Kinetics of the Thermal Decomposition of Aqueous Manganese( II ) Nitrate Solutions on Porous Tantalum

Abstract

Porous tantalum electrodes were immersed in aqueous solutions of manganese ( II ) nitrate and the kinetics of the thermal decomposition of the adhering solution were determined, in situ. The rate laws for each of the stages in the decomposition were found to be different from those which best described the decomposition of the bulk solution. However, the activation energies were essentially the same as those for the bulk. The last stage of the decomposition, i.e., the decomposition of the intermediate manganese ( III ) oxynitrate, exhibited the same dependence on atmospheric moisture content as previously observed for the bulk material. The activation energy was reduced about 12 kcal/mole by the presence of moisture and the pre‐exponential term of the Arrhenius equation was lowered by about 106 sec−1. Surface area measurements gave smaller values for samples decomposed in moist atmospheres, and scanning electron micrographs indicated such surfaces were also more continuous and homogeneous. The decomposition occurred at lower temperatures for subsequent immersions.