Titanium: Key Chemical Properties and Corrosion Behavior

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Titanium: Key Chemical Properties and Corrosion Behavior

Titanium, first isolated in the 1950s, has become indispensable across aerospace, medical, energy, and sporting goods industries due to its lightweight strength and excellent corrosion resistance. Its chemical behavior, however, is complex and highly dependent on temperature, surface finish, and purity.

Reactivity Overview

At elevated temperatures, titanium can react with a wide range of elements. Its reactions are traditionally grouped into four categories:

• Category I: Halogens and oxygen‑group elements form covalent/ionic compounds such as TiCl₄ and TiO₂.
• Category II: Transition metals, hydrogen, beryllium, boron, carbon, and nitrogen form intermetallics or limited solid solutions.
• Category III: Elements like zirconium, hafnium, vanadium, chromium, scandium, and other transition metals yield virtually infinite solid solutions.
• Category IV: Noble gases, alkali/alkaline‑earth metals, most lanthanides (except scandium), and actinides show negligible reactivity.

Reactions with Specific Compounds

Hydrogen Fluoride (HF) and Fluorides

Hydrogen fluoride gas reacts with titanium to form TiF₄ when heated: Ti + 4HF → TiF₄ + 2H₂ + 135 kcal. The non‑aqueous liquid forms a dense TiF₄ film that protects the surface.

Even 1 % HF is highly aggressive: 2Ti + 6HF → 2TiF₃ + 3H₂. Hydrofluoric acid is the strongest solvent of titanium.

Hydrogen Chloride (HCl) and Chlorides

Dry HCl corrodes titanium above 300 °C: Ti + 4HCl → TiCl₄ + 2H₂ + 94.75 kcal. At room temperature, <5 % HCl shows no reaction; 20 % HCl yields purple TiCl₃:

2Ti + 6HCl → 2TiCl₃ + 3H₂. Dilute HCl can still corrode at elevated temperatures.

In contrast, anhydrous metal chlorides (e.g., MgCl₂, FeCl₃) and their aqueous solutions are largely inert toward titanium.

Sulfuric Acid (H₂SO₄) and Hydrogen Sulfide (H₂S)

Titanium reacts readily with 5 % H₂SO₄; the fastest corrosion rate occurs at 40 %–60 % concentration, but re‑accelerates at 80 %. Heating dilute acid or 50 % acid yields TiSO₄:

Ti + H₂SO₄ → TiSO₄ + H₂; 2Ti + 3H₂SO₄ → Ti₂(SO₄)₃ + 3H₂.

At high temperature, concentrated acid reduces titanium to SO₂:

2Ti + 6H₂SO₄ → Ti₂(SO₄)₃ + 3SO₂ + 6H₂O + 202 kcal.

Hydrogen sulfide forms a protective TiS film at room temperature, but at 600–900 °C it reacts to produce TiS or Ti₂S₃:

Ti + H₂S → TiS + H₂ + 70 kcal. Powdered titanium reacts at 600 °C, producing TiS; at 900 °C the dominant phase is TiS, and at 1200 °C Ti₂S₃.

Chemical Properties of Titanium

Nitric Acid (HNO₃) and Aqua Regia

Polished titanium remains stable in nitric acid because a dense TiO₂ layer forms instantly. Rough or porous forms (sponge or powder) react with hot dilute HNO₃:

3Ti + 4HNO₃ + 4H₂O → 3TiO₄ + 4NO or 3Ti + 4HNO₃ + H₂O → 3TiO₃ + 4NO.

Concentrated HNO₃ above 70 °C attacks titanium:

Ti + 8HNO₃ → Ti(NO₃)₄ + 4NO₂ + 4H₂O.

At elevated temperatures, aqua regia can also corrode titanium to TiCl₂ via the same pathway.

Key Takeaways

Titanium’s chemical reactivity is governed by temperature, surface condition, and alloy purity. While highly resistant to many acids and oxidants, it can be aggressively corroded by fluorides, chlorides at high temperatures, and certain acid concentrations. Understanding these interactions is critical for selecting appropriate processing conditions and service environments.

Further Resources

For more detailed information on titanium and other refractory metals, visit Advanced Refractory Metals (ARM). ARM, headquartered in Lake Forest, California, is a leading supplier of high‑quality refractory metals including tungsten, molybdenum, tantalum, rhenium, titanium, and zirconium.