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Effect Of Build Geometry And Build Parameters On Microstructure, Fatigue Life, And Tensile Properties Of Additively Manufactured Alloy 718, Anna Dunn
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Additive Manufacturing (AM), particularly laser powder bed fusion, is being studied for use in critical component applications. Tensile and fatigue testing shows differences when built using different laser powers. However, when fabricated in an as-printed geometry, the gauge sections of the two specimens are different and experience different thermal behavior. This work explores microhardness, microstructure size, Niobium segregation, and porosity from samples made with varying laser power and different build geometry sizes representative of the gauge sections in the tensile and fatigue bars. Results show that microhardness varies spatially across the sample. Smaller diameter metallographic coupons (fatigue diameter) have a …
Influence Of Fill Percentage And Baking Parameters On The Feedability Of Metal-Cored Arc Welding Wires, Angelica Marie Black
Influence Of Fill Percentage And Baking Parameters On The Feedability Of Metal-Cored Arc Welding Wires, Angelica Marie Black
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Adequate feedability is essential for GMAW processes to ensure efficiency. The feedability of a wire refers to the wire’s ability to feed continuously through the contact tip. While there are several known causes of feedability difficulties when using cored welding wires, there are many variables that have yet to be explored thoroughly. Three factors are investigated in this research to determine their effects on feedability of cored wires: fill percentage, baking time, and baking temperature. A set of metal-cored arc welding wires were created with various fill percentages, baking times, and baking temperatures. Tension testing, microhardness testing, microstructural characterization, and …
Aqueous Fabrication Of Pristine And Oxide Coated Znse Nanoparticles, Nicholas L. Van Zandt
Aqueous Fabrication Of Pristine And Oxide Coated Znse Nanoparticles, Nicholas L. Van Zandt
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Semiconducting nanoparticles have received significant attention due to their unique optoelectronic properties. Quantum dots (QDs), a class of spherical nanoparticles, possess a size-dependent bandgap and photoluminescence at visible wavelengths. QDs have many applications including biological labelling, solar cells, chemical impurity detection, and optical glasses. Doping QDs into optical glasses is highly desirable. High-quality QDs can be synthesized via liquid solution methods. However, solution-synthesized QDs often degrade over time and they cannot survive incorporation into a glass melt without protection. In this work, the aqueous synthesis of ZnSe QDs and coating with nanometer silica and alumina protective shells are investigated. The …
Fabrication And Analysis Of High-Performance Thermochemically Densified Wood, Victor Arulappan Pushparaj
Fabrication And Analysis Of High-Performance Thermochemically Densified Wood, Victor Arulappan Pushparaj
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While wood construction may be as ancient as humanity itself, wood remains one of the most utilized structural materials because of it’s availability, low cost, durability, surprisingly high specific mechanical properties, and renewability. Recent research into wood-based materials has focused on strategies for enhancing the strength and stiffness of as-grown materials. We fabricated densified wood by thermochemically treating raw white oak wood in Na2SO3 and NaOH solutions, followed by compressing the treated wood at 5MPa at high temperature. Treating the raw wood in NaOH and Na2SO3 cleaves the alpha-O-4 ether bond and beta-O-4 ether bonds, thus dissolving most of the …
Ab Initio Methylammonium Orientation And Monolayer Effects In Hybrid Perovskite Solar Cells, Jacob M. Artz
Ab Initio Methylammonium Orientation And Monolayer Effects In Hybrid Perovskite Solar Cells, Jacob M. Artz
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Methylammonium lead triiodide (MAPbI3) has garnered attention due to their high solar cell efficiencies and low cost to manufacture, but commercialization is not yet possible owing to poor environmental stability. Thus, researchers seek ways which optimize the performance of the MAPbI3 solar cell by modifying the architecture and through interfacial engineering of the charge transport layers. Difficulties in understanding these devices arise from ion migration, charge separation and recombination, and metastable, thermally active precessions of the methylammonium (MA) moiety in the lead iodide framework. In this work, focus is given to the perovskite and an adsorbed monolayer, 2,3,4,5,6-pentafluorothiophenol (C6F5SH), which …
Functionalizing Ceramic Matrix Composites By The Integration Of A Metallic Substructure With Comparable Feature Size, Elizabeth Pierce Heckman
Functionalizing Ceramic Matrix Composites By The Integration Of A Metallic Substructure With Comparable Feature Size, Elizabeth Pierce Heckman
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A metallic network has been embedded in a silicon carbide fiber– silicon carbide (SiC) matrix ceramic composite (CMC) in order to combine the functional properties of the metal and the structural properties of the CMC. The processing of the composite involves iterative pre-ceramic polymer infiltration and heating to temperatures at 1100°C. The metallic structure embedded in the CMC must retain its unique properties during processing and cannot convert to a silicide or carbide resulting from diffusion of Si and C species from the SiC matrix. To gain an understanding of the diffusion process, a fully processed CMC with tungsten, tantalum, …
Ab Initio Methylammonium Orientation And Monolayer Effects In Hybrid Perovskite Solar Cells, Jacob M. Artz
Ab Initio Methylammonium Orientation And Monolayer Effects In Hybrid Perovskite Solar Cells, Jacob M. Artz
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Methylammonium lead triiodide (MAPbI3) has garnered attention due to their high solar cell efficiencies and low cost to manufacture, but commercialization is not yet possible owing to poor environmental stability. Thus, researchers seek ways which optimize the performance of the MAPbI3 solar cell by modifying the architecture and through interfacial engineering of the charge transport layers. Difficulties in understanding these devices arise from ion migration, charge separation and recombination, and metastable, thermally active precessions of the methylammonium (MA) moiety in the lead iodide framework. In this work, focus is given to the perovskite and an adsorbed monolayer, 2,3,4,5,6-pentafluorothiophenol (C6F5SH), which …
Stabilization Of Β-Cristobalite In The Sio2-Alpo4-Bpo4 System, Kathryn Doyle
Stabilization Of Β-Cristobalite In The Sio2-Alpo4-Bpo4 System, Kathryn Doyle
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Fused silica (silica glass) is transparent in the optical and near-infrared and has a low dielectric constant, making it suitable as a window material for radio frequency radiation. However, at high temperatures (>1100C), fused silica will easily creep and lose dimensional stability. Crystallized silica is much more creep resistant than fused silica. Silica crystallizes to many different structures including quartz, tridymite, and α- and β cristobalite. The only cubic polymorph, which is suitable for both optical and radio frequency transmission in polycrystalline form, is β -cristobalite. Unfortunately, this polymorph transforms to α-cristobalite at ~300C, and the volume change during …
Ab Initio Modeling Of An Electron Transport Layer Interface In Hybrid Perovskite Solar Cells, Krantikumar Subhash Pawar
Ab Initio Modeling Of An Electron Transport Layer Interface In Hybrid Perovskite Solar Cells, Krantikumar Subhash Pawar
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Hybrid organic-inorganic perovskite solar cell is an emerging technology which has shown the fastest advancement in power conversion efficiency within a few years since introduction, thus making it one of the clean energy breakthroughs. These cells are based on thin-film technology which makes them suitable to manufacture using low-cost solution processing methods. As these types of cells are easily tunable with the selection of different materials, interfacial engineering is an important approach to increasing their efficiency. One of the main hurdles in this regard is the loss caused by the recombination of separated charges. An approach to tackle these issues …
Metal Coupon Testing In An Axial Rotating Detonation Engine For Wear Characterization, Gary S. North
Metal Coupon Testing In An Axial Rotating Detonation Engine For Wear Characterization, Gary S. North
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Rotating Detonation Engines (RDE) are being explored as a possible way to get better fuel efficiency for turbine engines than is otherwise possible. The walls of the RDE are subjected to cyclic thermal and mechanical shock loading at rates of approximately 3 KHz, with gas temperatures as high as 2976 K. This project performed testing with Inconel 625 and 304 stainless steel coupons in an RDE outer body to attempt to measure material ablation rates. Significant microstructural changes were observed to include grain growth in both alloys, carbide formation and grain boundary melting in Inconel, and formation of delta ferrite …
The Thermal And Mechanical Characteristics Of Lithiated Peo Lagp Composite Electrolytes, Jacob Michael Denney
The Thermal And Mechanical Characteristics Of Lithiated Peo Lagp Composite Electrolytes, Jacob Michael Denney
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Lithium-ion batteries are part of a multibillion-dollar industry that strives to meet the demands for an increasingly advanced technological future. Flexible batteries can be easily adapted from emerging novel wearable electronics to electrical vehicles and advanced solar panels. Solid-state batteries can greatly reduce the risk of fire or leaking hazardous materials due to puncture. For the development of solid-state flexible lithium based batteries polymer-ceramic composites are attractive electrolyte candidates because of their combined properties, such as electrical, thermal and mechanical properties, that not only overcome limitations from the base materials but may also render some enhanced performances resulting from the …
Hierarchical Carbon Structures With Vertically- Aligned Nanotube Carpets For Oil-Water Separation Under Different Conditions, Kimia Kiaei
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The primary purpose of this study is to investigate the role of surface nano-structuring in fluid separation. It is hypothesized that hierarchical carbon structures consisting of aligned carbon nanotube arrays strongly adhered to the surface of porous carbon solids such as fabric and foam, can be used for separation of polar and non-polar fluids by selective wettability of one fluid and rejection of another. The vertically-aligned carbon nanotube arrays, as synthesized, possess super hydrophobicity demonstrated by high water contact angle on their surfaces. On the other hand, they are incredibly oleophilic, showing a high affinity to adsorb oil. These properties …
Multi-Sensor Approach To Determine The Effect Of Geometry On Microstructure In Additive Manufacturing, Joseph R. Walker
Multi-Sensor Approach To Determine The Effect Of Geometry On Microstructure In Additive Manufacturing, Joseph R. Walker
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Laser powder bed fusion (LPBF) is an additive manufacturing technique used for making complex parts through a layer-by-layer process with fine feature resolution. However, the layer-by-layer process, with complex scanning patterns within each layer, introduces variability in thermal behavior leading to inconsistent microstructure and defects. The in- situ process monitoring approach in this work uses sensors including a high-speed visible camera, thermal camera, and spectrometer to evaluate each location in the LPBF process. Each sensor focuses on a different process phenomenon such as the melt pool or thermal behavior. An experimental study, using metallographic analysis and collection of sensor data, …
Preparation And Characterization Of Porous Pdms For Printed Electronics, Eyad Khalid M. Balbaid
Preparation And Characterization Of Porous Pdms For Printed Electronics, Eyad Khalid M. Balbaid
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Fabricating an elastomeric substrate with internal features could provide a novel structure with distinctive mechanical properties that allow them to stretch, bend and absorb the impact force. To date, polydimethylsiloxane (PDMS) is a great candidate as a substrate for flexible electronic applications, due to easy fabrication, high stability and low cost. In the current thesis, porous PDMS samples are fabricated and characterized based on the particle size and the fusion of salt and sugar treated micro-regions. The liquid PDMS is prepared by mixing the silicon elastomer base (Sylgard 184) and elastomer curing agent using volume ration 10:1. The salt and …
Deposition Of Nanoparticles Or Thin Films Via Magnetron Sputtering Towards Graphene Surface Functionalization And Device Fabrication, Bridget Jul Larson
Deposition Of Nanoparticles Or Thin Films Via Magnetron Sputtering Towards Graphene Surface Functionalization And Device Fabrication, Bridget Jul Larson
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Graphene, a 2-dimensional single layer of carbon, has high carrier mobility, strength and electrical conductivity. Due to the absence of a band gap and chemical reactivity, pristine graphene has less competitiveness in semiconductors and sensors. Functionalizing graphene is imperative in the development of advanced applications. Among various wet chemical or physical vapor deposition, magnetron sputtering is cost-effective, minimum maintenance, user-friendly, and can be used to rapidly deposit nano-particulates or thin films with less contaminations on any substrates surface. This study is to investigate the morphology evolution of the deposited films using magnetron sputtering and to find appropriate conditions for nanoparticulate …
Growth Of Two-Dimensional Molybdenum Disulfide Via Chemical Vapor Deposition, Zachary Durnell Ganger
Growth Of Two-Dimensional Molybdenum Disulfide Via Chemical Vapor Deposition, Zachary Durnell Ganger
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Graphene has successfully been a 2D material applied in various fields, but it is not the most appropriate candidate for many electronic devices unless its bandgap structure is tuned through functionalization. Among all other 2D material families, transition metal dichalcogenides (TMDs), represented by molybdenum disulfide (MoS2), are promising and emerging in power electronics due to their large direct bandgap and other electronic properties. 2D MoS2 has been fabricated through different approaches such as mechanical exfoliation, chemical etching, and chemical vapor deposition (CVD). The current major challenge in fabricating 2D MoS2 films is to produce a high-quality large-area monolayer film at …
Defect Engineering: Novel Strengthening Mechanism For Low- Dimensional Zinc Oxide Nanostructures, Seyed Emad Rezaei
Defect Engineering: Novel Strengthening Mechanism For Low- Dimensional Zinc Oxide Nanostructures, Seyed Emad Rezaei
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The advent of nanomaterials has opened a new avenue for designing and fabricating materials with unique properties, e.g., superior mechanical properties. Based on a common notion, the perfect structures are assumed to exhibit better mechanical properties, such as higher yield strength and Young's modulus. Therefore, researchers have devoted an extensive amount of time to decrease defect concentration by fabricating materials with the micro/nanoscale, e.g., nanowires (NWs) and nanobelts (NBs), to enhance the mechanical characteristics of the system. However, defects are a part of the fabrication process and precise control over synthesizing procedure is needed to eliminate them from the material. …
Functionalization And Characterization Of Chemical Vapor Deposited Graphene Sheets Towards Application In Chemical Vapor Sensing, Nicholas Alexander Engel
Functionalization And Characterization Of Chemical Vapor Deposited Graphene Sheets Towards Application In Chemical Vapor Sensing, Nicholas Alexander Engel
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Chemical/biological sensors serve many purposes in protecting machinery, the environment, and human life/wellness. Graphene, a two-dimensional (2-D) material made up of carbon atoms in a honeycomb-like lattice, is promising for applications to chemical/biological sensing due to its unique properties. Functionalization of graphene by surface decorating with nanoparticles and increasing interior adsorption sites can tailor its catalytic activity and electrical properties, and hence, important for detecting and distinguishing trace hazardous gases. This research introduces two different approaches to functionalize graphene towards enhanced sensitivity and selectivity of graphene-based sensors. The morphologies, structures, and electrical properties of the functionalized graphene are systematically characterized. …
Microstructural Characterization Of LensTm Ti-6al-4v: Investigating The Effects Of Process Variables Across Multiple Deposit Geometries, Laura Christine Davidson
Microstructural Characterization Of LensTm Ti-6al-4v: Investigating The Effects Of Process Variables Across Multiple Deposit Geometries, Laura Christine Davidson
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Laser based additive manufacturing of Ti-6Al-4V components is under consideration for aerospace applications. The mechanical properties of the finished components depend on their microstructure. Process mapping compares process variables such as heat source power, heat source travel speed, material feed rate, part preheat temperature and feature geometry to process outcomes such as microstructure, melt pool geometry and residual stresses. In this work, the microstructure of two-dimensional pads, multilayer pads, thin walls, and structural components at the steady state location was observed. A method for measuring β grain widths that allows for the calculation of standard deviations, confidence intervals, and variances …
Electronic And Crystalline Characteristics Of Mixed Metal Halide Perovskite Semiconductor Films, Patrick Joseph Cleaver
Electronic And Crystalline Characteristics Of Mixed Metal Halide Perovskite Semiconductor Films, Patrick Joseph Cleaver
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Solar technology has a long history of incremental improvements in cost, reliability and efficiency. However, solar cells based on lead halide perovskite films have made more rapid leaps forward in the past 10 years, making it the fastest growing solar technology in terms of efficiency. Leaders in academia and industry continue to find success in overcoming manufacturability and stability issues, but have not yet discovered a high-efficiency perovskite film without the use of toxic lead. Probing less toxic analogs to the highly efficient lead halide, a series of thin films with perovskite structures, i.e. A2BB’X6 where A = Cs or …
An Experimental Investigation Of Residual Stress Development During Selective Laser Melting Of Ti-6al-4v, Nathan Charles Levkulich
An Experimental Investigation Of Residual Stress Development During Selective Laser Melting Of Ti-6al-4v, Nathan Charles Levkulich
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Selective laser melting (SLM) is an additive manufacturing (AM) process that gives rise to large thermal gradients and rapid cooling rates that lead to the development of undesirable residual stress and distortion. In this work, a number of different techniques (i.e., x-ray-diffraction, hole-drilling, layer-removal, and contour) were utilized to establish the effect of process parameters on residual stress development during SLM of Ti-6Al-4V. The measurements indicated that higher laser power, slower scan speed, smaller stripe width, reduced substrate overhang, and reduced build plan area each reduce the level of residual stress. In addition, the correlation between microstructure, crystallographic texture, and …
Synthesis And Characterizations Of Lithium Aluminum Titanium Phosphate (Li1+Xalxti2-X(Po4)3) Solid Electrolytes For All-Solid-State Li-Ion Batteries, Jianping Yang
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New-generation low-emission transportation systems demand high-performance lithium ion (Li-ion) batteries with high safety insurance at broad operable temperatures. Highly conductive solid electrolyte is one of the key components for such applications. The objective of this thesis is to synthesize and characterize aluminum doped lithium titanium phosphate, i.e. Li1+xAlxTi2-x(PO4)3 (LATP), one of the solid-state electrolytes for potential applications to all solid-state lithium-ion batteries. In this research, sol-gel method and one step solid-state reaction approaches were explored and critical processes were optimized towards maximizing lithium ion conductivities at room temperature. The impacts of the processing conditions on the structures, morphologies, compositions of …
Friction Stir Welding Between Similar And Dissimilar Materials, Khaled Yousif Ali
Friction Stir Welding Between Similar And Dissimilar Materials, Khaled Yousif Ali
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This thesis focuses on the friction stir welding (FSW) between similar and dissimilar alloys. FSW is a solid state joining process that welds the work-pieces through a combination of heat generated by friction and mechanical stirring of the metals in the region of the joint. Being a solid state process, FSW can be used to weld alloys with significantly different melting points. This provides a significant benefit over traditional fusion welding process in a variety of applications in automotive, biomedical, aerospace, nuclear and petroleum industries. Two materials - an aluminum alloy (6061-T6, m.p. 582 - 652°C) and a steel (SAE …
Studies Of Ionic Liquid Hybrids: Characteristics And Their Potential Application To Li-Ion Batteries And Li-Ion Capacitors, Mengxin Liu
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Ionic liquids (ILs) have attracted much attention in electrochemical energy storage systems for their advantageous properties over traditional lithium salt/carbonate solvent electrolyte in terms of higher electrochemical potential windows, comparable ionic conductivity, negative vapor pressure and non-flammability. Ionic liquids can be used as the solvent-free electrolyte in electrochemical double layer capacitors (EDLCs) or can act as the important additives to the carbonate electrolyte in lithium ion batteries (LIBs). Recently, lithium ion capacitors (LICs) have emerge as a novel energy storage system to satisfy the demands for higher energy density and higher power density in portable and transportation systems. This Master …
Processing Of Ultra-Thin Film Of Un Modified C60 Fullerene Using The Langmuir-Blodgett Technique. Effect Of Structure On Stiffness And Optoelectric Properties, Hasanain Basim Altalebi
Processing Of Ultra-Thin Film Of Un Modified C60 Fullerene Using The Langmuir-Blodgett Technique. Effect Of Structure On Stiffness And Optoelectric Properties, Hasanain Basim Altalebi
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Monolayer films of C60 fullerene were for the first time produced successfully by using the Langmuir-Blodgett technique. The processing parameters were optimized and the structure of these films has been investigated using Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM). Film stiffness was measured to be in the range of 15 MPa to 32 MPa depending on the nature of the solvent used to process the films. Optical transparency and electrical performance have been measured and correlated to the film structure. While 100% transparent, the film measured conductivity was in the range of 1013 S/m, that is orders of …
Investigation Of Residual Stresses In Melt Infiltrated Sic/Sic Ceramic Matrix Composites Using Raman Spectroscopy, Kaitlin Noelle Kollins
Investigation Of Residual Stresses In Melt Infiltrated Sic/Sic Ceramic Matrix Composites Using Raman Spectroscopy, Kaitlin Noelle Kollins
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Ceramic matric composites (CMCs) are being developed for use in extreme operating conditions. Specifically, there is interest to replace superalloys with Silicon Carbide/Silicon Carbide (SiC/SiC) CMCs in the hot section of gas turbine engines because of their lower densities, high temperature performance, and oxidation resistance. Residual stresses in SiC/SiC CMCs are a direct result of the high temperature processing conditions, a mismatch in the coefficients of thermal expansion between composite constituents, and silicon crystallization expansion upon cooldown. Understanding the residual stress state and magnitudes of these stresses will enable better prediction of behavior and life performance in application environments. This …
Quantifying Amorphous Content Of Commercially Available Silicon Carbide Fibers, Ian Mark Wolford
Quantifying Amorphous Content Of Commercially Available Silicon Carbide Fibers, Ian Mark Wolford
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SiC/SiC ceramic matrix composites (CMCs) with potential applications at =2700°F (1482°C) are of significant interest to the Air Force. The high temperature performance of SiC fibers used within these composites is greatly affected by the presence of amorphous SiOC and free carbon in the fibers. Therefore quantification of this non SiC material in commercially available SiC fibers is extremely important. In this work Hi Nicalon, Hi-Nicalon Type-S, Tyranno-SA3, Cef-NITE, and Sylramic SiC fibers were studied. Changes in mass, grain size, and amorphous content were measured as a function of processing temperature and time. The amorphous material in each fiber was …
Experimental Validation Of The Calphad Approach Applied To Multi-Principle Element Alloys, Nathan J. Bryant
Experimental Validation Of The Calphad Approach Applied To Multi-Principle Element Alloys, Nathan J. Bryant
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High entropy alloys (HEAs) are a recent area of research in materials science. Their namesake is because their high entropy of mixing due to multiple metallic elements in a near equimolar ratio. The high entropy of mixing is supposed to suppress unwanted, brittle, ordered intermetallic phases, and form a single, randomly mixed solid solution phase. This phenomena makes HEAs a good candidate for structural applications. However, this entropy of mixing may not be enough to suppress all intermetallic phases. For this reason, the CALculation of PHAse Diagrams (CALPHAD) approach is being explored to predict phase equilibrium in HEAs. This study …
Carbon-Based Nanostructured Materials As Electrode In Lithium-Ion Batteries And Supercapacitors, Zhuo Yao
Carbon-Based Nanostructured Materials As Electrode In Lithium-Ion Batteries And Supercapacitors, Zhuo Yao
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Carbon-based nancomposites attract much attention as electrode materials in electrochemical energy storage systems due to their low-cost, extraordinary high electrical and thermal conductivity, super high surface area etc. In this research, graphene nanosheets (GNS) and their nanocomposites with manganese oxides (GNS/MnOx) or silicon nanowires (GNS/SiNWs/CF) are studied for their applications in Li-ion batteries and supercapacitors. GNS powders are synthesized via a chemical oxidation of nature graphite followed by appropriate reduction process. GNS/MnOx composites are synthesized rendering MnOx nanoparticles embedded on the surfaces of GNS. SiNWs grown in carbon fibers are mechanically mixed with GNS powders. The impacts of the manganese …
Analysis Of Laser Induced Spallation Of Electron Beam Physical Vapor Deposited (Eb-Pvd) Thermal Barrier Coatings, David Allen Beeler
Analysis Of Laser Induced Spallation Of Electron Beam Physical Vapor Deposited (Eb-Pvd) Thermal Barrier Coatings, David Allen Beeler
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The use of thermal barrier coatings (TBCs) has been an important factor in the efficiency improvements of jet engines due to their ability to withstand the extreme environments within the engine. With this improved resistance, TBCs have also become more difficult to remove without damaging the substrate. Mound Laser & Photonics Center, Inc. (MLPC) has developed an innovative, laser based technique to spall this coating. The intention of this work was to investigate and better understand the removal mechanism. Through experimentation and analysis (such as high speed video, Scanning Electron Microscopy and Energy Dispersive Spectroscopy, semi-logarithmic analysis, and a numerical …