Determination of the critical surface tension of wetting of minerals treated with surfactants by shear flocculation approach

This paper contributes the shear flocculation method as a new approach to determine the critical surface tension of wetting of minerals treated with surfactants. This newly developed approach is based on the decrease of the shear flocculation of the mineral suspension, with decreasing of the surface tension of the liquids used. The solution surface tension value at which shear flocculation does not occur can be defined as the critical surface tension of wetting (gamma c) of the mineral. By using the shear flocculation method, the critical surface tensions of wetting (gamma c) for calcite and barite minerals, treated with surfactants, were obtained as 30.9 and 35.0 mN/m, respectively. These values are in good agreement with data reported previously on the same minerals obtained by the contact angle measurement and flotation methods. The chemical agents used for the treatment of calcite and barite particles were sodium oleate and sodium dodecyl sulfate, respectively.     

Electroanalytical investigation and determination of pefloxacin in pharmaceuticals and serum at boron-doped diamond and glassy carbon electrodes

The anodic behavior and determination of pefloxacin on boron-doped diamond and glassy carbon electrodes were investigated using cyclic, linear sweep, differential pulse and square wave voltammetric techniques. In cyclic voltammetry, pefloxacin shows one main irreversible oxidation peak and additional one irreversible ill-defined wave depending on pH values for both electrodes. The results indicate that the process of pefloxacin is irreversible and diffusion controlled on boron-doped diamond electrode and irreversible but adsorption controlled on glassy carbon electrode. The peak current is found to be linear over the range of concentration 2 × 10⁻⁶ to 2 × 10⁻⁴ M in 0.5 M H₂SO₄ at about +1.20 V (versus Ag/AgCl) for differential pulse and square wave voltammetric technique using boron-doped diamond electrode. The repeatability, reproducibility, precision and accuracy of the methods in all media were investigated. Selectivity, precision and accuracy of the developed methods were also checked by recovery studies. The procedures were successfully applied to the determination of the drug in pharmaceutical dosage forms and humans serum samples with good recovery results. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage forms and biological samples, respectively.     

Development of chromium-free iron-based catalysts for high-temperature water-gas shift reaction

Chromium-free iron-based catalysts were prepared and studied in regard to their performance in the high-temperature water-gas shift reaction (HTS). The effects of various catalyst preparation variables (i.e., Fe/promoter ratio, pH of precipitation medium, calcination and reduction temperatures) and preparation methods were investigated. Aluminum is a potential chromium replacement in HTS catalysts. Further improvement in WGS activity of Fe–Al catalysts can be achieved by the addition of small amounts of copper or cobalt. Catalysts were characterized using BET surface area measurements, temperature-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). As a textural promoter, aluminum and chromium prevent the sintering of iron oxides and stabilize magnetite phase by retarding its further reduction to FeO and metallic Fe. The promotional effect of Cu is found to be strongly dependent on the preparation method.     

Anodic voltammetric behavior of ascorbic acid and its selective determination in pharmaceutical dosage forms and some Rosa species of Turkey

Ascorbic acid is the most common electroactive biological compound found in some plant species (e.g., Citrus species, Rosa species). The electrochemical oxidation of ascorbic acid was investigated by cyclic, linear sweep, differential pulse (DPV), and square wave (SWV) voltammetry. For analytical purposes, a very well-resolved diffusion-controlled voltammetric peak was obtained in acetate buffer at pH 3.50 for DPV and SWV. The linear response was obtained in the range of 3.52–176.1 μg/mL with a detection limit of 0.88 μg/mL for DPV and 0.52 μg/mL for SWV. Based on this study, simple, rapid, selective, and sensitive voltammetric methods were developed for the determination of ascorbic acid in pharmaceutical dosage forms and Rosa species (R. dumalis ssp. boissieri var. boissieri, R. canina, R. pulverulenta, R. heckeliana ssp. vanheurckiana, and R. montana subsp. woronowii). The results obtained are compared with the HPLC data. The developed methods enable the extracts to be analyzed without the necessity of any time-consuming separation. The text was submitted by the authors in English.     

Electrokinetic properties of sepiolite suspensions in different electrolyte media

The present paper deals with the electrokinetic characterization of sepiolite. A series of systematic zeta potential measurements have been carried out to determine the isoelectric point (iep) and potential-determining ions (pdi), and the effect of mono-, di-, and trivalent electrolytes such as NaCl, KCl, LiCl, NaNO(3), NaCH(3)COO, MgCl(2), CaCl(2), BaCl(2), CoCl(2), CuCl(2), Pb(NO(3))(2), Na(2)CO(3), Na(2)SO(4), AlCl(3), FeCl(3), and Na(3)PO(4) on the zeta potential of sepiolite. Zeta potential has been calculated with the aid of Smoluchowski's equation. Sepiolite yields an isoelectric point at pH 6.6. The zeta potential for the sepiolite has ranged from +23.3 mV at pH approximately 2 to -22.4 mV at pH approximately 8 at 20 +/- 2 degrees C in water. The valency of the ions have proven to have a great influence on the electrokinetic behavior of the suspension. Monovalent cations were found to have a weak effect, while di- and trivalent cations made the zeta potential positive. Charge reversal was observed for divalent cations at 1 x 10(-2) M and for trivalent cations at 3 x 10(-4) M. As a result, it can be said that monovalent cations are indifferent ions when di- and trivalent cations are potential-determining ions.     

Electric-field induced strain in biological tissues

This paper reports a new effect whereby a physiological-level direct-current electrical field (at 1.4 V/cm) can induce time-varying mechanical strain in various types of biological tissues and gel phantoms. This effect cannot be explained by the piezoelectric effect, tissue contraction, temperature changes, and electrorestriction. The induced strain in tissues was analyzed by processing ultrasound echo signals. The sample expanded perpendicularly to the applied electric field. The expansion rate depended on the history of the applied electric field. The speed of sound changed little compared with the expansion. The new effect might be related to electrokinetic effects.     

Massively parallel low-cost pick-and-place of optoelectronic devices by electrochemical fluidic processing

We describe a novel electrochemical technique for the nonlithographic, fluidic pick-and-place assembly of optoelectronic devices by electrical and optical addressing. An electrochemical cell was developed that consists of indium tin oxide (ITO) and n -type silicon substrates as the two electrode materials and deionized water (R = 18 MOmega) as the electrolytic medium between the two electrodes. 0.8-20-microm-diameter negatively charged polystyrene beads, 50-100-microm-diameter SiO(2) pucks, and 50-microm LED's were successfully integrated upon a patterned silicon substrate by electrical addressing. In addition, 0.8-microm-diameter beads were integrated upon a homogeneous silicon substrate by optical addressing. This method can be applied to massively parallel assembly (>1000 x 1000 arrays) of multiple types of devices (of a wide size range) with very fast (a few seconds) and accurate positioning.