<報文>高レベル放射性廃棄物の固定化に関する研究 : V 硝酸バリウムと二酸化チタンの反応

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Titanates with a perovskite-type structure are expected as one of recommended materials which are capable of immobilizing high-level radio active waste for a long period. In the present paper, mechanism and kinetics for the reaction of Ba（NO3）2 with TiO2（anatase） were studied by use of thermobalance, DTA and X-ray diffraction methods. Barium is one of fission products with high yield, and TiO2 is used as a matrix for immobilizing the radwaste. According toTG/DTA, the melting point of Ba（NO3）2WaS5750C，Ba（NO3）2 began to be decomposed above the melting point. The reaction of Ba（NO3）2 with TiO2 occurred near 460℃ or at higher temperatures in the solid state. From the conversion vs. time curves at constant temperatures, it was deduced that the reaction obeyed the equation controlled by the phase boundary reaction : kt＝1-（1－α）l/3, where k is a reaction rate in min-1, t is time, and α is a conversion ratio of the reaction. The relationship between logarithm of the reaction rate and the reciprocal absolute temperature showed two straight lines, which were discreate at 580℃. This means that the reaction above 580℃ occurs in the solid-liquid state and that below 580℃ proceeds in the solid-solid state. The rate of the former was about a fifth of the value extrapolatlng the latter, but the reaction mechanism was not changed. Both lines gave the same apparent activation energy, 212 kJ moI-1.
横浜国立大学の論文