In-situ Observation of Oxide Films Formed During Thermal Oxidation of Liquid Al Alloy Using Raman Spectroscopy

点击翻译按钮获取中文摘要

The formation of oxide films on liquid Al and al alloys was observed during oxidation process at 1273 K in an oxygen atmosphere by Raman spectroscopy, and the mass change due to the oxidation was measured. The following results were obtained ;1.The oxidation process of liquid Al alloys was consisted of three stages, initial, incubation and accelerating. However, the accelerating stage was not observed for pure Al, Al-4mass% Mg, Al-4mass%Mg-1mass%Si and Al-4mass%Mg-4mass%Si.2.MgO and spinel (MgO・Al_20_3) were formed in the initial stage of oxidation by the reaction between Mg vapor and oxygen gas. The oxidation reaction is sustained in the incubation stage by the wicking of a liquid metal through the spinel layr formed in the initial stage. Completing of the wicking may lead the accelerating stage, in which alpha-Al_20_3 was mainly formed and remarkable mass gains were observed.3.In situ Raman spectra of oxide filmed were obtained during oxidation process of Al-1mass%Mg (with accelerating stage) and Al-4mass%Mg (without accelerating stage). The Raman peaks of spinel (MgO・Al_20_3) and alpha-Al_20_3 appeared for Al-1mass%Mg during holding at 1273 K.Both of the Raman peaks periodically disappear during the holding, which was caused by the presence of the liquid metal on the surface of the oxide film. The liquid metal flowed over the surface through cracks of the oxide films. The formation of cracks was confirmed by in situ observation of oxidation process using optical microscopy. On the other hand, the formation of spinel was observed for Al-4mass%Mg during holding at 1273 K,and the other Raman peaks were not detected for 5 hours, which means that the wicking of liauid metal through the spinel phase has not completed yat.