To date, the formation mechanisms of TiO₂, as well as its heterostructures, have not been clarified. Moreover, detailed research on the transition from a tetragonal anatase phase to the monoclinic phase of the TiO₂(B) phase and their interface structure has been quite limited until now. In the present study, we report on the sonochemical synthesis of TiO₂-anatase with a crystallite size of 5.2 ± 1.5 nm under different NaOH concentrations via the hydrothermal method. The use of alkaline solution and the effect of the temperature and reaction time on the formation and structural properties of TiO₂-anatase nanopowders were studied. The effects of NaOH concentration on the formation and transformation of titanate structures are subject to thermal effects that stem from the redistribution of energy in the system. These mechanisms could be attributed to three phenomena: (1) the self-assembly of nanofibers and nanosheets, (2) the Ostwald ripening process, and (3) the self-development of hollow TiO₂ mesostructures.

This paper reports the production of intermetallic microrods and microtubes from the decomposition of an intermetallic compound in an AlTiFe system. The intermetallic compound was obtained by mechanosynthesis of elemental powders of Al, Ti and Fe over 300 h at 400 rpm, sintering from compacted powder particles at 300 MPa per minute and at 900 °C for 3600 s in an argon atmosphere. The milled and sintered samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The intermetallic AlTi₃ and Fe₃Al phases were obtained during the milling process. After sintering, a decomposition of these intermetallic phases was found—Al₃Ti_0.75Fe_0.25, Al₃Ti, FeTi, AlTi₃, Ti₉Al₂₃, Fe₂Ti, Al₈₆Fe₁₄ and Al_0.4Fe_0.6. As a result of the decomposition, we observed the formation of hexagonal rods with intercalated phases of AlTi₃ and Fe₂Ti.

Carbides are used extensively as cutting tools, forming dies, and recently in catalysis applications, among other industrial applications. In this work, the synthesis and characterization of a nanostructured MoW bimetallic carbide were carried out by mechanical alloying with a mixture of elemental powders with a nominal composition of W_1.5Mo₆C_2.5 at different grinding times as follows: 25, 50, and 75 h in a low-energy ball mill at a speed of 500 rpm and 125 and 150 h in a high-energy ball mill at a speed of 1500 rpm. The formation of a solid solution was observed at 150 h of milling; the nanostructured bcc MoW carbide corresponded to the main phase in the sample, besides the presence of the nanostructured MoW alloy as a secondary phase with an average crystal size of 40.8 nm. The phases and morphology at every stage of milling were studied by: X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Vickers hardness. As the milling time increased, the hardness of these particles increased from 10.5 to 31.48 GPa for the powder particles milled for 150 h. The samples obtained at 125 and 150 h of milling were evaluated during catalytic aqua-thermolysis of heavy oil to analyze fuel desulfurization properties by Fourier transform infrared (FTIR) techniques. The results showed the breaking of S-S bonds, indicating the existence of a desulfurization reaction of heavy oil.

This study investigates the thermal decomposition of acetyl acetonates of Ni(II) and Fe(III) via a sonochemical process at 20 kHz for 50 min. In the absence of magnetic fields the reactions of Ni(II) and Fe(III) acetyl acetonates under ultrasonic treatment produce Ni(OH)₂ and FeO(OH) nanoparticles coated with carbon. The synthesized materials with different Ni-Fe stoichiometries, Ni90-Fe10, Ni80-Fe20, and Ni50-Fe50 wt%, were subjected to catalytic activity for dye decolorization of Reactive Black 5 (RB5, 100 mg/L) at room temperature using visible radiation. The correlation between the structural and optoelectronic properties and the catalytic performance of the Ni-Fe system with different stoichiometries is reported.

We analyze how crystallite size and thermodynamic driving forces govern the reversible phase transformation between tetragonal Hausmannite–Mn ₃ O ₄ and cubic Bixbyite–Mn ₂ O ₃ in Mn–O nanoparticles using x-ray diffraction (XRD) and electron microscopy (SEM, HRTEM), complemented by a semi-empirical enthalpy-trend analysis (extended Miedema model). Nanostructured samples were synthesized by combined sonochemical and hydrothermal routes and subsequently annealed in air from 200 ^∘ C to 900 ^∘ C in 100 ^∘ C increments. Crystallographic and morphological analyses show that the forward transformation Mn ₃ O ₄ → Mn ₂ O ₃ becomes detectable by XRD near 500 ^∘ C, where the phase coherent-domain sizes are 13.86 nm for Mn ₃ O ₄ and 25.57 nm for Mn ₂ O ₃ . The reverse transformation Mn ₂ O ₃ → Mn ₃ O ₄ is observed at 900 ^∘ C (for bulk crystals, the forward oxidation and reverse reduction are typically reported near 900 ^∘ C and 1100 ^∘ C, respectively, depending on atmosphere). The forward step proceeds via a topotactic, structure-preserving pathway governed by an operational critical crystallite size of the parent Mn ₃ O ₄ (defined here as the Mn ₃ O ₄ domain size at the onset of Mn ₂ O ₃ detectability, ∼13.9 nm in this dataset) and diffusion-controlled oxygen transport. The reverse step is attributed to oxygen loss and lattice reconstruction while retaining partial lattice coherence. The morphological evolution from granular aggregates to octahedral particles is consistent with Ostwald ripening and coalescence-driven growth. The thermodynamic analysis indicates a slight enthalpic preference for Bixbyite–Mn ₂ O ₃ (Δ H _s = −82.39 kJ/(mol atom)) over Hausmannite–Mn ₃ O ₄ (Δ H _s = −80.82 kJ/(mol atom)). In this context, the reversible behavior under annealing in air is interpreted within a Gibbs free-energy framework for an oxygen-open system, Δ G ( T , p O ₂ ), where entropy and oxygen chemical potential govern the transformation direction, while Miedema-derived Δ H _s values are used only as comparative stability trends.

In this work, the performance of a low-temperature solar collector (LTSC) is evaluated, using carbon nanoparticles in water as working fluid. The nanoparticles used are crystallized fullerenes, with a red parameter of 1.42 nm ± 0.5 nm, with different volume fractions in water. The thickness of the carbon film was approximately 140 to 520 nm. The study is divided into three parts: modeling and simulation of an LTSC, low-cost production and characterization of nanoparticles, and thermal evaluation of the LTSC. For the study, fullerenes were produced by microwave synthesis from a terpenoid resin (Camphor) and the nanoparticles were characterized by scanning electron microscopy (SEM) and High-Resolution Transmission (HRTEM). Tests were carried out with different volumetric flow rates, 0.0111 LT/s, 0.0166 LT/s and 0.0194 L/s, and two volumetric concentrations, 0.035% and 0.063%. The results obtained from the fullerene nanofluid showed an improvement in the thermophysical properties compared to the properties of water. The performance results showed that the efficiency increases up to 47.2% compared to that of water, with a volume fraction of 0.063%, and a flow rate of 0.0194 LT/s.