A method using Pulsed Field Gradient Nuclear Magnetic Resonance PFG-NMR for water-incrude oil emulsion droplet size determination has been optimized and compared with optical microscope for validation. The method applies a combination of Pulsed-Field Gradient (PFG) NMR, Stimulated Echo (STE), and Carr-Purcell-Meimboom-Gill (CPMG) sequences for measuring diffusion, resolving oil and water signal and for measuring the attenuation due to a distribution in T2 values. This returns the droplet size distributions of water-in-oil emulsions within a minute. No prior assumption is made on the shape of the droplet size distribution, which enables the method to resolve for instance bimodal distributions. To validate this method, three different crude oils were used in the experiment. The emulsions prepared had water cuts from 10 to 40 %. The correlation between PFG-NMR and optical microscopy was good for the emulsions. Any potential discrepancies between the two techniques are discussed, so are the limitations and advantages of the methods.

Preferential heat and mass transfer induces diffusive thermal instabilities in premixed laminar flames. Such instabilities in hydrocarbon flames are characterized by cellular structure and a tendency to promote flame extinction. We investigate the properties of such instabilities in C4H10-C3H8/air flames. The adiabatic burning velocity of the laminar premixed flame was measured at different equivalence ratios while exhibiting cellular instabilities. Direct photographs have been captured to qualitatively asses the effect of burner plate temperature on the cellular structure of the flame. The present study preliminarily suggests a normal logarithmic correlation to predict the adiabatic burning velocity of diffusive thermal instabilities in laminar premixed C4H10-C3H8/air flames.

Point defects in semiconductors play a decisive role for the functionality of semiconductors. A detailed, quantitative understanding of diffusion and defect reactions of dopants is required for advanced modelling of modern nanometer size electronic devices. With isotope heterostructures which consist of epitaxial layers of isotopically pure and deliberately mixed stable isotopes, we have studied the simultaneous self- and dopant diffusion in several major semiconductors such as silicon and germanium. Detailed analysis of the simultaneous diffusion of self- and dopant atoms in Si and Ge yields information about the ionization levels of native defects and about dopant-defect interactions in Si and Ge. The results of these diffusion studies are highlighted in this work.

The crystal structure of mayenite (ideal composition: Ca12Al14O33) consists of a (disordered) calcium-aluminate framework comprising 32 of the 33 oxygen anions. It contains large open cages, 1/6 of them being filled randomly by the remaining “free” oxygen which is available for diffusion and very high ionic conductivities. This extraframework oxygen could be substituted by nitrogen, opening up possibilities for a pure nitrogen ionic conductor. From high temperature neutron powder diffraction experiments, data analysis employing difference Fourier methods and anharmonic Debye-Waller factors and comparing pure O-mayenite with partly exchanged N/O-mayenite it is concluded that oxygen diffusion proceeds via jump-like processes, intimately coupled to relaxations of Ca and involving exchange of the “free” oxygen with framework oxygen, while nitrogen diffusion appears to proceed via an interstitial process.

The diffusion of Ag in CdTe exhibits anomalous concentration profiles, which essentially reflect the profile of the deviation from stoichiometry. At a diffusion temperature of about 800 K, the Ag dopant atoms are present as charged interstitials. The deviation from stoichiometry at diffusion temperature substantially changes upon an external source of Cd atoms. Such an external source can be represented either by the vapor pressure from metallic Cd or by a Cd layer arising at the interface to an evaporated layer of Cu or Au. Also, the Co diffusion in CdZnTe is shown to be strongly affected by the presence of an external vapor pressure of Cd, but in a substantially different way compared to the Ag diffusion in CdTe.

The modelling of electro-diffusion in the multicomponent system in open space and time domains has been only recently addressed and made numerous applications in biology, fuel cells, electrochemical sensors and reference electrodes possible. In this work we show the numerical simulations of electrical potential over time and resulting electrochemical impedance spectra of ion-selective membrane electrodes (ISE’s). The numerical results are obtained by use of the coupled Nernst-Planck, Poisson and continuity equations (forming the NPP model). The equations are solved by means of the finite difference method, the Rosenbrock solver with the use of Matlab (by MathWorks) platform. The potential-time response of the ISEs in open- and closed-circuit conditions as a function of varying heterogeneous rate constants, ionic concentrations and membrane thickness are computed. The potential-time response to small-current perturbation is applied for simulations of the impedance spectra. The results obtained show that the membrane with Nernstian response presents only one capacitive arc in the impedance spectra, related to conductivity and dielectric properties of the membrane material. Non-Nernstian behaviour is related to slow ionic transport through the membrane|solution interfaces and is manifested by the appearance of an additional (capacitive) arc between the highfrequency bulk and the low-frequency (Warburg) arcs. The presented approach directly relates the diffusivities in the membrane and the interface properties (heterogeneous rate constants determining the transport across interfaces) to the characteristic properties of the impedance spectra (characteristic radial frequencies). It is concluded that the Matlab platform allows solving the NPP problem and simulating the non-linear effects in electrodiffusion in a convenient way.

Long-range Li diffusion parameters of amorphous LiNbO3 are probed by 7Li two-time spin-alignment echo NMR spectroscopy which is sensitive to slow Li dynamics. The jump rates which were extracted from the spin-alignment echo decay curves exhibit Arrhenius behaviour between 293 K and 413 K. The activation energy (0.41(1)eV) is in good agreement with that of the high-temperature flank of the 7Li NMR spinlattice relaxation rate peak. The latter was predicted to be about 0.4 eV when taking into account the frequency dependence of the corresponding spin-lattice relaxation rates on the low-T flank (see Wilkening et al., Phys. Chem. Chem. Phys. 4 (2002) 3246). Previous measurements of the spin-lattice relaxation rate had to be restricted to temperatures below 450 K in order to avoid crystallization of the material. Thus, only the low-temperature flank of the diffusion induced spin-lattice relaxation rate peak had been accessible yielding information about short-range Li diffusion.

High temperature properties such as electrical conductivity (σ) and resonance behaviour of stoichiometric lithium niobate (LiNbO3) are determined in the temperature range from 20 to 950 °C. The activation energy of the conductivity is found to be 0.9 and 1.7 eV in the temperature range from 500 to 750 °C and from 800 to 950 °C, respectively. During thermal treatments in ambient air up to 950 °C and back, the conductivity remains unchanged at a given temperature, i.e., the crystal is stable under these conditions. The oxygen partial pressure (pO2) dependence of the conductivity shows two distinct ranges. At 750 °C, the property remains unchanged down to 10−15 bar. Below 10−15 bar, the conductivity increases according to σ ~ (pO2)−1/5. Z-cut LiNbO3 plates can be excited to thickness mode vibrations up to at least 900 °C. At this temperature, the quality factor Q is found to be between 30 and 100. As for changes of the conductivity, a decrease of the resonance frequency is observed below 10−15 bar indicating a correlation of both properties. In order to evaluate the lithium evaporation, the crystals are tempered at 900 °C in ambient air for 24 h. A depth profile of the constituents does not indicate lithium loss within the accuracy of the secondary ion mass spectroscopy. The preliminary results underline the potential of stoichiometric LiNbO3 for high-temperature applications and justify its closer investigation.

Zirconia powders doped with different amounts of dopants (CeO2, Gd2O3, and CaO) were synthesized by a citrate technique. X-ray diffraction for samples sintered at 1500 °C revealed that the zirconia ceramics were stabilized in the cubic phase above 12 mole % CaO and 10 mole % Gd2O3, while tetragonal zirconia is obtained above 15 mole % CeO2. Relative densities up to 99.5% were obtained. The effect of dopant concentration on the lattice parameter, average crystallite size, microstrain was studied. The cubic lattice parameter increases nearly linearly with increasing the concentration in case of CaO and Gd2O3. The tetragonal lattice parameters at and ct increase nearly linearly with increasing the concentration of CeO2. The average crystallite size was found to be larger than 600 nm for the samples investigated.

Cation doped zirconium oxynitrides (for example zirconium oxide doped with yttrium oxide and nitrogen, \''YZrON\''), having a fluorite-based structure, are suggested to have fairly high nitrogen diffusivity, besides their high oxygen mobility. In the present work, the tracer-diffusion of nitrogen and oxygen was measured in single crystalline \''YZrON\''. Results are compared to the migration pathways and migration enthalpies of nitrogen and oxygen ions as determined by elastic neutron diffraction studies. Excellent agreement of the measured activation enthalpies of nitrogen diffusion (about 2 eV) and oxygen diffusion (about 1 eV) determined by the two methods is found.