Solids

Additive manufacturing (AM) techniques are continuously evolving to meet the increasing demand for high-performance ceramics with intricate geometries. This review covers four widely investigated ceramic AM methods: stereolithography (SLA), digital light processing (DLP), fused deposition modeling (FDM), and direct ink writing (DIW). Each technique is analyzed from a technical standpoint, with particular attention given to feedstock formulation, printing parameters, debinding, sintering, and final densification. Vat photopolymerization provides high resolution and good surface quality, but remains constrained by photocurable slurry behavior. FDM offers accessible equipment and material versatility, though high ceramic loading can lead to feeding and printing difficulties. DIW can process highly loaded ceramic inks and is suitable for porous and architectured structures, but requires precise control of ink rheology and shape retention. The main challenges associated with ceramic printing are also examined, together with proposed solutions, emerging trends, and research gaps. This review provides a comparative overview of the critical parameters governing ceramic AM and helps identify the most suitable technique according to the targeted application.

Obsidian is a non-crystalline volcanic silicate glass that played a major role in human technological development from the Paleolithic onward, owing to its brittle fracturing and ability to produce sharp cutting and scraping edges. From the Upper Paleolithic, its long-distance circulation enabled the reconstruction of ancient exchange networks through the identification of geological sources. This study evaluates the non-destructive elemental characterization of obsidian using handheld portable energy-dispersive X-ray fluorescence (pXRF), with emphasis on compositional variability, analytical reproducibility, and inter-instrument comparability. Two pXRF spectrometers, the Thermo Niton XL3t GOLDD+ and Bruker Tracer 5, were assessed for precision, consistency, and robustness under standardized analytical conditions. A reference dataset comprising 23 archaeological obsidian fragments attributed to Aegean geological sources, Thira/Santorini, Melos, Nisyros, and Giali, was analyzed using both instruments. Statistical comparison demonstrated strong agreement in the clustering and discrimination of samples according to geological source, although differences in absolute elemental concentrations were observed, reflecting instrument-specific calibration procedures and measurement parameters. The results highlight the importance of standardized calibration using reference materials, rigorous quality control, and comprehensive methodological documentation for reliable interlaboratory comparison. Overall, handheld pXRF provides a reliable non-destructive approach for volcanic glass characterization and supports the development of transferable and reproducible datasets for silicate solid materials.

Periodic-layered structures form in some ternary diffusion couples, but their formation mechanism is still debated. Three mechanisms are proposed: unequal diffusion rates, chemical potential instability, and diffusion-induced stress. In the Ce–Mg–Zn system, periodic layers were reported at 300 °C without a mechanism. This study examines which mechanism the morphology supports. Two diffusion couples paired pure Zn with a binary Ce–Mg alloy. The alloy contained 24.54 at.% Ce in the first couple and 71.76 at.% Ce in the second. Both couples were annealed at 300 °C for 21 days. Phases were assigned from WDS compositions. Repeat distances were measured from grey value line profiles. Mg–Zn-rich and Ce-bearing layers alternated in both couples. The first couple formed Mg₂Zn₁₁, MgZn₂, Ce₂Zn₁₇ and ternary τ phases across seven reaction zones. The second formed Mg₂Zn₁₁, MgZn₂ and Ce–Zn-rich phases across eight. The coefficient of variation of the repeat distance ranged from 1.6% to 17.6%. In the first couple, spacing increased over the first three periodic zones and then levelled off. No cracks or voids were found at the layer boundaries. The initial Ce/Mg ratio strongly affected the phase sequence. The data could not separate the three mechanisms.