S. Armyanov

Crystallographic structure and magnetic properties of electrodeposited cobalt and cobalt alloys

The connection between plating conditions and elements of the structure (phase composition, texture and its perfection, grain size) is considered first and then is discussed the correlation between structure parameters and magnetic properties. The structure parameters’ influence on magnetic properties is explained in light of the contribution of different types of magnetic energy. The dependence of magnetic properties of cobalt layers on the phase composition and texture perfection is demonstrated using specific X-ray methods for their quantitative determination for the case of axial texture presence. The hierarchy of the structural parameters’ effect on the magnetic properties of electrodeposited cobalt is outlined. The influence of internal stress (caused by hydrogen desorption) on the magnetic properties of electrodeposited cobalt is illustrated in case, where the structure remains unchanged. The data for the calculated (on the base of the existing axial texture) and the measured values of magnetostriction of Co‐Fe coatings are compared. The dependence of coercivity on Co‐Ni alloy composition is explained by assuming simultaneous action of several structure parameters. A possible influence of interparticle separation along the grain boundaries on the magnetic properties of electrodeposited films is briefly considered.

Auger Electron Spectroscopy Element Profiles and Interface with Substrates of Electroless Deposited Ternary Alloys

Electroless NiMeP alloys (Me = Cu, Sn, Sb) with high phosphorus content (∼11 weight percent) and a low weight percent of the third component (Me) have been plated in acidic baths onto aluminum, iron, and nickel. Scanning Auger electron spectroscopy is applied to study the element profiles and interface with the substrates. Generally the third component follows the profiles of Ni and P, which proves the alloy formation. A surface enrichment in the third element (Me) is observed in all cases. It is very strong when tin is the third component and very weak in the case of antimony, which is more or less uniformly distributed through the thickness. Decrease of surface concentration of phosphorus is noticed when NiSbP is plated. In Cu profiles three different zones exist : a surface enrichment zone, a groove (a zone of reduced concentration), and a plateau (a zone of almost constant concentration). There is no enrichment in the third element at the interface with the substrate for all three alloys and three substrates. At the interface with aluminum prepared for electroless plating with double zincate pretreatment complete dissolution of the zincate layer has been established.

Electroless deposited Ni-Re-P, Ni-W-P and Ni-Re-W-P alloys

Coatings of electroless Ni–W–P, Ni–Re–P and Ni–W–Re–P alloys were plated in alkaline citrate baths containing amino alcohols, but not free ammonia ions. The reference Ni–P alloy was used as an intermediate layer in the sandwich: Ni–Me–P/Ni–P/substrate. An extremely homogeneous thickness distribution of all alloy components was found by applying scanning Auger electron spectroscopy (SAES(. The inclusion of refractory metals at the expense of nickel and without substantial change in phosphorus content was established. A non-oxidized state of the codeposited Re and W in Ni–W–P, Ni–Re–P and Ni–W–Re–P alloys was determined by means of X-ray photoelectron spectroscopy examination, as well as by SAES profiles, revealing the absence of oxygen throughout the coatings. All alloy films are amorphous and paramagnetic.

Incorporation of Zinc in Electroless Deposited Nickel-Phosphorus Alloys I. A Comparative Study of Ni-P and Ni-Zn-P Coatings Deposition, Structure, and Composition

The impact of zinc incorporation on the chemical composition of electroless Ni-Zn-P coatings and the elements distribution through the thickness was studied. Ni-Zn-P alloy was deposited on various metal substrates (Al, Fe, Au) with and without electroless Ni-P underlayer. The employed bath formulation and the substrates with a Ni-P intermediate layer allowed direct comparison between the binary Ni-P and Ni-Zn-P alloy coatings. A reduction in phosphorus content and deposition rate due to zinc inclusion was observed. Some physical characteristics (morphology, structure, magnetic properties) of Ni-Zn-P coatings were assessed in parallel with those of Ni-P. The localization of Zn mainly at the grain boundaries together with P was proved by transmission electron microscopy combined with energy dispersive X-ray analysis system, The particular role of the steel substrate is discussed as a source of iron, subsequently included in electroless Ni-P and Ni-Zn-P coatings.

Magnetothermal study of nanocrystalline particle formation in amorphous electroless Ni–P and Ni–Me–P alloys

Abstract The microstructure of amorphous Ni–P and Ni–Me–P materials and especially its change during the heat treatment is of great importance for their magnetic, mechanical and corrosion behavior. A new magnetic phase analysis method (magnetothermal) is presented that reveals the precipitation of nanoparticles with strong magnetic properties during phase transformation upon heat treatment. It is applied to electroless Ni–P, Ni–Cu–P and Ni–Sn–P amorphous alloys. The results acquired by this method are compared with data obtained by differential scanning calorimetry, as well as by microhardness measurements using identical heat treatment in all three cases. Due to the high sensitivity of the magnetothermal method a more detailed picture of the precipitation processes in Ni–P alloys is obtained and the new information is discussed. Magnetothermal measurements reveal several stages of precipitation of a phase with strong magnetic properties. This phase is Ni in the Ni–P alloy, and Ni(Me) solid solution in the Ni–Me–P alloys. Though Sn has a stronger effect on the Ni magnetization, Cu is more effective in preventing the appearance of high magnetization in a thermally treated Ni–Cu–P alloy. This is due to Cu incorporation in Ni particles in a quantity above four times larger than Sn.

Crystalline and Amorphous Electroless Co-W-P Coatings

Electroless deposition onto polycrystalline (Cu, Au) and amorphous (Ni-P) substrates was applied to prepare Co-W-P coatings of two types: crystalline (hexagonal close packed, hcp), with low phosphorus content about 2.4-2.7 atom %, and amorphous, with P concentration within 7.4-8.3 atom %. Tungsten content varied typically in the narrow range of 2.9-3.7 atom % in both types of coatings. Atomic force microscopy revealed substantial difference in their morphology. Polycrystalline Co-W-P coatings consist of grains of stacked plates (lamellas), confirmed by transmission electron microscopy also. Amorphous films are smoother and uniform. The crystalline structure promotes the surface oxidation to a higher extent than the amorphous structure, as shown by the X-ray photoelectron spectroscopy (XPS). Auger electron spectroscopy depth profiles display oxidation, smoothly diminishing toward the inside of the crystalline films. Amorphous coatings are oxidized only at the surface. Inside both types of coatings, however, all alloy components are in nonoxidized form, according to XPS data. Differential scanning calorimetry (DSC) studies of amorphous coatings revealed three transformation peaks, ascribed to a crystallization of hypoeutectic alloy and a transition of Co-based hcp phase into face-centered cubic. Magnetic properties variation with temperature is in agreement with DSC results.

Thermal stability of electroless NiMeP amorphous alloys

The thermal stability and the preservation of paramagnetic state of amorphous electroless NiP alloys are important for many industrial applications. The addition of third component (Me = Cu, Sn, or Sb) to NiP alloy should reduce the magnetic moment of precipitated ferromagnetic phase. The influence of Me on the thermal stability of ternary alloys is studied. Using differential scanning calorimetry, analysis of the crystallization kinetics is carried out. The remanence after annealing at different temperatures is presented.

Morphology, Structure and Photoelectrocatalytic Activity of TiO2 / WO3 Coatings Obtained by Pulsed Electrodeposition onto Stainless Steel

A simple two-step pulsed electrodeposition/ electrosynthesis technique is employed for the preparation of a bicomponent photocatalyst, TiO2/WO3, onto metal substrates. TiO2 can be activated under UV light illumination and is well known for its water detoxification capabilities. The coupling between this wide band-gap semiconductor with a suitable narrow band-gap one, WO3, is used for effective separation of the photogenerated charge carriers. Besides the reduced surface recombinetion due to directional charge transfer, the combination with the visible light (Vis)-activated WO3 entails an extended photoactivity towards Vis wavelengths. In addition, the photocatalytic decomposition of organic water pollutants at TiO2/WO3 layers supported on conductive substrates can be further enhanced by applying a positive bias in an appropriate electrochemical cell. Drawing the electrons away from the surface through the external circuit reduces surface recombination rates of photogenerated electron-hole pairs. Recently, bilayer TiO2/WO3 photocatalysts were prepared onto stainless steel substrates by continuous cathodic electrodeposition of WO3 followed by TiO2 electrosynthesis [1, 2]. Their photoelectrocatalytic efficiency is very promising and superior to both their single-component counterparts. Also, there have been indications of the considerable impact of composition, morphology and structure on photoelectrocatalytic activity [3]. This implicates the necessity for appropriate monitoring and design of these factors. By applying a consecutive pulsed electrodeposition/electrosynthesis method for WO3 and TiO2, a favorable modification of the electronic properties at the TiO2-WO3 junction and an increased catalyst surface area has been sought. The morphology, structure and related composition distribution of the pulsed-deposited films onto metal substrates have been characterized by high resolution Field Emission SEM (FE SEM) (Fig. 1), SEMEDS and Raman spectroscopy. The photocurrents at photoanodes with various loadings, structure and morphology have been evaluated in the presence and absence of the model pollutants Na-oxalate and 4chlorophenol under UV and Vis light illumination. Similar to the case of continuous electrodeposition [3], a trend was observed of the impact and the need for optimization of the TiO2/WO3 loading ratio, surface morphology, structure and composition distribution to design high-performance photocatalysts. The performance for bulk photo-decomposition of 4-chlorophenol has been evaluated at photoanodes WO3 and TiO2/WO3 prepared by continuous electrodeposition and compared with that at pulsed-plated TiO2/WO3. Long-term photoelectrolysis at constant potential was applied, using spectrophotometry to monitor the variation of the pollutant concentration.

Pt-Ni carbon-supported catalysts for methanol oxidation prepared by Ni electroless deposition and its galvanic replacement by Pt

Pt–Ni particles supported on Vulcan XC72R carbon powder have been prepared by a combination of crystalline Ni electroless deposition and its subsequent partial galvanic replacement by Pt upon treatment of the Ni/C precursor by a solution of chloroplatinate ions. The Pt-to-Ni atomic ratio of the prepared catalyst has been confirmed by EDS analysis to be ca. 1.5:1. No shift of Pt XPS peaks has been observed, indicating no significant modification of its electronic properties, whereas the small shift of the corresponding X-ray diffraction (XRD) peaks indicates the formation of a Pt-rich alloy. No Ni XRD peaks have been observed in the XRD pattern, suggesting the existence of very small pockets of Ni in the core of the particles. The surface electrochemistry of electrodes prepared from the catalyst material suggests the existence of a Pt shell. A moderate increase in intrinsic catalytic activity towards methanol oxidation in acid has been observed with respect to a commercial Pt catalyst, but significant mass specific activity has been recorded as a result of Pt preferential confinement to the outer layers of the catalyst nanoparticles.

Pretreatment of Al-Mg alloys for electrodeposition by immersion zinc and electroless nickel

Abstract Electron microscopy and X-ray methods were used to investigate the various stages of zincate treatment and electroless Ni-P deposition upon Al-Mg (4 wt.% Mg). It is shown that the roughening of the surface of the alloy during this treatment enhances the attachment of the Ni-P coating. No evidence was found within the sensitivity of the applied methods that new phases which could influence adhesion are formed during the annealing at 180 °C at the Al-(Ni-P) interface. It is proved that annealing affects the desorption of hydrogen included in the Ni-P layer durings its formation. Therefore annealing may be substituted by an adequate pause before the next coating is deposited.