Study On Reaction Mechanism Of Dry Barrier Material Of Aluminium Redu Ction Cell

With the development of aluminium electrolysis technology,people pay more attention to the life of aluminium electrolysis cells.As an important integral part of aluminium reduction cells,the ability of penetration resistance of the dry barrier material directly determines the life of aluminium reduction cells.The dry barrier material is used to prevent the further permeation of electrolyte and protect the insulation material at the bottom of the aluminium reduction cells by producing nepheline and albite with high viscosity.At present,the composition of dry barrier material used in industrial electrolyzer is different,and the ability of penetration resistance is also different.The reaction mechanism between dry barrier material and electrolyte penetrating from carbon cathode block is not clear.In this paper,the reaction mechanism of electrolyte and dry barrier materials in aluminium reduction cell is studied in laboratory,and the cause for deterioration of dry barrier materials is discussed.The main conclusions are as follows:(1)At electrolytic temperature,sodium fluoride can react with dry barrier material to form a glass-like barrier of nephelite which played a very important role for preventing further penetration of molten fluorides.It can also produce SiF4 gas in the process of electrolyte reacts with dry barrier.(2)At 920℃,aluminium metal reacts with silica in dry barrier material to form alumina and silicon.The aluminothermic reaction rate increases with the increase of silica and aluminium oxide ratio.When the sodium fluoride or cryolite was used as additives,the aluminothermic reaction rate increases for the close of radius of fluorine ion and oxygen ion atom.When the composite electrolyte was used as additive,the electrolyte in the form of liquid will wrap around the aluminium block and prevent the contact between the metal aluminium and silica.The aluminothermic rate decreases.(3)Metal sodium can intercalate into graphite and form sodium-graphite intercalation compounds,which improves the wettability of graphite and aluminium.Graphite intercaleted with metal sodium can easily react with aluminium block to form aluminium carbide.When the sodium fluoride was used as additive,it can easily react with aluminium to form metal sodium and aluminium fluoride.The metal sodium could intercalate the graphite and result in the formation of Al4C3 through the reaction of aluminium and graphite.(4)The dry barrier mainly reacts with NaF to form a glass-like barrier of nephelite which played a very important role for preventing further penetration of molten fluorides.The Na3AlF6 continuously penetrating from the carbon cathode can react with the nephelite to form β-Al2O3,and the formation of β-Al2O3 is one major cause for deterioration of dry barrier materials.It can also produce SiF4 gas in the process of electrolyte reacts with dry barrier,which makes the silicon migrate to the lower part and results in the decrease of silicon in the upper layer.