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The influence of the surface roughness of pearlitic grey cast iron discs on the formation of tribofilms and the evolution of the friction coefficient during a ring on disc tribotest with the addition of magnetite and magnetite–graphite nanopowders as interfacial media was investigated. The roughness parameters of the cast iron discs were varied by electro discharge machining (EDM) and grinding processes, producing four distinct surface roughness conditions. The evolution of the friction coefficient, however, did not reach the steady state for most of the samples and the role of the surface roughness on the friction coefficient could not be identified. Focused ion beam (FIB) microscopy on the cast iron discs was carried out to investigate the microstructure of the discs near the tribosurface. These results showed that the EDM process not only varied the surface roughness, but also changed the microstructure of the cast iron discs, promoting the incipient fusion of the cast iron surface, with the formation of ridges and casting defects (pores). As a result, a layer of rapidly solidified metal with a dendritic microstructure was formed near to the surface of the EDMed discs.
Hydroxyapatite (HA) is a bioceramic material with excellent biological properties. However, these properties are strongly dependent of ist crystallinity degree, with high values of crystallinity associated to poor resorption rates and bioactivity. This work evaluates the properties of HA samples produced by two different free-forming conformation methods, CNC machining and 3D printing. In both cases, porous gypsum samples were produced and subsequently converted into HA in a reaction with di-ammonium hydrogen phosphate at 100°C and pH 8. A total conversion of the samples was achieved after 36 h independently of the conformation method used. The microstructure, however, before and after the conversion is showed to be dependent on the method used. After conversion the machined samples achieved a Maximum compressive strength of 3.5 MPaforporosities of circa 80%, while 3D printed samples achieved a tensile strength of 2.0 MPa by porosities of 61%.
The N2 + CO2 co-electrolysis to urea synthesis has become a promising alternative to the energy intensive traditional processes for urea production. However, there are still challenges in this approach, especially due to the competition with HER (Hydrogen Evolution Reaction) leading to low efficiency. Electrochemistry assisted by localized surface plasmon resonance (LSPR) using metal nanoparticles has been reported to enhance different electrochemical reactions. Here we report an electrochemical LSPR assisted urea synthesis using Ag nanoparticles (NPs) supported on BiVO4/BiFeO3 catalyst mechanochemically synthesized. The electrochemical experiments were performed under dark and upon plasmon excitation at the LSPR region of Ag NPs. Our results demonstrated that exciting in the LSPR range, urea yield rate and Faradic efficiency were considerably improved with reduced overpotential, 19.2 μmol h− 1 g− 1 and FE 24.4% at +0.1 V vs RHE compared to 9.6 μmol h− 1 g− 1 and FE 9.4% at − 0.2 V vs RHE under dark conditions. Further in situ FTIR-RAS experiments for mechanism investigation revealed the presence of N-H and C-N intermediates and the real effect of Ag plasmon excitation on HER and N2 + CO2 co-electrolysis. Theoretical calculations confirm the energy of the species involved in C-N coupling as well the role of the complex catalytic sites, which agrees with XAS measurements.
