The fatigue crack propagation process in an Al-Mg-Si aluminum alloy was investigated using in situ high-resolution synchrotron radiation X-ray microtomography. Tomography datasets were obtained at periodic intervals throughout the 120000 fatigue cycles. 3D rendering of the through-thickness crack shape indicates that in a number of regions the adjacent sides of two branched cracks tend to overlap with fatigue cycling and form a crack overlapping region. Measured crack growth rates in each tomographic slice show that crack growth retardation generally occurs in these crack overlapping regions. The through-thickness variation in crack tip opening displacement was also measured and was used to account for the observed crack propagation behavior. Crack morphologies were observed at different load levels in a fatigue cycle. The crack closure level varied for two selected regions comprising different overlapping cracks. The correlation of the crack growth rate with both crack opening and closure levels was discussed and interpreted.

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The non-thermal plasma as one of the most promising technologies for removing NOx and SO2 has attracted much attention. In this study, a new plasma reactor combined with catalyst and additive was developed to effectively oxidize and remove NOx and SO2 in the flue gas. The experimental results showed that TiO2 could improve the oxidation efficiency of SO2 in the case of applying plasma while having a negative effect on the oxidation process of NO and NOx. With the addition of NH3, the oxidation rates of NOx, NO and SO2 were slightly increased. However, the effect of adding NH3 on NOx oxidation was negative when the temperature was above 200 o C.

To find out a new dry-type desulfurization process with high efficiency and cost performance, a hybrid-type reaction process combining pulsed streamer corona plasma and TiO2 catalyst was developed in order to oxidize SO2 to SO3. Experiments of both gas-phase reaction and surface reaction were performed to elucidate oxidation characteristics. Experimental results show that the oxidation fraction of SO2 to SO3 in the gas-phase reaction is below 5% at low temperatures (under 800 K). Similarly, when using TiO2 only as catalyst and applying the pulsed streamer corona plasma, respectively, the oxidation fraction is not increased significantly. Moreover, when simply combining the gas-phase reaction and the surface reaction, the oxidation fraction can reach and maintain only about 10% below 673 K. Contrary to the above two results, the oxidation fraction could be increased significantly by adding H2O of about 0.2 vol %. Hydrogen peroxide was demonstrated to have better oxidation promotion characteristics in comparison to the addition of H2O and H2O + plasma. The oxidation fractions of 60% and 90% can be achieved, respectively, by adding a very small amount of H2O2 and applying the pulsed streamer corona plasma in the reaction process. Finally, these experimental results confirmed our initial hypothesis that hydroxyl radicals (OH) enhance the oxidation of SO2 to SO3 in both the gas-phase reaction and the surface reaction on TiO2.