In order to reveal the reactivity of monosubstituted thiophenols, the hydrogen-isotope exchange reaction between T-labeled poly(vinyl alcohol) and each monosubstituted thiophenol (unlabeled) was studied in a liquid-solid system. Using both the data obtained and theA-McKay plot method, the reaction was analyzed, and the rate constant (k) for the monosubstituted thiophenol has been obtained. Consequently, it has been found that (1) the higher the temperature is, the larger is the reactivity of monosubstituted thiophenols, (2) the temperature dependence of the effect of the substituent (in a monosubstituted thiophenol) on the reactivity of the monosubstituted thiophenol is weak, (3) the reactivity of monosubstituted thiophenols follows the Hammett rule, (4) the reactivity of monosubstituted thiophenols can be enhanced with one of the electron-attractive substituents.
The alumina-dye composites were prepared by treating the basic alumina with the water solutions of Reactive Red 120 (RR 120)
and Reactive Blue 15 (RB 15) dyes. The bands of low intensities in the 1400–1600 cm−1 region and at 783 cm−1 in the IR spectra of these composites point out that the dye species is bound weakly to the surface. In the case of mechanochemical
adsorption of dye molecules, the asymmetric and symmetric S(=O)2 and the S-O-C stretching bands together with the vibrations of aromatic ring revealed that dye types under dry conditions
interacted effectively with alumina surface. After the heating of the alumina dye complexes in the temperature range 150–350°C,
the intensities of the IR and XRD peaks for adsorbed types decreased. The endothermic peaks over 200°C and the bigger total
mass losses for the alumina-dye composites can be ascribed to the decomposition of dye species retained by the alumina surface.
The mass losses on TG curves of the alumina-dye complexes up to ∼800°C exhibit the removal of black residues occurred by decomposition
of first adsorbed products. The thermal analysis data also point out that the water molecules bonded strongly to the alumina
surface and dye types compete to accommodate at the surface active sites.
Authors:Choon-ho Cho, Yun-sang Lee, Eung-soo Kim, Jeong-guk Kim, and Han-soo Lee
The uranium ingot casting process is one of the steps which consolidate uranium deposits produced by electrorefiner in an
ingot form in a pryprocessing technique. Since molten uranium metal reacts with a graphite crucible when the uranium is being
dissolved, a graphite crucible cannot be used. Accordingly, a ceramic material must be selected which does not react with
the dissolving uranium and this must be used as a coating material on the graphite crucible surface. As to this research,
a reactivity experiments were performed between the coating layer and uranium by applying a thermal spray coating to the graphite
material with alumina and YSZ ceramic material. As shown in the experimental result, the YSZ coating layer showed a stronger
adhesive property on the side where there is no Ni–Al binding material. Moreover, no reaction was apparent between the YSZ
coating layer and the uranium. Accordingly, the YSZ material and the process of thermal spray coating are considered to solve
the reactive problem between uranium and a graphite crucible.
Authors:J. Šubrt, J. Vinš, V. Zapletal, V. Balek, and I. S. Šaplygin
The kinetics of the reaction ofα-Fe2O3 (hematite) with K2CO3 was studied at 600–800 °C for hematite samples prepared in different ways. The results demonstrated that the hematite reactivity is not a simple function of the specific surface area (or particle size), but depends significantly on the sample preparation history, especially at lower reaction temperature. The effect of low-temperature sintering on the hematite reactivity is discussed.
Nano-ZnO flakes were synthesized by calcination of the precursor of Zn(OH)2 obtained via the reactive ion exchange method between an ion exchange resin and ZnSO4 solution at room temperature. Scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscope, UV-Vis
diffuse reflection spectrum and Na2EDTA titration were used to characterize the structure features and chemical compositions of the as-prepared ZnO. The results
show that the as-prepared ZnO flakes have uniform structure and high purity. Heat capacities in the temperature range of 83
to 396 K were measured. The measured heat capacities values were compared with those of coarse crystal powders and the difference
between this two heat capacity curves was analyzed.
Summary The aim of this work is to develop a simplified, though rigorously based thermogravimetric analysis (TG) method to estimate intrinsic reactivity parameters (activation energy, E, and pre-exponential factor, A) for the oxidation in air of engineering carbonaceous materials. To achieve this aim, a modified Coats-Redfern method for analysing linear curves has been devised. The new method assumes first-order reaction kinetics with respect to carbon, and uses a statistical criterion to estimate an ‘optimum’ heating rate. For the oxidation in air of a model carbon, an optimum rate of 27 K min-1 was determined, at which E=125.8 kJ mol-1. This is in good agreement with activation energies obtained using established, though more limited model-free or isoconversional methods.
The reactivity of SbVO5, a compound known since a short time, with T-Nb2O5 in solid state in air has been investigated over the whole component concentration range of a system built by these two reacting
substances. The investigation results have shown that an equimolar mixture of SbVO5 and T-Nb2O5 reacts with a subsequent formation of a hitherto unknown compound of the formula Nb2VSbO10. This compound has been characterized by the methods XRD, DTA/TG, and SEM. Its orthorhombic unit cell parameters have been
calculated, and its stability in air up to 880 ± 10 °C has been proved. At this temperature, the compound melts incongruently
with an accompanying deposition of solid Nb9VO25, i.e., of a compound that crystallizes in the binary oxide system V2O5–Nb2O5.
In the present study, UV and UV/S2O82− have been applied to decolorize and mineralize organic dye C. I. Reactive Red 45 (RR 45) in aqueous solution. The rate of
color removal was studied by measuring the absorbance at the characteristic wavelength while mineralization rates were obtained
on the basis of total organic carbon (TOC). A statistical study of the process was performed using an experimental design
method, particularly a response surface methodology (RSM) hexagonal design. Optimal operating conditions were established;
pH 5 to pH 7 and [K2S2O8] = 15 mM. A complete color removal was achieved in all studied combinations of process parameters, while almost complete
mineralization can be achieved at established optimal process conditions. According to the developed statistical model of
the process and performed kinetic study, experimental data were fitted into a model of homogeneous system.
Monodispersed fine metal nickel powders of uniform shape and high purity are increasingly required for specific uses in many technological areas, especially in the preparation of electronic materials such as the manufacture of conductive inks and pastes and the formation of catalysts. Metallic nickel powders were prepared in ethylene glycol by the reduction of a nickel solution. Hydrazine was used as a reducing agent. Metal powders were characterized by chemical analysis, scanning electron microscopy (SEM), thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). Particle size distributions were determined using laser light scattering. The reactivity and purity of these fine nickel powders were tested by repeated oxidation and reduction of nickel powders in oxidative and reductive atmospheres.
Authors:V. Balek, E. Vance, V. Zeleňák, Z. Málek, and J. Šubrt
analysis (ETA) was used to characterize the thermal reactivity of amorphous
brannerite mineral of general formula U1–xTi2+xO6
(locality El Cabril, near Cordoba, Spain). It was demonstrated that on sample
heating up to 880C microstructure changes taking place in the sample
were accompanied by the formation of new radon diffusion paths, followed by
their closing up during the final transformation of amorphous to crystalline
brannerite in the range 900–1020 C. Relative changes in structure
irregularities that served as radon diffusion paths during heating and subsequent
cooling of the sample to temperatures of 300, 550, 750, 880, 1020 and 1130C,
respectively, were determined from the ETA results. Mass losses in temperature
ranges of 230–315, 570–760 and 840–1040C were observed
by thermogravimetry. Mass spectrometry indicated the release of CO2 mainly
due to the decomposition of minor carbon amount in the brannerite mineral