The results of the effect of the three Ba:Ti molar ratios (MR) (1:1, 2:1, 4:1) and four sintering temperatures (1250, 1275, 1300, 1325 °C) on the structural and electrical properties of BaTiO₃ (BT)-type ceramics synthesized by the hydrothermal method are shown. The BT phase formed was analyzed by x-ray diffraction (XRD), Raman spectroscopy (RS), dielectric and ferroelectric measurements and high-resolution scanning electron microscopy (HRSEM). For the samples synthesized using a Ba:Ti MR of 4:1 and at all sintering temperatures analyzed, XRD results confirmed the presence of the tetragonal ferroelectric phase, BT. In the same way, these results corroborated the results obtained by the RS technique. Dielectric properties measured at 100 kHz and 1 MHz over a temperature range of 30 °C–200 °C indicated a relative permittivity value of 4280 at 1 MHz and 4200 at 100 KHz at a Curie temperature of 110 °C in both cases for the sample synthesized at with a Ba:Ti MR ratio of 4:1 and sintered at 1300 °C. Ferroelectric measurements for the samples showed a best remnant polarization (Pr) of 3.5 µC/cm² for the sample synthesized with a Ba:Ti MR ratio of 4:1 and sintered at 1325 °C. The HRSEM results showed grains composed of Ba, Ti, and O homogeneously distributed in the BT structure, and a trend of increasing average grain size with increasing sintering temperature was observed.

Magnetite nanoparticles were synthesized using the green chemistry technique; ferric chloride was used as a precursor agent and Moringa oleifera extract was used as a stabilizer agent. A black powder, characteristic of magnetite, was obtained. X-ray diffraction was performed on the synthesis product and identified as magnetite (Fe₃O₄). Scanning electron microscopy characterization shows that nanoparticles have a spherical morphology, with sizes ranging from 15 nm to 35 nm. The synthesis of carbon nanotubes was carried out by the pyrolytic chemical deposition technique, from which multiwalled carbon nanotubes were obtained with diameters of 15–35 nm and of varied length. The decoration was carried out using the wet and sonification technique, where a non-homogeneous coating was obtained around the nanotubes. The thermal decomposition for both decorated and undecorated nanotubes presents two mass losses but with different slopes, where the activation energy for the decorated carbon nanotubes was 79.54 kJ/mol, which shows that the decoration gives more stability to the nanotubes since the activation energy of the undecorated nanotubes is 25.74 kJ/mol.

In this work, a kinetic study and modeling of the decomposition of a rock sample in an ascorbic acid medium with a high content of lepidolite phase were carried out, the results of which are of great importance due to the sample’s high lithium (Li) content. The rock sample was characterized by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS), and the mineral species detected in the sample were lepidolite, at 65.3%, quartz, at 30.6%, and muscovite, at 4.1%, with a quantitative chemical analysis indicating the presence of elements such as Li, Si, K, Na, O, Al and, to a lesser extent, Fe and Ti; this highlights that the Li content present in the sample was 3.38%. Lithium was the element with which the chemical analysis of the kinetics was performed, resulting in decomposition curves comprising the induction period, progressive conversion and stabilization; this highlighted that the reaction progressed during the first two periods, obtaining a reaction order (n) of 0.4307 for the induction period and an activation energy (Ea) of 48.58 kJ mol⁻¹, followed by a progressive conversion period with n = 0.309 and Ea = 25.161 kJ mol⁻¹. This suggested a mixed control regime present in the lower temperature ranges, with a transition from chemical control to transport control present at high temperatures, with the study of the nature of the reaction and the concentration effect showing that chemical control predominates. The kinetic parameters and kinetic expressions for both periods were obtained, with the modeling showing that the calculated and experimental data do not present a major discrepancy.

Thallium is one of the most toxic elements on the planet, and one alternative method for its precipitation is through jarosite-type compounds. Therefore, in this work, the kinetics of thallium jarosite were evaluated in an alkaline medium (NaOH and Ca(OH)₂). Experiments were conducted to assess the effect of medium concentration from 0.03 M to 5.5 × 10⁻⁴ M and the effect of temperature from 20 °C to 60 °C. The sigmoidal curves showed an induction period, during which there was no release of sulfur or thallium ions into the solution, nor the formation of solid byproducts, according to the X ray diffraction (XRD) results. Similarly, a progressive conversion period was observed, evidenced by the release of sulfur and thallium ions into the solution and the formation of amorphous solids. Finally, a stability zone is reached, indicating that the decomposition reaction has ended, as there are no changes in the concentration of sulfur and thallium ions in the solution. The reaction was monitored by determining S using Inductively Coupled Plasma (ICP). The experimental results for the progressive conversion period show a better fit to the chemically controlled shrinking core kinetic model. The reaction order for the kinetics in NaOH medium is 1.09 for the induction period and 0.89 for the progressive conversion period, while for Ca(OH)₂ medium it is 0.78 for the induction period and 0.47 for the progressive conversion period. The activation energies for the progressive conversion period in the two proposed media are 91.87 kJ mol⁻¹ in NaOH and 71.14 kJ mol⁻¹ in Ca(OH)₂, indicating that the controlling mechanism in both systems is the chemical reaction. For the induction period, the activation energies are 101.52 kJ mol⁻¹ and 79.45 kJ mol⁻¹, respectively, indicating that the chemical reaction also controls the initiation of the reactions. The high activation energy in both reaction media suggests that high concentrations of OH⁻ and high temperatures are required to initiate the decomposition reaction. Thallium jarosite precipitates a large amount of thallium and requires high energy to decompose, so it could be a viable alternative in thallium retention.