The inclusions have a different chemical composition and give the steel different mechanical properties. These inclusions affect several properties of steel. In order to understand how the inclusions will affect the steel properties, the electrolytic extraction of 3D investigate method is applied on the steel grade of 42CrMo4. Then follow with Scanning Electron Microscope (SEM) observation. Steel samples from both ingot and rolling with and without heat treatment are observed and compared with different ratios. The result shown that, heat treatment can be applied for removing carbides successfully. And most inclusions are belonging to Type RS which is rod like MnS. The percentage of broken particles can be up to 80%, which means that the reason for the inclusions broken should be find. And heat treatment can affect the characteristics of elongated MnS.

Reducing carbon emissions is a looming challenge that will be required to limit global warming. One approach is to replace energy from fossil fuels with renewable electricity that has low carbon footprints. The continuous decrease of renewable electricity prices makes electrochemical processes very promising for environmentally friendly production of fuels and chemicals. One of the mature electrochemical processes is hydrogen (H₂) production from water electrolysis. If only excess solar/wind electricity is used to power water electrolyzers to produce green H₂, the intermittency of the electricity supply will require low-cost electrolyzer technologies. Emerging membraneless water electrolyzers offer an attractive approach to lowering the cost of H₂ production by eliminating membranes or diaphragms that are used in conventional water electrolyzers. One aim of this dissertation is to understand the performance limits of membraneless water electrolyzers compared to the conventional designs. Another key electrochemical process to reduce carbon emissions is the conversion of carbon dioxide (CO₂) to value-added fuels and chemicals. CO₂ captured from air or flue gas needs to be extracted from carbon capture solution and pressurized before feeding to a conventional CO₂ electrolyzer. In order to avoid these energy intensive steps to make pressurized CO₂, there is a growing interest in developing membrane-based electrolyzers that can directly utilize the carbon capture solution to conduct electrochemical CO₂ conversion. This dissertation also explores a scalable membrane-free electrolyzer design that can convert carbon capture solution to syngas. In Chapter 2, a parallel plate membraneless electrolyzer is used as a model system to demonstrate a combined experimental and modeling approach to explore its performance limits. This modeling framework quantitatively describes the trade-offs between efficiency, current density, electrode size, and product purity. Central to this work is the use of in situ high-speed videography (HSV) to monitor the width of H₂ bubble plumes produced downstream of parallel plate electrodes as a function of current density, electrode separation distance, and the Reynolds number (Re) associated with flowing 0.5 M H₂SO₄ electrolyte. These measurements reveal that the HSV-derived dimensionless bubble plume width serves as an excellent descriptor for correlating the aforementioned operating conditions with H₂ crossover rates. These empirical relationships, combined with electrochemical engineering design principles, provide a valuable framework for exploring performance limits and guiding the design of optimized membraneless electrolyzers. This framework shows that the efficiencies and current densities of optimized parallel plate membraneless electrolyzers constrained to H₂ crossover rates of 1% can exceed those of conventional alkaline electrolyzers but are lower than the efficiencies and current densities achieved by zero-gap polymer electrolyte membrane (PEM) electrolyzers. Chapter 3 presents a packed bed membraneless electrolyzer (PBME) design for which liquid bicarbonate electrolyte flows sequentially through alternating porous flow-through anodes and cathodes. Within this design, hydrogen oxidation at porous anodes is used to produce protons that trigger in situ CO₂ release immediately upstream of porous cathodes, where electrochemical CO₂ reduction generates the desired product and returns the solution pH back towards its inlet value. By using the sequential flow-cell arrangement, the PBME offers the ability to mitigate large concentration overpotentials and non-uniform current distributions that naturally arise during scale-up of conventional membrane-based devices that rely on lateral flow of catholyte parallel to the surface of the electrodes. This study uses in situ colorimetric imaging to highlight the ability of PBME to rebalance pH across electrodes. In addition, results obtained with a multi-cell PBME “stack” demonstrate the scalability of this concept and reveal the ability to increase CO₂ utilization from 12.9% for a single-cell PBME up to 20.5% for a four-cell PBME operated under baseline conditions. Modeling results indicate that current utilization values >80% are theoretically possible for optimized multi-cell PBMEs operated at ambient pressure. Chapter 4 demonstrates a stacked PBME design and an elevated pressure system. Hydrogen oxidation at the anode and hydrogen evolution at the cathode are conducted in this device at pressures up to 5 atm. The pressure of the system can be held at a constant value by the use of a back pressure regulator, and product gases can be collected with a gas sampling bag that’s directly connected to the back pressure regulator. The stereolithography 3D printing technology is used to fabricate components of the PBME from clear resin, which is suitable for the elevated pressure operation. Post-processing of the components makes surfaces transparent for imaging bubble dynamics in the device. Within this system, HOR current density of 120 mA cm-2 can be achieved at different pressures. Finally, Chapter 5 provides concluding remarks and discusses future opportunities and challenges for membraneless electrolyzers for water electrolysis and electrochemical CO₂ conversion.

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Engineered components can gain desirable properties when coated with surface materials. Wear-resistant coatings can improve the performance of contacting surfaces and allow for an extended life of the parts. Hard chromium has been the plating material of choice for certain wear and corrosion- resistant coatings because of its desirable combination of chemical resistance, adhesion, and mechanical properties. However, hexavalent chromium, a component of the process for applying hard chromium coatings, has been recognized by the EPA as having hazardous health and environmental impacts. Existing and planned environmental regulations restricts the use of process chemicals containing hexavalent chromium ions. This substantiates a need to develop an environmental friendly process for alternative coatings. Praxair has reported that Cr-Ni-C particles have a better corrosion resistance than current chromium carbide and nickel chromium powders. Today, Cr-Ni-C provides great qualities for flame spray and does not contain the toxic compounds used to deposit hard chromium, but is not compatible with application by cold spray. The purpose of this thesis project is to compare two processes for plating metal powder, chromium nickel carbide (Cr-Ni-C, CRC-410-1 from Praxair), with nickel. The particles were encapsulated using three different methods: one electroplating method previously used on particles, and two electroless plating processes using different solutions. The Cr-Ni-C particles were successfully encapsulated with Ni by one of the electroless deposition methods. The electrolytic deposition experiments did not yield the uniformity of coating without agglomeration that is being attained in industrial practice today. Further research on this method is recommended, due to the material operational cost in an industrial setting that is projected to be over 200 times cheaper than electroless deposition method. In the meantime, it should be possible to produce enough coated powder by electroless deposition to validate the utility of this coated powder in depositing wear- and corrosion-resistant coatings of Cr-Ni-C by cold spray.

A single-phase grid connected transformerless photovoltaic (PV) inverter for residential application is presented. The inverter is derived from a boost cascaded with buck converter along with a line frequency unfolding circuit. Due to its novel operating modes, high efficiency can be achieved because there is only one switch operating at high frequency at a time, and the converter allows the use of power MOSFET and ultra-fast reverse recovery diode. This dissertation begins with theoretical analysis and modeling of this boost-buck converter based inverter. And the model indicates small boost inductance will leads to increase the resonant pole frequency and decrease the peak of Q, which help the system be controlled easier and more stable. Thus, interleaved multiple phases structure is proposed to have small equivalent inductance, meanwhile the ripple can be decreased, and the inductor size can be reduced as well. A two-phase interleaved inverter is then designed accordingly. The double-carrier modulation method is proposed based on the inverter's operation mode. The duty cycle for buck switch is always one if the inverter is running in boost mode. And the duty cycle for boost switches are always zero if the inverter is running in buck mode. Because of this, the carrier for boost mode is stacked on the top of the carrier for buck mode, as a result, there is no need to compare the input and output voltage to decide which mode the inverter should operate in. And the inverter operates smoothly between these two modes. Based on similar concept, three advanced modulation methods are proposed. One of them can help further improve the efficiency, and one of them can help increase the bandwidth and gain, and the last one takes the advantage of both. Based on similar concept, another three dual-mode double-carrier based SPWM inverters are proposed. With both step-up and step-down functions, this type of inverter can achieve high efficiency in a wide range because only one switch operates at the PWM frequency at a time. Finally, the simulation and experiment results are shown to verify the concept and the tested CEC (California Energy Commission) efficiency is 97.4%. It performs up to 2% more efficiently better than the conventional solution. / Ph. D.

This thesis presents an investigation into the characteristics of and driving methods for light emitting diode (LED) lamp system. A comprehensive overview on the lighting development is proposed. The characteristic of the light emitting diode (LED) lamp is described and the requirements of the ballast for the light emitting diode (LED) lamp are presented. Although LED lamps have longer lifetime than fluorescent lamps, the short lifetime limitation of LED driver imposed by electrolytic capacitor has to be resolved. Therefore, an LED driver without electrolytic capacitor in the whole power conversion process is preferred. In this thesis, a single phase, power factor correction converter without electrolytic capacitors for LED lighting applications is proposed, which is a modified SEPIC converter working in discontinuous conduction mode (DCM). Different with a conventional SEPIC converter, the middle capacitor is replaced with a valley-fill circuit. The valley-fill circuit could reduce the voltage stress of output diode and middle capacitor under the same power factor condition, thus achieving higher efficiency. Instead of using an electrolytic capacitor for the filter, a polyester capacitor of better lifetime expectancy is used. An interleaved power factor correction SEPIC with valley fill circuit is proposed to further increase the efficiency and to reduce the input and output filter size and cost. The interleaved converter shows the features such as ripple cancellation, good thermal distribution and scalability. / Master of Science

Das Ziel dieser Dissertation besteht darin, einen Beitrag zur technologischen, ökonomischen und ökologischen Weiterentwicklung der anodischen Verfahren zur Oberflächenkeramisierung von Aluminium zu leisten. Die Arbeit ist in zwei thematische Schwerpunkte untergliedert. Im ersten Teil wird für die Hartanodisation eine hinsichtlich eines geringeren Energieeinsatzes optimierte Elektrolytzusammensetzung identifiziert und mit einem optimierten galvanostatischen Pulsmuster simultan appliziert. Im Ergebnis kann die Gesamtleistungsaufnahme um ca. 6 % reduziert werden, ohne die mechanischen Eigenschaften der Oxidschichten zu mindern. Im zweiten Schwerpunkt werden das Lichtbogen- und das Flammspritzen mit der plasmaelektrolytischen anodischen Oxidation kombiniert, um verschleißbeständige Aluminiumoxidschichten auf Stahl-, Titan- und Magnesiumsubstraten zu applizieren. Neben einer umfangreichen Mikrostrukturanalyse (REM, EDX, XRD, EBSD) werden die mechanischen Eigenschaften der Schichten untersucht und mit atmosphärisch plasmagespritzten Al2O3-Schichten verglichen. Insbesondere Oxidschichten auf lichtbogengespritztem AlCu4Mg1 zeigen dabei eine hohe Härte sowie eine sehr gute Verschleißbeständigkeit. / The aim of the present work is to contribute to the technological, economic and ecological improvement of the anodic processes for the surface ceramization of aluminum. The work is subdivided into two thematic priorities. In the first part, for the hard anodizing process an optimized electrolyte composition for a lower energy input is identified and applied simultaneously with an optimized galvanostatic pulse regime. As a result, the total power consumption can be reduced by approximately 6% without reducing the mechanical properties of the oxide coatings. In the second focus, arc and flame spraying are combined with plasma electrolytic anodic oxidation to apply wear resistant aluminum oxide coatings on steel, titanium and magnesium substrates. In addition to a comprehensive microstructural analysis (SEM, EDX, XRD, EBSD), the mechanical properties of the layers are investigated and compared with atmospheric plasma sprayed Al2O3 coatings. In particular, oxide layers formed on arc sprayed AlCu4Mg1 coatings show a high hardness as well as very good wear resistance.

To meet the growing energy world demands, and in conjunction, lower CO2 production levels, near zero emission energy sources must be pushed to the forefront as alternatives to fossil fuels. Photoelectrochemical (PEC) cells are a potential alternative to fossil fuels and have recently generated much interest because of their potential to electrolyze water into hydrogen fuel from sunlight. But in order to be competitive with fossil fuels, understanding the mass-transfer limitations in PEC systems is critical. This work focuses on the addressing the mass-transfer limitations in a conceptually novel PEC cell reactor, the Dual Bed Colloidal Suspension Reactor (DBCSR). Mass-transfer correlations for the DBCSR are presented. The correlations are based on experimental data obtained using two fabricated diffusion cells. The working correlation representative of both cells is given. An analysis of the orientation of the gas sparger suggests that the transport phenomena in both cells is not the same, and therefore using two correlations to represent similar systems is justified. An energy analysis is presented that shows that gas sparging is a low energy consumption option to mitigate mass-transfer limitations. Future work is suggested for better understanding the mass-transfer behavior in the DBCSR.