From Ore to Sponge
Titanium and zirconium are both extracted by the Kroll process, in which the metal chloride is reduced with molten magnesium in a sealed reactor. The product is a porous sponge metal containing residual magnesium, chloride salts and dissolved impurities. The sponge is crushed, leached and vacuum distilled before it is ready for consolidation and further purification.
The Crystal Bar Process
The crystal bar process, also called the Van Arkel-de Boer or iodide process, purifies both metals to very high levels. The sponge is heated with iodine to form a volatile metal iodide, which decomposes on a hot filament and deposits as high-purity crystal metal. The process is slow and costly, but it delivers purity levels that vacuum melting alone cannot reach, and it is used for research and specialty material.
Vacuum Arc Remelting
Vacuum arc remelting, VAR, is the standard consolidation route for titanium and zirconium ingots. The electrode is melted under vacuum by an electric arc, and the molten pool solidifies directionally, reducing gas content and segregating impurities into the top of the ingot. Multiple remelts are applied for aerospace and nuclear grades to improve homogeneity.
Electron Beam and Plasma Melting
Electron beam melting operates in high vacuum and removes volatile impurities such as magnesium and chlorides effectively, which suits titanium scrap recycling. Plasma arc melting uses inert gas and allows better control of alloy additions. Both processes are used where feed material is variable and consistent ingot quality is required.
Electrolytic Refining
Electrolytic refining of titanium and zirconium is performed in fused salt baths, where the metal dissolves at the anode and deposits in pure form at the cathode. The process can reach very low interstitial levels, but it is expensive and used mainly for high-purity applications where other routes fall short.
Purity Levels and Applications
Commercial purity grades for chemical and marine equipment.
Aerospace and medical grades with tight interstitial control.
Nuclear-grade zirconium with low hafnium for reactor cladding.
Electronics-grade titanium for sputtering targets.
Frequently Asked Questions
Q: What is the Kroll process?
A: The Kroll process reduces metal chlorides with molten magnesium to produce titanium or zirconium sponge.
Q: What is the crystal bar process?
A: The Van Arkel-de Boer iodide process decomposes a volatile metal iodide on a hot filament to deposit high-purity crystal metal.
Q: Why is vacuum arc remelting used?
A: VAR removes gases, reduces segregation and consolidates the sponge into homogeneous ingots.
Q: How is nuclear-grade zirconium made?
A: Zirconium is purified and hafnium is separated to very low levels for reactor cladding applications.
Q: Which process gives the highest purity?
A: The crystal bar process and electrolytic refining reach the highest purity levels, though at higher cost.
Q: Why does titanium scrap need electron beam melting?
A: Electron beam melting removes volatile impurities such as magnesium and chlorides from variable scrap feed.
