How is titanium sponge formed during the Kroll process?

In the Kroll process, titanium sponge is formed by reducing titanium tetrachloride (${\text{TiCl}}_4$) with magnesium (Mg) metal.1

This chemical reaction occurs within large, sealed steel vessels at temperatures ranging from approximately 800 to 1,000 °C (1,450 to 1,800 °F). To prevent contamination from air or moisture, the process is conducted in an inert argon atmosphere. The resulting product is a highly porous material known as sponge, which contains magnesium chloride (${\text{MgCl}}_2$) salts trapped within its pores.1

Following the reaction, the sponge is crushed, and the metal is separated from the salts through either a dilute acid leach or high-temperature vacuum distillation. The recovered salts are then recycled through electrolytic cells to regenerate magnesium and chlorine for further use in the production cycle.1