Recovery of Chromium from AOD‐Converter Slags

Slags from the production of high‐alloyed steel contain both chemically bound chromium (mainly as Cr₂O₃) in the mineral fraction and elemental chromium in the metallic remainders. Thermochemical post treatment of the slag in an electric arc furnace under reducing conditions enables the nearly complete recovery of the total amount of chromium in form of a metallic alloy. The best results were achieved by resistance melting (submerged electrodes) with addition of a reducing agent into the melt. The efficiencies of the reducing agents carbon, aluminium, silicon (as ferrosilicon) and silicon carbide were investigated and compared. As aluminium is the strongest reducing agent, it is less selective and reduces much more SiO₂ than Cr₂O₃. While SiC shows only low reactivity because of its high thermal resistance, carbon and silicon had the highest reducing potentials: More than 97% of the chemically bound chromium can be recovered by application of these reducing agents. Due to the high temperature required for the reduction of the chromium compounds, the reduction of SiO₂ as an undesired side reaction cannot be avoided. However, compared with mechanical procedures that are limited to the recovery of the metallic remainders, the total chromium recovery can be significantly increased by the described reductive melting procedure.     

Application of the FITSC method for characterization of PZT-type ceramics with the diffuse phase transition

In the present work the (Pb_0.84Ba_0.16)(Zr_0.54Ti_0.46)O₃ (PBZT 16/54/46) ceramics has been studied from the point of view of its electrical properties. Dielectric properties of PBZT were measured within the temperature range of the ferroelectric-paraelectric (FE-PE) phase transition region. The method of field-induced thermally stimulated currents (FITSC) was applied and thus the thermal relaxation effects were studied. The observed field dependence of thermally stimulated depolarization currents has revealed the existence of different frequency-dependent relaxation processes in the temperature range between 200 and 400 °C.Our experiment demonstrates that modification of ferroelectric materials with isovalent ions, but bigger radii than the origin atom, significantly affect its properties, particularly the PBZT real part of electrical permittivity shows the phase transition character change from ferroelectric to relaxor and finally, that electrical examination can be effectively used for drawing decisive applications conclusions considering polarization parameters distribution.     

Fabrication of composite coatings of 4-(pyrrole-1-yl) benzoate-modified poly-3,4-ethylenedioxythiophene with phosphomolybdate and their application in corrosion protection

We propose a novel composite (hybrid) organic/inorganic system that can be prepared as a coating (on 1 μm level) on glassy carbon and metal electrode substrates. Poly(3,4-ethylenedioxythiophene) or PEDOT based composite coatings were electrodeposited using cyclic voltammetry on glassy carbon and stainless steel substrates in the presence of 4-(pyrrole-1-yl) benzoic acid (PyBA) and phosphododecamolybdic acid (PMo₁₂). The coating growth was facilitated by the addition of polyoxyethylene-10-laurylether (BRIJ10) neutral surfactant at the level of 0.04 mol dm⁻¹ to improve solubility of the 3,4-ethylenedioxythiophene monomer and to form an aqueous micellear solution in the reaction medium. The fact that carboxylate-containing PyBA units link positively charged PEDOT structures tends to improve overall stability and adherence of composite coatings to stainless steel. The PEDOT/PyBA composite serves as a stable host matrix for large negatively charged polymolybdate inorganic species. Consequently, due to the formation of denser polymeric structures and to the existence of electrostatic repulsion effects, the polyanion-containing composite coatings are capable of largely blocking the access of pitting-causing anions (chlorides) to the surface of stainless steel. Interaction of phosphomolybdate with metal ions, namely with chromium(III) or even iron(III) or iron(II) that exist at the stainless steel–composite coating interface, may lead to the formation of insoluble deposits and exhibit overall passivating effect.     

Triplet-state quenching by photostabilizers of polyolefins

Paramagnetic nickel(II) complexes which are used as commercial photostabilizers of polyolefins are shown in laser photolysis studies to quench the triplet state of benzophenone in dilute benzene solution. The efficiency of quenching observed is less than that of diamagnetic square-planar nickel(II) complexes which are more effective photostabilizers of polypropylene in “Xenotest” experiments. The observed rate constants for quenching of triplet benzophenone are compared with those observed by other workers for quenching of singlet oxygen, O₂^*(¹Δ_g), in dilute solution. The relevance of these studies to the understanding of photodegradation in polyolefins is discussed.     

Transfer of brownian particles to continuous moving surfaces

A theoretical analysis of particle deposition from a dilute suspension (or aerosol) subject to laminar flow onto moving continuous plates (sheets) and cylinders (wires) is presented. Complete transport equations have been formulated, taking into account specific surface interactions such as London-van der Waals and electrical double-layer forces. By solving these equations numerically the dimensionless mass transfer Sherwood number has been determined for a variety of conditions characteristic for suspensions and aerosols. It has been found that the effects of attractive double-layer forces are very important, especially for thin double-layers, increasing mass transfer rates by more than an order of magnitude for larger particles (at distances close to the entrance point). For Péclet numbers Pe < 10^?6 (small particles) the specific interactions play a less important role and the Sherwood number can be accurately approximated by an analytical expression derived for neglible particle dimensions (ions).The major finding of this study is that compared to deposition on a stationary surface, deposition on moving continuous surfaces is larger by at least one order of magnitude, both in the presence or absence of specific surface forces.     

Computation of the integrated flow of particles between polygons

To quantify the flow of particles over a heterogeneous area, some models require the integration of a pointwise dispersal function over source and target polygons. This calculation is a non-trivial task and may require a great deal of computing time. In this paper, an efficient and accurate algorithm is presented to integrate general individual dispersal functions between pairs of convex or non-convex polygons. Geometric calculations are performed using standard tools from computational geometry. Numerical integration is then performed either by a grid method or by an adaptive cubature method. The procedure is illustrated with a case study. It is shown that the cubature method is much more efficient than the grid method and that its error estimates are accurate. The algorithm is implemented in a C++ program, Califlopp.     

Particle transfer to a plate in uniform flow

A theoretical analysis of particle deposition from a dilute suspension onto a plate immersed in a uniform laminar flow with zero angle of incidence is presented. The complete transport equation was solved numerically, taking into account specific surface interactions such as London-van der Waals dispersion and electrical double-layer forces, as well as external forces such as gravity and electric fields. From these solutions, the dimensionless mass transfer Sherwood number was determined for a variety of conditions characteristic for suspensions and aerosols. It is shown that the theoretical analysis applies also to particle deposition within the entrance region of a parallel-plate channel, provided that the hydrodynamic boundary layer is much smaller than the distance between the plates. It is found that the effects of specific surface interactions are important for distances close to the suspension inlet point (leading edge) and for large particles. The effects are generally less pronounced for aerosols in which gravity and electrostatic forces (if present) play a dominant role.     

XANES investigation of co-precipitated Fe and Cr fluorides catalytically active in heterogeneous dehydrochlorination

In this X-ray absorption near-edge structure (XANES) study we focused our interest on co-precipitated Fe and Cr fluorides. Compounds with a low Cr content are catalytically active in the dehydrochlorination of 1,1,1-trichloroethane. XANES reveals for these samples an incorporation of a modified CrF_3-x(OH)x pyrochlore structure into the β-FeF₃ host lattice and an electron-deficient Cr 3d orbital, which may act as a Lewis acid site in the catalytic process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Food of marine origin: Between benefits and potential risks. Part I. Canned fish on the Polish market

Chemical analyses were performed on 12 of the most popular varieties of canned fish on the Polish market. The contents of the nutritive substances of canned fish (protein, micro and macroelements, vitamins A₁, D₃, E, and fatty acids) and certain contaminants were determined. It was confirmed that canned fish is a good source of digestible proteins, fluoride, iodine, selenium, and vitamin D₃. The fundamental nutritive benefit of processed fish is the highly advantageous fatty acid composition, which imparts healthful effects. The high content of long-chained polyunsaturated fatty acids, which is not noted in other food products, is especially important.