Monte Carlo simulation to reveal the copper dissolution kinetics of an ion selective electrode based on copper sulfide

The present work aims at studying copper dissolution of a Cu²⁺ ion-selective electrode based on a CuS thin film. The electrode is prepared using electrochemical deposition of CuS on a silicon substrate. The obtained film exhibits an apparent cohesive granular structure with an average grain size of about 33 μm, a small porosity content (<4%) and a thickness of about 7.48 μm. The Cu²⁺ electrochemical response shows a nearly Nernstian behavior in the range of pCu 6–1. The copper dissolution is experimentally studied in a wide pH range. In order to quantitatively predict copper mass dissolution, an original numerical model is developed based on Monte Carlo simulation. Our main hypothesis is based on dissolution probability that triggers the whole dissolution process through solution/electrode surface exchanges. Several probability forms are suggested accounting for the real observed electrochemical kinetics. The experimental results show that, under a low pH, the dissolution process severely leads to the consumption of large material. Moreover, our predictions suggest a dissolution profile as a two-stage process irrespective of pH. Our numerical model is able to fit correctly the observed kinetics considering an exponential probability form under all pH conditions.     

Asymptotic continuous Petri nets

A Petri net is basically a discrete model. However, continuous Petri nets, such that the markings are real numbers have been defined. Two continuous Petri net models involving time have been drawn up. They differ by the calculation of the instantaneous firing speeds of the transitions. Both can be used to approximate a timed Petri net. The former considers constant firing speeds (CCPN) and is very easy to simulate (few events have to be considered, even when it approximates a timed Petri net with many reachable markings). The latter considers firing speeds depending on the marking (VCPN). Although it provides a better approximation, its simulation is longer because the markings and speeds are given by differential equations. This paper introduces a third model (ACPN) which presents the advantages of the two preceding ones. In most cases, this model represents the asymptotic behavior of the VCPN. Then their precisions are similar. Since the firing speeds of the ACPN are constant, it is as easy to simulate as the CCPN.     

Electrochromic effect in WO3 thin films prepared by spray pyrolysis

Polycrystalline WO₃ thin films were produced by spray pyrolysis on corning glass or ITO coated glass substrates. The optical, electrical and structural properties of these films were studied as a function of preparation conditions in their colored state. The transmittance value decreased from 80% to 5% when the films were colored. This was accompanied by an increase of the reflectivity in the NIR region. In addition, the electrical conductivity varied with heat treatment temperature. The change in electrical conductivity indicates that WO₃ films exhibit a semiconducting behavior in their colored state. Furthermore, a change in the structure of the films from monoclinic to cubic was observed upon coloration. The electrochemical behavior was investigated in 1 M H₂SO₄/H₂O solution using a three-electrode cell.     

Study and characterization by acoustic emission and electrochemical measurements of concrete deterioration caused by reinforcement steel corrosion

The durability of reinforced concrete structures becomes a matter of concern, due primarily to the increase of damage by the corrosion of steel reinforcements. This corrosion is not only related to the composition and to the procedure of concrete manufacturing (water/cement, sand/cement, etc.), but also to the aggressive agents as chlorides, carbon dioxide, etc. present in the surrounding medium (Cl⁻, CO₂, etc.). It is well known that the first kind of rebar corrosion (chloride) is more detrimental and that this process contains three basic components: chloride diffusion, electrochemical corrosion and concrete fracture. Therefore the early detection of possible degradation of structures by means of non-destructive testing is essential in order to ensure the functionality of these structures.

This paper presents the results of an experimental investigation on the use of acoustic emission during the corrosion of steel rebars embedded in mortar and immersed in sodium chloride solution. The process of corrosion is accelerated by various imposed potentials and is followed by acoustic emission coupled to electrochemical techniques. The experimental results show that electrochemical techniques can evaluate the corrosive character of the medium used. The acoustic emission showed an activity characteristic of the corrosion initiation phase and the corrosion propagation phase. Thus, it was significantly possible to highlight the acoustic signature of the concrete damage related to the porosity of the mortar and to chloride concentration. The results also show a perfect correlation between the evolution of the acoustic activity and the current of corrosion density.     

Advanced quantum chemical and electrochemical analysis of ravage drugs for corrosion inhibition of mild steel

The blocking of corrosive sites of soft (mild) steel has been studied using ravage drugs Pyrazinamide (Z), Isoniazid (H) and Rifampicin (R) in 0.5?M HCl medium. The degree of ability of these drugs to act as corrosion controlling agents was investigated by gravimetric measurements, potentiostatic polarization and electrochemical impedance spectroscopy. Their inhibition efficacy has, further been validated through theoretical and simulation studies. Though, all the drugs have shown good anticorrosive impact, but, rifampicin (R) has proven its greater efficacy as 97.06% at 1000?ppm and at 303?K. Polarization curves depict that the H and R drugs act through mixed mode of inhibition while Z drug is predominantly anodic in nature. The result of electrochemical impedance spectroscopy specifies that the corrosion reaction is resisted by charge transfer process. Morphology of un-corroded and corroded coupons was studied by scanning electron microscopy. The mechanism of adsorption is obeyed well through Langmuir isotherm and advocated a significant physiochemical type of interaction by the compounds on the metal surface. Thus, all the findings got via various experimental techniques along with that of obtained using Molecular Dynamics (MD) and Density Functional Theory (DFT) for the three compounds are in proper harmony.     

Viscoelasticity and mechanical properties of reactive PVC plastisols

Reactive poly(vinyl chloride) (PVC) plastisols have been developed to substitute the hydrocarbon diluents generally used in low viscosity PVC plastisols. For this purpose, methacrylate monomers (5–15%) were added in the PVC suspension (based on diisononyl phtalate plasticizer) to reduce the viscosity at room temperature and to polymerize (by radical polymerization initiated by an organic peroxide) during the gelation process. Both the reactive processing and the gelation process were carried out between the plates of a rheometer cell in the linear viscoelasticity domain (small deformation) and under increasing temperature from room temperature up to 160°C (ω = 6.283 rad s^?1, = 5°C min^?1). A temperature criterion was proposed to define the right balance between the polymerization and the gelation to get the best mechanical properties (i.e., elongation and stress at break). The polymerization process must be slower than the gelation process as the polymerization must take place when PVC grains have fused together to form a homogeneous medium at least at the microscale. Actually, the polymerization kinetics can be controlled by the decomposition kinetics of the organic peroxide. Finally, triethylene glycol dimethacrylate and lauryl methacrylate monomers and dicumyl peroxide as initiator turned out to be the best reactive system for some potential industrial applications. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Presence of aflatoxin M1 in pasteurized milk from Morocco

Fifty four samples of pasteurized milk produced by five different dairies from Morocco were surveyed for the presence of aflatoxin M1 (AFM1) using immunoaffinity columns and liquid chromatography coupled to fluorescence detection. Confirmation of AFM1 identity in positive samples was based on the formation of AFM1 hemi-acetal derivative (AFM2a) after derivatization with trifluoracetic acid. Analytical results showed that 88.8% of the samples were contaminated with AFM1; 7.4% being above the maximum level of 0.05 microg/L set by the Moroccan and European regulations for AFM1 in liquid milk. The incidence of AFM1 in milk from these dairies was 100, 92.3, 90, 83.3 and 77.7% respectively, with AFM1 levels ranging from 0.001 to 0.117 microg/L and a mean value of 0.0186 microg/L. Based on the results presented in this study, the estimated daily intake of AFM1 was 3.26 ng/person/day. In this work, data on the natural occurrence of AFM1 in pasteurized milk produced in Morocco is presented for the first time.     

IR spectroscopy study of polypropylene natural aging

Structural modifications of a commercial polypropylene (PP) sample are studied by IR spectroscopy. Aging this sample under an ambient atmosphere with or without the presence of ambient light shows the oxidation process to be the most predominant. Spectral analysis reveals that the commercial sample is isotactic and also indicates that, for the new sample, oxygen establishes single bonds with carbon. However, through the aging process, spectral changes essentially occur in the regions of ∼3400, ∼1712, and 1170 cm⁻¹ which correspond to hydroxyl and/or hydroperoxide groups, a carbonyl group, and C O, respectively. The deconvolution of the bands corresponding to a carbonyl group reveals the presence of a complicated mixture of oxidation products: aldehydes, ketones, esters, acids, peresters, and peracids. Spectral analysis also shows that the most favorable site for oxidation is at the methylene group. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1742–1748, 2000