Giovanni Zangari

Corrosion resistance of ternary NiP based alloys in sulfuric acid solutions

Abstract NiP based alloy films were prepared by autocatalytic deposition and their structure, chemistry and corrosion behaviors in sulfuric acid solutions were studied as a function of their composition. The as-prepared Ni-based alloys are nanocrystalline, and their grain size decreases with increasing P content. Addition of a third element (W or Mo) influences the observed grain size. At low anodic overpotential NiP based alloys present a lower exchange current and lower reactivity than Ni, both improving with increasing P content. Contrary to Ni however, the NiP based alloys do not passivate at higher anodic overpotentials. Addition of W to NiP alloys can improve their corrosion resistance, while addition of Mo has little or no beneficial effects on corrosion properties.

Electrodeposition of soft, high moment Co–Fe–Ni thin films

The electrodeposition of Co–Fe–Ni films from electrolytes without additives and their magnetic and structural properties in the as-deposited and vacuum annealed states are reported. Co52Fe26Ni22 alloy films exhibit a saturation magnetization Bs of 20 kG, coercivity Hc around 1 Oe, resistivity of 22 μΩ cm and saturation magnetostriction of about 10−6. Crystalline structure from bcc to fcc changes with increasing Ni content; films with best soft magnetic properties are obtained when bcc and fcc structures coexist. Varying electrolyte formulation or using pulse plating, the deposition parameters which yield optimum soft magnetic properties vary, but alloy composition and crystalline structure of optimum films are unchanged. dc plated films exhibit Ni enrichment at the interface in a region of about 1 μm thickness. Easy axis annealing in a vacuum of 10−7 Torr at 200–280 °C for 30 min decreases Hc and slightly decreases the anisotropy field. Annealing, however, does not change Bs, crystalline structure or latt...

Electrodeposition and Characterization of Manganese Coatings

Manganese coatings of high quality are electrodeposited on steel substrates from simple sulfate solutions with addition of ammonium sulfate. Potentiodynamic scans and galvanostatic experiments are used to study manganese electrodeposition in a wide range of pH and current density. The effect of these variables on the microstructure, crystallography, mechanical, and corrosion resistance properties of manganese deposits are investigated, It is found that ammonium sulfate enhances the reduction reaction of the manganese ion and provides a buffering effect. Two types of manganese deposits can be obtained depending on current density: crystalline films (type I, body-centered tetragonal γ-Mn) at low current density and amorphous films (type II) at high current density, Bright manganese films with (002) preferential orientation are electrodeposited at low pH. Type I structures show recrystallization at room temperature with phase transformation; the rate of phase transformation from γ-Mn to α-Mn (body-centered cubic) follows a Johnson-Mehl-Avrami kinetics, Crystalline films obtained at relatively high current density and low pH tend to have higher phase transformation rates. Amorphous films show good corrosion resistance both in acidic sodium sulfate/ borate and sodium chloride electrolytes.

Electrodeposition of highly uniform magnetic nanoparticle arrays in ordered alumite

We report the fabrication of nanometer scale ordered arrays of magnetic cylindrical nanoparticles with low aspect ratio (height/radius a=0.2–7) and ultrahigh uniformity. Anodization and electrochemical deposition are employed for template synthesis and metal particle growth, respectively. Particle uniformity is achieved by an electrodeposition scheme, utilizing pulse reverse voltage wave forms to control nucleation and growth of the particles. The resulting nanoparticles are polycrystalline and grains are randomly oriented. The magnetic properties of the array are dominated by particle shape and by interparticle magnetostatic interactions. A very clear transition of the anisotropy from perpendicular to in plane is observed at an aspect ratio a of about two. The arrays exhibit good thermal stability, demonstrating a great potential of these structures as future recording media in a patterned scheme. The pulse reverse electrodeposition technique shows great promise for the synthesis of nanostructures of var...

Lattice symmetry and magnetization reversal in micron-size antidot arrays in Permalloy film

The magnetization reversal in four arrays of micron-size circular holes (antidots) in a Permalloy film has been studied by means of quantitative magneto-optic Kerr vector magnetometry and magnetic force microscopy. The primitive antidot meshes of the arrays investigated here can be classified as square, rectangular, hexagonal, and oblique. The vector magnetometry data show that the hole arrays induce a magnetic anisotropy completely different from that of the unpatterned film, with new hard axes along the directions connecting nearest neighboring holes. Also the coercive field is strongly affected by the pattern. The results of the vector magnetometry analysis indicate that the reversal process takes place through a collective and periodic domain nucleation and expansion process. The domain structure in the remanent state has been investigated by magnetic force microscopy imaging. The images display well-defined domain structures, which are periodic and commensurate with the holes array.

Electrocatalytic Properties of Ni-Based Alloys Toward Hydrogen Evolution Reaction in Acid Media

The electrocatalytic performance toward the hydrogen evolution reaction (HER) of a series of Ni-based alloys prepared by electroless deposition was studied by means of linear polarization, cyclic voltammetry, and potential step techniques. Ni-W-P and Ni-Mo-P alloy electrodes exhibit good electrocatalytic activity toward HERs, with some Ni-Mo-P alloys approaching the performance of Pt foils. The electrocatalytic activity of Ni-based alloys decreases with increasing P content but increases with increasing content of W or Mo. The experimental results can be interpreted in terms of a pronounced synergy between Ni, which has internally paired d electrons, and W or Mo, which have empty or half-filled d orbitals and therefore, bind hydrogen atoms strongly. The absorption of hydrogen in these alloys is also found to have an important effect on their activity. Electrodes with higher activity are capable to incorporate larger amounts of hydrogen during cathodic charging.

Structural and Magnetic Characterization of Electrodeposited, High Moment FeCoNi Films

We investigated the electrochemical deposition process of Fe-Co-Ni alloys from sulfate electrolytes containing no organic additives and the structural, magnetic, and electrical properties of the resulting films. The effect of pH and Co and Fe concentrations in the electrolyte on alloy composition is examined. The pH of the solutions is kept at 2.8 to minimize the incorporation of nonmagnetic matter. With increasing Ni content, a transition of the film structure from body-centered cubic (bcc) to face-centered cubic (fcc) is observed. X-ray diffraction and transmission electron microscopy results show that the smallest grain size of about 10 nm is obtained when the bcc and fcc phases coexist. Films with biphasic structure exhibit soft magnetic properties (coercivity about 1 Oe), high magnetic moment (about 2.1 T), narrow dispersion of the easy axis (less than 3°), and good high frequency response, with a resonance frequency above 1.8 GHz. Stress anisotropy has an important role in determining soft magnetic properties.

Electrodeposition of sacrificial tin–manganese alloy coatings

Abstract Sn–Mn coatings have been electrodeposited on steel substrates from simple ammonium sulfate baths, with or without the addition of citrate, tartrate, EDTA or gluconate additives. The effect of current density and additives on the coating composition, microstructure, crystallography and corrosion resistance of Sn–Mn deposits has been investigated. It is found that ammonium sulfate brings Sn2+ and Mn2+ discharging potentials closer, allowing codeposition of manganese with tin. Sn–Mn coatings obtained from simple ammonium sulfate baths at low current density contain a large amount of oxygen and are microstructurally heterogeneous, while at high current density amorphous, bright and homogenous Sn–Mn coatings can be obtained. The addition of tartrate, EDTA or gluconate can improve coating quality at low current density and suppress Mn2+ reduction, with a corresponding decrease of Mn content in the alloy. Sn–Mn coatings show an anodic potentiodynamic behavior intermediate between that of pure manganese and pure tin, and their electrochemical characteristics can be adjusted by varying alloy composition and structure. Coatings with a high percentage of the intermetallic Mn1.77Sn phase show good sacrificial protection for steel.

Electrodeposition of Co-Pt films with high perpendicular anisotropy

Co 8 0 Pt 2 0 alloy films from 125 to 1000 nm thick have been grown by electrodeposition on Cu(111) seed layers under constant current. Their structure, morphology, and magnetic properties have been investigated. Growth conditions can be identified for which the resulting Co-Pt films consist of a hexagonal close-packed phase only, with the c axis perpendicular to the substrate. Grain size in the film plane remains almost constant with increasing thickness, X-ray, atomic force microscopy, and magnetic data pointing toward a columnar growth. The films exhibit hard magnetic properties in the out-of-plane direction with coercivity up to 6.1 kOe.

Influence of Chloride Anions on the Mechanism of Copper Electrodeposition from Acidic Sulfate Electrolytes

We investigate the influence of chloride Cl - ions in a broad range of chloride concentrations on the kinetics and mechanism of copper electrodeposition from sulfate-based acidic electrolytes. Chloride ions influence copper deposition through two competitive effects: at low Cl - concentration (few mM), chloride ions depolarize the Cu reduction process, while higher Cl - concentrations induce complexation of copper species and cause a cathodic polarization of the deposition process. Cu reduction proceeds through two parallel mechanisms, a direct two-step reduction and a chloride-mediated route, whose relative importance depends on the amount of chloride present. A transition between these two mechanisms can be identified both by steady-state and impedance methods; however, the chloride concentration at which it occurs depends on the time scale probed by the two techniques. Impedance measurements further demonstrate that the presence of chlorides changes the double-layer structure.