Titanium has a strong corrosion resistance, which is due to the strong affinity between titanium and oxygen. In the air or oxygen-containing medium, a layer of dense, highly adhesive, and inert oxide film will be formed on the titanium surface to protect the titanium internal matrix from corrosion by the medium. Even if the titanium surface is mechanically worn, it will quickly self-heal or regenerate the oxide film, which ensures the status of titanium corrosion resistance.
The corrosion-resistant material that people usually think of must be stainless steel, but titanium has much stronger corrosion resistance than stainless steel. At room temperature, titanium can lie in solutions of various strong acids and alkalis without being corroded. Even the first strong acid “aqua regia” has no way to deal with it. The corrosion resistance of titanium in seawater is stronger than that of stainless steel, which is comparable to that of platinum. Someone once made an experiment to put a piece of titanium into the seabed. Five years later, when he took it out, he found that there were many small animals and undersea plants stuck on it, but there was no rust. It was still silver and white. As we all know, ships are sailing on the vast sea all year round, and the underwater part must be de-rusted and painted, otherwise, it will soon become “scrap metal”.
However, if titanium and titanium alloys are used to manufacture parts for warships, submarines, and ships, such troubles and losses can be avoided. The weight of submarines made of titanium has been reduced, and the diving depth of submarines made of stainless steel has increased by 80% to more than 4500 meters. In the past, the parts containing hot nitric acid in the chemical reactor were made of stainless steel, but the stainless steel could not resist the corrosion of the strong corrosive agent hot nitric acid. Every six months, all such parts should be replaced, so that the cost of each replacement and the loss caused by the shutdown are not small. Now, although the cost of making these parts with titanium is more expensive than that of stainless steel, it can be used continuously for five years, and the total cost is much lower.