Laminated glass is comprised of multiple glass plates coupled together in a sandwich construction through the use of a polymorphous interlayer that acts as a bonding agent between the glass plates. Laminated glass offers several advantages over monolithic glass including the ability to resist post fracture collapse, improved sound insulation, lower ultraviolent light trans-mission, and improved thermal insulation. Because the stiffness of the interlayer is often many orders of magnitude less than that of the glass, plane sections prior to loading do not remain plane throughout the laminate?s thickness after load is applied. The behavior of laminated glass is controlled by the stiffness of the interlayer. This behavior rules out the use of classical theoretical formulations for thin plates. In such cases, it is necessary to use specially formulated equations or finite element analyses to evaluate the performance of laminated glass. Previous attempts have been made to develop procedures to quantify the interlayer stiffness for use in laminated glass design. However, there is no widely accepted technique that can be referenced for use. It is known that the interlayer stiffness is a function of both temperature and load duration. The primary objective of this thesis is to formalize a standard procedure to estimate the in situ interlayer shear modulus through the use of nondestructive testing. Physical experiments were carried out on simply supported laminated glass beams subject to three point loading in a temperature controlled environmental testing chamber. Strains and temperatures were recorded as a function of time. These data were used in combination with results from finite element analyses to quantify the variation of the interlayer stiffness as a function of temperature and load duration for a given laminated glass beam. This procedure was applied to three common types of interlayer materials: freshly man-factured polyvinyl butyral (PVB), over a decade old PVB, and freshly manufactured SentryGlas Plus (SGP). Results from these efforts provide specific design guidance for laminated glass that incorporates these interlayer materials. Further, the procedure was applied to various data presented in open literature by previous researchers. In addition, a standardized procedure to estimate interlayer stiffness is provided for the development of additional interlayer properties as required.

In this study, the experimental apparatus with a friction stir welding dynamometer was employed to investigate the joint characteristics of Cu-Ni alloy plate in thickness of 3.6mm lap-welding to low carbon steel plate in thickness of 4 mm using cylinder type tool (without probe) under the welding parameters of rotating speeds (800~1400 rpm) and traveling speed of tool (10~80 mm/min). To prevent the joint interface from oxidizing during the welding process, the joint interfaces of Cu-Ni alloy and low carbon steel respectively were electroplated with Ni coating layer in different thicknesses before the welding. The effect of the thickness of Ni coating layer on shear strength of joint interface and the mechanism of welding are also investigated. Experimental results show that under the rotating speed of 1000 rpm and travelling speed of 10 mm/min, the shear strength for without Ni coating layer is measured about 100 MPa. On the other hand, the shear strength is increased to saturated value of 290 MPa with increasing the thickness of Ni coating layer. Especially, the shear strength of joint interface for the Cu-Ni alloy with 5£gm thickness of Ni coating layer lap-welding to low carbon steel with thickness of 20£gm thickness of Ni coating layer is about 2.9 times of that for without Ni coating layer. Moreover, the downward force (Fd) is decreased and the maximum interface temperature (Tmax) and shear strength (£n) are increased with increasing the rotating speed (N). The downward force is increased and the maximum interface temperature and shear strength are decreased with increasing the traveling speed (f). This complex relationship is discussed by the new parameter of Fd¡EN/f, the relationship among Fd¡EN/f, maximum interface temperature and shear strength shows that the maximum interface temperature is increased and shear strength is increased to saturated value of 290 MPa with increasing Fd¡EN/f. The phenomenon is explained that the diffusion bonding between the joint interface of two plates become more homogeneous.

Carbon Nanotubes (CNTs) have great potentials for Field Electron Emission (FEE) and Flow Boiling Heat Transfer (FBHT) applications. However, their weak adhesion on metallic substrates limits the development of CNTs in both applications. Diamond has high thermal conductivity and develops strong bonding with CNTs. The development of a diamond interlayer between CNTs and substrates is a feasible approach to address the adhesion problems. The purpose of this research was to develop a new CNT-based materials with a diamond interlayer for FEE and FBHT applications by focusing on four objectives: (1) enhancement of diamond thin film adhesion on a Cu substrate, (2) improvement of the CNT FEE stability, (3) reduction of the CNT FEE turn-on field, and (4) investigation of the FBHT performance of CNT based structures. The CNTs and diamond thin films in this thesis were prepared by Microwave Plasma enhanced Chemical Vapor Deposition (MPCVD) and Hot Filament enhanced Chemical Vapor Deposition (HFCVD). The structure and chemical states of the diamond films and CNTs were characterized by Scanning Electron Microscopy (SEM), cross-sectional Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Raman spectroscopy, synchrotron based X-ray Absorption Spectroscopy (XAS). To deposit diamond thin films on a Cu substrate with sufficient adhesion strength, a sandblasting pretreatment and alloying with a tiny amount of Al were investigated. The adhesion of diamond thin films to substrates was evaluated by Vickers micro-hardness indentation. The FEE stability and turn-on field were measured by a Keithley 237 high voltage measuring unit. The FBHT property of the structures was tested repeatedly at different flow velocities to explore the dependence of heat transfer performance on certain parameters, including the flow patterns, Critical Heat Flux (CHF), and stability. The results show that sandblasting pretreatment increases the surface roughness and surface defect density, thereby increasing diamond nucleation density and adhesion to the Cu substrate. Al alloying appears to inhibit the formation of graphite at the interface between diamond and the Cu substrate, which improves the chemical bonding between diamond and the Cu substrate and increases the adhesion strength between them. The FEE testing results show that ultra-high FEE stability (more than 5000 minutes) was achieved for the CNTs with a diamond interlayer. This is attributed to the good contact at the diamond-CNT and diamond-substrate interfaces. The main factors that affect the CNT FEE turn-on field were also studied. By optimizing the structure, an FEE turn-on field of 5.1 V/μm was achieved and an emission barrier model for CNTs with a diamond interlayer on Cu substrate was used to explain the results. FBHT testing was done on CNTs with different structures and the results show that high heat transfer efficiency can be achieved on CNTs with a diamond interlayer at low mass fluxes.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Long term performance of a road pavement structure is significantly influenced by its potential to distribute traffic loading from the surface to the natural subgrade. The interlayer adhesion conditions play a substantial role in the induced stress-strain distribution across all layers of the entire structure. For layers constructed in stages like a granular base (GB) and a cement treated subbase (CTSB), the state of adhesion is questionable. Therefore a detailed investigation on the achievable adhesion and its influence on pavement performance is essential. In this study, the direct shear test was used to assess the interlayer adhesion strength in terms of resistance of the GB layer to slide on top of the CTSB. To evaluate the level of achieved shear strength, the interlayer shear results were compared to the inlayer strength for a granular base and cemented subbase. The shear test results were presented in terms of relationships between shear stress and displacement, shear stress and normal pressure and vertical and horizontal displacements. Based on frictional and dilatant approaches, shear test results demonstrated that the interlayer adhesion strength between the GB and CTSB is significantly influenced by the roughness conditions of the CTSB before placing the GB. Compacting materials of the base layer on top of the scarified CTSB produces a unified compound structure due to intimate interaction between the two layers. Moreover, the achievable adhesion depends on the maximum grain size available in the CTSB layer, confining pressure and moisture condition. The increase in maximum aggregate size deepens the interaction zone between the GB and scarified CTSB which results in high shear resistance. Ingress of water induces lubricant behaviour and weakens the shear resistance. In the design example, it was shown that the assumption of full adhesion between pavement layers, currently used in many design methods, over-estimates the pavement life. The routine construction process of placing the GB on top of quasi-smooth CTSB induces poor adhesion between the layers which therefore affects stress-strain distribution behaviour across all layers of the pavement structure and then reduces the life of every single layer. According to the design example, the granular base layer is the most susceptible to early failure due to its stress-dependent behaviour. The significant difference between pavement life when full adhesion is considered and when partial adhesion is allowed indicates that the achievable adhesion should be considered during the design of the structure rather than assuming full adhesion. Furthermore, the development of practical specifications and technical guidelines for improving the anticipated conditions in the field is recommended. / AFRIKAANSE OPSOMMING: Die langtermyngedrag van 'n plaveiselstruktuur word tot 'n groot mate beïnvloed deur die vemoë daarvan om om verkeerslaste vanaf af die oppervlakte na die natuurlike grondlaag te verprei. Die adhesie tussen die plaveisellae speel 'n belangrike rol in die verspreiding van spannings en vervormings deur al die lae van die struktuur. In lae wat in fases gebou word, soos 'n grofkorrelrige kroonlaag (GB) en 'n sementgestabiliseerde stutlaag (CTSB), is die adhesie onder verdenking. 'n Detailondersoek van die adhesie wat behaal kan word, en die invloed daarvan op plaveiselgedrag, is daarom noodsaaklik. In hierdie ondersoek is die direkte skuiftoets gebruik om die tussenlaag-adhesie vas te stel in terme van die weerstand van die GB-laag om oor die CTSB-laag te skuif. Om die vlak van skuifsterkte wat behaal kan word, te bepaal, is die tussenvlakskuifsterkte vergelyk met die interne skuifweerstand van die grofkorrelrige laag en van die gestabiliseerde laag. Die skuiftoetsresultate is uitgedruk in terme van die verbande tussen skuifspanning en skuifverplasing, tussen skuifspanning en normaalspanning en ook tussen vertikale en horisontale verplasings. Gebaseer op skuifweerstand en dilatansie het skuitoetsresultate gedemonstreer dat adhesie tussen die GB- en CTSB-lae baie beïnvloed word deur die ruheid van die CTSB voordat die GB gebou word. Indien die GB-laag bo-op 'n grofgemaakte CTSB-laag geplaas word, word 'n baie goeie verband en interaksie tussen die twee lae verkry. Die beskikbare adhesie hang ook af van die maksimum korrelgrootte in die CTSB-laag, die inperkspanning en die waterinhoud. Die toename in maksimum aggregaatgrootte maak die interaksiesone tussen die GB en die grofgemaakte CTSB dieper en dit lei tot hoër skuifweerstand. Infiltrasie van water dien as smeermiddel wat die weerstand verlaag. In die ontwerp-voorbeeld is gedemonstreer dat die aanname van volle adhesie tussen plaveisellae, soos wat tans in baie ontwerpmetodes gedoen word, tot oorskatting van die leeftyd van die plaveisel lei. Die normale konstruksiemetode waarin die GB-laag bo-op 'n semi-gladde CTSB-laag geplaas word, lei tot swak adhesie tussen die lae wat verspreiding van spannings en vervormings deur die plaveisel minder gunstig maak en die leeftyd van alle lae in die plaveisel verlaag. Volgens die ontwerp-voorbeeld is die grofkorrelrige kroonlaag die vatbaarste vir voortydige faling as gevolg van die sy spannings-vervormingsgedrag. Die beduidende verskil tussen plaveiselleeftyd wanneer volle adhesie aanvaar of slegs gedeeltelike adhesie toegelaat word, illustreer dat die werklike haalbare adhesie gebruik moet word eerder as om volle adhesie te aanvaar. Verder word die onwikkeling van praktiese spesifikasies en tegniese riglyne om die verwagte toestande in die plaveisel beter in ag te neem, voorgestel.

In order to meet the increasing fuel efficiency requirements, the automotive industry has strived for component weight reduction in order to improve the performance of automotive vehicles through the use of light Al and Mg alloys. Resistance spot welding (RSW) currently is the primary joining method in the manufacturing of automotive assemblies. With the increased use of Al and Mg, there is a pressing need for a technology to produce dissimilar Al/Mg joints, and preferably by RSW since this technology is already prevalent in the industry. Direct welding of Al to Mg usually results in formation of hard and brittle intermetallic compounds and poor quality of the welds. Employing an interlayer is a promising approach to overcome this problem. Current literature, however, does not consider the effects of different interlayers on RSW of Al to Mg. This thesis examines effects of different interlayers on microstructure and mechanical properties of Al/Mg joints made by RSW. Effects of three types of interlayers, specifically pure Ni foil, Au-coated Ni foil and Zn-coated were investigated in details. While only brief investigation of joints made with Sn-coated steel, Zn foil, and Cu foil interlayers was conducted. No joints were achieved with a bare Ni interlayer during Al to Mg alloy resistance spot welding, as coupons separated without applying any force. The Ni interlayer remained intact and Al-Mg intermetallic compounds did not form. Addition of Au coating on Ni surface greatly contributed to the metallurgical bonding at the interfaces and welds easily met requirements of the AWS D17.2 standard. Average lap-shear strength reached 90% of that in similar AZ31B resistance spot welds. Acceptable welds were also produced using galvanised Zn-coated steel interlayer, which easily met strength requirements of the AWS D17.2 standard. Average failure load reached 74% of same size similar AZ31B joints. The steel interlayer was not melted which prevented mixing of Al and Mg. The Zn coating on the steel interlayer was melted and squeezed to the nugget periphery, providing a clean steel surface for welding-brazing in the center and acting as a solder metal at the periphery. A feasibility study of Al/Mg RSW with Sn-coated steel, Zn foil and Cu foil interlayers was also conducted. Mechanical properties of welds made with Sn-coated steel interlayer were very similar to those made with Zn-coated steel interlayer. While welds made with only a Zn foil interlayer were much weaker. The Zn foil completely melted during the welding which resulted in formation of brittle Al-Mg-Zn phases. None of the welds made with Zn foil interlayer met requirements of the AWS D17.2 standard. RSW of Al to Mg with Cu foil interlayer also could not produce welds with acceptable strength.

My research on metal oxide electron-harvesting interlayers for organic solar cells was focused as three interrelated projects in this dissertation: i) development of a chemical vapor deposition (CVD) system for titanium dioxide (TiO₂) film; ii) an electrochemical methodology to evaluate ZnO thin film charge (hole) blocking ability; iii) the effects of plasma modifications on sol-gel ZnO and sol-gel ZnO/organic (active layer) interfaces. In i), we showed that nanoscale (12-36 nm) CVD TiO₂ film deposited at 210 °C from our system obtains properties of conformal growth with ITO substrate, superior hole blocking ability, stoichiometric metal to oxide ratio, and close energetic alignment with electron acceptors, e.g., fullerenes. The introduction of CVD TiO₂ film as an electron transport layer (ETL) into organic solar cell significantly improves its J-V characteristics compared to bare ITO electrode. The optimum TiO₂ thickness in the OPV device applications was found to be 24 nm with a high fill factor (0.58) and power conversion efficiency (3.7%) obtained. In ii), simple electrochemical methods, i.e., cyclic voltammetry, impedance spectroscopy have been used to evaluate sol-gel derived ZnO (sg-ZnO) and sputtered ZnO (sp-ZnO) porosity and pinhole density. We showed that sg-ZnO with high surface area porous structure allows the probe molecules and poly-thiophene (P3HT) thin layer to direct contact ITO substrate, whereas sp-ZnO with dense structural property efficiently eliminates the probe molecule diffusion and the penetration of P3HT layer to ITO substrate. This electrochemical property difference also directly reflects on the device shunt resistance (Rp), where we observed larger leakage current for the devices using sg-ZnO than that of devices using sp-ZnO. We envision these simple electrochemical characterizations can be applied into other similar metal oxide interlayers as well as on flexible TCO substrates, in which pinholes and physical imperfections, e.g., cracking may occur after multiple bending processes. In iii), we demonstrated low power (10.5 watts) radio frequency (RF) O₂ and Ar plasma treatments have significant impacts on sg-ZnO near-surface chemical compositions, which in turn influence the onset potential of sg-ZnO electron injection from the underlying ITO substrate and its energetic alignment with electron acceptors, e.g., C₆₀. Using UPS, we found the presence of localized mid-gap states near the Fermi-level (Ef) of sg-ZnO, which induces the most favorable band bending and the largest vacuum level shift due to significant electron transfer from sg-ZnO to C₆₀. As a result, the resultant solar cells show the best device performance. Upon the plasma treatments, the passivation effects eliminate the mid-gap state. Therefore, we observed less degree of band bending at ZnO/C₆₀ interface and poorer device performance for the plasma treated sg-ZnO. The study demonstrates the importance of oxide/organics interface in operations of organic solar cells and provides a modification method to tune surface properties of oxide materials which can apparently be applied in other organic electronic devices, e.g., field effect transistors (FETs), organic light emitting diodes (OLEDs), etc.

In order to meet the increasing fuel efficiency requirements, the automotive industry has strived for component weight reduction in order to improve the performance of automotive vehicles through the use of light Al and Mg alloys. Resistance spot welding (RSW) currently is the primary joining method in the manufacturing of automotive assemblies. With the increased use of Al and Mg, there is a pressing need for a technology to produce dissimilar Al/Mg joints, and preferably by RSW since this technology is already prevalent in the industry. Direct welding of Al to Mg usually results in formation of hard and brittle intermetallic compounds and poor quality of the welds. Employing an interlayer is a promising approach to overcome this problem. Current literature, however, does not consider the effects of different interlayers on RSW of Al to Mg. This thesis examines effects of different interlayers on microstructure and mechanical properties of Al/Mg joints made by RSW. Effects of three types of interlayers, specifically pure Ni foil, Au-coated Ni foil and Zn-coated were investigated in details. While only brief investigation of joints made with Sn-coated steel, Zn foil, and Cu foil interlayers was conducted. No joints were achieved with a bare Ni interlayer during Al to Mg alloy resistance spot welding, as coupons separated without applying any force. The Ni interlayer remained intact and Al-Mg intermetallic compounds did not form. Addition of Au coating on Ni surface greatly contributed to the metallurgical bonding at the interfaces and welds easily met requirements of the AWS D17.2 standard. Average lap-shear strength reached 90% of that in similar AZ31B resistance spot welds. Acceptable welds were also produced using galvanised Zn-coated steel interlayer, which easily met strength requirements of the AWS D17.2 standard. Average failure load reached 74% of same size similar AZ31B joints. The steel interlayer was not melted which prevented mixing of Al and Mg. The Zn coating on the steel interlayer was melted and squeezed to the nugget periphery, providing a clean steel surface for welding-brazing in the center and acting as a solder metal at the periphery. A feasibility study of Al/Mg RSW with Sn-coated steel, Zn foil and Cu foil interlayers was also conducted. Mechanical properties of welds made with Sn-coated steel interlayer were very similar to those made with Zn-coated steel interlayer. While welds made with only a Zn foil interlayer were much weaker. The Zn foil completely melted during the welding which resulted in formation of brittle Al-Mg-Zn phases. None of the welds made with Zn foil interlayer met requirements of the AWS D17.2 standard. RSW of Al to Mg with Cu foil interlayer also could not produce welds with acceptable strength.

No description available.

No description available.

The overall goal of this dissertation research was to design, tailor and understand layered metal oxides in the context of electrocatalytic energy conversion and storage processes. To accomplish this goal the thesis research combined electrochemistry, state-of-the-art structural characterization and theoretical calculations. The hypothesis examined in this dissertation is that incorporation of metal atoms or metal ions into the sheets and/or interlayer region of the layered materials will enhance the properties of selected 2D materials for chemistry relevant to electrochemical energy conversion (i.e. electrochemical water splitting catalysis; H2O ® H2 + 1/2O2) and energy storage (i.e., as pseudocapacitors). The primary 2D layered materials investigated in this thesis research were birnessite (nominally MnO2) and Fe:Ni double hydroxide materials. Metals (cations) used to modify the geometric and electronic structure of the layered materials include Cu, Ni, and Co. Perhaps the result with broadest impact to result from the integration of experimental and theoretical studies in the thesis research was that the confinement of solvated redox active metals within the interlayer region of 2D layered materials can be used to facilitate their electron transfer reaction rates (relative to the respective unconfined metal) and energy related electrochemistry. This new paradigm for electron transfer has implications for the development of novel electrocatalytic materials for energy conversion. Research showed that the electrocatalytic activity of birnessite toward water oxidation (2H2O® 4H+ + 4e- + O2) was increased by intercalating zero valent copper into the interlayer region of the layered manganese oxide. Electrocatalytic studies showed that the Cu-modified birnessite exhibited an overpotential for water oxidation of ∼490 mV (at a current density of 10 mA cm 2) and a Tafel slope of 126 mV/decade compared to ∼700 mV (at 10 mA cm-2) and 240 mV/decade, respectively, for birnessite without copper. Impedance spectroscopy results suggested that the charge transfer resistivity of the Cu-modified sample was significantly lower than Cu-free birnessite, suggesting that Cu in the interlayer increased the conductivity of birnessite leading to an enhancement of water oxidation kinetics. It was experimentally shown that the oxygen evolution reaction (OER; water oxidation) catalysis of redox active transition metal ions (Ni2+ and Co2+) can be enhanced by individually confining them in the interlayer region of birnessite. It was demonstrated that the metal confined electrocatalyst reached a current density of 10 mA cm−2 at much lower overpotentials than pure Ni and Co oxides, and pristine birnessite. For example, with interlayer nickel and cobalt, overpotentials of 400 and 360 mV, respectively, were achieved for the OER. Molecular dynamics (MD) simulations suggested that electron transfer reaction rates relevant to OER and involving Ni or Co were enhanced when the metal cations were confined in the interlayer of birnessite. The strategy of metal confinement, which was successfully applied to layered manganese oxide to improve OER activity was extended to Ni-Fe based layered double hydroxide. It was demonstrated that the electrocatalytic activity of NiFe layered double hydroxides (NiFe LDHs) for the OER could be significantly enhanced by systematic cobalt incorporation using coprecipitation and/or intercalation. Electrochemical measurements showed that cobalt modified NiFe LDH possessed an enhanced activity for the OER relative to pristine NiFe LDH. The cobalt doped NiFe LDH exhibited overpotentials in the range of 290−322 mV (at 10 mA cm−2), depending on the degree of cobalt content. The cobalt intercalated NiFe LDH achieved a current density of 10 mA cm−2 at a much lower overpotential of ∼265 mV (compared to 310 mV for NiFe LDH). With regard to energy storage, it was shown that the pseudocapacitive charge storage in layered manganese oxide was a sensitive function of interlayer composition and distance. Even though pristine layered manganese oxide shows a 7 Å interlayer spacing, the interlayer engineering via metal (Mg2+) intercalation and thermal annealing led to layered manganese oxide materials with variable interlayer spacings of 10 and 5.6 Å respectively. The interlayer expanded layered manganese oxide (10 Å interlayer spacing) exhibited an improved specific capacitance of 380 Fg-1, in comparison to synthetic Na-birnessite (specific capacitance of 200 F g-1). Dehydrated Na-birnessite (~5.6 Å spacing) produced by annealing to expel interlayer water, showed the lowest specific capacitance of 50 Fg-1. Experimental results showed that interlayer expanded manganese oxide (with intercalated Mg2+) was unstable if exposed to a solution containing only Na+ cation electrolyte. In this circumstance, the interlayer distance decreased from the expanded 10 Å value back to an interlayer distance of 7 Å and a specific capacitance of ~200 F g-1; values associated with synthetic Na-birnessite. Finally, a highly active alkaline medium hydrogen evolving electrocatalyst based on earth abundant materials (Co, Mo and P) was developed and the catalyst exhibited a ~0 V onset for the hydrogen evolution reaction (HER; 2H+ + 2e- ® H2). This value was comparable to that of the precious metal platinum. The Co-Mo-P catalyst was prepared by room temperature electrodeposition and it exhibited an overpotential of ~ 25-30 mV for HER at a geometrical current density of 10 mA cm-2 in an alkaline medium. A DFT theoretical investigation revealed that a Co-Mo center acts as the water-dissociation site enhancing the alkaline medium HER. / Chemistry