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Titanium dioxide (TiO _2 ) sol was added to the cerium conversion coating (CeCC) for preparing the CeCC-TiO _2 composite coating covered on the surface of 211Z aluminium alloy. The anticorrosive and self-healing performances of the composite coatings were further investigated. The result shows the increasing Eg of CeCC-TiO _2 could improve the anticorrosive and anti-intergranular corrosion performances of 211Z aluminium alloy under NaCl solution. Because the composite coating with high Eg value can effectively suppress the anodic reactions, provide greater coating resistance, and bring more compact surface structure. The self-healing ability of CeCC could be improved by adding TiO _2 sol and the Eg value of the CeCC-TiO _2 composite coating with the best self-healing performance is 3.38 eV. The cause of it lies in that the coeffect of the dynamic inhibition of Ce ^3+ and the inert inhibition of Ce ^4+ influences the self-healing performance of the composite coatings.

A plasma injector element was designed to experimentally study the mechanism of methane-air diffusive flame stabilized by a discharge plasma. The air plasma was generated within the annulus gap of the injector by alternating current dielectric barrier discharge. The discharge voltage, current and photographs were recorded first. Three internal effects of the plasma on combustion were later investigated separately through several diagnostic methods, including optical emission spectrometry (OES), infrared thermography, thermocouple, infrared thermometer, schlieren imaging, photos and CH* chemiluminescence. Finally, the return on investment (ROI) was calculated. The results showed that a large number of filamentary micro discharge paths occur within the discharge gap. These discharge paths rotate anticlockwise at high speed and act as a virtual ‘fan’ to induce the flow jet. The velocity of the induced jet increases with increasing discharge voltage. The original jet expansion angle is enlarged by the radial velocity component of the induced jet, resulting in the mixing enhancement of the air and methane. The plasma rotational temperature (the first negative system ) obtained from OES is close to the discharge gas temperature measured by infrared thermography, indicating that the discharge gas temperature can be approximately represented by the rotational temperature. According to the measured temperature of the injector and the jet, the impact of the thermal effect of the plasma on flame stabilization is negligible. Due to the plasma, the height of the flame center and its representative length are generally reduced as the voltage rises, and the methane-air mixture becomes ignitable, and a stable flame can be reached under the conditions in which direct ignition fails. The combustion is enhanced with increasing heat release rate of the flame by the plasma. This finding revealed that the ROI of plasma-assisted flame stabilization is lower under a higher flowrate and a larger equivalence ratio for unstable flame situations. [ABSTRACT FROM AUTHOR]