The paper presents research on evaluation of corrosion resistance of Ni-W alloy coatings subjected to heat treatment. The corrosion resistance was tested in 5% NaCl solution by the use of potentiodynamic polarization technique and electrochemical impedance spectroscopy. Characteristics of the Ni-W coatings after heat treatment were carried out using scanning electron microscopy, scanning Kelvin probe technique and X-ray diffraction. Suggested reasons for the improvement of properties of the heat treated Ni-W coating, obtained at the lowest current density value (125 mA∙cm⁻²), are the highest tungsten content (c.a. 25 at.%) as well as the smallest and the most homogeneous electrochemically active surface area.

Polyaniline (PANI) was synthesized chemically with the modified rapid mixing protocol in the presence of sulfuric acid of various concentrations. A two-step synthetic procedure was utilized maintaining low-temperature conditions. Application of the modified rapid mixing protocol allowed obtaining a material with local ordering. A higher concentration of acid allowed obtaining a higher yield of the reaction. Structural characterization performed with Fourier-transform infrared (FTIR) analysis showed the vibration bands characteristic of the formation of the emeraldine salt in both products. Ultraviolet–visible light (UV–Vis) spectroscopy was used for the polaronic band and the p–p* band determination. The absorption result served to estimate the average oxidation level of PANI by comparison of the ratio of the absorbance of the polaronic band to that of the π–π* transition. The absorbance ratio index was higher for PANI synthesized in a more acidic solution, which showed a higher doping level for this polymer. For final powder products, particle size distributions were also estimated, proving that PANI (5.0 M) is characterized by a larger number of small particles; however, these particles can more easily agglomerate and form larger structures. The X-ray diffraction (XRD) patterns revealed an equilibrium between the amorphous and semicrystalline phase in the doped PANI. A higher electrical conductivity value was measured for polymer synthesized in a higher acid concentration. The time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis showed that the molecular composition of the polymers was the same; hence, the difference in properties was a result of local ordering.

Ni + W, Ni + W + Si and Ni + W + Mo + Si composite coatings were obtained by electrolytic codeposition of crystalline nickel from an electrolyte containing suspension of W, Mo and Si powders. These coatings were obtained under galvanostatic conditions, at the current density of j _{dep .} = 0.100 A cm ⁻² and at the temperature of 338 K. Chemical composition of obtained coatings was determined by energy dispersive X‐ray spectroscopy (EDS) method. The electrochemical activity of these coatings was studied in the process of hydrogen evolution reaction (HER) from 5 M KOH solution using steady‐state polarisation and electrochemical impedance spectroscopy (EIS) methods. On the basis of the results of EIS measurements, the rate constants of the HER as well as the surface roughness factor were determined. It was found that Ni + W + Mo + Si composite coatings are characterised by enhanced electrochemical activity toward hydrogen evolution as compared with Ni + W + Si and Ni + W coatings. The reason for this is connected with the presence of additional composite components (W, Mo, Si). Thus, obtained coatings may be useful in application as electrode materials for the hydrogen evolution reaction. Copyright © 2008 John Wiley & Sons, Ltd.