Zugl.: Aachen, Techn. Hochsch., Diss., 2003.

Zugl.: Stuttgart, Univ., Diss., 2004. / Dateien im PDF-Format

The particle growth characteristics of active MgO in the size range 70-400 Å have been studied by the x-ray line broadening technique. The starting material was a synthetic magnesium hydroxide, which was decomposed and then heat treated under isothermal conditions in the temperature range 400-900° C in vacuum and in H₂O vapor. The particle growth rate was very much higher in vapor than that in vacuum. The results were analysed by the conventional grain growth equation, Dn=Kt and newly developed models. In these models, surface diffusion, bulk diffusion and evaporation-condensation have been considered for mass transport mechanisms. The activation energy for the particle growth process of MgO in H₂O vapor was calculated to be about 31 Kcal/mole. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Solid solution strengthening in magnesium polycrystals containing Zn, Al, Cd, In and Pb as solute has been investigated over the temperatures between 78° and 513°K with particular emphasis on the dilute alloys. The variation of yield stress with concentration occurs in either two or three stages. In stage I, the yield stress increases rapidly and linearly with concentration; in stage II, the rate of increase of yield stress is very much less than in stage I; in stage III, the yield stress decreases with solute additions. The solution hardening rates and the transition concentrations from stage I to stage II (C[subscript T]) depend on the size-difference between Mg and the solutes. The results are discussed in terms of the variation with concentration of the CRSS for both basal and prismatic slip. It is proposed that at concentrations less than C[subscript T], the increase in CRSS for prismatic slip is the dominant factor; beyond C[subscript T], yield is governed by a balance between basal hardening and prismatic softening. The effect of solute on the ductility of magnesium at elevated temperatures is discussed in terms of a stress induced polygonization process and the ductility maxima observed in the Mg-Al alloys are explained. Single crystals of Mg-Zn alloys oriented for basal slip have been deformed in tension over the temperature range from 78°K to 423°K. The variation of the basal dislocation density caused by the addition of solute has been studied using transmission electron microscopy of thin foils. The increase in dislocation density which was found to be proportional to the square root of the solute concentration, cannot account for the observed increase in the athermal stress. A dislocation etch pit technique has been developed and used to measure the variation in the forest dislocation density with solute concentration. The forest density increases linearly and rapidly up to a certain minimum solute concentration, beyond which it remains almost constant. The results are in good agreement with the observed thermally activated flow stress for low solute concentrations. The observed variation in the athermal component of CRSS has been discussed in the light of an increased friction stress arising due to a random distribution of solute. Using rate theory, it has been shown that the forest intersection remains the rate controlling mechanism up to a certain low concentration of solute beyond which the single solute atom pinning of dislocations becomes the rate determining process. The solute dependence of the work hardening parameters are also reported and examined in the light of the existing theories of work hardening. Single crystals of Mg - Zn and Mg- Al alloys have also been deformed so as to suppress basal slip and {1012} twinning and to induce prismatic slip. The results have been explained in terms of an increasing athermal stress and a decreasing Peierls stress with the addition of solute. Peierls stress has been shown to be the rate controlling mechanism below room temperature. The observed variation of CRSS for prism slip with solute concentration accounts adequately for the concentration dependence of yield stress in the polycrystalline aggregate. The results also suggest that the decrease in Peierls stress with solute addition is not necessarily associated with a decreasing c/a ratio and the monovalent nature of the solute. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

The effect of Li additions to Mg on the texture and mechanical properties in both the hot and cold rolled condition has been examined. It was found that using the texture goniometer (Schulz technique) only the surface texture is obtained. As a result average textures were prepared for each alloy. Lithium additions to Mg causes a loss in sharpness of the (0001) texture. No indication of a <1120> directional texture was found. The change in texture was explained successfully on the basis of deformation systems active during rolling. Cold rolling of the alloys caused a loss in sharpness of the (0001) texture for low Li alloys. In the high Li alloys (6 at. % and 12.4 at. %) a pronounced split occurred. A definite <1120> directional texture was observed on the surface of the cold-rolled low Li alloys but this disappeared in the "average" pole figure. Again the change in texture was explained on the basis of deformation systems active during rolling. Tensile tests of hot-rolled Mg-Li alloys agreed completely with those of Yoshinaga & Horiuchi (9) but showed some variance with those of Hauser, Landon, and Dorn (8). Tensile tests of cold-rolled Mg-Li alloys showed appreciable strain hardening and a loss of ductility due to the cold work. The higher the Li content the higher the rate of strain hardening observed for large increments of strain. The ratio of the transverse to longitudinal tensile properties decreased with increasing Li content. A qualitative explanation of the above was made on the basis of active deformation systems. Limited success was obtained in attempts to correlate mechanical properties and texture in low Li alloys. No attempt was made for high Li alloys. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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Magnesium hydroxide, a stable flame retardant, can be obtained by mining or by the hydration of magnesium oxide. In this study, the effect of different hydrating agents on the pH of the hydrating solution, rate of hydration of MgO to Mg(OH)2 and product surface area were studied as a function of the temperature of hydration. Ammonium chloride, magnesium acetate, magnesium nitrate, nitric acid, acetic acid, water, magnesium chloride, sodium acetate and hydrochloric acid were used as hydrating agents. The hydration experiments were carried out in a water bath between 30 - 80 oC for 30 minutes. Dried MgO samples were introduced to the hydrating solution and the slurry was stirred at a constant speed. At the end of each experiment, the slurry was vacuum filtered, washed with water, dried at 200 oC and hand ground. The products were then characterized by TGA, XRF, XRD and BET surface area analyses. There was not a significant difference in the hydration behaviour of the hydrating agents up to 50 oC, where less than 10 % of magnesium hydroxide was formed. When compared to the hydration in water, all the hydrating agents with the exception of sodium acetate showed a significant increase in the degree of hydration. Sodium acetate formed the lowest amount of magnesium hydroxide, ranging between 1.2 and 12.2 % magnesium hydroxide. Hydrations performed in hydrochloric acid and magnesium nitrate formed the largest percentage (11.8 %) of magnesium hydroxide at 60 oC. Magnesium acetate, magnesium nitrate, magnesium chloride and hydrochloric acid seemed to be the most effective hydrating agents at 70 oC with the percentage magnesium hydroxide being formed ranging between 20.0 and 23.9 %. The amount of hydroxide formed doubled at 80 oC, with the largest percentage (56.7 %) formed from the hydration in magnesium acetate. The hydration reaction seemed to be dependent upon the presence of Mg2+ and acetate ions. It seemed that magnesium oxide hydration is a dissolution-precipitation process controlled by the dissolution of magnesium oxide. The results have also indicated that the pH and temperature of the hydrating solution strongly influence the degree of hydration. / Chemistry / M.Sc. (Chemistry)

The study was initiated to examine magnesium intake, supplementation and their relation to inflammation. Magnesium is the second most abundant extracellular ion following potassium. Outside the cell, magnesium can be found in bone tissue, cardiac muscle tissue, other tissues and in the blood. Magnesium form compounds which operate in several essential metabolic processes in the body. Magnesium deficiency may have an impact on insulin resistance and endothelial dysfunction, which may result in an increased level of inflammation. Increased inflammation over a longer period has been seen to increase the risk of common lifestyle induced diseases such as diabetes type II and coronary heart diseases. The study of magnesium and its influence on inflammation is thereby becoming important and interesting for all societies and in their effort to find solutions to maintain and increase the well-being of its individuals. The study is a literature study based on searches made in One Search and Pub Med databases. A total of ten studies were included, five for magnesium intake and five for supplementation. The majority of the studies showed a significant correlation between increased magnesium intake, dietary and supplementary, with decreased levels of inflammatory biomarkers and hints that magnesium might have a role in the inflammation process. What needs to be taken into account is that fiber intake in two studies attenuated magnesium’s inverse relation to inflammation. In addition of a decrease in inflammatory biomarker levels the risk for developing diabetes type II seemed to decrease as well with an increased intake of magnesium in one of the studies. Further studies need to be executed in order to establish the role of magnesium in inflammation and optimal dosage for prevention of metabolic and cardiovascular diseases. / Studien undersöker magnesiumintag och supplementering med magnesium samt dess inverkan på inflammation. Magnesium är den vanligast förekommande jonen intracellulärt efter kalium.  Extracellulärt magnesium förekommer i benvävnad, hjärtmuskelvävnad och i blodet. Magnesium bildar ämnen som medverkar i flera viktiga metabola processer i kroppen. Magnesiumbrist kan ha en inverkan på insulin resistans och endotel dysfunktion som följaktligen skulle kunna resultera i en ökad nivå av inflammation. Ökad inflammation under en längre tid har visat sig öka risken för vanliga livsstilssjukdomar som diabetes typ II och hjärt- och kärlsjukdomar. Forskning om magnesium och dess effekt på inflammation blir därmed viktig och intressant för samhällen i deras strävan att hitta lösningar till att bibehålla och öka välmåendet hos populationen. Studien är en litteraturstudie och är grundad på sökningar via databaserna One Search och Pub Med. Totalt tio studier inkluderades i arbetet, fem som undersökte magnesiumintag och inflammation samt fem som undersökte supplementering av magnesium och inflammation. Majoriteten av studierna visade på en signifikant korrelation mellan ett ökat magnesiumintag, via kosten och kosttillskott, och minskade nivåer av biomarkörer för inflammation. Det antyder att magnesium kan ha en roll i inflammationsprocessen. I de två studier som mätte fiberintaget var relationen mellan magnesiumintag och inflammation försvagad. Utöver en minskning av biomarkörer för inflammation sågs en minskad risk för att utveckla diabetes typ II vid ett ökat magnesiumintag i en av studierna. Fler studier krävs för att fastställa magnesiums betydelse vid inflammation samt den optimala doseringen för prevention av metabola och kardiovaskulära sjukdomar.