Fabrication and characterization of graphene-reinforced waterborne polyurethane nanocomposite coatings by the sol–gel method

Functionalized graphene-reinforced polyurethane nanocomposite coatings were prepared using the sol–gel method. This method not only provides a “green” strategy for fabricating the graphene-based nanocomposites, but also realizes the covalent functionalization of graphene nanosheets with polymer matrix. The functionalization of graphene with conjugated organosilanes is favorable for improving mechanical and thermal properties of the nanocomposite coatings, which is mainly attributed to the homogeneous dispersion of functionalized graphene in the polymer matrix and strong interfacial interactions between the two components. A 71% increase in tensile strength and a 86% improvement of Young's modulus are observed by the addition of 2.0 wt.% of functionalized graphene. The experimentally determined Young's modulus corresponds well with the theoretical simulation under the hypothesis that the graphene sheets are randomly dispersed in the polymer matrix.     

Preparation and properties of atomic oxygen protective films deposited on Kapton by solvothermal and sol–gel methods

Due to a smooth hydrophobic surface of Kapton, it is very difficult for other materials to bond to it. In this study, using solvothermal method to modify the surface of Kapton substrates, the adhesion between silica film and Kapton substrate was greatly improved. Silica films were prepared on Kapton substrate via sol–gel method and the samples were irradiated by atomic oxygen (AO) in a ground-based simulation system. The AO erosion yield values of the samples after AO irradiation were tested. The surface morphology and the structure of silica films were investigated by scanning electronic microscope (SEM) and Fourier transformed infrared spectroscopy (FTIR). The results indicated that a uniform thin film was easily formed on the surface of Kapton. After AO exposure, the silica films become smoother and more uniform, without peeling off, and the AO erosion yield of coated Kapton was sharply down, equivalent to only 4.7% of pristine Kapton.     

Elaboration and characterization of nanocrystalline TiO2 thin films prepared by sol–gel dip-coating

Nanocrystalline TiO₂ thin films were deposited on a ITO coated glass substrate by sol–gel dip coating technique, the layers undergo a heat treatment at temperatures varying from 300 to 450 °C. The structural, morphological and optical characterizations of the as deposited and annealed films were carried out using X-ray diffraction (XRD), Raman spectroscopy, Atomic Force Microscopy (AFM), visible, (Fourier-Transform) infrared and ultraviolet spectroscopy, Fluorescence and spectroscopic ellipsometry. The results indicate that an anatase phase structure TiO₂ thin film with nanocrystallite size of about 15 nm can be obtained at the heat treatment temperature of 350 °C or above, that is to say, at the heat treatment temperature below 300 °C, the thin films grow in amorphous phase; while the heat treatment temperature is increased up to 400 °C or above, the thin film develops a crystalline phase corresponding to the titanium oxide anatase phase. We have accurately determined the layer thickness, refractive index and extinction coefficient of the TiO₂ thin films by the ellipsometric analysis. The optical gap decreases from 3.9 to 3.5 eV when the annealing temperature increases. Photocatalytic activity of the TiO₂ films was studied by monitoring the degradation of aqueous methylene blue under UV light irradiation and was observed that films annealed above 350 °C had good photocatalytic activity which is explained as due to the structural and morphological properties of the films.     

Hybrid materials on the basis of gelatin and hydrophilic–hydrophobic silica

Silica–gelatin films with different proportions of gelatin and silica have been prepared on the basis of gelatin and hydrophilic or hydrophilic–hydrophobic silica. The wettability of the hybrid materials, their swelling in aqueous media, and the thermal desorption of water from the obtained films are studied. It is shown that the presence of hydrophilic silica in the material gives rise to inhibition of swelling of the gelatin films and to a decrease in their affinity to water, while the replacement of hydrophilic silica by hydrophilic–hydrophobic silica allows one to additionally increase the hydrophobicity of hybrid materials.     

Evaluation of corrosion inhibition performance of silica sol–gel layers deposited on galvanised steel

The present work reports a comparative investigation of the electrochemical behaviour of some new types of silica sol–gel coatings with enhanced corrosion resistance deposited on electrolytically or thermally (hot-dip) zinc-coated steel. The coatings were rendered hydrophobic by silylation. Dichlorodimethylsilane or trimethylchlorosilane were used as silylating agents and cetyltrimethylammonium bromide or Pluronic PE 10300, as templating agents. The morpho-structural and optical properties of compact and mesoporous silica coatings were characterised with different methods. The corrosion behaviour of the coatings was evaluated by open circuit potential measurements, Tafel interpretation of the polarisation curves and electrochemical impedance spectroscopy. Both silylating agents improve significantly the corrosion resistance of both porous and compact coatings by reducing the corrosion current density with at least one order of magnitude. The possibility to use the porous structure of the coatings as corrosion inhibitor carriers was explored by loading of mesoporous silica layers with 1H-benzotriazole.     

Room temperature ferromagnetism of Si-doped ZnO thin films prepared by sol–gel method

Pure ZnO and Si-doped ZnO thin films were deposited on quartz substrate by using sol-gel spin coating process. X-ray diffraction analysis shows that all the thin films have hexagonal wurtzite structure and preferred c-axis orientation. Si-doped ZnO films show room temperature ferromagnetism (RTFM) and reach the maximum saturation magnetization value of 1.54 kAm-1 at 3% Siconcentration. RTFM of Si-doped ZnO decreases with the increasing annealing temperature because of the formation of SiO 2 . Photoluminescence measurements suggest that the RTFM in Si-doped ZnO can be attributed to the defect complex related to zinc vacancies V Zn and oxygen interstitials Oi .     

Glass-like CexOy sol–gel coatings for corrosion protection of aluminium and magnesium alloys

This work reports the preparation of glass-like, environmentally-friendly, cerium-based coatings for active corrosion protection of aluminium and magnesium alloys. It describes the production of cerium sol–gel sols from cerium nitrate and their deposition by immersion and automatic spray onto aluminium and magnesium alloys to produce uniform coatings with amorphous (glass-like) structures (Ce_xO_y). The coatings have been characterised by profilometry, scanning electron microscopy (SEM), spectral ellipsometry and UV–visible, in order to analyse the structure and density of the glass-like cerium coatings as well as their redox ratio Ce⁴⁺/Ce³⁺ as a function of pH and sintering temperature. Finally, electrochemical measurements (EIS) and standard corrosion tests (neutral salt spray, filiform corrosion, immersion–emersion test and adhesion on embossing and T-bend test) have been performed to study the corrosion behaviour of the cerium glass-like coatings on aluminium and magnesium alloys. EIS measurements confirm the healing or blocking of the defects by the corrosion inhibiting species. Excellent corrosion protection is provided by cerium glass-like coatings, satisfying the most demanding industrial requirements.     

Microstructural control of Cr–Si–N films by a hybrid arc ion plating and magnetron sputtering process

The microstructural evolution of Cr–Si–N films deposited by a hybrid arc ion plating and magnetron sputtering process was investigated by varying the sputtering power of Si target and substrate bias voltage. Detailed nanocomposite microstructures of the films were studied by high-resolution transmission electron microscopy. The results indicated that the incorporation of Si into the growing CrN films at 0 V led to the formation of a nanocomposite containing CrN nanocolumns embedded in amorphous SiN_x matrix or near-amorphous microstructure. For the films having a Si content of ～10 at.% and ～15 at.%, a negative bias voltage of ?50 V resulted in the aggregation of nanocolumns in the amorphous matrix. Further increase of negative bias voltage to ?250 V led to the formation of a three-dimensional CrN/a-SiN_x nanocomposite microstructure. The mechanism of microstructure evolution is discussed by considering the thermodynamic and kinetic factors.     

Polyindole top coat on TiO2 sol–gel films for corrosion protection of steel

The protection efficiency of polyindole film on stainless steel was enhanced via titanium dioxide pre-coating. The characterization of coatings was achieved by nuclear magnetic resonance and Fourier-transform infrared spectra. The surface morphology of electrodes was monitored with scanning electron microscope. The corrosion performance was investigated in 3.5% NaCl solution by electrochemical impedance spectroscopy and potentiodynamic measurements. The quantum calculations were employed, and theoretical parameters were determined. Results showed that the correlation between experimental and theoretical parameters. The high protection efficiency was observed against corrosion on the steel surface via forming a protective polyindole top coated titanium dioxide film.     

Fabrication of YBCO films on Ag substrate by TFA-MOD method

Biaxial aligned YBCO films have been successfully deposited on Ag { 110 } (110) textured polycrystalline substrates by metal-organic decomposition (MOD) method using Trifluoroacetate Salt (TFA). The influence of firing temperature and Ag surface defects on phase purity and texture, surface morphology of YBCO films was studied. Holding temperature at 900℃ for 30 rain benefits to improve orientation and connectivity of YBCO films. The surface of YBCO films deposited on unpolished Ag substrate has many holes and stripes, which are parallel to the rolling stripe on Ag substrates. To eliminate the rolling stripe on the Ag surface, Ag substrates were polished prior to films deposition. The film grown on polished Ag substrates has a smooth surface and good connectivity of grains without parallel stripes. The YBCO films have an onset of transition around 90K and critical current densities of 15000 A/cm^2.     

Investigation of high concentration of benzotriazole on corrosion behaviour of titania–benzotriazole hybrid nanostructured coating applied on Al 7075 by the sol–gel method

Nowadays, surface modification with self-healing ability is a valuable technique to improve chemical stability, oxidation behaviour and corrosion resistance of materials without interference with its physical, chemical or mechanical properties of bulk material underneath. In this paper, hybrid organic amorphous titania coatings are deposited on 7075 aluminium alloy substrates by using the sol–gel method. A titania–benzotriazole (BTA) nanostructured hybrid sol–gel coating is impregnated with three different high concentrations of BTA, 1.4, 2.8 and 4.2%. The bonds existing in the hybrid coating, structure and morphology and coating corrosion behaviour have been studied using the FTIR, GIXRD, field emission scanning electron microscopy and electrochemical impedance spectroscopy (EIS) test in a 3.5?wt-% NaCl solution during different immersion times, 24, 48, 72, 96 and 120?h. EIS studies indicated that a higher coating resistance value was gained for titania–4.2% BTA even after 120?h of immersion and BTA acted mainly on the amorphous titania coating as a corrosion inhibitor and a healing agent that acts by two mechanisms: first, release of a healing agent to the formation of corrosion products, then finally blocking surface defects; second, release of a healing agent during 48?h of immersion and its adsorption to produce an insulating layer on the surface of the coating in contact with the solution.     

Fabrication and anticorrosion performance of Ni–P–BN nanocomposite coatings on mild steel

Ni–P–BN composite coatings were successfully obtained on low carbon steel by the electroless plating technique. Deposits were characterized by the X-ray diffraction, scanning electron microscopy, and energy-dispersive analysis. The hardness and microstructure of as plated and heat treated Ni–P and Ni–P–BN composites were analyzed. Change in microstructure and higher hardness was noticed for the heattreated composite. The corrosion resistance of as plated and heat treated Ni–P and Ni–P–BN coatings was investigated by the Tafel plots and electrochemical impedance spectroscopy studies in 3.5 wt % NaCl. The heat-treated composite coatings exhibited enhanced corrosion resistance over that of Ni–P coatings.     

Photoluminescence and optical properties of nanostructure Ni doped ZnO thin films prepared by sol–gel spin coating technique

In this work, the spin coating sol–gel technique has been successfully used to deposit highly uniform and good adhesion of nano structure thin films of ZnO doped with different Ni concentrations. The morphological properties of ZnO:Ni films were studied by atomic force microscopy (AFM) technique. The surface morphology of the nanostructure films is found to depend on the concentration of Ni. The effects of Ni contents on the structural and photoluminescence (PL) properties of ZnO films were investigated. Optical constants (refractive index, n, and absorption index, k) of the undoped and Ni-doped ZnO of 0.2%, 0.4%, 0.6%, 0.8%, 1%, 3%, 5% and 7% concentrations have been obtained in the wavelength range 200–1000 nm by using spectrophotometric measurements. The dispersion parameters were determined and discussed based on the single oscillator model.     

Thermal stability of sol–gel p-type Al–N codoped ZnO films and electric properties of nanostructured ZnO homojunctions fabricated by spin-coating them on ZnO nanorods

The thermal stability of sol–gel p-type Al–N codoped ZnO films was investigated by high-resolution X-ray photoelectron spectroscopy (XPS). XPS revealed the chemical bonding states and solubility of N-related complex defects in the ZnO films. The concentrations of N_O and (NC)_O varied with annealing temperature, which led to the change in conduction between p-type and n-type. Variable-temperature Hall-effect measurement showed that N_O acted as a shallow acceptor, with its energy level locating at ～114 meV above the valance band maximum. Transmission electron microscopy confirmed the presence of undesired carbon clusters as a graphite state in the ZnO films. In order for Al–N codoped ZnO films to exhibit p-type conductivity, samples could only be annealed in a certain range of temperatures. A hybrid structure with nanostructured ZnO homojunctions was fabricated by spin-coating the p-type Al–N codoped ZnO film on an n-type ZnO nanorod array (ZNA). The hybrid nanostructure was demonstrated to possess rectification behavior characteristic of a p–n junction. The leakage current of the nanostructured ZnO homojunctions was smaller by a factor of 2 than that of the film-based ZnO homojunction at a reverse bias of 5 V. The p-type ZnO film/n-type ZNA structure can be applied as a versatile p–n optoelectronic device.     

Y and Al modified silicide coatings on an Nb–Ti–Si based ultrahigh temperature alloy prepared by pack cementation process

Y and Al modified silicide coatings were prepared on an Nb–Ti–Si based ultrahigh temperature alloy by co-depositing Si, Al and Y at 1150 °C for up to 10 h, respectively. The deposition of Al and Si occurred in a sequential manner during the pack cementation process. At the initial stage, the element deposited was primarily Al with very little Si and an Al₃(Nb,X) (X represents Ti, Cr and Hf elements) layer formed preferentially. After a short period of holding time, Si started depositing and Si–Al co-deposition took place. However, this Si–Al co-deposition period was not long. When the holding time was longer than 1 h at 1150 °C, Si deposition dominated the coating growth process. The coating growth kinetics at 1150 °C followed a parabolic law. The coating prepared at 1150 °C for 10 h had a multi-layer structure, with a thick (Nb,X)Si₂ outer layer, a thin (Ti,Nb)₅Si₄ middle layer and an Al, Cr-rich inner layer. The coating could protect the Nb–Ti–Si based alloy from oxidation at 1250 °C in air for at least 100 h. The excellent oxidation resistance of the coating was attributed to the formation of a dense scale mainly consisted of TiO₂, SiO₂ and Al₂O₃.     

Fabrication of ceramic layer on an Al-Si alloy by MAO process

The MAO (Micro-Arc Oxidation) process is applied to a eutectic Al-Si alloy (Al-12.0%Si-1.0%Cu-0.9%Mg (mass fraction)). The oxide ceramic layer was fabricated with about 220 (J.m thickness and 3000 Hv micro-hardness. By XRD (X-ray diffractometry) and DSC (differential scanning calorimetry) analyses, the oxide layer consists of amorphous A12O3, which is distinct from the results reported by the other researchers. The SEM photographs of such layer show that the layer is fixed tightly on the substrate alloy. So this alloy can be used in the high temperature and friction environment after it is treated with such process.     

Ceramic nanocomposites obtained by sol–gel coating of submicron powders

MgAl₂O₄–ZrO₂ nanocomposites were fabricated by conventional sintering of composite powders obtained by sol–gel coating of a submicron spinel powder. In the composite powder the zirconia grains remain narrow sized and completely tetragonal even after being heat treated at temperatures where a free xerogel is completely monoclinic. The sintered material exhibits a dense, fine and highly homogeneous microstructure. The zirconia nanoparticles are located at both inter- and intragranular positions and exhibit heteroepitaxial relationships with the surrounding crystals. Tetragonal zirconia seems to be stabilised by an interface effect. Both the scale of the microstructure and the fraction of intragranular grains were controlled by adjusting the mean grain size of spinel grains before coating and sintering conditions.     

Fabrication of ZnO films by radio frequency magnetron sputtering and annealing

ZnO thin films were deposited on Si（111） substrates through a radio frequency （rf） magnetron sputtering system. Then the samples were annealed at different temperatures in air ambience and ammonia ambience respectively. The structure and composition of the ZnO films were studied by X-ray diffraction （XRD） and X-ray photoelectron spectroscopy （XPS）. The morphology of the samples was studied by scanning electron microscopy （SEM）. Measured results show that ZnO films with hexagonal wurtzite structure were grown on Si（111） substrates when annealed in the two ambiences. The volatilization process of ZnO in the ammonia ambience at high temperature was discussed and the mechanism of the reaction was analyzed.     

Effect of current density on deposition process and properties of nanocrystalline Ni–Co–W alloy coatings

The nanostructure Ni–Co–W alloy coatings were electrodeposited onto a copper substrate using different applied current densities, in a modified Watts-type bath. The coatings were single-phase solid solutions with average grain sizes about 6–11 nm, calculated from X-ray diffraction patterns using the Scherrer equation. EIS results showed that the adsorption and reduction of W-containing ion complexes dominated at all applied current densities. However, the diffusion of the ion complexes reached to a limitation at higher current densities. The W and Co contents of the coatings decreased with an increase in the applied current density. A homogeneous nodular surface morphology was obtained at all current densities. The coatings produced at low current densities, containing higher amount of alloying elements, showed lower corrosion resistance.