Assessment of the Fe-Sn-Zn phase diagram at 450°C

The Fe-Sn-Zn system is of interest because Sn is one element added to the Zn galvanizing bath to overcome the drawbacks due to the presence of Si in semi-killed steels. This work has been undertaken with the aim to understand the tin effect on the microstructure and the layers growth in batch galvanized coatings on low alloyed steels. Various experimental techniques such as metallography, scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDX) are used in order to characterize the microstructure and the properties of such coatings elaborated in a zinc bath enriched with tin. Solidification phenomena and layers growth mechanisms during galvanization are explained by means of the ternary phase diagram Fe-Sn-Zn at 450°C. The Calphad method allows to obtain this phase diagram from the three optimized binary phase diagrams Fe-Sn, Fe-Zn and Sn-Zn and some experimental data inside the ternary Fe-Sn-Zn system.     

Synthesis of 2′,3′-dihydrosolanesyl analogues of β-d-arabinofuranosyl-1-monophosphoryldecaprenol with promising antimycobacterial activity

Two new hydrolytically stable analogues of β-d-arabinofuranosyl-1-monophosphoryldecaprenol, the donor substrate for mycobacterial arabinosyltransferase, have been prepared. Biological evaluation of these compounds in vitro against Mycobacterium tuberculosis H₃₇Rv strain revealed a promising activity.     

Influence of medium on the kinetics of oxidation of iron(II) ion with t-butyl hydroperoxide

The oxidation of iron(II) with tert-butyl hydroperoxide was investigated in the absence of oxygen in water, methanol, and the dichloromethane—methanol solvent mixture (φ_r = 2:1). The oxidation rate depends on solvent polarity; measured in the presence of SCN⁻ at constant 0.8 mmol dm⁻³ HCl, the rate constant increases with the polarity decrease passing from water and methanol to the dichloromethane—methanol solvent mixture. Further, in non-aqueous solutions at this acid concentration the rate constant was higher than the rate constant in the presence of Cl⁻ only. The oxidation rate measured in the [FeCl]²⁺ complex in dichloromethane—methanol was slow in acidic medium and increased by decreasing the acid concentration. Approaching the physiological pH conditions the rate constant attained the value of an order of magnitude of 10³ dm³ mol⁻¹ s⁻¹, while very little alteration of stoichiometry of the oxidation reaction was observed. The rate constant measured in the presence of Cl⁻ strongly depends on electrolyte concentration at concentrations less than 0.5 mmol dm⁻³ HCl, both in MeOH and the solvent mixture. Based on these results, a possible mechanism of the influence of solvent, acidity, and ligand type on the rate constant is discussed. We assume that the oxidation proceeds by an inner-sphere mechanism considering that the breakdown of the successor inner-sphere complex forming reactive alkoxyl radicals is probably the rate-limiting step. Presented at the 20th International Conference on the Coordination and Bioinorganic Chemistry organized by the Slovak Chemical Society, Slovak University of Technology, Comenius University, and the Slovak Academy of Sciences, Smolenice Castle, 5–10 June 2005.     

TTT Cure Diagram

Curing reactions of the epoxy system consisting of a diglycidyl ether of bisphenol A (BADGE n=0) and m-xylylenediamine (m-XDA) were studied to calculate time-temperature-transformation (TTT) isothermal cure diagram for this system. Gel times were measured as a function of temperature using solubility test. Differential scanning calorimetry (DSC) was used to calculate the vitrification times. DSC data show a one-to-one relationship between T _g and fractional conversion, a independent of cure temperature. As a consequence, T _g can be used as a measure of conversion. The activation energy for the polymerization overall reaction was calculated from the gel times obtained using the solubility test (41.5 kJ mol^-1). This value is similar to the results obtained for other similar epoxy systems. Isoconversion contours were calculated by numerical integration of the best fitting kinetic model. This revised version was published online in July 2006 with corrections to the Cover Date.     

A re-statement of the Hohenberg–Kohn theorem and its extension to finite subspaces

Bearing in mind the insight into the Hohenberg–Kohn theorem for Coulomb systems provided recently by Kryachko (Int J Quantum Chem 103:818, 2005), we present a re-statement of this theorem through an elaboration on Lieb’s proof as well as an extension of this theorem to finite subspaces. Contribution to the Serafin Fraga Memorial Issue.     

Pozzolanic properties of a residual FCC catalyst during the early stages of cement hydration

The catalyst used in fluidized catalytic cracking (FCC) units of refineries after several recovery cycles in regeneration units, reduces its activity and it is partially substituted by new catalyst in the process. As it has a high silicon and aluminum oxides content, the pozzolanic properties of a Brazilian FCC spent residual catalyst, used in different substitution degrees to cement, were evaluated by three thermal analysis techniques during the early stages of hydration of a type II Portland cement. NCDTA curves show in real time that the residual catalyst, accelerates the stages of cement hydration. TG and DSC curves of respective pastes after 24 h of hydration evidence the pozzolanic activity of the waste, respectively, by the lower water mass loss during the dehydroxylation of the residual calcium hydroxide and by the lower dehydroxylation endothermal effect. Within the analyzed period, the higher is the cement substitution degree, the higher is the pozzolanic activity of the residual catalyst.     

Sorption behavior of Co(II) on γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the presence of humic acid

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The extent of sorption of divalent metal cations is controlled by a number of factors including cosorbing or complexing. In this work, the effects of pH, humic acid HA/Co(II) addition orders, ionic strength, concentration of HA, and foreign cations on the Co(II) sorption on γ-Al₂O₃ in the presence of HA were investigated. The sorption isotherms of Co(II) on γ-Al₂O₃ in the absence and presence HA were also studied and described by using S-type sorption model. The experimental results showed that the Co(II) sorption is strongly dependent on the pH values, concentration of HA, but independent of HA/Co(II) addition orders, ionic strength, and foreign cations in the presence of HA under our experimental conditions. The results also indicated that HA enhanced the Co(II) sorption at low pH, but reduced the Co(II) sorption at high pH. It was hypothesized that the significantly positive influence of HA at low pH on the Co(II) sorption on γ-Al₂O₃ was attributed to strong surface binding of HA on γ-Al₂O₃ and subsequently the formation of ternary surface complexes such as ≡S-OOC-R-(COO⁻) _x Co^2−x . Chemi-complexation may be the main mechanism of the Co(II) sorption on γ-Al₂O₃ in the presence of HA.     

Selected ion flow tube mass spectrometry analyses of stable isotopes in water: Isotopic composition of H3O+ and H3O+(H2O)3 ions in exchange reactions with water vapor

A new method has been developed for the determination of the isotope abundance ratios of deuterium, D, and oxygen-18, 18O, in water vapor (and water) using selected ion flow tube mass spectrometry (SIFT-MS). H3O+ ions are injected into the helium carrier gas where they associate with the H2O and HDO molecules in a sample of water introduced into the carrier gas. The D and 18O contents of the product cluster ions H8DO4+ and H9(18)OO3+ at m/e = 74 and 75, respectively, are determined by reference to the majority cluster ion H9O4+ at m/e = 73. Allowance is made for the contribution of the H8(17)OO3+ ions to the m/z = 74 ions. Absolute isotopic ratios are measured within seconds without the need for precalibration of the SIFT-MS instrument, currently to an accuracy of better than 2%.     

Synthesis,Crystal Structure,and Electrochemical Behaviour of an Azido μ‐bridged Ni2+ Complex

A homo‐dinuclear Ni^II complex was prepared from 2, 6‐bis(3, 5‐dimethylpyrazolyl)pyridine (Me₄‐bpp) and azide ions in nonaqueous media. It was characterized by single crystal X‐ray structural analysis, IR spectroscopy, and elemental analysis. In addition, the electrochemical properties of the compound were determined with cyclic voltammetry in DMF. The title compound crystallizes in the P2₁/n monoclinic space group, with unit cell parameters a = 8.978(1), b = 12.459(1), c = 17.764(1) Å, ß =100.603(3)°, V = 1953.0(3) ų, Z = 2. The Ni²⁺ ion has a distorted octahedral environment involving three nitrogen atoms of the Me₄‐bpp ligand, two nitrogen atoms from the bridged azide group, and one nitrogen atom from the terminal azide group. The Ni···Ni distance is 3.273(5) Å.     

Preconcentration and separation of copper(II), cadmium(II) and chromium(III) in a syringe filled with 3-aminopropyltriethoxysilane supported on silica gel

In this study, a syringe was filled with silica gel loaded with 3-aminopropyltriethoxysilane, for the separation and preconcentration of copper, cadmium and chromium prior to their determination by graphite furnace atomic absorption spectrometry (GFAAS) in seawater. For this purpose, a syringe was filled with 0.5 g of modified silica gel and the sample solution was drawn into the syringe and ejected back again. The analyte elements were quantitatively retained at pH 5. Then, the elements sorbed by the silica gel were eluted with 2.0 M of HCl and determined by GFAAS. At optimum conditions, the recovery of Cu, Cd and Cr were 96-98%. Detection limits (3delta) were 6.6, 7.5 and 6.0 micro g L(-1) for Cu, Cd and Cr, respectively. The elements could be concentrated by drawing and discharging several portions of sample successively but eluting only once. Cu, Cd and Cr added to a seawater sample were quantitatively recovered (>95%) in the range of the 95% confidence level. The method proposed in this paper was compared with a column technique. Optimum experimental conditions, reproducibility, precision and recoveries of both techniques are the same, but the syringe technique is much faster, easier and more practical than the column technique. It is a portable system and allows one to make the sorption process in the source of sample. In addition, the risk of contamination is less than in the column technique.