Coatings

In this study, B₄C nanoparticles were incorporated into AA2024, one of the aluminum alloys with superior mechanical and wear properties, with the aim of further enhancing its mechanical, tribological, and corrosion performance. The nanocomposites were produced using mechanical milling followed by powder metallurgy techniques. The effects of nano-sized B₄C additions on powder characteristics, microstructure, and physical, mechanical, tribological, and corrosion properties were systematically investigated through microhardness, density, SEM, XRD, bulk hardness, wear, and corrosion tests. B₄C was added at weight fractions of 0–2 wt.%, and all samples were mechanically milled for 8 h. The results revealed a gradual reduction in powder particle size and a corresponding increase in particle microhardness with increasing B₄C content. The sample reinforced with 2 wt.% nano-B₄C exhibited an approximately 80% increase in hardness and around a 55% improvement in tensile strength compared to the unreinforced alloy. Wear resistance was significantly enhanced, showing up to an 8-fold improvement under a 5 N load and a 6-fold improvement under a 25 N load. Furthermore, corrosion resistance nearly doubled with the addition of B₄C nanoparticles.

This paper investigates the feasibility of CaZr₄(PO₄)₆ as a novel thermal barrier coating for SiO_2f/SiO₂, serving as a radome at 1200 °C. Initially, CaZr₄(PO₄)₆ powder undergoes TG-DSC testing across a temperature range from room temperature to 1200 °C, demonstrating excellent phase stability within this range. Subsequently, the coating’s properties and the thermal cycling performance are examined. The results indicate that the thermal conductivity of CaZr₄(PO₄)₆ falls within the range of 1.05 to 1.02 W·m⁻¹·K⁻¹ (RT ~ 1200 °C), with thermal expansion coefficients of the coating ranging from 2.07 to 5.55 × 10⁻⁶ K⁻¹. Moreover, the thermal cycling lifetime of the CaZr₄(PO₄)₆ coating is evaluated by performing 100 cycles (50 h) at 1200 °C. Mechanical properties are assessed through Vickers and Knoop hardness tests, revealing a fracture toughness of 1.4 Mpa·m^1/2. The primary cause of coating failure and peeling is the excessive internal stress between the coating and the expansion of transverse cracks. Fracture toughness serves as a key performance indicator reflecting the material’s resistance to unstable crack expansion, so the failure of the coating is attributed to the limited fracture toughness and the thermal mismatch stress between the coating and the substrate. Based on the aforementioned research findings, CaZr₄(PO₄)₆ might be the potential coating for SiO_2f/SiO₂ systems.

The 17th-century stucco altar dedicated to St. Michael the Archangel is an interesting, but very damaged, artwork located in the complex of St. Angel in the little town of Barbarano Romano in Central Italy. During the recent and quite necessary restoration carried out by University of Tuscia students on the Conservation and Restoration of Cultural Heritage Master’s program, some problems with the surface coating were encountered in the cleaning phase. Diagnostic and scientific analyses were crucial to better understanding the composition of these materials to perform the safest and most efficient cleaning procedures. The first of many steps required by this approach was an in situ analysis, starting from on-site analysis and diagnostic documentation through X-ray fluorescence spectroscopy and ultraviolet fluorescence photography, followed by laboratory investigations. The latter included µ-Raman and Fourier transform infrared spectroscopies, gas chromatography coupled with mass spectrometry, and scanning electron microscopy equipped with an energy-dispersive detector. Each technique provided useful data to determine the chemical composition of the white surface coating, which was found to be a non-original overpaint containing lead and organic binder. This overpaint had been applied to retouch the white stucco during a previous restoration project. All this new information contributed to achieving the final decision to remove this layer.