Surface Review and Letters

In this paper, the electrochemical performance of a novel gradient-distributed wire beam electrode (WBE) is measured in different corrosion medium. This electrode contains three kinds of carbon steel with different carbon content. WBE was consisted of 100 carbon steel wires and regularly prepared into a $10\times 10$ matrix. The carbon steel wires for each row is the same, but the adjacent rows are different. The electrochemical corrosion behavior of regions with different carbon steel wires can be tested clearly. The results revealed that the heterogeneity of local corrosion of metal, which can be well studied by WBE, meanwhile, the phenomenon of polarity reversal can also be detected. Corrosion potential–current distribution map of the novel WBE showed obvious striped features when immersed in 3.5wt.% NaCl solution with different pH (pH$=$2, 6 and 12). Corrosion firstly occurred in the high carbon steel region in the acidic conditions, and then quickly spreads to other areas, eventually causing the entire surface of the WBE to be corroded. While in the neutral salt solution, only the regions of high carbon steel and some part of medium carbon steel area appeared obvious anode currents during a long time testing. When the pH of corrosive solution reached to 12, the corrosion rate is greatly reduced and then corrosion process is suppressed. This new method can evaluate the corrosion resistance of materials more accurately.

Eco-friendly biodegradable Rhododendron schlippenbachii (R. schlippenbachii) green inhibitors, R. schlippenbachii methanolic (RSMeOH) extract, which can effectively reduce low carbon steel corrosion rate, were investigated using weight-loss and electrochemical (electrochemical impedance spectroscopy) techniques. The inhibitors exhibited higher efficiency by retarding the corrosion process in 1M H₂SO₄ and the inhibition efficiency is found to be concentration dependent. The reactivity of the predominant phytochemical components of the extract are analyzed. The adsorption of inhibitors on low carbon steel is followed the Langmuir adsorption. The protective inhibitor film formed on the metal surface was confirmed by SEM and AFM techniques.

The corrosion characteristics of Inconel 600 were investigated at 650^∘C in air and 76%${\text{N}}_2+6$%${\text{O}}_2+16$%${\text{CO}}_2+2$%SO₂ gas environment up to 500h. Specimens exposed to each condition were characterized by weight gain, scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction. The oxide structure consisting of the thin Cr₂O₃ layer and Cr₂O₃ nodules was observed, which increased the weight gain of specimens. In the SO₂-bearing gas, it showed a bigger weight gain due to the coarsening of Cr₂O₃ nodules. Therefore, it was suggested that the sulfur-accelerated coarsening of Cr₂O₃ nodules at the high temperature.

In this study the effects of ${}^{60}$Co gamma-ray irradiation on the electrical properties of the poly (methyl methacrylate)/lead oxide nanoparticle (PMMA/PbO) have been investigated. To show the influence of ${}^{60}$Co gamma-ray irradiation on the current–voltage ($I$–$V$) characteristics of the composite structure, which are based on the PMMA/PbO, have been measured before and after gamma-ray irradiation at room temperature and in dark. The analyze of the electrical parameters which are found out as strong function of voltage. Thus, structures has been investigated in the wide range of voltage (– 2 V to + 4 V) using Standard and Cheung methods.

An investigation was made on the effects of the boriding process and of quenching and tempering after boriding on the microstructure, hardness and wear of AISI 5140 steel. In this study, a new boriding agent (Baybora${}^{\text{®}}$–1) developed for the solid boriding method was used. It was observed that the wear resistance of the borided samples increased by about four times, but the wear resistance of the sample subjected to quenching and tempering after boriding increased by only about two times. Thus, it was determined that quenching and tempering after boriding worsen wear resistance.

This study applied piston-valve coating for an engine that worked 100% on biodiesel fuel and investigated the wear characteristics after the experiment. The plasma spraying method was used as the coating method. Al₂O₃ and ZrO₂ ceramics, which are the most frequently used ones in the literature, were selected as coating material. The deformations on the coated and uncoated surfaces were determined after running the engine at different time intervals. The deformations on the piston surfaces were interpreted by conducting SEM and EDX analyses. In particular, the deformation on the coating material, thermal fatigue cracks, abrasive wear and elements that clang to the piston surface after combustion were determined. Additionally, post-combustion engine oil analysis was carried out to determine the elements that were released as a result of the thermal wear in connection to combustion. The relationship of the coating with thermal efficiency was investigated for all types of coatings by determining temperatures from a certain point on the engine by using a thermal camera and a surface temperature measurement device. As a result of the SEM, EDX and engine oil (ICP) analyses, it was seen that the elements that are released as a result of wear such as Al, Fe and Cr had lower quantities with the aluminum oxide (Al₂O₃) coating with the Nickel–Chromium (Ni–Cr) bonding agent in comparison to the other coating materials. Additionally, as a result of oil analyses, the coated engine was observed to have more positive outcomes in comparison to the uncoated engine.

This paper aims to study the influence of molecular structural difference between deformed soft and hard coal on methane adsorption and obtains the quantitative indexes that reflect the above influence degree. In this paper, XRD and FTIR experiments were adopted to determine the molecular structure of typical deformed soft and hard coals with different ranks. The molecules structural parameters of deformed soft and hard coal were compared and analyzed. Based on the above structural difference characteristic, four corresponding physical models of macromolecular structure are established. A simulation for deformed soft and hard coals was established to test out the behavior difference of adsorption and its mechanism; by using Materials Studio (MS) software, same scenario is also applied on the other four physical models listed above. Then, the isothermal adsorption methane experiments of four kinds coal samples were carried out to verify the above simulation results. The results show that the molecular structure of deformed soft and hard coals has significant differences, i.e. comparing with hard coal, deformed soft coal has smaller interlayer spacing $d_{002}$; greater lateral sizes $L$a, stacking heights $L$c and the crystal nuclei sizes $L$a/$L$c. Deformed soft coal had a more orderly structure crystal nuclei, bigger crystal volume, the larger basic structure unit (BSU) and more flattened. Deformed soft coal has less oxygen-containing functional groups, lower fatty hydrocarbon content and more $\mathrm{\text{C}}=\mathrm{\text{C}}$. These findings verified that dynamic metamorphism promotes aromatization and large molecular polycondensation of the coal, thus improving the aromatic degrees of the crystal nucleus. Due to the increasing of the lateral sizes being beneficial and the stacking heights being not conducive to the adsorption of the coal, the $L$a/$L$c was proposed as an indicator of the coal adsorption methane ability. The isothermal adsorption experiments show that the adsorption capacity of deformed soft coal with the same rank is greater than that of hard coal, which is in good consistency with the above research results. Also, the above experimental results provide a theoretical basis for the determination of coalbed methane content and the estimation of CBM.

In this work, attempt is made to carry out post weld heat treatment (PWHT) on NiTinol samples using laser power source. Initially, 1mm thick NiTinol sheets were welded in butt joint position using Ytterbium: Yttrium aluminum garnet (Yb: YAG) laser power source. Laser welding was carried out in continuous mode, and the quality of the weld was assessed with respect to phase transformation temperatures, microhardness, tensile strength, and corrosion resistance. To improve the quality of the welded samples, PWHT was done by passing a laser beam over the welded samples. It was found that PWHT had a significant effect on the phase transformation temperatures, microhardness, tensile strength and corrosion behavior of the welded NiTinol joints.

The effect of graphene content (0.08, 0.16 and 0.33wt.%) on the thermal conductivity and thermal aging performance of an Sn based composite material with 0.7wt.% Cu and various graphene additions was investigated via X-ray diffraction (XRD), scanning electron microscope (SEM) and accelerated thermal aging test. The XRD results showed that the graphene diffraction intensity was weak (approximately 10^∘) due to little content and distribution of the graphene on the surface of the composite materials. After thermal aging testing the diffraction intensity on some crystal planes of the composite materials was enhanced, proving that preferential growth occurs on the crystal plane. SEM results showed that before aging testing no whiskers were generated on the surface of the composite materials. After the accelerated thermal aging at 100^∘C for 24h, whisker growth became apparent in the composite materials. All the whiskers were located in the grains rather than on the grain boundaries of the composite materials. The highest thermal conductivity was obtained at 0.16wt.% graphene addition (indicated as 0.16wt.% graphene–0.7wt.% Cu/Sn). After the accelerated thermal aging at 100^∘C for 24h, the bamboo-shaped whiskers with a low aspect ratio grew in large quantities on the surface of the 0.16wt.% graphene–0.7wt.% Cu/Sn composite material, while when the aging was at 100^∘C for 366h the thermal conductivity decreased from 67W${\text{m}}^{-1}$${\text{K}}^{-1}$ to 52W${\text{m}}^{-1}$${\text{K}}^{-1}$. When the graphene addition was 0.33wt.% (indicated as 0.33wt.% graphene–0.7wt.% Cu/Sn) the thermal conductivity maintains a value above 59W${\text{m}}^{-1}$${\text{K}}^{-1}$ after the accelerated thermal aging.

The Ti/C modified layers were prepared on Ti–6Al–4V alloy by double glow plasma surface alloying technique. The microstructure and composition of the modified layers were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). The bonding strength, micro-hardness and friction performance of the modified layers were examined by the scratch tester, micro-hardness tester, reciprocating wear tester, and white light interferometer. The results show that both of the microstructure and properties of the Ti/C modified layer get the remarkable effects when the temperature reaches 910^∘C. Belonging to metallurgical bonding with the substrate, the modified layer possesses a continuous, compact and uniform packet-like particle structure. Compared with the Ti–6Al–4V substrate, the surface micro-hardness and wear resistance of Ti/C modified layer are significantly improved.

In this work, a facile method combined with PdCl₂ solution immersing and electroless deposition to fabricate nickel-plated plant fiber non-woven sheet is demonstrated. The effect of ${\text{Pd}}^{2+}$ concentration on the structural property of plated sheet was investigated using X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. Results showed that increasing activated time and PdCl₂ concentration would facilitate the enhancement of Pd-adsorbed amount on the substrate surface. It would facilitate the deposition of nickel atom, the reduction of the surface electrical resistivity and the crystallization of plated coating due to the high catalytic sites. In addition, the lowest PdCl₂ effective concentration was reduced with the increased of activated time.

In this contribution, we provide a theoretical model to study the effect of different cutting edges on the appearance of localized electronic states. The system under study is a three-dimensional atomic chain that ends with an open cut forming a semi-infinite structured layer in the (1 0 0), (1 1 0) and (1 1 1) directions. We investigate the surface electronic characteristics of the monoatomic chain of a simple cube (sc), orthorhombic (orth), and tetragonal (tetr) structures. We have adopted in our approach the tight-binding approximation to build up the surface Hamiltonian matrix. Additionally, the number of secular equation, at the surface, has been determined by using phase field matching theory (FPMT). In fact, the Hamiltonian system obtained from different cutting orientations provides an inhomogeneous system. To solve the surface eigenvalue problem, we integrate the calculation of the scattering reflection probabilities as given in Landauer–Büttiker formalism. Next, based on the computed scattering probabilities, we build up the surface core states which provide the surface Hamiltonian matrix which can be solved numerically. Our model calculation has been applied to the following elements: (i) fluorite (F), manganese (Mn), polonium (Po), bromine (Br), indium (I), tin (Sn), and protactinium (Pa). The results emphasize the influence of cutting direction on the electronic characteristic of surface and on the scale of energy values. We report the appearance of new electronic curves that characterize the surface states. Those surface states are localized down, within, and above the bulk spectrum. They also provide different characteristic features, of the metals under study, in a given cutting orientation. Furthermore, we have integrated the calculation of non-structured cuts on the outer layers. The relaxation effect on the surface is a standard process which leads to stabilize the changes in the internal energy until the equilibrium. The spacing geometry caused by the relaxation on the surface could be determined by using the molecular dynamic algorithm. We account in this case the lift of degeneracy and the rise of additional localized branches within and outside the bulk range.

The study of the corrosion inhibition of mild steel in acid medium 1 M HCl by the Schiff base compounds named {4,4′-Bis(pyrrole-2-carboxaldehyde) diphenyl diimino sulfide (L1) and 4,4′-Bis(thiophene-2-carboxaldehyde) diphenyl diimino sulfide (L2)} was carried out using various techniques: weight loss measurements, polarization curves, electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The influence of the concentration, immersion time and temperature was examined and the mode of adsorption of these inhibitors on the surface of the metal was highlighted by assigning the appropriate isotherm. The experimental results indicate that these compounds are effective corrosion inhibitors and the inhibitory competence rises with increasing inhibitor concentration. The adsorption of these compounds on the mild steel surface obeys the isotherm of Langmuir. The correlation between the molecular structures and the inhibitory properties of the compounds studied was performed using the Density Functional Theory (DFT) method. Furthermore, molecular dynamics (MD) simulation has been taken into account. The results indicate that the adsorption energy of L1 was less than L2, which is in accordance with the experimentally determined inhibition effect.

Preparation, characterization and application of protective phosphonic acid monolayers formed by 1-Aminohexyl phosphonic acid (AHP), 1,4-butanediphosphonic acid (BDPA), 1-amino-1,3-dimethylbutyl phosphonic acid (ADBP) on copper surface as anticorrosive self-assembled molecular monolayers (SAMs) have been investigated by atomic force microscopy (AFM) analysis, electrochemical impedance spectroscopy (EIS) and in situ electrochemical quartz crystal microbalance (EQCM) techniques. Film formation and growth were monitored by EQCM and the step-by-step construction of monolayer was investigated through measurement of the frequency change, which corresponds to mass change due to the adsorption of molecules. Observed increase in electrode mass suggests that SAMs formed on copper surface by the adsorption of phosphonic acids. Results clearly demonstrate that adsorbed amounts of phosphonic acids were strongly influenced by immersion time and molecular structure. Quantum chemical calculations were performed by semi-empirical PM6 method, in order to explain the relationship between molecular structure and adsorption mechanism. Quantum chemical parameters of phosphonic acids propound that adsorption of molecules on copper surface has a chemical mechanism. Corrosion protection ability of SAMs against the acidic corrosion of copper has been evaluated in 0.1M H₂SO₄ solution. It was found that phosphonic acid SAMs act as protective barrier and the protection efficiencies increased in the following order: $\mathrm{\text{AHP/Cu}}>\mathrm{\text{BDPA/Cu}}>\mathrm{\text{ADBP/Cu}}$.

The rapid growth in the usage of polymers/polymer composites demands innovative welding techniques for joining. In this research work, Polypropylene (PPE) is chosen as the thermoplastic matrix and the filler selected is Spheri Glass 3000 (SGE) at 2.5wt.%. In this work, Friction Vibration Joining (FVJ) is used for joining PPE/SGE composites. The FVJ experiments were carried out according to Taguchi ${\text{L}}_{27}$ orthogonal array with input parameters as (i) Tool Profile (TP), (ii) Frequency of Vibrating Tool (FVT) and (iii) Feed Rate of Workpiece (FRW). The joints were analyzed mechanically (tensile strength, impact strength and shore D hardness) and metallurgically (scanning electron microscope). Analysis of Variance (ANOVA) is used for studying the significance of the input factors over output factors. The mechanical characteristics of FVJ joints were optimized by Technique for Order Preference by Similarity to Ideal Solution (TOPSIS).