Adsorption properties of carbonized polyacrylonitrile deposited on γ-alumina and silica gel by precipitation polymerization

The precipitation polymerization method was used for the deposition of various contents of polyacrylonitrile on two oxide-type supports (γ-alumina and silica gel). The synthesized materials were characterized by thermal analysis performed in inert and oxidizing atmospheres. The mechanism of polyacrylonitrile decomposition was proposed. In order to gain effective adsorbents of volatile organic compounds the polyacrylonitrile/support composites were carbonized at elevated temperatures. The texture and morphology of the calcined materials were examined by low-temperature sorption of N₂ and scanning electron microscopy, respectively. An influence of thermal treatment conditions and carbonaceous species loading on adsorption capacity of methyl-ethyl ketone vapour was also determined. Attenuated total reflection Fourier transform infrared spectroscopy measurements revealed that the ladder-type polyacrylonitrile species formed above 250 °C and stable up to about 350–400 °C are the most effective sites for methyl-ethyl ketone sorption. The carbonaceous species dispersion was found to be an additional factor influencing the adsorption capacity of the carbonized polyacrylonitrile/support composites.     

The effect of processing parameters on the properties of γ-alumina washcoats deposited on ceramic honeycombs

The coating of cordierite honeycomb specimens with -alumina slurries for the preparation of washcoats for automotive applications was investigated. The dependence of slurry viscosity on factors such as the solids content, the pH and the particle size distribution of the powder used, was determined. Slurry viscosity was correlated to the loading percentage achieved, as well as to the quality of the washcoat in terms of homogeneity and reproducibility. It was found than an adequate solids content in the slurry is necessary for the achievement of satisfactory loading per impregnation. When, though, the particle size of the powder employed is of colloidal dimensions, high solids content leads to extremely high viscosity values. Adjustment of the slurry viscosity is therefore necessary and this was achieved with the use of either HCl or ammonium poly-methacrylate, an organic polyelectrolyte. Optimum loading conditions were achieved when the slurry viscosity lied between 50–150 mPa·s. For a specific solids content, the organic polyelectrolyte led to lower viscosity slurries and resulted in better reproducibility of the loading percentage. With the use of ammonium poly-methacrylate, slurries of fine particles, up to 40 wt% solids content could be handled, resulting in reproducible loading percentages of the order of 15 wt%     

Wetting characteristics of sodium on β″-alumina and on nasicon

The sessile drop technique was used to determine the wetting characteristics of liquid sodium on -alumina and nasicon (Na₃Zr₂Si₂PO₁₂). The effects of moisture and temperature were studied using the wetting experiments. A range of contact angles (from 0 to 160°) were observed. The samples exposed to moisture exhibited poor wetting. The fact that good wetting is a prerequisite for improved cell performance was demonstrated via Na ¦-alumina¦ Na cell tests. Cells baked out in a vacuum passed in excess of 1100 Ah cm^–2 at 4 A cm^–2 current density without any degradation. Unbaked cells under similar conditions failed under 200 Ah cm^–2.     

A comprehensive study of structural and magnetic properties of sputter deposited nickel–silica thin films

The present work reports the formation of Ni nanoparticles inside the SiO₂ matrix and deals with the influence of Ni concentration on structural and magnetic properties of Ni–SiO₂ nanocomposite thin films. The films with varying Ni concentration (20–55 at% measured by Rutherford back scattering spectroscopy) were deposited using DC/RF magnetron co-sputtering. TEM and XRD analysis reveal the formation of FCC Ni nanoparticles in all the samples. The particle size varies from 3 to 10 nm as a function of Ni concentration. The surface roughness of the films is also found to increase with increase in nickel concentration. Magnetic measurements show that the Ni nanoparticles behave as superparamagnets when their size is ≤6 nm, in spite of their large volume fractions. The results show that the magnetic properties of the nanoparticles can be controlled by their size and Ni concentration in the samples.     

Growth of γ-alumina on crystallographically distinct aluminium substrates

The growth of-alumina on crystallographically distinct aluminium substrates has been studied using transmission electron microscopy and diffraction and Rutherford backscattering. Oxides grown thermally on single-crystal substrates showed a preferred epitactic orientation relationship with the substrate, while oxides grown by the same technique on polycrystalline substrates did not exhibit a preferred orientation relationship. The grain size of the oxide was found to be at least one order of magnitude smaller than the initial grain size of the polycrystalline aluminium substrate.     

Structural and optical properties of γ-alumina thin films prepared by pulsed laser deposition

Preparation of γ-alumina thin films by pulsed laser deposition from a sintered α-alumina target is investigated. The films were deposited on (100) silicon substrates at 973 K with varying oxygen partial pressures in the range 2.0 × 10⁻⁵-3.5 × 10^− 1 mbar. X-ray diffraction results indicated that the films were polycrystalline γ-Al₂O₃ with cubic structure. The films prepared in the oxygen partial pressure range 2.0 × 10^− 5-3.5 × 10^− 2 mbar contained nanocrystals of sizes in the range 10-16 nm, and became amorphous at pressures > 3.5 × 10^− 1 mbar. Topography of the films was examined by atomic force microscopy using contact mode and it showed the formation of nanostructures. The root-mean square surface roughness of the film prepared at 2.0 × 10^− 5 mbar and 3.5 × 10^− 1 mbar were 1.4 nm and 3.5 nm, respectively. The thickness and optical properties were studied using ellipsometry in the energy range 1.5-5.5 eV for three different angles of incidence. The refractive index was found to decrease from 1.81 to 1.73 with the increase of oxygen partial pressures from 2.0 × 10^− 5 to 3.5 × 10^− 2 mbar. The variation in the refractive index has been found to be influenced by the microstructure of the films obtained as a function of oxygen partial pressure.     

Structure,properties and production of β-alumina

The crystal structures of the -alumina compositions have been described and used to explain the fast ion transport for which these materials are renowned. Measured values of both the single crystal and polycrystalline ionic conductivity show a wide variation; this is explained in terms of the range of chemical compositions of the -alumina system and also the variety of measuring techniques used. Dopants or impurity ions can have a significant effect on the physical properties of the -aluminas. The ionic conductivity, the stability of the material and the densification during sintering have been considered in relation to the nature and level of a range of dopants described in the literature. The optimization of the ionic and mechanical properties has been achieved by development of the fabrication techniques and it is this which accounts for much of the present research. Thus the many different methods of producing both single and polycrystalline material have been described, including the range of sintering routes currently available. The advantages and disadvantages of each production route in terms of the resulting properties have also been discussed.     

Morphology and composition of nickel–boron nanolayer coating on boron carbide particles

This work is focused on electroless coating of Ni–B nanolayer on B₄C particle surfaces. The B₄C particles used are approximately 2 μm in average size. Effects of activation agent PdCl₂, complexing agent C₂H₈N₂, and reducing agent NaBH₄ addition rate are studied. The solids loading of B₄C is 0.625 g/L and the concentration of Ni²⁺ ions is 0.004 mol/L in the electroless coating solution. Scanning electron microscopy (SEM) shows that when B₄C:Pd²⁺ molar ratio is 1:0.005, a Ni–B nanolayer with the smallest Ni–B nodule size covers the B₄C particle surfaces. Complexing agent C₂H₈N₂ decreases Ni²⁺ ion release rate. Ni:C₂H₈N₂ ratio of 1:6 is the preferred complexing agent amount for achieving a continuous Ni–B nanolayer. The Ni–B nanolayer formation is also strongly dependent on the rate that Ni²⁺ ions are reduced. Slow Ni²⁺ reduction leads to increased Ni content in the Ni–B nanolayer. When the above three factors are combined at the optimal values for the electroless coating process, well-defined Ni–B nanolayer is obtained. SEM cross section analysis shows the Ni–B nanolayer completely covers the B₄C particles with less than 55 nm thickness.     

Effect of zinc on the magnetic properties of acicular cobalt-modified γ-Fe2O3 particles

Acicular -FeOOH particles with a particle length of about 0.35 m and an axial ratio of about 7 were synthesized by the coprecipitation method using the reaction of FeCl₂-NaOH. The (Co, Zn)-modified -F₂O₃ particles were produced by absorbing Co²⁺ and Zn²⁺ ions on the surfaces of -FeOOH particles followed by dehydration, reduction and oxidation. The saturation magnetization and thermal stability of the coercivity of (Co, Zn)--Fe₂O₃ particles were all higher than those of Co--F₂O₃ particles. For the same (Co+Zn) content, the saturation magnetization of (Co, Zn)--Fe₂O₃ particles increased with increasing zinc content but the coercivity decreased.     

Effects of γ-ray irradiation and thermal annealing on structural,optical and electrical properties of vacuum deposited vanadyl 2,3-naphthalocyanine thin films

Vacuum deposited vanadyl naphthalocyanine (VONc) crystalline thin films were produced. The films showed a completely different structural and growth pattern on thermal annealing and γ-ray irradiation. The XRD spectra revealed polycrystalline nature for both annealed and γ-ray irradiated films. Raman spectra observes that the γ-irradiated films had a higher disorder producing broad and diffuse peaks in comparison to its annealed samples. In the absorption spectra, the γ-irradiated films shows a broad Q-band with a shift of 50 nm towards the IR region enabling VONc to be used in a lot of applications using the commercially available semiconductor NIR lasers. Films on 97.9 krad γ-ray irradiation showed some interesting properties with a better conductivity compared to either it’s higher γ-ray irradiated counterpart (195.8 krad) or the annealed films. Also the activation energy values, which is the minimum amount of energy required to liberate charge carriers from traps or to ionize levels within the band gap, was found to be lowered to half of its value for the films irradiated at 97.9 krad promising its performance in optical data recording, photo-sensitizer in photodynamic therapy, etc.     

Effect of hydrolysed aluminium treatment on rheological characteristics of α-alumina slurries

This paper describes the process for the hydrolysed aluminium treatment (HA) on alumina surface and its influence on the rheological characteristics of alumina slurries. Three different commercial grade aluminas were provided with the surface treatment with hydrolysed aluminium using aluminium nitrate and hexamethylenetetramine (HMTA) under controlled conditions. The HA treatment increased the concentration of Al-OH surface sites resulting in higher H⁺ adsorption on the alumina surface. A highly concentrated (>55 vol%) electrostatically stabilized alumina slurry was prepared from HA treated alumina powders. The rheology of such slurry was studied and the results on the viscosity and yield stress are presented. The alumina slurries followed the Casson Model flow behaviour. The wet and flow behaviour of the alumina with and without HA treatment was also studied and the results are compared. The surface treatment showed the advantage of maintaining low viscosity and yield stress of alumina slurries even at higher solids loading (>55 vol%) that are prepared in the acidic aqueous medium. The results on viscosity and yield stress were compared with that of the polyelectrolyte dispersed system.     

Effect of adding nanometric ZnO particles on thermal,microstructure and tensile creep properties of Sn–6.5 wt%Zn–3 wt%In solder alloy

Mechanical properties of solders benefit from uniform dispersion of fine precipitates and small effective grain sizes. Metallurgical methods of attaining such a beneficial microstructure have been investigated in the plain Sn–6.5 wt%Zn–3 wt%In (plain) solder and Sn–6.5 wt%Zn–3 wt%In–0.3 wt%ZnO (composite) solder. It has been found that a small alloying addition of ZnO nano particles has a beneficial effect on the microstructure. It improves the tensile creep properties of the composite solder alloy. The improvement is attributed to uniform distribution and refining of the β-Sn dendrites and the effective refined grain size in the solidified microstructure. Thereby the composite solder has better mechanical properties than the plain solder alloy.     

Effect of γ-irradiation on the physical and mechanical properties of chitosan powder

In this study, locally produced chitosan powder was irradiated with pre-determined doses of γ-ray (Co-60) of 10 kGy, 25 kGy, 50 kGy and 100 kGy respectively. The properties of both chitosan powder and the chitosan film were examined and compared with unradiated chitosan. Physical characteristic of the irradiated powder and film was studied using stereo microscope. It was observed that the γ-ray induces a noticeable colour tone intensity change to the chitosan. Further investigation using Fourier Transformed Infrared Spectroscopy (FT-IR) analysis has confirmed that the chain scission reaction was occurred as a result of γ-ray exposure through the depolymerization mechanisms. Interestingly, the degree of deacetylation (DD) of chitosan measured using FT-IR showed a negligible effect due to the exposure of γ-ray radiation. Further investigation on the viscosity average molecular weight (M_v) showed a reduction of M_v from 577 kD of pure chitosan to 458 kD, 242 kD, 159 kD and 106 kD for 10 kGy, 25 kGy, 50 kGy and 100 kGy of γ-radiated chitosan respectively. In addition, the tensile strength and elongation at break showed a similar decreasing trend with increasing dosage of γ-ray.     

Experimental study on capillary and mechanical properties of a porous nickel–copper composite

A novel porous nickel–copper composite was designed and fabricated by sintering a mixture of a high-porosity open-cell copper foam plate and fine nickel powder. The microstructure of the porous nickel–copper composite was characterised by the scanning electron microscope. The effects of sintering temperature and dwelling time on the sintering shrinkage, sintered porosity, capillary performance and mechanical properties of the porous composite and monoporous sintered nickel powder were investigated experimentally. The nickel–copper composite presented significant lower sintering shrinkage, higher porosity, lower tensile strength and better capillary performance than the sintered nickel powder under all sintering conditions. The sintering temperature has more influence than the dwelling time on both the capillary performance and tensile strength of the sintered composite.     

Crystallization of γ-Fe2O3 particles with the aid of barium oxide as a catalyst and the effects on magnetic properties

-Fe₂O₃ particles with BaO additives (up to 20 mol%) have been crystallized by solid state reaction of the stoichiometric compositions containing 20 mol% B₂O₃ as a sintering aid. This markedly effects the crystallization and magnetic properties of -Fe₂O₃. The microstructure of the samples shows growth of crystallites of considerably smaller sizes and with fairly sharp size distribution after the additions. Crystallites as small as 5 m size (normally 25 m) were obtained using 15 to 20 mol% BaO additives in the reaction performed at 1230 °C/20h. This leads to a variation in coercivity over a wide range from 35 to 3500 Oe. Measurements of X-ray diffractometry, magnetization, microstructure and magnetic resonance have been carried out to characterize the magnetic applications of the material. The results are all consistent and elucidate promotion by thermal-treatment of the incorporation of Ba²⁺ into the -Fe₂O₃ particle cores.     

Field emission and I–V characteristics of template synthesised nickel nanowires on semiconducting substrate

Ion track technology makes it possible to produce a low cost template for the synthesis of nanowires. In this article, spin-coated polycarbonate films have been irradiated by energetic 150?MeV Ni ion at a fluence of 8E7, followed by UV irradiation and chemical etching in aqueous NaOH (6N,?29°C). Ni nanowires were electrochemically synthesised in the pores created in the polycarbonate film. The nanostructures thus synthesised were morphologically analysed using scanning electron microscopy and further studied for their electrical and field emission properties.     

Controlled synthesis and catalytic properties of mesoporous nickel–silica core–shell microspheres with tunable chamber structures

In 550 °C and H₂ current, the mesoporous nickel–silica composite core–shell microspheres with tunable chamber structures have been successfully prepared by reduction of Ni₃Si₂O₅(OH)₄ microspheres, which are synthesized by the reaction between Ni(Ac)₂·4H₂O and SiO₂ microspheres via a self-template approach. The chamber (SiO₂ core sizes) and shell thickness (40–150 nm) of the nickel–silica microspheres can be controlled by adjusting the synthetic parameters of Ni₃Si₂O₅(OH)₄, such as the reaction time. After reduction, these microspheres still have the same sizes, morphologies, and core–shell structures with porous shell as before. These mesoporous nickel–silica microspheres with large BET surface area, exhibit good catalytic activity in m-dinitrobenzene (m-DNB) and high selectivity of m-phenylenediamine (m-PDA) after 3.5 h, but different selectivity of m-PDA in the progress, showing good potential in the catalyst industry.