The application of polytetrafluoroethylene (PTFE) coatings to metal surfaces is a well-known procedure carried out to avoid fouling phenomena on food-processing surfaces. Fluorine-based polymers are generally chemically and thermally stable, thus allowing them to be the preferred choice when designing anti-stick coatings in the food service industry. Their lifespan, however, depends on the environmental conditions. It is well known that thermal ageing can affect the properties of PTFE polymers and reduce their mechanical, thermal, and chemical properties causing failures and contaminating food. The main goal of the study is to identify the different failure mechanisms occurring in PTFE-based coatings, using both SEM/EDXS and ATR FT-IR data to reveal the starting point of degradation phenomena in food processing applications. The results from this research reveal that the preferential points for failures are mainly the polymer/substrate interfaces, the polymer/filler interfaces, or the polymer matrix itself.

The use of Type IV cylinders for gas storage is becoming more widespread in various sectors, especially in transportation, owing to the lightweight nature of this type of cylinder, which is composed of a polymeric liner that exerts a barrier effect and an outer composite material shell that primarily imparts mechanical strength. In this work, the failure analysis of an HDPE liner in a Type IV cylinder for high-pressure storage was carried out. The breakdown occurred during a cyclic pressure test at room temperature and manifested in the hemispherical head area, as cracks perpendicular to the liner pinch-off line. The failed sample was thoroughly investigated and its characteristics were compared with those of other liners at different stages of production of a Type IV cylinder (blow molding, curing of the composite material). An examination of the liner showed that no significant chemical and morphological changes occurred during the production cycle of a Type IV cylinder that could justify the liner rupture, and that the most likely cause of failure was a design-related fatigue phenomenon.

The commercial use of Si₃N₄ ceramics in the biomedical field dates back to the early 1980s and, initially, did not show promising results, which is why their biocompatibility was not then investigated further until about 10 years later. Over the years, a change in trend has been observed; more and more studies have shown that this material could possess high biocompatibility and antibacterial properties. However, the relevant literature struggles to find mechanisms that can incontrovertibly explain the reasons behind the biological activity of Si₃N₄. The proposed mechanisms are often pure hypotheses or are not substantiated by comprehensive analyses. This review begins by studying the early references to the biological activity of Si₃N₄ and then reviews the literature regarding the bioactivity of this ceramic over time. An examination of the early insights into surface chemistry and biocompatibility lays the foundation for a detailed examination of the chemical reactions that Si₃N₄ undergoes in biological environments. Next, the analysis focuses on the mechanisms of bioactivity and antipathogenicity that the material exhibits both alone and in combination with modern bioglass. However, it is highlighted that despite the general consensus on the biocompatibility and bioactivity of Si₃N₄ ceramics, sometimes the proposed biological mechanisms behind its behavior are discordant or unsupported by the direct evaluation of specific biochemical activities. This review highlights both the reliable information in the literature and the gaps in research that need to be filled in order to fully understand the reasons behind the biological properties of this material.

Production and characterization of geopolymers prepared by mixing metakaolin, end-of-life dolomite refractories, sodium silicate solution, and sodium hydroxide solution have been performed. The as-received refractory was crumbled in order to obtain products having, respectively, 250 μm, 1 mm, and 2.5 mm maximum particles size. Each batch of powder was added in different proportions to a blank geopolymeric matrix. It has been observed that the addition of waste refractory reduces workability of the reference refractory-free slurry. After hardening, only the set of samples prepared with powders with maximum size of 250 μm maintain integrity while the others resulted affected by the presence of fractures caused by volumetric instabilities; samples with composition R100 showed the highest compressive strength, whereas higher refractory addition lowers strength. Specific surface area appears independent by materials composition; conversely pore volume slightly increases with the addition of dolomite refractory powder. During the thermodilatometric tests all compositions display a shrinkage of about 0.1% between 170 and 400 °C; however, sintering starts at higher temperature (above 600 °C) and samples melt in the range between 650 and 750 °C as a function of their composition, thus showing that the resulting materials loose refractoriness with respect to both the reference geopolymer and the dolomite refractory. Graphical Abstract