Waheed Qamar Khan

Electrochemical deposition of nickel graphene composite coatings: effect of deposition temperature on its surface morphology and corrosion resistance

The present work describes the fabrication of Ni–graphene composite coatings on carbon steel at different deposition temperatures (15 °C, 30 °C, 45 °C and 60 °C, respectively) by an electrochemical codeposition method. The surface morphology, compositions, roughness and phase structures were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic force microscopy (AFM) and X-ray diffractometer (XRD), respectively. The polarization test and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical properties of composite coatings. The results showed that the Ni–graphene composite coatings deposited at 45 °C exhibit coarser surface morphology with increased carbon content, refined grain sizes, high micro hardness and better corrosion resistance performance. At lower temperature relatively flat Ni–graphene composite coatings were obtained and the same characteristics of the coatings were investigated at higher than the peak value of the bath temperature. Thickness increased with the increasing of deposition temperature. The linear changes in composition and surface morphology of the Ni–graphene composite coatings were observed when the deposition temperature reached up to 45 °C.

The Effect of Sputtering Parameters and Doping of Copper on Surface Free Energy and Magnetic Properties of Iron and Iron Nitride Nano Thin Films on Polymer Substrate

The objective of this study was to deposit thin films on PET polymer substrate and examine the functional properties systematically. Their properties have been studied as a function of the N2-Ar flow rates, deposition time span and Cu doping. Iron nitride film deposited on both sides exhibits ferromagnetic phases, γ′-Fe4N and ε-Fe3N co-existed, shows negligible magnetic anisotropy. Other samples show the evolution of N-rich (FeN, Fe2N) and N-poor (Fe16N2, Fe3N, Fe4N) phases under different deposition time conditions. XPS analysis and free energy calculations confirmed that co-sputtered Fe-Cu thin films are more stable than layer deposited counterparts. From VSM results it is evident that the dominant phase, changes steadily from the ferromagnetic α-Fe (N) to the paramagnetic ξ-Fe2N with the increase of nitrogen flow rates and the ordering of the nitrogen atoms. Binding energy increases steadily from 733 eV to 740 eV with the increasing thickness of thin films from 74 nm to 94 nm. It was observed that surface energy decreases as the contact angle of glycol increases and changes the thin film surface from polar to nonpolar. TEM images indicate that cubic γ′-Fe4N and ε-Fe3N nano particles oriented in preferred directions dispersed uniformly in the amorphous iron nitride matrix.

Effect of surfactant concentration in electrolyte on the fabrication and properties of nickel-graphene nanocomposite coating synthesized by electrochemical co-deposition

Long-time environmental protection of metallic materials is still required in the manufacturing and engineering applications. Nickel-graphene nanocomposite coatings have been prepared on carbon steel using sodium dodecyl sulfate (SDS) as a dispersant in the electrolyte by an electrochemical co-deposition technique. In this study, the effects of surfactants on graphene dispersion, carbon content in the coatings, surface morphology, microstructures, microhardness and corrosion resistance properties of the nanocomposite coatings are explored. The results indicate that the reasonably good graphene dispersion, coarser surface morphology and reduction in grain sizes are achieved upon increasing the surfactant concentration in the electrolyte. The surfactant also influences the preferred orientation of grains during electrodeposition; the (200) plane is the preferred orientation for the nanocomposite produced with SDS in the bath electrolyte. The microhardness, adhesive strength and corrosion performance of the nickel-graphene nanocomposite coatings are found to increase with the increasing concentration of sodium dodecyl sulfate in the deposition bath. Moreover, the influencing mechanism of surfactant concentration on the properties of nanocomposite coatings has been discussed.

Effect of Target Composition and Sputtering Deposition Parameters on the Functional Properties of Nitrogenized Ag-Permalloy Flexible Thin Films Deposited on Polymer Substrates

We report the first results of functional properties of nitrogenized silver-permalloy thin films deposited on polyethylene terephthalic ester {PETE (C10H8O4)n} flexible substrates by magnetron sputtering. These new soft magnetic thin films have magnetization that is comparable to pure Ni81Fe19 permalloy films. Two target compositions (Ni76Fe19Ag5 and Ni72Fe18Ag10) were used to study the effect of compositional variation and sputtering parameters, including nitrogen flow rate on the phase evolution and surface properties. Aggregate flow rate and total pressure of Ar+N2 mixture was 60 sccm and 0.55 Pa, respectively. The distance between target and the substrate was kept at 100 mm, while using sputtering power from 100–130 W. Average film deposition rate was confirmed at around 2.05 nm/min for argon atmosphere and was reduced to 1.8 nm/min in reactive nitrogen atmosphere. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, vibrating sample magnetometer, and contact angle measurements were used to characterize the functional properties. Nano sized character of films was confirmed by XRD and SEM. It is found that the grain size was reduced by the formation of nitride phase, which in turns enhanced the magnetization and lowers the coercivity. Magnetic field coupling efficiency limit was determined from 1.6–2 GHz frequency limit. The results of comparable magnetic performance, lowest magnetic loss, and highest surface free energy, confirming that 15 sccm nitrogen flow rate at 115 W is optimal for producing Ag-doped permalloy flexible thin films having excellent magnetic field coupling efficiency.

Synthesis of Carbon-Encapsulated Iron and Iron Nitride Nanoparticles from Ferrocene Through Reactive Radio-Frequency Thermal Plasma

In this paper, carbon-encapsulated nanoparticles of iron and iron nitride were synthesized using ferrocene by reactive radio-frequency thermal plasma. The properties of the prepared nano-powders were investigated by TEM, XRD, Raman spectroscopy and VSM. The samples obtained with zero-nitrogen plasma, contains the carbon-encapsulated iron nanoparticles. There cores mainly composed of ferromagnetic α-Fe and paramagnetic γ-Fe, with carbon shell thicknesses of about 5 nm. The samples synthesized by the plasma with varying nitrogen flow rates, mainly consists of iron nitride and oxide having spherical and irregular shape with deteriorated and disappearing carbon shell. Particle size in all samples were 20-90 nm. Synthesized sample at zero-nitrogen condition showed a room-temperature saturation magnetization of 19.65 emu/g, with a coercivity of 375.1 Oe. The sample prepared with optimal nitrogen flow rate had a saturation magnetization of 35.25 emu/g at room temperature, with a coercivity and remanence of 49.1 Oe and 0.56 emu/g, respectively.

Analytical computation of distributed capacitance for NFC coil antenna

A new method for formulating the equivalent distributed capacitance of NFC coil antenna is proposed. This method is based on an analytical approach by conformal mapping for quantifying the capacitance per unit length and then applied the capacitance network method for calculating the equivalent distributed capacitance. The results of this method are verified with simulated and measured results of two different types of antenna and the agreement is >91%. It is also tested that the capacitance between nonadjacent turns cannot be ignored in the equivalent distributed capacitance computation. Furthermore, the effects of the coil width and gap between the two adjacent coils are predicted in calculating the equivalent distributed capacitance for a specific coil antenna. The proposed method will be useful for designing NFC coil antennas with a better accuracy of capacitance.