Effects of SiC particle size on electrochemical and mechanical behavior of SiC-based refractory coatings

Refractory paints are designed to display good thermal resistance, as well as excellent corrosion and mechanical properties in service. The present work investigates the corrosion and mechanical performance of SiC-based refractory paints. Refractory paints containing varying amounts of silicon carbide (β-SiC) along with alkali inorganic binders were used. The alkali activator used was an aqueous solution of NaOH/Na2SiO3, with metakaolin used as the aluminosilicate material. Five samples with varying proportions of β-SiC particles of varying size fraction were used to prepare the bimodal β-SiC. The samples used were 100% micron, 70% micron + 30% nano, 50% micron + 50% nano, 30% micron + 70% nano, and 100% nano-SiC as the aggregate, and this was mixed with the binder and then applied on nickel-based super alloy (Inconel 738) and then cured at 80 °C for 24 h and then exposed to 1100 °C for 8 h. Abrasion, corrosion, and electrochemical tests were used to determine the properties of the coating. The analyses showed that by increasing the proportion of nano-SiC, the porosity decreased which in turn helped to enhance the corrosion and abrasion resistance

Solid solubility and charge compensation/exchange mechanisms in Ga- or Mn-Doped CeO<inf>2</inf> thin films on 3D printed biomedical titanium alloy

CeO2 films doped with 0–9 mol% Ga/Mn were fabricated by spin coating on 3D-printed Ti6Al4V, calcined at 650 °C for 2 h, and characterised by TEM, FESEM, 3D laser scanning confocal microscopy, GAXRD, and XPS. The results depend on the roles of several factors: (1) Sol-gel precursor viscosity affected pore filling and surface coverage. (2) Lattice contraction and resultant intervalence charge transfer increased the Ce3+ concentration as a minority effect. (3) Substitutional solid solubility and associated redox charge compensation controlled the defect equilibria, which highlight the majority role of this solid solubility mechanism in decreasing the Ce3+ concentration. (4) Electronegativity played a negligible role in affecting the valences but was important in initiating intervalence charge transfer. (5) Multivalence charge transfer combined electron exchanges between film matrix, dopants, and Ti substrate. The present work provides a foundation to interpret the effects of extrinsic effects from both dopant and substrate on the properties of films