抄録
A novel Ni electroless plating method using Ti(III) as a reducer, which was characterized as a zero-emission process, was proposed. In this process, Ti(IV) formed during electroless plating reaction of Ni was electrolytically reduced to recycle Ti(III). This paper mainly deals with the electrolytic reduction behavior of Ti(IV) in a weak alkaline solution determined by cyclic-voltammetry measurement. Both Ti(IV) and Ti(III) are stable in soluble form in the pH range of 7 to 9 under the presence of complexing agents such as trisodium citrate and nitrilotriacetic acid. Cyclic-voltammetry measurements were made for Ni, Ti, Pb and Carbon felt, each was used as a negative electrode, and Carbon felt showed the most superior behavior as a negative electrode. It was demonstrated that electrolytic reduction of Ti(IV) was possible in a weak alkaline solution of pH 7 to 9 in the presence of trisodium citrate and nitrilotriacetic acid, obtaining 65% regeneration efficiency. However, if the Ni(II) ions remained in the plating solution it interfered with current efficiency by preferentially plating Ni on the Carbon felt electrode, evolving hydrogen gas. To avoid such trouble, it was proposed that the concentration of Ti(III) be increased to twice the Ni(II) concentration or that of pH 0 waste solution be applied.
