Refrigeration apparatus with expansion turbine, European patent EP 0 676 600 B1, September 6, 2000, Joost J. Brasz, Carrier Corporation EP 0 676 600 B1 (this website requires registration).
Turbine for Low Temperature Gas Separation, U.S. Patent 2,165,994, July 1939 (Continuation of an application in March 1934), Guido Zerkowitz, Linde AG United States Patent US2165994 (this website requires registration).