Surface Review and Letters

In this report, micro-emulsion method was used to obtain La, Mn-doped Ba₃Co₂ ${\text{Fe}}_{24}$${\text{O}}_{41}$ single-phase Z-type hexa-nanoferrites by maintaining annealing temperature at 1200^∘C. X-ray diffraction (XRD) analysis shows lattice parameters, crystallite size, and volume are significantly enhanced by introducing La and Mn ions instead of Ba and Fe, respectively. Moreover, La and Mn ion doping improved the preferred orientation of atoms through the basal plane of Z-type hexaferrite. Field emission scanning electron microscopy (FESEM) study reveals that the surface morphology of La- and Mn-doped Ba₃Co₂ ${\text{Fe}}_{24}$${\text{O}}_{41}$, Z-type ferrites show ultrafine and small particle size. The analysis of X-Ray absorption near edge spectroscopy (XANES) suggests that transition in ${\text{La}}^{+3}$ has occurred from 3d core level to empty electronic state above the Fermi level. Furthermore, it is observed that in the Z-type ferrites Co exist as divalent ion and Fe as trivalent ion by analyzing XANES. Vibrating samples magnetometer (VSM) indicated that the samples are ferromagnetic as they have narrow hysteresis loops. The decrease in coercivity is due to paramagnetic dopant element Manganese (Mn).

The inhibitive performance of 2-[(5-phenyl-1,3,4-oxdiazol-2-yl)methyl]-2H-benzo[b] [1,4] thiazin-3-one (POBT) for low carbon steel corrosion in 1 M H₂SO₄ has been evaluated by non-electrochrmical, and electrochemical measurements. Efficiency of the inhibitor enhanced with inhibitor concentration and declined with rise in temperature. 92.39% inhibition efficiency was attained using 0.1mM of POBT. Anticorrosive effect of the inhibitor is owing to the adsorption of POBT molecules on the metal surface. Mono layer adsorption of inhibitor was favored by observing the best fit with Langmuir isotherm. Polarization measurements reveal that the inhibitor behaves as mixed type. Surface analysis by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) confirm the existence of a protective film of POBT on low carbon steel surface. Quantum chemical parameters obtained using density functional theory (DFT) method complements the above results.

From the defects-free self-assembled organic layers (SAMs) of CH₃(${\text{CH}}_2{)}_{n-1}$SH molecules with short chain lengths ($n=4,6,8$) electrodeposited on the (111) surface of monocrystalline gold previously prepared, monitored defects (pinholes) were potential-induced from cyclic partial reduction of SAMs at an appropriate potential. Electrochemical impedance measurements were in-situ conducted and [Fe(CN)₆]${}^{3-∕4-}$ ions were used as probes for mass and charge transfer. Interface evolution was modeled with an equivalent electrical circuit containing two distinct constant-phase elements (CPEs). One is a generalized semi-infinite Warburg element in series with a charge transfer resistance attributed to subdiffusion phenomenon through leaky sublayers at low frequencies; the other CPE is used for characterizing the interface heterogeneity at medium and high frequencies. At low frequencies, electrochemical impedance measurements show subdiffusion phenomenon, which depends on the remaining sublayer and its thickness. When the defect density increases, diffusion tends to be ordinary, obeying the Fick’s law.

This paper concerns deposition of nano and micro structures of Lithium Niobate (LiNbO₃) on a quartz substrate using sol–gel method. The nanostructure was deposited based on spin coating technique with speed of 3000rpm for 30s. Samples were exposed for different annealing temperature ranges from 100^∘C to 600^∘C. The optical properties and the morphological results of the grown films have been investigated using the scanning electron microscope (SEM), atomic force microscopy (AFM), optical study through UV–Visible and Photoluminescence (PL). The results showed that good transmission and bandgap properties can be obtained as the annealing temperature increases. In contrast, the higher annealing temperature results in reduction of the refractive index value, and the grains are regularly distributed within the film as a result of increasing the annealing temperature. This comes from the growing effect of packs density as a result of oxidation process during heating process.

Ni-TiO₂ nanocomposite have been prepared by electrodeposition. The microstructure and tribological behavior of Ni-TiO₂ nanocomposite before and after annealing have been investigated compared with as-deposited Ni-TiO₂ composite. The results demonstrated that TiO₂ nanoparticles usually collected along the grain boundaries and nickel grains changed from columnar grains into equiaxed grains after annealing. HRTEM photographs indicated that the diffusion between crystalline nickel and TiO₂ nanoparticles did happen after annealing. Wear results indicated that the main wear mechanism of as-deposited Ni-TiO₂ nanocomposite was adhesion wear. The wear resistance of Ni-TiO₂ nanocomposite heat-treated is better than as-deposited Ni-TiO₂ nanocomposite because the oxidation layers on the worn surface of Ni-TiO₂ nanocomposite masked the strengthening effect of small grain size. The corrosion behavior also has been studied and it is found that annealing reduces the corrosion resistance of composite coatings.

Aluminized steels possess excellent corrosion resistance due to the formation of Al-Fe solution phases and intermetallic compounds in coatings. Ni was added to baths to further improve the corrosion resistance of the coatings at high temperature. Here, the role of Ni in the formation of coatings and the effect of diffusion process on the developing of coatings were investigated. 45 steels were immersed in Al-Ni baths (Al-1mass% Ni, Al-3mass% Ni, and Al-5mass% Ni) and diffusion-treated at 1023 and 1123K for 20, 40 and 100min, respectively. The coatings of samples were analyzed via scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDS). X-ray diffraction (XRD) was further used to confirm the types of phases that formed during diffusion treatment. The formations of intermetallic coating layers were also analyzed via the diffusion path. More continuous Al₃Ni layer and compact coating were obtained with diffusion treatment at 1023K for 40min.

This study deals with the investigation on the effect of Electrical Discharge Machining (EDM) parameters during machining of hybrid composite (Al 7075/TiC/B₄C). The optimum process parameters of die sinking EDM like pulse current, pulse duration and gap voltage on metal removal rate, tool wear rate and surface finish were investigated. Full factorial experimental design was selected for experiments. Analysis of variance was employed to study the influence of process parameters and their interactions on response variables. Among the process parameters considered, it was observed that the pulse current was found to be more influential in affecting MRR, TWR and SR. The other parameters have little effect on the response variable. Multi-objective optimization study was also performed using genetic algorithm to find the optimum parameter setting for controversial objective function combination such as high MRR and low SR and High MRR and low TWR. Scanning electron microscope study was performed to study the surface characteristics.

In this paper, we demonstrate the formation of Schottky contact formed by Al with a new class of synthesized conjugated pure poly(Schiff base) (PSB) and its blend with varied concentrations of polyaniline (PANI). The Schottky behavior was transformed into Ohmic in the blended polymer. PSB was synthesized from the solution of polycondensation of terephthaloyl chloride (T) and 4-(4-hydroxybenzylideneamino)phenol (SB). The polymer showed good thermal stability with $T_g$ of 312^∘C as determined by thermal gravimetric analysis–differential scanning calorimetry TGA–DSC and high molecular weight $3.5\times 10^5$ (g/mol) with coiled conformation as determined by laser light scattering. PBS was blended with various weight percentage ratios of PANI (0, 3, 6, 9, 12, 15 percent by weight of the pristine polymer). The metal contact (Au) was formed and studied in the temperature range of 293–373K, which showed that Schottky behavior in the intrinsic polymer with an ideality factor was close to 2 and then reduced to 1.0–1.2 in the blended polymers. In blended polymers, the conduction across the junction was characterized by Schottky emission at low field and Poole–Frenkel emission at high field. The Schottky barrier height showed a small increase with temperature, which was attributed to reduction in the built up of image charge. The Schottky and Poole–Frenkel emission coefficients were also determined and Schottky emission coefficient agreed with the theoretical value, while Poole–Frenkel emission coefficient was small. In short, the metal–semiconductor junction was affected by the blending, while conduction within the polymer remained independent of PANI concentration.

We have fabricated Ni/$n$-Si metal–semiconductor (MS) and Ni/Ta₂O₅/$n$-Si metal-insulator–semiconductor (MIS) Schottky barrier diodes at room temperature and studied their current density–voltage (J–V) and capacitance–voltage (C–V) characteristic properties. The forward bias J–V characteristics of the fabricated MS and MIS devices have been evaluated with the help of the thermionic emission (TE) mechanism. Schottky barrier height (SBH) values of 0.73 and 0.84eV and ideality factor values of 1.75 and 1.46 are extracted using J–V measurements for MS and MIS Schottky barrier diodes without and with Ta₂O₅ interfacial oxide layer, respectively. It was noted that the incorporation of Ta₂O₅ interfacial oxide layer enhanced the value of SBH for the MIS device because this oxide layer produced the substantial barrier between Ni and $n$-Si and this obtained barrier height value is better than the conventional metal/$n$-Si (MS) Schottky diodes. The rectification ratio (RR) calculated at $\pm 2$V for the MS structure is found to be $1.27\times 10^1$ and the MIS structure is found to be $7.39\times 10^2$. Using Chung’s method, the series resistance ($R_s$) values are calculated using $dV$/$dln(I)$ vs I plot and are found to be 21,603$\mathrm{\Omega }$ for the Ni/$n$-Si (MS) and 5489$\mathrm{\Omega }$ for the Ni/Ta₂O₅/$n$-Si (MIS) structures, respectively. In addition, $H(I)$ vs $I$ plot has been utilized to evaluate the series resistance ($R_s$) values and are found to be 14,064$\mathrm{\Omega }$ for the Ni/$n$-Si (MS) and 2236$\mathrm{\Omega }$ for the Ni/Ta₂O₅/$n$-Si (MIS) structures, respectively. In conclusion, by analyzing the experimental results, it is confirmed that the good quality performance is observed in Ni/Ta₂O₅/$n$-Si (MIS) type SBD when compared to Ni/$n$-Si (MS) type SBD and can be accredited to the intentionally formed thin Ta₂O₅ interfacial oxide layer between Nickel and $n$-type Si.

This study explored the friction and wear behavior of a Ni-based exhaust valve at high temperatures. Nickel-based superalloy was used with two types of processing states: the original forged sample and the sample under the standard T1 heat treatment. At room temperature and a loading force of 10N, the average friction coefficient of the T1 heat-treated specimen is 0.61, which was lower than that of the forged sample (0.78). The wear rate of this specimen was also lower than that of the forged sample at the same temperature and loading force. Thus, T1 heat treatment can significantly improve the wear resistance of the alloy because of ${\gamma }^{\prime }$ phase and carbides. The wear rate was the minimum at 550^∘C and increased again at 750^∘C dominated by the formation and flake-off of the oxide film.

In this study, the tribological properties of Cr₂O₃–40% TiO₂ coating for brake disc materials were investigated in braking performances. Plasma spraying technique was used in order to deposit coating materials onto cast iron disc with ventilation channels substrate. The braking performances of discs were tested according to SAE J2430 test standard. Microstructures of discs were characterized by means of light microscope (LM), scanning electron microscope (SEM) and energy-dispersive spectrometry (EDS). The surface hardness and roughness were measured with testers. In general, it is noted from the LM and SEM images that there was an infinite gradation between coating layer, binding material and the lamellar graphite cast iron and that bonding resistance was excellent. The coated disc exhibited less wear, approximately the same coefficient of friction and longer life than the uncoated disc. As a result, the coated disc could be a much better alternative for new-generation brake discs in the motor vehicles than the uncoated disc.

The surface tension and viscosity in the liquid Cu-Ag-In ternary alloys have been estimated using Muggianu and Toop geometric models and Seetharaman–Sichen equations, respectively along a cross-section of $x_{\mathrm{\text{Ag}}}$/$x_{\mathrm{\text{In}}}=1∕2$, 1/1 and 2/1. The surface tension has also been estimated using Butler equation. In addition, the enthalpies of the same ternary alloys have been predicted at different temperatures along five cross-sections $x_{\mathrm{\text{Cu}}}$/$x_{\mathrm{\text{In}}}=1∕3$, 1/2, 1/1, 2/1 and 3/1 using Kohler, Toop and Chou models. The geometric models are used in this work in order to verify their effectiveness since they are considered as the most widespread theoretical models used for metallic alloys. The estimated values obtained show that the surface tension decreases with increasing temperature for the all studied models and equations and increase with increasing copper-composition, except for few Cu-compositions where an opposite tendency is observed. It should be noted that the surface tension has a negative and positive temperature coefficient (d$\sigma$/d$T)$. The viscosity decreases with increasing temperature but increases with increasing copper-compositions. The calculated surface tension and enthalpy of mixing of the investigated system are compared with the reachable experimental data and a relatively excellent accord was obtained.

In this paper, TiC reinforced composite coatings were fabricated on TC4 alloy by laser cladding Ti,Al,Si, TiC and Y₂O₃ mixed powders. Microstructures and properties of the clad coatings with and without Y₂O₃ were discussed by comparative experiments. SEM, XRD and EDS were employed to discover the microstructures and the composition of phases. The hardness and wear resistance of the coatings were tested by the MM200 wear test machine and a HV-1000 digital hardness tester, respectively. The results showed that the coating was majorly composed of Ti₅Si₃, Ti₇Al₅${\text{Si}}_{12}$, Ti₃AlC₂, Ti₃Al, Al₃Ti, TiAl and Y₂O₃. The dilution zone exhibited a metallurgical bonding without pores and cracks. Compared with the TC4 substrate, the hardness and wear resistance of the coatings were heightened by 5–6 and 4.5–5.8 times, respectively. With 2.0wt.% Y₂O₃ addition, the microstructure of the coating was refined significantly, and the microhardness and dry sliding wear resistance were enhanced further. The effects of Y₂O₃ were attributed to heterogeneous nucleation of the residual Y₂O₃.

In the present study, carbon nanostructures were synthesized by laser ablation of graphite in de-ionized water. Q-switched Nd:YAG laser of 1064nm wavelength, 9ns pulse width, and different laser fluences (3.6, 5.4, 10.6, and 14.6J/cm²) were utilized to irradiate the target. XRD measurements demonstrated the presence of the two carbon phases (002, 111) except for the sample prepared at 3.6J/cm² laser fluence; it showed disappearance of (002) phase. This result can be an indication of changing the phase of carbon nanomaterials when prepared at this fluence. TEM revealed that carbon nanoparticles had a spherical shape and were 10–90nm in size, while nanostructure carbon prepared at 3.6J/cm² has nanosheets 45mm in width and 275mm in length. The absorption of CNPs indicated the appearance of the absorption peak at about 305nm, which is attributed to the $\pi$–$\pi$* transition of the C $=$ O band. PL emission was decreased at the higher laser fluence (14.6J/cm²) due to the quenching of the carbon nanoparticles luminescence.

Magnetite (Fe₃O₄) nanoparticles (MPs) capped with polyethylene glycol (PEG) were prepared by a hydrothermal method, and their antibacterial activity was examined against Staphylococcus aureus, Escherichia coli and Psudomonas aeruginosa. The functionalized NPs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), Fourier transform infrared (FTIR) spectroscopy, and Thermogravimetry (TG). The average size of the Fe₃O₄ was in the range 9–20nm, while the functionalized PEG–Fe₃O₄ had an average size of 5–15nm. The PEG–Fe₃O₄ exhibited superparamagnetism and high saturation magnetization at room temperature. The antibacterial activity of the Fe₃O₄ and PEG–Fe₃O₄ were evaluated against E. coli, S. aureus, and P. aeruginosa using the agar well diffusion method. The changes in the morphology of the studied bacterial species were observed via SEM, while the mode of action of the studied agents was determined via the detection of reactive oxygen species (ROS) using Acridine orange-ethidium bromide (AO/EtBr) staining method. The results showed that PEG-functionalized magnetic (Fe₃O₄) NPs as a novel DNA-mediated antibacterial agent. The PEG–Fe₃O₄ NPs were observed to destroy the bacterial cells by permeating the bacterial nucleic acid and cytoplasmic membrane, resulting in the loss of cell-wall integrity, nucleic acid damage, and increased cell-wall permeability. The PEG–Fe₃O₄ NPs could serve as a potential antibacterial agent in future biomedical and pharmaceutical applications.

Graphene oxide (GO) sheet and ultrasonic field (UF) were successfully employed to produce Ni–B/GO and UF–Ni–B/GO composite coatings on Q235 mild steel by electroless plating. The composite coatings’ structure and surface morphology were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Results showed that GO was successfully co-deposited in the Ni–B alloy. Moreover, UF–Ni–B/GO composite coatings have smoother surface and thicker cross-section than others. The microhardness and corrosion resistance of the sample coatings were determined using Vickers hardness tests, Tafel electrochemical tests and electrochemical impedance measurements (EIS) in 3.5wt.% NaCl solution to receive the effect of GO and ultrasonic. The findings indicated that UF–Ni–B/GO exhibited optimum hardness (856HV) and enhanced corrosion resistance (6.38 $\mu$${\text{A cm}}^{-2})$ over the Ni–B and Ni–B/GO coatings. Due to these interesting properties of the coating, it could be used as a protective material in the automotive and aerospace industries for parts of machines that were manipulated in high temperature and corrosive environments.