Surface Review and Letters

In this paper, a new method for fabricating Ni₈₀Fe₂₀/Cu composite wires is presented. A series of samples were prepared by alternating the rotating direction of the Cu wire during RF magnetron sputtering. In order to keep the overall coating thickness of all the samples constant, the alternating intervals and rotating period of each sample during sputtering were varied. As the rotating period increased, the samples showed different magneto-impedance profiles. Experimental results indicated that there was a critical thickness for single sputtered layer which the MI ratio was significantly enhanced at a relatively low driven current frequency. Qualitative discussion on these phenomena was explained in terms of exchange interaction and electromagnetic interactions.

Mesoporous carbons prepared using a templating method under different carbonization temperatures are sulfonated with concentrated H₂SO₄. Without the moving of silica template carbon–silica composites were prepared, which can maintain the pore structure well during sulfonation reaction process. The resultant samples are characterized using nitrogen adsorption, transmission electron microscope, field-emission scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and elemental analysis techniques. The catalytic performances of the sulfonated carbons and composites are evaluated by esterification reaction of methanol with acetic acid. The results show that a low-temperature carbonization process is favorable for improving the reaction conversion of acetic acid. In addition, the sulfonated carbon–silica composites show a higher acetic acid conversion than the sulfonated mesoporous carbons.

A theoretical model is presented for the study of magnons heat transfer across an integrated nanostructure acting as interface material between two ultrathin Heisenberg ferromagnetic films. This is done by calculating the transmission rates of the spin wave modes through the consideration of the magnon group velocity modification in the system. The group velocities are calculated explicitly for all propagating frequencies and spin wave incidence angles. The matching method is used with nearest neighbor ferromagnetic interactions to calculate the coherent transmission coefficients for magnons incident on the nanostructure boundaries. They are investigated for different nanostructure thickness over the entire propagating frequency range of the system, in order to calculate the heat transport across the nanostructure. The model is applied to a system of three Iron ferromagnetic atomic layers and Gadolinium integrated nanostructure. The thermal conductivities are numerically calculated for individual magnon modes of the system. The results yield an understanding of the relationship between the magnons thermal conductivity of the system and the structural configuration of the integrated nanostructure.

The paper presents the results of the investigation performed on a stand for model testing of the friction pair like a car disc brake. The tests were performed for the mating operation of a frictional node with the dosage of hard abrasive particles into the friction zone. Based on the observation of the phenomena in the friction zone and the analysis of the parameters describing operating conditions of a frictional node, physical models of the frictional node cooperation in the presence of hard abrasive particles have been proposed. During the tests, using the transparent material of a friction cover plate and a fast recording camera, a visual analysis of the material transfer in the friction zone was done. It allowed to positively verifying the proposed physical models of the frictional node cooperation in the presence of hard abrasive particles.

We investigate experimentally the interference in far-field radiation of two contra-propagating evanescent fields using a conventional optical microscope. A laser beam illuminates a glass-air interface under total internal reflection condition and through the proper setup a double evanescent illumination was produced. The evanescent fields radiate from the surface into the far-field domain due to small surface scatterers. Thus, coherent interference is produced in the far-field region which is correlated with the relative positions of the evanescent illumination sources. Finally, the above-described could be considered as a device for high accuracy micro-scale measurements as well as a direct visualization method of evanescent phenomena.

The interfacial surface activity of a protein, ovalbumin (OVA) at bare air/water interface in presence and also in absence of electrolyte (KCl) in subphase has been investigated. The surface activity was measured as a function of time. It has been found that, the presence of KCl in aqueous subphase enhances the adsorption rate of the protein. The changes of area/molecule, compressibility, rigidity and unfolding of OVA are trivial up to 10 mM KCl concentration. These properties of OVA, above 10 mM KCl concentration are significant and have been explained in the perspective of DLVO theory and many-body ion–protein dispersion potentials. The presence of high concentration of electrolyte increases the β-structure of OVA, resulting into larger unfolding as well as larger intermolecular aggregates. The overall study indicates that KCl perturbs the OVA monolayer.

Zn–1.26 wt.% Al alloy was directionally solidified upward with a constant growth rate (V = 16.6 μm/s) in a wide range of temperature gradients (G = 1.94–5.15 K/mm) and with a constant temperature gradient (G = 5.15 K/mm) in a wide range of growth rates (V = 8.3–500 μm/s) with a Bridgman-type directional solidification furnace. Microstructure parameters, the primary dendrite arm spacing (λ₁), secondary dendrite arm spacing (λ₂) and dendrite tip radius (R), were measured and expressed as functions of G and V by using a linear regression analysis method. It was found that the values of λ₁, λ₂ and R decrease with increasing values of V and G. The experimental results were compared with the main predictive theoretical and experimental works for dendritic spacings.

The temperature field due to laser-induced discharge surface strengthening (LIDSS) has significant influence on the microstructure transformation and also the formation quality of discharge pit. A transient axisymmetric thermal model is developed to estimate the temperature distribution during LIDSS based on Fourier heat conduction equation. In the model, a Gaussian heat input distribution is assumed; temperature-dependent material properties are applied and the latent heat of fusion and vaporization is calculated on an enthalpy method. As an application, we use this model to compute the temperature field during the process of tungsten tool electrode machining 1045 steel workpiece and find that the computational results are well consistent with the experimental data.

Al-Cu alloy castings are obtained using centrifugal casting. The regularity of mechanical property gradient distribution of Al-Cu alloy castings with the same centrifugal radius at different positions is investigated. The result shows that the tensile strength, yield strength, elongation and microscope hardness exhibit the following gradient distribution characteristic — high on both sides and low on the center. The trend of mechanical property gradient distribution of Al-Cu alloy increases with the increase in the rotation speed. Moreover, the mechanical properties of casting centerline two sides have asymmetry. The reason is that the grain size of casting centerline two sides and Al₂Cu phase and Cu content change correspondingly.

The effect of two pyridin-pyrazol derivatives, N-[(3,5-dimethyl-1H-pyrazol)methyl]pyridine-2-amine (TB5) and 5-bromo-N-[(3,5-dimethyl-1H-pyrazol)methyl]pyridine-2-amine (TB6), newly synthesized, on the corrosion of mild steel in 1.0 M HCl was investigated by weight-loss and various electrochemical techniques. Results obtained reveal that these pyridin-pyrazol derivatives perform excellently as corrosion inhibitors for mild steel in hydrochloric solution. Polarization curves showed that both TB5 and TB6 are mixed-type inhibitors in acidic medium. A kinetic study of steel in uninhibited and inhibited acid for TB6 was also achieved to provide suitable investigations on corrosion inhibition mechanism in 1.0 M HCl solution. The effect of concentration and temperature on the inhibiting efficiency has been examined. The thermodynamic parameters for both dissolution and adsorption processes were calculated and discussed for TB6. The adsorption of inhibitor TB6 on the mild steel surface obeys the Langmuir adsorption isotherm equation.

We apply a first-principles molecular-dynamics method based on the density functional theory to calculate several initial configurations of an O₂ molecule adsorbed on a Si(001) surface. The bonding processing, adsorption energy, dynamic track, and diffusion coefficient are investigated. The results indicate that the adsorption process may be divided into four stages: physical adsorption, chemical adsorption early stage, chemical adsorption late stage, and the superficial stable state. The Si=O structure, the Si–O–Si surface oxygen-bridge structure, and the Si–O–Si oxygen-bridge structure where oxygen atoms are inserted into the backbonds between the surface and the second layer of silicon atoms in the stable adsorption structures, are beneficial to the formation of the silica tetrahedral structure. We conclude that the remarkable difference between the diffusion coefficients during the physical adsorption stage leads to different diffusion paths, which results in the formation of two concomitant stable structures in the early process of silicon surface oxidation.