What is titanium sponge?

Titanium sponge is a highly porous form of titanium metal produced during the extraction and refining process. It is created by reducing titanium tetrachloride ($TiC{l}_4$) with either sodium (in the Hunter process) or magnesium (in the Kroll process).1

These chemical reactions occur within sealed steel vessels at temperatures ranging from 800 to 1,000 °C (1,450 to 1,800 °F) under an inert argon atmosphere to prevent contamination. The resulting material contains entrapped salts—either sodium chloride ($NaCl$) or magnesium chloride ($MgC{l}_2$)—within its pores. To obtain pure metal, the sponge is crushed, and these salts are removed through high-temperature vacuum distillation or a dilute acid leach. Once purified, the sponge serves as the raw material that is consolidated into titanium ingots for structural use.12