Generally speaking, furnace purification includes flux method, gas refining method (active and degradable gas), vacuum purification, and field purification. Among them, flux purification and gas purification are the most widely used furnace refining methods in the industry. Flux purification is in the process of aluminum alloy smelting, the flux is added into the melt, through a series of physical and chemical effects, to achieve the purpose of degassing and impurity removal. The impurity removal ability of the flux is determined by the adsorption and dissolution of the oxidized inclusions in the melt by the flux and the chemical interaction between the flux and the melt. The smaller the interfacial tension between the flux and the inclusions, the better the adsorption of the flux and the stronger the removal of impurities. In addition to the flux refining methods for degassing and impurity removal, there are some other fluxes, such as covering agent, slag cleaning agent, etc. This article mainly discusses the flux for degassing and slagging.
Compared with flux purification, gas purification mainly relies on blowing active or inert gas into the melt. In addition to using the law of gas partial pressure to achieve the purpose of degassing and the purpose of bubble adsorption and inclusion, the active gas can also be combined with melting The hydrogen in the body directly reacts to produce gaseous products to achieve diffusion and degassing, flotation and slag removal. In addition, the active gas can also react with the alkali metals or alkaline earth metals in the melt to generate low-density salts, which float up to the surface of the molten aluminum to remove alkali metals/alkaline earth metals. Taking the typical reactive gas chlorine as an example, the basic reaction of chlorine entering the melt is as follows:
3Cl2+2Al=2AlCl3↑
Cl2+H2=2HCl↑
Cl2+2Na=2NaCl
It can be seen that chlorine itself and the chlorination reaction products AlCl3 and HCl are all gases, which will rise spontaneously in the melt. Purification is achieved. In addition, it can directly react with the hydrogen in the melt to achieve the purpose of hydrogen removal. It is an efficient melt refining medium.
