ABSTRACT
A swarf of aluminum alloy with high corrosion resistance and ductility was successfully converted into fine hydro reactive powders via ball milling with silver powder and either lithium chloride or gallium. The latter substances significantly intensified particle size reduction, while silver formed 'cathodic' sites (Ag, Ag2Al), promoting Al corrosion in aqueous saline solutions with hydrogen generation. The diffraction patterns, microphotographs, and elemental analysis results demonstrated partial aluminum oxidation in the samples and their contamination with tungsten carbide from milling balls. Those factors were responsible for obtaining lower hydrogen yields than expected. For AlCl3 solution at 60 °C, Al-LiCl-Ag, Al-LiCl, Al-Ga-Ag, and Al-Ga composites delivered (84.6 ± 0.2), (86.8 ± 1.4), (80.2 ± 0.5), and (76.7 ± 0.7)% of the expected hydrogen, respectively. Modification with Ag promoted Al oxidation, thus providing higher hydrogen evolution rates. The samples with Ag were tested in a CaCl2 solution as well, for which the reaction proceeded much more slowly. At a higher temperature (80 °C) after 3 h of experiment, the corresponding hydrogen yields for Al-LiCl-Ag and Al-Ga-Ag powders were (46.7 ± 2.1) and (31.8 ± 1.9)%. The tested Ag-modified composite powders were considered promising for hydrogen generation and had the potential for further improvement to deliver higher hydrogen yields.
ABSTRACT
Two sorts of tablets were manufactured from ball-milled powder (aluminum scrap and copper) by cold pressing and spark plasma sintering. Their microstructure, phase, and elemental compositions were investigated via scanning electron microscopy, X-ray diffraction analysis, and energy-dispersive X-ray spectroscopy. New phases, Al2Cu and MgCuAl2, were detected in the samples. Their microstructure was formed by welded scrap particles, the intermetallides, and Cu-rich regions located majorly along 'interparticle boundaries' and, to a lesser extent, within small, micro- and nanosized 'intraparticle spots'. The tablets were sealed with adhesive, so only the top surface was exposed to the environment, and tested in a chlorine aqueous solution for hydrogen generation performance. For both sample sorts, hydrogen yields of nearly 100% were achieved. The sintered tablets reacted faster than the cold-pressed ones: at 60, 70, and 80 °C, their entire 'conversion into hydrogen' took ~80, 40, and 30 min. vs. ~220, 100, and 70 min. The experimental kinetic curves were fitted with a contracting geometry equation, and those for the sintered samples were approximated with higher precision. The key effect of the additive was to enhance hydrogen evolution through the galvanic corrosion of Al in the regions adjacent to the intermetallic inclusions and Cu-rich spots.
ABSTRACT
In modern energy, various technologies for absorbing carbon dioxide from the atmosphere are being considered, including photosynthetic microalgae. An important task is to obtain maximum productivity at high concentrations of CO2 in gas-air mixtures. In this regard, the aim of the investigation is to study the effect of light intensity on the biomass growth and biochemical composition of five different microalgae strains: Arthrospira platensis, Chlorella ellipsoidea, Chlorella vulgaris, Gloeotila pulchra, and Elliptochloris subsphaerica. To assess the viability of microalgae cells, the method of cytochemical staining with methylene blue, which enables identifying dead cells during microscopy, was used. The microalgae were cultivated at 6% CO2 and five different intensities: 80, 120, 160, 200, and 245 µmol quanta·m-2·s-1. The maximum growth rate among all strains was obtained for C. vulgaris (0.78 g·L-1·d-1) at an illumination intensity of 245 µmol quanta·m-2·s-1. For E. subsphaerica and A. platensis, similar results (approximately 0.59 and 0.25 g·L-1·d-1 for each strain) were obtained at an illumination intensity of 160 and 245 µmol quanta·m-2·s-1. A decrease in protein content with an increase in illumination was noted for C. vulgaris (from 61.0 to 46.6%) and A. platensis (from 43.8 to 33.6%), and a slight increase in lipid content was shown by A. platensis (from 17.8 to 21.4%). The possibility of increasing microalgae biomass productivity by increasing illumination has been demonstrated. This result can also be considered as showing potential for enhanced lipid microalgae production for biodiesel applications.
