Physical and electrochemical characterizations of Ni-SiO2 nanocomposite coatings

Advances in materials performance often require the development of composite system. In the present investigation, SiO₂-reinforced nickel composite coatings were deposited on a mild steel substrate using direct current electrodeposition process employing a nickel acetate bath. Surface morphology, composition, microstructure and crystal orientation of the Ni and Ni-SiO₂ nanocomposite coatings were investigated by scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction analysis, respectively. The effect of incorporation of SiO₂ particles in the Ni nanocomposite coating on the microhardness and corrosion behaviour has been evaluated. Smooth composite deposits containing well-distributed silicon oxide particles were obtained. The preferred growth process of the nickel matrix in crystallographic directions <111>, <200> and <220> is strongly influenced by SiO₂ nanoparticles. The average crystallite size was calculated by using X-ray diffraction analysis and it was ~23 nm for electrodeposited nickel and ~21 nm for Ni-SiO₂ nanocomposite coatings. The crystallite structure was fcc for electrodeposited nickel and Ni-SiO₂ nanocomposite coatings. The incorporation of SiO₂ particles into the Ni matrices was found to improve corrosion resistance of pure Ni coatings. The corrosion potential (E _corr) in the case of Ni-SiO₂ nanocomposite coatings had shown a negative shift, confirming the cathodic protective nature of the coating. The Ni-SiO₂ composite coatings have exhibited significantly improved microhardness (615 HV) compared to pure nickel coatings (265 HV)     

Nanocomposites of Poly(vinyl alcohol) Reinforced with Chemically Modified AL2O3: Synthesis and Characterization

The surface of α-alumina (Al₂O₃) nanoparticles was first modified with γ-aminopropyltriethoxy silane as a coupling agent. Then a series of poly(vinyl alcohol)/ surface modified Al₂O₃ nanocomposite suspensions were prepared in ethanol by a simple ultrasonic irradiation process. Composite films with 5, 10, and 15 wt % of inorganic Al₂O₃ nanoparticles were achieved after solvent evaporation. The formation of the composite materials were confirmed by Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and optical transparencies. The FE-SEM and TEM results showed a homogenous dispersion of nanoscale inorganic particles in the poly(vinyl alcohol) matrix. TGA thermographs showed that the thermal stability of the prepared Al₂O₃-reinforced nanocomposites was improved, increasing with increasing content of the nanoparticles. According to the optical transparencies, the optical clarity of poly(vinyl alcohol)/Al₂O₃ nanocomposite films was only slightly affected by the presence of the Al₂O₃ content.     

Improvement of corrosion resistance of AA6061 alloy by tapioca starch in seawater

This study examines the use of tapioca starch for improvement of corrosion resistance of AA6061 alloy in seawater. Gravimetric, potentiodynamic polarization, linear polarization resistance and electrochemical impedance measurements were employed to study the corrosion behavior of AA6061 alloy in seawater. The electrochemical measurements for AA6061 alloy in seawater showed that the presence of tapioca starch significantly decreases the corrosion rates, corrosion current densities (i_corr), and double layer capacitance (C_dl), simultaneously increases the values of polarization resistance (R_p). The inhibition efficiencies increase with increasing of tapioca starch concentration. The Langmuir adsorption isotherm fits well with the experimental data. The nature of adsorption of tapioca starch on the metal surface has also been examined. The analysis of SEM and EDS confirmed the formation of precipitates of tapioca starch on the metal surface, which reduced the overall corrosion reaction.     

Composite coatings of polyamide/graphene: microstructure,mechanical, thermal,and barrier properties

This effort reports on novel fluorinated polyamide (FPA) and polyamide 1010 (PA1010)-based blends and graphene reinforced nanocomposite. PA1010/FPA (80:20) blend was opted as matrix material on the basis of molecular weight, thermal, and shear stress performance. Graphene was obtained through in situ chemical method of graphene oxide reduction. PA1010/FPA/Graphene nanocomposites was developed using various graphene loadings (up to 5 wt.%). Thin film coatings were prepared on glass substrate. Consequently, the PA1010/FPA/Graphene attained regular spongy morphological pattern. PA1010/FPA/Graphene 3 also showed improved T₀ and T_max of 534 and 591 °C relative to the neat blend (T₁₀ 423 °C; T_max 551 °C). Limiting oxygen index measurement indicated better non-flammability of PA1010/FPA/Graphene 1–3 nanocomposite series (57–60%) relative to the blend series (28–31%). UL94 tests also showed V-0 rating for nanocomposites. Furthermore, PA1010/FPA/Graphene 3 nanocomposite revealed significantly high tensile strength (62 MPa), flexural modulus (1690 MPa), and adhesive properties to be utilized as coating materials. The nanocomposite coatings also displayed outstanding barrier properties against O₂ and H₂O compared with neat blends.     

Structural,optical and electrical properties of 60 MeV C5+ ion-irradiated poly(3-methylthiophene) films

The structural, optical and electrical properties of 60 MeV C⁵⁺ ion-irradiated poly(3-methylthiophene) (P3MT) synthesized by the chemical oxidation polymerization method have been studied. The P3MT powder was dissolved in chloroform (CHCl₃), and thin films of thickness 2 μm were prepared on glass and Si substrates. The polymerization was confirmed by the FTIR spectrum. Then films were irradiated by 60 MeV C⁵⁺ ions at different fluences. FTIR spectra show methyl group evolution after irradiation. The optical band gap decreases slightly after irradiation and the DC conductivity increases by about one order of magnitude after irradiation at the highest fluence. The role of S _e has also been discussed when compared with 60 MeV Si⁵⁺ ion irradiation of P3MT. The morphological changes are observed using SEM.     

EMI shielding effectiveness of graphene decorated with graphene quantum dots and silver nanoparticles reinforced PVDF nanocomposites

Graphene decorated with graphene quantum dots (G-D-GQDs) have been successfully synthesized using solvothermal cutting of graphene oxide. The incorporation of G-D-GQDs in polyvinyledene fluoride (PVDF) matrix shows the total EMI shielding effectiveness (SE_T) of 31 dB at 8 GHz. The main mechanism of high EMI shielding effectiveness is reflection and absorption of EM radiation. The high absorption of EM radiation is due to tunneling of electrons from GQDs. Further, decoration of G-D-GQDs with conducting Ag nanoparticles (G-D-GQDsAg) enhances the SE_T value to 43 dB at 8 GHz of PVDF/G-D-GQDsAg nanocomposite, due to increase in electrical conductivity of PVDF/G-D-GQDsAg nanocomposite and enhanced dispersion of G-D-GQDsAg in PVDF matrix. The incorporation of G-D-GQDs and G-D-GQDsAg in PVDF matrix also increases the thermal stability and crystallinity of PVDF. The increase in thermal stability and crystallinity are more for PVDF/G-D-GQDsAg nanocomposite as compare to PVDF/G-D-GQDs nanocomposite, due to better dispersion of G-D-GQDsAg in PVDF matrix. Thus, PVDF/G-D-GQDsAg nanocomposite having high SE_T value can shield 99.9% of electromagnetic radiation in X-band range, which make it suitable for EMI shielding application for consumer electronic equipment’s.     

Sonochemical approach for synthesis of zinc oxide-poly methyl methacrylate hybrid nanoparticles and its application in corrosion inhibition

Hybrid nanoparticles (HNPs) with zinc oxide and polymethyl metha acrylate (inorganic/ polymer) were synthesized through the exploitation of ultrasound approach. The synthesized HNPs were further characterized employing transmission electron microscopy and x-ray diffraction. ZnO-PMMA based HNPs exhibit excellent protection properties to mild steel from corrosion when gets exposed to acidic condition. Electrochemical impendence spectroscopy (EIS) analysis was accomplished to evaluate the corrosion inhibition performance of MS panel coated with 2 wt% or 4 wt% of HNPs and its comparison with bare panel and that of loaded with only standard epoxy coating., Tafel plot and Nyquist plot analysis depicted that the corrosion current density (I_corr) decreases from 16.7 A/m² for bare material to 0.103 A/m² for 4% coating of HNPs. Applied potential (E_corr) values shifted from negative to positive side. These results were further supported by qualitative analysis. The images taken over a period of time indicated the increase in lifetime of MS panel from 2 to 3 days for bare panel to 10 days for HNPs coated panel, showing that ZnO-PMMA HNPs have potential application in metal protection from corrosion by forming a passive layer.     

Synchrotron infrared reflectance microspectroscopy study of film formation and breakdown on copper

This work demonstrates the utility of synchrotron infrared reflectance microspectroscopy in the far‐ and mid‐IR for the determination of the composition of electrogenerated surface films formed during the general and localized corrosion of copper in alkaline and bicarbonate solutions. Back‐reflection geometry has been employed to identify the anodic film formed on copper in 0.1 M NaOH solution at 0.3 V (versus a Ag/AgCl reference) to be mainly CuO. In 0.01 M NaHCO₃ solution general corrosion occurs with passive film formation below 0.2 V. The surface film at 0.2 V consisted mainly of bicarbonate, copper carbonate dihydroxide or malachite [CuCO₃·Cu(OH)₂], Cu(OH)₂ and possibly some CuO. At higher potentials the passive film breaks down and localized corrosion occurs leading to the formation of pits. The composition of the surface films inside the pits formed at 0.6 V was found to be essentially the same as that outside but the relative amount of Cu(OH)₂ appears to be higher.     

Ferroelectric characteristics of MFIS structure with P(VDF–TrFE)/BaTiO3 nanocomposite as ferroelectric layer

A metal–ferroelectric–insulator–semiconductor (MFIS) structure has been made using poly(vinylidene difluoride–trifluoroethylene)/barium titanate [P(VDF–TrFE)/BaTiO₃] nanocomposite as ferroelectric layer, on silicon/silicon dioxide (Si/SiO₂) substrate. Different concentrations of BaTiO₃ were added to P(VDF–TrFE) polymer using bath sonication method, and the films were prepared using spin coating method. The structure was annealed to 120 °C for 2 h and then the top aluminium electrode was deposited by thermal evaporation method. Capacitance–voltage shows an increase in accumulation capacitance as the BaTiO₃ nanoparticle concentrations increases. Dielectric constant was estimated from the capacitance voltage (C–V) characteristics and found to be changing as the concentration of BaTiO₃ is varied. Polarization–electric field analyses show hysteresis behaviour of the nanocomposite. A comparison of MFIS and metal–ferroelectric–semiconductor structures was done with varying ferroelectric film thicknesses. All these results suggest that this polymer nanocomposite can be a promising material which can be used in non-volatile memory devices.     

Effect of ZnO filler concentration on the conductivity, structure and morphology of PVdF-HFP nanocomposite solid polymer electrolyte for lithium battery application

The polyvinylidene difluoride-co-hexafluoropropylene (PVdF-HFP) nanocomposite solid polymer electrolyte films were developed by solution-casting method. PVdF-HFP as a polymer host, lithium perchlorate (LiClO₄) as a salt for lithium ion, and ZnO nanoparticles as fillers were used to form the nanocomposite solid polymer electrolyte films. All the prepared samples were characterized by X-ray diffraction (XRD), differential scanning calorimetry, and scanning electron microscopy. The XRD patterns of the pure and nanocomposite solid polymer electrolyte samples indicate the formation of amorphous phase with 17.5 wt.% of lithium salt and ZnO fillers up to 3 wt.%. The total conductivity and lithium ion transference number were studied at room temperature by using impedance spectroscopy and Wagner’s polarization methods. The highest conductivity at room temperature for solid polymer electrolyte and nanocomposite solid polymer electrolyte are found to be 3.208?×?10^?4 and 1.043?×?10^?3 S/cm, respectively. Similarly, the lithium ion transference number is evaluated for the optimized solid polymer electrolyte and nanocomposite solid polymer electrolyte films with 3 wt.% of ZnO fillers. And it is found that ionic transference number could be enhanced from 92 to 95 % with the addition of nanosized ZnO fillers to the solid polymer electrolyte.     

Morphological,photovoltaic, and electron transport properties of In2O3-based DSSC with different concentrations of MWCNTs

This study focuses on the influence of loading MWCNTs in In₂O₃-based DSSCs. In₂O₃-MWCNTs were prepared by sol-gel method via spin coating technique and annealed at 450 °C. The structural, morphology, and electrical properties of the photoanodes were characterized by means of XRD, AFM and FESEM, and J-V curve measurement and EIS properties, respectively. Incorporation of MWCNTs in In₂O₃ improved the J _sc and V _oc of the cell. However, excess loading of MWCNTs in In₂O₃ caused a serious aggregation of MWCNTs that increased the recombination rate. Thus, In₂O₃-MWCNTs with 0.3 % of MWCNTs achieved the highest PCE of 1.23 % with large surface area for efficient dye adsorption. Moreover, In₂O₃-MWCNTs_(0.3%) exhibited large D _eff about 25.7 × 10⁻³ cm² s⁻¹ with low recombination effect that increased the PCE. This study suggests an optimum MWCNT incorporation of 0.3 % in the photoanode by sol-gel synthesis method of developing In₂O₃-based nanocomposite.

     

Polypyrrole–NiO hybrid nanocomposite films: highly selective,sensitive, and reproducible NO2 sensors

Polypyrrole–nickel oxide (PPy–NiO) hybrid nanocomposite thin-film sensor was prepared by spin-coating method on glass substrate. The PPy–NiO hybrid nanocomposite thin film sensors were used to study room temperature gas-sensing properties for oxidizing (NO₂, Cl₂) as well as reducing (NO₂, H₂S, C₂H₅OH, NH₃, and Cl₂) gases. It was revealed that PPy–NiO (50 %) hybrid nanocomposite thin-film sensor could detect NO₂ at low concentration (100 ppm) with very high selectivity (47 % compared with Cl₂) and high sensitivity (47 %), with better stability (90 %) and reproducibility. The response and recovery times were changed significantly with NO₂ concentration.     

A selective sensor for nanolevel detection of lead (II) in hazardous wastes using ionic-liquid/Schiff base/MWCNTs/nanosilica as a highly sensitive composite

An effective potentiometric sensor had been fabricated for the rapid determination of Pb²⁺ based on carbon paste electrode consisting of room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆), multiwalled carbon nanotubes (MWCNTs), nanosilica, synthesized Schiff base, as an ionophore, and graphite powder. The constructed nanocomposite electrode showed better sensitivity, selectivity, response time, response stability, and lifetime in comparison with typical Pb²⁺ carbon paste electrode for the successfully determination of Pb²⁺ ions in water and in waste water samples. The best response for nanocomposite electrode was obtained with electrode composition of 18% ionophore, 20% BMIM-PF₆, 49% graphite powder, 10% MWCNT, and 3% nanosilica. The new electrode exhibited a Nernstian response (29.76?±?0.10 mV decade^?1) toward Pb²⁺ ions in the range of 5?×?10^?9?C1.0?×?10^?1 mol L^?1 with a detection limit of 2.51?×?10^?9 mol L^?1. The potentiometric response of prepared sensor is independent of the pH of test solution in the pH range of 4.5?C8.0. It has quick response with response time of about 6 s. The proposed electrode show fairly good selectivity over some alkali, alkaline earth, transition, and heavy metal ions.     

Formation mechanisms of nanocomposite layers based on multiwalled carbon nanotubes and non-stoichiometric tin oxide

Nanocomposite layers based on multiwalled carbon nanotubes (MWCNTs) and non-stoichiometric tin oxide (SnO _x ) have been grown by magnetron deposition and CVD methods. In the case of the CVD method, the study of the structure and phase composition of obtained nanocomposite layers has shown that a tin oxide “superlattice” is formed in the MWCNT layer volume, fixed by SnO _x islands on the MWCNT surface. During magnetron deposition, the MWCNT surface is uniformly coated with tin oxide islands, which causes a change in properties of individual nanotubes. Electrical measurements have revealed the sensitivity of nanocomposite layers to (NO₂)⁻ molecule adsorption, which is qualitatively explained by a change in the conductivity of the semiconductor fraction of p-type MWCNTs.     

Structural,thermal and electrical properties of polyvinyl alcohol/poly(vinyl pyrrolidone)–sodium nitrate solid polymer blend electrolyte

Sodium ion conducting solid polymer blend electrolyte thin films have been prepared by using polyvinyl alcohol (PVA)/poly(vinyl pyrrolidone) (PVP) with NaNO₃ by solution cast technique. The prepared films were characterized by various methods. The complexation of the salt with the polymer blend was identified by X-ray diffraction (XRD) and Fourier transforms infrared spectroscopy (FTIR), Differential scanning calorimetry was used to analyze the thermal behavior of the samples, and the glass transition temperature is low for the highest conducting polymer material. The scanning electron microscopy gives the surface morphology of the polymer electrolytes. The frequency and temperature dependent of electrical conductivities of the films were studied using impedance analyzer in the frequency range of 1 Hz to 1 MHz. The highest electrical conductivity of 50PVA/50PVP/2 wt% NaNO₃ concentration has been found to be 1.25 × 10^?5 S cm^?1 at room temperature. The electrical permittivity of the polymer films have been studied for various temperatures. The transference number measurements showed that the charge transport is mainly due to ions than electrons. Using this highest conducting polymer electrolyte, an electrochemical cell is fabricated and the parameters of the cells are tabulated.     

Intensification of corrosion resistance of 2 K epoxy coating by encapsulation of liquid inhibitor in nanocontainer core of sodium zinc molybdate and iron oxide

A unique approach for the synthesis of an iron oxide-blended sodium zinc molybdate nanocontainer using an ultrasound-assisted method and its application for 2?K epoxy polyamide nanocomposite coatings has been presented. Sodium zinc molybdate blended with iron oxide was used as the core of the nanocontainer and layer-by-layer assembly of oppositely charged species of polyelectrolyte and inhibitor was made over this core of nanoparticles. The release of imidazole from iron oxide-blended sodium zinc molybdate nanocontainer has been quantitatively evaluated in water at different pH. It has been observed that imidazole plays a major role in the release profile of polyelectrolyte-modified nanocontainer and deciding the corrosion inhibition characteristics. Addition of 4 wt% nanocontainer in coatings results in shifting of corrosion potential (E_corr) value towards positive direction. The maximum concentration of imidazole released at the end of 1?h was found to be 0.545?mg?L^?1/g of nanocontainer at pH of 10. The results of corrosion rate analysis, Tafel plots and electrochemical impedance spectroscopy studies of an iron oxide-blended sodium zinc molybdate nanocontainer-based coatings indicated better inhibition performance compared with neat coating.     

Evolution of the interfacial phases in Al2O3–Kovar® joints brazed using a Ag–Cu–Ti-based alloy

Abstract

A systematic investigation of the brazing of Al₂O₃ to Kovar^® (Fe–29Ni–17Co wt.%) using the active braze alloy (ABA) Ag–35.25Cu–1.75Ti wt.% has been undertaken to study the chemical reactions at the interfaces of the joints. The extent to which silica-based secondary phases in the Al₂O₃ participate in the reactions at the ABA/Al₂O₃ interface has been clarified. Another aspect of this work has been to determine the influence of various brazing parameters, such as the peak temperature, T_p, and time at T_p, τ, on the resultant microstructure. As a consequence, the microstructural evolution of the joints as a function of T_p and τ is discussed in some detail. The formation of a Fe₂Ti layer on the Kovar^® and its growth, along with adjacent Ni₃Ti particles in the ABA, dominate the microstructural developments at the ABA/Kovar^® interface. The presence of Kovar^® next to the ABA does not change the intrinsic chemical reactions occurring at the ABA/Al₂O₃ interface. However, the extent of these reactions is limited if the purity of the Al₂O₃ is high, and so it is necessary to have some silica-rich secondary phase in the Al₂O₃ to facilitate the formation of a Ti₃Cu₃O layer on the Al₂O₃. Breakdown of the Ti₃Cu₃O layer, together with fracture of the Fe₂Ti layer and separation of this layer from the Kovar^®, has been avoided by brazing at temperatures close to the liquidus temperature of the ABA for short periods of time, e.g., for T_p between 820 and 830 °C and τ between 2 and 8 min.     

Synthesis, characterization and catalytic oxidation properties of multi-wall carbon nanotubes with a covalently attached copper(II) salen complex

Hydroxyl functionalized copper(II) Schiff-base, N,N′-bis(4-hydroxysalicylidene)-ethylene-1,2-diaminecopper(II), [Cu((OH)₂-salen)], has been covalently anchored on modified MWCNTs. The new modified MWCNTs ([Cu((OH)₂-salen)]-MWCNTs) have been characterized by TEM, thermal analysis, XRD, XPS, UV-vis, DRS, FT-IR spectroscopy and elemental analysis. The modified copper(II) MWCNTs solid was used to affect the catalytic oxidation of ethylbenzene with tert-butylhydroperoxide as the oxidant at 333 K. The system is truly heterogeneous (no leaching observed) and reusable (no decrease in activity) in three consecutive runs. Acetophenone was the major product though small amounts of o- and p-hydroxyacetophenones were also formed revealing that C-H bond activation takes place both at benzylic and aromatic ring carbon atoms. Ring hydroxylation was more over the “neat” complexes than over the encapsulated complexes.     

Carbon nanotubes supported Cu-Ni bimetallic catalysts and their properties for the direct synthesis of dimethyl carbonate from methanol and carbon dioxide

Multi-walled carbon nanotubes (MWCNTs) supported Cu-Ni bimetallic catalysts for the direct synthesis of dimethyl carbonate (DMC) from CH₃OH and CO₂ were synthesized and investigated. The supporting materials and the synthesized catalysts were fully characterized using FTIR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) techniques. The catalytic activities were investigated by performing micro-reactions. The experimental results showed that the metal phase and Cu-Ni alloy phase in the catalyst were partially formed during the calcination and activation step. Active metal particles were dispersed homogeneously on the surface of the MWCNTs. Cu-Ni/MWCNTs catalysts were efficient for the direct synthesis of DMC. The highest conversion of CH₃OH was higher than 4.3% and the selectivity of DMC was higher than 85.0% under the optimal catalytic conditions of 120 °C and around 1.2 MPa. The high catalytic activity of Cu-Ni/MWCNTs in DMC synthesis can be attributed to the synergetic effects of metal Cu, Ni and Cu-Ni alloy in the activation of CH₃OH and CO₂, the unique structure of MWCNTs and the interaction between the metal particles and the supports.     

AC conductivity and relaxation behavior in ion conducting polymer nanocomposite

We report the ac conductivity and relaxation behavior analysis for a heterogeneous polymer–clay nanocomposite (PNC) having composition (polyacrylonitrile)₈LiCF₃SO₃ + x wt.% dodecylamine modified montmorillonite. Charge transport behavior in an ionically conducting PNC has been analyzed systematically and correlated with the macroscopic parameters like polymer glass transition temperature and available free mobile charge carriers. Intercalation of cation coordinated polymer into the nanometric clay channels has been confirmed by high-resolution transmission electron microscopy. The electrical properties of the intercalated PNC films have been studied using complex impedance/admittance spectroscopy. Excellent correlation of relaxation behavior with polymer glass transition temperature (T _g) confirmed the objectives of the work. An analysis of dielectric relaxation indicates that PNC films are lossy when compared with polymer–salt film. This result is a direct outcome of faster ion dynamics leading to strong electrode polarization effect due to the accumulation of charge carriers at the interface.