Coumarin Derivatives as Corrosion Inhibitors for Zinc in HCl Solutions

(a) 4-hydroxy - coumarin

The inhibiting effect of some coumarin derivatives toward the corrosion of Zinc in 0.1M HCl solution was studied using weight loss and galvanostatic polarization techniques. Addition of KI to acidic medium containing the coumarin derivatives increases the inhibition efficiency of the system. The obtained results showed that the inhibition efficiency of these compounds increased by increasing their concentrations and decreased by rising the temperature, so that the adsorption of these compounds is physically adsorbed on the zinc surface. Temkin’s adsorption isotherm fits the experimental data for the studied compounds. Some thermodynamic parameters for the adsorption and activation process were computed. The values of Tafel slopes indicate that these compounds act as a mixed type inhibitors but cathode is more polarized when an external current was applied. The inhibitors are explained in terms of adsorption on the zinc surface. The order of inhibition efficiency are interpreted on the basis of the molecular structure, the subsistent groups and their charge densities of the coumarin derivatives.


    

Phosphorus Determination of Electroless Nickel Depositions from Printed Circuit Boards (PCB) by means of EDXRF

Fig. 9: The standard-less XRF results for the P concentration correlate well with the ICP-OES results. From [6].

The principles of energy dispersive x-ray fluorescence (EDXRF) technique and its elemental analysis applications were described in some books and reviews [1-4]. PCBs are an important application for nickel-phosphorus (NiP) coatings, on top of which, additional gold and/or palladium coatings are applied. Phosphorous concentration of chemically (or electroless) deposited nickel-phosphorus (NiP) coating can be analyzed in nondestructive manner in atmosphere without stripping Au and Pd coatings. The FP-based WinFTM software allows a reliable determination of both the mass per unit area of the NiP layer and its P concentration [5]. The reproducibility and accuracy of the analysis is verified by means of certified standard reference material. Their quantification is traceable to accurate mass per unit area primary standards analyzed by several suitable techniques [6]. The typical measurement spot size is about 1mm, but in case of micro-spot instruments even smaller spot sizes (less than 100 µm) are achievable.


    

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Electrochemical removal of nitrate from waste water

Fig. 1: SEM micrographs showing the surface morphologies of CuSn films obtained at i = 80 mA/cm2 (A), i = 120 mA/cm2 (B), E = -0.5 V (C) and E = -0.6 V (D) with stirring (2000 rpm)

The reduction process of nitrate at copper based electrodes was investigated. The cyclic voltammetry (CV) studies allowed us to establish the specific parameters concerning the electrodeposition of the individual metals and their alloys. It was demonstrated that the products resulting from electrochemical nitrate reduction (ENR) in alkaline media can be detected by cyclic hydrodynamic voltammetry (CHV) and square wave voltammetry (SWV) techniques at Cu and CuSn plated Pt electrodes. Moreover, using SWV ammonium can be electrochemically detected with good accuracy. An enhancement of the electrocatalytic activity of Cu by alloying it with Sn was observed. The reduction of nitrate was investigated in an engineering laboratory scale flow reactor under different operating conditions. On the two investigated types of cathode materials (Cu and CuSn), the concentration of nitrate was reduced electrochemically to the maximum permissible limit (50 mg/L) with a energy consumption in the range of 2 – 16 kWh/kg NaNO3 at a CuSn cathode.


    

Electrofabrication of Composition Modulated Multilayer Alloy (CMMA) of Co-Ni for Better Corrosion Protection

Fig. 1: Pictorial representation of direct current (DC) and modulated current used for deposition of monolayer and multilayer coatings

Electrofabrication of multilayer Co-Ni alloy coatings were accomplished successfully on mild steel (MS) for better corrosion protection. Multilayer comprised of alternatively formed ‘nano-size’ layers of Co-Ni alloy of different composition have been produced from single electrolyte having Co+2 and Ni+2 ions using modulated (i.e. periodic pulse control) current density. The deposition conditions were optimized for both composition and thickness of individual layers for best performance against corrosion. The process and product of depositions were analyzed using cyclic voltammetry and SEM, PXRD, Hardness Tester, electrochemical AC and DC methods, respectively. The corrosion behavior of multilayer coatings was found to be improved drastically when the thickness of individual layer approached nano regime. The coating having 300 layers, deposited at cyclic cathodic current densities of 2.0 and 4.0 Adm-2 was found to show the least corrosion rate (CR = 0.02 mmpy) compared to monolayer (Co-Ni)4 alloy coating (CR = 2.8 mmpy) deposited from the same bath for same deposition time. Drastic improvement in the corrosion performance of multilayer coatings were explained in the light of changed kinetics of mass transfer at cathode and increased surface area due to layering, respectively.