4,528 research outputs found

    Ultraclean Si/Si interface formation by surface preparation and direct bonding in ultrahigh vacuum

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    Silicon surfaces have been cleaned and bonded in ultra-high vacuum at a pressure in the 10-10 torr range. The bonded interfaces show extremely low contamination levels as measured by secondary ion mass spectroscopy. Nevertheless, a potential barrier could be detected at the interface spreading resistance and current vs. temperature measurements. This suggests that the barrier is caused by inevitable dislocation networks due to wafer misorientation, as well as residual oxygen at the interfac

    MS

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    thesisGiven high strength-to-weight and stiffness-to-weight ratios, sandwich composite materials are continually being considered for automotive applications. Thermoplastic materials, while difficult to bond, have an increased ease of manufacture and are recyclable making them even more attractive than thermoset composites. This investigation evaluates the adhesion of 13 adhesives with 8 surface treatments on both nylon and polypropylene thermoplastic adherends made from Towflex® preimpregnated fabric. A method of manufacture of these plates without contaminating the bonding surface while establishing an acceptable surface finish was developed. Adhesives and surface treatments were investigated and the candidates with the greatest likelihood of success without overlap were chosen. Initial testing was performed using the qualitative spot adhesion test (ASTM D3808) to identify the most likely adhesive and surface treatment parameter groups with each thermoplastic. From these results, 10 parameter groups were identified and tested quantitatively using the lap shear test (ASTM D 3163). Comparative bond strengths are calculated from the peak load and bonded area of each specimen. The results for the nylon were similar between the two tests, but the polypropylene was generally inconsistent. The results indicate that further testing to completely develop joining methods with nylon thermoplastic treated at least with an acid wash and bonded with Lord 320/322 could result in a method of adhesively joining thermoplastic sandwich composites

    NANOTEXTURED TITANIUM SURFACES FOR IMPLANTS: MANUFACTURING AND PACKAGING ASPECTS

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    It has been shown that nanotexturing the surface of otherwise smooth titanium orthopedic materials increases osteoblast proliferation in vitro, and the bone-implant contact area and pullout force in vivo. However, this prior work has not focused on the requirements for scale-up to industrial processes. This dissertation reports on titanium surface modifications by electrochemical anodization using a benign NH4F electrolyte, and a hybrid electrolyte also containing AgF, rather than hazardous hydrofluoric acid used elsewhere. Nanotube fabrication of Ti6Al4V foils, rods, thermal plasma sprayed commercial implants, and laser and e-beam melted powder materials was demonstrated. It was found that the nanotextured morphology depends on electrolyte composition, and dimensional variation depends on anodization conditions using different NH4F and ethylene glycol electrolytes. The fluorine concentration was found to be the most influential factor affecting formation of porous nanostructures. Recognizing the importance of packaged implant storage, the wetting behavior of nanotube surfaces was investigated. It was found that increased surface hydrophobicity due to aging in air can be restored by annealing, and the release of residual fluorine from the surface was measured. The kinetics of the amorphous to crystalline anatase transformation of nanotubes was quantified with isochronal and isothermal experiments by X-ray diffraction and transmission electron microscopy. The anatase phase transformation of TiO2 nanotubes was achieved in as little as 5 minutes at 350C, in contrast to reports of higher temperature and for hours. The fluorine consumed by the formation of the nanotubes during anodization was analyzed and sources of fluorine consumption were identified. Fluorine from the electrolyte is removed and retained in the nanotubes and by the metal removed to form the nanotubes. A metric describing the fluorine removed from the electrolyte per anodized area was developed to help quality control in manufacturing scale-up. A single-step anodization with controlled nanosilver deposition within and among the nanotubes, using a new hybrid electrolyte of NH4F and AgF was demonstrated. Successful fabrication of potentially antibacterial nanotubes on foils, rods and thermal plasma sprayed surfaces was demonstrated and nanosilver concentration was quantified. These new understandings led to improved manufacturing and storage technologies needed for regulatory approvals of nanotextured titanium surfaces for better orthopedic implants

    Master of Science

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    thesisGiven their high strength-to-weight and stiffness-to-weight ratios, sandwich composites continue to be considered for automotive applications. Thermoplastic materials, while difficult to bond, have an increased ease of manufacture and may be reprocessed, making them an attractive alternate to thermoset composites. This investigation focused on the evaluation of adhesives and surface treatments for both nylon and polypropylene thermoplastic composite adherends made from Towflex® pre-impregnated composite fabric. A manufacturing method was established for thermoplastic plates, which produced an acceptable surface finish without contaminating the bonding surface. Adhesives and surface treatments were evaluated using lap shear (ASTM D 3163) and cleavage (ASTM D 3433) test methods. The most promising adhesive/surface treatment combinations were selected for bonding of sandwich composites with two different core materials: balsa wood and polyurethane foam. Initial sandwich configuration testing consisted of flatwise tensile (ASTM C 297) and core shear (ASTM C 273) test methods. These tests provided insights into the sandwich properties and revealed any incompatibilities between the adhesive and the core. Follow on sandwich configuration evaluation consisted of edgewise compression testing, both statically (ASTM C 364) and dynamically. These tests determined the strength and ability of these sandwiches to absorb energy under two different types of loading
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