Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010. / Includes bibliographical references. / Molten salts are important heat transfer fluids used in nuclear, solar and other high temperature engineering systems. Dispersing nanoparticles in molten salts can enhance the heat transfer capabilities of the fluid. High temperature and high ionicity of the medium make it difficult to make a colloidally stable dispersion of nanoparticles in molten salts. The aggregation and sedimentation kinetics of different nanoparticles dispersed in molten salts is studied, and trends of settling rates with system parameters like particle size, temperature and concentration are observed. Finally, a hypothesis based on ultra low values of Hamaker coefficient is suggested in order to achieve long term colloidal stability in molten salts medium. / by Vaibhav Somani. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references (leaf 73). / The potential for land-based turbine buckets material rejuvenation presents a significant commercial and scientific interest. Ni-based superalloy GTD111 is used at a number of GE-manufactured power generation turbines. The outstanding creep resistance features of Ni-based superalloys can be attributed to a large extent, to the gamma prime ([gamma]') precipitates found within the FCC [gamma]-matrix. Service-induced material degradation mainly involves coarsening and shape transformation of [gamma]'-phase precipitates; therefore, any bucket repair attempt should primarily address the restoration of [gamma]' precipitates to the original configuration. In the present study a quantitative metallographic analysis of GTD111 alloy under different conditions was performed. Several micrographs were taken and analysed using image analysis software. Gamma prime precipitate size was measured and compared between the different alloy conditions, leading to useful conclusions concerning material degradation as a result of high-temperature service exposure. In addition, microstructural transformations observed as a result of different heat treatments, formed the basis for investigation of procedures that can potentially restore the alloy microstructure in the original condition. High temperature solution and aging heat treatments sequence is considered as potentially sufficient for restoring the GTD111 microstructure. Finally, the measurements were examined for correlation with existing [gamma]' particle coarsening theory, by calculating and evaluating the metal service temperature during service. A satisfactory correlation exists. / by Apostolos Kountras. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (leaves 33-35). / The performance of a biological scaffold formed by the self-assembling peptide RADA16 is comparable to the most commonly used synthetic materials employed in the culture of neural stem cells. Furthermore, improvements in the performance of RADA16 have recently been made by appending the self-assembling peptide sequence with various functional motifs from naturally occurring proteins. The focus of this work is to further analyze the performance of these functionalized self-assembling peptide scaffolds when used for the culture of neural stem cells, and to characterize these newly developed materials for comparison with RADA16. The effect of the functional motifs on the structure of the peptide scaffold was evaluated with circular dichroism and scanning electron microscopy, and the mechanical properties of the peptide scaffolds were examined through theological analysis. The functionalized peptides were found to have lower percentages of beta-sheet structure as well as reduced storage moduli in comparison with RADA16. SEM images confirmed the ability of the functionalized peptides to form three-dimensional nanofiber scaffolds capable of encompassing, neural stem cells. Three-dimensional cell culture techniques were used to evaluate the ability of the functionalized peptide scaffolds to promote neural stem cell proliferation, and a scaffold formed by the combination of different functionalized peptides was found to increase the proliferation of neural stem cells in comparison to non-functionalized RADA 16. / by Angus M. Hucknall. / S.M.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references. / Block copolymer photonic gels are a simple and easily processed material which responds rapidly to environmental stimuli through a color change. The diblock copolymer that forms the gel self-assembles into a lamellar structure that has the potential to reflect light over a broad range of wavelengths, from the IR to the UV. Application of a stimulus causes a change in the periodicity and/or index of refraction of layers that result in a shift of the stop band. The types of stimuli include temperature, pressure, pH, electric field, salt concentration, and humidity. Due to the high level of tunability of the polymers, it is possible to tailor the response of the gel to achieve a desired effect. This thesis is an assessment of the commercial applications of the photonic gel technology. First a cost model was developed for the polymerization of the block copolymer, polystyrene-b-poly(2-vinyl pyridine). The results indicate that it is cost effective to invest in a small scale production facility at large production volumes. Next, an evaluation of three potential markets was conducted. The anti-counterfeit market is most promising because of large profit margins and the opportunity for future company growth through R&D of new anti-counterfeit measures. The other two markets in color cosmetics and food preservation present potential opportunities for licensing. / by Sally S. Lou. / M.Eng.

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.