ChemInform Abstract: The Behavior of Titanium in Nitric‐Hydrofluoric Acid Solutions.

Abstract

022ChemInform Abstract A corrosion mechanism is proposed on the basis of electrochemical and weight loss measurements for Ti in HNO3-HF solutions and Raman and XPS results.

Analytical Method to Monitor Industrial Pickling Baths Initially Constituted by HF, HNO<sub>3</sub>

“…The pH = f(V KOH ) curve obtained with an initial composition bath, exhibits two waves respectively attributed to the neutralization of nitric and hydrofluoric acids. In general, the pickling of the alloys produces cations which were complexed by fluoride ions and the resulting adducts behave as acids, able to be neutralized by KOH in a similar way as HNO 3 and HF.…”

“…Concerning titanium alloys pickled by HF alone, studies achieved by Sutter [3] [5], conclude that oxidation takes place according to the reaction (R1): 3 2 2Ti 6HF 2Ti 6F 3H…”

“…Moreover, its corresponding salt (K 2 TiF 6 ) appears to be solid in aqueous media as claimed by Mecaprotec company [8], which processes to the pickling bath regeneration by addition of KF according to the reaction (R7): Galvez et al [10] claim that fluoride-metal complexes with high stabilization constants appear during the pickling of stainless steels by HF/HNO 3 bath. They propose a model of the various equilibria involving 25 reactions and 31 species, and conclude that FeF 3 , CrF 2+ and Ni 2+ are the main metallic forms in the solu-tion.…”

“…Al (III) is also known to be complexed by fluoride ions [15] and this section expects to examine the plausible reaction of the complex Al (III) /fluoride (produced by the pickling of titanium alloys) with KOH (0.85 M in the ethanol solvent) and to determine possible interferences on the waves of the neutralization of HNO 3 and HF. Nona-hydrated salt of aluminum nitrate was added, into the pickling bath HNO 3 /HF, at various mass concentration in agreement with the aluminum contents into the pickling baths (Figure 3 …”

“…The commonly used pickling solution are aqueous mixtures containing HNO 3 [5]), which could also be used to pick other metals such as silicon [6]. Several studies deal with the oxidation of these alloys and various reactions were proposed for the oxidation of their constituting metals.…”