The interest for core-shells has been increased in the recent years due to their improved and modifiable properties. In this work, Fe 3 O 4 -TiO 2 and Fe 3 O 4 -SiO 2 core-shells were successfully synthesized from an industrially produced magnetite-rich powder with micro-and nanometric particle sizes, superparamagnetic behavior and saturation magnetization of 49 emu/g. The reverse microemulsion method was used to the synthesis of these core-shells. X-ray diffraction, energy dispersive X-ray analysis, electron microscopy (SEM-TEM), and magnetization curves were used to characterize the solids. Core-shells with different morphology and size, coating of crystalline TiO 2 (anatase) or amorphous silica, and superparamagnetic performance at room temperature (300 K) were obtained.

Table of Chemical Elements (IYPT 2019). For that reason, it is considered pertinent to highlight the importance of the periodic system in the scientific and technological development of the chemistry; therefore, a discussion of some applications of the periodicity of the elements for designing new materials is carried out. In this work, some periodic trends of both molecules and complex structures of materials are discussed, by selecting different cases of the chemical periodicity applied to improve and design steels with higher wear resistance, prepare refractory materials and synthesize chalcogenides glasses, among others. Finally, the proposed subjects and the regularities argued in this work are considered complementary contexts of exceptional interest to motivate the meaningful learning of the periodic table taking into account the current scientific and technological researches.