Methods to determine activation energies for the two kinetic states of the oscillatory Bray-Liebhafsky reaction

Six different methods are suggested to calculate the apparent activation energies of the overall decomposition of hydrogen peroxide, both by oxidative and reductive pathways, in the Bray-Liebhafsky oscillatory chemical system. The activation energies of the reduction pathway lie between 31 and 35 kJ/mol and those of the oxidation one between 75 and 78 kJ/mol.     

Quantum simulation of bound-free spectra

We have performed quantum simulations of the 2³Π _g ?1³Σ _u ⁺ bound-free transition. Assuming Boltzmann and different non-Boltzmann distributions for the population in the 2³Π _g state, we have calculated the corresponding spectral shapes. The results show that the shape of the emission spectrum can be used to obtain information about the population distribution within rovibration levels of the upper state. Comparison with several experiments is presented.     

Cleaning of Porous Aluminium Titanate by Oxygen Plasma

The removal of organic contaminants from porous Al₂TiO₅ during treatment in oxygen plasma was studied by optical emission spectroscopy (OES). The samples of Al₂TiO₅ were immersed into water emulsion of mineral oil for 3 h to get soaked. Then, they were thoroughly cleaned in ultrasound to remove oil from the surface. Samples were later exposed to RF oxygen plasma at the pressure of 75 Pa. The plasma density was about 2 × 10¹⁶ m⁻³, the electron temperature was about 6 eV and the density of neutral oxygen atoms was about 2 × 10²¹ m⁻³. Optical emission spectra between 200 and 1,000 nm were measured continuously during plasma treatment. The CO peak resulting from oil oxidation reached a well-pronounced maximum between 100 and 150 s of plasma treatment. The maximum in CO corresponded well with a minimum in O peaks. Concentration of oil in the samples was estimated by energy dispersion X-ray analysis. Initially the samples showed high concentration of carbon (about 38 at.%), while after plasma treatment the carbon concentration decreased below the detection limit. The cleaning efficiency was explained by diffusion of oil towards the surface where it was removed by oxidation with oxygen radicals.     

Spectral simulation and interpretation of LiZn and LiCd blue-green emission

Magnetic hyperfine interaction constants (A factors) have been determined for nine levels in the 4d5s and 4d5p configurations of the Y⁺ ion by Doppler-free saturation spectroscopy and level crossing spectroscopy in a sputtered vapour.     

Prediction of excess molar volumes of binary mixtures of organic compounds from refractive indices

The excess molar volumes of 51 binary mixtures containing diverse groups of organic compounds: alcohols (methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol, hexan-1-ol, and heptan-1-ol), (cyclo-) alkanes (hexane, heptane, octane, nonane, decane, undecane, dodecane, and cyclohexane), esters (diethyl carbonate and ethyl chloroacetate), aromatics (o-xylene, m-xylene, p-xylene, and ethylbenzene), ketones (acetone), and ethers (anisole), were predicted from the refractive index data, using three types of equations coupled with several different mixing rules for refractive index calculations: the Lorentz-Lorenz, Dale-Gladstone, Eykman, Arago-Biot, Newton, and the Oster. These systems were chosen since they belong to different classes of organic species forming molecular interactions and intermolecular forces during mixing resulting in positive or negative, smaller or larger deviations from ideal behaviour. The obtained results were analysed in terms of the applied equation and mixing rule, the nature of compounds of the mixtures and the influence of alkyl chain length of the alkane or alcohol molecule. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Chemical imaging of pharmaceutical granules by Raman global illumination and near-infrared mapping platforms

Raman global illumination and near-infrared (NIR) mapping instruments were used to chemically image pharmaceutical granules obtained by the wet granulation process in order to determine whether the API was mixed with the major excipient or granulates on its own. The granules were randomly distributed onto a microscope slide and an average area of about 3.5 mm × 3.5 mm, covering 50-100 granules, was analyzed by both instruments. Light microscopy images of the separated granules were collected before the spectroscopic data acquisition. Both Raman and NIR signals of API and major excipient (mannitol) were easily detected by both techniques which allowed the chemical structure of the granules to be characterised. Most of the granules were found to contain both API and mannitol but pure mannitol and a few pure API granules were also identified. Raman global illumination was found to provide a comprehensive insight into chemical structure of the granules being able to more clearly determine the API in comparison with NIR mapping. Owing to the differences in shapes of the particles and reflection characteristics, visual microscopy and methods based on reflection can be potentially useful for analyzing this particular formulation.     

On the Index of Necklaces

We consider the following two classes of simple graphs: open necklaces and closed necklaces, consisting of a finite number of cliques of fixed orders arranged in path-like pattern and cycle-like pattern, respectively. In these two classes we determine those graphs whose index (the largest eigenvalue of the adjacency matrix) is maximal.     

The analysis of hardening of metal materials

There has been researched the interdependence of the process of microalloying, thermomechanical treatment and obtained mechanical characteristics of steel and AIMgSi alloys. There have been analyzed the hardening mechanisms of the mentioned alloys in correlation with grade, speed and temperature of strain. The achieved effects of alloys hardening are the consequences of combined operations of grain raffination, precipitation of dispersing particles of microalloying elements and increased density of dislocation.