Defect and Diffusion Forum Vols. 303-304

Abstract: The electron paramagnetic resonance (EPR) gyromagnetic factors for the Ni3+ center in MgO are theoretically investigated using the improved g formulas for a tetragonally elongated octahedral 3d7 complex suffering the dynamical Jahn-Teller effect. From the studies, the impurity Ni3+ center is found to undergo the relative elongation along the tetragonal axis by about 1%. The calculated g value shows good agreement with the observed result, and the improvement in the theoretical calculations is achieved in this work as compared with the previous treatments. The local structure of the impurity center is discussed.

Abstract: This is a study of data analyzing by using a theoretical model for mixed-valence manganites Ln1−xAxMnO3, which exhibit a complex transport behaviour. In the high-temperature (T>TP) paramagnetic insulating regime, the resistivity of samples obeys the T-1/4 law, characteristic of variable range hopping (VRH). We address this kind of transport process as involving variable-range hopping of small polarons, and derive the resistivity expression: .

Abstract: The electron paramagnetic resonance (EPR) parameters g factor and the hyperfine structure constant A factor for the substitutional Rh+ in NaCl are theoretically studied from the perturbation formulas of these parameters for a 4d8 ion in cubic octahedra. In these formulas, the ligand orbital and spin-orbit coupling contributions which were normally omitted in the previous studies are taken into account using the cluster approach. The calculated g and A factors are in good agreement with the experimental data. The ligand contributions to the EPR parameters are somewhat important and should be considered in the analysis of the EPR spectra for a 4d8 ion in chlorides. The local structure of this center is also discussed.

Abstract: The hydrocyclone is an alternative for produced water treatment in the petroleum industries, especially at offshore fields. Many parameters, such as oil droplet diameter affect the separation performance of the hydrocyclone. In this sense, the purpose of this work is study the effect of oil droplet diameter and inlet fluid on the separation efficiency of a hydrocyclone to remove dispersed heavy-oil from a water continuous stream. Results of the streamline, pressure drop, volume fraction and efficiency of separation as a function of oil droplet diameter and feed velocity are presented and analyzed.

Abstract: The excellent spreading and wetting behaviour of superspreader solutions has been known and extensively studied over recent years. However, explanations for spreading dynamics and accompanying mathematical models have not yet proved completely successful. Many attempts have been made to quantify the spreading exponents, but none of the models so far was able successfully to describe the whole wetting process of trisiloxane solutions, especially on hydrophobic surfaces. We have investigated the partial wetting of Silwet L-77® superspreader solutions of high concentrations (well above CMC) on polymer coated substrates of varying hydrophobicity. Results obtained can be explained in terms of the Marangoni effect as the major driving force for trisiloxane enhanced spreading. A simple theory, which involves surface tension gradients governing the spreading process, was developed in order to explain the specific evolution of the drop radius and consequent decrease in the contact angle. The proposed model was found to be in excellent agreement with the experimental results. Determined equation coefficients were shown to be dependent on both surfactant concentration and the hydrophobicity of the substrate.