Zinc Ferrite Nanoparticle Coatings on Austenitic Alloy Steel.

The phase transition of austenitic stainless steel of commercial label CL20ES and zinc ferrite nanoparticles was studied in an oxidative atmosphere of dry air to develop a low-cost, effective technique for covering-layer fabrication. CL20ES powder and zinc ferrite powder were mechanically mixed. This mixture was studied in an atmosphere of dry air at different annealing temperatures from room temperature to 900 °C. The employed characterization techniques are X-ray powder diffraction, Mössbauer spectroscopy in the transmission geometry, and scanning electron microscopy with elemental mapping. The fabricated layers were also characterized by surface-specific techniques such as conversion electron Mössbauer spectroscopy and grazing incidence X-ray powder diffraction. The analyzed powder mixture shows resistance against oxidation in dry air and high temperatures. These results were employed to produce zinc ferrite covering layers on 3D-printed cylinders of CL20ES. The results show a predisposition of zinc ferrite to be recrystallized at temperatures above 350 °C without the production of corrosive substances on steel. The zinc ferrite layers were analyzed by an ultrasonic hardness tester as well, which proved the hardness enhancement.

Mössbauer Study on the Conversion of Different Iron-Based Catalysts Used in Carbon Nanotube Synthesis.

The phase composition and comparison of iron-based catalysts used for the synthesis of carbon nanotubes were investigated. This work reflects typical catalyst conditions and their evolution during the growth of carbon nanotubes. The preparation of carbon nanotubes was carried out by chemical vapour deposition at temperatures between 800 and 1100 °C. Ferrocene or zero-valent iron nanoparticles were used as "catalysts", and toluene, ferrocene and the ferrocene-toluene solution played the role of carbon precursors, respectively. The phase composition of the prepared product was studied by Mössbauer spectroscopy and X-ray powder diffraction. Mössbauer analysis was particularly useful for samples with a low content of the nanoparticle form of the catalyst. The composition of the prepared samples differed depending on the synthesis temperature, catalyst and precursor. Phase analysis revealed the presence of α-Fe and Fe3C in all samples. In addition, γ-Fe and iron oxides were identified under certain conditions. Scanning and transmission electron microscopy confirmed the carbon nanotube/nanofibre-like morphology and the presence of iron species.