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Author: search.filters.author.Thangaraj, V.

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    Electrodeposition and characterisation of zinc-nickel alloy
    (2006) Thangaraj, V.; Hegde, A.C.
    Electrochemically alloys can be designed to produce different corrosion potentials than their alloying elements. This paper deals with investigations on the development of a stable acid chloride bath of zinc-nickel alloy on mild steel in presence of sulphamic acid as brightener. A suitable bath is reported on the basis of Hull Cell studies. The effect of bath variables and operating parameters were studied and discussed. Plating efficiency and the composition of the alloy were determined. Effects of operating parameters on the deposition characteristics and properties were also reported. The corrosion properties of zinc-nickel alloy plating were studied under different operating conditions of the bath after passivation. It was found that the optimized bath composition gave bright and smooth zinc-nickel alloy plating with high performance against corrosion.
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    Anomalous codeposition and characterization of Zn-Fe alloy
    (2006) Chitharanjan Hegde, A.; Thangaraj, V.
    A sulphate bath containing ZnSO4. 7H2O, FeSO 4.VH2O, ascorbic acid and hexamine is proposed for the deposition of bright iron rich Zn-Fe alloy onto mild steel substrate. Due to inherent character of Fe+2 ions to oxidize into Fe+3, the main part of the current applied during electroplating is spent on the reduction of ferric ions into ferrous ions. This results in decrease of cathode current efficiencies and will give instability to the bath. Hence the present work has been carried out with ascorbic acid as antioxidant with hexamine as brightener. Hull cell studies were used to optimize the concentrations of the all constituents in the bath. The influence of bath constituents, current density (c.d.) and pH on the appearance and composition of the deposits were examined. A stable bath has been formulated for deposition of Zn-Fe alloy having about 60% Fe for automobile application, by choosing very less zinc content (8 g/1) in the bath. The bath exhibits the anomalous codeposition with preferential deposition of zinc as characterized by any Zn-Fe group metal alloys. It was found that the due to less Zn+2 ions in the bath, the deposition of more noble iron has not been inhibited resulting in formation of Fe rich alloy. The compositions of the deposit at different conditions were related with their brightness, thickness, hardness and their corrosion behavior. Increase of the bath temperature enhanced the percentage of more readily depositable metal (zinc) in the deposit. Thickness of the deposit increased with c.d. as a characteristic of its iron content. A very thin and bright deposit obtained at about 1 A.dm-2 is found to have about 53% iron and a thick and bright deposit at 4.0 A.dm-2 contains about 80% iron. Photomicrograph observation showed that the phase structures of the deposits are influenced by the applied c.d. and pH of the bath. The proposed bath found to give a smooth and uniform deposit (64% Fe) with good performance against corrosion at about 2.0 A.dm-2. A stable acid sulphate bath has been proposed for iron rich Zn-Fe alloy plating for automobile applications.
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    Electrodeposition and compositional behaviour of Zn-Ni alloy
    (2007) Thangaraj, V.; Chitharanjan Hegde, A.
    This paper discusses the optimization of an electroplating bath for smooth and uniform deposition of zinc-nickel alloy on mild steel. Electroplating has been carried out in a chloride bath using glycine and gelatin as additives. The effect of bath conditions and operating parameters on chemical composition, micro-hardness and appearance of the deposit have been studied and discussed. The experimental results reveal that a bright Zn-Ni alloy having about 13.6 %Ni is showing good performance against corrosion. The corrosion resistance of the deposit is found to be characteristic of its %Ni content, and is improved drastically after chrome passivation. The bath follows anomalous codeposition with preferential deposition of Zn over the entire current density range used for the study. The increase of %Ni in the deposit with current density is due to the depletion of more readily depositable Zn2+ ions at the cathode. No transition current density, at which the codeposition behaviour changed from the anomalous to normal type, was observed during the study. The increase of %Ni in the deposit at high current density (cd.) is attributed to high ratio of Ni2+/Zn2+ in the bath. The effect of temperature on the plating process showed that codeposition of metals on the cathode is diffusion controlled.
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    Development of Zn-Co alloy coatings by pulsed current from chloride bath
    (2008) Thangaraj, V.; Udayashankar, N.K.; Hegde, A.
    Zinc-M (where M = Ni, Co and Fe) alloy is of great interest owing to their better mechanical and corrosion properties compared with pure zinc coatings. Corrosion resistance of Zn-Co alloy coatings can be improved considerably by pulse plating. The paper details the optimization of Zn-Co alloy bath using pulsed current and details the superiority of pulse plating over direct current plating. Electroplating of Zn-Co alloys over mild steel was carried out under different conditions of pulse parameters like duty cycle, frequency and peak current density. The production and properties of the deposits were found to be influenced by pulse parameters employed. Within the ranges studied, the bath follows anomalous codeposition with preferential deposition of less noble zinc. The influence of current density on %wt. of Co in the deposit and cathode current efficiencies was studied. It was observed that the deposit at average current density of 5.0 A.dm-2, 50% duty cycle and 100 Hz frequency showed excellent corrosion resistance with fine structure. The peak performance of pulse electrodeposit against corrosion was attributed to the change in the surface homogeneity as evidenced by scanning electron microscope (SEM) image. The drastic decrease of corrosion rate in pulse electrodeposit was attributed to the formation of semiconductor films on the surface as supported by impedance spectroscopy signals.
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    Corrosion behavior of composition modulated multilayer Zn-Co electrodeposits produced using a single-bath technique
    (2009) Thangaraj, V.; Eliaz, N.; Hegde, A.
    Composition modulated alloy (CMA) electrodeposits of Zn-Co were produced from acid chloride baths by the single-bath technique. Their corrosion behavior was evaluated as a function of the switched cathode current densities and the number of layers. The process was optimized with respect to the highest corrosion resistance. Enhanced corrosion resistance was obtained when the outer layer was slightly richer with cobalt. At the optimum switched current densities 40/55 mA cm-2, a coating with 600 layers showed ~6 times higher corrosion resistance than monolithic Zn-Co electrodeposit having the same thickness. The CMA coating exhibited red rust only after 1,130 h in a salt-spray test. The increased corrosion resistance of the multilayer alloys was related to their inherent barrier properties, as revealed by Electrochemical Impedance Spectroscopy. The corrosion resistance was explained in terms of n-type semiconductor films at the interface as supported by Mott-Schottky plots. © 2008 Springer Science+Business Media B.V.
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    Electrodeposition and characterization Zn-Co alloy
    (2009) Hegde, A.; Thangaraj, V.
    The present work details optimization of a stable acid chloride bath for electroplating of bright Zn-Co alloy on mild steel using gelatin and glycine as additives. It was found that the addition of gelatin along with glycine changed the deposition pattern markedly. A suitable bath has been formulated using conventional Hull cell experiments. The bath under plating conditions were found to exhibit anomalous codeposition with preferential deposition of less noble (zinc) over more noble (cobalt) as characterized by Zn-Fe group metal alloys. Investigation revealed that the current density (c.d.), temperature, and pH of the bath have strong effect on the composition of the deposit. Influence of bath constituents and operating parameters on appearance and composition of deposits were studied as measure of their performance against corrosion. A variety of deposits were obtained and their corrosion resistances were measured by Tafel method with/without chrome passivation. Experimental results demonstrated the fact that the corrosion resistances of Zn-Co alloys increased with percent of Co in the deposit except at very high c.d. This is due to the fact at very high c.d. the deposit becomes very porous and thick as evidenced by SEM image. The formation of Zn-Co alloy is confirmed by EDAX analysis. A stable chloride bath for Zn-Co alloy deposition has been proposed and discussed. The formation of passive film on chromatization is indicated by almost same E corr value of all Zn-Co electroplates irrespective of the current densities at which they have been deposited. © 2009 Pleiades Publishing, Ltd.