Improvement in corrosion resistance of micro arc oxidation coating formed on AZ91D magnesium alloy via applying a nano-crystalline sol–gel layer

Although magnesium is used in many industries, it is reactive and requires protection against aggressive environments. In this study, oxide coating was formed on AZ91D magnesium alloy using micro-arc oxidation (MAO) process in an alkaline electrolyte. Then, in order to seal the pores in the oxide film, a sol–gel layer was applied to the surface of the MAO coating by dipping. For investigation of heat treatment temperature of the sol–gel layer on the properties of the coatings, two different temperatures (150 and 350 °C) were chosen. Surface morphologies and compositions of the coatings were analyzed by Scanning Electron Microscope and X-ray Diffraction (XRD). Surface roughness of the coatings was also measured. The corrosion behavior of the coatings was evaluated with Electrochemical Impedance Spectroscopy and potentiodynamic polarization tests in 3.5 wt%NaCl solution. The porosity percent of the coatings was measured by potentiodynamic polarization tests results. It is found that the sol–gel layers successfully cover the pores of the MAO coatings. The results of the corrosion tests show that the sol–gel layers significantly increase the corrosion resistance of the substrate by reducing the percent of the porosity. The grain size measurements by XRD analysis shows that the grain size of the sol–gel layer heated in 350 °C is about 50 nm.     

Determination of Set-Membership Identifiability Sets

This paper concerns the concept of set-membership identifiability introduced in Jauberthie et al. (Proceedings of the 18th IFAC World Congress. Milan, Italie, 12024–12029, 2011). Given a model, a set-membership identifiable set is a connected set in the parameter domain of the model such that its corresponding trajectories are distinct to trajectories arising from its complementary. For obtaining the so-called set-membership identifiable sets, we propose an algorithm based on interval analysis tools. The proposed algorithm is decomposed into three parts namely mincing, evaluating and regularization (Jaulin et al. in Applied interval analysis, with examples in parameter and state estimation, robust control and robotics. Springer, Londres, 2001). The latter step has been modified in order to obtain guaranteed set-membership identifiable sets. Our algorithm will be tested on two examples.     

Simultaneous extraction of trace amounts of cobalt, nickel and copper ions using magnetic iron oxide nanoparticles without chelating agent

The present study investigates the application of Fe₃O₄ nanoparticles as an adsorbent for solid phase extraction and their subsequent determination of trace amounts of cobalt, nickel and copper from environmental water samples using flame atomic absorption spectrometry. The analyte ions were adsorbed on magnetic nanoparticles in the pH range of 10–12 and then, Fe₃O₄ nanoparticles were easily separated from the aqueous solution by applying an external magnetic field and decantation. Hence, no filtration or centrifugation was needed. After extraction and collection of magnetic nanoparticles, the analyte ions were desorbed using 1.0 M HNO₃. Several factors that may affect the preconcentration and extraction process, including pH, type and volume of eluent, sample volume, salt effect and matrix effect were optimized. Under the optimized conditions, linearity was maintained from 0.005–3.0 μg/mL for cobalt and nickel and 0.001 to 1.25 μg/mL for copper in the initial solution. The detection limits of this method for cobalt, nickel and copper ions were 0.9, 0.7 and 0.3 ng/mL, respectively. Finally, the method was successfully applied to the extraction and determination of the analyte ions in natural waters and reference plant samples.     

Finding a suitable shield for mixed neutron and photon fields based on an Am–Be source

This study aimed to investigate a shielding design against neutron and photon rays from neutron irradiators based on Am–Be sources, using the Monte Carlo simulation. Different shielding materials were studied, including borated polyethylene, DaGa concrete, and epoxy resin with colemanite. The Monte Carlo N-particle code (MCNP) was used to design shielding. A new type of neutron and photon shielding material based on 40 % galena, 55 % polyethylene, and 5 % boric acid is proposed. The results show that the total effective dose of radiation is significantly reduced by the optimum radius of this shielding system.     

The operator dose assessment of landmine detection systems using the neutron backscattering method

Personal safety issue is one of the major limitations in landmine detection by nuclear techniques. In this paper, the dose rate received by the operator of different hand-held landmine detection systems using the neutron backscattering method was investigated. Monte Carlo method was used to simulate a computational model of the body, instruments with different shielding configurations and soil with various moisture contents. The effective dose received by the different organs of the operator has been estimated by using two different approximation methods including average equivalent dose and dose equivalent assessment. The results obtained by these two methods were compared. The common results showed that the operator dose rate depends on the facility shielding, soil moisture level, and source-to-operator distance. Also, although the absorbed dose received by most organs generally decreases as a function of source to operator distance, for some organs such as kidneys and lungs it firstly increases when source-to-operator distance increases up to 0.7–1.2 m and after that the absorbed dose decreases. Furthermore, the results showed that the effective dose received by the operator has its maximum value when the source to operator distance is 0.60 m.     

Combining a Click–Multicomponent Reaction: One-Pot Synthesis of 1,2,3-Triazol-4-ylmethyl 3-Amino-5,10-dihydro-5,10-dioxo-1H-pyrazolo[1,2-b]phthalazine-2-carboxylate Derivatives

(1,2,3-Triazol-4-yl)methyl-3-amino-5,10-dihydro-5,10-dioxo-1H-pyrazolo[1,2-b]phthalazine-2-carboxylate derivatives were synthesized by a four-component, one-pot condensation reaction of benzaldehyde derivatives, an active methylene compound (prop-2-ynyl-2-cyanoacetate), azides, and phthalhydrazide in the presence of Cu(OAc)₂/sodium ascorbate as catalysts and 1-methyl-1H-imidazolium trifluoroacetate ([Hmim]TFA) as an ionic liquid medium in good to excellent yields.     

An estimator of the stable tail dependence function based on the empirical beta copula

The replacement of indicator functions by integrated beta kernels in the definition of the empirical tail dependence function is shown to produce a smoothed version of the latter estimator with the same asymptotic distribution but superior finite-sample performance. The link of the new estimator with the empirical beta copula enables a simple but effective resampling scheme.     

Catalytic activity of manganese(III)-oxazoline complexes in urea hydrogen peroxide epoxidation of olefins: The effect of axial ligands

The catalytic activity of two manganese(III)-oxazoline complexes [Mn(phox)₂(CH₃OH)₂]ClO₄ and Mn(phox)₃ (Hphox = 2-(2′-hydroxylphenyl)oxazoline), was studied in the epoxidation of various olefins. All of epoxidation reactions were carried out in (1:1) mixture of methanol:dichloromethane at room temperature using urea hydrogen peroxide (UHP) as oxidant and imidazole as co-catalyst. The epoxide yields clearly demonstrate the influence of steric and electronic properties of olefins, the catalysts and nitrogenous bases as axial ligand. [Mn(phox)₂(CH₃OH)₂]ClO₄ catalyst with low steric properties has higher catalytic activity than Mn(phox)₃. The highest epoxide yield (95%) was achieved for indene at the presence of [Mn(phox)₂(CH₃OH)₂]ClO₄ within 5 min. The proximal and distal interactions of strong π-donor axial ligands such as imidazole with the active intermediate are efficiently increased activity of the catalytic system.     

How to insulate a reactive site from a perfluoroalkyl group: photoelectron spectroscopy, calorimetric, and computational studies of long-range electronic effects in fluorous phosphines P((CH(2))(m)(CF(2))(7)CF(3))(3)

This study advances strategy and design in catalysts and reagents for fluorous and supercritical CO(2) chemistry by defining the structural requirements for insulating a typical active site from a perfluoroalkyl segment. The vertical ionization potentials of the phosphines P((CH(2))(m)R(f8))(3) (m = 2 (2) to 5 (5)) are measured by photoelectron spectroscopy, and the enthalpies of protonation by calorimetry (CF(3)SO(3)H, CF(3)C(6)H(5)). They undergo progressively more facile (energetically) ionization and protonation (P(CH(2)CH(3))(3) > 5 > 4 approximately equal to P(CH(3))(3) > 3 > 2), as expected from inductive effects. Equilibrations of trans-Rh(CO)(Cl)(L)(2) complexes (L = 2, 3) establish analogous Lewis basicities. Density functional theory is used to calculate the structures, energies, ionization potentials, and gas-phase proton affinities (PA) of the model phosphines P((CH(2))(m)()CF(3))(3) (2'-9'). The ionization potentials of 2'-5' are in good agreement with those of 2-5, and together with PA values and analyses of homodesmotic relationships are used to address the title question. Between 8 and 10 methylene groups are needed to effectively insulate a perfluoroalkyl segment from a phosphorus lone pair, depending upon the criterion employed. Computations also show that the first carbon of a perfluoroalkyl segment exhibits a much greater inductive effect than the second, and that ionization potentials of nonfluorinated phosphines P((CH(2))(m)CH(3))(3) reach a limit at approximately nine carbons (m = 8).