Chemical characteristics, mechanical and thermo-optical properties of black anodic films prepared on 7175 aluminium alloy for space applications

Abstract

Black anodic coatings are usually used on space vehicles for their thermo-optical properties. This paper presents a study of the chemical characteristics of these black anodic films, as well as their mechanical and thermo-optical properties as a function of the operational conditions of the process. The influence of the anodizing parameters was seen to affect the morphology of the coating (thickness and porosity). In particular, the electrolyte temperature was found to have a major impact on the porosity as it modifies the chemical kinetics during anodization. The impact of the preparation steps on Young's modulus was also investigated. The colouring and sealing steps thus modified the mechanical properties at the coating surface, resulting in a Young's modulus gradient in the film. Finally, a decrease of film porosity seemed to limit the risks of crazing then flaking, while thermo-optical properties were not affected.

Impact of the type of anodic film formed and deposition time on the characteristics of porous anodic aluminium oxide films containing Ni metal

“…Within the time range considered, the correlations were linear, except for pore density (Table 2). The thicknesses (h p , h b ) were directly proportional to the time and the current density, in agreement with Faraday's law (Goueffon et al, 2010), while porosity, especially the pore diameter (d p ), increased with the time and thus with film thickness. By contrast, the changes in pore density were more unexpected and, as yet, unexplained.…”

Alternative black coatings prepared on aluminium alloy 1050

“…First, it was placed in a solution of cobalt acetate (200 g L −1 ) regulated at 43 ± 2°C for 15 min to impregnate the pores then, second, the impregnated sample was dipped in a solution of ammonium sulphide (30 g L −1 ) at room temperature for 10 min. A precipitation of CoS black pigments occurred in the porous anodic films as described by Goueffon et al [19][20][21][22][23]. After each step, the samples were immediately rinsed in distilled water to remove the excess solution.…”

“…Black anodic films are usually prepared on aluminium alloys [18] by anodising the aluminium surface, followed by inorganic colouring based on the precipitation of CoS pigments. Goueffon et al [19][20][21][22][23] extensively studied this black inorganic colouring process and highlighted in particular the punctual location of the black pigments, i.e. mainly at the top of the pores of the anodic films.…”

Synthesis of Nanoporous Anodic Alumina by Anodic Oxidation of Low Purity Aluminum Substrates

“…On the other hand, Goueffon et al extensively studied the formation and properties of black anodic films on aluminum alloys which are often used in space industry due to their promising thermo-optical properties [114][115][116]. The AA7175 alloy was anodized galvanostatically in the sulfuric acid electrolyte.…”

“…On the other hand, the quantity of CoS precipitates was increased with the AAO porosity, however, the precipitated dyes were mainly allocated near the oxide surface. The authors proved that the reduction of initial porosity could be a good way to limit the risk of crazing and flaking without affecting thermo-optical properties of colored layers [116].…”