[en] The influence of combination of Cu and Sn on pitting resistance of ultra-purified medium chromium ferritic stainless steel in 3.5 wt.% NaCl at 25°C was investigated by using electrochemical method. The results show that there is synergy effect between Cu and Sn, and the strong interaction between Cu and Sn in ferritic stainless steels clearly affects their pitting corrosion behaviour in 3.5% NaCl. A mechanism of the synergy of Cu and Sn was discussed. (paper)

[en] The dynamic compressive and static normal stresses of magnetic powders (MPs) with the constant volume squeezed between two parallel plates were experimentally studied. The compressive stress increased in a power law as the gap distance decreased, with an exponent range of −0.73 (0.04 T) to −2.63 (0.77 T). The values of the scale factor to normalize the compressive curves were mainly dominated by the applied magnetic field. The compressive behavior of the MPs showed a less significant velocity effect and initial gap distance effect than those of the magnetorheological (MR) and electrorheological (ER) fluids because of the absence of a host liquid. The compressive stress was generated by the serious particle aggregation, which was induced by a magnetic field and friction during compression. This study is designed to further the understanding of the behavior of smart ER/MR materials and the application of MP actuators in squeeze mode. (technical note)

[en] The dual-color laser action from the Rh6G solution with TiO₂ scattering particles is investigated by solving Maxwell’s equations and rate equations of electronic population simultaneously. A one-dimensional (1D) dispersive model is proposed to explain the experiment results. The results indicate that, although the dispersion in optical domain is relatively small, the dispersion for both gain materials and scattering particles has significant influence on modes of random lasing, which lead to more lasing modes and lower spectral intensity. (paper)

[en] Two different kinds of FePO₄ : amorphous FePO₄ and crystalline FePO₄ , were synthesized as a precursor to synthesize LiFePO₄ / C. The crystalline FePO₄ was obtained by treating amorphous FePO₄ with phosphoric acid refluxing. Inductively coupled plasma-atomic emission spectrometry was used to evaluate the impurity content. The obtained materials were characterized by chemical analysis, scanning electron microscopy and X-ray diffraction. The results showed that the performance of LiFePO₄ / C synthesized by crystalline FePO₄ is significantly better than when LiFePO₄ / C is synthesized from amorphous FePO₄ . The capacity retention and capacity fade of LiFePO₄ / C synthesized from crystalline FePO₄ was 70.9% at − 20 ℃ and 0.012% per cycle after 150 cycles at 1 C, respectively. The better performance from using crystalline precursor resulted from a more uniform powder with fewer crystalline defects and impurities. (author)

[en] The rheological properties of magnetic powders (MPs) excited by magnetic fields under parallel-plate shear were experimentally studied. The results showed that the shear stress increased with increasing magnetic field strength and volume fraction. It was also influenced by the plate gap distance, and was independent of the shear rate. The shear stress could be ascribed to the contributions of magnetic force and friction force, dominated by the normal force, the shear strain and the friction coefficient. The ratio of shear stress to normal stress, a form of friction coefficient, was influenced by volume fraction, magnetic field strength and gap distance. These results provide a better understanding of the mechanisms of magnetic field excited magnetic powders under parallel-plate shear. (paper)

[en] The rheological properties of magnetorheological (MR) fluids are usually determined by particle structures and polarized particle interactions. However, the particle structures may undergo various evolutions at different shear states and history; this evolution leads to shear stress hysteresis. Therefore, the shear history effect of MR fluids was experimentally investigated in this study. In a shear rate ramp test, the shear stress at low shear rate was higher in the shear rate ramp-down process than in the shear rate ramp-up process. If the next shear test started after a rest time, the start shear stress decayed slowly and approached the original value of the first test when the interval was long enough. The MR fluids also displayed obvious hysteresis loops during the current ramp test. A high shear rate and magnetic field could reduce the shear history effect by accelerating particle structure evolutions, and then hysteresis decreased. This effect was ascribed to the evolution of particle structures during different test modes and durations, and the evolution is governed by interparticle interactions, viscous forces, and the Brownian motions of particles. These results indicated that the accuracy of the force control of MR fluids could be enhanced under high magnetic fields and high shear rates. Thus, these factors should be considered in MR actuator designs. (paper)

[en] The linear dynamic viscoelastic properties of carbonyl iron particle suspensions under external magnetic fields were studied. Results revealed a frequency-independent viscoelasticity under a certain critical magnetic field. The characteristic magnetic field intensity decreased as the increase of particle volume fraction of the suspension, corresponding to a similar value of characteristic loss tangent. By considering the competitions among hydrodynamic, friction and magnetic forces of particles under different magnetic fields, a theoretical linear viscoelastic model was proposed to describe and analyze the tested frequency dependence of viscoelasticity of the suspensions. The model could also be applied to polymer gels with similar viscoelastic behaviors and inspire the design of novel broad frequency vibration damping materials with frequency-independent viscoelasticity. (paper)

[en] The influence rules of square micro-pillar array porosity on the liquid motion characteristics of the near-surface layer are investigated by quartz crystal microbalance (QCM). QCM is a powerful and promising technique in studying the interfacial behavior, which exhibits great advantages in investigating the effects of surface microstructure, roughness, and array. In our experiments, three different arrays with the same height of about 280 nm and center distance of 200 μm, but different diameters of about 78 μm, 139 μm, and 179 μm are investigated. The results indicate that when the surface array has a large porosity, its influence on the liquid motion of the near surface layer is slight, thus resulting in a small increase of half-bandwidth variation due to the additional friction energy dissipation. When the surface array has a small porosity, the array tends to make the liquid film trapped in the array oscillating with the substrate, then there may be a layer of liquid film behaving like rigid film, and it also will make the liquid motion near the array layer more complicated. Thus for the #3 surface with a small porosity, both the absolute values of frequency shift |Δf ₃| and half-bandwidth variation ΔΓ ₃ increase obviously. The experimental results show good consistence with the theoretical model of Daikhin and Urbakh. This study sheds light on understanding the influence mechanism of surface array porosity on the liquid motion of near-surface layer. (paper)

[en] The electrorheology (ER) of suspensions based on polystyrene/polyaniline (PS/PANI) core/shell structured microspheres and those based on disk-like zeolite particles at different electric fields and particle volume fractions have been studied, respectively. Both types of ER fluids showed abrupt shear thickening under high electric fields and low shear rates, as well as shear thinning when the shear rate increased. A normalized method that considers the effects of electric field strength, shear rate and particle volume fraction was proposed to compare the rheological curves of the two ER fluids. The curves evaluated from the normalization method showed similar shear thinning at low shear rates and the hydrodynamic effect at high shear rates. Shear thinning represents the structure destroyed by shearing, and shear thickening at low shear regions indicates the dramatic structure change. The particle volume fraction and structure factor effects demonstrate that the mechanical contact between particles and the wall of the electrodes is crucial to the shear strength of ER fluids, indicating an electric/magnetic field modulated friction mechanism of the ER and magnetorheological (MR) effects. (paper)

[en] Granular bainite, where M-A constituents dispersed in bainitic ferrite matrix usually presents at the half thickness region in thermo-mechanically processed heavy gauge offshore platform steel. In the present work, the decomposition of M-A constituents during tempering at 600 °C was firstly revealed by transmission electron microscopy (TEM) analysis, which primarily involves the precipitation of cementite, recovery and recrystallization of highly dislocated ferrite matrix. Then, the effect of tempering on mechanical properties was investigated by tempering at different temperature for 60 min. Results indicated that, at tempering temperature of 500–600 °C, large quantity of micro-alloying carbides precipitated and partially compensated the loss of strength mainly due to the decomposition of M-A constituents. Compared with the as-rolled state, the decomposition of M-A constituents and softening of bainitic ferrite matrix after tempering have resulted in higher density of microvoids and substantial plastic deformation before impact failure