Conventional black-anodised coatings with organic dyes used as spacecraft thermal control materials are considered not to have stable thermo-optical properties after environmental exposures in a space environment. The recommended black anodising use Nickel sulphide or Cobalt sulphide as the inorganic black dye [1]. These chemicals are considered to have environmental and health concerns. Even conventional hard anodising techniques are not fully environmentally friendly because of the use of strong acids and their disposal. Moreover, there is a limitation with the hard anodising process to achieve fully black finish on certain aluminium alloys. The Keronite? is a revolutionary coating method and is based on plasma electrolytic oxidation (PEO). It is an environmentally friendly and safe process for the preparation of corrosion and wear resistant black finish [2] ceramic layers on aluminium alloys that has seen increasing interest over recent years in aerospace, defence, optical instruments and general industrial applications. Evaluations of black Keronite coatings on AA7075-T6 alloy have been undertaken through extensive characterisation (microstructure, porosity, coating roughness, uniformity, sharp corner / edge retention, hardness and phase structure). Furthermore, the coatings have been subjected to environmental exposures such as severe thermal shock and salt spray tests. Thermo-optical properties such as solar absorptance, thermal emittance and peel adhesion of the coatings have been determined in as-prepared condition and after environmental exposures. Comparisons have been made with a sulphuric acid black hard-anodised coating on the same alloy.
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