Photodegradation mechanism of deltamethrin and fenvalerate

To understand the degradation and environmental fate of pyrethroids, the process of their photodegradation under simulated natural conditions was investigated. The results showed that the degradation process follows first-order kinetics. The degradation intermediates were identified with gas chromatography-mass spectrometry. A plausible mechanism was discussed to explain the process. Several influences on degradation process were investigated and reported such as the effects of initial concentration of pyrethroids, total time of light irradiation, solvents, and light source, as well as the effect of a few substances that exist in the environment. This study could be a good reference for the degradation of pyrethroids in practical circumstances.

Effect of oxide film on nanoscale mechanical removal of pure iron

In this paper, the properties of an oxide film formed on a pure iron surface after being polished with an H_2O_2-based acidic slurry were investigated using an atomic force microscope(AFM), Auger electron spectroscopy(AES), and angle-resolved X-ray photoelectron spectroscopy(AR-XPS) to partly reveal the material removal mechanism of pure iron during chemical mechanical polishing(CMP). The AFM results show that, when rubbed against a cone-shaped diamond tip in vacuum, the material removal depth of the polished pure iron first slowly increases to 0.45 nm with a relatively small slope of 0.11 nm/μN as the applied load increases from 0 to 4 μN, and then rapidly increases with a large slope of 1.98 nm/μN when the applied load further increases to 10 μN. In combination with the AES and AR-XPS results, a layered oxide film with approximately 2 nm thickness(roughly estimated from the sputtering rate) is formed on the pure iron surface. Moreover, the film can be simply divided into two layers, namely, an outer layer and an inner layer. The outer layer primarily consists of FeO OH(most likely α-FeOOH) and possibly Fe_2O_3 with a film thickness ranging from 0.36 to 0.48 nm(close to the 0.45 nm material removal depth at the 4 μN turning point), while the inner layer primarily consists of Fe_3O_4. The mechanical strength of the outer layer is much higher than that of the inner layer. Moreover, the mechanical strength of the inner layer is quite close to that of the pure iron substrate. However, when a real CMP process is applied to pure iron, pure mechanical wear by silica particles generates almost no material removal due to the extremely high mechanical strength of the oxide film. This indicates that other mechanisms, such as in-situ chemical corrosion-enhanced mechanical wear, dominate the CMP process.

Exploring the role of --NH2 functional groups of ethylenediamine in chemical mechanical polishing of GCr15 bearing steel

Ethylenediamine with two-NH2 functional groups was used as a critical complexing agent in chemical mechanical polishing(CMP)slurries for a high carbon chromium GCr15 bearing steel(equivalent to AISI 52100).The polishing performance and corresponding mechanism of-NH2 functional groups were thoroughly investigated as a function of pH.It is revealed that,when polished with ethylenediamine and H2O2-based slurries,the material removal rate(MRR)and surface roughness Ra of GCr15 steel gradually decrease as pH increases.Compared with acidic pH of 4.0,at alkaline pH of 10.0,the surface film of GCr15 steel has much higher corrosion resistance and wear resistance,and thus the material removal caused by the pure corrosion and corrosion-enhanced wear are greatly inhibited,resulting in much lower MRR and Ra.Moreover,it is confirmed that a more protective composite film,consisting of more Fe3+hydroxides/oxyhydroxides and complex compounds with-NH2 functional groups of ethylenediamine,can be formed at pH of 10.0.Additionally,the polishing performance of pure iron and a medium carbon 45 steel exhibits a similar trend as GCr15 steel.The findings suggest that acidic pH could be feasible for amine groups-based complexing agents to achieve efficient CMP of iron-based metals.