الفهرس 
CHAPTER ONE : INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Most of the metallic structures and metallic equipment’s in different engineering industries especially in chemical industries are corroded by the action of environmental conditions like atmospheric air and the emission of gases and acidic liquids ... etc. this result in a big losses of these components and so increasing the expenses for their protection.
Both of metallic and non metallic coatings are widely used to minimize these losses. Pack diffusion coating is one of the simplest methods which has variety in applications especially to the metallic parts that need special properties like highly resistance to both of chemical attack and wear deterioration when its exposed to different corrosive media whether at high or low temperatures.
The aims of this study are the evaluation of pack aluminizing of low carbon steel in different corrosive media, exposure to static air at high temperatures and to aqueous solutions at different temperatures also studying the process parameters affecting diffusion coatings, such as effect of coating time, coating temperature and the effect of pack compositions.
Tests are performed to measure the coating thickness and microhardness using optical microscope, also determining the oxidation rate at high temperatures using change in weight gain and measuring the wet corrosion behavior using potentiostat, moreover the microstructure and elements analysis is determined using scanning electron microscope (SEM) attached with EDS unit.
The obtained results are plotted in tables and figures and discussed, these results can be summarized as follow:
1-the kinetics of pack aluminizing of low carbon steel are parabolic in behavior and the rate constant is increased with increasing coating temperature.
2- the parabolic rate constants of pack aluminizing of low carbon steel were found to be, 0.2374, 0.2774 and 0.319 mm2/h. at coating temperatures 850, 900 and 950 °C respectively. The activation energy reaches to 33.9kJ/mol and the rate controlling step is solid diffusion.
3- the coating thickness (80-870pm) with surface composition reached to 74% Al, when the pack mixture contains 15% Al depending on coating time which in the range from 2-8h and coating temperature from 850 to 950 °C.
4- the microhardness reached to a maximum value of 943VHN at the topcoat of a specimen coated at 900 °C for 8h.
5- the kinetics of oxidation is parabolic in behavior and the inward oxygen diffusion is the rate-controlling step for the formation of a protective alumina layer on steel surface to protect it from further oxidation in comparison to the uncoated ones.
6- the microstructure examinations using SEM showed that the alumina scale well adherent to coating surface at 800 °C but at higher temperature both microcacks and microvoids were observed in the protective layer.
7- the corrosion rate of aluminized steel in aqueous solution is increased with increasing acid concentration from 1 N to 5N and solution temperatures from 25 °C to 70 °C.