Portugaliae
Electrochimica Acta

The effect of various surfactants on the volume% codeposition of SiC in a nickel matrix was evaluated. Of the various surfactants tried, tetra methyl ammonium hydroxide (TMAH) was found to be the best for improving the quality of the deposits as well as the homogenous distribution of particles and with reasonable volume% of silicon carbide incorporation in the matrix. Composites were produced using 1 μm and 50 nanometer size powders. The effect of silicon carbide concentration and bath operating variables on the volume% of SiC incorporation in the deposit and the deposition rates were estimated. Substantial improvement in mechanical properties such as hardness and wear resistance was obtained with the nano SiC composite compared to the micro SiC composite.

Two poly(vinyl chloride) matrix membrane electrodes responsive to some drugs affecting the cardiovascular system, Amlodipine besilate (AM) and Valsartan (VL), were developed, described and characterized. A microsized graphite selective sensor was investigated with dibutylsebacate (DBS) as a plasticizer in a polymeric matrix of carboxylated polyvinyl chloride (PVC-COOH) in case of (sensor 1). This sensor 1 was prepared using 2- hydroxy propyl β-cyclodextrin (2HP β-CD) as an ionophore. While sensor 2 preparation was based on precipitation technique with bathophenanthroline iron (II) as electroactive materials in poly(vinyl chloride) (PVC) matrix. Fast and stable Nernstian responses near 1xE-5-1xE-3 M for the two drugs over the pH range 3-6 and 7-9 for the two sensors, respectively, were obtained. The method was successively applied for the determination of AM and VL in presence of each others, in their pharmaceutical formulations and in human plasma samples. The percentages recoveries for the determination of the drugs by the proposed selective electrodes were 99.78 ±0.382 %, 100.23 ± 0.440 %, for sensors 1 and 2, respectively. Statistical comparison between the results obtained by this method and those obtained by the official method and the reported method of the drugs was done and no significant difference was found.

Five solid membrane sensors responsive to memantine hydrochloride (MEM) and pramipexole dihydrochloride monohydrate (PXL) are described for simple and fast determination of these drugs in pharmaceutical preparation and human plasma. The first and the second sensors are based on the formation of an ion association complex between MEM as a cationic drug with Na tetra phenyl borate and ammonium reineckate (as anionic exchanger), respectively. The third sensor is based on the formation of an ion association complex between PXL with ammonium reineckate. The produced electroactive material is dispersed in PVC matrix. While the other fourth and fifth sensors are based on using functionalized lipophilic cyclodextrin derivative (2-hydroxypropyl-β-cyclodextrin) as sensor ionophore for the determination of MEM and PXL. The performance characteristics of these sensors-evaluated according to IUPAC recommendations-reveal fast, stable and near Nernstian response for 1x10-4-1x10-1 M and 1x10-6-1x10-2 M for (MEM) and (PXL), respectively. Many inorganic and organic substances such as drug excipients and diluents normally used in drug formulations do not interfere with drugs response. Statistical comparison between the results obtained by applying the proposed potentiometric method for the determination of the (MEM) and (PXL) in their pure powder forms and those obtained by applying the reported methods was done and no significant difference was found at p=0.05. Validation of the method according to ICH guidelines shows the suitability of the sensors for quality control analysis of the cited drugs in pharmaceutical formulations and human plasma. The proposed sensors can also be used as a detector for HPLC.

Conductivity measurements of solutions of terbium soaps in benzene-methanol show that these soaps behave as weak electrolytes in dilute solutions and Debye-Hückel-Onsager’s equation is not applicable to these soap solutions. The thermodynamic results indicate that the micellization process is favoured over the dissociation process.

Phenyltetrazole substituted compounds, namely 5-phenyl-1H-tetrazole (PT), 5-(4-chlorophenyl)-1H-tetrazole (Cl-PT), 5-(4-methoxyphenyl)-1H-tetrazole (MO-PT) and 5-p-tolyl-1H-tetrazole (M-PT) were synthesized to study their inhibition behavior on mild steel in 1 M HCl by weight loss measurement, potentiodynamic polarization studies and electrochemical impedance spectroscopy (EIS). It has been observed that corrosion rate decreases and inhibition efficiency increases with increasing in phenyltetrazole substituted concentration and dependence on molecular structure. Polarization data indicate that these compounds act as very good cathodic inhibitors of mild steel in 1 M HCl. The result showed that the inhibition efficiency decreased with temperature and increased with immersion time. EIS has the same trend of inhibitive effect as that of the polarization data, which indicates the formation of a protective layer on mild steel surface by molecules adsorption.

The corrosion behavior of mild steel (MS) in HCl solution containing various concentrations of electropolymerized P(p-phenylenediamine), P(pPD), has been investigated using weight loss and potentiodynamic polarization techniques. The data obtained from the two techniques are comparable and showed that the presence of P(pPD) in the acid solutions suppresses the corrosion rate of MS indicating that these polymers act as corrosion inhibitors (predominantly as anodic inhibitors). The inhibition efficiency (IE%) of the polymer enhances with increasing their concentrations and decrease with an increase in temperature. The inhibition occurs through adsorption and formation of barrier film on the metal surface which separates the metal from direct contact with the corrosive medium and hence protects the metal against the corrosion. The adsorption followed the Langmuir isotherm. The thermodynamic functions of the adsorption and dissolution processes were evaluated.