Browsing by Subject "Magnesium"

Now showing 1 - 3 of 3
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    Bentonite Quality - The Effect Of Water Chemistry And Antifreeze Agents On Bentonite Binding Characteristics
    (University of Minnesota Duluth, 2000-10-17) Engesser, John
    The primary objective of the project was to determine what test or tests best predict pre-fired pellet binding characteristics of bentonite clay. A secondary objective was to determine which antifreeze chemicals have detrimental affects on pre-fired pellet quality and which antifreeze chemicals have no affect and/or positive affects on pre-fired pellet quality.
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    Magnesium based materials and their antimicrobial activity
    (2011-09) Robinson, Duane Allan
    The overall goals of this body of work were to characterize the antimicrobial properties of magnesium (Mg) metal and nano-magnesium oxide (nMgO) in vitro, to evaluate the in vitro cytotoxicity of Mg metal, and to incorporate MgO nanoparticles into a polymeric implant coating and evaluate its in vitro antimicrobial properties. In the course of this work it was found that Mg metal, Mg-mesh, and nMgO have in vitro antimicrobial properties that are similar to a bactericidal antibiotic. For Mg metal, the mechanism of this activity appears to be related to an increase in pH (i.e. a more alkaline environment) and not an increase in Mg2+. Given that Mg-mesh is a Mg metal powder, the assumption is that it has the same mechanism of activity as Mg metal. The mechanism of activity for nMgO remains to be elucidated and may be related to a combination of interaction of the nanoparticles with the bacteria and the alkaline pH. It was further demonstrated that supernatants from suspensions of Mg-mesh and nMgO had the same antimicrobial effect as was noted when the particles were used. The supernatant from Mg-mesh and nMgO was also noted to prevent biofilm formation for two Staphylococcus strains. Finally, poly-ε-caprolactone (PCL) composites of Mg-mesh (PCL+Mg-mesh) and nMgO (PCL+nMgO) were produced. Coatings applied to screws inhibited growth of Escherichia coli and Pseudomonas aeruginosa and in thin disc format inhibited the growth of Staphylococcus aureus in addition to the E. coli and P. aeruginosa. Pure Mg metal was noted to have some cytotoxic effect on murine fibroblast and osteoblast cell lines, although this effect needs to be characterized further. To address the need for an in vivo model for evaluating implant associated infections, a new closed fracture osteomyelitis model in the femur of the rat was developed. Magnesium, a readily available and inexpensive metal was shown to have antimicrobial properties that appear to be related to its corrosion products and that nMgO has similar effects. Incorporation of nMgO into a PCL composite was easily achieved and revealed similar, although not identical antimicrobial results. This work has provided a strong foundation and methodology for further evaluation of Mg based materials and their antimicrobial properties.
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    Superconductivity and Magnetism in Strontium Titanate Thin Films and Heterostructures
    (2020-06) Ayino, Yilikal
    In this thesis we present our investigation of magnetism and superconductivity in SrTiO3 thin films and heterostructures in the polar/non-polar interface of NdTiO3/SrTiO3, using milli-Kelvin transport measurements. In Chapter 2 we describe our experimental method, including our low temperature transport measurement setup. In Chapter 3 we present our investigation of the magnetic properties of NdTiO3/SrTiO3 using milli-Kelvin temperature magnetotransport measurements. We observe large negative magnetoresistance (in excess of -90%) and robust hysteresis. We interpret our data in the context of spin-dependent transport and argue for the presence of ferromagnetic ordering in this anti-ferromagnetic/ paramagnetic interface. In addition, using time dependent magnetoresistance measurement we observe butterfly-shaped transit hysteretic features near zero-magnetic field. Such butterfly-shaped hysteretic features are previously interpreted as evidence for interfacial magnetism. We argue that these transient hysteretic signals are consistent with magnetocaloric effects arising from magnetic materials extrinsic to the sample. In Chapter 4 we discuss our investigation of effects of paramagnetic pair breaking and spin-orbital coupling on multi-band superconductivity. Using low temperature critical field measurements, we observe robust evidence for multi-band superconductivity from the unconventional dependence of critical field on temperature. We observe a pronounced positive curvature of the critical field curve as function temperature. Furthermore, we observe that the out-of-plane critical field exceeds the Pauli limit, while typically the out-of-plane critical field saturates about an order of magnitude smaller than the Pauli limit. We interpret this as due to the enhancement of the critical field due to multi-band superconductivity, as has been theoretically predicted. Furthermore, we propose an original model for critical field for multi-band superconductors, which includes orbital pair breaking, paramagnetic pair breaking and spin-orbital coupling. We find excellent agreement of this model with our data and that this model has wide reaching applications to any multi-band superconductors in the dirty limit, in which all these effects are present. Chapter 5 focuses on the comparison of effects of magnetic impurity scattering and non-magnetic impurity scattering in the context of multi-band superconductors. We did extensive measurements of magnetically doped (Nd-doped STO) and non-magnetically doped (La-doped STO) samples. We measured samples with carrier densities spanning about an order magnitude, for both sets of samples. We find that for magnetically doped samples the superconducting dome (critical temperature as a function of carrier density) is shifted to lower densities. As a result, at lower densities we observe that the critical temperatures of magnetically doped samples are higher than those of non-magnetically doped samples, while at higher densities it is the opposite. Analysis of out-of-plane critical field measurements reveals the multi-band nature of superconductivity in both sets of samples. In–plane critical field data reveal the importance of spin-orbital coupling in Nd doped samples. We argue that the reason why, at lower densities, Nd doped samples have higher critical temperature despite being magnetically doped is the suppression of magnetic scattering by spin-orbital coupling. Furthermore, we studied several very high mobility samples at extremely low densities (<1018 cm-3) and we did not observe superconductivity down to less than 30mK, contrary to observations reported in literature on oxygen vacancy doped samples.