Electrochemical Corrosion of Titanium and Titanium Alloys Anodized in H2SO4 and H3PO4 Solutions

Abstract

Titanium and its alloys have superior electrochemical properties compared to other alloy systems due to the formation of a protective TiO2 film on metal surfaces. The ability to generate the protective oxide layer will depend upon the type of alloy to be used. The aim of this work was to characterize the electrochemical corrosion behavior of titanium Ti-CP2 and alloys Ti-6Al-2Sn-4Zr-2Mo, Ti-6Al-4V, and Ti Beta-C. Samples were anodized in 1 M H2SO4 and H3PO4 solutions with a current density of 0.025 A/cm2. Electrochemical tests on anodized alloys were carried out using a three-electrode cell and exposed in two electrolytes, i.e., 3.5% wt. NaCl and 3.5% wt. H2SO4 solutions at room temperature. Scanning electron microscopy (SEM) was used to observe the morphology of anodized surfaces. The electrochemical techniques used were cyclic potentiodynamic polarization (CPP) and electrochemical noise (EN), based on the ASTM-G61 and G199 standards. Regarding EN, two methods of data analysis were used: the frequency domain (power spectral density, PSD) and time-frequency domain (discrete wavelet transform). For non-anodized alloys, the results by CCP and EN indicate icorr values of ×10−6 A/cm2. However, under anodizing conditions, the icorr values vary from ×10−7 to ×10−9 A/cm2. The PSD Ψ0 values are higher for non-anodized alloys, while in anodized conditions, the values range from −138/−122 dBi (A2·Hz−1)1/2 to −131/−180 dBi (A2·Hz−1)1/2. Furthermore, the results indicated that the alloys anodized in the H3PO4 bath showed an electrochemical behavior that can be associated with a more homogeneous passive layer when exposed to the 3.5% wt. NaCl electrolyte. Alloys containing more beta-phase stabilizers formed a less homogeneous anodized layer. These alloys are widely used in aeronautical applications; thus, it is essential that these alloys have excellent corrosion performance in chloride and acid rain environments.

Molecular Insights into the Stability of Titanium in Electrolytes Containing Chlorine and Fluorine Ions

“…The titanium passive film can be corroded by F – and resist Cl – in a neutral environment at room temperature. − ,,, As these are two of the most common anions in seawater, it is crucial to investigate their adsorption behavior on a titanium surface to understand the passive film stability in an aqueous electrolyte system, regardless of whether it is in the film repassivation or stabilization stage.…”

“…Previous research examined the corrosion electrochemical behavior of corresponding ions. 9,11,12 Under neutral room-temperature conditions, halogen ions generally promote spontaneous passivation of the passivation film through a dissolution formation mechanism. 13 The initial step is to attack the titanium passivation film with halogen ions to form titanium halide.…”

“…Titanium and its alloys, as typical passive metals, exhibit strong resistance to seawater corrosion due to their compact and stable titanium oxide passive films on the surface. − Therefore, these materials are widely used in marine engineering structures, ship hulls, and seawater desalination plants. − Chloride ion (Cl – ) and fluoride ion (F – ) are the primary corrosive anions to be considered in seawater, with concentrations of 19,000 and 1.3 mg/L, respectively. , They may even be concentrated multiple times in industrial wastewater and seawater desalination. Previous research examined the corrosion electrochemical behavior of corresponding ions. ,, Under neutral room-temperature conditions, halogen ions generally promote spontaneous passivation of the passivation film through a dissolution formation mechanism . The initial step is to attack the titanium passivation film with halogen ions to form titanium halide .…”

Citric Acid as an Alternative to Sulfuric Acid for Hard Anodizing in Aluminum Alloys Used in the Aeronautical Industry

“…CPP with a potential sweep of -0.3 to 1.0 V against the saturated calomel electrode (SCE) was measured using one complete polarization cycle at a scan rate of 0.06 V/min. Following the norm ASTM G61-11 [22][23][24][25][26][27].…”

A Brief Summary of Publications in the Special Issue: Advances in Corrosion Resistant Coatings

“…Generally, Ti and its alloys are better than other alloys in terms of electrochemical properties because of the formation of the protective TiO 2 coating on their surfaces. In [7], the corrosion behaviors of anodized titanium and its alloys with a TiO 2 protective coating are investigated. First, the paper demonstrated the procedures for the formation of the protective oxide coating.…”