Chloride Bath Research Articles

A Study on the Effect of Additive Combination on Improving Anticorrosion Property of Zinc Electrodeposit from Acid Chloride Bath

The presence of polyethylene glycol (PEG) and syringaldehyde (SGA) mixture in a chloride bath produces nanocrystalline, bright zinc electrodeposition on steel substrate. The effect of the combination of additives PEG and SGA and simultaneous influence of deposition current density in the presence of the PEG+SGA mixture on the deposit surface morphology, texture, and grain size were systematically studied. The effects of these additives on cathodic current efficiency and throwing power of the bath and corrosion resistance of the deposit were analyzed. The presence of the PEG and SGA mixture remarkably changes both the morphology and orientation of growing zinc platelets. This study revealed the synergistic influence of additives on enhancing the corrosion resistance property of the deposit.

Electrochemical and spectroscopic investigation of a binary Ni-Co oxide active material deposited on graphene/polyvinyl alcohol composite substrate

A composite material based on Polyvinyl alcohol (PVA) and graphene oxide (GO) was used as electrode substrate for the Ni-Co electrodeposition in neutral chloride bath containing 1.5mM Ni(NO3)2 and 4.5mM Co(NO3)2. Ni-Co particles were cathodically deposited by voltage cycling between −0.5V and 0.2V vs. SCE (35cycles). Voltammetric data show clearly an inhibition phenomenon of nickel oxide deposition upon increasing [Co2+] in the electroplating baths. Nevertheless, the presence of electrodeposited Co oxide species induces beneficial effects on the redox electrochemical behavior of the GC/PVA/GO/Ni-Co electrode in alkaline medium (0.1M NaOH). The resulting electrode shows, a unique and reversible symmetrical cathanodic wave centered at about 0.3V vs SCE. The SEM analysis shows the graphene oxide disposed as platelets in a agglomerate distribution randomly oriented within the PVA matrix. The electrodeposition process of Ni-Co species proceeds preferentially on the GO platelets surfaces. After the charge/discharge process in alkaline medium, the Ni-Co deposit shows a globular inhomogeneous distribution with an average diameter comprised between 50nm and 300nm. The XPS characterization of the electrodeposited Ni-Co catalyst reveals a surface chemical composition of about Ni16Co84, confirming an “anomalous” co-deposition process of the metals on the PVA/GO electrode substrate.

Zn–Mn alloy coatings from acidic chloride bath: Effect of deposition conditions on the Zn–Mn electrodeposition-morphological and structural characterization

Zn–Mn alloy electrodeposition on steel electrode in chloride bath was investigated using cyclic voltammetric, chronopotentiometric and chronoamperometric techniques. Cyclic voltammetries (CV) reveal a deep understanding of electrochemical behaviors of each metal Zn, Mn, proton discharge and Zn–Mn co-deposition.The electrochemical results show that with increasing Mn2+ ions concentration in the electrolytic bath, Mn2+ reduction occurs at lower over-potential leading to an enhancement of Mn content into the Zn–Mn deposits. A dimensionless graph model was used to analyze the effect of Mn2+ ions concentration on Zn–Mn nucleation process. It was found that the nucleation process is not extremely affected by Mn2+ concentration. Nevertheless, it significantly depends on the applied potential.Several parameters such as Mn2+ ions concentration, current density and stirring were investigated with regard to the Mn content into the final Zn–Mn coatings. It was found that the Mn content increases with increasing the applied current density jimp and Mn2+ ions concentration in the electrolytic bath. However, stirring of the solution decreases the Mn content in the Zn–Mn coatings. The phase structure and surface morphology of Zn–Mn deposits are characterized by means of X-ray diffraction analysis and Scanning Electron Microscopy (SEM), respectively. The Zn–Mn deposited at low current density is tri-phasic and consisting of η-Zn, ζ-MnZn13 and hexagonal close packed ε-Zn–Mn. An increase in current density leads to a transition from crystalline to amorphous structure, arising from the hydroxide inclusions in the Zn–Mn coating at high current density.

Electrodeposition of compact and porous Cu-Pd alloy layers and their application to nitrate reduction in alkali

Compact Cu-Pd alloys of compositions extending over the entire range are deposited at low overpotentials, from acidic sulphate/perchlorate baths of the two metal ions. XRD data show a lattice parameter following Vegard’s law. Porous alloy layers can be deposited from acidic chloride baths under large current densities causing vigorous hydrogen evolution. Good deposits with regular morphology are obtained only from Cu-rich baths, and for Pd contents up to ca 33 at%. XRD investigations indicate a biphasic structure, made of pure Cu and a Cu17Pd83 phase, in variable ratios depending on composition. Single phase porous Cu-Pd materials are obtained by prolonged galvanic displacement of porous Cu layers. Selected electrode materials are tested in the nitrate reduction in alkaline media, comparing the effects of composition and surface area.

New extraction process for recovery of metals in glass deposits

A new process, named salt extraction process, has been developed to enable recovery of metal values from secondary sources e.g. scrap and waste materials such as slag and flue dust. It is also feasible in extracting metals from certain ores that normally are difficult to enrich and process by traditional metallurgy – two examples are nickel and cobalt. The salt extraction process has also been applied in the recovery of metals from silicates including lead from glass wastes.The process is based on the extraction of metal values from the raw materials into a molten salt bath consisting of NaCl, LiCl, and KCl corresponding to the ternary eutectic composition and with AlCl3 dissolved in the salt melt acting as the chlorinating agent. This is followed by the electrolysis of the salt bath in the same reactor. The normal processing temperature is in the range 973 K (700 °C) to 1173 K (900 °C). The aluminium chloride in the salt bath reacts with the metals in the fine comminuted raw material and metal ions are formed in the chloride bath. During the electrolysis, the metal ions reach the solid cathode and get deposited in metallic form. Liquid aluminium is used as the anode. Chlorine gas formed at the anode reacts with aluminium forming aluminium chloride in situ, which gets dissolved in the salt melt supplying the required amount of the flux.The salt extraction process has been used successfully in the extraction of Cr and Fe from electric arc furnace (EAF) silicate slag. Experiments have also been carried out in which lead has been recovered with high yield from spent cathode ray tubes. The process was shown to be successful in the extraction of the rare-earth metals neodymium and dysprosium from permanent magnet scrap. The method is a highly promising process route for the recovery of strategic metals. It also has the added important advantage of being environment-friendly, with only small amount recyclable, potentially useful rest products like alumina and silica as with limited energy consumption.

The comparative study of the corrosion stability of Zn-Ni-Co alloy coatings deposited from chloride and sulphate baths

The ternary Zn-Ni-Co alloy coatings were electrodeposited on steel from chloride and sulphate baths. The deposition was carried out galvanostatically at different current densities at ambient temperatures from additives free baths with different ratios of Ni and Co. Corrosion behaviour of these coatings was evaluated from polarization measurements in 3% NaCl. The deposition current density exhibited small influence on the corrosion potential and corrosion current density of alloys obtained from both chloride and sulfate baths. On the other hand, [Co2+]/Ni2+] ion ratio showed a significant influence on corrosion behaviour of ternary alloy coatings, and this influence was more pronounced with alloys deposited from chloride baths. It was shown that increased corrosion protection of steel can be achieved by electrochemical deposition of ternary alloys that contained lower amount off the alloying elements, while the composition of the ternary alloy can be optimized by proper choice of the type and composition of the deposition bath.

Investigation of microstructural and physical characteristics of nano composite tin oxide-doped Al3+ in Zn2+ based composite coating by DAECD technique

In other to overcome the devastating deterioration of mild steel in service, Zn-based embedded Al/SnO2 composite coatings have been considered as reinforcing alternative replacements to the more traditional deposition for improved surface properties by using Dual Anode Electrolytic Co-deposition (DAECD) technique from chloride bath. The structural characterization of the starting materials and deposited coating are evaluated using scanning electron microscopy (SEM), equipped with energy dispersive X-ray spectroscopy (EDX) elemental analysis and atomic force microscope (AFM). The hardness behaviour, wear and intermetallic distribution was examined by diamond based microhardness tester, CETR reciprocating sliding test rig and X-ray diffractometer (XRD) respectively. The corrosion properties of the developed coating were examined in 3.5% NaCl. The microstructure of the deposited sample obtained at 7% SnO2, revealed fine-grains deposit of the Al/SnO2 on the mild steel surface. The results showed that the Al/SnO2 strengthening alloy plays a significant role in impelling the wear and corrosion behaviour of Zn-Al/SnO2 coatings in an aggressive saline environment. Interestingly Zn-30Al-7Sn-chloride showed the highest wear and improved corrosion resistance due to Al/SnO2 oxide passive film that forms during anodic polarization. This work established that co-deposition of mild steel with Al/SnO2 is auspicious in increasing the anti-wear and corrosion progression.

Template-Directed Electrodeposition of Iron-Palladium Nanowires and Their Electrical Transport and Sensing Properties

Template-directed electrodeposition was utilized to fabricate FexPd1-x nanowires where the dimension was controlled by template pore size (i.e., 30 and 200 nm) whereas the composition was tuned by varying the Fe+2/Pd+2 metal ion ratio in ammonium chloride baths at fixed deposition current density of 5 mA cm−2. A wide range of composition (i.e., Pd-rich, near equiatomic, and Fe-rich) were successfully fabricated and their magnetic properties were examined. Additionally, single nanowire was also integrated on to microfabricated gold electrodes by magnetic alignment, followed by post-annealing in a reducing environment to make good electrical contacts. Assembled single nanowire was utilized to determine their electrical transport properties including temperature-dependent resistance (TCR) and magnetoresistance (MR). Additionally, the feasibility of FexPd1-x nanowire based hydrogen sensor was examined at room temperature.

Reactions involved in the electrodeposition of hydrotalcite-type compounds on FeCrAlloy foams and plates

The cathodic electrodeposition of Mg/Al hydrotalcite-type (HT) compounds on FeCrAlloy plates and foams by the electro-base generation method, using nitrate salts as precursors, was studied. In order to characterize the main mechanisms governing the precipitation of HT compounds, potential sweeps or pulses were applied at both plates and foams dipped in nitrate and chloride baths, with and without Mg2+ and Al3+ precipitating cations. Moreover, nitrate reduction products were analyzed. The features of coatings and pH near foam supports were correlated to electrochemical results.Nitrate and oxygen reduction, as well as H2 evolution, contributed to a pH increase during the electrodeposition of HT compounds, but nitrate reduction was responsible for the highest pH increase at the electrode-electrolyte interface. FeCrAlloy showed a low activity in nitrate reduction to nitrite and ammonia. Mg2+ and Al3+ precipitating cations fostered electrochemical reduction and modified reaction products. The shape of the support, foam or plate, did not significantly alter the electrical conductivity and reduction potentials, but it did affect current density and H2 bubble formation. A higher current density was recorded at the foam, while H2 bubbles were smaller and dissipated rapidly; subsequently, a thicker coating was electrodeposited.

Electroless Deposition of Co-Mo-P (or B) Alloys for Ulsi Applications

The purpose of this work was on the one hand to produce Co-Mo-P (or B) deposits and on the other to use our Co-P electrolyte as universal and to obtain Co-W-P or Co-Mo-P thin films from common solution. The Co-W-P electrolyte with sodium tungstate Na2WO4 or tungsten phosphoric acid H3[P(W3O10)4] as a source of W-ions was well studied. In this paper we present the process of Co-Mo-P (or B) electroless deposition from either sulfate and chloride bath at basic conditions using sodium hypophosphite or sodium borohydride as a reducing agent. The material and chemical properties of the obtained films were characterized. The paper focuses on the deposition process and study of electroless deposited films for using in microelectronic technology. The Co-Mo-P and Co-Mo-B thin films were obtained from sulfate and chloride bath correspondingly. The refractory metal has been introduced to the solutions by adding molybdate ions. The Co-Mo-P and Co-Mo-B were obtained by chemical method. The structure of electroless deposited Co-Mo-P (B) films was amorphous as determined by XRD analyze. By this is meant that barrier properties of electroless deposited Co-Mo-P(B) thin films are bound to be reasonably good. The resistivity of the deposited on Co-seed Co-Mo-P thin films with thickness of 60nm after annealing was 80 μΩ.cm. The resistivity of the Co-Mo-B layers with thickness of about 50-60 nm was 100 μΩ.cm and 38-40 μΩ.cm for Co and Cu seed, respectively. Co-Mo-P deposition process is less expensive as compared to Co-W-P deposition by reason of very low Mo-concentration in bath (0.1 g/l). References E.J. O'Sullivan, A.G. Schrott, M. Paunovic, C.J. Sambucetti, J.R. Marino, P.J. Bailey, S. Kaja, and K.W. Semkow, IBM J. Res. Develop., 42, p. 607 (1998). F.Pearlstein, R.F.Weigman, Plating, 54, 714 (1967). Physico-chemical origins of the chemical reduction of cobalt, K.M. Gorbunova ed., Science Publishing, Moscow (1974) (in Russian).Y. Shacham-Diamand, Y. Sverdlov and N. Petrov, J. Electrochem. Soc., 148, C162 (2001). 5. Y.Shacham-Diamand, A.Zylberman, N.Petrov, Y.Sverdlov, Microel. Eng., 64, p.315-320 (2002) Figure 1

Influence of a metallic nickel interlayer on the performance of solar absorber coatings based on black nickel electrodeposited onto copper

Black nickel is an interesting, economical, and abundant solar absorber material for low temperature solar-to-thermal energy conversion systems, and thin films can be prepared by electrodeposition. Critical parameters include the energy conversion efficiency and thermal stability, which depend on the design of the selective coating and the substrate material. In this work, we show that a metallic nickel interlayer is required in order to achieve thermal stability of black nickel coatings on copper, although the solar-to-thermal conversion efficiency for these multilayer coatings is slightly lower than for coatings of black nickel directly electrodeposited onto copper. The black nickel films were electrodeposited from a nickel chloride bath at pH 6.5 in order to avoid thermal stability issues related to the presence of sulfur. XPS and Raman spectroscopy illustrate that the composition of the black nickel film is complex, containing Ni(OH)2, NiO, NiOOH and metallic Ni. We show that the electrodeposition parameters strongly affect the performance of the selective coating.

The Correlation Among Deposition Parameters, Structure and Corrosion Behavior in ZnNi/Nano-SiC Coating

The present work explores how deposition parameters affect structural and morphological characteristics of ZnNi/nano-SiC composites in order to engineer an environmentally benign corrosion-resistant coating. In this regard, ZnNi and ZnNi coatings containing SiC nanoparticles were electrodeposited from chloride bath by direct current method, and the effects of SiC concentration, deposition current density and two types of surfactant (sodium dodecyl sulfate, SDS, and hexadecyltrimethyl ammonium bromide, HTAB) were investigated. Increasing SiC nanoparticles concentration in the electrolyte enhances the SiC content of the coating and can affect the coating composition, structure and morphology. Elevation of deposition current density may reduce SiC content of the coating, yet this decline can be compensated by the addition of HTAB. Application of 11 g/L SiC nanoparticles produced a coating with a more even surface and less porosity that had the highest corrosion resistance. The presence of nanoparticles seemingly reduces the available surface for electrochemical reactions and decelerates corrosion.

Mn3O4 nanorods with secondary plate-like nanostructures; preparation, characterization and application as high performance electrode material in supercapacitors

Mn3O4 nanorods with secondary plate-like structures were prepared through precipitation from a 0.005 M manganese chloride bath, under the applying direct current mode (i = 2 mA cm−2). The structural analysis through XRD and FTIR confirmed that the deposited nanopowder has pure monoclinic phase of Mn3O4. Further morphological assessment through SEM proved the product to have the Mn3O4 nanorods in large quantity, which constructed the secondary plate-like building blocks. Cyclic voltammetric and charge–discharge experiments on the product indicated the prepared Mn3O4 to possess high specific capacitance (SC) values of 298 F g−1, as well as an outstandingly durable cycling stability (95.1 % of initial capacity after discharging 1000 cycles).

Characterization of Nickel Silicide Formation by a Selective Electroless Plating Process for Crystalline Silicon Solar Cells

The nickel (Ni) electroless plating process is an encouraging method for selectively depositing Ni onto silicon (Si) wafers to form front electrodes of Si solar cells. Ni has the ability to block diffusion in copper (Cu), which is used for further thickening of the Ni contacts. The contact between Ni and Si can be optimized by an additional sintering step to form nickel-silicide (NiSix). This paper presents the characterization of NiSix according to bath conditions, deposition time, and sintering process. The selective electroless deposition of Ni was achieved by plating from an alkaline nickel chloride (NiCl2) bath with ammonia as the pH control and sodium hypophosphite as the reducing agent. Thin clusters of Ni were deposited on top of Si, which ensured the formation of uniform Ni seed layers with better surface coverage on both textured and non-textured Si surfaces. The dominant phase of NiSi that offered the lowest series resistance was confirmed by X-ray diffraction (XRD) analysis at sintering temperatures of 350 oC and 400 oC. Selective deposition of Cu over the Ni seed layer was achieved by light induced plating arrangements, and thin finger lines with widths up to 28.4 μm were realized. (Received July 1, 2015)

Granular gel support-enabled extrusion of three-dimensional alginate and cellular structures

Freeform fabrication of soft structures has been of great interest in recent years. In particular, it is viewed as a critical step toward the grand vision of organ printing—the on-demand design and fabrication of three-dimensional (3D) human organ constructs for implantation and regenerative medicine. The objective of this study is to develop a novel granular gel support material-enabled, two-step gelation-based ‘printing-then-gelation’ approach to fabricate 3D alginate structures using filament extrusion. Specifically, a granular Carbopol microgel bath holds the ungelled alginate structure being extruded, avoiding the instantaneous gelation of each printed layer as well as resultant surface tension-induced nozzle clogging. Since Carbopol microgels react with multivalent cations, which are needed for alginate crosslinking, gelatin is introduced as a sacrificial material to make an alginate and gelatin bioink for extrusion, which gels thermally (step-one gelation) to initially stabilize the printed structure for removal from Carbopol. Then gelatin is melted and diffused away while alginate is ionically crosslinked in a 37 °C calcium chloride bath (step-two gelation), resulting in an alginate structure. The proposed ‘printing-then-gelation’ approach works for alginate structure fabrication, and it is also applicable for the printing of cellular constructs and other similar homogeneous soft structures using a two-step or even multi-step approach. The main conclusions are: (1) 0.8% (w/v) Carbopol bath with a neutral pH value may be most suitable for soft structure printing; (2) it is most effective to use a 0.9% (w/v) NaCl solution to facilitate the removal of residual Carbopol; and (3) alginate structures fabricated using the proposed approach demonstrate better mechanical properties than those fabricated using the conventional ‘gelation-while-printing’ approach.

Morphological, physicochemical and magnetic characterization of electrodeposited Mn-Bi and Mn-Bi/Bi thin films on Cu Substrate

Mn-Bi thin films were electroplated on Cu (111) substrates in an acidic chloride bath. In order to determine the deposition potential of each element, cyclic voltammetry using a rotating disk electrode was performed. Two types of thin films were obtained using two deposition mode: the first one called thin Mn-Bi layers by using a single applied potential and the second one called Mn-Bi/Bi bilayers by using a double pulse potential. Annealing treatments at 300°C for 1hour under vacuum condition were carried out in order to cause an interdiffusion between manganese and bismuth. The morphological and crystalline structure of the various deposits was investigated by scanning electron microscopy with field effect (SEM-FEG) and by X-ray diffraction analysis (XRD). Magnetic characterizations were also made using a superconducting quantum interference device (SQUID) magnetometer.The morphological and the structural properties of the thin layers and the bilayers are completely different, indicating that the growth process changes according to the plating mode. After annealing a mixed MnBiCu phase with a coercivity of 300Oe and 400Oe was observed on the thin layers and the bilayers respectively.

Electrodeposition, microstructural characterization and anticorrosive properties of Zn-Mn alloy coatings from acidic chloride electrolyte containing 4-hydroxybenzaldehyde and ammonium thiocyanate

Abstract Zn Mn coatings were electrodeposited at fixed applied potential on steel substrate from an acidic chloride bath containing 4-Hydroxybenzaldehyde (4-HB) and Ammonium Thiocyanate (NH4SCN) as additives. Voltammetric and Electrochemical Quartz Crystal Microbalance (EQCM) studies were carried out to study the related electrochemical system in order to determine the optimal deposition conditions. Several parameters such as deposition potential, plating bath composition and additives were investigated with regard to the Mn content in the final coatings. The composition, morphology and crystallographic structure of the coatings were studied using Atomic Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD). In addition, the corrosion behavior of the Zn Mn alloys was investigated by means of potentiodynamic polarization curves and polarization resistance (Rp) measurements. Manganese contents of 11 wt% were obtained with plating baths without additives and increased up to 17 wt% Mn in presence of both additives. The 17 μm-thick coatings obtained from the bath with additives consisted of a compact and smooth e-Zn Mn hexagonal close-packed (HCP) single phase with a fiber texture along the 〈110〉 direction. By contrast, coatings deposited from additive-free electrolytes were rough with a dendritic morphology and consisted of a single e-Zn Mn phase. Zn Mn coatings deposited in absence of additives were found to provide lower protective ability than Zn coatings, presumably due to their dendritic morphology and rough surface. Oppositely, better corrosion protection was obtained for coatings deposited in presence of additives compared to pure Zn coatings.

New Perspectives for the Encapsulation of Hydrophilic Compounds

Encapsulation of a hydrophilic extract was performed with complex coacervation and immobilization into the gel matrix to compare the encapsulation efficiency. Sodium alginate and gelatin suspensions containing different ratios of maltodextrin were selected as the wall material for cross-linking and immobilization, respectively. Olive leaf extract was chosen as the core material. The mixtures were injected as droplets in the solution of calcium chloride and oil bath with syringe pump. Several characteristics including particle volume, swelling rate, microstructure and release profiles at gastric pH 1 and intestinal pH 7.4 at 20 and 37C of the gelled beads were determined. Encapsulation efficiency of cross-linked and gelled beads were 31.12 ± 0.75 to 44.66 ± 0.78% and 94.28 ± 0.46 to 98.64 ± 1.08%, respectively. Statistical analysis of the results revealed that the effect of maltodextrin content on particle volumes, swelling rates and release rates was significant. Additionally, the release rate was significantly affected from temperature and pH. Practical Applications Oleuropein extraction process from olive leaf was performed effectively and practical according to the most of method. Therefore, it is available for analysis and large-scale extraction processes. In process of encapsulation of hydrophilic compounds, low yield by cross-linking and high efficiency by immobilization were demonstrated. And, some properties of the beads (encapsulation efficiency, particle size, swelling rate, microstructure and release profiles) which produced by immobilization were analyzed. The obtained data from this study is thought to be guiding for food industries, nutraceutics production and pharmacy. High efficient cross-linking process for hydrophilic components could be improved.

Enantioselective Hetero-Diels-Alder Reaction of Aromatic Aldehydes Catalyzed by ((R)-1,1-Bi-2-naphthoxy)titanium Dichloride: Experimental and Theoretical Results

Background: The hetero-Diels-Alder (HDA) reaction of the carbonyl compounds with conjugated dienes, sometimes referred to as oxa-DA reaction, is an important method for the preparation of dihydropyrans, which are useful starting materials for the synthesis of several natural products including carbohydrates. However, carbonyl group as such is a less reactive dienophile and usually requires the use of a catalyst to enhance its reactivity. Methods: The catalyst, namely ((R)-1,1´-bi-2-naphthoxy)titanium dichloride (15% mol) was generated in situ. On adding aldehyde, red brown colour developed and the solution was cooled to -15ºC followed by addition of dimethylbutadiene. The reaction mixture was stirred at the same temperature for 4-5 h under nitrogen atmosphere. Results: The hetero-Diels-Alder reaction of X-C6H4CHO (X=m-NO2, o-OMe, p-CF3, m-CF3) with DMB in the presence of ((R)-1,1´-bi-2-naphthoxy)titanium dichloride (15% mol) at ~ -10 - -15°C (ice-sodium chloride bath)) gave 3,6-dihydro-2H-pyrans in 37- 74% yields with 68- 95% ee. Diels-Alder reaction of the 1:1 complex of benzaldehyde with the catalyst, ((R)-1,1´-bi-2-naphthoxy)titanium dichloride with 2,3-dimethyl-1,3- butadiene was investigated at the DFT (B3LYP) level using minimal basis set, (STO-3G). The values of the activation enthalpies (ΔH≠) for the attack of DMB on the Re and Si faces differ by 1.37 kcal mol-1 indicating ee >90% for the Si face. Conclusion: Aromatic aldehydes undergo HDA reaction with DMB in the presence of ((R)-1,1´-bi-2- naphthoxy)titanium dichloride as catalyst to give the cycloadducts in 37-74% yields with the ee ranging from 68 to 95%. Keywords: Hetero-Diels-Alder reaction, ((R)-1, 1´-Bi-2-naphthoxy)titanium dichloride catalyst, 3, 6- Dihydro-2H-pyrans, Enantioselectivity, Aromatic aldehydes, DFT calculations.

Electrodeposition, Microstructural Characterization and Anticorrosive Properties of Zn-Mn Alloy Coatings

Zinc alloy coatings are widely used for sacrificial corrosion protection of ferrous materials, in particular in the automotive industry. Zinc-Manganese (Zn-Mn) alloys were reported by Boshkov et al. to provide higher corrosion protection than pure zinc coatings due to a double protective effect involving corrosion products with low dissolution rates as well as higher cathodic protection than pure zinc due to the use of Mn [1-5]. In the framework of this work, various chloride baths with and without additives were investigated by means of voltammetric and Electrochemical Quartz Crystal Microbalance (EQCM) studies in order to define optimal deposition parameters such as deposition potential, plating bath composition and additives in regards with the Mn content in the final coatings. The composition, morphology and crystallographic structure of the coatings were studied using Atomic Absorption Spectroscopy (AAS), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD). The aim of this study is to obtain compact, smooth and monophasic Zn-Mn alloy coatings with a high Mn content. A transition from 11 wt.% Mn to 17 wt.% Mn was observed in the case of coatings deposited in presence of additives. Coatings deposited from the additive free electrolyte were rough with a dendritic morphology. By contrast, the 17 µm-thick coatings obtained from the bath with additives consisted of a compact and smooth monophasic single ε-Zn-Mn hexagonal close-packed (HCP) phase with a highly textured crystallography along the <110> direction. The corrosion behavior of the Zn-Mn alloys and pure zinc deposits was investigated by means of potentiodynamic polarization curves and polarization resistance (Rp) measurements. Higher corrosion protection was obtained for coatings deposited in presence of additives compared to pure Zn coatings. Zn-Mn coatings deposited in absence of additives found to provide lower protective ability than Zn coatings. The results clearly show that the alloying of Zn with Mn is not a sufficient condition to provide higher corrosion protection than that of pure zinc layers. In fact, coating morphology and crystallographic orientation have a significant influence on the anticorrosive properties of Zn-Mn alloys. 1. Boshkov, N., et al., Galvanic alloys Zn–Mn—composition of the corrosion products and their protective ability in sulfate containing medium. Surface and Coatings Technology, 2005. 194(2-3): p. 276-282. 2. Boshkov, N., S. Vitkova, and K. Petrov, Corrosion Products of Zinc-Manganese Coatings: Part I - Investigations Using Microprobe Analysis and X-Ray Diffraction. Metal Finishing, 2001. 99(9): p. 56-60. 3. Boshkov, N., Galvanic Zn–Mn alloys—electrodeposition, phase composition, corrosion behaviour and protective ability. Surface and Coatings Technology, 2003. 172(2-3): p. 217-226. 4. Boshkov, N., et al., Influence of the alloying component on the protective ability of some zinc galvanic coatings. Electrochimica Acta, 2005. 51(1): p. 77-84. 5. Boshkov, N., K. Petrov, and G. Raichevski, Corrosion behavior and protective ability of multilayer Galvanic coatings of Zn and Zn–Mn alloys in sulfate containing medium. Surface and Coatings Technology, 2006. 200(20-21): p. 5995-6001.