“In the autumn of 1938 I went on a visit to the U.S.A. to sell my titanium-reduction process.”


In 1937 Kroll filed his two first patent applications on the “titanium” process in Germany. The first application, filed on 10 July 1937 (K147,211) claimed the use of calcium as a reducing agent for the tetrachloride of titanium and the second application, filed on 7 October 1937 (K148,168), claimed the use of magnesium as a reducing agent. Only the first patent application issued as patent in Germany (DE 674,625). This is surprising as it is limited to the use of calcium and does not explicitly cover the use of magnesium as reducing agent.

The corresponding US application initially claimed the priority of both German applications but only the earlier Germany priority was maintained during prosecution of the application. The US Patent Office, however, allowed a broad patent claim for an “alkaline earth metal” as reducing agent, and, in particular, for magnesium.

Kroll also obtained a patent for his “titanium” process in the UK (GB 632,564). While the US patent application was filed on 6 July 1938, claiming German priority of 10 July 1937, the British application was filed on 11 July 1938, just one day outside the priority year, thereby forfeiting the benefit of the 10 July 1937 filing date. There is no good reason for explaining this late filing of the British application other than that the British agent missed filing the application within the priority year ...

The British patent issued on 28 November 1949, more than 11 years after its filing date, another surprising element in the British patent file. It was followed by a patent of addition (GB 658,213), filed on 12 April 1949 and granted on 3 October 1951, specifically claiming the use of helium rather than argon as a protective gas during the reduction process.

Finally, in the context of Kroll’s “titanium” investigations in 1937, a further German patent (DE 718,822) needs to be mentioned, as it claims alloys of titanium with metals such as tantalum, niobium, molybdenum, tungsten, etc. as corrosion resistant high optical reflective power alloys, possibly for use as mirrors ...