Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996. / Includes bibliographical references (p. 191-197). / by Stephen Hans Foulger. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 139-143). / In recent years Ni-Mn-Ga has attracted considerable attention as a new kind of actuator material. Off-stoichiometric single crystals of Ni2MnGa can regularly exhibit 6% strain in tetragonal martensites and orthorhombic martensites have shown up to 10% strain when subjected to a magnetic field. These crystals are brittle and the production of single crystals can be quite costly. Terfenol-D, a commercially available giant-magnetostrictive material, suffers from some of the same drawbacks. It was found that composite materials made from Terfenol-D particles in a polymeric matrix could solve the issue of the brittleness while retaining a large fraction of the strain output of the alloy. At first glance a similar approach could be used to solve the brittleness issue of Ni-Mn-Ga, but the low blocking force of these alloys reduces the chances of achieving a Ni-Mn-Ga/polymer composite actuator. However, the stress-strain loops for Ni-Mn-Ga show a large mechanical hysteresis. This ability to dissipate energy makes this alloys very desirable for damping applications, and by putting particles of Ni-Mn-Ga in a composite, their brittleness becomes less of an issue. / (cont.) It is shown that by curing Ni-Mn-Ga/polymer composites under a magnetic field it is possible to align the particles in chains and to orient them so they will respond to a uniaxial load. The magnetic measurements show that there are twin boundaries in the particles that can be moved by an external stress. Stress-induced twin boundary motion in the particles is confirmed more directly by x-ray diffraction measurements, transmission electron microscope micrographs, and scanning electron microscope micrographs. Finally we demonstrate the ability of the Ni-Mn-Ga/polymercomposites to dissipate mechanical energy when subjected to cyclic loads. The Ni-Mn-Ga/polymercomposites can dissipate more than 70% of the energy they are given in every cycle, while pure polymer, Fe-filled and Terfenol-filled control samples dissipate less than 50% of the input energy in every cycle. The additional loss in these composites is shown to be due to the motion of twin boundaries. Simple numerical models reproduce the cyclic stress-strain behavior of the composites and explain non-conventional features observed in the Ni-Mn-Ga composites. / by Jorge Feuchtwanger. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 130-142). / Fossil fuels depletion and climate change are driving the need for sustainable development and renewable energy sources globally [1]. Solar being the most abundant and widespread source of renewable energy is resulting in a rapidly growing, with a growth rate more than 35% annually for the past 10 years [4]. Hydrogen is an ideal energy carrier for next generation given its high efficiency, environmental friendliness, wide application as well as several attractive methods for storage and distribution [17]. The hydrogen economy, a proposed system of producing, delivering and employing energy by using hydrogen, is under intensive research and development, and is projected to be realized at the end of this century as one of the leading suppliers [60]. Photo-electrochemical (PEC) cells connect the solar energy and hydrogen economy together by directly converting solar energy into chemical energy in the form of hydrogen gas. The metal oxide based PEC cell has advantages of low cost, high stability and durability and environmental friendliness [14], a good option for commercialization. With the rapid development of nanotechnology in recent years, novel nano-structured metal oxide PEC cells can have higher efficiency and better performance due to the effects of quantization, large surface areas, improved charge transport, etc. In this thesis, the current status and future development of the hydrogen economy in terms of identifying the markets, opportunities and risks of solar-hydrogen has been reviewed and accessed. The technology review of PEC cells in terms of the working mechanism and efficiency determining factors has been studied. The current research efforts on metal oxide based PEC cells for optimizing the performances and processing methods have also been studied. A case study and cost modeling in the context of scenario has been conducted; the analysis showed the cost of PEC cells was still very high mainly due to the high materials and processing costs. Thus, future research development should focus on the technological approaches with low materials and processing costs and high energy conversion efficiency for earlier commercialization of PEC cells. Besides, hydrogen storage, distribution, safety codes and standards, education and training as well as fuel cell technology must also require intensive research and development to insure the realization of solar-hydrogen economy. / by Jianfeng Zhu. / M.Eng.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1983. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Includes bibliographical references. / by Dodd Harrison Grande. / M.S.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references (p. 33-34). / Ferromagnetic shape memory alloys (FSMAs) are a class of alloys that exhibits the shape memory effect, as in the alloy nickel-titanium, sometimes known as Nitinol. In FSMAs, though, the shape changes are not brought on just by changes in temperature or mechanical stresses, but can also be driven by the application of a relatively small magnetic field. The large strains exhibited by such materials are a result of the coexistence of several features, including a thermoelastic martensitic transition, and a ferromagnetic martensite (non-equilibrium, low-temperature) phase. The magnetocrystalline anisotropy must also be large, as seen in similar alloys such as iron-palladium (Fe₇₀Pd₃₀) [1]. Nickel-manganese-gallium is an FSMA that has shown up to 10% strain in certain orientations as an effect of unconstrained magnetic actuation [4]. To achieve cyclic actuation in FSMAs, the field-induced extension has conventionally been reversed by a compressive mechanical stress from a spring or field orthogonal to the actuating field. The use of a second FSMA crystal to provide the reset force was unreported. Collinear single crystals are shown here to be able to induce a 2.8% reset strain against one another when subjected alternately to individual pulsed magnetic fields in a custom designed and constructed apparatus. A setup of this type could be used in a bistable microswitch, linear motion actuator, or shutter controller where a low actuation stress is sufficient or the electrical contacts required to activate a piezoelectric device are undesirable. / by Catherine A. Jenkins. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 19-21). / With conventional water sources in short and decreasing availability, new technologies for water supply have a crucial role to play in addressing the world's clean water needs in the 21st century. In this thesis, we examine how nanometer-scale pores in single-layer freestanding graphene can effectively filter NaCl salt from water. Using classical molecular dynamics, we report the desalination performance of such membranes as a function of pore size, chemical functionalization, and applied pressure. Our results indicate that the membrane's ability to prevent the salt passage depends critically on pore diameter, with pores in the 0.7-0.9 nm range allowing for water flow while blocking ions. Further, an investigation into the role of chemical functional groups bonded to the edges of graphene pores suggests that commonly occurring hydroxyl groups can roughly double the water flux thanks to their hydrophilic character. The increase in water flux comes at the expense of less consistent salt rejection performance, which we attribute to the ability of hydroxyl functional groups to substitute for water molecules in the hydration shell of the ions. Overall, our results indicate that the water permeability of this material is several orders of magnitude higher than conventional reverse osmosis membranes, and that nanoporous graphene may have a valuable role to play for water purification. / by David H. Cohen-Tanugi. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2003. / Includes bibliographical references. / Addition cure (X1-2672) and condensation cure (4-3136) silicone resins have been studied for their mechanical property change with temperature. Properties include maximum flexural stress, flexural modulus and fracture toughness K[sub]IC. Temperature effect on mechanical properties of addition cure resin is substantial and also depends on the crosslinkers used. Generally the maximum stress and flexural modulus decrease with temperature, and the dependence upon crosslinkers in addition cure resin is obvious. Fracture toughness data of addition cure silicone resins have a peaking behavior with the peak appearing [approximately] 58-101C̊ (depending on the crosslinker) below their glass transition temperatures. This can be explained by the competing effect between network mobility and rigidity of the silicone polymer. Rate effect on fracture toughness of silylphenylene crosslinked 2672 has also been studied. It is concluded that the temperature effect on such a system is more dominant compared to the rate effect. The condensation resins also experience decrease in modulus and strength but the toughness changes little with temperature. This is due to its tight network structure. Silylphenylene crosslinked addition cure resin (2672B) and the toughened condensation cure resin (3136T) were used to make silicone fiberglass laminates. They have been successfully processed with a vacuum bagging technique. Silicone resin composites are proved to be thermally stable, moisture resistant and fire resistant. However, they have weak strength and modulus. Their temperature dependence of mechanical properties is also big and results in poor property retention at high temperatures. 2672B was used to produce hybrid composites with an organic resin-vinyl ester. The processes of curing the hybrid composites in both sequential cure and co-cure methods prove to be successful. The hybrid composites are stronger and their property retention at elevated temperatures is improved compared to silicone resin composites. They also have improved moisture resistance, thermal stability and fire resistance over vinyl ester composites. The co-cured V/B 8/4 structure has excellent strength and rigidity and also extraordinary property retention at high temperatures, which can be explained by the chemical reaction at the silicone resin and vinyl ester resin interface. The hybrid composites prove to be successful in having balanced mechanical and environmental properties. / by Yuhong Wu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (p. 190-195). / We have conducted a study of the optical properties of sputtered silicon-rich silicon dioxide (SRO) thin films with specific application for the fabrication of erbium-doped waveguide amplifiers and lasers, polarization sensitive devices and devices to modify the polarization state of light. The SRO thin films were prepared through a reactive RF magnetron sputtering from a Si target in an O2/Ar gas mixture. The film stoichiometry was controlled by varying the power applied to the Si target or changing the percentage of 02 in the gas mixture. A deposition model is presented which incorporates the physical and chemical aspects of the sputtering process to predict the film stoichiometry and deposition rate for variable deposition conditions. The as-deposited films are optically anisotropic with a positive birefringence (nTM > nTE) that increases with increasing silicon content for as-deposited films. The dependence of the birefringence on annealing temperature is also influenced by the silicon content. After annealing, samples with high silicon content (>45 at%) showed birefringence enhancement while samples with low silicon content (<45 at%) showed birefringence reduction. A birefringence of more than 3% can be generated in films with high silicon content (50 at% Si) annealed at 11000C. / (cont.) We attribute the birefringence to the columnar film morphology achieved through our sputtering conditions. Er was incorporated through reactive co-sputtering from Er and Si targets in the same O2/Ar atmosphere in order to investigate the energy-transfer process between SRO and Er for low annealing temperatures. By studying the photoluminescence (PL) intensity of Er:SRO samples annealed in a wide range of temperatures, we demonstrated that the Er sensitization efficiency is maximized between 600°C and 700°C. Temperature-resolved PL spectroscopy on SRO and Er:SRO samples has demonstrated the presence of two different emission sensitizers for samples annealed at 6000C and 1 100°C. This comparative study of temperature-resolved PL spectroscopy along with energy Filtered Transmission Electron Microscopy (EFTEM) has confirmed that the more efficient emission sensitization for samples annealed at 6000C occurs through localized centers within the SRO matrix without the nucleation of Si nanocrystals. Er-doped SRO slab waveguides were fabricated to investigate optical gain and loss for samples annealed at low temperatures. / (cont.) Variable stripe length gain measurements show pump dependent waveguide loss saturation due to stimulated emission with a maximum modal gain of 3 ± 1.4 cm-1 without the observation of carrier induced losses. Pump and probe measurements on ridge waveguides also confirms the presence of SRO sensitized signal enhancement for samples annealed at 6000C. Transmission loss measurements demonstrate a significant loss reduction of 1.5 cm-1or samples annealed at 600°C compared to those annealed at 1000°C. These results suggest a possible route for the fabrication of compact, high-gain planar light sources and amplifiers with a low thermal budget for integration with standard Si CMOS processes. / by Michael Anthony Stolfi. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. 154-165). / To facilitate commercialization of fuel cell systems as alternative energy device, the enhancement of Pt electrocatalysts activity is one of the most challenging issues. The first step to the solution is elucidating relationship between surface structure and chemical reactivity as electrocatalysis occurs on its surface. However, in spite of concerted experimental and theoretical research over the last decades, the detailed mechanism is still in debate. This thesis explores a structural sensitivity of the chemical reactivity in the Pt-based alloy electrocatalysts by combining ab-initio density functional theory (DFT) with relevant thermodynamic and kinetic approach. We developed a rigorous statistical mechanical formalism, which can parameterize the energetics obtained by first principles calculations as a function of surface topologies. This methodology enables kinetic Monte Carlo simulations to provide thermally equilibrated structures as a function of partial pressures of adsorbates and alloy compositions. With our consistent methods, we characterize surface structures on the atomic scale, and quantify chemical reactivity of various Pt-alloy model systems. Our methodology reproduced accurate and consistent results of available experimental measurements. We find that our methodology is considerably useful for studying the structural effect on the heterogeneous catalysis. Through the thesis, we understood better how surface structures evolve according to environmental conditions and hence, the structure-activity relationship, which is useful for design of electrocatalysts. / by Byungchan Han. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (p. 21). / Soluble protein antigens used in vaccines have shown lower immune responses when compared with certain particulate forms of these same antigens. For example, it has been shown that micro- and nano-particle mediated delivery of protein antigen can use up to 100 times less protein and still produce an effective immune response [1]. In order to use this phenomenon to make vaccines more efficient, we need a biodegradable delivery particle. This thesis modifies a particle created by Jain et al., which consists of a polymer network surrounding and trapping a protein, by removing the non-degradable crosslinker used in the original particle design and replacing it with a poly (ethylene glycol) acrylate molecule attached to ovalbumin protein. When a dendritic cell degrades the particle, the ovalbumin protein will be degraded, as will the connections between the polymer network that holds the particle together [2]. The particles degraded to 56% of their original size in 3 days, while the non-degradable particle degraded to only 80% of its original size. / by Kendall Werts. / S.B.