Chris Rudolf

Electrolytes for lithium ion batteries which work over a wide range of temperatures are of interest in both research and applications. Unfortunately, most traditional electrolytes are unstable at high temperatures. As an alternative, solid state electrolytes are sometimes used. These are inherently safer because they have no flammable vapors, and solid state electrolytes can operate at high temperatures, but they typically suffer from very low conductivity at room temperatures. Therefore, they have had limited use. Another option which has been previously explored is the use of ionic liquids. Ionic liquids are liquid salts, with nominally zero vapor pressure. Many are liquid over the temperature of interest (20–200°C). And, there is a tremendous range of available chemistries that can be incorporated into ionic liquids. So, ionic liquids with chemistries that are compatible with lithium ion systems have been developed and demonstrated experimentally at room temperature. In this stud...

Traditional metal forming requires large forces and substantial tooling, high power, and large amounts of energy. Passing an electric current through the metal during forming has been shown to reduce the deformation energy and increase the materials’ formability, leading to the possibility of increased formed-shape complexity. The primary challenge in characterizing electric current effects on plastic deformation has been decoupling the current and intrinsic Joule heating effects. Many of the experiments reported in the literature have specimen geometry and fixturing features that can lead to concentrations of stress, deformation, current, and/or temperature. The presence of one or more localized field concentrations in the specimen gage length can bias the observed deformation behavior and lead to erroneous conclusions. In this work, we addressed this challenge by conducting independent electro- and thermo-mechanical experiments for the current- and temperature-controlled character...

The demand for high‐power electrical transmission continues to increase with technical advances in electric vehicles, unmanned drones, portable devices, and deployable military applications. In this study, significantly enhanced electrical properties (i.e., a 450% increase in the current density breakdown limit) are demonstrated by synthesizing axially continuous graphene layers on microscale‐diameter wires. To elucidate the underlying mechanisms of the observed enhancements, the electrical properties of pure copper wires and axially continuous graphene–copper (ACGC) wires with three different diameters are characterized while controlling the experimental conditions, including ambient temperature, gases, and pressure. The study reveals that the main mechanism that allows the application of extremely large current densities (>400 000 A cm−2) through the ACGC wires is threefold: the continuous graphene layers considerably improve: 1) surface heat dissipation (224% higher), 2) elect...

Silicon, the earth’s second most abundant element ushered in new age of computing capability. More recently, silicon is enjoying a second wave of technological adoption as a constituent of lithium-ion battery negative electrodes; made possible in practice by reducing the dimensions to the nanoscale and/or compositing with traditional carbon-based lithium host materials. The large lithium capacity and subsequent volumetric expansion and mechanical fracture have been documented extensively and the nano and composite routes mentioned above provide strategies to overcome this obstacle. We take a new exploratory approach elevating the working temperature to demonstrate reversible alloying and dealloying of lithium and silicon, in its most basic bulk form, a wafer. The brittle nature of silicon may be made more elastic when operated above its brittle-to-ductile transition temperature, potentially leading to more elastic behavior capable of maintaining its structure with modulation of its ...

Abstract Ti2AlC based MAX phase coatings were successfully deposited on Inconel 625 substrate by a cold spraying technique. A dense coating of 70 μm thickness was deposited. Ball-on-disk wear behavior of Ti2AlC coating at room temperature (25 °C), and high temperature (600 °C) were studied. The coefficient of friction (COF) and wear volume loss at 600 °C reduced by ~ 21% and ~ 40% respectively, due to the lubricious nature of oxide layer formed at a higher temperature. Mechanical properties of the Ti2AlC coating were also studied by carrying out nanoindentation and nano-scratch tests at room temperature and 300 °C and varying loads. For a low load of 7000 μN at room temperature, Ti2AlC coating exhibited a higher elastic modulus of 273 GPa compared to the elastic modulus of 191 GPa at high temperature (300 °C). The room temperature nano-scratch at 7000 μN displayed brittle behavior with fracture, chipping and wear debris formation along the scratch path. However, high temperature (300 °C) scratch path exhibited ductile nature with plowing, cutting and no wear debris formation. The wear volume loss was several orders of magnitude higher at 8 N load scratch. The overall wear behavior in MAX phase Ti2AlC coating at multiple load scales is elucidated in terms of the interaction volume varying from a single to several splats in the cold sprayed structure.

In situ mechanical property testing has the ability to enhance quantitative characterization of materials by revealing the occurring deformation behavior in real time. This article will summarize select recent testing performed inside a scanning electron microscope on various materials including metals, ceramics, composites, coatings, and 3-Dimensional graphene foam. Tensile and indentation testing methods are outlined with case studies and preliminary data. The benefits of performing a novel double-torsion testing technique in situ are also proposed.