RIASSUNTO
ABSTRACT:
Cadmium coatings have been widely used to protect ferrous substrate, mainly fasteners, against corrosion. In spite of presenting excellent properties, such as lubricity, low voluminous corrosion products, high performance and compatible cost, cadmium presents high toxicity. For this reason worldwide researchers are engaged to find replacers for cadmium coating. With this purpose, a project to identify cadmium coating replacers was conducted. In a previous way of this project, a wide bibliographical research was done in order to identify the potential replacers of cadmium available in the national and international market. Eleven coatings obtained through different application processes, including zinc alloy coatings, organometallic coatings and other trademark coatings were identified. This work presents the main results of the atmospheric corrosion tests conducted with and without intermittent spraying of a salt solution (Scab Test) for the twelve coatings.
INTRODUCTION
Cadmium is traditionally used as a protective coating for carbon steel fasteners, especially in marine environments. This widespread use is due to the cadmium ability to provide cathodic protection to carbon steel at regions of coating discontinuities and due to the lubricant characteristic as well as the low volume of its corrosion products. However, cadmium presents high toxicity. In this sense, the politics of environmental preservation and safety at work are restricting, worldwide, the use of cadmium and they are stimulating the development of studies to identify replacers for it. The main goal of this study was to identify organometallic and/or metallic coatings that could replace the cadmium coating with satisfactory performance. To achieve this goal, eleven different coatings, available in the market, were selected.
EXPERIMENTAL PROCEDURE
For a comparative study of the eleven selected coatings with the cadmium coating (reference), screws, nuts (made of AISI 4140 carbon steel) and panels (made of AISI 1020 carbon steel) were coated.