Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 99-102).

Thesis (M.S.)--University of Wisconsin--Madison, 1970. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / eContent provider-neutral record in process. Description based on print version record. Bibliography: l. 67-72.

Thesis--University of Washington. / Vita. Another copy has number: Thesis 27816. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1970. / Title from title screen (viewed July 30, 2007). Includes bibliographical references. Online version of the print original.

The use of magnesium hydroxide (Mg(OH)2) as a flame retardant and smoke-suppressor in polymeric materials has been of great interest recently. Because it contains no halogens or heavy metals, it is more environmentally friendly than the flame retardants based on antimony metals or halogenated compounds. Mg(OH)2 can be produced by the hydration of magnesium oxide (MgO), which is usually produced industrially from the calcination of the mineral magnesite (MgCO3). The thermal treatment of the calcination process dramatically affects the reactivity of the MgO formed. Reactivity of MgO refers to the extent and the rate of hydration thereof to Mg(OH)2. The aim of this study was to investigate the effect of calcination time and temperature on the reactivity of MgO, by studying the extent of its hydration to Mg(OH)2, using water and magnesium acetate as hydrating agents. A thermogravimetric analysis (TGA) method was used to determine the degree of hydration of MgO to Mg(OH)2. The reactivity of MgO was determined by BET (Brunauer, Emmett and Teller) surface area analysis and a citric acid reactivity method. Other techniques used included XRD, XRF and particle size analysis by milling and sieving. The product obtained from the hydration of MgO in magnesium acetate solutions contains mainly Mg(OH)2, but also some unreacted magnesium acetate. Magnesium acetate decomposition reaction takes place in the same temperature range as magnesium hydroxide, which complicates the quantitative TG analysis of the hydrated samples. As a result, a thermogravimetric method was developed to quantitatively determine the amounts of Mg(OH)2 and Mg(CH3COO)2 in a mixture thereof. The extent to which different experimental parameters (concentration of magnesium acetate, solid to liquid ratio and hydration time) influence the degree of hydration of MgO were evaluated using magnesium acetate as a hydrating agent. Magnesium acetate was found to enhance the degree of MgO hydration when compared to water. By increasing the hydration time, an increase in the percentage of Mg(OH)2 formed was observed. In order to study the effect of calcining time and temperature on the hydration of the MgO, the MgO samples were then calcined at different time periods and at different temperatures. The results have shown that the calcination temperature is the main variable affecting the surface area and reactivity of MgO. Lastly, an attempt was made to investigate the time for maximum hydration of MgO calcined at 650, 1000 and 1200oC. From the amounts of Mg(OH)2 obtained in magnesium acetate, it seems that the same maximum degree of hydration is obtained after different hydration times. A levelling effect that was independent of the calcination temperature of MgO was obtained for the hydrations performed in magnesium acetate. Although there was an increase in the percentage of Mg(OH)2 obtained from hydration of MgO in water, the levelling effect observed in magnesium acetate was not observed in water as a hydrating agent, and it seemed that the extent of MgO hydration in water was still increasing. The results obtained in this study demonstrate that the calcination temperature can affect the reactivity of MgO considerably, and that by increasing the hydration time, the degree of hydration of MgO to Mg(OH)2 is enhanced dramatically. / Chemistry / M. Sc. (Chemistry)

Substituted zinc and magnesium phthalocyanine and porphyrazine derivatives were synthesized according to the reported procedures. The magnesium and zinc phthalocyanine and porphyrazine derivatives were synthesized by ring enlargement of subphthalocyanine and statistical condensation of the two phthalonitrile derivatives. Characterization of the complexes involved the use of infrared spectroscopy, nuclear magnetic resonance spectroscopy, ultraviolet and visible spectroscopy, and Maldi-TOF spectroscopy (for selected compounds) and elemental analysis. Photochemical and photophysical properties of the complexes in non-aqueous solution was then investigated. Photobleaching quantum yields are in order of 10⁻⁵ indicating their relative photostability. Complexes containing more electron-donating substituents were more easily oxidized. For complexes 66 and 69 (as these complexes have the same number of substituents but differ in the metal center) photobleaching quantum yield for the ZincPc complex 69 was slightly less than that of the MgPc complex 66. Singlet oxygen quantum yields of the various complexes in DMSO using diphenylisobenzofuran (DPBF) as a quencher in organic solvents were determined. Singlet oxygen quantum yields of the complexes range from 0.23 to 0.67. High values of Φ[subscript]Δ ZnPc complexes was observed compared to the corresponding MgPc, complexes. This was evidenced by complexes 66 and 69 with Φ[subscript]Δ values of Φ[subscript]Δ = 0.26 and 0.40, respectively. Varying number of phenoxy substituents, complex 71 gave significantly large value of Φ[subscript]Δ compared to 70 (that is, the presence of more electron-donating substituted group, gave higher singlet oxygen quantum yields (0 .67 and 0.25 for 71 and 70 repectively). The triplet quantum yields and triplet lifetimes were determined by laser flash photolysis for selected compounds. The triplet quantum yields increase as the number of substituents increases e.g 68 > 67 > 66. Comparing porphyrazine complexes (63, 64 and 65), 63 with benzene attached to the ring, has higher triplet state lifetime (420 μs) compared to 64 and 65 containing long alkyl chain and tertbutyl substituents, 350 and 360 μs,respectively). The observed Φ[subscript]f values for 68 and 63 were quiet suprising, since low values are observed compared to the rest of the complexes (e.g 0.03 and 0.02 respectively). Although these values seem so low, they are sufficient for fluorescence imaging applications. The Φ[subscript]f values for the complexes under study are within the range reported for complexes currently used for PDT. / KMBT_363 / Adobe Acrobat 9.54 Paper Capture Plug-in

The effect of aluminium additions on the structure and morphology of the corrosion products formed on the surfaces of rapidly solidified Mg-Al alloy splats immersed at room temperature in a solution of 3%NaCl saturated with Mg(OH)2; has been studied under different analytical techniques. The adverse effect of contamination from copper particles during processing on the corrosion behaviour of the alloys is also highlighted. Aluminium additions were beneficial to the corrosive behaviour of the alloys with a marked improvement in their anti-corrosion resistance occurring in alloys containing more than 10 wt.% Al. This is attributed to the presence of aluminium ions in the prior oxide/hydroxide in the surface of the alloy. The thickness of the latter decreased with enrichment of aluminium ions and was 10-50nm for the Mg-16Al alloy splats as compared with 200nm for the Mg-3.5Al alloy splats. Hydromagnesite (3MgCO3. Mg(OH)2. 3H2O) formed as an overlayer on the surface of the alloy splats depending on the handling conditions. For the Mg-10Al and Mg-16Al alloy splats an admixture of a high temperature spinel (MgA12O4) in perlclase (MgO) and/or brucite (Mg(OH)2) was detected by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It Is proposed that in the corrosive environment the Al3+ ions on the surface compete successfully with the chlorine ions for the anodic sites on the surface and anchor the growth of the layered brucite structure by the formation of a compound belonging to the pyroaurite-sjogrenite group of compounds. Hydroxyl ions, water, chlorine ions and carbonate ions are incorporated in The interlayers of the layered brucite structure. The formation of a double hydroxide with an acicular morphology and a structure close to that of hydrotalcite-manasseite (Mg6A12(OH)16. CO3. 4H2O) has been supported by scanning transmission electron microscopy (STEM), XPS, XRD, multi-element mapping by electron probe microanalysis (EPMA) and Rutherford backscattering spectrometry (RBS) analyses on the corroded splats. A growth mechanism is proposed on the basis of the structural chemistry, surface morphology and crystal structure of the corrosion products. The implications of this work for the design of Mg base alloys with improved corrosion properties are also discussed. The selected alloying elements are in excellent agreement with those selected from other studies on the development of corrosion resistant Mg alloys.

The use of magnesium as a bioresorbable implant material has been gaining large amounts of interest over the last five years. Mg alloys by nature corrode rapidly comparative to other engineering metals, Mg is also naturally found in the body, meaning it offers a potential degradable material which can support far higher stresses than the current biodegradable polymers. Magnesium Elektron wanted to gain an understanding of how Mg alloys would work in this new environment and find a potential alloy fit for purpose. This thesis outlines the progress the author and Magnesium Elektron have made in achieving those goals. Initally, to form an understanding of what occurs when Mg is implanted into the body. Osteoblast trials were used to determine in vitro responses and effects on the various Mg alloys. These studies showed that high corrosion rates initially seen when Mg alloys are placed in cell culture medium have a lower cell numbers. Most likely due to local pH rise. The effect is inherent to all Mg alloys irrespective of their overall corrosion rate. However, after the initial corrosion spike, surviving cells on the surface would proliferate and attach well. The attached cells on Mg also showed a phenotype expression change compared to those on glass. It was then established that lowering the corrosion rate of the current Mg alloys was now key. Initially this involved modifications to current alloys. Annealing ML4 at 350°C for 8 hours was found optimal and lowered corrosion rates by 20-30%. Further work looked at modifing alloys by changes to chemical composition. It was discoveredd that additions of 8wt% Er to ML4 made corrosion rates drop by 6-8 times in SBF. Additions of Gd in ML4 also gave low corrosion, 2 times less than ML4. Calcium also lowered corrosion rates slightly. The modifications to the Mg surface was also looked into to lower the initial corrosion rate and potentially alter the biocompatibility of the alloys. Two successful techniques were found. Firstly organo-silanes were found to protect Mg for around 4 days, with reductions in corrosion rate of 6 times in the first hours. Silanes were also successfully used as anchors to graft polythene gycol to create a non fouling surface, which could protentially lower stent restenosis. Secondly, Magnetron sputtered hydroxyapatite was used to lower corrosion rates by 6 times in the first 24 hours with no visible hydrogen gas being evolved in the first hours.

Development of sustainable manufacturing and conservation of primary materials are the key challenges to environmental degradation and climate change. Recycling of primary materials is one of the approaches suggested for sustainable green manufacturing. In the present study, an attempt has been made to encompass both these concepts, i.e. recycling of waste machined chips of magnesium and development of sustainable manufacturing process. Chips generated during machining operations are of significant importance; they dissipate the heat from the work-piece and control the quality of the finished products. In recent years researchers have shown that by controlled machining it is possible to tailor size, shape and microstructure of chips and this has added new dimensions to the utility of these machined chips. Chips in the form of thin strips, rods, very fine powders with varying aspect ratio have been successfully machined with grain structure having nano size (~80nm) to submicron size. Consolidation of such machined chips and subsequent fabrication of products is of great interest from the point of view of sustainable manufacturing. Consolidation of machined chips by cold compaction followed by hot extrusion was proposed and has been termed as solid state recycling (SSR). This alternative method of manufacturing using machined chips circumvents melting and casting. Although several materials have been tried by this route, magnesium appears to be the most investigated material. Being lightest among the structural materials, magnesium and its alloys have wide ranging applications especially in automotive industry. Further, magnesium melting is cumbersome and environmentally hazardous which necessitates researchers to explore methods of overcoming the melting route. In this pursuit, SSR appears to be a choice for a soft material like magnesium whose products are fabricated by conventional processing techniques which include cold compaction followed by hot extrusion. Most of the work in literature with regard to SSR of magnesium has been centered around development of new alloys and their characterisation at room and elevated temperatures. Effect of oxide contaminants has also been widely studied. However, studies on microstructural evolution during processing (i.e. microstructure prior to and after extrusion) have not been reported. Further, such studies with pure metal is important since it is possible to separate the effect of secondary phases including precipitates which are otherwise present in alloys of Mg. Hence, commercial grade pure magnesium is the material of interest in the present work. Process of consolidation includes room temperature compaction followed by hot extrusion. The aim of the present work includes: Consolidation of machined chips of magnesium into billets by cold compaction at room temperature followed by hot extrusion, Microstructural characterisation of these cold compacted billets prior to and after extrusion, Evaluation of mechanical properties after extrusion at different temperatures. Correlating the mechanical properties with microstructure. In the present study mechanical properties evaluated include: strength properties (hardness, tensile and compressive properties), and damping properties As-cast billet of pure magnesium was turned in a lathe to produce chips at ambient conditions. The chips were cold compacted into billets of 28 mm diameter at a pressure of 350 MPa and held for 30 minutes. The billets of compacted chips (referred here as CC) were later extruded at four different temperatures, viz. 250, 300, 350 and 400°C, with an extrusion ratio of 49:1. Prior to extrusion, the CC was soaked at the desired extrusion temperature for 1 hour. Here, extrusions of compacted chips are designated as CCE (chip compacted and extruded). For comparison, the as-cast billet was extruded under similar conditions and is designated as AE (as-cast and extruded). The extruded rods had a diameter of 4 mm. Microstructural characterisation was done prior to and after extrusion, which forms the first part of the thesis. The extruded rods were characterised for their room temperature strength properties in the second part of the thesis. In the third and last part, damping properties were characterised as a function of time and temperature. Microstructural changes at the end of temperature sweep tests were also examined. Optical microscopy did not reveal the grain structure of CC due to the intense strains associated with chip formation and subsequent cold compaction. However, chip boundaries were found randomly oriented and tri-junctions were found to be porous. The CC showed a relative density of 95.4% and this happens to be the highest amongst the values reported in literature for SSR machined chips. TEM images of CC revealed an average grain size of 0.75µm. Synopsis CCs were soaked at extrusion temperature and quenched to unravel the microstructure that exists prior to extrusion. Grain size and hardness measurements indicate that the material was recrystallised prior to extrusion. Bulk texture estimated from X-ray diffraction, showed weak crystallographic textures. The CC had a typical texture with c-axis aligned along the compaction direction which subsequently got randomised during soaking (pre-heating at extrusion temperature). After extrusion, the 250°C extruded AE had slightly stronger texture than CCE: with clear preference for < 1010 > and < 1120 > plane normals. High working temperatures removed such preference and made the textures randomised for both AE and CCE. In-grain misorientations and the relative presence of the twins, estimated from EBSD scans show a clear pattern for higher in-grain misorientations in CCE compared to AE. The values for AE at higher extrusion temperatures approached that of fully recrystallised magnesium. Higher twin fraction in AE was attributed to its relatively larger grain size compared to CCE. The chip boundaries that were randomly oriented before extrusion appeared aligned along the extrusion direction after extrusion. On the contrary AE had an equiaxed structure. Both longitudinal and transverse section micrographs showed pronounced chip boundaries in the 250°C extruded CCE while it was no so pronounced in the case of 400°C extruded material. Density measurements showed 98.6% relative density for 250°C extruded CCE as compared to 99.9% densification achieved in 400°C extruded CCE. Dislocation density estimated using Variance method from the peaks of the X-ray diffraction data showed higher values for CCE compared to AE. Dislocation density reduced with increase in extrusion temperature. For comparison extruded rods were annealed at 250°C for 2 hours and their dislocation density was estimated. Vickers hardness indentations were done at low load (25g) and higher load (200g). Both showed decreasing values with increase in extrusion temperature. Grain size dependent hardness variation followed the Hall-Petch relationship. CCE showed higher hardness compared to AE. Room temperature tensile test showed higher 0.2% tensile proof stress (TPS) in CCE material and obeyed the grain size dependent Hall-Petch relationship, though the strain to failure was poor. CCE extruded at 250°C showed fibrous fracture surface and was different from the rest of the CCEs with evidence of shearing at chip boundaries before fracture. Synopsis The rest of the CCEs had a typical fracture surface which was similar to AE material. Strain hardening behaviour, measured in terms of hardening exponent (n), hardening capacity (Hc) and hardening rate (θ) was quiet different for CCE compared to AE. Room temperature compression test showed different kind of failure for 250°C extruded CCE with longitudinal splitting (de-bonding at chip boundaries) and shearing at an angle to loading direction. The rest of the CCEs failed in a typical manner similar to AE material. The 0.2% compressive proof stress (CPS) as a function of grain size obeyed the Hall-Petch relationship for AE while the fit was not so good for CCE. Moreover, except 400°C extruded CCE (CPS was higher by ~22%) the rest of the CCEs had lower CPS compared to AE despite having finer grain size. This was contrary to the TPS and hardness findings wherein CCE was consistently higher compared to AE owing to grain refinement. Density measurements showed presence of 1.4%, 0.8% and 0.5% porosity in 250°, 300° and 350°C extruded CCE samples respectively. Prompted by density, hardness and TPS findings, the CPS values were back-calculated using the Hall-Petch relationship of AE. The back-calculated CPS values of CCE were higher than corresponding AE. Strength asymmetry, measured as a ratio of compressive proof stress to tensile proof stress was higher in CCE compared to AE. Damping capacity (tanφ) and dynamic modulus were determined as a function of time (tested upto 30 minutes) and temperature (from RT to 300°C) at a constant frequency (5 Hz). CCE material displayed higher tanφ during time and temperature sweep tests (by 10-15%) with CCE extruded at 250° showing the highest values. Dynamic modulus was comparable for both the materials (with less than 5% difference) though, modulus was higher in materials extruded at higher temperature. Microstructural changes were examined at the end of temperature sweep test, both at the point of loading and away from the point of loading. A significant grain growth was observed in region under the loading point (in a 3-point bending set-up) and was insignificant at regions away from the loading point. Coarsening was low in CCE material on account of suppression at chip boundaries. Microstructure of CCE and AE specimens subjected to similar heating conditions but without loading showed no such coarsening.