Andrey V. Tsarenko

Dispersed ferrospheres (FSs) are a valuable component of coal fly ash, whose application potential is determined by their microspherical design, fine particle size, and high concentration of magnetic iron compounds. This study proposes an efficient technological scheme for extracting dispersed FSs from high-calcium fly ash, comprising (i) aerodynamic classification and (ii) dry magnetic separation. The isolated fractions were characterized, including determination of the particle-size distribution, morphology, chemical and phase composition, Mössbauer parameters, magnetic properties, and surface distribution of magnetic phases. It was shown that the average particle diameters of the FS narrow fractions are 3 and 8 µm. The major chemical components are FeO, CaO, and SiO₂, whose total content amounts to 81–83 wt %. Regarding the phase composition, Fe-spinel and calcium ferrites are predominant, accounting for 38–46 and 13–16 wt %, respectively. The efficiency of the proposed process for extracting FSs reaches the level achieved by conventional wet magnetic separation. The saturation magnetization of the dispersed FS samples increases by more than an order of magnitude (up to 23–28 emu/g) compared to the initial fly-ash fractions (1.7–1.8 emu/g). For the first time, magnetic topography investigation of single microspheres directly demonstrates that the surface of the aluminosilicate matrix is enriched with magnetic microcrystals formed during coal combustion. The obtained results may prove useful in the design of functional materials with magnetically active surfaces for advanced applications.

Gold nanoparticles (AuNPs) exhibit unique optical properties due to localized surface plasmon resonance (LSPR), making them valuable for applications in nanophotonics, sensing, and biomedicine. This study investigates the formation of ordered AuNP monolayers on Au/Si(100) substrates with controlled roughness prepared by magnetron sputtering and thermal evaporation. We examine how substrate morphology influences nanoparticle organization and analyze collective optical properties using reflection spectroscopy. Ordered AuNP ensembles were formed at the air/water interface and transferred onto Au/Si(100) substrates. Our results demonstrate that substrate roughness significantly affects monolayer packing density and uniformity. Reflection spectra revealed two characteristic resonances: an LSPR peak at ~525 nm and a low-energy resonance at ~800 nm associated with collective particle-substrate interactions. Significantly, encapsulation with cetyltrimethylammonium chloride (CTAC) molecules suppressed the long-wavelength resonance. Comparative analysis with colloidal AuNP dimers suggests charge-mediated interactions in plasmon resonance formation. These findings demonstrate effective control of collective plasmonic modes through substrate morphology tuning and nanoparticle surface functionalization, offering promising avenues for developing advanced optical materials and sensor platforms.