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

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)

Thesis (Ph. D.)--Northeastern University, 2008. / Title from title page (viewed May 19, 2009) Graduate School of Engineering, Dept. of Chemical Engineering. Includes bibliographical references p. 271-281).

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 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)

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Thesis (Ph.D.)--University of California, Berkeley, 1961. / "UC-4 Chemistry" -t.p. "TID-4500 (16th Ed.)" -t.p. Includes bibliographical references (p. 54-55).

Thesis (M.S. in Chemistry)--University of California, Berkeley, Jan. 1957. / Includes bibliographical references (leaves 19-20).

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