The corrosion resistance of three different TiN coatings on iron (single TiN layer, Ti/TiN bilayer and Ti/TiN/Ti/TiN multilayer) subjected to a salt (ammonium sulphate and sodium chloride) fog spray (Prohesion) test has been investigated by means of x‐ray photoelectron spectroscopy (XPS). The relative intensities of the Fe 2p and O 1s signals in the XPS spectra of the corroded samples increase with their extent of degradation. The results show that the corrosion resistance of these coatings decrease in the order bilayer>multilayer>single layer. Copyright © 1999 John Wiley & Sons Ltd.

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In the current work, we studied dc conductivity and its relaxation in glycerol-plasticized starch membranes at various concentrations using impedance spectroscopy in frequency ranges between 20 Hz and 3 MHz and temperature ranging from 303 K to 423 K. We observed thermally activated dc conductivity following the Arrhenius model: ln s ¼ ln s o À E s =k B T , where the activation energy, E σ , diminished as glycerol increased. Non-Debye relaxation phenomena were observed in the actual portion of the conductivity as a function of the frequency, s 0 w ð Þ $ w n n % 1 ð Þ. Also, the symmetry of the relaxation peak observed in the imaginary part of the electric module remained unaltered as a function of temperature and glycerol content in the membranes, corresponding to a constant exponent, β=0.80±0.02, if we assume the ФðtÞ ¼ exp À t=t ð Þ b h i correlation function in the ionic transport. The angular velocity, ω p , registering the maximum peak, M ″ max , was fitted to the Arrhenius model, ln w ¼ ln w o À E w =k B T , finding great similarity between E ω and E σ values for each sample, indicating that the corresponding ionic processes have the same origin, in other words, due to the correlated jump of the charge carriers. The independence found between n and β indicates that the correlation processes or cooperative effects among ions in these materials deviate from the empirical description expressed by Ф(t). However, these processes were identical when varying temperature glycerol content in the membranes, as suggested by the M″(ω) spectra.

The corrosion behavior in humid SO2-polluted atmospheres of three different TiN coatings on iron [single layer TiN (1000 nm), bilayer Ti(100 nm)/TiN(1000 nm) and multilayer Ti(100 nm)/TiN(100 nm)/Ti(100 nm)/TiN(100 nm)] have been investigated by means of x-ray photoelectron spectroscopy. Only the single layer coating shows some degradation in low concentration (0.001% v/v) SO2 atmospheres after 14 days of exposure, the other two coatings remaining stable. Exposure to higher SO2 concentration (0.04% v/v) for 7 days results in the total degradation of the single layer coating. Exposure to this latter atmosphere for 14 days brings about a considerable degradation of the bilayer and multilayer coatings, the results showing that the multilayer coating, even with the lowest total thickness, presents the highest resistance against these corrosion conditions. Corrosion of the TiN coatings results in the formation of TiO2 and several N species [probably of the type (NH4)2SO4 and species containing N–O bonds]. The degradation of the coatings results in the corrosion of the underlying iron. Fe2+ sulphates and sulphites, as well as FeOOH, are the main iron corrosion products.

A b s r a c t. Effects of temperature and glycerol concentration on rheological properties of potato starch solutions were investigated. The flow behaviour (shear stress against shear rate) was fitted to various models: power law, Herschel-Bulkley, Bingham, modified Bingham and Casson models. However, it was found that the Herschel-Bulkley model describes better the flow behaviour observed at various temperatures and glycerol concentrations, for flow behaviour index values between 0.44 and 0.78, typical of pseudoplastic solutions. The effect of glycerol concentration on each of the fitting parameters for Herschel-Bulkley model was well modelled by a second-degree polynomial at various temperatures. The simultaneous influence of glycerol concentration and temperature on shear stress could be represented empirically by a seconddegree polynomial function that includes linear coupling between concentration and temperature. Finally, the variation of the consistency coefficient with both temperature and glycerol concentration was well described by an exponential expression, with an activation energy value of 2.78 kJ mol -1 . The results indicate that both glycerol content and temperature have the effect of diluting potato starch solutions.K e y w o r d s: glycerol, potato starch solutions, pseudoplastic behaviour, rheological models