Editing Group 4 element (section)

==Production==
The production of the metals itself is difficult due to their reactivity. The formation of [[oxide]]s, [[nitride]]s, and [[carbide]]s must be avoided to yield workable metals; this is normally achieved by the [[Kroll process]]. The oxides (MO<sub>2</sub>) are reacted with [[coal]] and [[chlorine]] to form the chlorides (MCl<sub>4</sub>). The chlorides of the metals are then reacted with magnesium, yielding [[magnesium chloride]] and the metals.

Further purification is done by a [[chemical transport reaction]] developed by [[Anton Eduard van Arkel]] and [[Jan Hendrik de Boer]]. In a closed vessel, the metal reacts with [[iodine]] at temperatures above 500&nbsp;°C forming metal(IV) iodide; at a tungsten filament of nearly 2000&nbsp;°C the reverse reaction happens and the iodine and metal are set free. The metal forms a solid coating on the tungsten filament and the iodine can react with additional metal resulting in a steady turnover.<ref name="Holl"/><ref name="Ark1925"/>
::M + 2 I<sub>2</sub> (low temp.) → MI<sub>4</sub>
::MI<sub>4</sub> (high temp.) → M + 2 I<sub>2</sub>