The Influence of Vanadium Microalloying on Voids Occurence in Low-Alloyed Cr-Mo Steels After Continuous Casting

We discuss the correlation between segregation of carbide forming elements (vanadium) and void initiation and propagation in low-alloyed Cr-Mo steels. The internal defects are created during blooms straightening in radial type of casting machine due to strain deformation field in the temperature range characteristic for vanadium nitride, carbide or carbonitride precipitation. Based on the statistical analysis (1097 continuously cast blooms) of three low-alloyed Cr-Mo steel variants with different vanadium content, we conclude that the void occurence is strongly associated with the level of vanadium content. The experiments performed by means of microstructural, fractographic investigations and microchemical point analysis proved that preffered areas for void initiation are interdendritic segregations in the core of bloom. We observed vanadium carbide precipitates that are situated close to the cracks, whereas the content of vanadium was 7,5 times more then in an average smelt composition. The further development of defects is connected with fast heating up to the austenization temperature in soaking pit. Our results confirm that marked decrease of defects can be achieved by optimization of production process, i. e. optimized casting speed, steel overheat above the liquidus temperature and/or application of M-EMS.     

Replacement of traditional emulsifying salts by selected hydrocolloids in processed cheese production

Different hydrocolloids were examined as possible replacements for traditional phosphate- and citrate-based emulsifying salts in processed cheese production. The following hydrocolloids (at concentrations in the final product of ≤1.0%, w/w) were chosen: modified starch (with bound sodium octenyl succinate), low methoxyl pectin (alone or combined with lecithin), locust bean gum, κ-carrageenan and ι-carrageenan. The products were assessed by sensory analysis, microscopic image analysis and dynamic oscillatory rheometry. Modified starch, locust bean gum and low methoxyl pectin could not be recommended as replacements for traditional emulsifying salts. Model processed cheeses without traditional emulsifying salts of 40% (w/w) dry matter and 55% (w/w) fat-in-dry matter containing 1.0% (w/w) κ-carrageenan or ι-carrageenan were found to be homogeneous, however the products were hard with fracturable texture.     

N-level Atom Interacting with Single-mode Radiation Field: An Exactly Solvable Model with Multiphoton Transitions and Intensity-dependent Coupling

Abstract

We study the dynamics of an N-level atom coupled in a lossless cavity to a single-mode near-resonant quantized field. The atomic levels are coupled by the multiphoton transitions and the coupling constants between the field and the atomic levels are supposed to be intensity dependent. We find the exact solution for the state vector describing the dynamics of the atom-plus-field system. As an illustration we use the model for studying (i) the time evolution of the atomic occupation probability with the initially coherent field and (ii) the light squeezing, when the cavity field is initially in the vacuum state and the atom is prepared in the atomic ‘coherent state’ (a superposition of atomic states).     

Thermal Noise and Hydrodynamic Memory Effects on Force Measurements at Microscales

The paper is devoted to the problem of the determination of regular forces acting on microscopic and smaller objects in fluids when the presence of thermal noise affects the results of measurements. One of the methods on how these forces are determined is the measurement of the drift velocity of Brownian particles. Traditionally such experiments are interpreted on the basis of the overdamped Langevin equation. An exact expression has been obtained for this velocity within the linear hydrodynamic theory of the Brownian motion in incompressible fluids, when the external force is constant and when the particle is in a harmonic potential well. It is shown that for sufficiently short experimental times the influence of the hydrodynamic memory effects in the drift velocity determination is significant. The obtained solutions contain algebraic long-time tails due to which the results expected from the standard theory are approached very slowly with the increase of time.     

Advantageous mechanochemical synthesis of copper(Ⅰ)selenide semiconductor,characterization,and properties

Copper(I)selenide-nanocrystalline semiconductor was synthesized via one-step mechanochemical synthesis after 5 min milling in a planetary ball mill.The kinetics of synthesis was followed by X-ray powder diffraction analysis and specific surface area measurements of milled 2Cu/Se mixtures.The X-ray diffraction confirmed the orthorhombic crystal structure of Cu₂Se with the crystallite size～25 nm.The surface chemical structure was studied by X-ray photoelectron spectroscopy,whereby the binding energy of the Cu 2p and Se 3d signals corresponded to Cu⁺and Se^2?oxidation states.Transmission electron microscopy revealed agglomerated nanocrystals and confirmed their orthorhombic structure,as well.The optical properties were studied utilizing ultraviolet-visible spectroscopy and photoluminescence spectroscopy.The direct bandgap energy 3.7 eV indicated a blue-shift phenomenon due to the quantum size effect.This type of Cu₂Se synthesis can be easily adapted to production dimensions using an industrial vibratory mill.The advantages of mechanochemical synthesis represent the potential for inexpensive,environmentally-friendly,and waste-free manufacturing of Cu₂Se.     

Long-term material balance of iron in aluminum reduction cells

The distribution of iron was evaluated using the total material balance of iron in aluminum cells. The data on the Fe₂O₃ content in primary and secondary alumina, in aluminum fluoride, and in melted and crushed baths, and the data on the iron content in prebaked anodes, anode butts, and produced aluminum in the period 1998 through 2002 were determined using statistical analysis. The average content for the standard deviation of iron oxide, with respect to the iron in each material, was studied for each year, and a trend was calculated for the entire period. From a statistical point of view, the content of Fe in aluminum systematically increased during the years 1998 through 2002. Conversely, it was observed that the content of Fe₂O₃ in the crushed bath decreased during the same period. The crushed bath seems to be a very important flow in the process, since it accumulates most of the iron content. One can expect that a substantial part of the iron is distributed directly into the aluminum and the dry scrubbers. Based on the statistical analysis, the material balance of the iron in the prebaked anode cells resulted in the production of 1 t of aluminum. The total iron material balance (for both input and output materials) in the whole period of investigation totaled −642 g Fe. This value was approximately the same for each year. The higher content of Fe in the output materials is most probably caused by secondary sources of iron, which were not incorporated into the balance.     

The synthesis and electron structure of oligothiophenes terminated with (10H-anthracen-9-one) methylene chromophores

The synthesis, spectral measurements and theoretical study of simple model oligothiophenes terminated symmetrically or asymmetrically by (10H-anthracen-9-one) methylene chromophore are presented. The electron absorption spectra of these novel molecules were measured in polymer matrices and chloroform solution. The absorption spectra of investigated systems measured in chloroform are characterised by a broad low energy band with partially distinguished vibrational structure. Theoretical calculations of electronic ground state structures have been performed at the density functional theory (DFT) level of the theory. The vertical excitations energies were calculated using the time-dependent version of DFT (TD-DFT) and semiempirical Zerner's Intermediate Neglect of Differential Overlap methods. The role of the termination group upon the vertical excitation was estimated from the localisation of highest and lowest occupied orbitals. This analysis showed that the excitation energy transfer upon the optical excitation leads from the thiophene chromophores into the central part of (10H-anthracen-9-one) methylene unit.     

Removal of pyridine from liquid and gas phase by copper forms of natural and synthetic zeolites

Zeoadsorbents on the basis of copper forms of synthetic zeolite ZSM5 and natural zeolite of the clinoptilolite type (CT) have been studied taking into account their environmental application in removing harmful pyridine (py) from liquid and gas phase. Sorption of pyridine by copper forms of zeolites (Cu-ZSM5 and Cu-CT) has been studied by CHN, X-ray photoelectron spectroscopy, X-ray powder diffractometry, FTIR spectroscopy, thermal analysis (TG, DTA and DTG) and analysis of the surface areas and the pore volumes by low-temperature adsorption of nitrogen. The results of thermal analyses of Cu-ZSM5, Cu-(py)(x)ZSM5, Cu-CT and Cu-(py)(x)CT zeolitic products with different composition (x depends on the experimental conditions of sorption of pyridine) clearly confirmed their different thermal properties as well as the sorption of pyridine. In the zeolitic pyridine containing samples the main part of the pyridine release process occurs at considerably higher temperatures than is the boiling point of pyridine, which proves strong bond and irreversibility of py-zeolite interaction. FTIR spectra of Cu-(py)(x)zeolite samples showed well resolved bands of pyridine. The results of thermal analysis and FTIR spectroscopy are in a good agreement with the results of other used methods.     

Annealing of gold nanostructures sputtered on polytetrafluoroethylene

Gold nanolayers sputtered on polytetrafluoroethylene (PTFE) surface and their changes induced by post-deposition annealing at 100°C to 300°C are studied. Changes in surface morphology and roughness are examined by atomic force microscopy, electrical sheet resistance by two point technique, zeta potential by electrokinetic analysis and chemical composition by X-ray photoelectron spectroscopy (XPS) in dependence on the gold layer thickness. Transition from discontinuous to continuous gold coverage takes place at the layer thicknesses 10 to 15 nm and this threshold remains practically unchanged after the annealing at the temperatures below 200°C. The annealing at 300°C, however, leads to significant rearrangement of the gold layer and the transition threshold increases to 70 nm. Significant carbon contamination and the presence of oxidized structures on gold-coated samples are observed in XPS spectra. Gold coating leads to a decrease in the sample surface roughness. Annealing at 300°C of pristine PTFE and gold-coated PTFE results in significant increase of the sample surface roughness.