A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics

The acid-base properties of titanium 6-4 plates (low surface area) were investigated after three different pretreatments, namely Turco, phosphate-fluoride and Pasa-Jell. A series of indicators was used and color changes were detected using diffuse reflectance visible spectroscopy. Electron spectroscopy for chemical analysis was used to examine the indicator on the Ti 6-4 surface. Specular reflectance infra-red spectroscopy was used to study the adsorption of stearic acid from cyclohexane solutions on the Ti 6-4 surface

An investigation of adhesive/adherend and fiber matrix interactions

Research during the report period focused on continued scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) of lap shear samples and flatwise tensile specimens and on the surface characterization of TiO2, Ti 6-4, and Ti powders with particular emphasis on their interaction with primer solutions of both polyphenylquinoxaline and LaRC-13 polyimide. The use of SEM and XPS in the analysis of Ti 6-4 adherend surfaces is described as well as differences in Ti 6-4 surface composition after different chemical pretreatments. Analysis of fractured surfaces is used to established the failure mode. The surface acidity of Ti 6-4 coupons can be established by reflectance visible spectroscopy using indicator dyes

A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics

Several techniques were used to study pretreated Ti 6-4 surfaces including scanning electron microscopy (SEM), electron spectroscopy of chemical analysis (ESCA), and, reflectance visible spectroscopy. Each pretreatment type gave a characteristic surface morphology as seen by SEM. Elemental analysis of the Ti 6-4 surfaces was done using ESCA. Trace residual contaminants from particular chemical pretreatments were identified readily. Results indicate that reflectance visible spectroscopy using indicator dyes placed on Ti 6-4 surfaces appears to be a feasible approach to establish surface acidity. Differences in surface acidity were observed using bromthymol blue on Ti 6-4 surfaces pretreated by two different methods

A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics

Pretreated and primed Ti 6-4 surfaces were characterized by scanning electron microscopy/energy dispersive analysis of X-rays (SEM/EDAX) and electron spectroscopy for chemical analysis (ESCA). Fractured lap shear bonded Ti 6-4 specimens were also characterized by SEM/EDAX and ESCA. A number of surface techniques were used to characterize Ti02 powders

Fabrication and evaluation of a collagen-based fiber-gel three-dimensional construct for peripheral nerve repair

Nerve regeneration following a peripheral nerve injury often relies on growth cone- mediated guidance and the presence of Schwann cells to support the regenerating axons and remyelinate portions of denervated nerve pathways. The emphasis of this work is to develop a synthetic nervous tissue construct that contains similar basal lamina or extracellular matrix to peripheral nerve in order to achieve a level of effectiveness in nerve repair and future peripheral nerve regeneration applications. To this end, three- dimensional nervous tissue constructs consisting of type I collagen are fabricated into a composite biomaterial scaffold to promote contact-guided growth of neuronal and glial cultures in vitro. The growth of adult tissue on these collagen-based materials is further evaluated. These constructs are assembled by wet spinning synthetic collagen fibers and loading them onto a soft collagen gel matrix composed of type I collagen. Wet-spun collagen fibers serve as a rigid substrate to reinforce the gel while facilitating axon growth cone advancement along a polarized direction. In this study, the emphasis is to characterize the mechanical stability, thermal properties, and swelling response of the collagen fiber component of the construct. To improve these properties in the fiber component, chemical cross-linking with genipin and glutaraldehyde are evaluated. The result is a construct exhibiting mechanical integrity for facilitating adult Schwann cell orientation and the guidance and survival of adult dorsal root ganglion neurons in a co-culture 3-D system

First-Principles Studies Of Two-Dimensional Transition Metal Carbides For Spintronics And Energy Applications

Next-generation spintronic nanoscale devices require two-dimensional (2D) materials with robust ferromagnetism. Among 2D materials, MXenes are favorable for spintronic applications due to their high electron conductivity, mobility, and chemical diversity. Since 2D materials have greater elastic strain limits than their bulk counterparts, their properties can be tuned effectively using strain engineering. In this dissertation, we discuss density functional theory (DFT) based first-principles studies on ferromagnetic MXenes for spintronics applications. In Chapter III, we investigated modifications in the structural, electronic, and magnetic properties produced by strain on 2D Hf2MnC2O2 and Hf2VC2O2 ferromagnetic semiconductors. The calculations in Chapter III reveal that the conduction bands near the Fermi-level are extremely sensitive to the biaxial and uniaxial strain. As a result, semiconductor-to-metal phase transitions occur at around 1-3 % biaxial compressive strain for both monolayers. At around 8-9 % biaxial tensile strain, those monolayers become half-metals. It could be shown that those results can be produced by applying uniaxial strain on Mn-based monolayer. In Chapter IV, surface defects were introduced to tune the electronic and magnetic properties of those two monolayers. Bare-Hf2MnC2O2 nanosheet exhibits easy-plane anisotropy, whereas bare-Hf2VC2O2 has easy-axis anisotropy. It could be found that defects change the anisotropy of Mn-based monolayer to easy- axis anisotropy. Moreover, the Curie temperature of Hf2MnC2O2H0.22 was predicted as 171 K by using the Monte Carlo simulations of the classical Heisenberg model . Recently, extensive studies have been carried out to discover new techniques to improve the properties of the materials to meet the demand of high cycling stability, charge capacity, and energy density of rechargeable battery applications. The 2D materials have been highly investigated for energy storage due to their large surface areas, which facilitate enhanced ion adsorption. In this dissertation, several possible techniques were explored to modify the electrochemical properties of 2D battery electrodes. Chapter V studied the B-doped-graphene (B-Gr) based systems to intercalate highly abundant Na and Mg to lower the production cost. The Na and Mg intercalated bare graphene bilayers are energetically not favorable. Nevertheless, we could show that B-Gr bilayers provide a considerable capacity (238 mAh/g for Na and 320 mAh/g for Mg). Na intercalated T2CO2/B-Gr, and B-Gr/B-Gr systems provide energy barriers as low as 0.46 and 0.18 eV, respectively. So far, hydroxyl, oxygen, and fluorine-terminated MXenes have been widely studied for energy storage applications. In Chapter VI, sulfur functionalized MXene structures (i.e., M2CS2 with M= Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W) have been proposed as candidate materials to enhance battery performance. It was found that all the M2CS2 monolayers provide the energy barriers less than 0.22 eV for single Li adsorbed systems. Among the considered MXenes, Ti2CS2 provides the highest gravimetric capacity (417.4 mAh/g). Chapter VII introduced pillared Ti3C2O2 bilayers for enhancing the ion storage capacity, minimizing the change in the interlayer distance between MXene layers and lowering the diffusion barrier of ions. Two different quinone molecules, namely 1,4-Benzoquinone (C6H4O2) and Tetrafluoro-1,4-benzoquinone (C6F4O2) were considered as the linkers between Ti3C2O2 layers. Even though only a single Li layer can be intercalated between Ti3C2O2 layers, quinone molecules provide enough space to store two layers of Li. Thus, high capacity can be expected. Moreover, pillared structures show a very lower diffusion barrier, which is around 0.3 eV, than that of Ti3C2O2 bilayers without quinone molecules (1.0 eV)

Direct and Indirect Influence of Mining Related Subsidence on Structural Damages - a Case Study

An investigation of causes of damages to a structure located at a toe of a hillside over an undermined area is described. The investigation included a finite element analysis and an analysis of landslide susceptibility of the hillside. Direct and Indirect influence of mining activity appears to be the cause of structural damages

Nonlinear fatigue life prediction model based on the theory of the S-N fatigue damage envelope

A nonlinear model is proposed in light of the theory of isodamage curves, to assess the cumulative fatigue damage under multistage loading. The isodamage curves were developed through the theory of the S-N fatigue damage envelope, proposed by Pavlou. The adopted functional form of the fatigue damage is a commonly accepted general form. In the present work, a stress function for the fatigue life exponent is derived with the aid of the S-N curve only. In the proposed nonlinear model, no adjusting parameters are necessary for fatigue damage estimation. The fatigue life prediction of the derived model is compared with experimental results of various alloys and existing models. The comparison is made for C35, C45, Al-2024-T42, 15HM, A336 GR 5, and A387 GR22 for two-stage loading high-low and low-high, and Al 6082-T6 for multistage loading.publishedVersio

Durable zinc oxide-containing sorbents for coal gas desulfurization

Durable zinc-oxide containing sorbent pellets for removing hydrogen sulfide from a gas stream at an elevated temperature are made up to contain titania as a diluent, high-surface-area silica gel as a matrix material, and a binder. These materials are mixed, moistened, and formed into pellets, which are then dried and calcined. The resulting pellets undergo repeated cycles of sulfidation and regeneration without loss of reactivity and without mechanical degradation. Regeneration of the pellets is carried out by contacting the bed with an oxidizing gas mixture

Durable regenerable sorbent pellets for removal of hydrogen sulfide from coal gas

Pellets for removing hydrogen sulfide from a coal gasification stream at an elevated temperature are presented in durable form, usable over repeated cycles of absorption and regeneration. The pellets include a material reactive with hydrogen sulfide, in particular zinc oxide, a binder, and an inert material, in particular calcium sulfate (Drierite), having a particle size substantially larger than other components of the pellets. A second inert material and a promoter may also be included. Preparation of the pellets may be carried out by dry, solid-state mixing of components, moistening the mixture, and agglomerating it into pellets, followed by drying and calcining. Pellet size is selected, depending on the type of reaction bed for which the pellets are intended. The use of inert material with a large particle size provides a stable pellet structure with increased porosity, enabling effective gas contact and prolonged mechanical durability