铟在碱性溶液中的阳极钝化过程

用线性电位扫描、循环伏安、计时电量及电位衰减等电化学方法，研究了铟在3mol／L KOH溶液中的阳极钝化过程．铟在强碱性溶液中表现为一种活化一钝化金属．在活化区铟发生两步氧化，首先一电子氧化形成InOH]ad，接着InOH]ad二电子氧化成In(OH)3]ad，较低电位下前者较快后者较慢，表现为一电子反应；较高电位下两者均较快，表现为三电子反应，两者均受扩散步骤控制．单层In(OH)3]ad形成后使铟进入钝化区，In(OH)3]ad不稳定，在碱液中可以溶解和转变为In2O3．在钝化区，铟直接氧化成三价铟，较高电位下形成稳定的In2O3，较低电位下形成非化学计量的三价铟氧化物，其稳定性介于In(OH)3]ad和In2O3之间。

ANODIC PASSIVATION PROCESSES OF INDIUM IN ALKALINE SOLUTION

The anodic passivation processes of indium in 3mol/L KOH solutions are investigated by using linear potential sweep,cyclic voltammetry,chronocoulometry and chronopotentiometry.Indium behaves as an active-passive metal in concentrated alkaline solution.The oxidation processes of indium proceed by two steps at active region,forming InOH]_ ad from In and In(OH)_3]_ ad from InOH]_ ad .At lower potential,the formation of InOH]_ ad is fast but the formation of In(OH)_3]_ ad is slow,so the reaction behaves as one electron transfer.At higher potential,both formations of InOH]_ ad and In(OH)_3]_ ad are fast,so the reaction behaves as three electron transfer.Two kinds of the reactions at active region are controlled by mass transport step.With the formation of monolayer In(OH)_3]_ ad,indium goes into the passive region.In(OH)_3]_ ad is not stable.It can dissolve into the solution and be transformed into more stable In_2O_3.Indium is oxidized directly to trivalent indium at the passive region.Within the passive region,the oxidation product is stable In_2O_3 at higher potential,and nonstoichiometric In_2O_3 which is more stable than In(OH)_3]_ ad but less than In_2O_3 at lower potential.