Spectroscopic and electrical studies of sodium tetraborate glasses containing nickel oxide

The infrared spectra. X-ray diffraction and electrical conductivity of sodium tetraborate glasses containing nickel have been studied as a function of nickel oxide content. It was found that addition of nickel oxide does not seem to introduce any new absorption band as compared with the infrared spectrum of pure sodium tetraborate glass. The electrical conductivity measurements revealed that the activation energy for conductivity increases with nickel oxide content. This could be explained on the basis of the concept of Hubbard bands, and possibly by a block effect of the nickel ion on the overall mobility of the sodium ion. Measurements were made on unannealed samples and some samples annealed at different temperatures. Annealing the samples at temperatures in the range 460 to 480° C causes the appearance of a crystalline phase, resulting in an increase of electronic conductivity.     

Positron annihilation studies of defects and fine size effects in nanocrystalline nickel oxide

Ultrafine nickel oxide nanoparticles were prepared by sol–gel method using a solution of nickel nitrate hexahydrate and ammonium hydroxide and subsequently annealed in air at different temperatures in the range 200–275?°C for different hours to vary the particle sizes. They were characterised for phase, purity, structure and sizes by X-ray diffraction and high-resolution transmission electron microscopy. They were found polycrystalline in nature and possessed face-centred cubic (NaCl-type) structure with lattice parameter varying with annealing temperature. The ultrafine structure clearly revealed the formation of hexagons with average diameter about 5?nm. Ultraviolet–visible absorption spectroscopy was carried out to study the optical properties and for the estimation of the bandgap. The nanoparticles exhibited weak and strong quantum confinement in the size ranges of 10.47–8.47 and 6.57–5?nm. The samples were then investigated through positron annihilation spectroscopy to characterise and closely monitor the evolution of vacancy-type defects and defect clusters during particle growth in the samples. The positron lifetime drastically increased at very low particle sizes, supporting the confinement effects demonstrated by optical absorption studies. The results from coincidence Doppler broadening measurements were consistent and indicated changes also in the electron momentum distribution during the occurrence of these finite size effects in the nanoparticles.     

A new perspective on carbon nano-onion/nickel hydroxide/oxide composites: Physicochemical properties and application in hybrid electrochemical systems

Carbon nano-onion (CNO) and Ni(OH)₂ or NiO composites were prepared by chemical loading of Ni(OH)₂ on the carbon surface. The samples were characterized by transmission electron microscopic (TEM) and scanning electron microscopic (SEM) methods, powder X-ray diffraction (XRD) technique and by differential-thermogravimetric analyses (TGA-DTG). The porosity properties were characterized by using nitrogen gas adsorption analyses. Pristine inorganic samples of NiO and Ni(OH)₂ revealed different morphologies and porous characteristics when compared to those of the CNO composites, which showed unique electrochemical properties. The electrochemical performance of the CNO/Ni(OH)₂ or CNO/NiO composites is largely affected by the mass, the morphology, the crystal phases of the inorganic component and the distribution of the Ni(OH)₂/NiO phase. The CNO composites were used as materials for hybrid charge-storage devices.     

IV-curve and structural studies of the composite mixture of reduced graphene oxide and silver nanopowders

Journal of Materials Science: Materials in Electronics - Nanoparticles today have the upper hand in its manufacturing desirability in more or less every aspect of the working areas, from industrial...     

Bonding of partially-stabilized zirconia and nickel with nickel oxide layer

Bonding of partially-stabilized zirconia (PSZ) and nickel has been investigated. The couples of PSZ and nickel were bonded at 1073 to 1273 K for 300 to 3600 sec under a pressure of 0.75 to 262 MPa in air. PSZ was bonded to nickel with a nickel oxide layer. The nickel oxide layer filled the interstices between PSZ and nickel. The maximum shear strength (about 90 MPa) was obtained in the couple bonded at 1173 K for 900 sec under pressure above 18 MPa. The stresses generated by the differential thermal contraction and the oxide growth stresses are discussed.     

Preparation and characterization of metalorganic chemical vapor deposited nickel oxide and lithium nickel oxide thin films

Thin films of nickel oxide and lithium nickel oxide were deposited through the pyrolysis of nickel acetylacetonate and lithium nickel acetylacetonate, respectively in the temperature range 350–420 °C. The single solid source precursors, nickel acetylacetonate and lithium nickel acetylacetonate were prepared and characterized using Energy Dispersive X-Ray Fluorescence (EDXRF), X-Ray Diffraction (XRD) and infrared spectroscopy. The composition, optical and electrical properties of the prepared thin films were analysed using a variety of techniques, including, Rutherford Backscattering Spectroscopy (RBS), EDXRF, XRD, UV–Visible Spectrophotometry and van der Pauw conductivity method. The amount of metals in the prepared thin films did not reflect the ratio of the metals in the precursor but was found to depend on the deposition temperature. The energy gaps of the nickel oxide and lithium nickel oxide thin films are 3.7 and 3.2 eV, respectively. The electrical conductivity showed that lithium nickel oxide thin film has an activation energy of 0.11 eV. The conduction was explained by a hopping mechanism.     

Sintering of cobalt-doped nickel oxide

The influence of Co additions on the sintering of nickel oxide was studied. On the basis of the density, specific surface area and Me³⁺ ion concentration changes, in the Co _y Ni_1?y O samples, having 0, 1, 5 and 10 cation % of Co, a positive effect of Co ions on the densification was assumed, during sintering at 500 to 900° C in an argon atmosphere. Using special heat-treatment, the differences in specific surface area of the investigated powders were eliminated. The differences in green densities were excluded as well and from the results, it was possible to show that dissolved Co ions enhance nickel oxide densification process.     

Nanostructural and optical properties of cobalt and nickel–oxide/silica nanocomposites

Cobalt, nickel and mixed cobalt–nickel nanostructured oxides have been obtained by thermal treatments in oxygen of Co, Ni and Co₅₀Ni₅₀/silica nanocomposites produced by ion implantation technique. The thermal treatment produces the total or partial oxidation of the original metallic species, which diffuse towards the surface and in the depth of the substrate. This process gives rise to the growth of different oxides in both regions depending on the kind of metal. In the Co sample, mainly Co₃O₄ is formed; in the Ni sample, Ni and NiO nanoparticles are present, while in the Co–Ni sample Co₃O₄, Ni₂SiO₄ and mainly (Co_xNi_1−x)O nanostructures are formed. The optical features of cobalt and nickel samples are determined by the optical properties of the Co₃O₄ and NiO p-type semiconductor phases, respectively, with energy gaps littler than the corresponding bulk ones. The Co–Ni mixed nanostructured oxide is characterized by a direct absorption gap at 3.4 eV that is smaller than the band gaps of CoO and NiO oxides.     

环形对苯二甲酸丁二醇酯与催化剂混合体系的流变性能

利用高温旋转黏度计,采用梯度降温的方法,研究CBT(环形对苯二甲酸丁二醇酯)树脂与CBT/催化剂混合体系在特定条件下的流变性能。结果表明:采用梯度降温方法可准确获得CBT纯树脂的真实表观黏度。CBT树脂的表观黏度随温度的降低而升高,随转速的加快而降低,在170~180℃下呈现出明显的剪切变稀现象。CBT/催化剂混合体系的反应速率随催化剂浓度的增加而加快。相同浓度下,锡含量较高的CBT/T9体系相对CBT/DBTL体系反应速率更快。较高的温度使催化剂的挥发程度加剧,结晶速率变慢,导致CBT/催化剂混合体系的反应速率随温度升高而变慢。最后研究了催化剂种类、浓度和成型温度对成型窗口时间的影响。     

SIMS / XPS studies of the passive film on nickel

Passive films were formed on nickel in borate buffer solution (pH 8.4) at various anodic potentials. XPS and SIMS techniques were used to determine the passivating species present on the surface film. It is shown that the film formed at low passivating potentials consists of Ni (OH)₂ and NiO, and the film formed preceding oxygen evolution consists mainly of Ni₂O₃.     

Green synthesis of nickel oxide nanoparticles and studies of their photocatalytic activity in degradation of polyethylene films

Nickel oxide nanoparticles (NiO NPs) were synthesized using Ananas comosus leaf extract, and were characterized by UV–Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, high resolution transmission electron microscopy (HRTEM), Energy dispersive X-ray (EDX) and X-ray diffraction (XRD) techniques. The FTIR analysis confirms the formation of the NiO with appearance of NiO band at 468 cm⁻¹. The HRTEM analysis reveals that the NiO NPs size was in the range of 0.63–5.75 nm, with an average particle size of 1.42 ± 1.76 nm. The EDX analysis shows clear peaks of Ni (2.7%) and O (5.74%) in the spectrum. The peaks of XRD analysis at (2θ) 30°, 43.89°, 60.16°, 77.95° and 82.94° were assigned to (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) planes of the face-centered cubic (fcc) lattice of NiO. The photocatalytic properties of the NiO NPs were studied through the solid phase degradation of low-density polyethylene (LDPE) film. We observed that polymeric nanocomposites (NCs) showed a significant weight loss of 33 ± 1.6% compared with the pure LDPE (8.6 ± 0.7%) after exposure to solar light irradiation for 240 h, while the nanocomposites under the dark condition gave a weight reduction of 1.90 ± 0.05 at the end of 240 h. The FTIR analysis also confirms the presence of carbonyl group, a degradation product of LDPE, with carbonyl index of 0.4. All these important factors showed that NiO is an effective photocatalyst. The study therefore suggests the incorporation of NiO NPs into the polymer matrix so as to enhance its photodegradation.     

Dielectric properties of nanostructured nickel oxide

Nanostructured NiO samples having different average particle sizes were prepared and the variations of the real and imaginary components of the complex dielectric function * were studied as a function of the frequency of the applied signal and temperature. The dielectric relaxation mechanism is discussed considering nanostructured NiO as a carrier dominated dielectric with high density of hopping charge carriers. The observed ^{n – 1} dependence of the real and imaginary components of * is discussed in the light of the 'Universal' model of dielectric response. The various contributions to the measured dielectric loss such as the steady state charge transport, delayed readjustment of screening charges and the Debye delays are discussed. It is shown that the temperature dependence of both the real and imaginary components of * are in accordance with the models used for discussing the dielectric relaxation and loss mechanisms. The variation of with average particle size seems to be rather complex depending on a number of parameters associated with the interfacial region which vary with the average particle size.     

AC conductivity of nanostructured nickel oxide

AC conductivity of consolidated nanoparticles of NiO, having different average particle sizes (2.5 nm–17 nm) was measured in the temperature range 313 K to 413 K and over the frequency range 50 Hz to 3 MHz. The ac conductivity of the samples was found to be enhanced by six to eight orders of magnitude over that of NiO single crystals reported in the literature. This large enhancement in conductivity is attributed to the high density of Ni²⁺ vacancies in the nanoparticles. The variation of ac conductivity with frequency of the applied signal and temperature is discussed on the basis of the Correlated Barrier Hopping (CBH) Model. The observed spread in activation energy and slope of the log _ac Vs log plots is attributed to the distribution of the charge carrier hopping distance and localization energies in the nanoparticle samples. The effect of the interfacial region on the electrical conductivity of the samples is analyzed by taking into account the contributions due to grain boundaries and triple junctions. The observed variation of measured ac conductivity with average particle size is semi-quantitatively explained based on the reasoning that the role of the triple junctions is to reduce the conductivity.