William Justin Kroll (Inventor): An enduring legacy of scientific discovery
The discoveries of Luxembourg-born metallurgist William Justin Kroll, who developed techniques to extract titanium and zirconium in industrial quantities, left an enduring legacy for 21st century applications ranging from nuclear energy to space exploration.
Titan of Luxembourg science
Today’s scientific, engineering and technological advances owe a huge debt to William Justin Kroll, one of Luxembourg’s greatest scientific innovators. Working between 1923 and 1940 from a private laboratory at the Villa Leclerc in Luxembourg City’s then-as-now fashionable district of Belair, Kroll devised a method for industrial production of titanium, and he would later do the same for zirconium. Born as Guillaume Kroll to a steel industry family in Esch-sur-Alzette in 1889, he moved to the United States shortly before Luxembourg was occupied by the German army. His discoveries would play an important role in the post-war technology and consumer products boom through the adoption of titanium in a host of military and commercial applications. What is today known as the Kroll process has led to the use of titanium in a vast range of products and construction and engineering processes, ranging from aircraft, ship and racing car components to tennis rackets and golf clubs, paints, jewellery and surgical implants.
"What is today known as the Kroll process has led to the use of titanium in a vast range of products"
The titanium breakthrough
Kroll, who studied and initially conducted research in Germany, first produced ductile metallic titanium in 1924 following his return to Luxembourg through a pyrometallurgical procedure combining titanium tetrachloride extracted from ore with calcium. Testing at the Cerametal – now CERATIZIT - plant in Bereldange convinced him of its potential thanks to its strength and corrosion resistance. Meanwhile, he calmed the fears of Belair neighbours that he might blow up the entire district by planting roses throughout the gardens surrounding the villa. After leaving Europe, Kroll refined the process with Union Carbine and later as a consulting metallurgist to the US Bureau of Mines, using magnesium as a reducing agent. The ability to produce titanium economically in usable form and industrial quantities paved the way for its widespread adoption, especially after the US Air Force identified titanium-based alloys as critical for the development of jet engine structures and engines, because of their superiority in strength-to-weight ratio over steel and aluminium.
A life devoted to science
With the Bureau of Mines, Kroll worked on the production of zirconium, which had been identified in 1789, and for which he developed a production process involving the reduction of zirconium tetrachloride by magnesium. Today zirconium is used in jet engines, radar equipment, surgical instruments and fibre optics. Its most important application, however, is in nuclear reactors for cladding fuel rods and reactor core structures, thanks to a unique combination of strength at elevated temperatures, resistance to corrosion from coolants as well as mechanical damage from neutron bombardment, and the fact it does not form highly radioactive isotopes. Kroll returned to Europe in 1955 and settled in Brussels. On his death in 1973, he bequeathed financial resources to support undergraduate and graduate students through the Kroll Institute for Extractive Metallurgy at the Colorado School of Mines – the institution that has just cemented another link with Luxembourg by creating the first graduate degree in space mining.