Materials Science and Engineering Commons^™

Processing And Characterization Of Boron Carbide-Hafnium Diboride Ceramics, Harlan J. Brown-Shaklee

Doctoral Dissertations

"Hafnium diboride based ceramics are promising candidate materials for advanced aerospace and nuclear reactor components. The effectiveness of boron carbide and carbon as HfB₂ sintering additives was systematically evaluated. In the first stage of the research, boron carbide and carbon additives were found to improve the densification behavior of milled HfB₂ powder in part by removing oxides at the HfB₂ surface during processing. Boron carbide additives reduced the hot pressing temperature of HfB₂ by 150⁰C compared to carbon, which reduced the hot pressing temperature by ~50⁰C. Reduction of oxide impurities alone could not explain the difference in sintering enhancement, however, …

Effect Of Nickel On Castability Of Chromium Molybdenum Steel & The Dynamic Fracture Toughness Of Hy-130, Abhilash Dash

Masters Theses

"The fill lengths of Ni alloyed Cr-Mo steels obtained from fluidity studies (Paper 1) varied linearly with superheat. A 5% Ni steel showed a maximum fill length compared to other steels tested. Ni decreased the liquidus, solidus, and dendritic coherency temperature, but it did not have any significant effect on volume fraction (0.27-0.31) of the solid phase at the dendrite coherency point. The filling time obtained experimentally at 150 C⁰ superheat for 5% Ni steel (HY 130) was close to 1.4 s. For similar conditions, the predicted fill time using a Magmasoft model was close to 1.9 s. Modeling results …

Stress Measurement And Development Of Zirconium Diboride-Silicon Carbide Ceramics, Jeremy Lee Watts

Doctoral Dissertations

"Research presented in this dissertation focused on the production of ZrB₂-SiC composites and their characterization; in particular their mechanical properties and thermally generated residual stresses. Thermally generated stresses were measured using Raman spectroscopy as well as both neutron and x-ray diffraction. For 70 vol% ZrB₂ - 30 vol% SiC composites neutron diffraction revealed that the SiC phase was under ~880 MPa compressive stress and the ZrB₂ phase was under ~450 MPa tension at room temperature. It was also discovered that stresses began to accumulate at ~1400 ⁰C upon cooling from the processing temperature (1900 ⁰C -2000 ⁰C). Raman spectroscopy and …

Two-Point Bend Studies Of Glass Fibers, Zhongzhi Tang

Doctoral Dissertations

"The principal objective of this research is to advance our understanding of how glass breaks. Glass, a material well known for its brittleness, has been used widely but within a frustrating limit of its strength. Generally, strength is not considered as an intrinsic property of glass, due to the difficulty of avoiding the presence of flaws on the sample surface. The fiber drawing system and two-point bending (TPB) equipment developed at Missouri S&T allow the fabrication of pristine glass fibers and failure strain measurements while minimizing the effects of strength limiting critical flaws. Several conditions affect the failure behavior of …

Alloy Dissolution In Argon Stirred Steel, Darryl S. Webber

Doctoral Dissertations

"Alloying is required for the production of all steel products from small castings to large beams. Addition of large quantities of bulk alloys can result in alloy segregation and inconsistent alloy recovery. The objective of this research was to better understand alloy dissolution in liquid steel especially as it relates to Missouri S&Ts' patented continuous steelmaking process. A 45-kilogram capacity ladle with a single porous plug was used to evaluate the effect of four experimental factors on alloy dissolution: alloy species, alloy size or form, argon flow rate, and furnace tap temperature. Four alloys were tested experimentally including Class I …

Tof-Sims Analysis Of Hydrogen In Niobium, From 160°K To 475°K, P. Maheshwari, G. R. Myneni, G. Ciovati, C. Zhou, F. A. Stevie, J. M. Rigsbee, D. P. Griffis, A. D. Batchelor

Physics Faculty Publications

Niobium (Nb) is the material of choice for superconducting radio frequency (SRF) cavities due to its high critical temperature and critical magnetic field. Interstitial impurity elements such as H directly influence the efficiency of these cavities. Quantification of H in Nb is difficult since H is extremely mobile in Nb with a very high diffusion coefficient even at room temperature. In the presented work, Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was used to characterize H in Nb over a wide temperature range (160°K to 475°K) in situ to check for changes in mobility. Multiple experiments showed that as …

Nonuniformity In Lattice Contraction Of Bismuth Nanoclusters Heated Near Its Melting Point, A. Esmail, M. Abdel-Fattah, Hani E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

The structural properties of bismuth nanoclusters were investigated with transmission high-energy electron diffraction from room temperature up to 525 ± 6 K. The Bi nanoclusters were fabricated by thermal evaporation at room temperature on transmission electron microscope grids coated with an ultrathin carbon film, followed by thermal and femtosecond laser annealing. The annealed sample had an average cluster size of ∼14 nm along the minor axis and ∼16 nm along the major axis. The Debye temperature of the annealed nanoclusters was found to be 53 ± 6 K along the [012] direction and 86 ± 9 K along the [110] …

Precise Control Of Highly Ordered Arrays Of Nested Semiconductor/Metal Nanotubes, Diefeng Gu, Helmut Baumgart, Kandabara Tapily, Pragya Shrestha, Gon Namkoong, Xianyu Ao, Frank Müller

Electrical & Computer Engineering Faculty Publications

Lithographically defined microporous templates in conjunction with the atomic layer deposition (ALD) technique enable remarkable control of complex novel nested nanotube structures. So far three-dimensional control of physical process parameters has not been fully realized with high precision resolution, and requires optimization in order to achieve a wider range of potential applications. Furthermore, the combination of composite insulating oxide layers alternating with semiconducting layers and metals can provide various types of novel applications and eventually provide unique and advanced levels of multifunctional nanoscale devices. Semiconducting TiO₂ nanotubes have potential applications in photovoltaic devices. The combination of nanostructured semiconducting materials …

Purification Of Solar Grade Silicon Using Electromagnetic Field, Anping Dong, Lucas N.W. Damoah, Lifeng Zhang, Hui Zhu

Materials Science and Engineering Faculty Research & Creative Works

Non-metallic particles and the metallic impurity elements in the solar cell silicon have a strong detrimental effect on the conversion efficiency of the solar cell. Removing these impurities is one of the important tasks for silicon refining. the current paper proposed a new approach to purify silicon - electromagnetic (EM) separation. Since the non-metallic particles and the metallic impurity elements are non- or less conductive while the molten silicon is well conductive, under EM field, the Lorenz force will push the particles to the boundary layer, thus separate these inclusions. in the current study, a high frequency EM field was …

Non-Metallic Particles In Solar Grade Silicon (Sog-Si), Lucas Nana Wiredu Damoah, Anping Dong, Lifeng Zhang, Hui Zhu

Materials Science and Engineering Faculty Research & Creative Works

This study investigated the non-metallic inclusions in Solar 2rade Silicon (SoG-Si), especially the distribution of inclusions in the top 15mm layer of multicrystalline silicon ingot. the SoG-Si ingot produced from directional solidification process usually pushes the impurities to the top and finally cut off and discarded, which leads to material loss. the hard inclusions lead to wire breakages during the cutting of the ingot into wafers. the main kinds of inclusions found in top-cut silicon scraps from two manufacturers have been investigated using acid extraction, automated feature analysis techniques and SEM-EDS and optical Microscope: They are needle-like Si3N4 and lumpy …

Investigating Wood Welding Parameters Using A Prototype Welding Machine, Timothy R. Melin

Master's Theses

Understanding how different processing variables influence wood welded bonds is vital if the technique will ever be used to create engineered lumber without using adhesives. A variation of vibration welding, wood welding uses pressure and friction to bond materials together. During welding, heat causes a softening in the wood, a naturally occurring composite material. This softening leads to fiber entanglement and a bond forms upon cooling.

The goal of this research was to investigate several processing aspects of the wood welding procedure. A prototype wood welding machine, designed and fabricated from the ground up, was used to investigate the effects …

Corrosion Assessment Of Carbon Steel In Thailand By Atmospheric Corrosion Monitoring (Acm) Sensors, W Pongsaksawad, E Viyanit, S Sorachot, T Shinohara

Journal of Metals, Materials and Minerals

Atmospheric corrosion of metal depends on material compositions, weather condition (dry, dew, and rain period), temperature, relative humidity, and airborne sea salt of specific location. General testing procedure to obtain the corrosion rate is by actual exposure test of the specimen panels based on time interval plan. In Japan, atmospheric corrosion monitoring (ACM) sensor, made of an iron-silver galvanic couple, has been developed and used to sense the corrosivity in terms of galvanic current. Under some atmospheric conditions, these data can be converted to time of wetness and related to the corrosion rate of carbon steel. With ACM sensors, it …

Microstructural Evolution Of Surface Layers During Electrolytic Plasma Processing, Cristian Cionea

Material Science and Engineering Dissertations - Archive

Electrolytic Plasma Processing is an emerging technology for surface modification. The EPP process is based on electrolysis of an aqueous electrolyte by application of an electrical potential between the workpiece and counter-electrode, and the production of plasma (micro-arc discharges on the workpiece surface). The plasma micro-arcs provide a heat source for surface modification via localized surface melting and rapid cooling (cleaning process) and, if desirable, enhance ion deposition on a given substrate (coating). Three substrates (low carbon steel, pure Al and pure Ti) were "cleaned" by EPP and their near surface layer microstructure was studied. It was found that the …

Bubble Template Synthesis Of Hollow Gold Nanoparticles And Their Applications As Theranostic Agents, Chienwen Huang

Material Science and Engineering Dissertations - Archive

Hollow gold nanoparticle with a sub-30nm polycrystalline shell and a 50 nm hollow core has been successfully synthesized through the reduction of sodium gold sulfite by electrochemically evolved hydrogen. Such hollow gold nanoparticles exhibit unique plasmonic properties. They strongly scatter and absorb near infrared light. In this thesis we seek to understand the formation mechanism of hollow gold nanoparticles in this new synthesis process and their plasmonic properties. Also, we explore their biomedical applications as theranostic agents (therapeutic and diagnostic imaging). A lithographically patterned electrode consisting of Ag stripes on a glass substrate was used to investigate the formation process …

Study On The Leakage Current Behavior And Conduction Mechanism Of Porous Low-K In Cu/Porous Low-K Interconnects: The Influence Of Extrinsic Factors, Liangshan Chen

Material Science and Engineering Dissertations - Archive

This study investigates the influence of extrinsic factors including moisture and impurities trapped in porous low-k (PLK) and defective diffusion barrier on the leakage current behavior and the associated conduction mechanism of PLK in advanced Cu/PLK interconnects. For this purpose, a voltammetry technique that was previously developed for diffusion barrier characterization was extended to detect the trapped impurities in PLK. With this technique in hand, the influence of extrinsic factors was then studied. Cu was found to diffuse out into PLK through barrier defects in the presence of electric stress. Its out-diffusion and subsequent migration in PLK manifested as a …

Nanocrystalline Piezoresistive Polysilicon Film Obtained By Aluminum Induced Crystallization For Pressure Sensing Applications, Suraj Kumar Patil

Material Science and Engineering Dissertations - Archive

The overall objective of our research was to integrate various sensors on to a single flexible substrate for multi-sensory information gathering. Additional capabilities could be incorporated towards the realization of 'smart skin' for simultaneous and real time sensing of various mechanical, biological and chemical stimuli. Recent research venues are dictated by the trend of shifting from conventional silicon (Si) substrates to lower weight, low profile, structurally robust and lower cost flexible substrates. These flexible substrates easily conform to non-planar objects, could be batch fabricated at lower cost and enable multilayer construction. This would eventually evolve into seamless assimilation of sensors …

An Investigation Of Initially Delaminated Composite Sandwich With Delamination Arrest Mechanism Under Buckling Loading, Tony D. Tran

Master's Theses

This thesis involves the development of a fiberglass-foam composite sandwich structure with the introduction of delamination arrestment keys; therefore, a study of an initially delaminated composite sandwich structure was the experimental analysis on multiple configurations in how the arrestment keys are placed.

The first part of this thesis research was to the experimental design and manufacturing of the composite sandwich plates. These plates were later cut down to the specific test dimensions and manufacturing processes for the composite sandwich plates and test specimens were created. The composite sandwich plates were manufactured using a vacuum resin infusion process. The dimensions of …

College Of Engineering Senior Design Competition Fall 2010, University Of Nevada, Las Vegas

Fred and Harriet Cox Senior Design Competition Projects

Part of every UNLV engineering student’s academic experience, the senior design project stimulates engineering innovation and entrepreneurship. Each student in their senior year chooses, plans, designs, and prototypes a product in this required element of the curriculum. A capstone to the student’s educational career, the senior design project encourages the student to use everything learned in the engineering program to create a practical, real world solution to an engineering challenge.

The senior design competition helps to focus the senior students in increasing the quality and potential for commercial application for their design projects. Judges from local industry evaluate the projects …

Processing And Composition Effects On The Fracture Behavior Of Spray-Formed 7xxx Series Al Alloys, Mala M. Sharma, Constance W. Ziemian, Timothy J. Eden

Faculty Journal Articles

The fracture properties of high-strength spray-formed Al alloys were investigated, with consideration of the effects of elemental additions such as zinc,manganese, and chromium and the influence of the addition of SiC particulate. Fracture resistance values between 13.6 and 25.6 MPa (m)^1/2 were obtained for the monolithic alloys in the T6 and T7 conditions, respectively. The alloys with SiC particulate compared well and achieved fracture resistance values between 18.7 and 25.6 MPa (m)^1/2. The spray-formed materials exhibited a loss in fracture resistance (KI) compared to ingot metallurgy 7075 alloys but had an improved
performance compared to high-solute powder …

Effect Of Temperature And Pressure On The Densification Of Titanium Silicide Compound, P Thapnuy, S Larpkiattaworn, T Luangvaranunt, J Ikeuchi

Journal of Metals, Materials and Minerals

Titanium silicide compound was synthesized from the mixture of titanium and silicon powder with atomic ratios of 60:40 and 70:30. The powders were mixed by ball milling and pressed by different methods: by using uniaxial pressing at 64 MPa, cold isostatic pressing (CIP) at 200 MPa, hot forging (HF) at 648 MPa, and hot pressing (HP) at 24 MPa. The samples were then sintered at 1300o C or 1600o C for 2 hours soaking time in argon atmosphere. The sintered samples were subsequently characterized for phase constitution using X-ray diffraction (XRD). Ti5Si3 was observed as main compound of mixtures with …