10 research outputs found
Thermodynamic properties and atomic structure of Ca-based liquid alloys
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 159-164).To identify the most promising positive electrodes for Ca-based liquid metal batteries, the thermodynamic properties of diverse Ca-based liquid alloys were investigated. The thermodynamic properties of Ca-Sb alloys were determined by emf measurements. It was found that Sb as positive electrode would provide the highest voltage for Ca-based liquid metal batteries (1 V). The price of such a battery would be competitive for the grid-scale energy storage market. The impact of Pb, a natural impurity of Sb, was predicted successfully and confirmed via electrochemical measurements. It was shown that the impact on the open circuit voltage would be minor. Indeed, the interaction between Ca and Sb was demonstrated to be much stronger than between Ca and Pb using thermodynamic modeling, which explains why the partial thermodynamic properties of Ca would not vary much with the addition of Pb to Sb. However, the usage of the positive electrode would be reduced, which would limit the interest of a Pb-Sb positive electrode. Throughout this work, the molecular interaction volume model (MIVM) was used for the first time for alloys with thermodynamic properties showing strong negative deviation from ideality. This model showed that systems such as Ca-Sb have strong short-range order: Ca is most stable when its first nearest neighbors are Sb. This is consistent with what the more traditional thermodynamic model, the regular association model, would predict. The advantages of the MIVM are the absence of assumption regarding the composition of an associate, and the reduced number of fitting parameters (2 instead of 5). Based on the parameters derived from the thermodynamic modeling using the MIVM, a new potential of mixing for liquid alloys was defined to compare the strength of interaction in different Ca-based alloys. Comparing this trend with the strength of interaction in the solid state of these systems (assessed by the energy of formation of the intermetallics), the systems with the most stable intermetallics were found to have the strongest interaction in the liquid state. Eventually, a new criteria was formulated to select electrode materials for liquid metal batteries. Systems with the most stable intermetallics, which can be evaluated by the enthalpy of formation of these systems, will yield the highest voltage when assembled as positive and negative electrodes in a liquid metal battery.by Sophie Poizeau.Ph.D
Multicomponent Gas Diffusion in Porous Electrodes
Multicomponent gas transport is investigated with unprecedented precision by
AC impedance analysis of porous YSZ anode-supported solid oxide fuel cells. A
fuel gas mixture of H2-H2O-N2 is fed to the anode, and impedance data are
measured across the range of hydrogen partial pressure (10-100%) for open
circuit conditions at three temperatures (800C, 850C and 900C) and for 300mA
applied current at 800C. For the first time, analytical formulae for the
diffusion resistance (Rb) of three standard models of multicomponent gas
transport (Fick, Stefan-Maxwell, and Dusty Gas) are derived and tested against
the impedance data. The tortuosity is the only fitting parameter since all the
diffusion coefficients are known. Only the Dusty Gas model leads to a
remarkable data collapse for over twenty experimental conditions, using a
constant tortuosity consistent with permeability measurements and the Bruggeman
relation. These results establish the accuracy of the Dusty Gas model for
multicomponent gas diffusion in porous media and confirm the efficacy of
electrochemical impedance analysis to precisely determine transport mechanisms
Production of Oxygen from Lunar Regolith using Molten Oxide Electrolysis
This slide presentation reviews the possible use of molten oxide electrolysis to extract oxygen from the Lunar Regolith. The presentation asserts that molten regolith electrolysis has advanced to be a useful method for production of oxygen and metals in situ on the Moon. The work has demonstrated an 8 hour batch of electrolysis at 5 amps using Iridium inert anodes