ENTHALPY OF SOLUTION OF CALIFORNIUM OXYCHLORIDE - CALCULATION OF THE STANDARD ENTHALPY OF FORMATION OF CFOCL

The enthalpy of solution of CfOCl in 1.022 mol dm(-3) HCl was measured on the 0.4-1.5 mg scale, and the standard enthalpy of formation at 29 8 K for this compound was calculated. The CfOCl was prepared by heatin g in air at 280-320 degrees C the solid hydrated trichloride, obtained by slow evaporation of Cf(III) in HCl solution. X-ray powder diffract ion analysis confirmed the material to be the expected oxychloride, wh ich exhibits the PbFCl-type tetragonal structure. Dissolutions of the oxychloride were made at 25.0 degrees C in an isoperibol solution micr ocalorimeter. Enthalpy of solution values were calculated according to the equation: CfOCl(cr) + 2HCl((sln)) --> CfCl3(sln) + H2O(sln). The Delta(f)H(0) (CfOCl(cr)) was determined to be -920 +/- 7 kJ mol(-1). I nterpolation within Delta(f)H(0) (AnOCl((cr))), where An = U, Pu, Am, Cm, and Cf, as a function of An(III) ionic radius yielded Delta(f)H(0) (BkOCl(cr)) = -944 +/- 10 kJ mol(-1). (C) 1998 Elsevier Science S.A.