This study investigated the effect of Al and Mg content and immersion time on the formation of periodic layered structure during hot-dip galvanizing in Al-Zn-Mg bath. The steel substrates were immersed in Al-Zn bath for 10 s to 120 s, with five levels of Al content in the range of 15 to 55 wt.%, and four levels of Mg additions, in the range of 0.5 to 3.0 wt.%. The microstructure and constituent phases of the periodic layered structure were characterized by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The coating with periodic layered structure contains a thin light gray Fe 2 Al 5 Zn x layer near substrate and outer periodic layered structure.The periodic layered structure consists of alternating light gray layer (FeAl 3 Zn x ) and black 2 gray layer (Al dendrites and Zn-rich interdendritic regions). The formation of periodic layered structure requires an incubation period t 1 , while if the immersion time is over t 2 , the periodic layered structure is destroyed. In addition, t 1 and t 2 varies with the Al content and Mg addition.

Abstract-Experimental study on spontaneous combustion of grain dust was carried out in a cylindrical combustion chamber with vertical flow. Thermocouples and gas sample analyzer were used to measure the temperature and gas of spontaneous combustion respectively. The influence of ventilation volume, bulk density and percentage of dust of sample on the spontaneous combustion propagation velocity was investigated. The results indicated that the self-propagation spontaneous combustion is more likely to happen at relatively low ventilation volume. At early stage, the characteristic gas of spontaneous combustion are CO2 and CO. Spontaneous combustion velocity is proportional to ventilation volume while in inverse proportion to bulk density. The spontaneous combustion could transform into flaming easily under certain ventilation volume.

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