Mechanical Engineering Technologies and Applications

Zied Driss

• Publisher: Bentham Science Publishers
• Year: 2006
• Print ISBN: 9789814998208
• eBook ISBN: 9789814998185
• Topic: Physical Sciences
• Subtopic: Energy

This book focuses on cases and studies of interest to mechanical engineers and industrial technicians. The considered applications in this volume are widely used in several industrial fields particularly in the automotive and aviation industries. Readers will understand the theory and techniques which are used in each application covered in each chapter. The book contents include the following topics: Numerical analysis of hydrokinetic turbines Computational fluid dynamics of a CuO based nanofluid in mini-channel cross-sections Orthodontic biomechanics of a NiTi arch wires Reynold's number effects on fluid flow through Savonius rotors Effect of operating parameters on Zn-Mn alloys deposited from additive-free chloride bath Optical properties and stability of a blue-emitting phosphor (Sr2P2O7: Eu2+) Under UV and VUV excitation Numerical study of the influence of nanofluid type on thermal improvement in a three dimensional mini channel Electrochemical studies and characterization of Zn-Mn coatings deposited in the presence of novel organic additives Prediction of fire and smoke propagation under a range of external conditions Structural design of a 10 kW H-Darrieus wind turbine The presented case studies and development approaches aim to provide the readers, such as graduate students, PhD candidates and professionals with basic and applied information broadly related to mechanical engineering and technology.

Electrochemical Studies and Characterization of Zn-Mn Coatings deposited in the presence of Novel Organic Additives

Nouha Loukil^{1, *}, Mongi Feki²

¹ Laboratory of Material Engineering and Environment, ENIS-Tunisia, University of Sfax, Sfax, Tunisia

² Laboratory of Material Engineering and Environment, ENIS-Tunisia, University of Sfax, Sfax, Tunisia

Abstract

A novel additive based on alkylphenol ethoxylate sulphite was investigated in Zn-Mn electrodeposition on steel from a chloride bath. Electrochemical study via cyclic voltammetry showed that the tested additive increases the over-potential of the Zn deposition, resulting from strong adsorption of molecules additives on the cathode surface. Thus, Mn-rich alloy containing 16.3% of Mn is successfully co-deposited. The morphology and crystallographic structure of Zn-Mn co-deposits were analyzed using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD), respectively. SEM micrographs showed that Zn-16.3% Mn alloy obtained in the presence of the tested additive displays hexagonal pyramid morphology. XRD analysis exhibited that Zn-16.3% Mn alloy is monophasic with hexagonal close-packed ε-Zn-Mn phase.

Keywords: Additive, Electrodeposition, Morphology, Structure, Zn-Mn alloy.

---

^* Corresponding author Nouha Loukil: Laboratory of Material Engineering and Environment, ENIS-Tunisia, University of Sfax, Sfax, Tunisia; E-mail: [email protected]

INTRODUCTION

Numerous zinc-based coatings Zn-X (X= Fe, Co, Ni, Mn…) have been electrodeposited on steel to improve the corrosion resistance of conventional pure zinc [1]. Currently, fundamental researches have been made to assess the corrosion resistance of these binary alloys into automotive applications [2^-5]. Among Zn binary alloys, there is a growing interest in Zn-Mn coatings owing to the highest anticorrosive properties in the saline environment [4^-7]. Indeed, Zn-Mn alloys show sacrificial corrosion protection for both Zn and steel components. Boshkov et al. reported that the alloying element Mn has been proposed due to its dual protective role [8, 9]. Mn is anodic to Zn and primarily dissolves [8, 9].

Accordingly, pH locally increases and promotes the formation of Zn₅(OH)₈Cl₂.H₂O (ZHC) and Zn₅(OH)₆SO₄xH₂O (ZHS) protective layers in chloride and sulfate aggressive media, respectively [8, 9]. These protective layers are thick, compact, uniform, and with low solubility [8^-13]. This is recognised by the homogeneous distribution of Mn in the coatings [14].

Several existing reports investigated the effect of the Mn content on the corrosion behavior of Zn-Mn coatings. Zn-11% Mn shows the highest anticorrosive resistance [10, 11]. Muller et al. proved that 10 to 40% of Mn substantially affords better corrosion resistance [11]. It is well documented that low Mn content ranging from 0.3 to 2.5% provides suitable mechanical properties for automotive applications and good plastic deformability [7], weldability and paintability. However, Zn-Mn co-deposition from aqueous solutions is a complex process in view of the large gap between the deposition potentials of Zn (E° (Zn²⁺/Zn) = - 0.76 V/HSE and Mn (E° (Mn²⁺/Mn) = -1.18 V/HSE). These two potentials are more negative than that of hydrogen evolution, which is a concurrent reaction.

According to Brenner [15], Zn and Mn co-deposition is a normal co-deposition, implying that Mn-rich coatings require high current densities to be electrodeposited [1, 13, 14, 16]. This occurrence leads to (i) low current efficiency [13, 14, 16] and (ii) burned and non-adherent Zn-Mn deposits [13, 14, 16]. These drawbacks result from the intensive hydrogen evolution reaction at high cathodic potentials required to reduce Mn²⁺ ions.

Zn-Mn coatings deposited from aqueous solution have comprehensively been reported in the literature. Main electrolytic baths being used are, chloride-based [1, 6, 17^-19], pyrophosphate-based [6, 18] or citrate-based electrolytes [18, 20].

One way to partially overcome the drawbacks of Zn-Mn co-deposition is the use of additives. Using a strong organic complexing agent for Zn²⁺ ions is the common way to reduce the gap between Zn and Mn deposition potentials [2, 6, 7, 11, 13, 15]. This is ascribed to the high relative formation constant of the complex formed with Zn²⁺ ions [11]. Meanwhile, they must be avoided due to environmental problems related to effluent treatment.

Few alternative organic additives are reported in the literature, which generally fall into two classes: the carrier additive and the brightener. Commonly, the carrier additive permits the (i) minimization of the potential gap between Zn and Mn co-deposition and/or hydrogen evolution [1, 17] and (ii) the grain refinement [17, 19], while the brightener additive has a complementary effect to obtain bright deposits [17, 21].

The present study deals with the development of a suitable formulation for Zn-Mn bath, including a proprietary additive. The additive formulation includes two parts: a carrier and a brightener, which are alkylphenol ethoxylate sulphite and Benzenlideneacetone (BDA), respectively. This formulation has not been explored before. The aim of the present work was to study the influence of the retained additive on Zn²⁺ and Mn²⁺ ions reduction from chloride acidic bath through cyclic voltammetry (CV). Morphological and structural characterizations of Zn-Mn coatings will also be discussed.

EXPERIMENTAL DETAILS

The electrodeposition tests were performed using an acidic chloride electrolyte. Blank expe...

Table of contents

• Welcome
• Table of Content
• Title
• BENTHAM SCIENCE PUBLISHERS LTD.
• PREFACE
• List of Contributors
• Numerical Study of a Hydrokinetic Turbine
• CFD Simulation of the Heat Transfer using a Cuo-water Nano-fluid in Different Cross-sections of Mini-channels
• Influence of the Force Delivery of Orthodontic NiTi Arch Wire on its Tribological Behavior
• Reynolds Number Effects on the Flow through a Savonius Wind Rotor
• Effect of Operating Parameters on Zn-Mn Alloys Deposited from Additive-free Chloride Bath
• Optical Properties and Stability of a Blue-Emitting Phosphor Sr2P2O7:Eu2+ Under UV and VUV Excitation
• Numerical Study of the Influence of Nano-fluid Type on Thermal Improvement in a Three Dimensional Mini Channel
• Electrochemical Studies and Characterization of Zn-Mn Coatings deposited in the presence of Novel Organic Additives
• Prediction of Fire and Smoke Propagation under a Range of External Conditions
• Structural Design of a 10 kW H-Darrieus Wind Turbine