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

What is Titanium?

Titanium, identified by the symbol Ti and atomic number 22, is a light, silvery metal found in Group 4 of the periodic table. Known for its notably high melting point and impressive tensile strength, titanium also stands out for its efficient thermal and electrical conductivity.

While it’s true that titanium is present in trace amounts in nearly all rocks, finding it in significant concentrations is quite rare. As a metal, titanium has a bright, grey appearance and is well-regarded for both its strength and its remarkable resistance to corrosion. These qualities have made it invaluable across a broad range of uses.

The aerospace industry, for example, accounts for about 80 percent of titanium’s total usage, with the rest going toward armor plating, medical devices, and a variety of consumer products.

One of the most striking features of titanium is its ability to resist corrosion from both water and chemicals. This property comes from a thin layer of titanium dioxide (TiO₂) that naturally forms on its surface, creating a barrier that is not easily breached.

Another interesting aspect of titanium is its relatively low modulus of elasticity. In practical terms, this means the metal is flexible and can bend, yet it readily returns to its original form.

This characteristic is particularly important in the development of memory alloys, which can be deformed at low temperatures and then recover their original shape when heated a feature essential in many modern technological applications.

History of Titanium

Following the end of World War II, titanium began to attract significant attention in its metallic form. Interestingly, titanium was not isolated as a metal until 1910, when Matthew Hunter, an American chemist, successfully reduced titanium tetrachloride (TiCl₄) using sodium. This process would become known as the Hunter method.

Commercial-scale production did not emerge until the 1930s. At that time, William Justin Kroll demonstrated that titanium could be extracted from its chloride form with the help of magnesium, introducing what is now called the Kroll process. Remarkably, this method remains the backbone of titanium production today.

The breakthrough for titanium’s practical use came with its first major application in military aviation, once manufacturing became economically feasible. By the 1950s and 1960s, both Soviet and American militaries were incorporating titanium alloys into aircraft and submarine designs.

Not long after, in the early 1960s, commercial aircraft manufacturers also began adopting titanium alloys for their builds.

Meanwhile, Swedish physician Per-Ingvar Brånemark was conducting research in the 1950s that revealed another notable property of titanium: its compatibility with the human body. His studies demonstrated that titanium does not provoke an adverse immune response, making it possible for the metal to bond with bone tissue, a phenomenon now known as osseointegration.

Manufacturing Process of Titanium

Titanium metal is produced using a method called the Kroll process, which unfolds in five distinct stages. It begins with extraction, followed by purification.

Once these initial steps are complete, the process moves on to sponge manufacture. Afterward, alloy creation takes place, and finally, the titanium is formed and shaped to meet specific requirements.

1. Extraction

The Kroll process begins with the extraction of titanium ores, a stage that relies on a steady supply from mining operations. Within these ores, minerals such as ilmenite and rutile are present, among others. Of these, rutile is typically suitable for direct use, thanks to its naturally high purity.

Ilmenite, in contrast, undergoes an initial treatment to separate the iron content. This step is crucial because it leaves behind a material with about 85% titanium dioxide. To accomplish this, the ores are heated to approximately 900 °C in a fluidized bed reactor, where they react with chlorine and carbon.

This process triggers a chemical reaction that produces titanium tetrachloride, though not in its pure form, and carbon monoxide as a by-product. Even after the iron is removed, titanium dioxide in the form of TiCl₄ still contains various impurities, which must be addressed in subsequent steps.

2. Purification

In this stage, TiCl₄ is heated within a large distillation vessel. Through a combination of fractional distillation and precipitation, impurities are gradually separated out. These methods effectively remove various contaminants, such as vanadium, silicon, magnesium, zirconium, and iron, ensuring a purified product.

3. Sponge Formation

Sponge formation marks the third stage of the Kroll process. At this point, the previously refined titanium tetrachloride is introduced into a stainless-steel reactor vessel in its liquid state. Magnesium is then added and the entire vessel is heated to around 1100 °C. Under these conditions, magnesium reacts with chlorine, resulting in the formation of magnesium chloride.

Since the presence of oxygen and nitrogen could trigger unwanted reactions, argon gas is used to purge the vessel’s atmosphere, ensuring these elements are kept at bay. This step is crucial for maintaining the integrity of the process.

Interestingly, titanium’s melting point is much higher than that of steel, so the titanium that collects inside the vessel doesn’t melt—it remains as a solid mass. This solid titanium, which isn’t yet pure, must be mechanically removed from the vessel. The next step involves washing it with a solution of water and hydrochloric acid to eliminate any residual magnesium or magnesium chloride.

What you end up with at the conclusion of this cycle is titanium in a porous, sponge-like form—hence, the term ‘sponge formation.’

4. Alloy Creation

During the fourth stage of processing in a consumable-electrode arc furnace, pure titanium sponge is blended with selected alloys and scrap metals to create practical, usable alloys.

The resulting mixture is first crushed and then welded together, forming what is known as a sponge electrode. By ensuring the correct proportions of each metal, the mixture achieves the desired properties before this step.

Once the sponge electrode has been prepared, it undergoes melting in a vacuum arc furnace to produce titanium ingots. To ensure that these ingots meet both quality and economic standards, it is common practice to remelt them multiple times. This repeated melting helps achieve a consistent composition and minimizes impurities in the final product.

5. Forming and Shaping:

Once the ingots are removed from the furnace, they undergo careful inspection for any defects. Only those that meet quality standards move on to the next phase, where they are used to manufacture titanium alloy components—the final step in the Kroll process.

Depending on the required specifications for the end product, these ingots may be shaped through various techniques such as welding, casting, forging, or powder metallurgy. Ultimately, the choice of method depends entirely on the desired characteristics of the finished item.

Compounds of Titanium

1. Titanium Oxide

Titanium oxide (TiO₂) stands out as the most significant of the titanium oxides, and it can be found in three distinct crystalline forms: rutile, anatase, and brookite.

Among these, rutile is the most commonly found in nature. Its practical value is notable, especially as a pigment in the chemical industry. In the structure of rutile, each titanium atom is surrounded by six oxygen atoms arranged in an octahedral geometry, although this configuration disrupts the ideal octahedral environment found in other compounds.

There is also Ti₂O₃, which appears as a violet solid and represents titanium in the +3 oxidation state. Structurally, it shares similarities with α-Al₂O₃ (corundum). Another interesting compound is titanium monoxide (TiO), which forms when TiO₂ is heated with metallic titanium. TiO adopts a cubic crystal structure, much like sodium chloride.

However, TiO is often non-stoichiometric, meaning that about one-sixth of both the titanium and oxygen sites remain vacant. This irregularity gives TiO its metallic conductivity.

2. Titanium Disulfide

Titanium disulfide (TiS₂) stands out as a significant sulfide compound, characterized by its distinctive layered arrangement of sulfur atoms. This unique structure has made TiS₂ a material of particular interest, especially for its application as an electrode in the advancement of lithium battery technologies.

3. Halides

Titanium tetrachloride (TiCl₄) is a colorless, highly volatile liquid and represents the most prevalent halide form of titanium. When exposed to air, the typically yellowish industrial TiCl₄ readily undergoes hydrolysis, producing striking white clouds—an effect often observed during its handling.

This compound plays a central role in the extraction of titanium from its ores, serving as an intermediate in the production of titanium dioxide, which is widely used as a pigment in white paints. Titanium halides, particularly as Lewis acids, also find frequent application in various chemical processes.

Another notable titanium halide is titanium tetraiodide (TiI₄), synthesized through the Van Arkel process to yield exceptionally pure titanium metal.

Beyond Ti(IV) halides, titanium is capable of forming stable lower halide compounds in the +3 and +2 oxidation states, such as titanium trichloride and titanium dichloride. Both of these halides are of industrial importance, especially as catalysts in the production of polyolefins.

4. Organometallic Complexes

Titanocene dichloride, with the formula (C₅H₅)₂TiCl₂, stands out as perhaps the most recognized organometallic compound of titanium. Researchers have shown considerable interest in titanium organometallic complexes, especially when it comes to their use as polymerization catalysts.

Alongside titanocene dichloride, other notable examples include the Petasis reagent and Tebbe’s reagent, both of which are well-established titanium-based organometallic compounds.

Alloys of Titanium

1. Alpha Alloys

To enhance both the hardness and tensile strength of commercially pure titanium, manufacturers typically introduce small quantities of oxygen. By carefully adjusting the oxygen content, it is possible to produce several grades of commercially pure titanium, each with distinct strength properties that can range from 290 up to 740 MPa.

Generally, these titanium grades are considered to have an entirely alpha-phase structure. However, if there are notable amounts of beta-stabilizing impurities like iron, there may be traces of the beta phase present. Still, the material’s core remains predominantly alpha.

It’s important to note that alpha titanium alloys do not respond to heat treatment methods designed to increase strength. Interestingly, introducing about 2.5 percent copper into titanium changes this behavior: the resulting alloy becomes amenable to solution treatment and ageing, showing a response similar to what is observed in aluminum-copper systems.

2. Alpha-Beta Alloys

Vanadium, molybdenum, iron, and chromium each play a role in stabilizing the beta phase, leading to the development of a variety of alpha-beta alloys. These materials are generally recognized for their medium to high strength, with tensile strengths ranging from 620 to 1250 MPa, and they maintain solid creep resistance within the 350 to 400°C range.

In practical applications, factors such as low and high cycle fatigue and fracture toughness are becoming increasingly important in design considerations. To achieve optimal mechanical performance across different uses, researchers have devised a combination of thermomechanical processing and heat treatment methods tailored to these alloys.

When temperatures rise above 450°C, alloys with a composition closer to the alpha phase are typically selected for their superior creep resistance, remaining reliable even up to 600°C.

 3. Beta Alloys

Another important category of titanium materials is the beta alloys. These alloys form when titanium is combined with a sufficient amount of beta-stabilizing elements.

Although beta alloys have been known for quite some time, their popularity has increased in recent years. Compared to alpha-beta alloys, they tend to be easier to harden, and certain types even offer better corrosion resistance than what you’ll find in commercially pure titanium.

For aerospace applications, there are both international and national standards that define the requirements for titanium materials. However, outside the aerospace sector, such specific standards do not exist. In practice, most non-aerospace uses rely on the ASTM set of specifications.

Grades of Titanium

Grade 1

Among the commercially pure titanium grades, Grade 1 stands out for its exceptional softness and malleability. Its ability to withstand corrosion and impacts, combined with remarkable formability, makes it especially valuable for applications where flexibility and resistance to harsh environments are required.

Grade 2

Often described as the “workhorse” of commercially pure titanium, Grade 2 owes its popularity to its versatility and widespread availability. While it shares many characteristics with Grade 1—such as corrosion resistance—it offers a modest improvement in durability. As a result, it is commonly chosen for applications demanding a reliable balance between strength and workability.

Grade 3

Although Grade 3 is less commonly encountered than the first two grades, it should not be underestimated. This grade provides increased strength compared to Grades 1 and 2, while maintaining similar flexibility. While it is slightly less formable, its enhanced mechanical properties make it suitable for more demanding situations.

Grade 4

Grade 4 represents the strongest option among the four commercially pure titanium grades. What sets it apart is its unique combination of strength, excellent formability, weldability, and notable resistance to corrosion. These qualities allow it to perform reliably in environments where both toughness and ease of fabrication are priorities.

Grade 5

Known in technical circles as Ti 6Al-4V, Grade 5 titanium is the most widely used titanium alloy. In fact, it accounts for about half of all titanium consumption globally. The alloy’s strength can be further increased through heat treatment, allowing for even broader utility.

What truly makes Ti 6Al-4V stand out is its impressive combination of high strength and low weight, along with its ease of forming and robust resistance to corrosion. Its adaptability explains why it finds use in such varied industries as aerospace, medicine, marine technology, and chemical processing.

Grade 7

While Grade 7 shares its mechanical and physical properties with Grade 2, what sets it apart is the addition of palladium as an interstitial element. This subtle change transforms Grade 7 into an alloy and dramatically enhances its corrosion resistance.

Thanks to this property, it also performs exceptionally well in terms of weldability and ease of fabrication. You’ll often find Grade 7 titanium alloy being used in chemical processing environments and in components for various types of industrial equipment.

Grade 11

If you’re familiar with Grade 1 titanium, you’ll notice that Grade 11 is almost identical, but with a slight twist: a small amount of palladium is introduced to bolster its resistance to corrosion, turning it into an alloy. This grade stands out for more than just its corrosion resistance.

It also maintains an ideal balance of ductility, cold formability, and strength. Add to that its impact toughness and its reputation for being easy to weld, and it becomes clear why Grade 11 is chosen for demanding applications.

Grade 12

When it comes to welding, Grade 12 titanium is top of its class, frequently earning a reputation for “excellent” weldability. This alloy doesn’t just handle the heat; it thrives under extreme temperature conditions.

Interestingly, Grade 12’s characteristics are quite similar to those found in 300-series stainless steels. In practice, this alloy adapts well to various forming methods, including hot or cold forming with tools like press brakes, hydro presses, stretch formers, or drop hammers.

Grade 23

Grade 23, often referred to by its designation Ti 6Al-4V ELI, is essentially a refined version of the classic Ti 6Al-4V alloy. Its versatility allows it to be drawn into coils, strands, wires, and flat wires, depending on the application.

What makes Grade 23 particularly attractive is its combination of high strength, low weight, excellent corrosion resistance, and outstanding toughness. In fact, when durability is a priority, this alloy frequently outperforms others in terms of damage resistance.

Ti 5Al-2.5Sn

Ti 5Al-2.5Sn is a non-heat-treatable alloy known for its impressive welding capabilities and overall stability. It excels in maintaining its strength and corrosion resistance, even when exposed to high temperatures for extended periods.

Notably, this alloy also demonstrates strong creep resistance—that is, it resists the tendency to deform slowly over time under sustained stress at elevated temperatures.

Properties of Titanium

• At Standard Temperature and Pressure, it is found as a 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 lightweight. 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 hold the distinction of being the first non-platinum compounds explored for cancer therapy in the medical field. Their appeal stems from a combination of notable efficacy and relatively low biological toxicity.
• These alloys find use across a broad range of chemical and industrial sectors. They are valued for their reliability in storing alkaline solutions, chlorine-based compounds, and various aggressive chemicals. In addition, they play a role in the production of rails, railway wheels, and excels.
• Alloys incorporating elements such as manganese, chromium, iron, molybdenum, aluminum, vanadium, and tin are prized for their low weight and impressive mechanical strength. As a result, these materials are predominantly chosen for aerospace and missile applications.
• The process of producing ferrotitanium involves smelting rutile together with iron and coke in an electric furnace. In the steel industry, ferrotitanium is introduced as a scavenger to eliminate oxygen and nitrogen impurities from steel.
• Titanium oxide (TiO₂) is well known for its excellent covering ability, which is why it serves as a widely used white pigment in the chemical industry. Interestingly, its production closely mirrors the techniques used for extracting titanium metal itself.

Conclusion

Titanium is recognized for its distinct bright grey appearance, notable strength, and impressive resistance to corrosion. Thanks to its elevated melting and boiling points, titanium is highly valued for its refractory properties. This metal forms a variety of compounds, including oxides, sulfides, alkoxides, nitrides, and carbides, among others.

Because of its outstanding strength, both pure titanium and its alloys play significant roles in sectors such as medicine, aerospace, and automotive manufacturing. However, it is important to note that certain titanium compounds can pose risks to both human health and the environment.

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