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Articles 211 - 220 of 220

Full-Text Articles in Materials Science and Engineering

Solar Driven Photoelectrochemical Water Splitting For Hydrogen Generation Using Multiple Bandgap Tandem Of Cigs2 Pv Cells And Thin Film Photocatalyst, Anant Jahagirdar Jan 2005

Solar Driven Photoelectrochemical Water Splitting For Hydrogen Generation Using Multiple Bandgap Tandem Of Cigs2 Pv Cells And Thin Film Photocatalyst, Anant Jahagirdar

Electronic Theses and Dissertations

The main objective of this research was to develop efficient CuIn1-xGaxS2 (CIGS2)/CdS thin film solar cells for photoelectrochemical (PEC) water splitting to produce very pure hydrogen and oxygen. Efficiencies obtained using CIGS2 have been lower than those achieved using CuInSe2 and CuIn1-xGaxSe2. The basic limitation in the efficiencies is attributed to lower open circuit voltages with respect to the bandgap of the material. Presently, the main mechanism used to increase the open circuit voltage of these copper chalcopyrites (CuInSe2 and CuInS2) is the addition of gallium. However, addition of gallium has its own challenges. This research was intended to (i) …

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Instrumented Nanoindentation Studies Of Deformation In Shape Memory Alloys, Sudhir Rajagopalan Jan 2005

Instrumented Nanoindentation Studies Of Deformation In Shape Memory Alloys, Sudhir Rajagopalan

Electronic Theses and Dissertations

Near equi-atomic nickel titanium (NiTi) shape memory alloys (SMAs) are a class of materials characterized by their unique deformation behavior. In these alloys, deformation mechanisms such as mechanical twinning and stress induced phase transformation between a high symmetry phase (austenite) and a low symmetry phase (martensite) additionally occur and influence mechanical behavior and thus their functionality. Consequently, applications of SMAs usually call for precise phase transformation temperatures, which depend on the thermomechanical history and the composition of the alloy. Instrumented indentation, inherently a mechanical characterization technique for small sampling volumes, offers a cost effective means of empirically testing SMAs in …

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Cryogenic Shape Memory Alloy Actuators For Spaceport Technologies: Materials Characterization And Prototype Testing, Jennifer Lemanski Jan 2005

Cryogenic Shape Memory Alloy Actuators For Spaceport Technologies: Materials Characterization And Prototype Testing, Jennifer Lemanski

Electronic Theses and Dissertations

Shape memory alloys (SMAs) possess the unique ability to change their shape by undergoing a solid-state phase transformation at a particular temperature. The shape change is associated with a large strain recovery as the material returns to its "remembered" shape. Their ability to act as both sensor and actuator has made them an attractive subject of study for numerous applications. SMAs have many characteristics which are advantageous in space-related applications, including generation of large forces associated with the strain recovery, smooth and controlled movements, large movement to weight ratio, high reliability, and spark-free operation. The objective of this work is …

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Self-Assembled Supramolecular Structures Of Chiral Phospholipids: Structure, Mechanical Properties And Patterning, Nidhi Mahajan Jan 2005

Self-Assembled Supramolecular Structures Of Chiral Phospholipids: Structure, Mechanical Properties And Patterning, Nidhi Mahajan

Electronic Theses and Dissertations

Lipid molecule is well known natural building block to form different supramolecular structures with specific shape, size and functionality. In my thesis work, I have used DC8,9PC 1,2-bis(tricosa-10,12-dinoyl)-sn-glycero-3-phosphocholine), a type of chiral lipid to form the vesicles, tubules and ribbons . By using Atomic Force Microscope, I have studied the morphological features of these particular structures. Also, the mechanical properties of lipid tubules have been studied using AFM. Softlithography has been used to pattern the lipid vesicles and tubules into 2-dimensional and 3-dimensional ordered arrays. The structure of self-assembled hollow spherical vesicles was studied using AFM. The applications of soft …

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Structural Evolution In Mechanically Alloyed Fe-Based Powder Systems, Umesh Patil Jan 2005

Structural Evolution In Mechanically Alloyed Fe-Based Powder Systems, Umesh Patil

Electronic Theses and Dissertations

A systematic study of iron-based binary and multi-component alloys was undertaken to study the structural evolution in these powders as a function of milling time during mechanical alloying. Blended elemental powders of Fe100-XBX (where x = 5, 10, 17, 20, 22, 25, 37.5 and 50 at. %) and a bulk metallic glass (BMG) composition (Fe60Co8Zr10Mo5W2B15) were subjected to mechanical alloying in a SPEX 8000 mixer mill. X-ray diffraction technique was employed to study the phase evolution, crystallite size, lattice strain and also to determine the crystal structure(s) of the phases. Depending on the milling time, formation of supersaturated solid solutions, …

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Processing, Microstructural And Mechanical Characterization Of Mechanically Alloyed Al-Al2o3 Nanocomposites, Pushkar Katiyar Jan 2004

Processing, Microstructural And Mechanical Characterization Of Mechanically Alloyed Al-Al2o3 Nanocomposites, Pushkar Katiyar

Electronic Theses and Dissertations

Aluminum-alumina nanocomposites were synthesized using mechanical alloying of blended component powders of pure constituents. This study was performed on various powder mixtures with aluminum as the matrix and alumina as the reinforcement with volume fractions of 20, 30, and 50 % and Al2O3 particle sizes of 50 nm, 150 nm, and 5 µm. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used for the crystal structure and microstructural characterization of the powders at different stages of milling. Al2O3 powders with 50 nm and 150 nm particle size were predominantly of γ-type, while Al2O3 of 5 µm size was …

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Development Of Titanium Nitride/Molybdenum Disulphide Composite Tribological Coatings For Cryocoolers, Anil Pai Jan 2004

Development Of Titanium Nitride/Molybdenum Disulphide Composite Tribological Coatings For Cryocoolers, Anil Pai

Electronic Theses and Dissertations

Hydrogen is a clean and sustainable form of carrier of energy that can be used in mobile and stationary applications. At present hydrogen is produced mostly from fossil sources. Solar photoelectrochemical processes are being developed for hydrogen production. Storing hydrogen can be done in three main ways: in compressed form, liquid form and by chemical bonding. Near term spaceport operations are one of the prominent applications for usage of large quantities of liquid hydrogen as a cryogenic propellant. Efficient storage and transfer of liquid hydrogen is essential for reducing the launch costs. A Two Stage Reverse Turbo Brayton Cycle (RTBC) …

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Phenomenology And Experimental Observations In High Temperature Ternary Interdiffusion, Abby Lee Elliott Jan 2004

Phenomenology And Experimental Observations In High Temperature Ternary Interdiffusion, Abby Lee Elliott

Electronic Theses and Dissertations

A new method to extract composition dependent ternary interdiffusion coefficients from a single diffusion couple experiment is presented. The calculations involve direct determination of interdiffusion fluxes from experimental concentration profiles and local integration and differentiation of Onsager's formalism. This new technique was applied to concentration profiles obtained from selected semi-infinite, single-phase diffusion couple experiments in the Cu-Ni-Zn, Fe-Ni-Al, and Ni-Cr-Al systems. These couples exhibit features such as uphill diffusion and zero flux planes. The interdiffusion coefficients from the new technique along with coefficients reported from other methods are graphed as functions of composition. The coefficients calculated from the new technique …

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Commissioning Of An Arc-Melting/Vacuum Quench Furnace Facility For Fabrication Of Ni-Ti-Fe Shape Memory Alloys, And The Characterization, Jagat Singh Jan 2004

Commissioning Of An Arc-Melting/Vacuum Quench Furnace Facility For Fabrication Of Ni-Ti-Fe Shape Memory Alloys, And The Characterization, Jagat Singh

Electronic Theses and Dissertations

Shape memory alloys when deformed can produce strains as high as 8%. Heating results in a phase transformation and associated recovery of all the accumulated strain, a phenomenon known as shape memory. This strain recovery can occur against large forces, resulting in their use as actuators. The goal of this project is to lower the operating temperature range of shape memory alloys in order for them to be used in cryogenic switches, seals, valves, fluid-line repair and self-healing gaskets for space related technologies. The Ni-Ti-Fe alloy system, previously used in Grumman F-14 aircrafts and activated at 120 K, is further …

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A Laser Hydrophone, Steven Kenneth Barnoske Jan 1977

A Laser Hydrophone, Steven Kenneth Barnoske

Retrospective Theses and Dissertations

This report proposes a novel technique for measuring of acoustic fields in water. A Laser Hydrophone is proposed taking advantage of the properties of Total Internal Reflection. A theoretical analysis of the idea is presented followed by a prediction of the operating characteristics of an actual system. Actual data were taken with the proposed system and it is compared to the predicted.

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