Sensing of silver ions by nanotubular polyaniline film deposited on quartz-crystal in a microbalance

Nanotubular polyaniline film was deposited onto the electrode of the quartz-crystal microbalance (QCM). The film in the form of emeraldine base was exposed to a solution of silver nitrate. The reduction for silver ions took place and silver nanoparticles were produced at the film surface. The deposition of silver was monitored by using the QCM and the UV–vis spectroscopy. The morphology of the film before and after the silver deposition was studied by the scanning and transmission electron microscopy. Silver nanoparticles had sizes of about 50–120 nm and globular and triangular shape. X-ray diffraction and infrared spectroscopy were used to characterize the structure of the composite. The present approach could be used for noble-metal recovery in waste waters.     

Influence of storing time and temperature on the viscosity of an egg yolk

The influence of storing time and temperature on rheological behavior of egg yolk was investigated. The eggs of two brown egg-laying breeds (Bar Plymouth Rock and Rhode Island Red) were stored for 1, 2, 3, 4, and 8 weeks at constant temperatures: 4 °C, 8 °C, 12 °C, and 16 °C. The apparent viscosity was measured by a rotational viscometer as a function of shear rate. It was found that yolk samples exhibited shear-thinning (pseudoplastic) behavior. The shear-thinning behavior was fitted well into Herschel–Bulkley model (with a satisfying correlation of R² > 0.95). For the selected shearing rate, viscosity was measured in relation to shearing time. The time-dependant viscosity decreased rapidly with time and, at lower share rates, reached an equilibrium state. The time-dependant viscosity was also found to decrease with storage time. The value of pH changed (increased) during storing. No clear dependence between pH value and viscosity was confirmed.     

Propagation-invariant electromagnetic fields: Theory and experiment

Abstract

The vector concept of the propagation invariance is formulated to be applied to the stationary electromagnetic fields. The analysed exact solutions of the Maxwell equations are obtained on the basis of general propagation-invariant solutions of the scalar Helmholtz equation. A possible classification of the propagation-invariant fields based on quantities which appear in the complex Poynting theorem is proposed. The longitudinal periodicity of the electromagnetic field obtained due to the superposition of two Bessel beams is verified by a simple experiment.     

Effect of a gas–liquid separator on the hydrodynamics and circulation flow regimes in internal‐loop airlift reactors

The role of the gas–liquid separator on hydrodynamic characteristics in an internal‐loop airlift reactor (ALR) was investigated. Both gas holdup and liquid velocity were measured in a 30 dm³ airlift reactor with two different head configurations: with and without an enlarged separator. A magnetic tracer method using a neutrally buoyant magnetic particle as flowfollower was used to measure the liquid velocity in all sections of the internal‐loop airlift reactor. Average liquid circulation velocities in the main parts of the ALR were compared for both reactor configurations. At low air flow rates the separator had no influence on gas holdup, circulation velocity and intensity of turbulence in the downcomer and separator. At higher superficial air velocities, however, the separator design had a decisive effect on the hydrodynamic parameters in the downcomer and the separator. On the other hand, the gas holdup in the riser was only slightly influenced by the separator configuration in the whole range of air flow. Circulation flow regimes, characterising the behaviour of bubbles in the downcomer, were identified and the effect of the separator on these regimes was assessed. © 2001 Society of Chemical Industry     

Effect of acids and bases on electrophoretic deposition of alumina and zirconia particles in 2-propanol

The effects of acids (monochloroacetic, dichloracetic, trichloroacetic and sulfuric acids) and bases (diethanolamine, triethanolamine, piperidine) on electrophoretic mobility and electrophoretic deposition (EPD) of particles of amphoteric Al₂O₃ and ZrO₂ in anhydrous 2-propanol were studied. It was found that the ζ-potential of Al₂O₃ and ZrO₂ particles had in acidic and alkaline 2-propanol media opposite charge to that in aqueous medium. This phenomenon was explained by the low dissociation constants of acids and bases in 2-propanol. This enables electrosteric stabilization of Al₂O₃ and ZrO₂ particles by acid anions and base cations. Similar electrophoretic behaviour of Al₂O₃ and ZrO₂ particles in 2-propanolic dispersions stabilized by MCAA allowed the preparation of compact, regular layered laminates with high cohesion at the interface of layers.