Search Results (3)

Increasing the serviceability of industrial components intended for the petrochemical industry is possible through their superficial saturation with silicon (silicon cementation). Obtaining a silicon-rich surface coating results in a considerable increase in corrosion resistance, refractoriness, and wear resistance. One of the most economically convenient options for silicon cementation is pack siliconizing in powdery solid media. This paper presents the possibility of pack siliconizing that contains ferrosilicon (FeSi75C) and a thermite mixture (SiO₂ + Al) as active, silicon-providing components, in P265GH grade steel, which is frequently used in the petrochemical industry. The aim of the study was to determine the most suitable active component of the two that were analyzed and at the same time identify the processing conditions in which the siliconized coating has the greatest thickness, is free of porosity, and is in direct contact with the support. The use of experimental programming methods allowed the optimization of the operation to obtain the optimal solution. It was concluded that the thermite mixture is not compatible with pack siliconizing because it results in a superficial saturation predominantly composed of aluminum. When ferrosilicon is used as the active component, it determines the particularly intense formation kinetics of the non-porous siliconized coating with its maximum thickness being reached at high processing temperature values (over 1100 °C) with a proportion of 60% FeSi75 and, simultaneously, with the lowest possible proportion of ammonium chloride (max. 3%), which is the surface activation/cleaning component. Full article

Fe–Si intermetallics–Al₂O₃ composites were fabricated by thermite-assisted combustion synthesis. Combustion reactions were conducted with powder compacts composed of Fe₂O₃, Al, Fe, and Si. The starting stoichiometry of powder mixtures had an atomic Fe/Si proportion ranging from Fe-20% to Fe-70.5% Si to explore the variation of silicide phases formed with Si percentage. Combustion in the mode of self-propagating high-temperature synthesis (SHS) was achieved and the activation energy of the SHS reaction was deduced. It was found that the increase of Si content decreased the combustion temperature and combustion wave velocity. Three silicide compounds, Fe₃Si, FeSi, and α-FeSi₂, along with Al₂O₃ were identified by XRD in the final products. Fe₃Si was formed as the single-phase silicide from the reactions with Si percentage from Fe-20% to Fe-30% Si. FeSi dominated the silicide compounds in the reactions with atomic Si content between Fe-45% and Fe-55% Si. As the Si percentage increased to Fe-66.7% Si and Fe-70.5% Si, α-FeSi₂ became the major phase. The microstructure of the composite product showed that dispersed granular or nearly spherical iron silicides were embedded in Al₂O₃, which was dense and continuous. Most of the silicide grains were around 3–5 μm and the atomic ratio of silicide particles from the EDS analysis confirmed the presence of Fe₃Si, FeSi, and FeSi₂. Full article

Formation of MoSi₂–Al₂O₃ composites with a broad range of the MoSi₂/Al₂O₃ ratio was conducted by thermite-based combustion synthesis in the SHS mode. The addition of two thermite mixtures composed of MoO₃ + 2Al and 0.6MoO₃ + 0.6SiO₂ + 2Al into the Mo–Si reaction systems facilitated self-sustaining combustion and contributed to in situ formation of MoSi₂ and Al₂O₃. The samples adopting the former thermite reagent were more exothermic and produced composites with MoSi₂/Al₂O₃ from 2.0 to 4.5, beyond which combustion failed to proceed. Because of lower exothermicity of the reactions, the final products with MoSi₂/Al₂O₃ from 1.2 to 2.5 were fabricated from the SHS process involving the latter thermite mixture. Combustion temperatures of both reaction systems decreased from about 1640 to 1150 °C with increasing MoSi₂/Al₂O₃ proportion, which led to a phase transition of MoSi₂. It was found that the dominant silicide was β-MoSi₂ when the combustion temperature of the synthesis reaction exceeded 1550 °C and shifted to α-MoSi₂ as the combustion temperature fell below 1320 °C. The results of this study showed an energy-efficient fabrication route to tailor the phase and content of MoSi₂ in the MoSi₂–Al₂O₃ composite. Full article