沸騰塩化アンモニウム溶液中におけるチタンの間隙腐食

抄録

A heat exchanger made of titanium was used for boiling a solution containing a large amount of NH₄Cl, and crevice corrosion was observed at the gasket of the tube-sheet joint after about two months. The corrosion products were grayish blue, and contained TiO₂ (Rutile), crystalline Ti₂O₃ and amorphous Ti₂O₃⋅nH₂O. The crevice corrosion of Ti was studied in connection with hydrolysis of NH₄Cl in order to investigate the mechanism of the corrosion.
The results obtained were summarized as follows:
1) In the boiling 45% NH₄Cl solution, gaseous NH₃ was expelled from the solution, and the concentration of HCl increased until it finally reached to 0.002mol/kg H₂O. Ti would be dissolved at such a concentration of HCl.
2) However, the crevice corrosion of Ti in a boiling solution of 28% NaCl was observed even at about pH 4. It was, therefore, considered that the crevice corrosion of Ti was caused by the formation of the soluble Ti (III)-complex which was produced in a slightly acidic solution under the lack of oxygen.