Ni SiO Research Articles

Influence of surfactant concentration on structural properties and corrosion behaviour of electrodeposited Ni–SiO2 nanocomposite coatings

Abstract In this study, Ni–SiO2 nanocomposite coatings were deposited on the surface of X70 steel by performing direct current electrodeposition. The effect of different concentrations of cetyltrimethylammonium bromide surfactant (0.3, 0.5, 1, and 2 g L−1) on particle distribution and corrosion behaviour of the coatings was analysed. The structural properties of the obtained coatings were evaluated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis, X-ray diffraction, and atomic force microscopy. The corrosion behaviour of the coatings was tested by potentiodynamic polarisation and electrochemical impedance spectroscopy. The results showed that the electrodeposited coatings obtained from the electroplating bath with 1 g L−1 of surfactant modified the surface morphology of the Ni–SiO2 nanocomposite coating and presented a finer and more uniform microstructure. The results of the phase structure analysis showed that the addition of the surfactant in the electrodeposition process changed the preferred orientations for the coatings from (111) to (220) and (200) planes. The anti-corrosion performance of the resulting coating produced in the presence of 1 g L−1 of surfactant was significantly higher than the anti-corrosion performance of the other coatings and showed a lower corrosion rate.

Corrosion resistance, thermal diffusivity and mechanical properties of Ni–SiO2 nanocomposite coatings on a 316 stainless steel for heat exchanger applications

Abstract In this study, the effect of pure Ni and Ni–SiO2 nanocomposites coatings on corrosion, wear resistance and thermal conductivity of 316 stainless steel substrates was investigated with the purpose of extending the service life of 316 stainless steel plate heat exchangers. The nanocomposite coatings were developed by electroplating process in a Watts bath in different concentration values of SiO2 nanoparticles (10, 20 and 30 g l−1). Electrochemical corrosion was run to examine the corrosive performance of the coatings. The results showed that the Ni–SiO2 nanocomposite with concentration of 30 g l−1 had a higher corrosion resistance. A pin on disk wear test demonstrated that, in comparison to 316 stainless steel, the wear resistance of the Ni–SiO2 nanocomposite (30 g l−1) was up to 25% lower while its friction coefficient was almost the same. In addition, as measured via the laser flash method and differential scanning calorimetry, the thermal diffusivity and specific heat capacity of the sample respectively were found to be 32 and 43% lower in comparison to 316 stainless steel. Microhardness measurement via a Vickers microindenter showed that the microhardness of the Ni–SiO2 nanocomposite coating was more than three times higher than that of 316 stainless steel for all the reinforcement concentrations.

Synthesis of Ni-SiO₂/C Supported Platinum Catalysts for Improved Electrochemical Activity Towards Ethanol Oxidation.

A series of Pt/Ni-SiO₂/C catalysts with different mass proportions of Ni-SiO₂/C (0:100, 30:70, 50:50, 70:30 and 100:0) were prepared and studied towards ethanol electrochemical oxidation in acid medium. The support silica particles were initially synthesized via sol-gel and then modified with NiCl2. The Ni deposited on the silica surface plays a role promoting nucleation sites for the reduction of platinum. Pt was further chemically reduced onto Ni-SiO₂ using formic acid and loaded onto carbon Vulcan XC-72 R. The Pt/Ni-SiO₂/C catalysts were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, temperature-programmed reduction, X-ray photoelectron spectroscopy, transmission electron microscopy and inductively coupled plasma-optical emission spectroscopy. The physical characterizations reveal the formation of oxide-metal composite and strong interaction between Pt and the Ni-SiO₂ composite. The Pt/Ni-SiO₂/C catalyst with meso/macroporous structure exhibits higher electrocatalytic activity towards ethanol oxidation and better stability, after 48 h of electrolysis, than a commercial Pt/C catalyst. These improved features could be due to presence of Ni-SiO₂ composite that promotes corrosion resistance of the support and prevents the aggregation of Pt nanoparticles and their detachment from the support. The low poisoning of the Pt/Ni-SiO₂/C catalyst is probably due to the enhanced oxygen content on the composite surface. The high electrocatalytic activity and enhanced electrochemical stability of the Pt/Ni-SiO₂/C catalyst make it promising for further fuel cell applications.

Removal of hexavalent chromium from aqueous solutions using Ni–SiO$$_{2}$$ nanomaterials

This study describes an effective method developed for the removal of hexavalent chromium, Cr(VI), from an aqueous environment. In this study, the Ni– $$\hbox {SiO}_{{2}}$$ nanomaterial was synthesized by the sol–gel method and then characterized by field emission scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. The prepared nanomaterial was then employed as an adsorbent with significant properties of high surface area and uptake capacity. Adsorption conditions of Cr(VI) onto the Ni– $$\hbox {SiO}_{{2}}$$ nanomaterial were optimized by altering different parameters (pH, initial Cr(VI) concentration and different periods of time). An amount of 100.75 mg $$\hbox {g}^{-1}$$ was estimated as the maximum uptake capacity of the Ni– $$\hbox {SiO}_{{2}}$$ nanomaterial at pH 4.0. The experimental data of Cr(VI) adsorption onto the Ni– $$\hbox {SiO}_{{2}}$$ nanomaterial were fitted well to the Langmuir isotherm and pseudo second-order kinetic models. Moreover, the adsorption of Cr(VI) onto the Ni– $$\hbox {SiO}_{{2}}$$ nanomaterial was not influenced even in the presence of different coexisting ions. Finally, the recommended methodology was applied on several environmental water samples.

Ni-phyllosilicate structure derived Ni–SiO2–MgO catalysts for bi-reforming applications: acidity, basicity and thermal stability

In this work, Ni–SiO2–MgO materials synthesized via Ni-phyllosilicate (PS) intermediates were explored for bi-reforming of methane (BRM) reaction.

Highly Active and Stable Ni–SiO2Prepared by a Complex-Decomposition Method for Pressurized Carbon Dioxide Reforming of Methane

A series of Ni–SiO2 catalysts was synthesized by the complex-decomposition method using different amino acids as complexing agents and fuels and nickel nitrate and tetraethoxysilane as precursors of Ni and SiO2, respectively. For comparison, ammonium hydroxide and acetic acid were also used as complexing agents and fuels. Characterization by XRD, TEM, and N2 adsorption–desorption at low temperature indicated that the structural and textural properties of the Ni–SiO2 catalysts were strongly dependent on the complexing agent used. The dispersion of metallic Ni was increased by optimizing the complexing agent used. As revealed from H2-TPR patterns, Ni–SiO2 exhibited significantly different interactions between Ni and SiO2, the extent of which was influenced by the complexing agent used. The Ni–SiO2 catalysts were comparatively evaluated for carbon dioxide reforming of methane (CDR) under the following conditions: CH4/CO2 = 1.0, T = 750 °C, GHSV = 53200 mL·g–1·h–1, and P = 1.0 atm. The results indicate that the Ni–SiO2 materials prepared with glycine, alanine, serine, threonine, valine, and proline exhibited much higher activity and stability for CDR under atmospheric conditions than those prepared with lysine, acetic acid, and ammonium hydroxide. Moreover, the Ni–SiO2 material prepared with glycine was also tested at elevated pressures of 5.0 and 10.0 atm. The effect of pressure on the CDR performance was investigated. Importantly, a highly active and stable Ni–SiO2 material for pressurized CDR was obtained by tailoring the structure of Ni–SiO2 and adjusting the interactions between Ni and SiO2 by selecting the complexing agent. Thus, the main factors determining catalyst activity and stability for CDR were clearly revealed.

Synthesis of Ni–SiO 2 composite microspheres in situ in ethylene glycol

In this study, the Ni–SiO2 composite microspheres were synthesised in situ in ethylene glycol. The nickel colloidal suspension was synthesised by hydrazine reduction in ethylene glycol with the addition of polyvinylpyrrolidone, and then coated on by silica using the modified Stober process. The as-synthesised samples were characterised by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and vibrating sample magnetometer. XRD patterns showed that as-prepared nickel colloids are consistent with face-centred cubic phase and the broad peak at around 25° is attributed to amorphous SiO2 in Ni–SiO2 composite microspheres. TEM and SEM images indicated as-obtained Ni–SiO2 composite microspheres appear near spherical with a size of about 100–200 nm, and get well dispersed. Magnetisation curves demonstrated the saturation magnetisation value of as-prepared Ni–SiO2 composite microspheres is 4.4 emu/g with the content of nickel of about 20 wt.%.

Hollow Ni–SiO 2 nanosphere-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

Nickel clusters contained within silica nanospheres (20–30 nm) were synthesized by using a Ni(NH 3) 6Cl 2 crystal template method in a polyoxyethylene–nonylphenyl ether/cyclohexane reversed micelle system followed by an in situ reduction in aqueous NaBH 4/NH 3BH 3 solutions. Metallic nickel clusters exist inside the SiO 2 nanospheres prepared by the method while oxidized nickel clusters prepared by the conventional impregnation method were supported on the outer surface of silica as shown in the results of transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The nickel clusters inside of silica nanospheres show higher catalytic activity for hydrolysis of ammonia borane to generate stoichiometric amount of hydrogen than the supported nickel catalysts.

Cobalt, nickel and ruthenium-silica based materials synthesized by the sol–gel method

The physical and chemical characteristics of silica based materials and doped with different metals (Ni, Co and Ru) synthesized by the sol–gel method were investigated. The used techniques were: temperature programmed reduction, thermogravimetric analysis, specific surface area measurements, X-ray diffraction and Photoacoustic Spectroscopy. After calcination, higher surface areas were obtained, with the larger value for Ru–SiO 2 (550 m 2/g), followed by Ni–SiO 2 (337 m 2/g) and Co–SiO 2 (298 m 2/g). For Ni–SiO 2, the nickel oxide is present at the surface in two different forms. This also happens for the Co–SiO 2 material, which showed two reduction peaks, probably attributed to the Co III ⇒ Co II and Co II ⇒ Co 0 reaction. However, for Ru–SiO 2 only one peak reduction was observed. The X-ray diffraction data revealed the existence of an amorphous structure, while thermogravimetric analysis showed that the calcination procedure decomposes the organic residues adsorbed at the material surface.

Synthesis and magnetic properties of Ni–SiO 2 nanocomposites

Nanocomposite Ni (1 − x) /(SiO 2) x soft magnetic materials were synthesized by a simple sol–gel combined hydrogen reduction method. The crystal structure of the particles was determined by X-ray diffraction (XRD). The shapes and sizes of the metal particles embedded in the SiO 2 matrix were determined by transmission electron microscopy (TEM), and magnetic properties were measured by the vibrating samples magnetometer (VSM). The obtained nanocomposite material is composed of nanoparticles coated with a thin SiO 2 layer, and with the content of the silicon increase, the thickness of the silica shells increase and the saturation magnetization decrease. The diameter of Ni particle in the sample is about 30–40 nm. The influence of the Ni content and preparation conditions on the microstructures and magnetic properties were discussed.

Direct growth of the multi-walled carbon nanotubes as a tool to detect ammonia at room temperature

In this work, we report on the application of multi-walled carbon nanotubes as gas sensors. We use the vertical growth of aligned carbon nanotubes on structure surfaces composed by a set of Ni electrodes and SiO 2 surfaces fraction. The results show that carbon nanotubes could be efficient in terms of sensibility for detection of pollutant species like NH 3 even at ambient temperature. The determination of the adsorption energies for various species on the basis of a semi-empirical potential approach show that gases, particularly the polar one, are able to bind strongly on carbon nanotubes surfaces and could explain at least qualitatively the experimental results.

Proton transfer in SrCeO 3-based oxide with internal reformation under supply of CH 4 and H 2O

Mass and charge transfer in a proton-conducting ceramic with internal reformation under the supply of CH 4 + H 2O was experimentally investigated for application to a fuel detritiation system of a fusion reactor. The oxide used in the present experiment was SrCe 0.95Yb 0.05O 3− a , and the electrodes were composed of Ni–SiO 2 paste and Ni wire mesh. The system was described by CH 4 + H 2O∣Ni∣SrCe 0.95Yb 0.05O 3− a ∣NiO∣O 2 + H 2O. Plots of the I– V (electric current density versus cell potential) characteristic curve were determined under the conditions of different H 2O/CH 4 concentration ratios and temperatures of 600–800 °C. It was found that the system could work well even without any external CH 4 reformer. Mass-transfer process in/on the porous Ni electrode and in the ceramic electrolyte was experimentally clarified. The distribution of carbon depositions in the porous electrode was also determined with EDX by scanning over entire surface in the scope of SEM. The ratio of CH 4 to H 2 direct decomposition to its steam-reforming reaction was found to be different from location to location in the porous Ni electrode.

Optical properties of sol–gel SiO 2 films containing nickel

SiO 2 films containing nickel were prepared using the sol–gel method with nominal Si to Ni atomic ratios of 1.2, 3.1 and 7.1. After thermal annealing under different conditions, the optical properties of the films were studied using optical reflectance and transmittance measurements. It was found that samples annealed in air at 500 °C show an absorption band at wavelengths of about 440 nm associated with Ni 2+ ions in octahedral positions. In addition, in films with Si to Ni atomic ratios of 1.2 and 3.1, there is an absorption edge at short wavelengths, indicating the formation of NiO nanosized particles. Samples with a Si to Ni atomic ratio of 1.2 were also heat-treated in a H 2/N 2 atmosphere at 500 and 800 °C, producing metallic Ni nanoparticles embedded in the vitreous matrix. The effective dielectric function of both NiO–SiO 2 and Ni–SiO 2 composite films was modeled with the Maxwell–Garnett expression. X-ray diffraction measurements confirm the presence of NiO and Ni nanoparticles in the films.

Ni/SiO 2 and Fe/SiO 2 catalysts for production of hydrogen and filamentous carbon via methane decomposition

High-loaded Ni–SiO 2 and Fe–SiO 2 catalysts (85–90 wt.% of metal) for methane decomposition were prepared by the heterophase sol–gel method and studied at various stages of their preparation and operation using XRD, IR, TPR, TEM techniques and the stoichiographic method of differentiating dissolution. Carbon yield was demonstrated to depend on the interaction between nickel and silica. The yield equal to 384 g C/g Ni was characteristic of the catalyst free of silicates, while the presence of silicates in amount of 1.5–2 wt.% caused a decrease in the carbon yield to 40 g C/g Ni. The effect of silicates comprised in iron catalysts is not so unambiguous as for nickel catalysts, they can both inhibit and promote the process of carbon formation.

Rhodium–phosphine complex catalysts tethered on silica-supported heterogeneous metal catalysts: arene hydrogenation under atmospheric pressure

The rhodium–phosphine complex, RhCl(CO)[Ph 2P(CH 2) 3Si(OC 2H 5) 3] 2 (Rh–P), was tethered to silica-supported metal heterogeneous catalysts, Pd–SiO 2, Ni–SiO 2 and Au–SiO 2, to give the tethered complex catalysts Rh–P/Pd–SiO 2, Rh–P/Ni–SiO 2 and Rh–P/Au–SiO 2. An IR (DRIFTS) study shows that the structure of the tethered rhodium–phosphine complex (Rh–P) in all of these combination catalysts is the same as that of the free Rh–P complex. These heterogenized complex catalysts consisting of a tethered complex on a supported metal (TCSM) were used to catalyze the hydrogenation of arenes under the mild conditions of 40°C and 1 atm of H 2. The most active TCSM catalyst Rh–P/Pd–SiO 2 is not only much more active than the homogeneous Rh–P complex and Pd–SiO 2 but also much more active than the rhodium–phosphine complex tethered on just SiO 2 (Rh–P/SiO 2). The Rh–P/Pd–SiO 2 catalyst gives a maximum turnover frequency (TOF, mol H 2/mol Rh min) of 2.9 and a turnover (TO, mol H 2/mol Rh) of 1940 during a 23 h period in the hydrogenation of toluene. When the tethered rhodium–phosphine complex catalyst stands in air for 2 months or longer, the phosphine ligand is oxidized to the phosphine oxide. This air-aged Rh–P/Pd–SiO 2 is much more active than the fresh catalyst for the hydrogenation of toluene, but the air-aged Rh–P/SiO 2 becomes inactive for this reaction. These two air-aged catalysts were characterized by solid state 31 P NMR and DRIFTS using CO as a probe.

Thermoelectric Power and Hall Effect in Co–Al–O Granular Films

We have measured the thermoelectric power and Hall effect on three Co–Al–O granular films whose conduction mechanism varies from metallic to tunneling type depending on O content. We obtained a finite thermoelectric power (TEP) which decreases with increasing resistivity. In the tunneling type sample, a large field dependence of TEP correlated with the magnetoresistance has been observed. The Hall coefficient of Co–Al–O decreases with increasing sample resistivity, in contrast with the giant Hall effect reported for Ni–SiO 2 granular sample with a similar resistivity. The dominant electronic conduction mechanisms are found to be different between the giant magnetoresistance and the giant Hall effect in ferromagnetic-metal-oxide granular systems.

Sol–gel preparation and characterization of Ni–SiO 2 nanocomposites

A series of Ni–SiO 2 composites, in the range 7–80 mol% of nickel, were prepared by two gelation methods with tetraethylorthosilicate (TEOS) and nickel(II) nitrate as starting materials. In the first method an aqueous solution of the salt was used while the second employed an alcoholic solution. The methods also differed in the intermediate thermal treatments of the gels. All the systems were reduced at temperatures around 500°C in flowing hydrogen and were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Nanometre sized nickel particles, homogeneously dispersed over the silica support, were observed in the samples with the smaller Ni content obtained by both methods, but only the one which made use of the alcoholic solution was successful in providing nanometre sized particles with size increasing with increasing concentration.

Microcalorimetric study of the acidity and basicity of [formula omitted] catalysts modified by metallic additives Fe, Co, Zr and Ce

The acidity and basicity of silica-supported nickel catalysts modified by metallic additives such as Fe, Co, Zr and Ce have been determined by adsorption microcalorimetry. These catalysts have been tested in the catalytic reforming of methane with carbon dioxide. The results indicate that the metallic additives modify noticeably the acidity of the Ni SiO 2 catalysts, the acidity increasing in the order: NiCe < Ni < NiCo < NiFe < NiZr. Moreover, it was demonstrated that the most active catalyst in the CH 4 + CO 2 reaction is the least acidic, namely, NiCe SiO 2 .

Catalyst performance of MoS 2 and WS 2 for the CO 2-reforming of CH 4 Suppression of carbon deposition

The catalyst performance of MoS 2 and WS 2 was verified for the CO 2-reforming of CH 4 through the comparison with that of Ni SiO 2 . No catalyst deactivation was observed on the disulfides, although the rate was much smaller than that on Ni. It was found that the disulfides exhibited a poor ability for the direct decomposition of CH 4. The poor ability did not lead to carbon deposition during reforming reaction, which assured a stable activity. It was also observed that the rate equation was completely different between disulfide catalysts and Ni catalyst. The reaction order was positive with respect to the CH 4 partial pressure and negative with respect to the CO 2 partial pressure on the former catalysts, while negative with respect to CH 4 partial pressure and positive with respect to the CO 2 partial pressure on the latter. The observed reaction kinetics suggested that the surface of the disulfide catalyst was abundant in adsorbed CO 2, while the surface of Ni catalyst was abundant in adsorbed CH 4. The abundance in adsorbed CO 2 was considered an unfavorable condition for the direct decomposition of CH 4 and as a result, carbon deposition was suppressed during CO 2-reforming on disulfide catalyst. Sulfur tolerance was found to be an additional performance of the disulfide catalyst.

Critical behavior of resistivity and Hall resistivity in percolating ferromagnetic metal-insulator films

Resistivity ϱ xx and Hall resistivity ϱ xy were measured as functions of the magnetic field, temperature, and the metal volume fraction x, on a series of percolating NiSiO 2 granular films. At 5 K, the data for the metallic samples were fitted to power law dependencies of the forms, ϱ xx ∝ [( x − x c )/ x c ] − t and ϱ xy ∝ [( x − x c )/ x c ] − g , with x c = 0.6. The critical exponents of the resistivity t = 2.7 ± 0.2, the extraordinary Hall resistivity g s = 2.0 ± 0.2 and the ordinary Hall resistivity g 0 = 1.8 ± 0.3 were found to be notably larger than the predictions for discrete percolation models ( t ≈ 2 and g ≈ 0.4–0.5). We suggest that a percolation model incorporating localization can explain that contradiction. In the region of transition from metallic conduction to thermally activated tunneling, 0.53 < x < 0.6, the extraordinary Hall resistivity ϱ xys was found to be saturated at a value > 100μΩ cm , which is almost four orders of magnitude greater than that of pure Ni.