Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references (leaf 30). / Packer elements are traditionally rubber seals that can operate under specified downhole conditions and provide a seal for either a short-term, retrievable, or a long-term, permanent, completion. In this case a retrievable 19.7cm (7-3/4") packer element for a high-pressure high-temperature (HPHT) environment was designed and tested. The element created a seal between the mandrel, or tubing, and the casing. At high temperature and pressure rubber needs to be contained so that it will create and maintain an energized seal. In this study only Aflas rubber was tested. Various backup systems were examined; some more traditional designs such as the carbon steel foldback ring were compared to more experimental ideas. Results of theoretical simulations were compared to actual test results in order to gain a greater understanding of element behavior. Experiments were also performed to study the process of element setting, which is difficult to observe due to the high pressures and temperatures required. In a related study alternative materials to rubber such as annealed high-conductivity oxygen-free copper were tested to determine if the properties could be applied for packer element applications. The most successful design was the foldback ring with an anti-extrusion PEEK ring under the gage ring. This design passed a liquid test at 134 MPa (19.5k psi) differential pressure and a gas test at 87.6 MPa (12.7k psi) differential pressure. New designs such as the split ring with mesh and the garter spring with mesh did not pass fixture tests but could be successful with further modifications. FEA was used as an analytical tool to create simulations of the element after a setting force is applied. The modeling was shown to correlate to the actual test results and therefore it would be a good tool to use in future studies. / by Stephanie Berger. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1997. / Vita. / Includes bibliographical references (leaves 66-67). / by Anand Raghunathan. / M.S.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, February 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 131-144). / In this thesis we encounter the formulation of a rigorous theory of resonant Raman scattering in graphene, the calculation of the so-obtained Raman matrix element K2f,1o for the 2D Raman mode with the full inclusion of the matrix elements and a physically appealing bridge between theory and experiment by eschewing the problematic ascription of graphene with a finite thickness. Finally, we elucidate an experimental study of the Raman D and G modes of graphene and highly-defected pencil graphite over the visible range of laser radiation. Marking a departure from the usual practice for light scattering in semiconductors of including only the dynamics of the electrons and holes separately, we show via fourth-order quantum mechanical perturbation theory using a Fock state basis that for resonant Raman scattering in graphene the processes to leading order are those that involve the simultaneous action of the electrons and holes. Such processes are indeed an order of magnitude stronger than those prevalent in the literature under the double resonance [1, 2, 3] moniker. We translate our perturbation theoretic analysis into simple rules for constructing Feynman diagrams for processes to leading order and we thereby enumerate the 2D and D modes. Using expressions for the terms to leading order obtained from our theoretical treatment we proceed to evaluate the Raman matrix element [4] for the Raman 2D mode by using state-of-the-art electronic [5] and iTO phonon dispersions [6] fit to ab initio GW calculations. For the first time in the literature we include the variation of the light-matter and electron-phonon interaction matrix elements calculated via an ab initio density functional theory (DFT) calculation under the local density approximation (LDA) for the electronic wavefunctions. Our results for the peak structure, position and intensity dependence are in excellent agreement with experiments [7, 8, 9, 10]. Strikingly, our results show that depending on the combination of the input (polarizer) and output (analyzer) polarization of the laser radiation, very different regions of the phonon dispersion are accessed. This has a direct impact on the dominant electronic transitions according to the pseudo-momentum conservation condition satisfied by the scattering of an electron by a phonon ki = kf + q. Using sample substitution [11] we deconvolve the highly wavelength dependent response of the spectrometer from the Raman spectra of graphene suspended on an SiO2 - Si substrate and graphite for the D and G modes in the visible range. We derive a model that considers graphene suspended on an arbitrary stratified medium while sidestepping its problematic ascription as an object of finite thickness and calculate the absolute Raman response of graphene (and graphite) via its explicitly frequency independent Raman matrix element [K'2f10]2 vs. laser frequency. For both graphene and graphite the [K'2f10]2 per graphene layer vs. laser frequency rises rapidly for the G mode and less so for the D mode over the visible range. We find a dispersion of the D mode position with laser frequency for both graphene and graphite of 41 cm-YeV and 35 cm-YeV respectively, in good agreement with Narula and Reich 131 assuming constant matrix elements, the observed intensity follows the joint density states of the electronic bands of graphene. Finally, we show the sensitivity of our calculation to the variation in thickness of the underlying SiO2 layer for graphene. / by Rohit Narula. / Ph. D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, June 2003. / "June 2003." / Includes bibliographical references (leaf 44). / There is a surprising lack of good models for granular flow. In 2002, Bazant proposed a new stochastic kinematic model of granular drainage from a silo. The new model rests on the notion that flow in the silo is caused by the migration of extended regions of excess interstitial space upward from the orifice at the bottom. An implementation of this model with the purpose of simulating the behavior of particles in the silo was developed by the author, and several results were obtained using simulations carried out with this implementation. As regards particle streamlines, average velocity profiles, predictions of particle mixing and of particle diffusivity, it was found that qualitative and quantitative agreement with experiments was excellent, in particular for a specific version of the implementation. This version uses a self-correlated random walk to describe the motion of the excess interstitial space through the silo. The model can also be used to make predictions about many other features of the granular flow (such as granular temperature), that are not as accessible through experiment's, and for which empirical behavior is not well known. In particular, the implementation of the model developed in this work can be used to simulate three dimensional flow, whereas existing experimental techniques are limited to observing two dimensions. / R. Camilo Guáqueta. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / "February 2004." / Includes bibliographical references (p. 146-152). / The micron-scale manufacturing industry has grown to hundreds of billions of dollars since the advent of the transistor in 1947. Increasing demands for integration of surface mount components, greater use of portable electronic devices, and miniaturized medical diagnostic devices have given rise to the need for methods of fabricating and assembling micron-scale discrete components. Development of reliable non-contact assembly methods requires thorough understanding of electro-mechanics, surface adhesion, and gravitational forces acting on micron- scale objects. The impact of such a study will spread beyond microelectronics, and will also have broad significance in the development of micro-electromechanical systems (MEMS) for diverse applications such as biological assays, drug delivery devices, and tools for high throughput combinatorial materials development. This thesis will discuss methods for and challenges in fabrication, manipulation, and assembly of discrete micron-scale objects. The impact of these issues will be illustrated for the development of a micro-dispensing system used to manipulate microgram quantities of dry granular substances for combinatorial materials development. This method provides a model system to explore the forces on micron-scale objects, and is important in its own right as it will introduce a new range of materials that may benefit from combinatorial development. The applicability of traditional methods for computing dielectrophoretic forces on micron scale objects in the presence of spatially non-uniform electric fields will be discussed for the case of closely-spaced, interacting spheres. / (cont.) A dipole approximation model will be presented to quantitatively illustrate the limitations of existing techniques for calculating these forces, and to aid in explaining the observed motion of multiple interacting particles. / by Malinda M. Tupper. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Includes bibliographical references (p. 119-124). / Transition metal oxides comprise a fascinating class of materials displaying a variety of magnetic and electronic properties, ranging from half-metallic ferromagnets like CrO2, ferrimagnetic semiconductors like Fey's, and antiferromagnetic insulators like rocksalt-structured FeO. The accessibility of multiple electronic configurations and coordination of cations in these oxides enables the control of magnetism by external stimuli. One such stimulus is the insertion of Li+, as occurs during the discharge cycle of a lithium battery. This can lead to the change in valence and locations of the metal cations within the structure therefore a change in magnetic moment. Fey's and CrO2 are of considerable interest, primarily because they demonstrate room-temperature magnetism and high spin polarization.Previous studies focussed on use of these materials as cathodes and characterization of lithiated compounds made through solid state chemical synthesis or via chemical lithiation. In this work, changes in magnetization and structure of pulsed laser deposition (PLD)-grown Fey's (magnetite) thin films, Fe3O4 nanoparticles, and CrO2 nanoparticles have been investigated upon electrochemical lithiation. The reasonable electrical conductivity of magnetite opens the possibility of modifying the saturation magnetization by inserting Li+ ions into thin films grown on conducting substrates. A substantial decrease in M8 (up to 30%) was observed in PLD-grown thin films. Significantly larger reduction in moment (up to 75%) was observed in commercially available nanoparticles upon addition of 2 moles of Li per formula unit, along with changes in remanence and coercivity. The smaller drop in M8 observed in thin films is attributed to a kinetic effect due to high density and greater diffusion lengths in PLD-grown films. / (cont.) The electrochemical lithiation process has also been applied to needle-shaped particles of chromium dioxide and a model has been proposed to explain the observations. The effects of cycling and discharge-charge rate on these CrO2 particles have been studied. It has been shown that the process may be partially reversible for low Li contents. The effects of increasing the temperature of cycling and decreasing the length of the CrO2 particles have been explored. These changes in magnetic moment may be rendered useful in magnetomechanical or magnetoelectronic applications. / by Vikram Sivakumar. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, February 2014. / Cataloged from PDF version of thesis. "February 2014." Page 206 blank. / Includes bibliographical references (pages 195-205). / Lithium ion batteries for large-scale applications demand a strict safety standard from a cathode material during operating cycles. Lithium manganese borate (LiMnBO₃) that crystallizes into a hexagonal or monoclinic framework is one prominent polyanionic compound to cope with such requirement since it can possess high safety and high energy density simultaneously, without trading one for the other, theoretically. However, the hexagonal phase was nothing but a disregarded composition due to its negligible Li intercalation capacity. In contrast, the monoclinic LiMnBO₃ compound exhibited much more electrochemical activity than the hexagonal polymorph. In this thesis work, the discharge capacity of 100 mAh g 1 with acceptable capacity retention was achieved by simple optimization. The different electrochemical behaviors between them were understood in relation to their structural difference as it affects the Li migration barrier, structural stability of Li-deficient states, and even particle morphology. However, although promising, monoclinic LiMnBO₃ needed further improvement in terms of the achievable capacity and cyclability. Electrochemical analysis showed that the limited capacity of LiMnBO₃ mostly originated from transport limitation, a hindered Li migration through the one-dimensional diffusion channel. It also struggled from the phase decomposition and Mn dissolution due to the instability of the delithiated state, which led to gradual capacity fading in prolonged cycles. As an effective materials design strategy to overcome such limitations, systematic substitution of transition metal elements was proposed. To increase achievable capacity, Mn was partially substituted by Fe. Also, to fortify the structural integrity, Mg replaced Mn. In order to obtain both improved capacity and cyclability, Fe and Mg are co-doping led to an optimized composition. Prepared by cold-isostatic pressing, LiMg₀.₁Mn₀.₅Fe₀.₄4BO₃ showed near theoretical capacity of 200 mAh g-¹ with much improved capacity retention. These newly established materials outperformed most of the polyanionic cathode compounds. Therefore, it can be concluded a new promising candidate as a Li storage material has been developed through this thesis research. / by Jae Chul Kim. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995. / Includes bibliographical references (p. 312-314). / by Scott E. Deering. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 246-250). / by Steve Andrew Kramer. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2000. / Includes bibliographical references (leaves 124-126). / Morphology evolution in the melting regime during compounding of immiscible polymer blends. where most of the size scale reduction occurs. is studied. Starting from an initial solid pellet mixture of two components. the progression to the final two-phase viscoelastic melt involves an intermediate stage where either one or both the components are melting or softening. Our focus is identifying and quantifying the factors that determine morphologies in the melting regime. We identify blend systems that exhibit a transformation in morphology from a minor-component continuous phase with dispersed major component domains to that with the major component being the continuous matrix phase. as a function of mixing time. This phenomenon of phase inversion during compounding is demonstrated to occur even in blends with a higher melting point minor component. A low solid modulus and a low melt viscosity are shown to favor the formation of the continuous phase by the minor component. Polycaprolactone/polyethylene. polystyrene/polyethylene. polycarbonate/ polyethylene, poly(ethylene-co-cyclohexane dimethylene terephthalate)/ polyethylene. and polybutylene/polycaprolactone blends were studied. These model blends were chosen based on the melt viscosity ratio and the relative softening temperatures of the two components. These two parameters were used to develop a two-dimensional framework for summarizing the compounding behavior of blends. For compounding runs with a small amount of the minor component (-1 Owt. % ) at a constant mixer temperature, phase inversion was observed for blend viscosity ratios less than 0.2. irrespective of the relative transition temperatures of the two components. Using a temperature ramping program resulted in the low melting component forming the continuous phase initially. Selective dissolution studies were used to quantify the amount of minor component present in the continuous phase at different mixing times. A polystyrene/polyethylene blend with a melt viscosity ratio of -0.001. was used to study the effect of batch size on the time required to form a continuous phase of the compounding of batch sizes ranging from 12g to 240g. Upon a five-fold increase in batch size the time to phase inversion increased by a factor of 3. This increase was explained by a combination of reduced heat conduction and reduced mechanical energy input to the batch. To enable studies at different batch sizes in the same mixing bowl, a novel mixing blade with modular elements was designed and constructed. This design was used for both radial and axial scaleup studies. The effect of changing the blade configuration on the time to phase inversion was explained using a specific relative stagger parameter, which is a measure of the effectiveness of stress transfer to the batch. Flow visualization using a glass window and blend sampling was used to develop a detailed description of the deformation steps leading to phase inversion in a model low viscosity ratio blend. Intermediate morphologies of flattened pellets, stacks of pellets, fibers and clusters were identified. Based on these observations a micro-structural model was developed to predict the time to phase inversion. The model incorporates a simplified flow-field approximation and calculates the strain in the major component. A strain-based criterion was proposed which in conjunction with the model yielded an explicit expression for the time to phase inversion. Model predictions of the dependence of time to phase inversion on nominal maximum-shear-rate in the mixer, volume fraction of the minor component and blend viscosity ratio were shown to be in excellent agreement with experimental results. / by Ramabhadra Ratnagiri. / Ph.D.