Comparative study about the thermal stability and UV resistance of some paint layers for electro-energetic equipment
In order to determine the durability of polymer coatings using investigation techniques based on X-rays diffraction and combined techniques for thermal analysis (TG-DTA-DTG), were determined the changes of structure and of their thermo-oxidative characteristics (6 different paint types having different characteristics) after exposure to UV radiation (60W/m2 in range of 300-400nm). The experimental results, indicate that UV radiation induce different changes (function of the commercial type of any paint) of the investigated topcoat paint films respectively, increase of the crystallinity (and, implicit, of the fragility) function of the exposure dose, which was between 0,0005 and 0,0150%/Wh/m2.
Ageing behavior of acrylic polyurethane varnish coating in artificial weathering environments
Acrylic polyurethane varnish coatings were exposed in two artificial weathering environments produced by a fluorescent UV/condensation weathering device and a xenon lamp exposure and weathering equipment for different time periods. The ageing behavior of the coating was evaluated by using film thickness gauge, glossmeter, spectrophotometer, scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS). The results showed that the Xenotest protocol had a significant effect on the thickness loss and gloss. However, the yellow index measurements and low frequency impedance showed that greater degradation was caused by the UV exposure protocol. These findings were supported by the results obtained from FTIR analysis. In the two artificial weathering environments, the low frequency impedance modulus of intact coatings decreased exponentially with increase of ageing time, and correlated with the changes of other properties of ageing coatings, which can be used to predict coatings lifetime.
La inseguridad jurídica en normas de contratación estatal
It is established by different studies that the issue of government procurement has been marred by several factors, the test objective to publicize these factors, we take as starting point the constant conflict between the branches of government to try and organize this subject; will collect and analyze diverse regulatory and case material in order to achieve evidence and demonstrate the different concepts of constant change that produces excessive regulation of the subject procurement and is in turn causing rapid changes that result in legal uncertainty for our law on the Contract Status.