Jolanta Niedbała

Electrochemical Production and Characterization of Ni-Mo, Ni-Mo-P and Ni+Mo Coatings

The electrochemical layers with molybdenum were obtained by electrodeposition from citrate bath. The process was carried out under galvanostatic conditions. Structural investigations were conducted by X-ray diffraction method. It was ascertained that electrodeposited Ni-Mo-P alloys are characterized by amorphous structure, Ni-Mo alloys are characterized by nanocrystalline structure whereas Ni+Mo composite layers have a crystalline structure. The chemical composition was determined using X-ray fluorescence spectroscopy method. It was stated that Ni-Mo-P alloys contain 75%Ni, 10%Mo and 15%P, the Ni-Mo alloys contain 90%Ni and 10%Mo, Ni+Mo composite layers contain 90%Ni and 10%Mo. These layers were characterized by electrochemical methods (j=f(E) voltammetry and corrosion resistance by Stern method). The results of corrosion tests show that from among obtained layers the highest corrosion resistances exhibit nanocrystalline Ni-10%Mo alloys.

CoPSc2O3 layers for electrolytic oxygen evolution

Composite CoPSc2O3 electrolytic layers were obtained in galvanostatic conditions on a copper substrate at temperature 298 K in the current density range from 0.0039 to 0.062 A cm−2, from a cobalt electrolyte containing a suspension of Sc2O3. For comparison, CoP layers were also obtained in the same current conditions. Using the potentiodynamic method, the polarization curve was plotted for the process of oxygen electroevolution from the KOH solutions. On this basis it was possible to determine the values of the Tafel equation parameters for the oxygen evolution process. These values were then taken as the criteria for evaluating oxygen evolution capacity on the composite layers and on the CoP layers not containing Sc2O3.

Electrolytical obtaining of Ni-Mo coatings with polypyrrole

Electrolytic coatings Ni-Mo with PPy were obtained by electrodeposition and electropolymerization from a galvanic bath containing Ni2+, MoO4 2–, ClO4 – ions and pyrrole (Py). The cyclic chronovoltamperommetric curve was used to determine the potential and current density of electrodeposition process. As the electropolymerization is anodic process while the electrodeposition is cathodic one, the electrode was working alternately as anode and cathode. The process was conducted under alternating potentiostatic or galvanostatic conditions. Comparative tests were carried out for Ni-Mo alloy. The results of structural investigation of the obtained coatings by the X-ray diffraction method show, the Ni-Mo layers are nanocrystalline solid solution of molybdenum in nickel (α phase), whereas the Ni-Mo+PPy coatings are characterized by decreased peaks coming from Ni-Mo base. Surface morphology of obtained Ni-Mo+PPy and Ni-Mo coatings was investigated by scanning microscope. It was stated, that the coatings obtained by alternating potentiostatic method exhibit multilayer character, whereas the coatings obtained under alternating galvanostatic conditions are characterized by the presence of Ni-Mo nanoagglomerates plated on polymer surface.

NiPNiO electrolytic layers as anode materials

Composite electrolytic layers were obtained on an amorphous nickel base with the addition of nickel oxide, in galvanostatic conditions at a temperature of 293 K, from a nickel-plating electrolyte in the coating containing a suspension of nickel oxide. The content of nickel oxide in the coatings depends on the conditions in which they were obtained. Using the potentiodynamic method, for these composite layers the polarisation curves of the oxygen electroevolution process from the 1 M KOH solution were determined. For comparison, curves were also plotted for copper and an amorphous Ni-P electrode. The electrodes were subjected to anode-cathode cycling in the range from the potential of oxygen evolution to the potential of hydrogen evolution. For the modified electrode materials, the characteristics of the oxygen electroevolution process were again determined. From these results the influence of the electrode material, and also the influence and advantage of preliminary modification of the surfaces of the electrodes on the process of oxygen evolution in an alkaline environment, were estimated. It was indicated that a correlation exists between the values of the exchange current of the oxygen electroevolution reaction and the electro-oxidation ability of ethanoloamine on the electrode materials studied.

Electrolytic oxygen evolution on NiPSc2O3 composite layers

Abstract Composite NiPSc 2 O 3 electrolytic layers were obtained in galvanostatic conditions on a copper substrate at temperature 298 K at the current density 20 mA cm −2 , from a nickel electrolyte containing a suspension of 25–125 g crystalline Sc 2 O 3 . For comparison, NiP layers were also obtained in the same current conditions. The phase composition of the layers were investigated by the X-ray diffraction method using a Philips diffractometer and Cu Kα radiation. The chemical composition of the layers was determined by the atomic absorption method using a Perkin-Elmer spectrophotometer. The cyclic chronovoltamperometric method was used to determine the behavior of the NiPSc 2 O 3 and NiP layers as a function of their chemical and phase composition and also of KOH concentration in the solution. Using the potentiodynamic method, the polarization curve was plotted for the process of oxygen electroevolution from the 5M KOH solutions. On this basis it was possible to determine the values of the Tafel equation parameters for the oxygen evolution process. These values were then taken as the criteria for oxygen evolution on the composite NiPSc 2 O 3 layers and on the NiP layers.

The electrodeposition and properties of Zn-Ni + Ni composite coatings

The Zn-Ni+Ni coatings were deposited under galvanostatic conditions at the current density range from 20 to 60 mA cm−2. The influence of deposition current density on surface morphology, chemical and phase composition and corrosion resistance of obtained coatings, was investigated. Structural investigations were conducted by X-ray diffraction method. Surface morphology and surface chemical composition of the obtained coatings were determined by a scanning electron microscope. Studies of electrochemical corrosion resistance were carried out in the 5% NaCl solution, using potentiodynamic and Scanning Kelvin Probe (SKP) methods. A possibility of incorporation of nickel powder from a suspension bath to the Zn-Ni matrix, during galvanostatic deposition was demonstrated. The results of chemical composition analysis show that the Zn-Ni + Ni coatings contain approximately 15–18% at Ni. It was found that surface morphology, surface chemical and phase composition of Zn-Ni + Ni coatings depend in small degree on deposition current density. However, the current density influences distribution of nickel powder on the surface of these coatings. The optimal values of current density on account of corrosion resistance, are found to be j = 40–50 mA cm−2.

Influence of thermal treatment on the corrosion resistance of electrolytic Zn–Ni+Ni composite coatings

This study was undertaken in order to obtain and characterize the corrosion resistance of Zn–Ni+Ni composite coatings. The influence of thermal treatment on surface morphology, phase composition, and corrosion resistance of Zn–Ni+Ni coating was investigated. The Zn–Ni+Ni coating was deposited under galvanostatic conditions (j = 40 mA cm−2). Thermal treatment was carried out in argon atmosphere. The surface morphology of Zn–Ni+Ni coatings was carried using a scanning electron microscope (JEOL JSM-6480) and the surface chemical composition was determined by the EDS method. Structural investigations were conducted by X-ray diffraction method. The studies of electrochemical corrosion resistance were carried out in a 5% NaCl solution, using potentiodynamic and scanning vibrating electrode (SVET) methods. On the grounds of corrosion investigations, it was stated that thermal treatment improves both total and localized corrosion resistance of Zn–Ni+Ni coating in a 5% NaCl water solution. The higher corrosion resistance of the thermally treated Zn–Ni+Ni coating could be attributed to the increase in the amount of zinc bonded to nickel in the form of Ni2Zn11 and Ni5Zn21 intermetallic phases. The SVET analysis indicated that thermal treatment of Zn–Ni+Ni coating causes a decrease in the number of corrosion centers on their surface area.

Mechanical Synthesis and Heat Treatment of Ni75Ti25 Alloy

The investigations of the microstructure changes of Ni75Ti25 powder prepared by mechanical alloying in as-milled state and after annealing treatment were performed. The X-ray diffraction (XRD) method was used to investigate a mechanically induced solid state reaction between nickel and titanium powders. The crystallite sizes and lattice strains were analyzed by using Williamson-Hall method. The compacted powder morphology was analyzed by SEM method. The Ni(Ti) solid solution was formed as a result of the milling process. The crystallite sizes of all alloys are below 100 nm. The annealing treatment, in the temperature range of 773 K to 1173 K leads to reduction of the breadth of Ni(Ti) diffraction lines, which indicates at the increase in size of crystallites. However, the phase composition of annealed Ti75Ni25 powder does not change, so the presence of any Ni-Ti intermetallic phases is not stated.

Influence of thermal treatment on the corrosion resistance of electrolytic Zn-Ni coatings

This study was undertaken in order to obtain and characterize the corrosion resistance of Zn-Ni coating. The process was carried out under galvanostatic conditions (j = 50 mA·cm−2) chosen on the ground of an analysis of the deposition process in the Hull’s cell. The Zn-Ni coatings were deposited on austenitic (OH18N9) steel substrate from the ammonia bath. Thermal treatment of Zn-Ni coating was carried out in argon atmosphere. Structural investigations were conducted by X-ray diffraction method. Surface morphology of the obtained coatings was determined using a scanning electron microscope (JEOL JSM-6480) with EDS attachment. The electrochemical corrosion resistance of the prepared Zn-Ni coatings, austenitic (OH18N9) and (St3S) steels, was defined. The studies of electrochemical corrosion resistance were carried out in 5 % NaCl, using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. Examinations of localized corrosion resistance were conducted using scanning vibrating electrode technique (SVET). On the grounds of these investigations it was found that Zn-Ni coating after thermal treatment was more corrosion resistant than the Zn-Ni coating before thermal treatment. The relatively good corrosion resistance of Zn-Ni coatings is not as high as the resistance of (OH18N9) steel substrate, but higher compared to (St3S) steel. Therefore, the Zn-Ni coatings may be regarded as a protective coating for St3S steel.

Characterization of Ni75Mo25 Alloy Prepared by Mechanical Alloying and Heat Treatment

The process of Ni75Mo25 powder synthesis via mechanical alloying (MA) was studied. Process was carried out from pure elements: Ni and Mo with a particle size under 150 μm. A ball-to-powder weight ratio and the rotational speed were 5:1 and 500 rpm, respectively. Oxidation was reduced by milling under an argon atmosphere. The milling process was performed during up to 60 hours. X-ray diffraction (XRD) and scanning electron microscopy techniques have been used to investigate resulting products. It was found that the particle sizes decrease with the increase in milling time. The resulting powder consists of metastable Ni(Mo) and Mo(Ni) solid solutions. Milled Ni75Mo25 powder was subjected to heat treatment at temperature of 773K, 973K and 1173K. As a result of annealing the formation of Ni4Mo and NiMo intermetallic phases was observed.