Liquidus Temperature And Al₂O₃ Solubility Of The System Na₃AlF₆-K₃AlF₆-AlF₃ And Corrosion Test Of Inert Anodes In Low Temperature Aluminum Electrolytes

The inert anode is the key in developing of the new technology for aluminum reduction. And, low-temperature aluminum electrolysis is the important ways to solve the corrosion problem of inert anode. This thesis is founded by the National High Technology Research and Development Program (863 program) and the National Basic Research Program of China (973 program). Based on Na3AlF6-K3AlF6-AlF3 system, the liquidus temperature and alumina solubility of Na3AlF6-K3AlF6-AlF3 system are studied in detail, and the research range is 20wt.%< A1F3< 30 wt.%,15%< KR<30%. Furthermore, the effects of current density, alumina content and bath temperature on corrosion rate of inert anode are researched in the Na3AlF6-K3AlF6-AlF3 system, and then technological condition can be determined, which can offer a good working environment for cermet inert anode. The main results of the thesis can be summarized as follows:(1) The influence of KR content and A1F3 content on the liquidus temperature of Na3AlF6-K3AlF6-AlF3 low temperature electrolyte is investigated. Moreover, the relation of the liquidus temperature and phase compositions is indicated. An empirical formula showing the relationship between liquidus temperature of melts and melts composition is built. The ternary isotherm diagram on liquidus temperature of Na3AlF6-K3AlF6-AlF3 melts is obtained, too. The composition limitations are 20wt.%< AlF3< 30 wt.%, and 15%< KR<30%. The empirical formula is as follows, and the correlation coefficient of empirical formula is 0.992.T= 3478-1867×[KR]0.12-12.97×[AlF3]1.14+3.538×[AlF]×[KR0.98-0.505×[AlF3]1.24×[KR]1.23 (2) The influence of bath temperature, KR content and AlF3 content on alumina solubility in Na3AlF6-K3AlF6-AlF3 system is revealed. Based on the result of liquidus temperature and alumina solubility in the Na3AlF6-K3AlF6-AlF3 system, the aluminum electrolyte with the nature of low-temperature and high-alumina solubility is obtained, which is the system KR18%, AlF36%. And the liquidus temperature of this system is 866℃. When bath temperature is 870℃, Al2O3 solubility of this system can reach 5.21%.(3) The influence of current density(1.00,1.30,1.60,2.00,3.00, 4.00A/cm2), alumina consentration(2%,3%,4%,5.21%) and bath temperature (870,880,890℃) on corrosion rate of 22(20Ni+Cu) /(NiFe2O4-10NiO) cermet inert anode are invesitigated in the system KR18%, AlF326%. When current density is 1.60A/cm2, alumina concentration reaches 5.21%, and bath temperature is 870℃, anode anti-corrosion capacity is preferably well, whose corrosion rate can meet 0 nearly.