Catalytic soot oxidation over dried colloidal sols consisting of CeO₂ and CeO₂-ZrO₂ solid solution was studied before and after loading Ag catalyst. Ag-unloaded CeO₂ exhibited a higher activity than CeO₂-ZrO₂, but their activities after Ag-loading were comparable possibly because Ag activated oxygen responsible for soot oxidation. The CeO₂-ZrO₂ sol exhibited higher thermal stability against sintering than CeO₂ sols and thus retained a higher soot oxidation activity after thermal ageing above 800°C.

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  TIG welding process is often used to join thin metal plates because of the stability of arc compared with the other arc welding processes. However, the temperature of the tungsten electrode of the TIG welding torch sometimes increases and oxidation occurs during welding process. Therefore, the electrode tip is consumed considerably, and the arc stability tends to decrease with welding time. Accordingly, it is important to administrate the electrode tip condition in order to keep the welding process stable. On the contrary, the laser beam has extraordinary stability and directivity because of the nature of the light beam. Therefore, the authors have proposed a new process to stabilize and control the unstable TIG arc by the laser beam. In this study, in order to discuss the mechanism of arc behavior control by the laser beam irradiation into weld fused metal, the temperature distribution of the weld was calculated by heat conduction analysis using the finite element method (FEM). Then the control of the arc behavior in TIG welding of thin metal plates using the YAG laser beam with relatively low power was experimentally investigated. Furthermore, butt welding experiments of SUS304 stainless steel plates were performed, and the effectiveness of the new process to oscillate TIG arc using the laser weaving method was confirmed.

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