Thorium phosphate-diphosphate TPD

The authors have studied the dissolution of thorium phosphate diphosphate (TPD) with and without trivalent actinides they also studied a solid solution of Th(IV)/Pu(IV) phosphate diphosphate. The experiments consist of leaching studies where the rate of dissolution has been measured as a function of pH. This study does not provide any information on the solubility product of TPD. There is information on estimated equihb-rium constants for MP04(s) phases, where M = Am, Cm, Ce and Pr. These are secondary phases formed in the leach system. 

Thorium phosphate-diphosphate Th4(P04)4P207 (TPD, Pcam) is an actinide host phase due to its very high chemical durability and radiation stability [165-167]. TPD is synthesized by drying of thorium nitrate and phosphorus acid or ammonium phosphate solution, cold pressing at 300-800 MPa, and sintering of pellets at 1100-1250 for 10-30 hours. Th" in the TPD structure may be replaced by other tetravalent actinides but its isomorphic capacity is reduced with decreasing cationic radii in the following sequence > Np" > Pu". ... 

Pichot et al. (2001) conducted a preliminary study of irradiation effects on thorium phosphate-diphosphate. Powdered samples were irradiated with 1.5 Gy dose of gamma-rays. The formation of PO b and POO free radicals were detected using electron spin resonance (ESR) and thermoluminescence (TL) methods. These free radicals do not modify the macroscopic properties of the TPD and disappear when the sample is heated at 400°C. The implantation of 1.6 MeV He with a fluence of 10 ions/cm and 5 meV Au with a fluence 4 x 10 ions/cm causes some surface damage to sintered samples. Amorphization and chemical decomposition of the matrix were observed for the dose of 10 ions/cm and higher when irradiated with Pb (200 keV) and Au " (5 MeV). These effects were evidenced by means of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). 

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