Titanium is known as the most potential “future metal” because of its corrosion resistance, easy molding, high strength and low density, high temperature resistance, non-magnetic, good biocompatibility and good fatigue resistance.
The content of titanium in the formation is 6 thousandths, which is 61 times higher than the content of copper. The hardness of titanium is similar to that of steel, but its weight is only half of that of steel of the same volume. Compared with aluminum, titanium is twice as hard as aluminum. . The thermal conductivity and electrical conductivity of titanium are similar to those of stainless steel. Titanium has superconducting properties. The superconducting bow tie temperature of pure titanium is 0.38-0.4K. The elongation can reach 50-60% and the cross-section shrinkage is 70-80%, so it is used in some military industries. A large amount of titanium has replaced steel in the field and aerospace field, and titanium powder can also be used as fuel, once again confirming that titanium is a “cosmic metal, space metal”
Room temperature corrosion of titanium
Titanium is a very active metal, but in fact titanium is very stable in many media. For example, titanium is corrosion-resistant in oxidizing, neutral and weakly reducing media. This is because titanium reacts easily with oxygen in the air and forms a dense, highly adhesive and inert oxide film on the titanium surface, which protects the titanium matrix from corrosion.
- Acid corrosion
(a) Hydrochloric acid: Hydrochloric acid with a concentration <5% does not react with titanium at room temperature, while 20% hydrochloric acid reacts with titanium at room temperature. When the temperature becomes high, dilute hydrochloric acid will also corrode titanium. Although titanium is not resistant to corrosion by hydrochloric acid solution, the corrosion resistance of titanium materials can be improved through alloying, anode passivation and adding corrosion inhibitors. Therefore, in production practice, titanium materials still have value. (b) Sulfuric acid: At normal temperature, titanium has certain corrosion resistance to low-temperature and low-concentration sulfuric acid solutions. The corrosion rate of titanium is the fastest when the sulfuric acid solution is about 40%. When the concentration is greater than 40%, the corrosion rate is reversed when it reaches 60%. It slows down and reaches the fastest speed at 80%. Heated dilute acid or 50% concentrated sulfuric acid can react with titanium to form titanium sulfate. The corrosion resistance of titanium in sulfuric acid can be improved by introducing air, nitrogen into the solution, or adding oxidants or high-priced heavy metal ions. Therefore, titanium does not have much practical value in sulfuric acid. (c) Nitric acid and aqua regia: Titanium with a dense and smooth surface is very stable to nitric acid. This is because nitric acid can quickly form a strong oxide film on the surface of titanium, but the surface is rough, especially sponge titanium or powder. Titanium can react with sub- and hot dilute nitric acid, and both will react with it when the temperature rises.
- Seawater corrosion of titanium
Titanium is very stable in seawater and is not easily corroded by seawater. This is because a dense oxide film on the surface of titanium resists the erosion of the titanium matrix by chloride ions. After testing, titanium has been exposed to seawater at different depths for many years without any obvious corrosion. Even if there are deposits on the titanium surface, crevice corrosion and pitting corrosion will not occur. The presence of sulfides in seawater does not affect the corrosiveness of titanium. In the marine atmosphere, splash zone and tidal zone, titanium has no corrosion problem. Titanium is also resistant to erosion by high-speed seawater. Frictional particles suspended in seawater are very harmful to copper or aluminum alloys, but have little effect on titanium. Titanium has also been recognized as one of the best metal materials resistant to cavitation corrosion in seawater. Since titanium is not toxic to marine organisms, it is common for marine organisms to adhere to titanium surfaces. There is no crevice corrosion or pitting corrosion on the titanium underneath the marine organisms, and the surface still maintains the integrity of the anti-corrosion oxide film. Titanium almost does not suffer from pitting and crevice corrosion in seawater, so titanium is the most suitable material for use in seawater.Because of this good property, titanium is used to make propeller shafts, rigging and heat exchangers for desalination plants; it is also used in hot and cold water heaters in saltwater aquariums, fishing lines and diving knives. Titanium is used to make housing and other components for marine surveillance deployments, as well as monitors for scientific or military use. The former Soviet Union developed technology to manufacture submarines mainly from titanium. But when the temperature rises to 90 degrees Celsius, titanium becomes unstable in seawater and begins to corrode.