Oxidation stability of various Ti-alloys

Since titanium metal first became a commercial reality in 1950, corrosion resistance has been an important consideration in its selection as an engineering structural material. Titanium has gained acceptance in many media where its corrosion resistance and engineering properties have provided the corrosion and design engineer with a reliable and economic material. Titanium, like any other metal, is subject to corrosion in environments of air, oxygen, moisture, and so on. In this work, high-temperature stability of Ti and various Ti-alloys (by ASTM standard) was investigated. The best results showed that for Ti-Gr.5 alloy, the oxidation at 800 °C was 3.39% and at 900 °C 8.35%. For the comparison, commercial pure Ti-alloys Ti-Gr.2 and Ti-Gr.37 containing Al were used, whereas the oxidation resistance was much worse.     

On reactive solute transport through a curved pipe

The transport of a reactive solute by diffusion and convection in a thin (or long) curved pipe is considered. Using asymptotic analysis with respect to the pipe’s thickness, the effective model for solute concentration is formally derived. A simple approximation is computed, showing explicitly the effects of the pipe’s geometry in nature and magnitude.     

Polymerization of 3,6-Dibromo-9-(2,3-Epoxypropyl)Carbazole with Lewis Acids

Abstract

The kinetics of polymerization of 3,6-dibromo-9-(2,3-epoxypro-pyl) carbazole with stannic chloride and boron trifluoride etherate were studied by a microcalorimetric technique. Complex kinetics of the polymerization rate were observed. A spontaneous increase of the reaction rate was recorded after it decreased and after polymerization for some time at the minimal rate. This effect is explained by a change in the mechanism of polymerization. At the high enough degree of conversion, transition from an active chain end mechanism to an activated monomer mechanism takes place.     

Transformations of [Au(CN)2]− at the contact with activated carbon surface

We have studied the processes occurring when alkaline aqueous solution of Na[Au(CN)₂] is brought in contact with activated carbon surface. It has been shown that the adsorption of the gold cyanide complex occurs via several independent routes, one of them being accompanied with the partial breakdown of the inner sphere of the compound and free cyanide ions release into the solution. The latter process decreases the gold recovery by aqueous NaOH during the high-temperature (150°C) desorption. A prolonged storage of the adsorbent saturated with [Au(CN)₂]^? in air produces a similar result. The reasons of the observed phenomena have been discussed.     

Rearrangement of hexadecane molecules confined in the nanopores of a controlled pore glass using positron annihilation and differential scanning calorimetry

The solidification/melting of cetane confined in nine silica glasses with specific controlled pores (CPG) with different pore sizes (r _p ranging from 3.7–72 nm) has been studied. Samples with variable coefficient of filling of cetane were prepared and analyzed. Combining the indication of the evolving solidification heats (via differential scanning calorimetry, DSC) with the lifetime spectra of positron annihilation, the mechanism of filling of cetane molecules in the pores of the hosting silica glass matrices has been searched. Three independent solidification effects—three independent DSC peaks—were observed in each measuring cycle, namely one crystallization exotherm Rb of the bulk-cetane (if present) and two crystallization sub-peaks Rc1 and Rc2 of the confined cetane in the case of continuous cooling. The temperatures of both Rc1 and Rc2 effects decrease on decreasing the r _p of the CPG matrix. The mutual relation between Rc1 and Rc2 has been analyzed. The kinetics of all three steps of the solidification in the continuous-cooling as well as isothermal regimes have been specified.     

Parallel Interactions at Large Horizontal Displacement in Pyridine–Pyridine and Benzene–Pyridine Dimers

A study of crystal structures from the Cambridge Structural Database (CSD) and DFT calculations reveals that parallel pyridine–pyridine and benzene–pyridine interactions at large horizontal displacements (offsets) can be important, similar to parallel benzene–benzene interactions. In the crystal structures from the CSD preferred parallel pyridine–pyridine interactions were observed at a large horizontal displacement (4.0–6.0 Å) and not at an offset of 1.5 Å with the lowest calculated energy. The calculated interaction energies for pyridine–pyridine and benzene–pyridine dimers at a large offset (4.5 Å) are about 2.2 and 2.1 kcal mol^?1, respectively. Substantial attraction at large offset values is a consequence of the balance between repulsion and dispersion. That is, dispersion at large offsets is reduced, however, repulsion is also reduced at large offsets, resulting in attractive interactions.     

Mechanistic investigation and DFT calculation of the new reaction between S-methylisothiosemicarbazide and methyl acetoacetate

A study on the synthesis and mechanistical aspects of formation of 3-methyl-5-oxo-3-pyrazolin-1-carboxamide (MOPC) starting from S-methylisothiosemicarbazide hydrogen iodide and methyl acetoacetate was performed. In the alkaline aqueous solution, the intermediate methyl acetoacetate S-methylisothiosemicarbazone undergoes substitution of CH₃S^? anion by hydroxide anion, cyclization, carbanion formation, and elimination of methanol, thus yielding corresponding Na-enolate salt of pyrazol-5-one derivative. The structure of the compound obtained after protonation of the formed enolate salt was determined by means of spectroscopic techniques and single-crystal X-ray diffraction analysis. The mechanism of conversion of methyl acetoacetate S-methylisothiosemicarbazone into MOPC was investigated by means of the B3LYP functional, and it was found that the reaction is thermodynamically controlled.     

Comparison of comet assay parameters for estimation of genotoxicity by sum of ranking differences

The genotoxic potential of waters in six rivers and reservoirs from Serbia was monitored in different tissues of chub (Squalius cephalus L. 1758) with the alkaline comet assay. The comet assay, or single-cell gel electrophoresis, has a wide application as a simple and sensitive method for evaluating DNA damage in fish exposed to various xenobiotics in the aquatic environment. Three types of cells, erythrocytes, gill cells, and liver cells, were used for assessing DNA damage. Images of randomly selected cells were analyzed with a Leica fluorescence microscope and image analysis by software (Comet Assay IV Image analysis system, PI, UK). Three parameters (tail length—l, tail intensity—i, and Olive tail moment—m) were analyzed on 1,700 nuclei per cell type. The procedure for sum of ranking differences (SRD) was implemented to compare different types of cells and different parameters for estimation of DNA damage. Regarding our nine different estimations of genotoxicity: tail length, intensity, and moment in erythrocytes (rel, rei, rem), liver cells (rll, rli, rlm), and gill cells (rgl, rgi, rgm), the SRD procedure has shown that the Olive tail moment and tail intensity are (almost) equally good parameters; the SRD value was lower for the tail moment and tail intensity than for tail length in the case of all types of cells. The least reliable parameter was rel; close to the borderline case were rei, rll, and rgl (～5 % probability of random ranking).

Development and optimization of the determination of pharmaceuticals in water samples by SPE and HPLC with diode‐array detection

This paper describes the development, optimization, and validation of a method for the determination of five pharmaceuticals from different therapeutic classes (antibiotics, anthelmintics, glucocorticoides) in water samples. Water samples were prepared using SPE and extracts were analyzed by HPLC with diode‐array detection. The efficiency of 11 different SPE cartridges to extract the investigated compounds from water was tested in preliminary experiments. Then, the pH of the water sample, elution solvent, and sorbent mass were optimized. Except for optimization of the SPE procedure, selection of the optimal HPLC column with different stationary phases from different manufacturers has been performed. The developed method was validated using spring water samples spiked with appropriate concentrations of pharmaceuticals. Good linearity was obtained in the range of 2.4–200 μg/L, depending on the pharmaceutical with the correlation coefficients >0.9930 in all cases, except for ciprofloxacin (0.9866). Also, the method has revealed that low LODs (0.7–3.9 μg/L), good precision (intra‐ and interday) with RSD below 17% and recoveries above 98% for all pharmaceuticals. The method has been successfully applied to the analysis of production wastewater samples from the pharmaceutical industry.