Influence of Fluorozirconic Acid on Sulfuric Acid Anodizing of Aluminum

Abstract

The effects of additions of fluorozirconic acid to sulfuric acid on the anodizing behavior of aluminum have been investigated under a constant voltage at temperatures of 0 and 20 • C. The fluoroacid increased the rate of film growth, with a dependence on the fluoroacid concentration, the electrolyte temperature and the anodizing time. Compositional analyses showed that fluorine species were present in the films. However, zirconium species were absent. The fluoroacid generally enhanced film dissolution, although this effect was less important at low fluoroacid concentration, low electrolyte temperature and short anodizing times. Chromium (VI)-free conversion treatments that include fluorotitanic and fluorozirconic acids in the bath formulations have been developed for aluminum alloys.1-6 The resultant coatings comprise chromium (III) (if present in the bath), titanium and zirconium fluorides, oxides and hydroxides, which constitute the main part of the coating thickness, and a comparatively thin layer of aluminum oxyfluoride next to the substrate. In comparison with the findings from the relatively numerous studies of conversion coatings produced using fluoroacids, very little information is available on the use of fluoroacids in anodizing of aluminum and aluminum alloys. One study has been made of anodizing aluminum and aluminum alloys at a constant current density in fluoroboric acid solutions at temperatures ranging from 0 to 30• C. 7 Porous films were formed, with a pore size and population density that depended on the concentration and temperature of the fluoroboric acid solution and the time of anodizing. However, the information provided on the morphology and composition of the films was very limited and the role of the fluoroacid in the growth of the film was not considered. More recent studies examined the influence of ammonium hexafluorosilicate 8 and ammonium fluoride 8,9 additions to oxalic acid on the formation of porous anodic films on aluminum. The effect of hexafluorosilicate ions was more pronounced than that of fluoride ions, suggesting that Si

Defects of Porous Self-Structured Anodic Alumina Oxide on Industrial Aluminum Grades

“…To obtain nanoporous films with different ordering and different pore diameters, several methods are used.It is worth to note classical methods such as: one-and two-step anodizing, at normal, low or high temperatures. Also, some new methods use a change in the composition of the electrolyte, the electrochemical oxidation regime, and other parameters [5,6,7,8]. In the case of using the one-step anodizing method, often the ordering of pores on the surface of the films turns out to be dependent on the pre-fabrication of the material, including mechanical and electrochemical polishing, the effect is described in [9], degreasing the surface to be anodized [1].…”

Anodizing Aluminum and Its Alloys in Etidronic Acid to Enhance Their Corrosion Resistance in a Sodium Chloride Solution

“…The porous oxide film consisting of an outer porous layer and an inner barrier layer is typically formed by anodizing in sulfuric acid for industrial applications. [1][2][3][4][5][6][7] The aluminum substrate is only protected from the environment by the thin barrier layer due to the presence of vertical nanoscale pores in the outer porous layer. 8,9 Therefore, these nanopores are sealed with hydroxides formed in boiling water or steam or nickel acetates after anodizing to enhance the corrosion protection.…”

Effect of Joule Heating on Formation of Porous Structure of Thin Oxalic Acid Anodic Alumina Films

“…[5][6][7][8][9] The properties of nanoporous alumina can be easily changed by varying the synthesis modes: the composition and temperature of the electrolyte, anodizing voltage, current and time. [10][11][12] In the anodic alumina coating production solutions of sulfuric, phosphoric and oxalic acids are frequently used as electrolytes. However, most studies of the properties of anodic alumina are performed on samples obtained in the solutions of oxalic acid.…”