Diffusion measurements on organic coatings with cantilever beam deflection method
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Organic coatings are used to protect steel bands from corrosion which is important i.e. in the building industry. To enhance the barrier properties of organic coatings to achieve better quality of the product improved knowledge about the influence of glass transition temperature Tg and water diffusion properties is necessary. A climatic chamber equipped with a cantilever beam deflection set-up has been developed and built which enables to control and regulate temperature and humidity simultaneously. As samples coated steel band cut into cantilever (4.5 mm x 0.5 mm) are used which are fixed in a special sample holder. Due to the different expansion coefficient of steel and the polymer coating used varying temperatures and humidity lead to characteristic bending of the cantilever due to internal stresses. The cantilever bending is monitored using an optical deflection sensor. From the resulting deflection curves characteristic values such as Tg, as well as the water diffusion constant can be determined. Besides, the way how water diffuses through the coating may explain details about its barrier properties. Therefore, in addition to the cantilever beam deflection measurements the passway of the water adsorbed from the gasous and liquid phase inside the coating is analysed with confocal Raman microcopy.