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A Study on Directed Energy Deposition Process of Corrosion Resistant Coating for Lead-Bismuth Eutectic Environment
No full textDepartment of Nuclear EngineeringAs a means to respond to global climate change, many countries are developing the small modular reactor (SMR) as carbon-free energy. In addition to near-zero carbon emissions, SMR has many benefits, such as long operation time without changing fuels, low land occupancy, and fast manufacturing and installation. SMRs use various materials such as light water, inert gas, heavy metals (sodium, lead, lead-bismuth eutectic [LBE], etc.), molten salts, etc., as a coolant. Especially, a lead-cooled fast reactor using lead or LBE, as a coolant, has been recently considered to meet the requirements of Generation IV nuclear reactors. Lead-based heavy liquid metals exhibit good heat transfer capability and neutron moderation characteristics. Also, Lead-based heavy liquid metals have a high boiling point and are chemically stable with air and water. Thus, natural convection can remove decay heat in accidental conditions. These characteristics of lead or LBE enable the LFR to have inherent safety. The candidate materials for LFR are ferritic-martensitic steels, and austenitic stainless steels, among others. However, liquid metal embrittlement and liquid metal corrosion issues have been reported using these materials in liquid LBE environments. Many researchers have developed LBE corrosion-resistant materials. Among those materials, Fe-12Cr-2Si, Fe-15Cr-18Ni-3Al-0.3Ti, and Fe-13Cr-6Al alloy systems are candidate materials to have LBE corrosion resistance.
For newly developed materials to use pressure retaining parts of nuclear reactors, 10% or less surface thickness in cladding or coating is permitted. Also, surface coating on the final dimension product is preferred to avoid harsh post-processing, such as extrusion and pilgering.
In this study, the directed-energy deposition (DED) process using Fe-12Cr-2Si and Fe-15Cr-18Ni-3Al-0.3Ti alloy powders was carried out to make an LBE corrosion-resistant layer on the candidate material for fuel cladding (STS 316L). The optimized DED parameters (including powder requirements) were suggested for defect-free and restricted base metal dilution through the investigations of microstructures and corrosion properties of the LBE corrosion-resistant layers. Also, feasibility was verified to build a thin-surface coating of LMC-resisting materials on the final size of fuel cladding using a rotating tube DED process.clos
Behavioral Biometrics Optical Tactile Sensors That Decouple Dynamic Touch Signals Using Human-skin Mimetic Luminescence Microarchitectures
No full textSchool of Energy and Chemical Engineering (Chemical Engineering)clos
Designing Surficial Property for the Practical Use of Silicon-based Battery System
No full textSchool of Energy and Chemical Engineering (Energy Engineering (Battery Science and Technology))clos
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No full textSchool of Energy and Chemical Engineering (Energy Engineering)clos
Electrical Dipole Formation at Metal/Graphene Interface and Its Application for Junctionless CMOS Circuitry
Get PDFDepartment of PhysicsThe threshold voltage of metal/oxide/semiconductor field effect transistor (MOSFET) is primally determined by the work-function of gate metal electrode. In the aspect of device operation, the effective work-function of metal/oxide/semiconductor (MOS) capacitor gate stack is defined as the minimum energy required for electron at Fermi-level of metal to the vacuum level of semiconductor because there exist additional charge layers across MOS junction. The electrostatic potential variation from the metal to semiconductor surface makes effective work-function different to the intrinsic work-function of metal. In the real complementary MOS (CMOS) logic gate operation, the gate metal electrodes should be chosen to have effective work-functions suitable to control both n-channel MOSFET (NMOS) and p-channel MOSFET (PMOS). In order to modulate the threshold voltage on purpose, there are many researches beyond the conventional single metal gate electrode.
Among the several ideas, we adopted the method to form the interlayer contact with two-dimensional layer below the gate electrode. More specifically, we used the monolayer graphene as an insertion layer to modulate the effective metal work-function. When the monolayer graphene layer is inserted between metal/oxide interface it was found to from two kind of dipole layers. One is the charge layer consisted of free carrier doping due to the work-function difference between metal and graphene. Another is the dipole charge layer stemming from the asymmetric electron orbital overlapping of metal/graphene contact. We denote the latter as interaction dipole layer. In this research, we demonstrated the polarity and the magnitude of interaction dipole layer experimentally based on the theoretically expected results from the previous research using density functional theory (DFT) calculation.
In order to investigate the specific electrostatic potential change due to the graphene interlayer, first we used the Schottky junction which is consisted of metal/semiconductor interface supported by the Schottky barrier height modulation observed with direct carrier transport across the junction. Accordingly, it was found that the Schottky barrier height of low work-function metal become larger and that of high work-function metal become smaller with the aid of graphene interlayer. Next, we applied the effective work-function tuning observed in the Schottky junction to the MOS capacitor. In this case, the tendency of effective work-function tuning was observed quite similarly to that of Schottky junction extracted by the capacitance measurement. Here, the remarkable change was occurred when we use Al/SiO2/Si MOS capacitor showing that increasing more than 1 eV in effective work-function with the graphene interlayer. Hence, as considering the intrinsic work-function of Al is known as 4.08 eV which is quite similar to the electron affinity of Si, Al electrode with the selectively patterned underlying graphene interlayer can be one of the proper candidates to control NMOS and PMOS simultaneously because the Fermi-level of Al is close to the conduction band minimum and that of Al/graphene electrode is close to the valance band maximum of Si.
Supported by the convincing measurement result about large effective work-function tuning of Al electrode with the graphene insertion layer, we prepared MOSFET available with ambipolar operation in the low temperature based on the junctionless MOSFET fabrication process by using intrinsic Si substrate. At the low temperature, the fabricated junctionless ambipolar MOSFET can be used not only to construct complementary MOS (CMOS) logic gates such as inverter but also to explore about quantized conductivity. The experimental result that the gating region can be controlled by selectively patterned graphene layer can broaden the use of Al and Al/graphene electrodes to other applications. Beyond the two-dimensional conduction channel of conventional planar MOSFET, possible examples are the width-adjustable nanowire channel (one-dimension) or periodic quantum dots (zero-dimension). As a representative example, we provided the numerical calculation inducing nano-ribbon channel induced by partially-inserted graphene layer below Al gate electrode showing that the electron channel could have quantized energy states at the low temperature.ope
Enhancing the volumetric capacity of sodium ferrocyanide beyond its solubility limit in a Na-aqueous-catholyte redox flow battery
No full textSchool of Energy and Chemical Engineering (Energy Engineering (Battery Science and Technology))clos
Exploring new solid electrolyte materials for all-solid-state sodium-ion batteries
No full textSchool of Energy and Chemical Engineering (Energy Engineering (Battery Science and Technology))clos
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No full textGraduate School of Artificial Intelligenceclos
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No full textGraduate School of Artificial Intelligenceclos