In 1940, Luxembourg scientist W.J.Kroll used magnesium to reduce TiCl4 to obtain pure titanium. Since then, the magnesium reduction method (also known as the Kraul method) and the sodium reduction method (also known as the Hunter method) have become industrial methods for producing sponge titanium. The United States used the magnesium reduction method to produce 2 tons of sponge titanium in 1948, and the industrial production of titanium began.
In 1947, people began to smelt titanium in factories. That year, the output was only 2 tons. Production surged to 20,000 tons in 1955. In 1972, the annual output reached 200,000 tons. The yield strength of titanium is higher than that of steel, and its weight is almost only half of the same volume of steel. Although titanium is slightly heavier than aluminum, its yield strength is twice that of aluminum. The specific strength of titanium is higher than that of aluminum and steel, and the specific modulus is very close to that of aluminum and steel. In space rockets and missiles, titanium is used instead of steel. According to statistics, the world's annual titanium used in space navigation has reached more than 1,000 tons. Very fine titanium powder is also a good fuel for rockets, so titanium is known as cosmic metal and space metal.
Titanium easily reacts with air at high temperatures, but its melting point is as high as 1668°C. At normal temperature, titanium is not afraid of corrosion by aqua regia and dilute nitric acid, but it is not resistant to corrosion by sulfuric acid and 7% hydrochloric acid with a concentration of more than 5%. Titanium is not afraid of seawater at room temperature. Someone once sunk a piece of titanium to the bottom of the sea. Five years later, it was taken up to take a look. There were many small animals and seabed plants stuck on it, but there was no rust at all, and it was still shiny.
People began to use titanium to make submarines-titanium submarines. Because titanium is very strong and can withstand high pressure, this submarine can sail in the deep sea up to 4500 meters.
