Electropolishing of single crystal and polycrystalline aluminum to achieve high optical and mechanical surfaces

TL;DR

This study investigates electropolishing of aluminum to enhance surface quality and optical reflectance, optimizing parameters to improve its application in photovoltaic devices.

Contribution

It identifies optimal electropolishing conditions and solutions for aluminum, demonstrating improved surface reflectance relevant for PV concentrator applications.

Findings

Best solution: Phosphoric, Acetic, Nitric acids mixture

Reflectance increases with current density up to 25 A/dm2

Surface deterioration occurs beyond optimal current density

Abstract

Electropolishing has found wide application as the final surface treatment of metal products in mechanical engineering and instrumentation, medicine and reflective concentrators for PV cells. It was found that electropolishing (EP) not only reduces the surface roughness and changes its appearance, but improves many operational characteristics as well, such as corrosion resistance, endurance, tensile strength, and many others, and also changes the physicochemical properties, for example, reflectivity, electromagnetic permeability and electronic emission of some ferro-magnetic metals. This fact greatly expands the possibility of using this method in various fields of science and technology. This work is part of a study, examining electro polishing for reducing the crystalline defects adjacent to the surface, thus improving its physical properties, contributing to higher optical efficiency, when used in PV generation and storage devices. Five compositions were examined using different temperature and current density parameters. The polished samples were evaluated using reflectance spectrometry. The solution which was composed of Phosphoric acid - 85%, Acetic acid - 10%, Nitric acid - 5% was found to provide the best results. Another result obtained was that reflectance increased as the current density increased up to 25 A/dm2. Further increasing the current density resulted in deterioration of the surface and reduced reflectance. It was shown that careful lapping and polishing followed by electropolishing using the suggested solution may consist of an adequate treatment for preparing reflective concentrators for PV cells.