Distribution coefficients oxidation state, effect

Composite-based PTC thermistors are potentially more economical. These devices are based on a combination of a conductor in a semicrystalline polymer—for example, carbon black in polyethylene. Other fillers include copper, iron, and silver. Important filler parameters in addition to conductivity include particle size, distribution, morphology, surface energy, oxidation state, and thermal expansion coefficient. Important polymer matrix characteristics in addition to conductivity include the glass transition temperature, Tg, and thermal expansion coefficient. Interfacial effects are extremely important in these materials and can influence the ultimate electrical properties of the composite. 

Redox Reactions and Valence States. The proposed reduction of Tc and U to the tetravalent state is indirectly indicated from the distribution measurements in non-oxidizing systems (c.f. Figure 2 and Table VII). By the addition of 10-20 mg/1 of Fe (c.f. Table II) a drastic increase of the distribution coefficient was observed both for Tc and U. Minerals like magnetite and chlorite also seem to have some reducing effect even after a short contact time. 

In conclusion, we can state that additions of small amounts of phosphoric acid increase the rate of Am (III) oxidation by Ag + ions without drastically changing the distribution coefficients of the species involved, because no complexation of Am occurs in these solutions, contrary to what occured in the extensive studies of Myassoeodov et al. (12, 13) in more concentrated phosphoric acid, where the kinetic effects must be attributed to changes in americium and silver (II) ionic species. In our Am-Cm separations we added phosphoric acid, which accelerates the oxidation rates of Am (III), solubilizes argentic oxide, and makes it possible to obtain Am (VI) quantitatively and rapidly at room temperature. 

Advantage may be taken of the different distribution coefficients exhibited by ions in various oxidation states to effect their separation from uranium. Iron reduced to ferrous Ion by hydrogen lodlde or ascorbic aold Is separated by elution with HCl. U(IV) may be separated from Pa(lV) and Th(iv). U(lV) la adsorbed by Amberllte rRA-i 01 (100 mesh) and Dowex-l (100-200 mesh) from >8M HCl. 

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