Oxidation, initiation/spreading, imaging

Equation (13) appears to be a good approximation for describing isothermal chemiluminescence kinetics for homogeneous systems where oxidation takes place uniformly. However, as has been shown by several authors [53-58], the different sections of a polymer sample may oxidize with its autonomous kinetics determined by different rates of primary initiation. A chemiluminescence imaging technique revealed that the light emission may be spread from some sites of the polymer film and the isothermal chemiluminescence vs. time runs are then modified, particularly in the stage of an advanced oxidation reaction [59]. 

To help understand the process of nanotube formation, FESEM images of the surface of the samples anodized at 20 V for different durations were taken and analyzed. At the start the anodization the initial oxide layer [111], formed due to interaction of the surface Ti ions with oxygen ions (0 ) in the electrolyte, can be seen uniformly spread across the surface. The overall reactions for anodic oxidation of titanium can be represented as... 

Abstract The oxidation of polymers such as polypropylene and polyethylene is accompanied by weak chemiluminescence. The development of sensitive photon counting systems has made it comparatively easy to measure faint light emissions and polymer chemiluminescence has become an important method to follow the initial stages in the oxidative degradation of polymers. Alternatively, chemiluminescence is used to determine the amount of hydroperoxides accumulated in a pre-oxidised polymer. Chemiluminescence has also been applied to study how irradiation or mechanical stress affects the rate of polymer oxidation. In recent years, imaging chemiluminescence has been established as a most valuable technique offering both spatial and temporal resolution of oxidation in polymers. This technique has disclosed that oxidation in polyolefins is non-uniformly distributed and proceeds by spreading. 

Fig. 6 [79]. Metals such as copper are known to decompose hydroperoxides and thereby initiate oxidation [143]. The location of the copper wire is clearly seen at the centre of the PP film. The copper wire was placed in direct contact with the PP film surface. The images in Fig. 11 show the initiation and spreading of oxidation from the location where the PP film is in contact with the copper wire to the rest of the film the experiments were run at 150 °C in air. The initiation by copper was not caused by an increase in heat transfer since initiation with aluminium, which is not able to decompose hydroperoxides, failed.

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