Volumen 64 (2020): Heft 4 (December 2020)

The Brayton cycle with supercritical carbon dioxide is considered as an innovative technology with the potential to replace conventional steam cycles. The optimization of the supercritical CO₂ cycle (sCO₂) is necessary and important to achieve the required thermal cycle parameters. The above optimization focuses on the setting of the energy cycle as such, the design solution of the individual components and, the last but not least, on the selection of suitable construction materials. Due to the operating conditions, namely temperatures exceeding 550 °C and pressure up to 25 MPa, material research is one of the important areas of the research and development of sCO₂ energy cycles. Construction materials for sCO₂ power cycle equipment include HR6W, T92 and Haynes HR235 alloys. This work presents results of the corrosion test, in which samples of these materials were exposed to sCO₂ at 550 °C and 25 MPa for 1000 hours. Corrosion after exposure was examined using a light optical microscope (LOM) and a scanning electron microscope (SEM). The significant differences in corrosion attack between the investigated materials and the formation of a protective oxide layer on the surface were observed.

This work deals with behaviour of steel in liquid lead environment and possibilities of corrosion resistance improvement. Liquid metal cooled systems are under wide investigation and development and represent a good alternative. It is necessary to find materials, which would be affected by liquid lead minimally. Austenitic steel 316L without coating and coated with TiSiC was studied in flowing liquid lead. Conditions of the experiment simulated real environment of the system. Deposition of protective barrier reduced the metals dissolution and diffusion of liquid lead into the steel substrate, degradation of substrate due to high temperature and mechanical stress. Presence of Si in the layer increased the surface ability to form stabile oxide and contribute to steel´s protection.

The corrosion inhibition efficiency of the novel pyridine namely, 4-(Benzoimidazole-2-yl)pyridine has been studied for mild steel in a 1 M hydrochloric acid environment by utilizing gravimetrical techniques. The synthesized inhibitor exhibits a significant inhibitive efficiency of 93.8% at 0.005 M. The adsorption isotherm of the investigated inhibitor on mild steel surface obeys the Langmuir isotherm. Surface morphology investigated by utilizing scanning electron microscopy (SEM) demonstrates a smooth metal surface with the addition of 4-(Benzoimidazole-2-yl)pyridine in a hydrochloric acid environment. Quantum chemical calculations using density functional theory (DFT) have been used to investigate the molecular structure and behavior of 4-(Benzoimidazole-2-yl) pyridine as a corrosion inhibitor. Different parameters have been calculated using DFT, such as energies of highest occupied molecular orbital and lowest occupied molecular orbital (EHOMO and ELUMO), energy gap (∆E), and dipole moment (μ). These parameters were important to elucidate the behavior of the investigated molecule as a corrosion inhibitor in acidic solution and also suggest the mechanism of inhibition.

The paper focuses on the quality of coatings applied by cataphoretic deposition and cataphoretic deposition technology with a phosphate layer. The quality of the coatings was evaluated by determining the roughness of the coatings, the morphology of the coatings, spectral analyses were performed detecting the presence of individual elements in the coatings. There was analysed also defect – uncoated spot.