Corrosion resistant electrodeposited zinc coating from zinc dross

Electrodeposition of metals from aqueous solution produces a variety of metal alloy coatings. Zincalloy coatings are obtained by electrogalvanising of pure zinc. Properties of electrogalvanised steellike corrosion resistance spot weldability and adhesion are superior to hot-dip galvanisedsteel.Inthe present investigation, an attempt has been made to study electrodeposition of zinc from solidzinc drossas ananodic material on steel sheet acting as cathode and an aqueous bath containingdifferent concentration of Cl- ions, ammoniumsaltsandconducting substances at roomtemperature. An acid chloride bath was mainly used at different pH values. Very thin adherentand impervious coating was obtained on steel sheet. The zinc coating so obtained byelectrodepositionwas finally passivated to minimize white rust. X- ray diffraction, coatingthickness, atmospheric exposure test, electrochemical test, microhardness and cathodic efficiencyof zinc coated substrates were carried out. Salt -spray test on the coating was performed for 15days. Polarization experiments were carried out in 3.5 %NaCl solutionusingEG&G PARC-273Amodel Potentiostat Galvanostat. Open circuit potential (OCP) and corrosion potential (Ecorr) wererecorded. The process developed is very simple, economically viable and eco-friendly

Study of hot-dip galvanised zinc and zinc-copper alloy coatings in chloride and chloride containing carboxylic acids media

The purpose of the present paper is to have a comparative study on the response of hot dipped galvanised commercial zinc and zinc-copper alloy coating on mild steel towards chloride and chloride containing different carboxylic acids media. Response of Hot-dip galvanised Zinc & Zinc-Copper alloy coating on mild steel sheets were assessed in 3.5% NaCl solution and natural sea water obtained from Bay of Bengal. Weight loss was measured. Electrochemical test of the galvanised coatings was carried out in 2% & 3.5% NaCl solution and sea water. It was also carried out in 3.5% NaCl solution containing citric, formic and acetic acid respectively. OCP, Ecorr and icorr were obtained by using PARC 273 EG&G Potentiostat/Galvanostat. Minor alloying additions of copper in hot dip galvanised bath improves corrosion resistance of zinc coating on mild steel in chloride media. Aggressiveness of carboxylic acids in chloride medium on hot dip galvanised zinc-copper alloy and zinc coating can be arranged in the following order: Zinc-copper alloy-Formic acid < Citric acid < Acetic acid Zinc coating - Citric acid < Formic acid < Acetic aci

Microstructural studies on the effect of Si and Cr on the intergranular corrosion in Al---Mg---Si alloys

Microstructural studies on the effect of Si and Cr on the intergranular corrosion of two Al---Mg---Si alloys have been carried out as a function of aging treatment. It was observed that the degree of intergranular attack increases with increasing aging time with a maximum at peak aged condition and then declines. Presence of Si in the alloy has a tendency to segregate at the grain boundary which makes the alloy susceptible to intergranular corrosion. Addition of a small amount of Cr in the alloy improves the resistance to intergranular corrosion

Effect of temperatures of corrosive medium on corrosion of a high strength aluminium alloy

Aerospace high strength aluminium alloys are exposed to different environments and temperatures. In the present study, a high strength Al-Zn-Mg-Cu alloy and 3.5% NaCl solution have been selected. Potentiodynamic polarization test has been carried out using PARC 273 Potentiostat/Galvanostat (USA) at 298K, 313K, 328K and 343K. Saturated calomel electrode (SCE) and graphite rod have been selected as a reference and auxiliary electrode respectively. It has been observed that aggressiveness of the solution at above temperatures increases, resulting rapid dissolution and higher corrosion rate with the rise of temperature

Influence of ageing on corrosion behaviour of Al-Mg-Si alloys in chloride and acid media

This paper deals with studies on corrosion behaviour of two Al-Mg-Si alloys containing excess Si in 1 (N) NaCl and 0.1 (N) inorganic acids. Intergranular corrosion and immersion tests were carried out as per standards (MIL-H-6088F, ASTM G-31). Intergranular corrosion was assessed using optical, scanning and transmission electron microscopy. The effects of isothermal and isochronal ageing on corrosion resistance in 0.1 (N) HCl and on hardness changes were studied. The studies showed that the amount of intergranular attack in NaCl solution increases with ageing time and is maximum at peak aged condition. Segregation of Si particles and Mg2Si at the grain boundary contributes to intergranular corrosion. Corrosion rate was higher in HCl than in HNO3 and H2SO4 solutions, however it was maximum in 0.1(N) HCl during its peak aged period

A comparative study on the performance of inhibitors for protection of recirculating cooling water system

Although innumerable research and developments are being carried throughout the world for protection of materials in re-circulating cooling water system, yet there is huge amount of material loss due to corrosion. An attempt has been made to evaluate the comparative performance of NML developed inhibitor and a commercial product in re-circulating cooling water system at Coke-oven and LD of one of the leading steel industry. Lab-scale experimental set-up for re-circulating cooling water system was made. Corrosion rate of steel(pipe)- coupons determined in both raw and inhibited water (with both proprietary as well as NML developed inhibitor). Samples were exposed in re-circulating cooling water system at the steel industry and corrosion rates were determined. Total immersion and rotational test in raw water as well as inhibited water was carried out. It was found that NML developed inhibitor was superior to the commercial inhibitor under identical condition of exposure

Corrosion behaviour of magnesium alloys in chloride medium

Magnesium and its alloys find wide application as sacrificial anode in cathodic protection of pipelines and burried structures where hot zones exist. Magnesium alloys containing different alleging elements, such as Sn, Cd and Zn were cast in the form of rod of dia. 1/2" and studied potentiodynamically and galvanostatically. PARC-273 was used for the polarization studies. OCP,E-corr and I-corr were measured. The total immersion test was also carried out to record weight loss. It was observed that alloy containing Cd and Zn showed higher corrosion rate in comparison to other alloys studied under identical conditions. Addition of Sn to the alloy improves the corrosion resistance properties marginally. Magnesium alloy containing Sn and Cd only was found to have superiority over other alloys in respect to corrosion resistance properties. The weight loss data substantiate the polarization data. The data are discussed in detail in the paper

Microstructural studies on the effect of Si and Cr on the intergranular corrosion in Al-Mg-Si alloys

Microstructural studies on the effect of Si and Cr on the intergranular corrosion of two Al-Mg-Si alloys have been carried out as a function of aging treatment. It was observed that the degree of intergranular attack increases with increasing aging time with a maximum at peak aged condition and then declines. Presence of Si in the alloy has a tendency to segregate at the grain boundary which makes the alloy susceptible to intergranular corrosion. Addition of a small amount of Cr in the alloy improves the resistance to intergranular corrosion. (C) 1997 Elsevier Science Lt

Effect of some thiourea and quinoline derivatives on corrosion of mild steel in sulphuric acid at different temperatures

Effect of some thiourea and quinoline derivatives on corrosion inhibition of Mild steel in 10% (v/v) sulphuric acid (Sp.g.1.8) was studied at 298K, 323K & 348K. Total immersion and electrochemical polarisation test was carried out. It was found from the present comparative study that thiourea derivatives have better inhibition effect than quinoline derivatives at above temperatures

Studies on Structural Degradation of Aluminium/Alloy Conductor in L.T. Line in Coastal Regions

Although steel reinforced aluminium conductor is extens-ively used for overhead transmission and distribution line, it suffers from major deficiencies due to inherent limitations of EC aluminium and steel core being used to increase the strength. Excessive bimetallic corrosion, fatigue failure and bird caging (bulging of strands) reduce the line life considerably while the electro-magnetic losses in steel core increase the cost of power transmission