Lakeisha Walker

Transport of Ions in Mesoporous Carbon Electrodes during Capacitive Deionization of High-Salinity Solutions

Desalination of high-salinity solutions has been studied using a novel experimental technique and a theoretical model. Neutron imaging has been employed to visualize lithium ions in mesoporous carbon materials, which are used as electrodes in capacitive deionization (CDI) for water desalination. Experiments were conducted with a flow-through CDI cell designed for neutron imaging and with lithium-6 chloride ((6)LiCl) as the electrolyte. Sequences of neutron images have been obtained at a relatively high concentration of (6)LiCl solution to provide information on the transport of ions within the electrodes. A new model that computes the individual ionic concentration profiles inside mesoporous carbon electrodes has been used to simulate the CDI process. Modifications have also been introduced into the simulation model to calculate results at high electrolyte concentrations. Experimental data and simulation results provide insight into why CDI is not effective for desalination of high ionic-strength solutions. The combination of experimental information, obtained through neutron imaging, with the theoretical model will help in the design of CDI devices, which can improve the process for high ionic-strength solutions.

Neutron imaging of ion transport in mesoporous carbon materials.

Neutron imaging is presented as a tool for quantifying the diffusion of ions inside porous materials, such as carbon electrodes used in the desalination process via capacitive deionization and in electrochemical energy-storage devices. Monolithic mesoporous carbon electrodes of ∼10 nm pore size were synthesized based on a soft-template method. The electrodes were used with an aqueous solution of gadolinium nitrate in an electrochemical flow-through cell designed for neutron imaging studies. Sequences of neutron images were obtained under various conditions of applied potential between the electrodes. The images revealed information on the direction and magnitude of ion transport within the electrodes. From the time-dependent concentration profiles inside the electrodes, the average value of the effective diffusion coefficient for gadolinium ions was estimated to be 2.09 ± 0.17 × 10(-11) m(2) s(-1) at 0 V and 1.42 ± 0.06 × 10(-10) m(2) s(-1) at 1.2 V. The values of the effective diffusion coefficient obtained from neutron imaging experiments can be used to evaluate model predictions of the ion transport rate in capacitive deionization and electrochemical energy-storage devices.

The Use and Refinement of Neutron Imaging Techniques for Archaeological Artifacts

Abstract Neutron imaging is a nondestructive application capable of producing two- and three-dimensional maps of archaeological objects’ external and internal structure, properties, and composition. This report presents the recent development of neutron imaging data collection and processing methods at Oak Ridge National Laboratory (ORNL), which have been advanced, in part, by information gathered from the experimental imaging of 25 archaeological objects over the past three years. The dual objectives of these imaging experiments included (1) establishing the first methodological procedures for the neutron imaging of archaeomaterials involving the CG-1D beamline and (2) further illustrating the potential of neutron imaging for archaeologists to use in the reverse engineering of ancient and historical objects. Examples of objects imaged in two and three dimensions are provided to highlight the application’s strengths and limitations for archaeological investigations, especially those that address ancient and historic technologies, materials science, and conservation issues.

TEMPERATURE CONTROL DIAGNOSTICS FOR SAMPLE ENVIRONMENTS

In a scientific laboratory setting, standard equipment such as cryocoolers are often used as part of a custom “sample environment” system designed to regulate temperature over a wide range. The end user may be more concerned with precise sample temperature control than with base temperature. Cryogenic systems, however, tend to be specified mainly in terms of cooling capacity and base temperature. Technical staff at scientific user facilities (and perhaps elsewhere) often wonder how to best specify and evaluate temperature control capabilities. Here we describe test methods and give results obtained at a user facility that operates a large sample environment inventory. Although this inventory includes a wide variety of temperature, pressure, and magnetic field devices, the present work focuses on cryocooler‐based systems.