Molten salts play multiple important roles in the electrolysis of solid metal compounds,particularly oxides and sulfides,for the extraction of metals or alloys.Some of these roles are positive in assisting the extract...Molten salts play multiple important roles in the electrolysis of solid metal compounds,particularly oxides and sulfides,for the extraction of metals or alloys.Some of these roles are positive in assisting the extraction of metals,such as dissolving the oxide or sulfide anions,and transporting them to the anode for discharging,and offering the high temperature to lower the kinetic barrier to break the metal-oxygen or metal-sulfur bond.However,molten salts also have unfavorable effects,including electronic conductivity and significant capability of dissolving oxygen and carbon dioxide gases.In addition,although molten salts are relatively simple in terms of composition,physical properties,and decomposition reactions at inert electrodes,in comparison with aqueous electrolytes,the high temperatures of molten salts may promote unwanted electrode-electrolyte interactions.This article reviews briefly and selectively the research and development of the F ray-F arthing-Chen(FFC)Cambridge Process in the past two decades,focusing on observations,understanding,and solutions of various interactions between molten salts and cathodes at different reduction states,including perovskitization,non-wetting of molten salts on pure metals,carbon contamination of products,formation of oxychlorides and calcium intermetallic compounds,and oxygen transfer from the air to the cathode product mediated by oxide anions in the molten salt.展开更多
Powder compacted and sintered Nb205 pellets were cathodically polarised against graphite anode in calcium chloride melt at 1173 K to study the influence of various factors on the electrochemical reduction of the oxide...Powder compacted and sintered Nb205 pellets were cathodically polarised against graphite anode in calcium chloride melt at 1173 K to study the influence of various factors on the electrochemical reduction of the oxide. The parameters were; duration and temperature of electrolysis, open porosity of pellets, nature of anode, mode of electrolysis and configuration of the oxide cathode. The experiments were also conducted in KC1, KC1-25 tool% CaC12 and NaC1 melts to understand the effect of melt composition on the electroreduction. Different Ca-Nb-O and Nb-O intermediates were found in the pellets electrolysed for different durations of time in CaC12 melt which eventually reduced to Nb. The current efficiency of the process decreased with increasing duration of electrolysis. Decrease in electrolysis temperature from 1 173 to 1073 K led to the decrease in the rate of reduction of the oxide pellets. Pellets with high open porosity reduced faster. Carbon contamination of the melt was relatively less when pyrolytic graphite was used as anode. Of all the melts studied, the reduction was found to be better in calcium chloride melt, that too when alumina crucible was used as container of the melt.展开更多
文摘Molten salts play multiple important roles in the electrolysis of solid metal compounds,particularly oxides and sulfides,for the extraction of metals or alloys.Some of these roles are positive in assisting the extraction of metals,such as dissolving the oxide or sulfide anions,and transporting them to the anode for discharging,and offering the high temperature to lower the kinetic barrier to break the metal-oxygen or metal-sulfur bond.However,molten salts also have unfavorable effects,including electronic conductivity and significant capability of dissolving oxygen and carbon dioxide gases.In addition,although molten salts are relatively simple in terms of composition,physical properties,and decomposition reactions at inert electrodes,in comparison with aqueous electrolytes,the high temperatures of molten salts may promote unwanted electrode-electrolyte interactions.This article reviews briefly and selectively the research and development of the F ray-F arthing-Chen(FFC)Cambridge Process in the past two decades,focusing on observations,understanding,and solutions of various interactions between molten salts and cathodes at different reduction states,including perovskitization,non-wetting of molten salts on pure metals,carbon contamination of products,formation of oxychlorides and calcium intermetallic compounds,and oxygen transfer from the air to the cathode product mediated by oxide anions in the molten salt.
基金financial assistance from IGCAR, Department of Atomic Energy,India
文摘Powder compacted and sintered Nb205 pellets were cathodically polarised against graphite anode in calcium chloride melt at 1173 K to study the influence of various factors on the electrochemical reduction of the oxide. The parameters were; duration and temperature of electrolysis, open porosity of pellets, nature of anode, mode of electrolysis and configuration of the oxide cathode. The experiments were also conducted in KC1, KC1-25 tool% CaC12 and NaC1 melts to understand the effect of melt composition on the electroreduction. Different Ca-Nb-O and Nb-O intermediates were found in the pellets electrolysed for different durations of time in CaC12 melt which eventually reduced to Nb. The current efficiency of the process decreased with increasing duration of electrolysis. Decrease in electrolysis temperature from 1 173 to 1073 K led to the decrease in the rate of reduction of the oxide pellets. Pellets with high open porosity reduced faster. Carbon contamination of the melt was relatively less when pyrolytic graphite was used as anode. Of all the melts studied, the reduction was found to be better in calcium chloride melt, that too when alumina crucible was used as container of the melt.
