Investigation of the electrolyte volume effect in the anodizing process on the optical-thermal, wear and corrosion properties of the black anodic coating

The sandwich panel is an important element of the satellite structure which various metal and composite materials are used to make its faces. Anodizing is used as a conversion coating in order to achieve the final properties of the panel surface and stability in the space environment. Anodizing is an electrochemical process in which an oxide layer is formed using electricity. During the anodizing process, concentration polarization is created and the process is stopped when the limiting current resulting from the movement of electrical charges between the surface of the anodic layer and the electrolyte is increased. By stopping the process without spending enough time to obtain a thickness sufficient for colorability, a black anodic layer for use in space coatings is not obtained. In this research, by performing the anodizing process in four container of 250, 500, 2000 and 40000 cm3, the effect of the volume of the electrolyte on the wear and corrosion and optical-thermal properties of the layer obtained in each of the processes was investigated. The results showed that with the increase in the volume of the electrolyte caused by the increase in the volume of the container, the stopping time of the process increases. The evaluation of optical-thermal properties, wear resistance and corrosion resistance was done by infrared emission coefficient and solar absorption test, pin on disk test and salt spray test, respectively. The results of measuring optical-thermal and wear and corrosion properties for three container with volume of 500, 2000 and 40000 cm3 showed that with the increase in the volume of electrolyte and the process completion time of the process, the thickness of the anodic layer increased, which improved the optical-thermal properties, corrosion and wear resistance.