalk.org/titanium-element/
4. titanium processing – Extraction and refining. (n.d.). Encyclopedia Britannica; www.britannica.com. Retrieved May 23, 2022, from https://www.britannica.com/technology/titanium-processing/Extraction-and-refining
5. Titanium Grades Information – Properties and Applications for all Titanium Alloys & Pure Grades – Supraalloys.com. (n.d.). Titanium Grades Information – Properties and Applications for All Titanium Alloys & Pure Grades – Supraalloys.Com; www.supraalloys.com. Retrieved May 23, 2022, from
6. Titanium Metal: What Is It? How Is It Used? Properties. (n.d.). Titanium Metal: What Is It? How Is It Used? Properties; www.iqsdirectory.com. Retrieved May 23, 2022, from https://www.iqsdirectory.com/articles/titanium/titanium-metal.html