Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Vita. / Includes bibliographical references (leaves 90-93). / The Electron Beam Solid Freeform Fabrication process involves the use of an electron beam to make near-net-shape metal parts without the need for tooling. Material in wire form is fed into a melt pool maintained on the surface of the part by the electron beam and a positioning system causes the deposition to occur in a line-by-line, layer-by-layer fashion. Solidification occurs at a high rate, forming a fine dendritic microstructure and fine dispersion of primary carbides. This structure is believed to be optimal for the manufacture and safe use of certain nickel-base superalloy parts, notably turbine disks. The growth of carbide particles from the liquid during EBSFF processing of Alloy 718 has been modeled assuming diffusion control and isolated spherical carbides. The driving force for growth is assumed to increase in a linear manner throughout the temperature range of carbide precipitation. The model predicts the maximum carbide size as a function of EBSFF operating parameters and the alloy niobium and carbon levels. For the material and conditions used experimentally in this work, the model predicts a maximum diameter of approximately I .0 [mu]m. The maximum carbide size will become an important determining factor for turbine disk performance when oxide and nitride inclusions have been eliminated through improved melt practices. To illustrate this, the low-cycle fatigue life as a function of carbide size for a standard specimen geometry was calculated. Extraction replica transmission electron microscopy of EBSFF samples identified carbides in the 300-600 nm range, consistent with a population having the predicted maximum size. Another dispersion of carbides larger than 3 [mu]m was also observed in the EBSFF samples. These are believed to be original carbides that survived the EBSFF thermal cycle without completely dissolving. More thorough dissolution can probably be obtained with EBSFF process modifications. Control material from a conventional vacuum arc remelted ingot with similar composition was also examined and plate-like carbides up to 40 [mu]m in length were noted. This is an indication of the enormous potential of the EBSFF process to refine the carbide morphology and size distribution without the need for a reduction in carbon content. / by John Edward Matz. / Sc.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 33-34). / One of the key limitations in the wide-scale adoption of mature renewable energy technologies is the lack of grid-level energy storage solutions. One important figure of merit in these battery systems is a high rate capability to match fluctuating demands for electricity. Molten salt batteries are an attractive option for stationary storage due to fast kinetics and good cycling capability, but high temperatures (>300 °C) limit available materials. In this thesis, the molten NaCl-AlCl3-SnCl2 electrolyte and liquid Sn electrode couple at 250 °C is investigated as part of the potential cell Na I NaCl-AlCl 3-SnCl2 I Sn for a lower temperature molten salt battery. An electrochemical study of the kinetics in the molten salt electrolyte and at the liquid Sn electrode-electrolyte interface is conducted using cyclic voltammetry and the galvanostatic pulse method. The liquid metal electrode is found to have suitably fast kinetics with an exchange current density of 92 mA/cm2. Parameters for a new Na+ conducting membrane are proposed, requiring an ionic conductivity of 0.056 S/cm, which would allow for a hypothetical Na I NaCl-AlC 3-SnCl2 I Sn battery to operate with an energy efficiency of 70%. / by Raku Watari. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Vita. / Includes bibliographical references (leaves 112-113). / A fluxless low temperature transient liquid phase (LTTLP) bonding process was studied as a method of producing Cu/Cu joints below 125°C and 75°C using interlayer alloys from the In-Sn and In-Sn-Bi systems. Using thermodynamic models, three different compositions (wt. %) of base alloys were chosen to accomplish this task: 50In-43.6Sn-6.4Bi (Tm = 110°C) and eutectic 50.9In-49.1Sn (Tm = 120°C) alloys were used for bonding at 125°C and a eutectic 48.3In-15.6Sn-36.1Bi (Tm = 60°C) alloy was used for bonding at 75°C. In addition, novel approaches to TLP bonding, including the addition of base material to the interlayer alloy and application of an electroless Ni diffusion barrier layer, were employed in an attempt to optimize this joining method. The LTTLP processes were assessed based on their abilities to produce joints with minimal thickness, high reflow temperatures, and good mechanical properties at room/elevated temperatures. It was found that interlayer alloys containing higher Bi contents produced the thinnest joints, with the 48.3In-15.6Sn-36.1Bi alloy producing joints on the order of 10 gm. Increases in nominal Cu composition of the interlayer alloy tended to form larger joints. Application of the Ni layer was observed to decrease the growth rate of the eutectic In-Sn joints made with 5 wt % Cu additions. Shear tests were performed on the joints at room (25°C) and operating (service) temperatures (100°C). Most of the TLP joints had room temperature shear strengths around 13,000 - 17,000 psi (= 90 - 120 MPa), although increases in strength were observed for eutectic In-Sn joints with 2.5 and 5 wt% Cu additions. At operating temperature, TLP joints made within the In-Sn-Cu system were found to have strengths an order of magnitude higher than those made in the In-Sn-Bi-Cu system. / (cont.) Poor mechanical response of the Bicontaining joints was due to the presence of low melting In-Bi IPs present in the reaction zone. Eutectic In-Sn TLP joints made with 2.5 and 5 wt% Cu additions were found to have operational temperature shear strengths of 6,000 - 7,500 psi ( 40 - 50 MPa) and 7,500 - 9,500 psi (= 50 65 MPa), respectively. / by David S. Fischer. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1986. / Vita. / Includes bibliographical references (leaves 152-159). / by Ricardo I Fuentes. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1995. / Includes bibliographical references (leaves 221-231). / by Yong-Chae Chung. / Ph.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 59-62). / Single layer graphene is a nearly transparent two-dimensional honeycomb sp2 hybridized carbon lattice, and has received immense attention for its potential application in next-generation electronic devices, composite materials, and energy storage devices. This attention is a result of its desirable and intriguing electrical, mechanical, and chemical properties. However, mass production of high-quality, solution-processable graphene via a simple low-cost method remains a major challenge. Recently, electrochemical exfoliation of graphite has attracted attention as an easy, fast, and environmentally friendly approach to the production of high-quality graphene. This route solution phase approach complements the original micromechanical cleavage production of high quality graphite samples and also involved a chemically activated intermediate state that facilitates functionalization. In this thesis we demonstrate a highly efficient electrochemical exfoliation of graphite in organic solvent containing tetraalkylammonium salts, avoiding oxidation of graphene and the associated defect generation encountered with the broadly used Hummer's method. The expansion and charging of the graphite by intercalation of cations facilitates the functionalization of the graphene basal surfaces. Electrochemically enhanced diazonium functionalization of the expanded graphite was performed. The exfoliated graphene platelets were analyzed by Raman spectroscopy, to quantify defect states and the degree of exfoliation. Additional microscopy techniques provided additional insight into the chemical state and structure of the graphene sheets. / by Intak Jeon. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2004. / Includes bibliographical references (p. 237-248). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Ceramic/metal interfaces occur in a great number of important applications, such as ceramic/metal composites, microelectronics packaging, ceramic/metal seals, and so forth. Understanding the formation and evolution of such interfaces is therefore essential for the better design and optimization of these technologies. In this thesis, a methodology for the study of the thermochemical interactions at ceramic/metal interfaces, during both their formation and evolution, is proposed. Because of the importance of zirconia-based ceramics in increasingly important applications such as structural composites, thermal barrier coatings and Solid Oxide Fuel Cells, it was decided to illustrate the concepts developed in this thesis through the study of the interactions between zirconias and active metals. Semi-empirical thermodynamic models of all the phases likely to take part in the ceramic/metal interfacial interactions studied were developed. Phase diagram data and thermochemical information were critically assessed and use to adjust the thermodynamic parameters that allowed the description of the Ag-Cu-Ti, Cu-Ti-Zr, Ti-Zr-O, Cu-Ti-O and Cu-Zr-O systems. The thermodynamic models were used to predict the diffusion paths across zirconia/active metal interfaces through metastable phase diagrams calculations. Additionally, equilibrium calculations of activity diagrams were used to understand the complex interfacial reactions occurring during the active metal brazing of zirconia-based ceramics. / (cont.) By using simple one-dimensional interdiffusion simulations, it was demonstrated that the base metal in ceramic/metal joints plays an essential role in determine the thermochemical interactions at the ceramic/metal interface during ceramic/metal joining operations. In general it was found that, using all these techniques,it was possible to explain diffusion paths and reaction sequences observed in a great number of zirconia/active-metal systems, both in the solid and in the liquid states. In many cases, the morphology of the reaction layers formed at ceramic/metal interfaces determine their final properties. To address this problem, empirical thermodynamic models of the likely reaction products at zirconia/metal interfaces were coupled to kinetic models using the diffuse-interface formalism to successfully describe the formation and evolution of complex ceramic/metal interfacial structures. / by Raymundo Arróyave. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006. / Includes bibliographical references (p. 131-135). / A conceptual high-temperature battery system for large-scale grid power applications was proposed, described, and evaluated. Unlike conventional battery technologies whose maximum current rate is constrained by at least one solid phase, the novel three-layer liquid-phase electrode-electrolyte-electrode cell facilitates high diffusivity and facile interfacial kinetics, which results in rapid ion transport and low activation overpotential. In addition to the extremely high currents enabled by the absence of solid-liquid interfaces, this cell configuration represents a robust design that can be easily manufactured. The molten components will self assemble due to their immiscibility and different densities. Another key feature is that a molten metalloid acts as the positive electrode, while an alkali or alkaline earth metal acts as the negative electrode, providing two electronically conductive molten electrodes. The cell is estimated to have a lifespan of 10-15 years with >3,000 deep-discharge cycles, to require minimal maintenance, and to supply 1-5 A/cm2 at 0.9 V with 80% DC-DC cycle-efficiency. / (cont.) One embodiment comprising electrodes of magnesium (negative) and antimony (positive) and a molten sulfide supporting electrolyte served as the basis for a detailed feasibility assessment (alternative electrode and electrolyte materials were also discussed). A cost model was created based on an entire battery system, which included top and bottom current collectors, a corrosion resistant sheath, insulation, and other components. Materials were selected based on corrosion resistance, mechanical stability at the operation temperature, and cost. A DC-battery was estimated to cost $35-60/kWh. An AC-compatible system would also require power electronics, at an additional cost of $50/kWh. With a 50% gross margin on the battery unit, the price of an AC-system was estimated to be $120-170/kWh. Market analysis was performed to assess the commercial viability of a large-scale electricity storage device. A stand-alone, load-leveling device was found to generate minimal revenue, while a system for transmission-line and distribution-system upgrade deferral was found to be a much more attractive proposition. / (cont.) System requirements for this application include 75% AC-AC cycle-efficiency, >1 MW capacity, 8-hour discharge duration, re-locatable, a footprint <100 m2/MW, and a 10-15 year lifespan. Extensive market penetration would occur with a price of $150/kWh, which is achievable by the proposed system. Support for intermittent renewables is possible under circumstances where they contribute to more than 10% of the grid power. / by David Bradwell. / M.Eng.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015. / In title on title-page, double underscored characters appear as subscript (Prx̳Ce1̳-̳x̳O2̳-̳[̳d̳e̳l̳t̳a̳]̳) Cataloged from PDF version of thesis. / Includes bibliographical references (pages 129-134). / An improved fundamental understanding of oxygen defect equilibria and transport kinetics in oxides is essential for achieving enhanced performance and longevity in many oxide-based practical applications. The ability to diagnose a material's behavior in a thin film structure under operating conditions (in operando), ideally in situ, is therefore of importance. In this dissertation, a novel experimental technique capable of simultaneously performing in situ and in operando optical absorption and electrochemical impedance spectroscopy (EIS) measurements was developed and utilized, for the first time, over a range of temperatures and controlled atmospheres. The technique was applied to the Prx̳Ce1̳-̳x̳O2̳-̳[̳d̳e̳l̳t̳a̳]̳, (PCO) model thin film system. PCO shows mixed ionic and electronic conducting (MIEC) characteristics at relatively high pO2 regimes (e.g. air), which is beneficial for solid oxide fuel cells (SOFCs) cathode performance. The Pr impurity levels in PCO allow for optical transitions (2.0 - 3.3 eV), leading to the red coloration of oxidized samples. A change in the redox state of Pr results in a color change and so serves as a means of investigating the Pr oxidation state and thereby oxygen non-stoichiometry. Pr⁴⁺ concentrations, derived independently from optical and electrochemical measurements, and their corresponding trends, were found to be self-consistent, confirming that the oxygen reduction enthalpy in thin film 10PCO is lower than that in the bulk. The derived extinction coefficient, . . . , can now be utilized to study defect equilibria of PCO or other relevant oxide films by optical means alone. The oxygen surface exchange reaction kinetics, driven by chemical and electrical driving forces, were investigated and correlated to each other, with the aid of the thermodynamic factor. The impact of surface chemistry and metal current collector on the reaction kinetics was discussed. A specially designed cell structure enabled the extension of the oxygen diffusion pathway, allowing for the monitoring of color front migration in PCO films. Such optical color front motion experiments offer the opportunity for in situ, more rapid and reversible investigation of oxygen diffusion kinetics in thin films and open new opportunities to study materials' spatially distinguishable properties. / by Jae Jin Kim. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 207-217). / by Kwang Ki Baek. / Ph.D.