Effect of Operating Parameters and Foreign Ions on the Crystal Growth of Calcium Carbonate during Scale Formation: An Overview

Due to the insufficiency of freshwater resources and to supply the drinking water populations, many desalination processes such as reverse osmosis, electrodialysis and distillation are widely used. However, these processes are of large-scale consumers of energy and confronted with various problems such as corrosion and scale formation. In most cases, scales are made of calcium carbonate CaCO3. In the present chapter, an overview on the effect of operating parameters such as temperature, pH and supersaturation on the precipitation kinetics, microstructure, and polymorphism of CaCO3 is given. Additionally, I put special emphasis on the effect of foreign ions such as magnesium, sulphate, and iron ions on CaCO3 precipitation since they are present at significant concentrations in natural waters. Also, the mechanisms by which these ions affect the crystal growth of CaCO3 were pointed out. Knowledge about these operating parameters as well as the effects of foreign ions allow elucidating the polymorphs growth during water treatment. The control of these operating parameters allows reducing scale formation during drinking water and wastewater treatment. The economic impact is of greatest importance since this favorably affects the treatment costs, increases the equipment life, and allows enhanced product water recovery

Structure and microstructure evolution of Al-Mg-Si alloy processed by equal-channel angular pressing

An ultrafine grained Al–Mg–Si alloy was prepared by severe plastic deformation using the equal-channel angular pressing (ECAP) method. Samples were ECAPed through a die with an inner angle of F = 90° and outer arc of curvature of ¿ = 37° from 1 to 12 ECAP passes at room temperature following route Bc. To analyze the evolution of the microstructure at increasing ECAP passes, X-ray diffraction and electron backscatter diffraction analyses were carried out. The results revealed two distinct processing regimes, namely (i) from 1 to 5 passes, the microstructure evolved from elongated grains and sub-grains to a rather equiaxed array of ultrafine grains and (ii) from 5 to 12 passes where no change in the morphology and average grain size was noticed. In the overall behavior, the boundary misorientation angle and the fraction of high-angle boundaries increase rapidly up to 5 passes and at a lower rate from 5 to 12 passes. The crystallite size decreased down to about 45 nm with the increase in deformation. The influence of deformation on precipitate evolution in the Al–Mg–Si alloy was also studied by differential scanning calorimetry. A significant decrease in the peak temperature associated to the 50% of recrystallization was observed at increasing ECAP passes.Peer ReviewedPreprin

Grain Refinement and Strengthening of an Aluminum Alloy Subjected to Severe Plastic Deformation through Equal-Channel Angular Pressing

In the present study, the microstructure, mechanical properties, and stored energy of an aluminum alloy containing iron-rich fine precipitates, subjected to severe plastic deformation through equal-channel angular pressing (ECAP), were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Up to four passes through ECAP resulted in significant nanometer-scale grain refinement, as well as the accumulation of lattice defects, such as dislocations and mesoscopic shear planes. This resulted in a noticeable enhancement in the Vickers microhardness and the flow stress after ECAP. Differential scanning calorimetry results showed that the ECAP’ed material exhibited two exothermal peaks at 222 ± 2 °C and 362 ± 2 °C, with total thermal effects of ΔH = 4.35 and 6.5 J/g, respectively. Slight increases in the ECAP’ed material microhardness and flow stress were observed at 200 °C. The heat release, at a relatively low temperature, and the slight improvement in the mechanical properties were attributed to the evolution of low- and high-angle misorientation, with the strain and the pinning of tangled dislocation caused by the existing fine particles. The second peak was attributed to grain growth, resulting in a significant softening of the material

Chemistry journals and research trends in Arab countries: A bibliometric analysis

Arab countries have been working hard to establish centers of research excellence and industrial clusters, especially in chemistry, based on the best technologies and practices. It is of utmost importance for decision-makers and academics to estimate the extent of chemistry research progress in Arab countries which differ substantially in economic development and graduate and postgraduate education. This study aims to highlight the current chemistry research trends and analyze chemistry journals in Arab countries. The citation rates, H-Index, SJR (Scimago Journal and Country Rank), and co-occurrence of keywords and authorship were compared between chemistry journals that are published by Arab countries and those published by the rest of the world between 1996 and 2022, referring to SJR report. Saudi Arabia and Egypt are the Arab countries with the largest citations number, published documents, and SJR indicators. Despite Arab countries' efforts to promote scientific research and build industrial clusters, the comparison of Arab countries to the rest of the world revealed that the Arab countries' SJR, H-index, citations per document in the previous two years, and total citations in the last three years are statistically significantly lower than those of the rest of the world. Many topics, such as nanoparticles, graphene, drug delivery, and molecular docking, are addressed by Arab countries as well as by the rest of the world. Arab countries, on the other hand, are more interested in nanoparticles than the rest of the world, which is more interested in catalysis. To strengthen their impact on the chemistry research field, Arab countries should intensify their collaboration with the rest of the world and focus on more centered topics