| Low-temperature aluminum electrolysis is usually achieved by reducing the electrolyte molecular ratio.Low-temperature aluminum electrolysis aims to achieve the purpose of energy saving and environmental protection by lowering the electrolysis temperature,and has become one of the hot research directions in the field of aluminum electrolysis.Since the Li2O and K2O in the raw materials eventually exist in the form of LiF and KF in the electrolyte,it is more meaningful to consider adding different contents of LiF and KF to the electrolyte in the study.However,the addition of additives LiF and KF has a great impact on the solubility and dissolution rate of alumina,and the alumina that cannot be dissolved in time combined with the electrolyte will form a precipitate.This thesis focuses on the Na5Al3F14-KF-LiF-AlF3-Al2O3 system to study the three parts of precipitation,anode bubbles,and anode overvoltage.First,this article explored the rate of alumina dissolution in this system.Using the EMF method,the normal molecular ratio CR2.3 and the low molecular ratio CR1.7 and CR1.3 contain 6%LiF and 6%KF(this article describes the system as CR1.3 x[KF]=6,x[LiF]=6,the same below)The dissolution rate of the three different systems is determined by adding 1%alumina powder to the system at regular intervals.The dissolution rate of alumina in CR1.3 x[KF]=6 and x[LiF]=6 system is the lowest,and the electromotive force does not change after alumina powder is added for the fourth time.Then,SEM and XRD analysis were performed on the precipitate obtained in the laboratory.Then the heat transfer of the single alumina particles in the electrolyte was numerically simulated.The simulation results show that the normal temperature alumina particles can heat up to 716℃ in only 0.2s,and the electrolyte temperature gradient around the alumina particles is obvious.The addition of alumina particles reduces the temperature of the electrolyte around the alumina particles by about 100℃ in a short period of time.The generation and escape period of anode bubbles are analyzed by the potential time curves of CR1.3 system at different pole distances and different current densities.And add LiF alone,KF alone,and LiF and KF together in the CR1.3 system to explore the influence of additives on anode bubbles.For the CR1.3 system,the addition of LiF broadens the range of the current density and the pole distance that the anode bubbles periodically generate and escape,and the periodic generation and the pole distance of the anode bubbles can be observed under a wide current density and pole distance.Escape.Regardless of whether it is the addition of LiF or KF,the escape frequency of anode bubbles is accelerated.The CR1.3 system electrolyte has the best wettability to the graphite plate,and the addition of LiF and KF both makes the wetting angle of the electrolyte on the graphite plate larger,and then the wettability becomes worse.The wettability of the electrolyte containing LiF alone is the worst,and the wettability of the electrolyte containing LiF and KF is between that of the electrolyte containing LiF or KF alone.An aluminum reference electrode was used to measure the anode overvoltage of the Na5Al3F14-KF-LiF-AlF3-Al2O3 system.It is found that the anode overvoltage varies from 0.2 to 0.4V when the anode current density changes from 0.2 to 1.0A/cm2.The overvoltage increases with the increase of current density and conforms to the Tafel straight line within the current density range.The intercept of the Tafel straight line is 0.37 and the slope is 0.27.The equilibrium potential of the anode residual potential decay curve measured by the carbon reference electrode is finally stabilized at about-10mV,and the time to reach the equilibrium potential has nothing to do with the anode current density. |
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