The conversion of the waste Cr(VI) electroplating bath to Cr(III) electroplating bath
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ORIGINAL PAPER
The conversion of the waste Cr(VI) electroplating bath to Cr(III) electroplating bath R. Katirci1 · A. Altınsarı2 Received: 22 December 2019 / Revised: 8 April 2020 / Accepted: 4 May 2020 © Islamic Azad University (IAU) 2020
Abstract The scope of this study is to protect the environment from the waste of Cr(VI) electroplating bath and convert it to the useful product. As known, Cr(VI) is a toxic materials and harmful for the health of workers and environment. Therefore, this study has aimed to develop the conversion process of the waste Cr(VI) electroplating bath to Cr(III). To identify the significant factors affecting the quality of Cr coating during the conversion, experimental design methodologies were applied. A full factorial experimental design was performed to specify the effects and interactions of the main factors and optimize the conversion process. The results were analysed statistically. The surface response method was carried out to determine the stability of the Cr(III) bath after the conversion. The maximum brightness was observed when the amount of sodium sulphate was 80–90 g/L and boric acid 60–65 g/L at pH 3.25. Coating defects were investigated using a scanning electron microscope (SEM). EDS measurements were taken to analyse the composition of the Cr coating. SEM images and EDS measurements indicated that the blackness and matte defects are due to the formation of sulphur in the Cr coating. Keywords Cr(VI) electroplating · Cr(III) electroplating · Full factorial experimental design · Conversion process · Hazardous chemical · Chemical conversion process
Introduction Chrome (Cr) electroplating is widely used in the automotive and manufacturing industries due to its high hardness, bright appearance, excellent abrasion and corrosion resistance (Nam et al. 2004; Huang et al. 2009). It is applied as decorative and functional purposes. The thickness of decorative coating is between 0.8 and 3 μm. It provides good reflective, lubricity and durability as well as corrosion resistance to the material. Mostly, Cr coating is applied to nickel-coated parts. The thickness in hard chrome plating can be up to 300–400 μm. Unlike decorative coatings, it is often applied directly to parts. It is used in places requiring resistance to
Editorial responsibility: Fatih ŞEN. * R. Katirci [email protected] 1
Department of Metallurgical and Materials Engineering, Sivas University of Science and Technology, Sivas, Turkey
Metalurgical and Materials Engineering Department, Karabuk University, Karabük, Turkey
2
heat, corrosion, erosion and abrasion such as engine blocks (Mandich and Snyder 2000). Chromium coating cannot be directly performed in aqueous solution. The solution must contain one or more catalysts. The catalysts commonly used in Cr(VI) baths are based on sulphate and fluoride ions. The fluoride catalyst is generally added to the medium as silica fluoride (SiF−2 6 ). Sulphuric acid and/or sodium sulphate are used as the sulphate source (Fink 1926, 1931). Lead is used as an
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