Using PXRD to investigate the crystallisation of highly concentrated emulsion of NH4NO3

The process of crystallization of highly concentrated emulsions of ammonium nitrate can be studied using powder X-ray diffraction. The dispersed particles comprise a supercooled aqueous solution of the ammonium nitrate salt and are dispersed in a paraffin-based oil. This results in a thermodynamically unstable system that ‘ages’ with time resulting in changes in rheological properties and its phase composition where the collapse of the supercooled aqueous solution forms the crystallized salt. The crystallization processes of these emulsions are kinetically slow and can take up to a few months to crystallize completely. The general approach to this type of analysis is to determine the change in crystalline diffraction peak intensities relative to the halo due to the amorphous content. However, there are a number of problems associated with this method which are addressed by using Rietveld refinement methods which can take into account factors such as preferred orientation, crystallite size variations and mixtures of solid phases. The study showed that the ammonium nitrate emulsions kept at room temperature slowly crystallize predominantly to the room temperature solid ammonium nitrate phase IV. However, depending on the formulations used some samples showed crystallization to the high temperature ammonium nitrate phase II before changing to phase IV. The crystallization change could be modelled by the well-known JMAK kinetic relationship.South African National Research Foundation (NRF

Instability of highly concentrated emulsions with oversaturated dispersed phase. role of a surfactant

Instability of highly concentrated emulsions of the water-in-oil type which were investigated in this work is related to the existence of the internal phase as an oversaturated salt solution in water. The principal features of crystallization of these systems were studied by as earlier. This study is devoted to the development of this investigation and based on involving different surfactants and various concentrations of surfactants. It was shown that the originally proposed mechanism of crystallization, which suggested that growing crystals break through interfacial layers, was valid for all highly concentrated emulsions under investigation. Moreover, the Kholmogorov-Avrami kinetic equation with an unusually high exponent value equal to 6 is also applicable to different systems. It was proven that the general relationship between the growth of the yield stress and the degree of crystallization can be formulated for all surfactants studied in the work. The role of a surfactant consists in varying the characteristic time constant for the rate of crystallization. This time constant is much lower for a low-molecular-weight surfactant compared to oligomeric surfactants. This constant noticeably increases with an increase of concentration and the decrease of the average droplet size

Towards oxidative denitrogenation of fuel oils: Vanadium oxide-catalysed oxidation of quinoline and adsorptive removal of quinoline-N-oxide using 2,6-pyridine-polybenzimidazole nanofibers

The study provides a technological method for the removal of nitrogen compounds from fuels, via oxidation and extractive adsorption. The use of batch process resulted in lack of specificity of the quinoline oxidation reaction with several products produced via ring-opening while the flow micro-reactor presented a high degree of selectivity to quinoline-N-oxide (67%). The application of molecularly imprinted 2,6-pyridine-polybenzimidazole nanofibers displayed excellent quinoline-N-oxide removal (86%) with an adsorption capacity (qe) of 4.8 mg/g. Isothermal titration calorimetry (ITC) interactions between quinoline-N-oxide and 2,6-PyPBI confirmed a favourable interaction. DFT studies on quinoline-N-oxide vs 2,6-PyPBI further indicated: (i) a hydrogen bonding (through amino group of 2,6-PyPBI and oxygen atoms of the quinoline-N-oxide), (ii) pi-pi stacking and (iii) van der Waals interactions. The selective oxidation and adsorption of nitrogen compounds present in fuel, which has been demonstrated here, would be a sustainable green chemistry technology for the production of clean fuel. Keywords: Vanadium(V) oxide, tert-Butylhydroperoxide (t-BuOOH), Quinoline, Oxidatio

Electrochemical and Crystallographic Aspects of Lead Granular Growth

Lead granules synthesized by the potentiostatic regime of electrolysis were characterized by the scanning electron microscopy technique. Effect of the different parameters of electrolysis, such as solution composition, overpotential of electrodeposition, and quantity of the electricity, on lead granular growth has been systematically investigated. Aside from the electrochemical aspects of lead granular growth, crystallographic aspects of the obtained granules were also analyzed. In the dependence of the electrodeposition conditions, granules of various shapes were obtained. The granules, such as octahedrons and hexagons, as well as many various types of twinned particles: single-twinned, multiply-twinned, lamellar-twinned, and many other complicated shapes denoted as polyparticles, were synthesized through regulation of the parameters of electrolysis. Increasing both the concentration of Pb2+ ions and overpotential of the electrodeposition favored the formation of more complicated forms. Formation of granules of specified crystallographic characteristics was also correlated with the basic principle of metal electrocrystallization