Arthur Jeremy Kropf

Structural considerations of intermetallic electrodes for lithium batteries

Although metal alloys and intermetallic compounds have been researched extensively as possible negative electrodes for lithium batteries, only recently have efforts been made to monitor the phase transitions that occur during their reaction with lithium by in situ X-ray diffraction. These studies have lead to attempts to exploit those systems that show strong structural relationships between a parent structure and its lithiated products. In this paper, an overview of several systems is presented, particularly those that operate by lithium insertion/metal displacement reactions with a host metal array at room temperature. An analogy between these reactions and the high-temperature electrochemical reaction of sodium/nickel chloride cells, which is 100% efficient, is provided. On this basis, a prognosis for using intermetallic electrodes in lithium-ion cells is given.

Microscopic Examination of a Corrosion Front in Spent Nuclear Fuel

Spent uranium oxide nuclear fuel hosts a variety of trace chemical constituents, many of which must be sequestered from the biosphere during fuel storage and disposal. In this paper we present synchrotron xray absorption spectroscopy and microscopy findings that illuminate the resultant local chemistry of neptunium and plutonium within spent uranium oxide nuclear fuel before and after corrosive alteration in an air-saturated aqueous environment. We find the plutonium and neptunium in unaltered spent fuel to have a +4 oxidation state and an environment consistent with solid-solution in the U02 matrix. During corrosion in an air-saturated aqueous environment, the uranium matrix is converted to uranyl u ( v I ) o ~ ~ + mineral assemblage that is depleted in plutonium and neptunium relative to the parent fuel. At the corrosion front interface between intact fuel and the uranyl-mineral corrosion layer, we find evidence of a thin (20 micrometer) layer that is enriched in plutonium and neptunium within a predominantly U4+ environment. Available data for the standard reduction potentials for N ~ ~ ~ + / N ~ ~ + and U O ~ ~ / U ~ + couples indicate that Np(IV) may not be effectively oxidized to Np(V) at the corrosion potentials of uranium dioxide spent nuclear fuel in air-saturated aqueous solutions.