Precious Metals: Titanium Jewelry
Source: Australia, Canada, Norway, South Africa, Ukraine
Titanium jewelry, rings, and bracelets have a distinctive, dark and warm color that sets them apart from other "silvery/white" metals. Titanium is strong, lustrous, and corrosion-resistant, and is the ninth most abundant element to be found within the Earth's crust. It is present in most igneous rocks or in the sediments that have eroded from them. Titanium is a difficult metal to extract from the host ore, occurring primarily in iron ores and in minerals such as anatase, brookite, ilmenite, perovskite, rutile, and titanite.
Titanium was first discovered in 1791, by an amateur geologist named Rev. William Gregor from Cornwall, England. While studying a weakly magnetic mineral called ilmenite (titanium-iron oxide) he noticed a black sand that was also attracted by magnetism. This element was independently discovered several years later by a German chemist named Martin Heinrich Klaproth. Klaproth confirmed titanium as a new element and in 1795, naming it after the Latin word Titans, which symbolized the Earth and the race of powerful deities from Greek mythology.
Titanium mineral concentrate (photo: USGS)
Titanium & diamond rings by Bez Ambar
Pure titanium (99.9%) has always been difficult to extract from its various ore components. In 1910, metallic titanium in its pure form was produced by Matthew A. Hunter who heated titanium tetrachloride (derived from combining rutile, chlorine and coke) with sodium in a steel bomb at 700Ð800 ¡C. This method of extracting pure titanium became known as the "Hunter process."
The first industrial process for the production of pure titanium and zirconium was called the "crystal bar process" (aka: iodide process) invented in 1925 by Anton Eduard van Arkel and Jan Hendrik de Boer. The first commercially viable process for the production of pure titanium was not introduced until 1946, when William Justin Kroll proved that titanium could be produced by reducing titanium tetrachloride with magnesium. This extraction and production process is known as the "Kroll process," and is the method still used today in the manufacturing of titanium jewelry.
Another newer, and lower-cost process called the 'FFC Cambridge process' was developed in the mid 1990s, by scientists at the University of Cambridge. The Cambridge process is an electrochemical method in which solid metal compounds are cathodically reduced to the respective metals or alloys in molten salts.
Physical Properties of Titanium
Titanium engagement rings and wedding bands are one of the fastest growing segments of the titanium jewelry market. Titanium can be channel set, laminated, or inlayed without losing strength, and its high-strength makes it suitable for tension settings. Titanium's chemical inertness makes it an inexpensive alternative for those with allergies to white gold.
Titanium is used in strong light-weight alloys mixed with aluminium, iron, molybdenum, and vanadium. Titanium has a high level of resistance to corrosion and is almost as resistant to corrosion as platinum. Titanium's relatively high melting point makes it useful as a refractory metal.
In nature, titanium is always bonded to other elements, making it difficult to extract. Titanium is present in most igneous rock and in sedimentary material that was derived from igneous rock. In high concentrations, titanium is found associated with the minerals anatase, brookite, and rutile. Of the 801 types of igneous rocks analyzed by the United States Geological Survey, 784 contained titanium, and titamium exists in miniscule quantities within most living things.
The American Society for Testing and Materials (ASTM) recognizes 31 Grades of titanium metal and alloys, of which Grades 1 through 4 are considered to be commercially pure (unalloyed). These four grades are distinguished by their varying degrees of tensile strength, with Grade 1 being the most ductile, and Grade 4 being the least ductile.
Bibliography on Titanium
1. USGS, Titanium Mineral Concentrates . minerals.usgs.gov
2. Timet, Titanium Design and Fabrication . www.timet.com