Paola Palmero

Fracture toughness in transformation-toughened zirconia depends on the crack length at which it is measured, because the tetragonal-to-monoclinic transformation develops a shielding zone as the crack extends, so each geometry reports the toughness of the extension it samples. In ceria-stabilised zirconia (Ce-TZP), a low-temperature degradation-resistant alternative, the optimal CeO₂ content and the crack size at which that optimum changes remain largely undetermined. Three compositions (10, 11 and 12 mol% CeO₂), matched in density and grain size, were characterised by four fracture tests over three decades of crack length: critical-load micro-cantilevers, bridge-notch micro-cantilever resistance curves, pillar splitting from 3.5 to 17.5 µm radius and ASTM C1421 chevron-notched beams, with confocal micro-Raman mapping of the transformation on the same specimens. The composition ranking reverses across that range. At the cantilever scale, toughness rises with stabiliser content, 2.06 ± 0.38 to 3.42 ± 0.45 MPa·√m from 10 to 12 mol% CeO₂; at the macro scale, the order is opposite, 10 mol% reaching 8.77 ± 0.35 against 6.09 ± 0.76 and 4.59 ± 0.62 for 12 and 11 mol%. The full span of crack lengths brackets the crossover between 12.5 µm and the macro beam, locating it at 15–23 µm. Raman mapping shows the transformed zone growing with crack size and contracting with CeO₂ content. Higher ceria maximises short-crack initiation resistance, whereas lower ceria develops the long-crack shielding governing macroscopic toughness, so the optimal composition follows the flaw size the component must tolerate.

Digital Light Processing (DLP), which operates through a layer-by-layer deposition, has proven to be a promising technique for obtaining complex and customized architectures. However, there are still numerous unresolved challenges in ceramics additive manufacturing, among which is delamination due to suboptimal adhesion between the layers, which threatens the structural integrity and properties of samples. According to recent findings, excess surface hydroxyl groups were identified as being responsible for this defect; a suitable calcination pre-treatment of the ceramic powder could be effective in significantly mitigating delamination flaws in mullite DLP printed bodies. Therefore, in addition to optimizing the printable slurry formulation and printing parameters (mainly in terms of curing energy and layer resolution), this work aimed at investigating the influence of the calcination of a commercial mullite powder (added with magnesium nitrate hexahydrate, as a precursor of the sintering aid MgO) as a simple and effective treatment to additively shape ceramic bodies with limited flaws and enhanced density. The surface characteristics evolution of the mullite powder was investigated, specifically comparing samples after magnesium nitrate hexahydrate addition and ball-milling in water (labeled as BM), and after an additional calcination (BMC). In particular, the effect of the superficial -OH groups detected by FTIR analysis in the BM powder, but not in the BMC sample, was studied and correlated to the properties of the respective ceramic slurry in terms of rheological behavior and curing depth. The hydrophilicity of BM powders, due to superficial hydroxyls groups, affects ceramic powder dispersion and wettability by the resin, causing a weak interface. At the same time, it promotes photopolymerization of the light-sensitive resin, thus inducing the as-printed matrix embrittlement. Anyhow, its photopolymerization degree, equal to 67% and 55% for BM and BMC, respectively, was enough to guarantee the printability of both slurries. However, the use of BMC significantly reduced flaw occurrence in the as-printed bodies and the final density of the samples sintered at 1450 °C (without an isothermal step) was increased (approx. 60% and 50% of the theoretical value for BMC and BM, respectively). Thus, the target porosity of the ceramic bodies was guaranteed, and their structural integrity achieved without any increase in sintering temperature but with a simple powder treatment.

Preservation and enhancement of wood properties have become increasingly important due to the growing demand for sustainable materials in the construction and manufacturing industries. This study focuses on bleaching processes as an alternative to conventional delignification, aiming to retain a significant amount of lignin while achieving the desired whiteness of the wood template. In particular, stabilized alkaline hydrogen peroxide is investigated as a bleaching agent under mild conditions. The treatment preserves more than 90% of the native mass in both balsa and birch, ensuring that most of the wood’s structural components are maintained. This results in a high wood volume fraction, corresponding to reduced porosity and a structure closely resembling that of unbleached wood. Fourier Transform Infrared spectroscopy (FTIR) semi-quantitative analysis further confirms that the relative lignin content is retained, ranging between 70 and 80% depending on the species. Unlike conventional approaches that often degrade the wood structure and require long treatment times at high temperatures, the proposed process is performed at room temperature under mild conditions and completed in less than 2–4 h, thus reducing energy demand and avoiding harmful byproducts. Overall, this work provides a bleaching strategy that combines efficiency, structural integrity, and sustainability, offering bleached wood templates suitable for further characterization and advanced applications.

Three-dimensional-printed complex mullite structures based on triply periodic minimal surfaces (TPMSs, namely, Schwartz and Gyroid) with two different thicknesses (Schwartz 1 and Gyroid 1–4 mm, Schwartz 2 and Gyroid 2–6 mm) were fabricated and tested as humidity sensors. The samples were sintered at 1450 °C and tested in the range from 0% to 89% relative humidity (RH) at room temperature to evaluate the effect of geometry and thickness on humidity sensitivity. After water vapor exposure at room temperature, the response was 2.84 under 89 RH% for the Schwartz 1 structure (1.36 for the Schwartz 2 structure) and 1.21 for the Gyroid 1 structure (7.00 for the Gyroid 2 structure). The results showed that, at 89% RH, the best response of the sensors was achieved for the Gyroid 2 structure. Sensors exhibit good repeatability, and there was no interference in the presence of other gases.

At present, one of the strategies to reduce the embodied carbon of cement is to partly replace clinker with metallurgical slags. In this perspective, this study investigates the accelerated aqueous carbonation of electric arc furnace slag as possible treatment for its reuse in the cement industry. In view of developing a low-energy and industrially integrated process, mild carbonation conditions were selected: ambient pressure, low liquid-to-solid ratio, minimised temperature (between 20 °C and 60 °C) and short duration time (ranging from 20 to 60 min). To optimise the carbonation process, a design of experiments was developed. The Response Surface Methodology showed a non-representative trend along time. Therefore, a non-linear model was adopted for a better prediction of CO₂ content above 50 min. The results were satisfactory with an optimum CO₂ uptake of 7.7% and the carbonation degree obtained, 30.2%, was the highest registered in previous literature for open systems. Moreover, a literature analysis on previous aqueous and wet direct carbonation of Electric Arc Furnace slag was carried out using Principal Component analysis. This exploratory data analysis identified the most effective carbonation parameters based on the reactor type and suggested the investigation of further parameters such as liquid-to-solid ratio and CO₂ flow rate and partial pressure, maintaining the perspective of a sustainable process.

The aim of this work is to compare the traditional uniaxial pressing with an innovative shaping technique, Digital Light Processing (DLP), in the preparation of porous mullite (3Al₂O₃·2SiO₂) supports to be functionalized with an active coating for CO₂ capture. Indeed, the fabrication of complex geometries with 3D-printing technologies allows the production of application-targeted solid sorbents with increased potentialities. Therefore, this research focused on the effect of the purity of the selected raw materials and of the microstructural porosity of 3D-printed ceramic substrates on the Metal Organic Frameworks (MOFs) coating efficiency. Two commercial mullite powders (Mc and Mf) differing in particle size distribution (D₅₀ of 9.19 µm and 4.38 µm, respectively) and iron oxide content (0.67% and 0.38%) were characterized and used to produce the substrates, after ball-milling and calcination. Mc and Mf slurries were prepared with 69 wt% of solid loading and 5 wt% of dispersant: both show rheological behavior suitable for DLP and good printability. DLP 3D-printed and pressed pellets were sintered at three different temperatures: 1350 °C, 1400 °C and 1450 °C. Mf 3D-printed samples show slightly lower geometrical and Archimedes densities, compared to Mc pellets, probably due to the presence of lower Fe₂O₃ amounts and its effect as sintering aid. Mullite substrates were then successfully functionalized with HKUST-1 crystals by a two-step solvothermal synthesis process. Ceramic substrate porosity, depending on the shaping technique and opportunely tuned controlling the sintering temperature, was correlated with the functionalization efficiency in terms of MOFs deposition. Three-dimensional-printed substrates exhibit a higher and more homogeneous HKUST-1 uptake compared to the pressed pellets as DLP introduces desirable porosities able to enhance the functionalization. Therefore, this work provides preliminary guidelines to improve MOFs coating on mullite surfaces for CO₂ capture applications, by opportunely tuning the substrate porosity.

The utilisation of carbonation treatments to produce building materials is emerging as a valuable strategy to reduce CO₂ emissions in the construction sector. It is of great importance to regulate the degree of carbonation when the mineralisation process is combined with hydration, as a high CO₂ uptake may impede the development of adequate strength. A significant number of studies focus on attaining the maximum carbonation degree, with minimal attention paid to the examination of the evolution of CO₂ uptake over the initial stages of the process. In this context, the present study aims to investigate the evolution of CO₂ uptake over time during carbonation. Ordinary Portland Cement (OPC) is employed as material, with aqueous carbonation selected as the mineralisation process. This investigation encompasses a range of carbonation durations, spanning from 5 to 40 min. The analysis of the evolution of the mineral composition with time demonstrated that the rate of the carbonation reaction accelerates in the initial minutes, resulting in the conversion of all the portlandite produced during the hydration process in the initial 10 min. Quantitative analysis of the carbonation degree indicated that the CO₂ uptake at 40 min is equal to 19.1%, which is estimated to be approximately 70% of the maximum achievable value. By contributing to the understanding of the early carbonation mechanisms in aqueous conditions of OPC, this study provides valuable support for further investigation focused on the use of cement mineralisation processes to produce building materials.