Cyclic voltammetry and spectroelectrochemical study of nickel and cobalt diphenyltetraazaannulene complexes

The absorption spectra. cyclic voltammetry and spectroelectrochemistry of [Ni(II)DPTAA] and [Co(II)DPTAA] (DPTAA = 6,13-diphenyldibenzo[b,i][1,4,8,11] tetraaza[14]annulene) complexes in DMF are reported in detail. The ligand oxidation is observed for [Ni(II)DPTAA] at +0.70 V vs. SCE whereas Ni2(+/+) occurs at - 1.60 V. For [Co(II)DPTAA], a ligand oxidation redox couple is seen at +0.56 V while the Co2+/+ and Co2+/3+ redox couples appear at -1.21 and +0.24 V, respectively. All observed redox couples are assigned to reversible one-electron processes on account of peak separations and scan-rate dependency. These processes were further investigated by spectroelectrochemistry for [Co(II)DPTAA]. For [Co(II)DPTAA], axial ligation of pyridine was found to shift the Co2+/3+ redox couple more negative. while the ligand oxidation was shifted to more positive potentials. From a spectrophotometric titration of [Co(II)DPTAA] with pyridine an equilibrium constant, K-f, was determined for the binding of pyridine to [Co(II)DPTAA]. This was found to be 10.2 dm(3) mol(-1), slightly lower than that of [Co(II)TAA], indicating the influence of the phenyl groups. From this value and shifts in the Co2+/3+ redox couple upon ligation, an equilibrium constant for the binding of pyridine to [Co(III)DPTAA], K'(f), was found to be 5.06 x 10(6) dm(3) mol(-1). (c) 2007 Elsevier B.V. All rights reserved.

Crystallization and phase transformation behaviour of electroless nickel-phosphorus deposits with low and medium phosphorus contents under continuous heating

Electroless nickel-phosphorus deposits with 5-8 wt% P and 3-5 wt% P were analysed for the effects of continuous heating on the crystallization kinetics and phase transformation behaviour of the deposits. The as-deposited coatings consist of a mixture of amorphous and microcrystalline nickel phases, featuring in their X-ray diffraction patterns. Continuous heating processes to 300C-800C at 20C/min were carried out on the deposits in a differential scanning calorimetric apparatus. The subsequent X-ray diffraction analyses show that the sequence of phase transformation process was: amorphous phase + microcrystalline nickel, f.c.c. nickel + Ni3P stable phases. Preferred orientation of nickel {200} plane developed in the deposits after the heating processes. Differential scanning calorimetry of the deposits indicates that the crystallization temperatures increased with decreasing phosphorus content, and increasing heating rate. Crystallization activation energies of the deposits (230 and 322 kJ/mol, respectively) were calculated using the peak temperatures of crystallization process, from the differential scanning calorimetric curves at the heating rates ranging from 5 to 50C/min. It was found that the deposit with lower phosphorus content has higher activation energy.

Growth and properties of gold and nickel nanorods in thin film alumina

Arrays of nickel and gold nanorods have been grown on glass and silicon substrates using porous alumina templates of less than 500 nm thickness. A method is demonstrated for varying the diameter of the nanorods whilst keeping the spacing constant. Optical extinction spectra for the gold nanorods show two distinct maxima associated with the transverse and longitudinal axes of the rods. Adding small quantities of oxygen to the aluminium before anodization is found to improve the sharpness of the extinction peaks. The spectral position of the longitudinal peak is shown to be sensitive to the nanorod diameter for constant length and spacing. For the nickel nanorods it is shown that the magnetic properties are governed by both interactions between the wires and shape anisotropy.

Energy levels and radiative rates for transitions in Mg-like iron, cobalt and nickel

Energy levels and radiative rates for electric dipole (E1) transitions among the lowest 141 levels of the (IS2 2s(2) 2P(6)) 3l(2) , 3l3l', and 3l4l configurations of Fe XV, Co XVI, and Ni XVII are calculated through the CIV3 code using extensive configuration-interact ion (CI) wavefunctions. The important relativistic effects are included through the Breit-Pauli approximation. In order to keep the calculated energy splittings close to the experimental values, we have made small adjustments to the diagonal elements of the Hamiltonian matrices. The energy levels, including their orderings, are in excellent agreement with the available experimental results for all three ions. However, experimental energies are only available for a few levels. Since mixing among some levels is found to be very strong, it becomes difficult to identify these uniquely. Additionally, some discrepancies with other theoretical work (particularly for Ni XVII) are very large. Therefore, in order to confirm the level ordering as well as to assess the accuracy of energy levels and radiative rates, we have performed two other independent calculations using the GRASP and FAC codes. These codes are fully relativistic, but the CI in the calculations is limited to the basic (minimum) configurations only. This enables us to assess the importance of including elaborate Cl for moderately charged ions. Additionally, we report results for electric quadrupole (E2), magnetic dipole (MI), and magnetic quadrupole (M2) transitions, and list lifetimes for all levels. Comparisons are made with other available experimental and theoretical results, and the accuracy of the present results is assessed. (c) 2007 Elsevier Inc. All rights reserved.

Scanning electron microscopy study of microstructural evolution of electroless nickel-phosphorus deposits with heat treatment

This paper follows previous X-ray diffraction work on crystallisation and phase transformation of electroless nickel–phosphorus deposits, concentrating on microstructural changes. Amorphous or nanocrystalline coatings, depending on their phosphorus content, were heat treated at temperatures between 100 and 500 °C for 1 h. Changes in microstructure after the heat treatment were examined using high-resolution field emission scanning electron microscope. Crystallisation and grain growth effects are observed, as well as some inherent defect structures in the coatings and their changes. These are compared with the previous X-ray diffraction work and in general, good agreement is observed. The complementary strength and weakness of the different characterisation techniques are discussed.

Thermal study of selectively plated nickel sulfamate coatings

Nickel sulfamate solution was applied to mild steel substrates by the process of selective plating. The coated samples were heated to temperatures in the range of 50–1000 °C. Thermal analysis, X-ray diffraction and microscopy techniques were used to investigate the effect of secondary heating on the microstructure, mechanical properties and the composition of the surface coatings.

The microscopy analysis showed that the secondary heating caused diffusion within the coating itself and diffusion between the coating and the substrate as concentrations of iron increased in the coating and nickel appeared in the substrate. This diffusion redistribution also caused a phase transformation in the coating as NiO formed on the surface when the coating was heated in a furnace fitted with a nitrogen flow. However this transformation was found not to occur when the coating was heated in a sealed helium environment. Layer and grain growth occurred as temperature increased with the grains taking their preferred orientation as they were heated.

The surface hardness was found to initially rise up from 565 HV to 600 HV when heated to 200 °C. After 200 °C the surface hardness decreased in two stages before falling to 110 HV by 1000 °C. During tensile testing the coated samples performed marginally better in tension than the uncoated samples, however the temperatures used were not elevated high enough to show any real degradation during the tensile testing of the nickel coating that was shown during hardness testing and the microscopy analysis