The Science Behind Titanium's Corrosion Resistance
Titanium's corrosion resistance stems from its unique ability to form a stable, protective oxide film on its surface. When titanium is exposed to air or moisture, this film forms instantaneously. The growth of this film is further accelerated under strong oxidizing conditions. What makes this oxide film even more remarkable is its self - healing property. In the presence of moisture or oxygen, the film can repair itself immediately if damaged, ensuring continuous protection for the underlying metal. This inherent characteristic sets titanium apart from many other metals and makes it highly suitable for applications in corrosive environments.
Applications of Titanium in Corrosion - Prone Environments
Chlorine - Related Applications
In the realm of chlorine chemicals, titanium finds extensive use. For instance, in chloro - alkali cells, titanium is commonly employed as anodes and cathodes. It is also utilized in bleaching equipment for the pulp and paper industry, as well as in heat exchangers, piping, pressure vessels, and pumps involved in the manufacture of intermediate organic chemicals. Its excellent corrosion resistance in chlorine gas and chlorine - containing solutions forms the basis for these applications.
Seawater Applications
Titanium is a material of choice for seawater applications. It can resist corrosion from seawater up to temperatures as high as 500 °F (260 °C). Titanium tubing that has been exposed to polluted seawater in a surface condenser for 16 years showed only slight discoloration with no signs of corrosion. In the chemical, oil refining, and desalination industries, titanium has provided over thirty years of trouble - free seawater service. Even when exposed to depths over a mile below the ocean surface for many years, there is no measurable corrosion. Pitting and crevice corrosion are non - existent, and the presence of sulfides in seawater does not affect its corrosion resistance. The U.S. Navy incorporates titanium in many of its vessels for onboard equipment like tanks, piping, doors, and hatches due to the harsh seawater environments and the high maintenance and repair costs associated with other materials.
Acidic Environments
Nitric Acid
Titanium exhibits high resistance to nitric acid over a wide range of temperatures and concentrations. It is extensively used in process equipment for handling and producing nitric acid. At temperatures below boiling, titanium offers excellent resistance across the full concentration range. However, at higher temperatures, its corrosion resistance is highly dependent on the purity of nitric acid. In hot and very pure solutions, vapor condensates of nitric acid can lead to significant general corrosion in the 20 - 70 wt. % range. In such marginal high - temperature conditions, higher purity unalloyed grades of titanium (e.g., grade 1) are preferred to curtail accelerated corrosion of weldments.
Hydrochloric Acid
Titanium has useful corrosion resistance in dilute hydrochloric acid applications. Small amounts of multivalent metal ions in the solution can effectively inhibit corrosion. However, it is important to note that titanium should not be used in applications involving red fuming nitric acid, as it can cause a pyrophoric reaction that can damage equipment and endanger people.
Sulfuric Acid
Titanium is only corrosion - resistant to sulfuric acid at low temperatures and concentrations, such as 20% acid at 32 °F and 5% acid at room temperature. Similar to hydrochloric acid, small amounts of multivalent metal ions in the solution can help inhibit corrosion.
Other Applications
In phosphoric acid, unalloyed titanium is resistant to up to 30% concentration at room temperature, and this resistance extends to about 10% pure acid at 140 °F. In organic acids, unalloyed titanium generally has good resistance. Titanium is also used in various fabrications such as reactors, pressure vessels, and piping systems, where its corrosion - resistant properties are highly valued.
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