Study on the Inter-Electrode Process of Aluminum Electrolysis (II)--Digital Analysis of the Anode Gas Distribution Patterns on the Anode Surface Using a See-Through Cell  
[PERSON]  
1 Key Laboratory for Ecological Metallurgy of Multimetallic Mineral, Northeastern University, No. 3-11, Wenhua Road, Heping District, Shenyang 110819, China; [EMAIL_ADDRESS] (Y.Z.)  
[PERSON]  
1 Key Laboratory for Ecological Metallurgy of Multimetallic Mineral, Northeastern University, No. 3-11, Wenhua Road, Heping District, Shenyang 110819, China; [EMAIL_ADDRESS] (Y.Z.)  
[PERSON]L_ADDRESS] (J.Y.); [EMAIL_ADDRESS] (Z.W.)  
[PERSON]  
1 Key Laboratory for Ecological Metallurgy of Multimetallic Mineral, Northeastern University, No. 3-11, Wenhua Road, Heping District, Shenyang 110819, China; [EMAIL_ADDRESS] (Y.Z.)  
[PERSON]L_ADDRESS] (J.Y.); [EMAIL_ADDRESS] (Z.W.)  
[PERSON]  
1 Key Laboratory for Ecological Metallurgy of Multimetallic Mineral, Northeastern University, No. 3-11, Wenhua Road, Heping District, Shenyang 110819, China; 18842399409@163.  
and the anode. As a consequence, the anodic process becomes unstable and difficult to predict [5].  
Among all the influencing factors, the alumina concentration in the electrolyte and the anode gas evolution process contributes to most of the uncertainties. The lack of alumina, or uneven alumina distribution in the electrolyte would induce the anode effect due to the lack of Al-O-F complex ions in the anodic reaction [2; 6]. Meanwhile, the nucleation, growth, coalescence and release mechanism of the anode gas bubbles at the anode bottom surface could cause significant variation in the effective reaction area, and further the actual anode current density, which could trigger the anode effect as well [7; 8]. Once the anode effect happens, the current efficiency is reduced, and a large amount of PFCs greenhouse gas is released [9]. The CO2 bubble layer adhered on the anode surface also introduces an extra voltage drop of about 0.15-0.35 V to the cell voltage [10], causing a non-negligible waste of energy.  
The anode gas generated on the anode also has positive effects on the electrolysis process. The release of the bubble from the bottom surface of the anode drives the flow of the electrolyte in industrial cells, greatly enhancing the heat convection and accelerating the dissolution rate of alumina at the feeding zone [11; 12].  
Due to the high temperature and strong corrosive nature of cryolite electrolyte, the direct measurement of bubble properties on industrial cells cannot be conducted, and the observation of anode bubbles in a laboratory electrolysis experiment is not easy. However, the double-chamber see-through cell has been designed and used to study the bubble behavior during aluminum electrolysis. In the previous study [13], the thickness, coverage, and releasing frequencies of the bubbles on both laboratory and industrial cells were initially studied. The results showed that the influence of the bubble layer on the anode working condition is significant, and the evolution principle obtained from the lab-scale cell is similar to that from the industrial cell.  
The aim of this paper was to investigate the bubble generation and evolution behavior under the anode, and the results help to understand bubble-induced resistance during electrolysis, give insights into the anode working condition, and inspire the development of the method for reducing the bubble layer voltage drop.  
In this paper, the anode gas evolution phenomenon during aluminum electrolysis was observed and recorded with a bottom-view see-through cell through lab experiments. The bubble evolution principles were investigated with image processing and the data statistical analysis method. The influences of anode geometry and current density on the bubble evolution behavior were analyzed and discussed.