How is titanium smelted?
Titanium, an element known as "space metal", plays an irreplaceable role in aviation, aerospace, medical and other fields with its unique physical and chemical properties. So, how is titanium extracted from deep underground ore? Next, let's embark on this titanium smelting journey together.
1. Raw materials of titanium
The raw materials for making metallic titanium are mainly rutile, which contains more than 96% titanium dioxide. Countries that lack rutile mines use "high titanium slag" made from ilmenite, which contains about 90% titanium dioxide. Due to the price increase and decreasing reserves of natural rutile, countries tend to use ilmenite to make titanium-rich materials, namely high titanium slag and artificial rutile. Titanium was discovered in 1791, but the first pure titanium was produced in 1910, which took more than a hundred years. The reason is that titanium is very active at high temperatures and is easy to combine with elements such as oxygen, nitrogen, and carbon. It takes very harsh conditions to extract pure titanium.
2. Titanium smelting steps
When smelting titanium, it takes complicated steps. Turn ilmenite into titanium tetrachloride, put it in a sealed stainless steel tank, fill it with argon, and react with magnesium metal to get "sponge titanium". This porous "sponge titanium" cannot be used directly, and it must be melted into liquid in an electric furnace before it can be cast into titanium ingots. But how easy is it to make such an electric furnace! In addition to the air in the electric furnace must be evacuated, the more troublesome thing is that it is simply impossible to find a crucible for liquid titanium, because general refractory materials contain oxides, and the oxygen in them will be taken away by liquid titanium.
3. "Water-cooled copper crucible"
Later, people finally invented an electric furnace with a "water-cooled copper crucible". This electric furnace has only a part of the central area that is very hot, and the rest is cold. After the titanium melts in the electric furnace, it flows to the wall of the copper crucible cooled by water and immediately condenses into a titanium ingot. This method can produce titanium blocks weighing several tons, but its cost can be imagined.
4. Industrial extraction of titanium dioxide
In industry, titanium dioxide is often produced by decomposing ilmenite with sulfuric acid, and then titanium metal is produced from titanium dioxide. In order to remove the impurity Fe2(SO4)3, iron filings are added, Fe3+ is reduced to Fe2+, and then the solution is cooled to below 273K, so that FeSO4·7H2O (green vitriol) is crystallized as a byproduct.
5. Titanium dioxide is produced by calcining metatitanic acid to produce titanium dioxide. Titanium metal is produced industrially by reducing titanium tetrachloride by metal thermal reduction. Titanium dioxide (or natural rutile) and carbon powder are mixed and heated to 1000-1100K, chlorinated, and the generated TiCl4 vapor is condensed.
6. Titanium tetrachloride is reduced by magnesium metal.
Titanium tetrachloride is reduced by magnesium metal in an inert gas at a molar ratio, and the reaction temperature is controlled at about 900℃ to produce sponge-like titanium. The byproduct magnesium chloride can be separated from titanium by heating at 1000℃ in a vacuum.
7. Purification
Titanium dioxide can be reduced to TiCl4 in argon with molten magnesium at 1070K to produce porous sponge titanium. This sponge titanium is crushed, smelted in a vacuum arc furnace, and finally made into various titanium materials. The obtained TiCI4 is decomposed at high temperature (about 1250℃) to TiCI4=Ti+2CI2, thus obtaining pure titanium.
Looking back on the entire titanium smelting process, we can't help but sigh at the greatness of human wisdom. From the ore buried deep underground to the light and tough metal titanium, every step embodies the wisdom and sweat of countless people. It is the hard work of these seemingly ordinary workers that makes the precious metal titanium widely used in various fields and has made great contributions to the progress and development of human society.
