原位水解-硝酸镧电位滴定法测定钛合金化铣腐蚀溶液中总氟化物

基于氟钛配合物的原位水解以及硝酸镧电位滴定法建立了测定钛合金化铣腐蚀溶液中总氟化物浓度的新方法。在六次甲基四胺(HMTA)缓冲溶液中,氟钛配合物发生原位水解并释放出游离氟离子,以氟离子选择电极(F-ISE)为指示电极进行测定。对影响测定的各项参数(如p H值、HMTA溶液用量、钛离子浓度等)做了条件实验并予以优化。实验结果表明Ti(Ⅳ)浓度在0~20 g/L范围内对于氟离子测定无干扰,方法的相对标准偏差(RSDs,n=6)在0.27%~0.62%之间,加标回收率在99.5%~101.1%之间。此外,本文对氟钛配合物原位水解反应的机理也进行了探讨,溶液中氟钛配合物的主要存在形式为TiF_6~(2-),适宜的酸度是水解反应进行的必要条件,HMTA作为缓冲溶液为水解反应持续进行提供恒定的p H环境,La(NO_3)_3作为氟清除剂降低游离氟离子浓度促进水解反应的进行,伴随滴定过程氟钛配合物发生完全水解。

Determination of Total Fluoride in Chemical Milling Etching Solution for Titanium Alloys by in-situ Hydrolysis-Lanthanum Nitrate Potentiometric Titration Method

A new method for determination of total fluoride in chemical milling etching solution for titanium alloys based on in-situ hydrolysis of fluoride-titanium complex and on potentiometric titration with La(NO₃)₃ was developed. In hexamethylenetetramine(HMTA) buffer solution,the fluoride-titanium complex was hydrolyzed to release free fluoride ions. A fluoride ion-selective electrode(F-ISE) was used as the indicator electrode. Various parameters affecting the test(i.e., pH values of the solution, the dosage of HMTA solution and the concentration of titanium ion) were tested and optimized. It is shown that the test results are not interfered by the concentration of Ti(Ⅳ) in the range of 0~20 g/L, the relative standard deviation(RSDs, n=6) of the method ranges from 0.27% to 0.62% and the recovery by standard addition method is in the range of 99.5%~101.1%. The mechanism of hydrolysis of fluoride-titanium complex was discussed. The main form of fluoride presented in etching solution is TiF62-. Appropriate acidity is essential to the hydrolysis reaction. HMTA as a pH buffer provides a constant pH circumstance, while La(NO₃)₃ as the fluoride scavenger reduces the concentration of free fluoride and promotes the hydrolysis reaction dramatically. Accompanied by the titration reaction, the fluoride-titanium complex is hydrolyzed completely.