Preparation, characterization, and application of alkaline leached Ni/Zn–Ni binary coatings for electro-oxidation of methanol in alkaline solution

The Ni–Zn binary coating was electrochemically deposited on a copper electrode. Then, it was etched in a concentrated alkaline solution (30 wt% NaOH) to obtain a porous electrocatalytic surface suitable for methanol electro-oxidation in alkaline solution. The surface compositions of coatings before and after alkaline leaching were determined by atomic absorption spectroscopy and energy dispersive X-ray analysis. The surface morphologies were investigated by scanning electron microscopy. It was found that the leached Ni–Zn coating has a porous structure. Electrocatalytic activity toward the methanol electro-oxidation was assessed by cyclic voltammetry and electrochemical impedance spectroscopy techniques. The activation of electrode related to the removal of existing corrosion products and formation of pores and cracks during alkaline leaching. Cyclic voltammetry studies confirmed that the alkaline leaching process improved the activity of Ni–Zn coating in comparison with smooth Ni deposit for the methanol electro-oxidation.     

Synthesis,characterization, and infrared-emissivity study of Ni–P–CB nanocomposite coatings by electroless process

The Ni–P–CB (carbon black) nanocomposite coatings have been successfully deposited on an ABS plastic matrix via electroless plating process. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) spectrometry techniques were employed to examine the surface morphology and structure of the as-plated coating. Energy dispersive spectroscopy (EDS) was adopted to obtain the component analysis of the Ni–P–CB composite coating, and the infrared emissivity of the coating was determined by the IRE-I Infrared Emissometer. SEM and XRD results indicated that the nanoparticles were dispersed homogeneously in the Ni–P coating; the result of EDS showed that the increased rate of CB content is in correspondence with its concentration. In the case that CB concentration is lower than 4 g/L, the increase rate is sharp, whereas when the concentration is higher than 4 g/L, the increase rate is reduced significantly. Furthermore, study of infrared emissivity shows that the nanocomposite coatings possessed low emissivity value. A comparison of the infrared emissivity dependence on surface resistivity obtained from the analysis of the experimental results and those calculated using the Hagen–Rubens relation indicates that the Hagen–Rubens relation is good for modeling the infrared emissivity of the Ni–P–CB nanocomposite coatings.     

Electrochemical characterization of Ni–P and Ni–Co–P amorphous alloy deposits obtained by electrodeposition

Ni–P and Ni–Co–P amorphous alloy deposits were obtained by electrodeposition at 80 °C on carbon steel substrates. The influence of the electrolyte Co²⁺ concentration and of applied current density was investigated. The corrosion behaviour of amorphous and crystalline deposits was evaluated by polarization curves and electrochemical impedance spectroscopy in NaCl 0.1 M solution at room temperature. Impedances were measured for samples under total immersion (free potential against time) and for polarized samples in predefined regions of the polarization curves. It was found that the alloy deposit composition is highly affected by the composition of the electrolyte but displays no significant dependence on applied current density. The results showed that the presence of Co on Ni–P amorphous alloys improves the deposit performance in the studied corrosive medium. It was also verified that the amorphous structure provides higher corrosion resistance to both Ni–P and Ni–Co–P alloys.     

Deposition and characterization of nanocrystalline and amorphous Ni–W coatings with embedded alumina nanoparticles

Nanocrystalline and amorphous Ni–W coatings containing Al₂O₃ nanoparticles were electrodeposited from three different ammoniacal citrate baths by direct current (DC) method. The effects of nanoparticles on compositional, structural and morphological features of Ni–W coatings were investigated. The effects of bath chemical composition and current density on codeposition behavior of nanoparticles were also studied. Guglielmi model for particle deposition was applied to identify the kinetics of particle deposition. The presence of nanoparticles may affect on coating grain size, tungsten content and the rate of metal deposition. In addition, nanoparticles can result in more compact coatings with fewer defects. The extent of these effects depends on bath chemical composition and may be influenced by the synergistic effect of Ni on deposition of W. It was also found that the kinetics of particle deposition and the effect of current density on codeposition behavior of nanoparticles are highly dependent on bath chemical composition.     

Preparation and characterization of chitosan–zeolite composites

Double crosslinked chitosan–zeolite (CZ-2) and noncrosslinked chitosan–zeolite (CZ-0) composites were prepared and characterized by using Fourier transform infrared (FTIR) spectrometer, surface area analyzer, scanning electron microscope coupled with energy dispersive X-ray (SEM-EDX) spectrometer, thermogravimetric analyzer (TGA), X-ray diffraction analyzer (XRD) and carbon, hydrogen, nitrogen (CHN) analyzer. After crosslinking, CZ-2 showed a reduction in surface area and CHN content in comparison to chitosan, zeolite, and CZ-0. Crosslinking resulted in improved stability of CZ-2 in distilled water, acetic acid and NaOH as CZ-2 recorded the lowest percentage of swelling. XRD diffractograms confirmed the formation of composites as there was a marked difference in the peak intensity at 2θ = 19.8°. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of PLLA–ESO/surface-grafted silica nanocomposites

Various amounts of surface-grafted silica (g-SiO₂) and un-grafted (SiO₂) nanoparticles were solution blended with a copolymer of l-lactide and epoxidized soybean oil (PLLA–ESO) or PLLA. Chemical reaction between the low molecular weight (LMW) PLLA and surface of silica nanoparticles is confirmed by FTIR and TGA analyses. The amount of grafted LMW PLLA investigated by thermal gravimetric analysis (TGA) was about 14.9%–28.2% in weight. g-SiO₂ nanoparticles can be easily dispersed into PLLA–ESO matrix to form a uniform PLLA–ESO/g-SiO₂ composite. Thermal properties of PLLA–ESO/g-SiO₂ and PLLA/g-SiO₂ nanocomposites were subsequently investigated by the differential scanning calorimeter measurements (DSC). DSC analyses indicated that g-SiO₂ nanoparticles can serve as a nucleating agent for the crystallization of PLLA–ESO in the composites, while the melting temperature (T _m) and the glass transition temperature (T _g) of PLLA–ESO/g-SiO₂ nanocomposites seemed to be independent of loading of g-SiO₂ particles. The DSC curves of PLLA/g-SiO₂ nanocomposite obviously showed double melting peaks, while that of PLLA–ESO/g-SiO₂ nanocomposites only a single melting peak. PLLA–ESO/g-SiO₂ composites exhibited a higher tensile strength and elongation than that of PLLA–ESO/SiO₂ composites.     

Preparation and characterization of nanocrystalline Fe–Ni–Cr alloy electrodeposits on Fe substrate

Fe–Ni–Cr alloy layers were prepared by electrodeposition from trivalent chromium plating bath in chloride-sulfate based solution. The influences of bath composition and plating parameters on the alloy electrodeposition process and the properties of deposited alloy were studied. The effects of plating parameters and bath composition such as current density, bath pH, bath temperature, the concentrations of FeSO₄ · 7H₂O and CrCl₃ · 6H₂O on the contents of Fe and Cr in Fe–Ni–Cr alloy layer were investigated. Electrodeposited Fe–Ni–Cr alloy layers on Fe substrate were characterized by X-ray diffraction (XRD), Electronic Differential System (EDS) and a CHI600B electrochemistry workstation. The composition of the Fe–Ni–Cr coatings depends on bath composition and plating conditions including pH, current density, and temperature. The internal structure of the alloy is nanocrystalline, the average grain size is 87 nm, and the corrosion resistance of the alloy layers is better than that of pure nickel layers.     

Preparation of dendritic waterborne polyurethane-urea/Ni–Zn ferrite composite coatings and investigation of their microwave absorption properties

This study shows the preparation of microwave absorbing composite material by using Ni–Zn ferrite filler and dendritic waterborne polyurethane-urea (WPU) polymer as a matrix. Initially, waterborne polyurethane prepolymers were synthesized by using PEG1500 (WPU1) and PPG1000 (WPU2) polyols via prepolymer mixing process. Then, chain extended with water in the presence of hexamethylenetetramine (HMTA) as crosslinker. Then, 1/1 (w/w) amount of Ni–Zn ferrite was dispersed in the WPU polymer to be converted into a microwave absorbing composite coating (CWPU1 and CWPU2). Structural, mechanical and morphological properties were investigated. The microwave absorption measurements were performed by using transmission/reflection method via waveguide method in the frequency range of 8.2–12.4 GHz. Permittivity and permeability measurements were performed in the frequency range of 8.2–12.4 GHz. It has been found that CWPU1 which was prepared by using WPU1 polymer indicated broader microwave absorption between 9.4 and 11.7 GHz due to its dendritic structure. Besides, permittivity and permeability results indicated that CWPU1 and CWPU2 have distinctive magnetic properties.     

Effects of saccharin on the electrodeposition of Ni–Co nanocrystalline coatings

Nickel–Co nanocrystalline coatings were electrodeposited onto a carbon steel substrate with and without saccharin addition. In the absence of saccharin, current density and adsorption of hydrogen complexes and/or intermediate components were distinguished as two effective parameters causing nanocrystalline electrodeposits. In the latter case, the growth active sites can be blocked easily at low current densities. By increasing the current density, a lower degree of adsorption was associated by a significant increase in surface diffusion of adions resulting in grain growth. Although, the nucleation rate is expected to increase with current density, it seems that the Ni–Co grain size is not reduced by the nucleation rate. Adsorption of saccharin molecules and/or decomposed sulfide species occurred in the saccharin contained bath, resulting in slow surface diffusion of adions. Therefore, finer grains were obtained which produced a smooth morphology instead of the pyramidal forms obtained in the absence of saccharin.     

Preparation and characterization of phosphine oxide containing organosilica hybrid coatings by photopolymerization and sol–gel process

A series of UV-cured organic–inorganic hybrid coating materials containing up to 20 wt.% silica were prepared by sol–gel method from tetraethoxy silane (TEOS) which is used as the primary inorganic precursor, and diallylphenylphosphine oxide monomer (DAPPO), aliphatic urethane diacrylate resin (Ebecryl 210) are employed as the source of the organic components. In addition, methacryloxypropyltrimethoxy silane (MAPTMS) was used as both a secondary inorganic source and a silane-coupling agent to improve the compatibility of the organic and inorganic phases. The DAPPO content in all the coating formulations were from 0 to 20 wt.%. The physical and mechanical properties such as gel content, hardness, adhesion, gloss, contact angle as well as tensile strength were measured. These measurements revealed that all the properties of the hybrid coatings improved effectively, in case of adding the sol–gel precursor and DAPPO monomer content in the hybrid systems. The photo-calorimetric-DSC studies showed that the double bond conversion of the hybrid coatings was faster than the coating materials without silica. The thermal stabilities of the UV-cured hybrid materials were investigated by thermogravimetric analysis. The results showed that the addition of sol–gel precursor and DAPPO into the organic network also improves the thermal-oxidative stability of the hybrid coating materials. The surface morphology was also characterized by scanning electron microscopy (SEM). SEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix.     

Synthesis and characterization of polybenzimidazole–nanodiamond hybrids via in situ polymerization method

Poly[2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI) was polymerized in poly(phosphoric acid) (PPA) with the presence of the pristine nanodiamonds (NDs) (0.2–5 wt %) to fabricate NDs-g-OPBI/OPBI nanocomposites via Friedel–Crafts (F-C) reaction. The OPBI chains were successfully attached to the NDs through F-C reaction between carboxylic acid from OPBI and NDs, which was proved by nuclear magnetic resonance, X-ray photoelectron, and X-ray diffraction. NDs-g-OPBI/OPBI nanocomposites show more homogeneous dispersion than the physical blending containing pristine NDs and OPBI matrix, as showed through scanning electronic microscopy images. The mechanical properties, including Young's modulus, yield strength, and tensile strength are all improved by the introduction of NDs (<1 wt %) without loss of ductility, which overcomes the brittleness brought by the addition of inorganic reinforced agent in traditional composites. Dynamic mechanical analysis results showed that the modulus of the ND-g-OPBI/OPBI nanocomposites was significantly higher than OPBI matrix, and the NDs-g-OPBI/OPBI nanocomposites displayed more pronounced improvement than the physical blending, which could be ascribed to the homogeneous dispersion of NDs particles and the covalent bonding between NDs and OPBI via F-C reaction. Thermogravimetric analysis indicated that all the OPBI nanocomposites containing NDs displayed the improved thermal stability. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of electrospun polyurethane–polypyrrole nanofibers and films

Polyurethane (PU)–polypyrrole (PPy) composite films and nanofibers were successfully prepared for the purpose of combining the properties of PU and PPy. Pyrrole (Py) monomer was polymerized and dispersed uniformly throughout the PU matrix by means of oxidative polymerization with cerium(IV) [ceric ammonium nitrate Ce(IV)] in dimethylformamide. Films and nanofibers were prepared with this solution. The effects of the PPy content on the thermal, mechanical, dielectric, and morphological properties of the composites were investigated with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR)–attenuated total reflection (ATR) spectroscopy, dielectric spectrometry, and scanning electron microscopy. The Young's modulus and glass-transition temperatures of the composites exhibited an increasing trend with increases in the initially added amount of Py. The electrical conductivities of the composite films and nanofibers increased. The crystallinity of the composites were followed with DSC, the mechanical properties were followed with DMA, and the spectroscopic results were followed with FTIR–ATR spectroscopy. In the composite films, a new absorption band located at about 1650 cm⁻¹ appeared, and its intensity improved with the addition of Py. The studied composites show potential for promising applications in advanced electronic devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of silica sol/fluoroacrylate core–shell nanocomposite emulsion

The silica sol/fluoroacrylate core?Cshell nanocomposite emulsion was successfully synthesized via traditional emulsion polymerization through grafting of KH-570 onto silica particles. Comparing the performance of the polyacrylate copolymer, the fluorinated polyacrylate copolymer and the silica sol/fluoroacrylate core?Cshell nanocomposite emulsion, we can come to a conclusion that the silica sol/fluoroacrylate core?Cshell nanocomposite emulsion presents significantly excellent performance in all aspects. The products were characterized by Fourier transform infrared (FTIR), photon correlation spectroscopy (PCS), transmission electron microscopy (TEM), thermogravimetry (TGA), Contact angle and UV?Cvis analyses techniques. The chemical structure of polyacrylate copolymer, fluorinated polyacrylate copolymer and silica sol/fluoroacrylate nanocomposite were detected by FTIR. The size and stability of emulsion latex particles were determined by PCS technique. TEM analysis confirmed that the resultant latex particle has the core?Cshell structure, obviously. The water absorption and contact angle data also showed that the silica sol/fluoroacrylate nanocomposite film has good hydrophobic performance. TGA analysis indicated the weight loss of the silica sol/fluoroacrylate nanocomposite film begins at around 350?°C which testifies its good thermal stability. The UV?Cvis spectroscopy analysis showed that the silica sol/fluoroacrylate nanocomposite film possess UV?Cvis shielding effect when the added volume amount of KH570 modified silica sol is up to 5?mL. Therefore, the excellent properties of hydrophobicity, thermodynamics and resistance to ultraviolet provide the silica sol/fluoroacrylate nanocomposite film with potential applications in variety fields. In addition, the formation mechanism of core?Cshell structure silica sol/fluoroacrylate nanocomposite latex particles was speculated.     

Synthesis and characterization of hyperbranched polyester–urethane–urea/K10-clay hybrid coatings

A series of hyperbranched polyester–urethane–urea/K10-clay hybrid coatings (AHBPE-1 and AHBPE-2) have been prepared. Initially, the polyester polyols are synthesized separately in a step-wise manner using pentaerythritol (PE), phtallic anhydride (PTA) and trimethylol propane (TMP). The cetyltrimethylammonium bromide (CTAB) modified K10-clay is used as an organoclay for the hybrid composites preparation and dispersed into the polyester matrix by ultrasonication method. This clay-dispersed polyols are used for further synthesis. The degree of branching (DB), percentage of condensation reaction and quantity of dendritic (D), terminal (T) and linear (L) units present in the polyester are calculated, from the NMR peak integration value. The NMR result suggests that, there is formation of nearly 63% of condensation product in the polyester. A structure–property correlation is established, based on the hydrogen bonding effect with increasing clay content by using the FT-IR peak deconvulation technique. The dynamic mechanical and thermal analysis (DMTA) as well as thermo gravimetric analysis (TGA) results show, an increase in room temperature storage modulus (E′), glass transition temperature (T_g) and thermal stability of the hybrid coatings with increasing clay content and NCO/OH ratio. The contact angle measurement study suggests that, the hydrophilicity of the hybrid films increases with increasing clay content and decreases with increasing NCO/OH ratio.     

Preparation and characterization of polyhedral oligomeric silsesquioxane–titania aerogels

The novel polyhedral oligomeric silsesquioxane (POSS)–titania aerogels which contain different contents of titania were successfully prepared by the sol–gel process and subsequently supercritical drying with carbon dioxide. All the aerogels are monolithic and the densities of those aerogels are low. The FTIR spectra of the aerogels showed the resulting POSS–TiO₂ composite aerogels had homogeneous Si–O–Ti bonds. The microstructure, surface composition and thermal stability were measured by FESEM, XPS and TGA. With the increasing of titania contents, the aggregated particles of the aerogels in the microstructure got larger and larger. The texture of the aerogels was measured by XRD and nitrogen adsorption/desorption and showed that they were amorphous and had high surface area (>500 m²/g).     

Young's modulus and adhesion coefficient of amorphous Ni–P coatings on a metal substrate

In the present paper the Young's modulus and adhesion coefficient of amorphous Ni–P coatings obtained from aqueous solutions were determined. The measurements were carried out using a vibrating reed apparatus. In the temperature range 550–590 K, crystallization of Ni and formation of nickel phosphide Ni₃P were observed. The Young's modulus of Ni–P amorphous layers on stainless steel at room temperature was found to be about 112 GPa. The adhesion coefficient γ of the examined layers depends on the layer thickness a _f and strongly decreases for a _f > 8 μm. This dependence corresponds to the change of the relative adhesion coefficient of about 40% for 8 μm < a _f < 15 μm. It was also shown that the adhesion coefficient does not depend on the temperature, at least in the range 300–550 K.     

Structure and properties of electrodeposited Ni–Co–YZA composite coatings

The aim is to develop an economical composite coating with high thermal stability. Ni–Co alloys are found to possess better thermal, physical and mechanical properties compared to Ni. Also, oxide particles as distributed phase can impart better thermal stability. Hence, particulates of composite Yttria stabilised zirconia, a commonly used high temperature material and alumina (YZA) were reinforced in various Ni–Co alloy matrices through electrodeposition. The influence of YZA on the microhardness, tribology and corrosion behaviour of Ni–Co alloys with Co contents of 0 wt.%, 17 wt.%, 38 wt.% and 85 wt.% was evaluated. Optical and Scanning Electron Microscopy (SEM) confirmed the presence of YZA particles and Energy Dispersive X-ray Analysis (EDX) revealed the composition. Tribology testing showed that composite containing 38 wt.% Co displayed better wear resistance. It was found from the immersion corrosion studies that Ni–17Co–YZA coating displayed improved corrosion resistance. Thermal stability studies showed that Ni–85Co–YZA coating retained its microhardness at temperatures of 600 °C. Thus, these coatings can be tailored for various applications by varying the cobalt content.     

Electrodeposition and corrosion behavior of Zn–Ni and Zn–Ni–Fe2O3 coatings

A thin film of Zn–Ni–Fe₂O₃ on steel substrates was prepared by electrodeposition technique using Zn–Ni alloy plating solution with nano-sized Fe₂O₃ particles. The cathodic polarization and cyclic voltammetry techniques were used to explain deposition process. The corrosion behavior of deposits was evaluated by polarization and impedance studies. Scanning electron microscope (SEM) images were used to study the surface morphology of coating. The grain size and amount of Fe₂O₃ particles present in composite coating were measured by X-ray diffraction pattern (XRD) and energy dispersive X-ray diffraction spectrometer (EDS), respectively.     

Chemical synthesis of TiO2 nanoparticles and their inclusion in Ni–P electroless coatings

The work addresses the preparation of Ni3P3TiO₂ nanocomposite coatings on mild steel substrate by the electroless technique. Nanosized TiO₂ particles were first synthesized by the precipitation method and then were codeposited (4 g/l) into the Ni3P matrix using alkaline hypophosphite reduced EL bath. The surface morphology, particle size, elemental composition and phase analysis of as-synthesized TiO₂ nanoparticles and the coatings were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive analysis of X-ray (EDAX) and X-ray diffraction (XRD). Coatings with 20 µm thickness were heat treated at 400 °C for 1 h in argon atmosphere. The morphology, microhardness, wear resistance and friction coefficient characteristics (ball on disc) of electroless Ni3P3TiO₂ nanocomposite coatings were determined and compared with Ni3P coatings. The results show that as-synthesized TiO₂ nanoparticles are spherical in shape with a size of about12 nm. After heat treatment, the microhardness and wear resistance of the coatings are improved significantly. Superior microhardness and wear resistance are observed for Ni3P3TiO₂ nanocomposite coatings over Ni3P coatings.