Solid State Phenomena Vol. 228

Abstract: This study reports on Ni (II) ion adsorption onto TiO₂ powder of different concentration in suspension baths developed for electrodeposition of composite Ni-P+TiO₂ coatings. The experimental results were modeled with the Langmuir, Freundlich and Temkin adsorption isotherms. It was found that the best fit of Ni (II) ion adsorption data was obtained using the Langmuir isotherm. The study also revealed that adsorption of the nickel ions is a function of TiO₂ adsorbent dose in bath. The role of Ni (II) ion adsorption onto TiO₂ adsorbate in the elctrodeposition process of composite Ni-P+TiO₂ coatings was discussed.

Abstract: In this work an attempt of production of the composite coatings based on the amorphous nickel matrix with embedded different carrier (TiO₂, Ni (OH)₂) and PTFE particles as the composite component, was undertaken. The relaxation characteristics of the electrodeposition process of the composite Ni-P+TiO₂+PTFE and Ni-P+Ni (OH)₂+PTFE coatings was carried out. It was found that the obtained J = f (t) relaxation curves correlate with electrodeposition conditions of the coatings determined on the basis of the E = f (J) polarization curves. Usability of the relaxation methods for determination of the electrodeposition parameters of the composite coatings was also discussed.

Abstract: Co-deposition process of amorphous nickel and PTFE particles in the presence of Ni (OH)₂ carrier suspended in the bath by magnetic stirring, was investigated. Composite Ni-P+Ni (OH)₂+PTFE coatings and comparative Ni-P deposits, were electrodeposited on low carbon steel substrate under galvanostatic conditions at room temperature. The physical and chemical characterization of the coatings was carried out using X-Ray diffraction analysis and microanalysis, stereometric quantitative microscopy and atomic absorption spectroscopy. The optimum production conditions of the composite coatings based on the Ni-P matrix into which PTFE and Ni (OH)₂ components can be embedded uniformly, were found.

Abstract: The binary Ni-Mo alloy coatings of high Mo content were obtained on a steel substrate by dc current electrodeposition from alkaline solutions of pH 7.5-9.0. The pyrophosphate baths contained nickel chloride as a source of nickel ions, and dihydrate sodium molybdate supplied molybdenum. The constant current electrodpeposition at the deposition current denisty of j_d = 30-240 mA cm^-2 was performed at 60°C. The physical and chemical properties of the obtained electrocoatings were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray fluorescence (XRF) methods. All obtained Ni-Mo alloys reveal the amorphous structure, and their chemical composition strongly depends on the operating parameters of electrodeposition. The maximal content of Mo was found to be 45 at.%. The complicated mechanism of the induced co-deposition of the Ni-Mo alloy, has been discussed.

Abstract: The object of this work was to obtain the Ni+MoS₂ composite electrocoatings by in situ co-deposition of molybdenum (IV) sulfide particles (< 2 μm) and nickel from a suspension plating bath. Physical and chemical characterization of the coatings was carried out using SEM, EDS, and XRD methods. The chemical composition of these coatings of a diphase structure (Ni, MoS₂) was found to be dependent on the current density and temperature of electrodeposition. The optimal electrochemical conditions for embedding of the maximum amount of 26.4 wt.% of MoS₂ into the crystalline nickel matrix, were experimentally determined. The co-deposition process of MoS₂ particles and metallic nickel was discussed based on the adsorption mechanism. Such porous Ni+MoS₂ composite coatings can be proposed as electrode material for hydrogen electroevolution.

Abstract: The Ni-Mo+MoO₂ composite coatings were obtained onto the steel substrate using an in situ co-deposition of a Ni-Mo alloy and MoO₂ powder particles maintained in suspension in the potassium pyrophosphate bath. To characterize the physical and chemical properties of the obtained coatings, SEM, EDS, and XRD methods, were applied. It was found that the co-deposited MoO₂ particles strongly influenced the properties of the Ni-Mo alloy coating. In comparison with the comparable Ni-Mo deposit containing 45 at.% of Mo, the presence of MoO₂ embedded into the composite coating diminished the content of Mo alloyed with Ni to 23 at.%. The electrodeposited Ni-Mo+MoO₂ composite coating obtained under proposed electrochemical conditions contained 25 at.% of MoO₂. The effect of the embedded MoO₂ as composite component on changes of the surface morphology and structure of the Ni-Mo binary alloy, was also discussed.

Abstract: The present work deals with the influence of sodium hypophosphite content in the plating bath on the chemical composition and structure of the obtained nickel electrocoatings. Electrodeposition of the Ni-P coatings was conducted under galvanostatic conditions at room temperature from the Watts type bath containing different amounts of sodium hypophosphite (0-30 g dm^-3). The chemical and physical characteristics of the obtained Ni-P deposits and comparable Ni coating, were performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) methods. It was found that the addition of sodium hypophosphite as amorphizator to the Ni-plating bath influences both the structure and chemical composition of the obtained Ni electrodeposits. With increase in the content of sodium hypophosphite in the bath, surface morphology of the amorphous Ni-P coatings becomes more developed what is of key-importance for electroevolution of hydrogen on such electrodes.

Abstract: Activity of electrode material is strongly dependent on the structure, therefore, amorphous Ni-P electrocoatings deposited from a Watts type bath on the carbon steel substrate, were subjected to thermal activation through their isothermal heating under argon protective atmosphere at the temperature of 400, 500 and 800°C. After such a heat treatment, the investigations of the structure change of the Ni-P electrocoatings were carried out using X-ray qualitative phase analysis, which revealed the effect of thermal activation on the phase composition of the obtained coatings. It was found that after each applied thermal activation, the occurence of diphase system in the coating was observed which was consisted of nickel crystallites and nickel phosphide crystallites of the type Ni₅P₂.

Abstract: The Ni-W alloy coatings and Ni+W composite deposits were prepared by the electrodeposition under the galvanostatic conditions at the deposition current density of j_dep = -300 mA cm^-2. The surface morphology and chemical composition of the coatings were examined using a scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. Phase composition investigations were conducted by X-ray diffraction (XRD) method. It was found that introduction of tungsten powder into nickel matrix allowed to obtain the Ni+W composite coating with very rough surface as compared with the smooth Ni-W alloy coating. Thus obtained Ni+W porous coating may be useful for the need of hydrogen technologies.

Abstract: The Ni-P and Ni-Co-P coatings were electrodeposited at the deposition current density of j_dep = -20 mA cm^-2. Thermal treatment of these coatings was conducted in air at 400^oC for 1 h. Scanning electron microscopy (SEM) was used for surface morphology characterization of the coatings. Phase composition was investigated by X-ray diffraction (XRD) method. Atomic absorption spectrometry (AAS) was applied to specify chemical composition of obtained coatings. It was found that introduction of Co into amorphous Ni matrix caused the surface development of the obtained deposit. The Ni-P coating revealed an amorphous structure. The Ni-Co-P coating was formed of the amorphous matrix and the amorphous alloy ingredient. Thermal treatment of the coatings allowed to obtain new multi-phase materials with slightly developed surface.