The degradation behavior of polymer coatings is essential for their protective performance under various corrosive environments. Herein, electrochemical impedance spectroscopy (EIS) is employed to study the corrosion behavior and interfacial delamination of a polymer-coated metal system exposed to 0.1, 0.5, and 1 mol/L H2SO4 solutions at 50 °C. The electrochemical impedance spectra are analyzed using different equivalent circuits to derive the time dependence of the parameters of the coating, delaminated area, and interfacial processes. The phase angle at 10 Hz (θ10 Hz) is not appropriate in the case of higher delamination area ratio α, while θ10 kHz provides a rapid approach to evaluate the degradation of polymer-coated metal systems. The frequency of the phase angle at −45° (f –45°) leads to a wrong evaluation for higher α and can be no longer viewed as the breakpoint frequency. The frequency f p obtained by the changing rate of phase angle (CRPA) method is proposed to monitor the coating degradation and determine the breakpoint frequency with the consideration of dispersive number n. The frequency f EIS derived from fitting EIS spectra shows a good agreement with f p, which can contribute to clarify the evolution in the process of degradation.

Polyamide 6 (PA6) was melt-blended with an intumescent flame retardant (FR), multi-wall carbon nanotubes (MWNTs), and nanoclay particles to produce multi-component FR-PA6 nanocomposites. FR-PA6 nanofibers were processed from varied nanocomposite formulations via electrospinning. Electrospinnability, morphology, along with combustion and thermal properties of the nanofibers were investigated. Both the bulk-form nanocomposites and the electrospun nanofiber membranes exhibited significantly improved combustion properties, including both Heat Release Rate and Total Heat Release. On the other hand, thermal stability appeared compromised. With proper FR additive concentrations, synergism between MWNTs and nanoclay was observed.

Purpose The purpose of this paper is to investigate the effects of surface topography, including surface roughness, waviness and taper, on the cavitation of liquid film lubricated mechanical seals (LFL-MS). Design/methodology/approach A universal governing equation considering cavitation is established, and an equivalent relative density is defined to characterize the cavitation degree. The equation is discretized by the finite volume method and solved by the Gauss–Seidel relaxation scheme. Findings Results indicate that both radial length and a circumferential width of the cavitation zone and cavitation degree are affected significantly by the waviness amplitude and taper, but the effect of surface roughness is limited. Originality/value Effect mechanism of surface topography on the cavitation of LFL-MS is investigated and cavitation degree is reflected by an equivalent relative density. The results further help to comprehensively explore the cavitation mechanism.

Purpose The purpose of this paper is to study the effects of operating conditions including process coefficient, lubricant viscosity and cavitation pressure on the cavitation of spiral groove liquid-film seal (SG-LFS). Design/methodology/approach A mathematical model of SG-LFS is established based on the JFO boundary and a relative density is introduced. The universal governing equation after a coordinate transformation is discretized by the FVM method and solved by the Gauss-Seidel relaxation scheme. Findings The results indicate that the two-dimensional size of cavitation and cavitation degree are affected significantly by the process coefficient and lubricant viscosity but the effect of cavitation pressure can be ignored. Originality/value The effect mechanisms of operating conditions on the cavitation of SG-LFS are studied by the JFO boundary and cavitation degree characterized by a relative density. The results presented are helpful to perfect and deeply understand the cavitation mechanism of liquid-film seal. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2020-0083/

The unconstrained optimization method (UOM) plays an important role in the field of physics, mathematics, statistics, etc. Rosenbrock function is a 4-degree function with a curved canyon. It is most suitable for testing UOM. However, the test hasn't done. We have written 14 UOM computer programs, 12 of which contain our new algorithm. From the optimal result, the 2-order approximation direction is the best, followed by the conjugate direction, followed by the negative gradient direction. For quadratic fitting function method, linear fitting gradient method and unbounded polyhedron deformation method, a new algorithm for moving points was proposed. When the new point is better than all of the other points, the other points should close up to it. And when the new point is worse than all of the other points, it should close up to the best point or center point. The improvement of moving points makes these optimization directions be effective for complex objective functions.

Abstract. Conjugate direction is a better direction of optimization. The three-seeking method and the six-seeking method based on conjugate direction have strong theoretical. Using the advantages of one-dimensional blind walking optimization algorithm, the optimal point was given on the given direction. Three optimization method, six optimization method and computer program for the blind walking algorithm for 3D design space were put forward. The given programs were of universal significance. The results show that the three-seeking method and the six-seeking method have better performance than the negative gradient method.

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