Materials Science and Engineering Commons^™

The Effect Of Process Parameters And Surface Condition On Bond Strength Between Additively Manufactured Components And Polymer Substrates, Bharat Bhushan Chivukula

Graduate Theses and Dissertations

Additive patching is a process in which printers with multiple axes deposit molten material onto a pre-defined surface to form a bond. Studying the effect of surface roughness and process parameters selected for printing auxiliary part on the bond helps in improving the strength of the final component. Particularly, the influence of surface roughness, as established by adhesion theory, has not been evaluated in the framework of additive manufacturing (AM). A full factorial design of experiments with five replications was conducted on two levels and three factors, viz., layer thickness, surface roughness, and raster angle to examine the underlying effects …

Strain Phase Separation: Formation Of Ferroelastic Domain Structures, Fei Xue, Yongjun Li, Yijia Gu, Jinxing Zhang, Long-Qing Chen

Materials Science and Engineering Faculty Research & Creative Works

Phase decomposition is a well-known process leading to the formation of two-phase mixtures. Here we show that a strain imposed on a ferroelastic crystal promotes the formation of mixed phases and domains, i.e., strain phase separation with local strains determined by a common tangent construction on the free energy versus strain curves. It is demonstrated that a domain structure can be understood using the concepts of domain/phase rule, lever rule, and coherent and incoherent strain phase separation, in a complete analogy to phase decomposition. The proposed strain phase separation model is validated using phase-field simulations and experimental observations of PbTiO …

Design And Synthesis Of Dynamic Covalent Polymer Scaffolds With Controlled Architectures, Emily Annette Hoff

Dissertations

The design and synthesis of functional, controlled polymer architectures is essential to the development of new materials with precise and tailorable properties or applications. The work described in this dissertation focuses on the development of controlled polymer architectures with dynamic linkages for the design of multifunctional materials and surfaces via robust, efficient, and stimuli-responsive strategies.

In Chapter III, a post-polymerization modification strategy based on ambient temperature nucleophilic chemical deblocking of polymer scaffolds bearing N-heterocycle blocked isocyanate moieties is reported. Room temperature RAFT polymerization of three azole-N-carboxamide methacrylates, including 3,5-dimethyl pyrazole, imidazole, and 1,2,4-triazole derivatives, afforded reactive polymer scaffolds …

Nanostructured Morphologies In Glassy Polymer Networks, Brian Greenhoe

Dissertations

The body of this work describes a novel approach for the dispersion of multi-walled carbon nanotubes in a high T_g epoxy prepolymer matrix using a twin screw high-shear continuous reactor. The method demonstrated improves on previous dispersion methods in several ways. It offers increased efficiency through excellent heat transfer, while being solvent-less, scale-able, and tailorable to drive dispersion states to judiciously chosen dispersion states. Furthermore, it was shown that dispersion state and agglomerate morphology can be directed, in several ways, through processing conditions and also by controlling the matrix viscosity profile through cure. Broadband dielectric spectroscopy, optical hot-stage microscopy, …

Nanomanufacturing Outside Of The Lab: An Academic-Industry Partnership Case Study, Ann E. Delaney

Boise State University Theses and Dissertations

In 2003, policy entrepreneur Dr. Mihail Roco wrote in Nature Biotechnology, “The key goals of nanotechnology are advances in molecular medicine, increased working productivity, extension of the limits of sustainable development and increased human potential.” From initial visions like Roco’s until now, there has been significant investment and research progress in the field of nanotechnology. According to the White House, over $20 billion has been invested in nanotechnology research and development by the United States government since 2000.¹ There is now a growing emphasis on transitioning from a focus on fundamental research towards a focus on overcoming …

Empirical Models For Structural Effects Of A-Site Point Defects And Ordering In Perovskites, Kevin Ross Tolman

Boise State University Theses and Dissertations

Composition-structure-property relationships are essential keys to unlocking the strength of predictive crystal chemistry. Awkwardly, the electroceramics industry largely relies on various time-consuming and expensive trial-and-error experiments to address new questions which often could otherwise be interpolated from published data. Indeed, predictive models, which can be derived from empirical evidence, can greatly aid the direction and support of future development in a meaningful, apt, and cost-effective way. Theory suggests that intrinsic properties on the scale of a unit cell may be estimated from the sizes and charges of the chemical constituents alone. Ultimately, researchers could be provided a compositional recipe for …

Evaluation Of Efficiency Of Various Materials To Shield From Radiation In Space Using The Monte Carlo Transport Code Called Fluka, Roman Savinov

Master's Theses

The purpose of this study is to improve spacecraft shielding from radiation in space. It focuses on the evaluation of shielding efficiency of different materials. The efficiency of a shield is evaluated by the dose profile within the shield and the amount of dose absorbed by a target using the Monte Carlo transport code called FLUKA. The output of this code is validated by recreating the experiments from published papers and comparing the results. Once the FLUKA’s output is validated, the efficiency of sixteen materials, subject to SPE and GCR sources, are evaluated. The efficiency comparison is made by fixing …

Nanoindentation Techniques For The Evaluation Of Silicon Nitride Thin Films, Weston T. Mangin

Master's Theses

Silicon nitride thin films are of interest in the biomedical engineering field due to their biocompatibility and favorable tribological properties. Evaluation and understanding of the properties of these films under diverse loading and failure conditions is a necessary prerequisite to their use in biomedical devices. Three wafers of silicon nitride-coated silicon were obtained from Lawrence Livermore National Laboratory and used to create 96 samples. Samples were subjected to nanoindentation testing to evaluate the mechanical properties of the film. Samples were subjected to nanoimpact testing to compare the damage resistance of the film to separate nanoimpact types. Samples were subjected to …

Hot Ductility And Hot-Shortness Of Steel And Measurement Techniques: A Review, G Sahoo, M Deepa, B Singh, A Saxena

Journal of Metals, Materials and Minerals

Usage of steel scrap has become important in steel making from the view points of resource conservation and preventing environmental problems. High levels of steel scraps are used in the production of steel, especially, via electric arc furnaces (EAF). However, Copper, which is mainly contained in the scrap of cars and home electronic appliance, is problematic in mechanical workings at elevated temperatures and limits the usage of scrap iron. It is enriched at steel/scale interface by preferential oxidation of Fe, which leads to liquid embrittlement or surface cracking during hot working. This type of defect is well known as surface …

Petrographic Analysis Of Ceramic Artifacts From Ban Di Kiln, Pattani Province, Thailand, W Dhanmanonda, S Hongrittipun, D Aussavamas

Journal of Metals, Materials and Minerals

This research paper aims to investigate the components of archaeological ceramic artifacts collected from Ban Di kiln, Pattani province, Thailand. The procedure involves the petrographic examination of fragments of ceramic artifacts, focusing on raw materials, sources of materials, and production techniques. Ban Di ceramics date back to 16th and 17th centuries, the period in which ancient Patani had enjoyed its prosperity in domestic and foreign trade. This study shows that alluvial soils from coastal plains, with high content of sand, are predominant materials in the manufacture. The production process involves jiggering and hot pressing at the firing temperatures between 400-550 …

Dependence Of Electrical Resistivity On Plastic Deformation In Copper-Aluminum Alloy Cu0.975al0.025, J G Miranda Ramos, E Medrano Atencio, M Quiroga Agurto, F A Reyes Navarro

Journal of Metals, Materials and Minerals

We measure changes of electrical resistivity after a plastic deformation. We supposed that the changes are due to a large density of dislocation present in the polycrystalline samples; therefore, we also measure the amount of dislocations after the plastic deformation. Thus, for our aim, we elaborated copper-aluminum alloys Cu0.975Al0.025; next, with them, we fabricated metallographic specimens, which were submitted to traction subsequently. We measured the electrical resistivity before and after the traction. The obtained results are discussed in a theoretical framework of dislocations.

Role Of The Inner Shell Architecture On The Various Blinking States And Decay Dynamics Of Core-Shell And Core-Multishell Quantum Dots, Pooja Bajwa

Graduate Theses and Dissertations

Colloidal semiconductor nanocrystals (quantum dots, QDs) have received much attention in recent years due to their uniquely size-tunable properties leading to a number of promising applications. Some of their most popular applications include their use as fluorescent probes in biology, as electro-optical components and in photovoltaic devices. CdSe-based QDs are particularly important because of their ease of synthesis, high photoluminescence quantum yields (PL QYs) across the whole visible spectrum and their photostabilty. Shelling of core QDs is usually carried out to improve their optical properties, minimize outer environmental effects on their properties, and avoid toxic element exposure to the environment. …

Investigation Of The Optical Properties Of Pbse/Pbx Nanocrystals For Photodetector Applications, Haley Ann Morris

Graduate Theses and Dissertations

Lead selenide and lead selenide/lead sulfide core/shell nanocrystals were investigated for use in near infrared photodetectors. A colloidal synthesis method was used for both the core and core/shell configurations. The lead sulfide shell was examined in order to mitigate oxidation of the nanoparticle surface. Absorbance and photoluminescence spectra were measured at room temperature and 77 K, respectively. Transmission electron microscopy images were also obtained to confirm crystallography and size. Bulk lead selenide was simulated in WIEN2k utilizing the linear-augmented plane wave method of solving density functional theory to better understand the electronic structure of PbSe. The crystal structure, electron density, …

Photoluminescence Studies Of Amorphous Boron Carbide And Tungsten Diselenide Thin Films, David M. Allendorfer

Department of Electrical and Computer Engineering: Dissertations, Theses, and Student Research

For many years scientists and engineers have been researching semi-conducting materials for use in a broad array of electronic devices. With the growing demand for faster, smaller and more efficient electronics, new materials must be characterized and their properties quantified. The focus of this thesis is to develop a system to measure photoluminescence in opto-electronic materials. Photoluminescence measurements are important because it can give researchers valuable information about a material’s band structure. This thesis begins by presenting the carrier recombination mechanisms and how they apply to photoluminescence. A system was developed to measure photoluminescence spectroscopy. This system was tested with …

An Experimental And Computational Investigation Of The Mechanical, Structural, And Hydrothermal Properties Of Mesoporous Materials, Dayton Gage Kizzire

Graduate Theses/Dissertations

Periodic mesoporous materials have tunable pore sizes and high surface to volume ratios. Some of the most anticipated applications are those that call for energy harvesting in extreme environments, and these materials have a great structural stability to withstand the harsh conditions. In this work, the structural properties of mesoporous materials SBA-15 silica and Al-SBA-15 aluminosilica have been investigated by pressure dependent in situ small angle x-ray scattering (SAXS) using a diamond anvil cell (DAC) up to ~12 GPa in pressure. Hydrothermal measurements were also made in this manner to near supercritical water/steam conditions (to 255 °C and ~ 114 …

Sulfate Resistance Of Nanosilica Contained Portland Cement Mortars, Iani Batilov Batilov

UNLV Theses, Dissertations, Professional Papers, and Capstones

Soils, sea water and ground water high in sulfates are commonly encountered hostile environments that can attack the structure of concrete via chemical and physical mechanisms which can lead to costly repairs or replacement. Sulfate attack is a slow acting deteriorative phenomenon that can result in cracking, spalling, expansion, increased permeability, paste-to-aggregate bond loss, paste softening, strength loss, and ultimately, progressive failure of concrete. In the presented research study, Portland cement (PC) mortars containing 1.5% to 6.0% nanosilica (nS) cement replacement by weight were tested for sulfate resistance through full submersion in sodium sulfate to simulate external sulfate attack. Mortars …

Alkali-Activated Natural Pozzolan/Slag Binder For Sustainable Concrete, Meysam Najimi

UNLV Theses, Dissertations, Professional Papers, and Capstones

This study aimed to fully replace Portland cement (PC) with environmentally friendly binders capable of improving longevity of concrete. The new binders consisted of different proportions of natural Pozzolan and slag which were alkaline-activated with various combinations of sodium hydroxide and sodium silicate. A step-by-step research program was designed to (1) develop alkali-activated natural Pozzolan/slag pastes with adequate fresh and strength properties, (2) produce alkali-activated natural Pozzolan/slag mortars to assess the effects of dominant variables on their plastic and hardened properties, and (3) finally produce and assess fresh, mechanical, dimensional, transport and durability properties of alkali-activated natural Pozzolan/slag concretes. The …

Structure-Property Relationships Of Polyisobutylene-Block-Polyamide Thermoplastic Elastomers, Morgan Dunn Heskett

Master's Theses

Thermoplastic elastomers (TPEs) are a class of polymer fit for a wide variety of applications due to their customizability. In the synthesis of these types of materials, an elastically-performing polymer, deemed the “soft block,” is combined with a stiffer “hard block” polymer, each of which can be selected based on their own specific properties in order to achieve desired material behavior in the final copolymer. Recently, the use of polyisobutylene as a soft block in combination with a polyamide hard block has been investigated for use in TPE synthesis. While the material showed some promising behavior, many properties were still …

Dual Role Of Sb Ions As Electron Traps And Hole Traps In Photorefractive Sn2P2S6 Crystals, Brant E. Kananen, Eric M. Golden, Sergey A. Basun, D. R. Evans, A. A. Grabar, I. M. Stoika, John W. Mcclory, Nancy C. Giles, Larry E. Halliburton

Faculty Publications

Doping photorefractive single crystals of Sn₂P₂S₆ with antimony introduces both electron and hole traps. In as-grown crystals, Sb³⁺ (5s²) ions replace Sn²⁺ ions. These Sb³⁺ ions are either isolated (with no nearby perturbing defects) or they have a charge-compensating Sn²⁺ vacancy at a nearest-neighbor Sn site. When illuminated with 633 nm laser light, isolated Sb³⁺ ions trap electrons and become Sb²⁺ (5s²5p¹) ions. In contrast, Sb³⁺ ions with an adjacent Sn vacancy trap holes during illumination. The hole is primarily …

Focused-Based Multifractal Analysis Of The Wake In A Wind Turbine Array Utilizing Proper Orthogonal Decomposition, Naseem Ali, Hawwa Falih Kadum, Raúl Bayoán Cal

Mechanical and Materials Engineering Faculty Publications and Presentations

Hot-wire anemometry measurements have been performed in a 3×3 wind turbine array to study the multifractality of the turbulent kinetic energy dissipation. A multifractal spectrum and Hurst exponents are determined at nine locations downstream of the hub height, bottom and top tips. Higher multifractality is found at 0.5D and 1D downstream of the bottom tip and hub height. The second order of the Hurst exponent and combination factor shows the ability to predict the flow state in terms of its development. Snapshot proper orthogonal decomposition (POD) is used to identify the coherent and incoherent structures and to reconstruct the stochastic …