Alumina Particles In Suspension Research Articles

Microstructure and Deposition Relations in Alumina Particle Strengthened Ni-W Matrix Composites

The nanostructured Ni-W/Al2O3 composite coatings were prepared by electrodeposition technique on ferritic steel substrates from aqueous electrolyte solutions containing ultrafine alumina particles in suspension. The effects of plating parameters like current density, inert particle concentration in plating bath and ultrasonic field frequency on the incorporation of α-Al2O3 particles (TM-DAR Taimicron) into an Ni-W matrix were investigated. The MMC coatings microstructure, phase and chemical composition were studied by means of scanning (E-SEM FEI XL-30) and transmission (TECNAI G2 SuperTWIN) electron microscopies, as well as XRD measurements (Bruker D8 Discover). SEM and TEM observations of composite cross-section microstructure showed that the presence of ultrasounds considerably reduces the particles agglomeration and enables a uniform distribution of particles in the Ni-W matrix. The electron diffraction pattern analysis revealed that the composite metallic matrix consists of an α-Ni(W) solid solution. The matrix was characterized by quasifibrous, nanocrystalline grains of an average size about 10 nm.

貧溶媒比率がアルミナ懸濁液のレオロジー特性とグリーンシート特性に及ぼす影響

The influence of solubilization of the solvents for PVB binder on the rheological behavior and properties of alumina green sheets was investigated. Suspensions of alumina particles were prepared with various ratios of toluene (poor solvent) and n-butanol (good solvent) including PVB binder. Binder solutions of concentration 20 wt% were opaque at less than 5 wt% of n-butanol ratio, where turbidities, viscosities, TI values and thread-forming properties of binder solutions were large. These results indicate that the binder molecule exhibits a thread-like shape in poor solvent.The amount of binder adsorbed on alumina particles in suspension increased with decreasing the ratio of n-butanol, suggesting that binder at the adsorbed state on alumina particles is more stable than at the state of drifting in the poor bulk solvents. And this result suggests that occupation area of thread-like binder is small in poor solvent.Viscosities, TI values, sedimentation volumes and thread-forming properties of suspensions increased with decreasing the n-butanol ratio. Bulky cohesion structures of alumina particles in suspension with high TI values are supposed to be maintained in sedimentation cakes. However, the packing degree of green sheet after drying was high. The number of binder segments expanding into bulk solution is expected to be fewer, because hydroxyl groups in PVB binder are adsorbed on alumina particles via hydrogen bonding in poor solvent. Expanding binder segment is easy to shrink while drying. Distance between alumina particles decreases, and, as a result, it is thought that the packing degree of alumina particles became high.

Adhesion of nanosized nickel catalysts in the nanocatalysis/UF system

AbstractA system combining nanocatalytic reaction with crossflow ultrafiltration (UF) was used to prepare p‐aminophenol from p‐nitrophenol. In this system, nanosized nickel catalysts in suspension were employed during reaction, and then separated from slurry by an UF membrane filter. The adhesion of nickel particles to contact surfaces caused a rapid decline in the hydrogenation rate and UF flux. In order to understand the effect of materials properties, and operating parameters on adhesion of catalysts, the nickel adhesion was investigated by measuring the mass of nickel remaining on solid surfaces after contact. Surface materials with different roughness and hydrophilicity have been tested, such as poly(tetrafluoroethylene) (PTFE), stainless steel (AISI 304) and glass. The results show that rougher surfaces have more adhesion than smooth ones. Hydrophilic glass has less adhesion than hydrophobic PTFE, while intermediately hydrophilic stainless steel has the most adhesion due to its surface magnetic effect. During ultrafiltration, adhesion decreases with increasing crossflow velocity and increases with increasing suspension concentration. With the addition of microsized alumina particles in suspension, the adhesion of nanosized nickel can be inhibited effectively. © 2007 American Institute of Chemical Engineers AIChE J, 2007.

Alumina interaction with AMPS–MPEG random copolymers: I. Adsorption and electrokinetic behavior

Adsorption of brush copolymers, bearing sulfonate groups and polyethylene glycol segments, on to alumina particles in suspension in water has been investigated. Study of the adsorption isotherms revealed that the copolymers displayed a strong affinity for the surface of the alumina regardless of the fraction of ionic groups on the polymer. For poly(ethylene glycol) content greater than 50%, the adsorption isotherms revealed an initial adsorption plateau followed by a second one. The shape of the adsorption isotherms was interpreted in terms of the polymer configuration at the solid-to-liquid interface. The effects of the pH and the ionic force on adsorption were studied and connected to the effects of interaction between chain segments at the surface of the alumina particles. Changes in the electrokinetic properties of the alumina particles after addition of the copolymers were investigated by following the zeta potential of particles as a function of pH. In the presence of the copolymer continuous shift of the isoelectric point IEP to a more acidic values was observed. Beyond a certain concentration the zeta potential remained negative regardless of the pH.