The present volume, Thorium C5, deals with the compounds of thorium and
sulfur, selenium, tellurium, and boron, as well as with oxoacid
compounds of the three chalcogen elements. Thorium borates have already
been treated in Thorium C2. In contrast to the corresponding compounds
of uranium the thorium sulfides, etc., do not show any nuclear or other
technological application; they are only of academic interest, despite
some very interest- ing electronic properties, especially of the 1: 1
compounds. The thorium-sulfur and the thorium- boron systems in
particular were studied in detail, so that we have a clear picture of
them, whereas there are still a lot of open questions in the systems
Th-Se and Th-Te - not very different from other metal chalcogenide
systems. Thorium sulfates are of some technological importance because
they are formed in solution during recovery of thorium from monazite by
sulfuric acid leaching. The very detailed and critical treatment of the
chemical and physical properties of the compounds discussed also enables
us to find gaps still remaining in our knowledge and thus to initiate
new research in this field. I want to thank the two authors, Dr. Horst
Wedemeyer (Karlsruhe) and Dr. David Brown (Harwell), for their excellent
contributions, the "Literaturabteilung" of the Karlsruhe Nuclear
Research Center for its help in providing reports and other documents
difficult to procure, as well as the staff of the Gmelin-Institute,
especially to Dr. K. -C.