Question

Write a short note on Van Arkel Method.

Answer 1

Hint: As we know that Van Arkel method is generally related to the purification of metals in their extraction process and it is also called the Crystal Bar process as well. It is very important that the compound obtained after purification must be stable in order to identify the compounds formed by this method.

Complete answer:
Let us discuss about Van Arkel Method as follows:-
-Van Arkel Method: This process is also known as the crystal bar process and it was developed by Anton Eduard van Arkel in late 1925. This was the first industrial process used for the production of pure ductile metallic zirconium commercially.
-It is generally used in the production of small quantities of pure titanium and zirconium metals. This process primarily involves the formation of the metal iodides followed by their subsequent decomposition in order to produce pure metal.
-In this process, the impure titanium and zirconium are heated in an evacuated vessel with a halogen (usually iodine) at a temperature range of 50-250$^{\circ }C$ . The intermediates were formed such as $Ti{{I}_{4}}$ and $Zr{{I}_{4}}$ which were volatile substances and would leave impurities as solid. At atmospheric pressure conditions, Titanium tetraiodide ($Ti{{I}_{4}}$) melts at 150$^{\circ }C$and boils at 377$^{\circ }C$ whereas Zirconium tetraiodide ($Zr{{I}_{4}}$) melts at 499$^{\circ }C$ and boils at 600$^{\circ }C$.
-Usually the boiling points get lowered by reducing the pressure. The tetraiodide compound of gaseous metal is then decomposed on a hot tungsten filament at 1400$^{\circ }C$. As more metal gets deposited, the filament conducts better and hence a greater electric current is required so as to maintain the temperature of the tungsten filament.
-This method can be performed in the span of several hours or several weeks which usually depends on the particular type of setup being used.

Note:
-Remember that this method of purification of metals was commercially surpassed by the Kroll process. This is because the titanium metal obtained through this process was highly ductile in nature which reflects its high purity and stability. This method is dominant for the major production of Titanium and Magnesium metal.