Enhancement of Diffusion, Densification and Solid-State Reactions in Dielectric Materials Due to Interfacial Interaction of Microwave Radiation: Theory and Experiment

Abstract

A detailed theoretical model and experimental study are presented that formulate and prove the existence of a robust ponderomotive force (PMF) near the interfaces in a granular dielectric material under microwave radiation. The model calculations show that the net direction of the PMF is pore angle-dependent. For most of the pore angles, the net force is towards the interface creating a mass transport that fills the interfacial pores and facilitates densification. For small ranges of angles, near 180o and 360o, PMF drives the ions in the reverse direction and depletes the pores. However, the net force for such ranges of angles is small. The PMF also enhances the diffusion of the mobile ionic species and, consequently, accelerates the solid-state reaction by increasing the collision probability. The proof-of-concept experiments show that a mixture of elemental powders can diffuse, react, and form dense materials when radiated by the microwave in just a few minutes. Such characteristics, together with field-induced decrystallization, offer a novel and simple approach for the synthesis of nanostructured compounds, which can have practical implications in ceramic technologies and thermoelectric materials.

Thermal Management Systems and Waste Heat Recycling by Thermoelectric Generators—An Overview

“…Many more strategies have been studied to enhance the performance of thermoelectric compounds. The examples would be materials selection (as described in Figure 7) [64][65][66], sintering method (e.g., pondermotive force in microwave sintering enhances the diffusion of mobile ionic species and results in accelerating the solid-state reaction by increasing the collision probability) [67], band engineering (e.g., modulation doping, resonance level, and band convergence) [68][69][70][71][72][73][74], carrier pocket engineering [75][76][77], complex structures [78,79], carrier energy filtering [80,81], creation of resonant energy levels close [63] with permission), (c) GNPs precipitation at microstructural barriers of CoVSn compound (adapted from [28] with permission), (d) schematic band alignment of Schottky contact for graphene/n-type semiconductor (adapted from [28] with permission), (e) schematic band alignment of Schottky contact for graphene/p-type semiconductor (adapted from [28] with permission), (f) schematic diagrams of hole trap, hole barrier, electron trap, and electron barrier generated at grain boundaries (adapted from [28] with permission).…”

“…Many more strategies have been studied to enhance the performance of thermoelectric compounds. The examples would be materials selection (as described in Figure 7) [64][65][66], sintering method (e.g., pondermotive force in microwave sintering enhances the diffusion of mobile ionic species and results in accelerating the solid-state reaction by increasing the collision probability) [67], band engineering (e.g., modulation doping, resonance level, and band convergence) [68][69][70][71][72][73][74], carrier pocket engineering [75][76][77], complex structures [78,79], carrier energy filtering [80,81], creation of resonant energy levels close to the band edges [70], low dimensional structures [82,83], magnetic interaction (e.g., carrier trap-ping and magnon (spin wave) excitations) [84,85], and lowering the thermal conductivity (e.g., phonon scattering) [58,[86][87][88][89][90].…”

Far-from-equilibrium effects of electric and electromagnetic fields in ceramics synthesis and processing

“…Several additional mechanisms have also been suggested to explain the influence of microwave fields on chemical reactions, phase transformations, and microstructural evolution. Examples include field-induced ponderomotive driving forces, 3,5,9,78,79 localized heating around grain boundaries, 2,16,54 and the effect of ultrahigh heating rates that can radically alter mass-transport phenomena. 29,45 However, an important question remains unanswered: Can microwave radiation provide sufficient energy to break chemical bonds?…”

“…Microwaves at 2.4-2.5 GHz have been shown to induce chemical and structural changes in both organic and inorganic materials. 4,17,22,55,56,74,75,[77][78][79] However, the energy of these waves is not, in theory, sufficient to provide the 1-10 eV/atom required to bring changes in molecular, atomic and electronic structures of metallic, semiconducting, and molecular materials. Unlike microwaves, the strong electric fields in an ultrafast laser pulses can drive electrons and the lattice away from equilibrium, resulting in lattice disorder.…”

Applications of Thermoelectric Generators To Improve Catalytic-Assisted Hydrogen Production Efficiency: Future Directions

“…In this approach, thermoelectric generators (TEGs) have shown promising capabilities in recovering the low-grade waste energy. − This technology is an effective method employed to take full advantage of using wasted thermal energy to improve the efficiency of clean energy sources, such as solar and geothermal. Furthermore, TEGs offer the benefit of simple and durable design with no moving parts and noise and are easy to operate with zero emissions. − In addition to the recent advances in the development of TE materials − as the main recipe for manufacturing better TEGs, several applications have been proposed and designed to commercialize TEGs with enhanced efficiencies for energy-intensive industrial operations (Figure ). Figure a presents a setup to evaluate the performance of TEGs on the energy fluxes in a diesel engine, providing modifications in the energy flux distribution of the engine and improving its efficiency through a reduction in the heat loss by as much as 32% due to the incorporation of TEGs …”