Influence of pulse electrodeposition parameters on microhardness,grain size and surface morphology of Ni–Co/SiO<Subscript>2</Subscript> nanocomposite coating

Ni–Co/SiO ₂ nanocomposite coatings and Ni–Co alloy coatings were prepared on steel substrate using direct and pulse electrodeposition methods. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray map and energy dispersive X-ray spectroscopy (EDX) were employed to investigate the phase structure, surface morphology, and elemental analysis of coatings, respectively. In high discharge rates, the surface morphology was rough, disordered and gross globular; on the contrary, in the low rates, it was smoother, more ordered and fine globular. Also, effect of electrodeposition parameters such as average current density, pulse frequency and duty cycle on the microhardness and grain size of nanocomposite coatings that produced through the pulse current electrodeposition method have been investigated. By amplifying both duty cycles up to 50% and average current density from 2 to 6 A dm^?2, microhardness increased, while the grain size decreased. But when duty cycle mounted on more than 50% and the average current density went up to 8 A dm^?2, microhardness lessened, while the grain size rose. The optimum value for pulse frequency was about 25 Hz. Results showed that microhardness of nanocomposite coatings which were produced by pulse current method was higher than that of produced by direct current method.     

双脉冲工作时间对Ni-W-P/CeO2-SiO2纳米复合材料电沉积的影响

通过Ni,W,P与CeO2,SiO2纳米颗粒的双脉冲电沉积,在普通碳钢表面制备了Ni-W-P/CeO2-SiO2纳米复合材料沉积层.在正、反向脉冲占空比(10%,30%)和正、反向脉冲平均电流密度(15.0,1.5 A/dm2)恒定下,研究了正、反向脉冲时间对纳米复合材料电沉积的影响.采用能谱、硬度测试和扫描电镜等方法,对纳米复合材料沉积层的化学组成、沉积速率、显微硬度和表面形貌进行了表征.结果表明:当正、反向脉冲时间分别控制在300 ms和40 ms时,Ni-W-P基质金属轮廓清晰,晶粒细小而均匀,CeO2和SiO2纳米颗粒在基质金属中均匀弥散分布;沉积层的化学组成(质量分数)为:70.89%Ni,9.89%W,8.59%P,7.35%CeO2,2.81%SiO2;沉积速率为45.1μm/h,显微硬度为706 HV.     

Pulse and direct electrodeposition of Ni–Co/micro and nanosized SiO2 particles

Ni–Co/SiO₂ composite coating was electrodeposited on the steel substrate. The coatings were characterized by X-ray diffraction and scanning electron microscopy. The microhardness of the composite coatings was studied by variation of the electroplating parameters, such as the pulse current (PC) and direct current (DC) electrodeposition methods, deposition temperature, electrolyte pH, concentration of surfactants, sodium dodecyl sulfate (SDS), and cetyltrimethylammonium bromide (CTAB). Zeta potential of SiO₂ particles measurements was performed with various pH, SDS, and CTAB concentrations. The data depict that the hardness of Ni–Co/SiO₂ nanocomposite coatings manufactured by PC electrodeposition increases with the increase of bath temperature, pH, SDS, and CTAB concentration up to 50°C, 4.6, 0.3, and 0.2?g/L, respectively. Beyond mentioned optimum values, the microhardness of nanocomposite coating decreases. Using DC method led to reduce the microhardness. Utilizing SiO₂ microparticles instead of SiO₂ nanoparticles for reinforcing resulted in declining the microhardness. The friction coefficient and wear results demonstrated that using PC method and nanosized particles led to reduce the friction coefficient and increase the resistance to wear. Anodic polarization results illustrated that using SiO₂ nanoparticles and PC method to prepare coating caused corrosion resistance of coating in a 3.5?wt% NaCl solution to enhance.     

Pulse electrodeposition and corrosion properties of Ni–Si3N4 nanocomposite coatings

The development of modern technology requires metallic materials with better surface properties. In the present investigation; Si₃N₄-reinforced nickel nanocomposite coatings were deposited on a mild steel substrate using pulse current electrodeposition process employing a nickel acetate bath. Surface morphology, composition, microstructure and crystal orientation of Ni and Ni–Si₃N₄ nanocomposite coatings were investigated by scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction analysis, respectively. The effect of incorporation of Si₃N₄ particles in the Ni nanocomposite coating on the micro hardness, corrosion behaviour has been evaluated. Smooth composite deposits containing well-distributed silicon nitride particles were obtained and the crystal grains on the surface of Ni–Si₃N₄ composite coating are compact. The crystallite structure was face centred cubic (fcc) for electrodeposited nickel and Ni–Si₃N₄ nanocomposite coatings. The micro hardness of the composite coatings (720 HV) was higher than that of pure nickel (310 HV) due to dispersion-strengthening and matrix grain refining and increased with the increase of incorporated Si₃N₄ particle content. The corrosion potential (E _corr) in the case of Ni–Si₃N₄ nanocomposite had shown a negative shift, confirming the cathodic protective nature of the coating.     

A new method for surface modification of TiO2/Al2O3 nanocomposites with enhanced anti-friction properties

In this paper, the TiO₂/Al₂O₃ composite nanoparticles were prepared by a hydrothermal method and in situ modified with acrylic acid. It was found that the mean particle size of modified TiO₂/Al₂O₃ composite nanoparticles was about 80 nm with a uniform distribution by the particle size analysis. The modified TiO₂/Al₂O₃ composite nanoparticles can disperse in lubricating oil homogenously for several weeks. The dispersion stabilization of modified TiO₂/Al₂O₃ composite nanoparticles in lubricating oil was significantly improved in comparison with the as-prepared nanoparticles, which was due to the introduction of grafted polymers by surface modification. The formation of covalent bands was identified by Fourier transform infrared spectrum. Under an optimized concentration of 0.1 wt%, the averaged friction coefficient was reduced by 14.75%, when the modified TiO₂/Al₂O₃ composite nanoparticles were used as lubricating oil additivities.     

Preparation, characterization and photocatalytic activity of TiO2/polyaniline core-shell nanocomposite

Polyaniline (PANI) as a promising conducting polymer has been used to prepare polyaniline/TiO₂ (PANI/TiO₂) nanocomposite with core-shell structure as photocatalyst. Titanium dioxide (TiO₂) nanoparticles with an average crystal size of 21?nm were encapsulated by PANI via the in situ polymerization of aniline on the surface of TiO₂ nanoparticles. FT?CIR, UV-Vis-NIR, XRD, SEM and TEM techniques were used to characterize the PANI/TiO₂ core-shell nanocomposite. Photocatalytic activity of PANI/TiO₂ nanocomposite was investigated under both UV and visible light irradiations and compared with unmodified TiO₂ nanoparticles. Results indicated deposition of PANI on the surface of TiO₂ nanoparticles which improved the photocatalytic activity of pristine TiO₂ nanoparticles.     

Investigation of Structural, Magnetic and Magnetotransport Properties of Electrodeposited Co–TiO2 Nanocomposite Films

Nanocomposite Co?CTiO₂ thin films were prepared by simultaneous electrodeposition of Co and TiO₂ on a Cu substrate from a solution based on Co sulfate in which TiO₂ nanoparticles were suspended by stirring. We investigated the influence of the TiO₂ nanoparticles concentration in the bath on the morphology, composition, magnetic and magnetotransport properties of the films. The Co?CTiO₂ thin films were characterized by using scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction analyses, and their magnetic properties were evaluated by using an induction type device with data acquisition system and a torque magnetometer. The current in-plane transport properties of the films have been investigated. The results showed that the films were composed of a Co metal matrix containing embedded TiO₂ nanoparticles and cobalt hydroxide which is formed simultaneously with cobalt metal deposition. The amount of TiO₂ in the film increases with the rising concentration of TiO₂ nanoparticles in the plating bath. This complex structure favored the increase of the magnetoresistance. The Co?CTiO₂ nanocomposite films (containing about 1.3 at.% Ti) exhibit a giant magnetoresistance contribution of 47.6 %. From the magnetic measurements, we have found that the saturation magnetization, the magnetic susceptibility, and the effective magnetic anisotropy constant decrease with the increasing content of TiO₂ in the thin layer. The easy magnetization axis direction changes from in-plane to almost perpendicular-to-plane, with increasing TiO₂ nanoparticles content in the film. The existence of a giant magnetoresistance effect in Co?CTiO₂ is very promising for potential applications in spintronics.     

Synthesis and Characterization of Cr-ZrO2 Composite Coating Formed by DC and Pulse Electrodeposition

Chromium–zirconia (Cr-ZrO₂) composite coatings were developed on low-carbon steel substrate by direct current (DC) and pulse electrodeposition (PED) technique with different pulse frequency and duty cycles to enhance mechanical properties of the coating. The phases and morphology of the coating were studied with scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. Surface mechanical properties were analyzed by micro-hardness and ball-on-plate wear study. It was found that pulsing and higher pulse frequencies refine the matrix and increase the ZrO₂ content in the coating. Apart from fine structure and dispersion, crystallographic orientation of Cr matrix also gives its effect on hardness and wear properties. Wear mechanism was found to be mainly abrasive in nature with little adhesive inclination in case of DC deposition.     

Pulse electrodeposition of Ag,Cu nanoparticles on TiO2 nanoring/nanotube arrays for enhanced photoelectrochemical water splitting

In this paper, plasmonic Ag and Cu nanoparticles were co-deposited on TiO₂ nanoring/nanotube arrays (TiO₂ R/T) by using two-step pulse electrodeposition method for investigating the optical and photoelectrochemical properties, in comparison to monometallic Ag, Cu decoration. By optimizing the electrodeposition cycle times and electrolyte concentration, bimetallic Ag–Cu/TiO₂ R/T-0.5 with moderate densities and sizes of Ag and Cu nanoparticles was fabricated and shows great photocatalytic potential, in which, Ag mainly facilitates the generation of hot electrons by absorbing visible light and Cu plays an important role in accelerating the separation and transportation of hot electrons. The hydrogen production rate was tested as 425 μL h^?1 cm^?2, which is about 1.34-fold enhanced H₂ production over TiO₂ R/T. Furthermore, molecular dynamics simulations were made for analyzing the interface electrostatic properties between plasmonic nanoparticles of Ag or Cu and the semiconductor TiO₂. It is calculated that bimetallic Ag–Cu/TiO₂/H₂O system has larger interfacial Helmholtz potential than monometallic Ag/TiO₂/H₂O, Cu/TiO₂/H₂O and pure TiO₂/H₂O systems, accelerating the four-electron reaction occurring at the semiconductor/electrolyte interface. This research put forward a feasible and simple pulse electrodeposition method to fabricate bimetallic photoanodes for enhanced hydrogen evolution and an important analysis method of semiconductor/ metal/electrolyte interface characteristics.     

超声场中脉冲电沉积Ni-CeO_2纳米复合镀层的耐蚀性

在超声场中用脉冲电沉积法制备了Ni-CeO2纳米复合镀层,考察了镀层中CeO2含量及表面形貌,研究了镀层在10wt%HCl溶液中的耐蚀性,分析了超声作用下脉冲参数对镀层耐蚀性的影响.结果表明:脉冲参数和超声波对镀层中CeO2含量和微观组织均有影响,适宜的脉冲参数可以提高镀层中CeO2含量,细化镀层晶粒,而超声波可促使镀层晶粒进一步细化;Ni-CeO2纳米复合镀层的耐蚀性与镀层中CeO2含量、镀层晶粒大小及组织致密程度有关;在占空比0.2、脉冲频率1000Hz时超声作用下制备的镀层中CeO2含量较高,镀层晶粒细小、组织致密,腐蚀速率最低,表现出优良的耐蚀性.     

Probing the compositional, structural and morphological aspects of CdSe-TiO2 nanocomposites by surface-sensitive techniques

In this work, a colloidal suspension of trioctyl phosphine oxide/trioctyl phosphine (TOPO/TOP)-capped CdSe QD's of size ∼5 nm was prepared by chemical route and these QD's were anchored on the surface of sol-gel prepared nanoporous TiO₂ layers in THF-ethanol solvent either by direct adsorption or with the aid of bi-functional linker molecule mercaptoacetic acid (MPA). The particle size estimation of both TiO₂ and CdSe nanoparticles by X-ray diffraction (XRD) and transmission electron microscopic (TEM) measurements concur well with each other. Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) studies elucidate the signatures of TiO₂, CdSe nanoparticles and linker which is also supported by the presence of contrasting images in TEM studies respectively. XPS depth-profiling measurements have been used as a probe to determine the chemical composition and structure of CdSe nanocrystals and CdSe-TiO₂ nanocomposites respectively. The CdSe nanoparticles and CdSe-TiO₂ nanocomposites formed by different routes are modeled, based on the observations of several complimentary techniques.     

Preparation and hydrophilicity of TiO2 sol-gel derived nanocomposite films modified with copper loaded TiO2 nanoparticles

In this study, TiO₂ nanocomposite films with 10 g/L of TiO₂ and copper loaded TiO₂ nanoparticles as nanofillers were deposited on the glass substrates using the sol gel dip-coating method. FE-SEM and UV-vis spectrophotometer were used to evaluate morphological and optical properties of copper loaded titania nanoparticles. In addition, XPS and water contact angle techniques were used to study the surface properties and superhydrophilicity of titania nanocomposite films, respectively. The results indicated that copper loaded TiO₂ nanoparticles had a significant effect on the hydrophilicity of nanocomposite film and maintaining it in a dark place for a long time (6.2 degree for titania nanocomposite films with copper loaded nanoparticle and 23.7 degree for nanocomposite film with titania nanoparticles).     

Effect of pulse duration on characteristics of modulated radio-frequency SiH4/N2/NH3 discharges

A one-dimensional fluid model is developed to investigate the behavior of plasma in the afterglow of pulsed voltage modulated SiH₄/N₂/NH₃ discharges at radio-frequency (400 kHz), which are used for the deposition of silicon nitride (SiN_x) films. The model incorporates particle balances, electron energy balance, and Poisson's equation, allowing the equations solved self-consistently. The current work is an attempt to understand the effect of duty cycle on the characteristics of silicon nitride (SiN_x) films. Therefore, the influences of duty cycle on the plasma density, electron temperature, and ion energy at the powered electrode were carefully discussed. We find that by decreasing the duty cycle, the negative ions can be able to escape during the off-time, and the positive ion energy is effectively decreased. On the other hand, the positive ion density is slightly decreased.     

A comprehensive study of structural and magnetic properties of sputter deposited nickel–silica thin films

The present work reports the formation of Ni nanoparticles inside the SiO₂ matrix and deals with the influence of Ni concentration on structural and magnetic properties of Ni–SiO₂ nanocomposite thin films. The films with varying Ni concentration (20–55 at% measured by Rutherford back scattering spectroscopy) were deposited using DC/RF magnetron co-sputtering. TEM and XRD analysis reveal the formation of FCC Ni nanoparticles in all the samples. The particle size varies from 3 to 10 nm as a function of Ni concentration. The surface roughness of the films is also found to increase with increase in nickel concentration. Magnetic measurements show that the Ni nanoparticles behave as superparamagnets when their size is ≤6 nm, in spite of their large volume fractions. The results show that the magnetic properties of the nanoparticles can be controlled by their size and Ni concentration in the samples.     

Effect of deposition parameters on microstructure of electrodeposited nickel thin films

Nickel thin films were prepared using electrodeposition process on a copper substrate. The effect of deposition parameters on film microstructure has been investigated with and without an organic additive (saccharin). Electrodeposition has been carried out using direct current electrodeposition (DCED) method and pulsed electrodeposition (PED) method. Significant reduction in crystallite size has been observed with the increase in saccharin concentration (~10 g/L) irrespective of the electrodeposition method. In PED, it has been observed that an increase in pulse width causes a drastic reduction in crystallite dimension (~15 nm) of the deposited Ni-film. Further PED process yielded needle-shaped Ni grains under controlled process conditions unlike in DCED, where spherical grain structure was observed in the micrographs. However, these needle-shaped grains change their microstructure on addition of saccharin to the bath. A phenomenological model is presented to explain the observed microstructural changes.     

Generation of Si:H nanoparticles by a combination of pulse plasma and hydrogen gas pulses

Si:H nanoparticles have been generated from 3 nm to 500 nm in count mean diameter (CMD) using a plasma chemical vapor deposition (CVD) system. In the present work, the nanoparticles are synthesized using cold plasma in order to get monodispersed size distribution with a combination of square wave modulated RF pulse plasma and a hydrogen gas pulse for better control of their size. The size of synthesized nanoparticles was measured by scanning mobility particle sizer (SMPS). The synthesis was carried out using pulse plasma with on-time of 1 s and off-time of 4 s. During 1 s on-time of plasma we added hydrogen gas pulses varying from 0.1 s to 0.9 s. Our results show that by utilizing dual pulse plasma and by controlling hydrogen gas pulse on-time we achieved smaller diameter Si nanoparticles. Hence, it is easier to generate smaller nanoparticles which generally have quantum effect and be utilized for various applications especially in solar cell application.     

Facile preparation of TiO2/C nanocomposites as anode materials for lithium-ion batteries

TiO₂/C nanospheres with diameter of 300–400 nm were synthesized by controlled thermal decomposition of titanium glycolate spheres in inert atmosphere. The effect of the calcination temperature and atmosphere on the structure and composition of the product are investigated. The products obtained by calcination of the precursor in nitrogen at 500°C consist of anatase and rutile nanoparticles, and amorphous carbon that is in situ generated from the organic components of glycolate precursor. When used as anode material for lithium-ion batteries, the as-prepared TiO₂/C nanocomposite delivers a capacity of 166 mAh/g after 250 charge/discharge cycles at a current rate of 0.2 C and give a good rate capability. The native carbon not only improves the local conductivity but also prevents the aggregation and growth of TiO₂ nanoparticles during calcination, allowing efficient electronic conductivity and Li ion diffusion.     

Characterizations of electrodeposited Ni–CeO2 nanocomposite coatings

The expansion of current machinery requires metallic materials with better surface properties. In the present investigation, CeO₂ reinforced nickel nanocomposite coatings were deposited on mild steel substrate by direct current electrodeposition process employing nickel acetate bath. The effect of incorporation of CeO₂ particles in the Ni nanocomposite coatings on the micro hardness and corrosion behaviour has been evaluated. Smooth and compact nanocomposite deposits containing well-distributed cerium oxide particles were obtained. The crystallite structure was fcc for electrodeposited nickel and Ni–CeO₂ nanocomposite coatings. It has been observed that, the presence of CeO₂ nanoparticles favours the [111] and [200] texture of nickel matrix. The co-deposition of CeO₂ nanoparticles with nickel was found to be favoured at applied current density of 8 A dm⁻². The micro hardness values of the nickel nanocomposite coatings (725 HV) was higher than that of pure nickel (265 HV).The decrease in I_corr values and increase in Constant Phase Element values were investigated in 3.5% NaCl solution which showed the higher corrosion resistant nature of Ni–CeO₂ coatings.     

Green synthesis of zinc oxide nanoparticles using tomato (Lycopersicon esculentum) extract and its photovoltaic application

With an increasing awareness of green and clean energy, zinc oxide-based solar cells were found to be suitable candidates for cost-effective and environmentally friendly energy conversion devices. In this paper, we have reported the green synthesis of zinc oxide nanoparticles (ZnONPs) by thermal method and under microwave irradiation using the aqueous extract of tomatoes as non-toxic and ecofriendly reducing material. The synthesised ZnONPs were characterised by UV–visible spectroscopy (UV–vis), infra-red spectroscopy, particle size analyser, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction study (XRD). A series of ZnO nanocomposites with titanium dioxide nanoparticles (TiO₂) and graphene oxide (GO) were prepared for photovoltaic application. Structural and morphological studies of these nanocomposites were carried out using UV–vis, SEM, XRD and AFM. The current–voltage measurements of the nanocomposites demonstrated enhanced power conversion efficiency of 6.18% in case of ZnO/GO/ TiO₂ nanocomposite.