A model study of electric double layer capacitor (EDLC)-style capacitors in which the electrodes were composed of low surface area-oriented flakes of graphite that compressed to form a paper-like morphology has suggested that ion transport rates significantly impact EDLC energy and power density. Twelve capacitors were constructed, each using the same model electrode material and the same aqueous NaCl electrolyte, but differing in relative electrode orientation, degree of electrode compression, and presence/absence of an ionic transport salt bridge. All were tested with a galvanostat over a range of discharge currents. Significant differences in energy and power density and estimated series resistance were found as a function of all the factors listed, indicating that capacitor performance is not simply a function of the electrode surface area. This simple postulation was advanced and tested against data: net ion (Na+, Cl−) ‘velocity’ during both charge and discharge significantly impacts capacitive performance.

A method to modify ceramics using a low power microwave plasma torch is described.The size, shape, surface area, and phase of alumina particles were dramatically modified by passage through an atmospheric pressure argon plasma, operated at 1 kW or less power.Specifically, irregularly shaped particles of gamma-alumina with an average diameter of 11 mu m were converted to smaller (ca. 4 mu m) spherical particles primarily consisting of delta-and alpha-(corundum) phases.Also notable was the finding that modifications of the particles, such as changes in surface area, correlate to applied plasma energy.The plasma torch was operated with an argon flow rate of 5 slpm, power of between 400 and 1000 W, and average particle residence time in the plasma of 0.1 s.

The ability to translate the high electrical conductivity of individual carbon nanotubes to bulk carbon nanotube materials has proven challenging. In this work, we present the use of reduction expansion synthesis to attach copper nanoparticles to the surface of tubes within carbon nanotube sheets. Those metallic particulates serve as a link between the tube strands in the carbon nanotube network and promote an increase in electrical conductivity. The reduction expansion synthesis process included the introduction of copper salts into the carbon nanotube structure and thermal treatment of the sheets in the presence of urea, under inert atmospheres. As a result, through the reduction process promoted by the urea decomposition byproducts, copper nanoparticles directly nucleate on the nanotube surface. The enhanced conductive nature of the Cu-carbon nanotube sheets observed establishes reduction expansion synthesis as an inexpensive, rapid and scalable alternative to increase the electrical conductivity of bulk carbon nanotube materials.

Two theories of the fields generated by charges on parallel plate capacitors, the standard model (SM) found in virtually all text books and the recently proposed super dielectric material-theory (SDM-Theory), are described, and contrasted, in terms of theory and experimentally tested predictions. Only the SDM-Theory model is found to be consistent with thermodynamics, basic field theory, and experimental results. According to the SM, dielectrics in the volume between the electrodes of a parallel plate capacitor store the energy in a capacitor in the form of greatly, relative to the no dielectric case, increased electric field strength. This model is shown to be inconsistent with path independent changes in state property (e.g., voltage), and predicts, incorrectly, that dielectric material outside the volume between the electrodes will have no effect on any measurable properties such as capacitance and energy density. In contrast, according to SDM-Theory, a theory shown to be consistent with path independent changes in state properties, as well as “conservative field theory,” the increased stored energy in the presence of dielectrics is not associated with energy in fields, but rather it is due to the “extra” charges stored on the electrodes. The extra charge is required to create a given net field in the presence of a dielectric. Indeed, according to SDM-Theory, the effect of dielectric material, because its polarization is opposite to the electrodes, reduces the net field at all points in space, including within the volume of the dielectric. This is the absolute opposite of the “action” of a dielectric predicated by the SM. In the SDM-Theory, at a given capacitor voltage, virtually identical net fields exist with and without a dielectric, but the capacitance (amount of stored charge) and stored energy, a linear function of the amount of stored charge, of the latter configuration can be many orders of magnitude greater. Moreover, SDM-Theory predicts, consistent with recent observations, that dielectric material external to the volume between electrodes should be nearly as effective at increasing capacitance, etc., as the same dielectric material between the electrodes.

Carbon nanotube (CNT) conductive composites have attracted significant attention for their potential use in applications such as electrostatic dissipation and/or electromagnetic interference shielding. The focus of this work is to evaluate resistivity trends of extremely low loading (<0.1 wt%) epoxy-CNT composites that lack a connected CNT network, but still present electrical conductivity values appropriate for those uses. The impact of current, temperature, and cycle life on electrical properties are here identified and tied to possible performance limits. At extremely low loadings, the CNT content is not sufficient to form a completely interconnected grid, thus, electrons must travel through insulating media. While still in the semi-conductor range, resistivity values are observed to decrease with increasing direct current and demonstrate a non-ohmic behavior. CNT epoxy composites were subjected to elevated currents and/or temperatures over diverse periods of time to examine impacts on resistivity. Microstructural analyses of composite samples were conducted to observe signs of damage for specimens taken to extreme temperatures/currents. An understanding of the electrical conductivity characteristics of extremely low loading epoxy-CNT composites and their failure mechanisms will aid in understanding risks associated with their use in challenging environments that may include high temperatures, high currents, and/or high frequencies.

A simple, low temperature, method, hydrogen-enhanced atomic transport (HEAT), for creating metallic-bonded brown bodies of order 40% bulk density in molds of designed shape from Ti metal particles is introduced. In this initial study 40 micron titanium particles were poured into graphite molds, then heated to temperatures equal to or greater than 650 °C for four hours in a flowing ambient pressure gas mixture containing some hydrogen led to brown body formation that closely mimicked the mold shape. The brown bodies were shown to be dense, metallic bonded, and consisted of primarily Ti metal, but also some TiH. It is postulated that hydrogen is key to the sintering mechanism: it enables the formation of short-lived TiHx species, volatile at the temperatures employed, that lead to sintering via an Ostwald Ripening mechanism. Data consistent with this postulate include findings that brown bodies are formed with hydrogen present (HEAT process) had mechanical robustness and only suffered plastic deformation at high pressure (ca. 5000 Atm). In contrast, brown bodies made in identical conditions, except the flowing gas did not contain hydrogen, were brittle, and broke into micron scale particles under much lower pressure. HEAT appears to have advantages relative to existing titanium metal part manufacturing methods such as powder injection molding that require many more steps, particularly debinding, and other methods, such as laser sintering, that are slower, require very expensive hardware and expert operation.

It is well established that dramatic increases in conductivity occur upon the addition of conductive filler materials to highly resistive polymeric matrices in experimental settings. However, the mechanisms responsible for the observed behavior at low filler loadings, below theoretical percolation limits, of even high aspect ratio fillers such as carbon nanotubes (CNT) are not completely understood. In this study, conductive composites were fabricated using CNT bundles dispersed in epoxy resins at diverse loadings, using different dispersion and curing protocols. Based on electron microscopy observation of the CNTs strands distribution in the polymeric matrices and the corresponding electrical conductivities of those specimens, we concluded that no single electron transfer model can accurately explain the conductive behavior for all the loading values. We propose the existence of two different conductive mechanisms; one that exists close to the percolation limit, from low loadings' to higher CNT contents (CNT % wt > 0.1) and a second for extremely low loadings', near the percolation threshold (CNT % wt < 0.1). The high conductivity observed for composites at low CNT loading values can be explained by the existence of a percolative CNT network that coexists with micron size regions of non-conductive material. In contrast, samples with extremely low CNT loading values, which present no connectivity or close proximity between CNT bundles, show an electrical conductivity characterized by a current/voltage dependence. Data suggests that at these loadings, conduction may occur via a material breakdown mechanism, similar to dielectric breakdown in a capacitor. The lessons learned from the data gathered in here could guide future experimental research aimed to control the conductivity of CNT composites.

As predicted by the theory of super dielectric materials, simple tests demonstrate that dielectric material on the outside of a parallel plate capacitor dramatically increases capacitance, energy density, and power density. Simple parallel plate capacitors with only ambient air between the plates behaved as per standard theory. Once the same capacitor was partially submerged in deionized water (DI), or DI with low dissolved NaCl concentrations, still with only ambient air between the electrodes, the capacitance, energy density, and power density, at low frequency, increased by more than seven orders of magnitude. Notably, conventional theory precludes the possibility that material outside the volume between the plates will in any fashion impact capacitive behavior.

Described herein is a novel method, Reduction Expansion Synthesis-Sintered Metal (RES-SM), to create a sintered metal body of a designed shape at ambient pressure, hundreds of degrees below the metal melting temperature. The precursor to the metal part is a mixture of metal oxide particles and activated metal particles, and in this study specifically nickel oxide and activated nickel metal particles. It is postulated that the metal oxide component is reduced via exposure to chemical radical species produced via thermal decomposition of urea or other organic compounds. In the study performed, the highest temperature required was 950 °C, the longest duration of high temperature treatment was 1200 s, and in all cases, the atmosphere was inert gas at ambient pressure. As discovered using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD), the metal that forms via the RES process presents necks of completely reduced metal between existing metal particles. The 'as produced' parts are similar in properties to 'brown' metal parts created using more standard methods and require 'post processing' to full densify. Parts treated by hot isostatic pressing show fully self-supporting, robust structures, with hardness values like others reported in literature for traditional fabrication methods. This novel method uses affordable and environmentally friendly precursors to join metallic parts at moderate temperatures, produces fully reduced metals in a very short time and has potential to make many parts simultaneously in a standard laboratory furnace.

This work demonstrates that a version of the Reduction Expansion Synthesis (RES) process, Cr-RES, can create a micron scale Cr coating on an iron wire. The process involves three steps. I. A paste consisting of a physical mix of urea, chrome nitrate or chrome oxide, and water is prepared. II. An iron wire is coated by dipping. III. The coated, and dried, wire is heated to ~800 °C for 10 min in a tube furnace under a slow flow of nitrogen gas. The processed wires were then polished and characterized, primarily with scanning electron microscopy (SEM). SEM indicates the chrome layer is uneven, but only on the scale of a fraction of a micron. The evidence of porosity is ambiguous. Elemental mapping using SEM electron microprobe that confirmed the process led to the formation of a chrome metal layer, with no evidence of alloy formation. Additionally, it was found that thickness of the final Cr layer correlated with the thickness of the precursor layer that was applied prior to the heating step. Potentially, this technique could replace electrolytic processing, a process that generates carcinogenic hexavalent chrome, but further study and development is needed.

This study shows high stability Sn (10 wt %)/carbon Li-ion battery anodes can be made via the Reduction Expansion Synthesis (RES) process. Hybrid Sn/C anodes had an initial capacity of 425 mAh g-1 which stabilized to similar to 340 mAh g-1 after less than 10 cycles. Unlike earlier Sn/C anodes, capacity remained virtually constant for more than 180 additional cycles. Neat carbon independently tested for Li capacity had a steady specific capacity of 280 mAh g-1. The difference detected between the pure carbon and Sn/C cases are consistent with Sn having the theoretical capacity of similar to 1000 mAh g-1. The high stability of the RES derived anodes, relative to earlier Sn based electrodes, is postulated to exist because RES synthesis enables the formation of direct, strong bond between Sn and carbon substrate atoms, hence reducing the rate of Sn electrode disintegration and capacity fade due to expansion upon lithiation. X-ray diffraction and transmission electron microscopy are consistent with this postulate as both show an initial Sn particles size of only a few nanometers and minimal growth after cycling. Reduced interface resistance is also indicative of unique Sn-carbon bond. Published by Elsevier Ltd.

The discharge time dependence of key parameters of electrostatic capacitors employing a dielectric composed of the oxide film formed on titanium via anodization, saturated with various aqueous ion solutions, that is tube-super dielectric materials (T-SDM), was thoroughly documented for the first time. The capacitance, dielectric constant, and energy density of novel paradigm supercapacitors (NPS) based on T-SDM saturated with various concentrations of NaNO3, NH4Cl, or KOH were all found to roll-off with decreasing discharge time in a fashion well described by simple power law relations. In contrast, power density, also well described by a simple power law, was found to increase with decreasing discharge time, in fact nearly reaching 100 W/cm3 for both 30 wt% KOH and NaNO3 solution-based capacitors at 0.01 s, excellent performance for pulsed power. For all capacitors, the dielectric constant was tested, which was greater than 105 for discharge times >0.01 s, confirming the materials are in fact T-SDM. The energy density for most of the capacitors was greater than 80 J/cm3 of dielectric at a discharge time of 100 s, once again demonstrating that these capacitors are competitive for energy storage not only with existing commercial supercapacitors but also with the best prototype carbon-based supercapacitors.

Extensive testing showed, as predicted, that punched membranes, filled with a gel containing aqueous salt solutions, behave as superdielectric materials (SDM). Punched membrane superdielectrics employed herein consisted of a commercial cellulose based membrane material, Celgard 16 μ thick, a material frequently used as a separator material in supercapacitors, into which macroscopic holes (ca. 2.5 mm) were punched with a laser cutter, and the holes subsequently filled with a gel-like material composed of fumed silica, NaCl and water. The gross dielectric constants measured, generally > 105, and the energy densities, > 40 J/cm3 during slow discharge, were in the range expected for superdielectric materials. The measured capacitance and energy density tracked the number of holes punched/area filled with the dielectric gel. Also, the observed power law decrease in all parameters including energy, power and capacitance, followed the same trends observed in other classes of SDM. Control studies included testing dielectrics composed of Celgard into which no holes were punched, but the SDM gel spread, also produced values consistent with the SDM model: no measurable capacitance using the standard protocol. Finally, the values measured suggest these materials rival the energy density of some common battery types at low discharge rates, and surpass the best commercial supercapacitors at low discharge rates.

A new fundamental principle of the theory of dielectrics in capacitors is demonstrated. That is, dielectric material in any geometry that reduces the field generated by charges on capacitor electrodes is effective in increasing capacitance. Specifically, it is shown that super dielectric material on the outer surfaces of the electrodes of a parallel plate capacitor increases dielectric constant, as well as energy and power densities, by orders of magnitude. The implicit assumption in all current capacitor theory, that the “capacitor” is only that region occupied by the electrodes and the space between them, is shown to be incorrect.

The focus of the present work is the evaluation of the low-frequency dielectric performance of titanium dioxide nanotube arrays, created by anodization, filled with aqueous NaCl solutions. At low frequency (ca. <10 −2 Hz), capacitors made up of this so-called tube super-dielectric material were found to have extreme dielectric constants, greater than 1 billion. The same capacitors also registered unprecedented energy densities, nearly 400 J/cm 3 , better than that observed (<250 J/cm 3 ) for the same type of anodized titania filled with an aqueous solution of NaNO 3 , and about an order of magnitude better than commercial supercapacitors. Sufficient data were collected to propose a correlation relating dielectric thickness and salt concentration to overall energy density.

This work aimed to identify and address the main challenges associated with fabricating large samples of carbon foams composed of interwoven networks of carbon nanofibers. Solutions to two difficulties related with the process of fabricating carbon foams, maximum foam size and catalyst cost, were developed. First, a simple physical method was invented to scale-up the constrained formation of fibrous nanostructures process (CoFFiN) to fabricate relatively large foams. Specifically, a gas deflector system capable of maintaining conditions supportive of carbon nanofiber foam growth throughout a relatively large mold was developed. ANSYS CFX models were used to simulate the gas flow paths with and without deflectors; the data generated proved to be a very useful tool for the deflector design. Second, a simple method for selectively leaching the Pd catalyst material trapped in the foam during growth was successfully tested. Multiple techniques, including scanning electron microscopy, surface area measurements, and mechanical testing, were employed to characterize the foams generated in this study. All results confirmed that the larger foam samples preserve the basic characteristics: their interwoven nanofiber microstructure forms a low-density tridimensional solid with viscoelastic behavior. Fiber growth mechanisms are also discussed. Larger samples of mechanically-robust carbon nanofiber foams will enable the use of these materials as strain sensors, shock absorbers, selective absorbents for environmental remediation and electrodes for energy storage devices, among other applications.

The goal of this research was to describe the effects of the main anodization variables on the morphology of the resulting titania nanotube arrays. Four variables were considered in this study: applied voltage, fluoride and water concentrations, and time. The first three variables were studied simultaneously in a central composite design of experiments using SEM measurements of tube length as the response variable. The effect of time was modeled using transferred charge as the response variable. A field assisted oxidation-dissolution growth model was validated over a broad range of experimental conditions under which tube growth can be accurately predicted directly from the current transients using Faraday's laws. The effects of anodization variables were described based on this model and a simple, empirical kinetic expression was obtained and successfully tested against data from other authors with fairly small errors over a broad range of conditions.

A constant current charge/discharge protocol which showed fumed silica filled to the point of incipient wetness with aqueous NaCl solution to have dielectric constants >108 over the full range of dielectric thicknesses of 0.38–3.9 mm and discharge times of 0.25–>100 s was studied, making this material another example of a superdielectric. The dielectric constant was impacted by both frequency and thickness. For time to discharge greater than 10 s the dielectric constant for all thicknesses needed to be fairly constant, always >109, although trending higher with increasing thickness. At shorter discharge times the dielectric constant consistently decreased, with decreasing time to discharge. Hence, it is reasonable to suggest that for time to discharge >10 s the dielectric constant at all thicknesses will be greater than 109. This in turn implies an energy density for a 5 micron thick dielectric layer in the order of 350 J/cm3 for discharge times greater than 10 s.

The dielectric constants of nylon fabrics saturated with aqueous NaCl solutions, Fabric-Superdielectric Materials (F-SDM), were measured to be >105 even at the shortest discharge times (>0.001 s) for which reliable data could be obtained using the constant current method, thus demonstrating the existence of a third class of SDM. Hence, the present results support the general theoretical SDM hypothesis, which is also supported by earlier experimental work with powder and anodized foil matrices: Any material composed of liquid containing dissolved, mobile ions, confined in an electrically insulating matrix, will have a very high dielectric constant. Five capacitors, each composed of a different number of layers of salt solution saturated nylon fabric, were studied, using a galvanostat operated in constant current mode. Capacitance, dielectric constant, energy density and power density as a function of discharge time, for discharge times from ~100 s to nearly 0.001 s were recorded. The roll-off rate of the first three parameters was found to be nearly identical for all five capacitors tested. The power density increased in all cases with decreasing discharge time, but again the observed frequency response was nearly identical for all five capacitors. Operational limitations found for F-SDM are the same as those for other aqueous solution SDM, particularly a low maximum operating voltage (~2.3 V), and dielectric “constants” that are a function of voltage, decreasing for voltages higher than ~0.8 V. Extrapolations of the present data set suggest F-SDM could be the key to inexpensive, high energy density (>75 J/cm3) capacitors.

A theoretical and experimental study on atmospheric pressure microwave plasma-based assembly of free standing graphene sheets is presented. The synthesis method is based on introducing a carbon-containing precursor (C2H5OH) through a microwave (2.45 GHz) argon plasma environment, where decomposition of ethanol molecules takes place and carbon atoms and molecules are created and then converted into solid carbon nuclei in the 'colder' nucleation zones. A theoretical model previously developed has been further updated and refined to map the particle and thermal fluxes in the plasma reactor. Considering the nucleation process as a delicate interplay between thermodynamic and kinetic factors, the model is based on a set of non-linear differential equations describing plasma thermodynamics and chemical kinetics. The model predictions were validated by experimental results. Optical emission spectroscopy was applied to detect the plasma emission related to carbon species from the 'hot' plasma zone. Raman spectroscopy, scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS) techniques have been applied to analyze the synthesized nanostructures. The microstructural features of the solid carbon nuclei collected from the colder zones of plasma reactor vary according to their location. A part of the solid carbon was deposited on the discharge tube wall. The solid assembled from the main stream, which was gradually withdrawn from the hot plasma region in the outlet plasma stream directed to a filter, was composed by 'flowing' graphene sheets. The influence of additional hydrogen, Ar flow rate and microwave power on the concentration of obtained stable species and carbon−dicarbon was evaluated. The ratio of sp3/sp2 carbons in graphene sheets is presented. A correlation between changes in C2 and C number densities and sp3/sp2 ratio was found.