Jenia Georgieva

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.

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.

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.

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.

Gas Phase Photoelectrochemistry in a Polymer Electrolyte Cell with a Titanium Dioxide/Carbon/Nafion Photoanode

Mixtures of Ti0 2 and carbon powders are tested as photoanodes in mini-photoelectrochemical cells based on Nafion electrolyte-impregnated microporous membranes. The composite TiO 2 + C working electrode is formed onto one face of the membrane (where a Ag/AgCl reference electrode is also adhered), whereas a stainless steel mesh counter electrode is attached to its opposite face. Photovoltammetry and constant potential photoamperometry carried out under UV-A illumination in the presence of water and methanol vapors result in well-defined photoelectrochemistry, characteristic of water and methanol photo-oxidation, and point to the possibility of scaling up similar devices to be used in electrically enhanced photocatalytic air treatment.

Carbon-supported Pt(Cu) electrocatalysts for methanol oxidation prepared by Cu electroless deposition and its galvanic replacement by Pt

Bimetallic Pt–Cu carbon-supported catalysts (Pt(Cu)/C) were prepared by electroless deposition of Cu on a high surface area carbon powder support, followed by its partial exchange for Pt; the latter was achieved by a galvanic replacement process involving treatment of the Cu/C precursor with a chloroplatinate solution. X-ray diffraction characterization of the Pt(Cu)/C material showed the formation of Pt-rich Pt–Cu alloys. X-ray photoelectron spectroscopy revealed that the outer layers are mainly composed of Pt and residual Cu oxides, while metallic Cu is recessed into the core of the particles. Repetitive cyclic voltammetry in deaerated acid solutions in the potential range between hydrogen and oxygen evolution resulted in steady-state characteristics similar to those of pure Pt, indicating the removal of residual Cu compounds from the surface (due to electrochemical treatment) and the formation of a compact Pt outer shell. The electrocatalytic activity of the thus prepared Pt(Cu)/C material toward methanol oxidation was compared to that of a commercial Pt/C catalyst as well as of similar Pt(Cu)/C catalysts formed by simple Cu chemical reduction. The Pt(Cu)/C catalyst prepared using Cu electroless plating showed more pronounced intrinsic catalytic activity toward methanol oxidation than its counterparts and a similar mass activity when compared to the commercial catalyst. The observed trends were interpreted by interplay between mere surface area effects and modification of Pt electrocatalytic performance in the presence of Cu, both with respect to methanol oxidation and poisonous CO removal.

Electroless Deposition of Ni–Sn–P and Ni–Sn–Cu–P Coatings

The surface morphology and the elemental distribution of low- and high-tin Ni-Sn-P coatings have been investigated. It is shown that in low-tin Ni-Sn-P coatings there is a uniform distribution of the alloy components, both on the surface and through the thickness. The main mechanism of electroless alloy deposition in this case is based on the well-known hypophosphite oxidation as a source of electrons for the metals (Ni and Sn) and phosphorus reduction. In high-tin coatings, a nonuniform distribution of the components is observed, both on the surface and through the coating thickness. Three-dimensional areas enriched in tin and impoverished in Ni and especially in P have been observed using scanning electron microscopy with energy-dispersive X-ray spectroscopy, scanning Auger electron spectroscopy, and Auger electron spectroscopy. The disproportionation reaction of Sn(II) is suggested as being predominant over the hypophosphite oxidation in these three-dimensional areas and is responsible for their formation. The introduction of copper in the solution is giving an additional opportunity to reveal the role of the oxidation of Sn(II) into Sn(IV) as a source of electrons.

TiO2/WO3 photoanodes with enhanced photocatalytic activity for air treatment in a polymer electrolyte cell

The application of electrochemically enhanced photocatalysis in air treatment using a Nafion-based photoelectrochemical cell and TiO2/WO3 photoanodes for organic vapor photooxidation under both UV and visible light irradiation is briefly presented. In that direction, the obtained results regarding the preparation and characterization of the TiO2/WO3 photoanodes with enhanced photocatalytic activity are reviewed. Particular emphasis is given in the comparison of the photocatalytic behavior of bilayer TiO2/WO3 coatings, electrosynthesized on stainless steel mesh and powder C + mixed (WO3 + TiO2) photoanodes. The advantages of using a high surface area C + mixed (WO3 + TiO2) powder catalysts as photoanodes against their plain TiO2 + C and WO3 + C analogues are discussed.

Factors Affecting the Electroless Deposition of Ni-Cu-P Coatings

Because of the numerous usual and new applications of the electroless amorphous Ni-Cu-P alloys aiming for improvement of Ni-P properties, it is worth achieving adequate empirical modeling of the electroless Ni-Cu-P deposition process. It will enable the estimation of the effect of pH and complexing agents on the deposition rate, phosphorus and copper content. For this purpose, a statistical technique is selected: a full-effect factorial design (FD) of a planned experiment with three factors at two levels of the process variables. This FD experiment allows observation of the effects of each factor at different levels of the other variables, as well as the interactions between these factors. As a result, it was established that the deposition rate and copper content in the alloy are affected the most powerfully by pH and citrate concentration. All obtained regression models include interactions between the variables.

New Features in Electroless Deposition of Ternary Coatings on the Base of Ni-P and Co-P

Abstract The new features in the electroless (autocatalytic) deposition, structure and properties of Ni-Cu-P, Ni-Sn-P, Ni-Zn-P, Ni-W-P, Co-W-P, and Co-Re-P as well as the quaternary coatings Ni-Sn-Cu-P, Ni-W-Re-P, and Co-Re-Ni-P established in the Institute of Physical Chemistry of the Bulgarian Academy of Sciences (IPC BAS) are reviewed. The role of disproportionation reactions of Cu(I), Sn(II) and Re(VI) during electroless deposition of Ni-Cu-P, Ni-Sn-P and Co-Re-P is considered. The data about the localization and chemical state of Zn, W and Re are presented. The influence of Cu and Sn added to high P (> 10 wt. %) Ni-P coatings on the thermal stability of their amorphous state is illustrated. A comparison of the corrosion resistance of Ni-Cu-P and Ni-Sn-P with that of Ni-P with the same quantity of phosphorus is given. The application of Ni-Cu-P in a hybrid multilayer with TiN is demonstrated.