Ceramics: Processes, Microstructures, and Properties

Advanced ceramic materials have garnered significant attention due to their exceptional physical and mechanical properties, including high mechanical strength, high surface hardness, wear and corrosion resistance, etc. However, ceramics are hard to process owing to their brittleness and extremely high melting points, which greatly limits their applications. In recent decades, ceramic processing techniques such as additive manufacturing have been developed and improved. To review the rapid development of ceramic processes and encourage investigations on ceramic microstructures to tailor its properties and functionality, we have organized this Special Issue titled “Ceramics: Processes, Microstructures, and Properties”.

This Special Issue consists of 14 research articles from various perspectives. Calvo-Villoslada et al. focused on the rapid growth of Nb₂O₅ nanowires by Joule heating of Nb metal wires, which takes only tens of seconds [1]. Zhao et al. conducted a detailed study on the influence of compositions, sintering temperature, and duration on zirconia-toughened alumina (ZTA) ceramics. It is discovered that the addition of nano alumina or nano zirconia would result in a reduction in alumina grain size, and the highest degree of densification of alumina, only comprising reactive alumina powders, could be achieved at 1600 °C for 1 h. The results of their work are believed to guide the regulation of ZTA microstructures [2]. Csáki et al. investigated the influence of calcite and firing temperature on the sintering process of illitic clay. It was observed that the addition of calcite improves the ceramic porosity [3].

Functional ceramics with specialized applications are drawing attention from more and more researchers. Yang et al. proposed a novel method based on fast hot pressing for the fabrication of cermet matrix composites exhibiting superior friction performance in extremely high-temperature settings [4]. Sakhkhane et al. succeeded in introducing silver vanadate to a developed dental porcelain prepared from natural raw materials due to its antimicrobial properties, demonstrating the potential of silver vanadate as a candidate additive in ceramic dental material [5]. Chen et al. evaluated the influence of TiO₂ on microstructures and mechanical properties of the lunar regolith samples. It was found that as the content of TiO₂ increases, the relative density and flexural strength of lunar regolith simulant samples increase first, while dropping after reaching the peak with a TiO₂ content of 6 wt.%. The mechanics were further discussed based on scanning electron microscopy (SEM) and X-ray diffractometer (XRD) analysis [6]. Wu et al. proposed a special sandwich structure of HfO₂ ceramics consisting of a cubic (C) phase/monoclinic (M) phase/cubic (C) phase, which toughens the ceramic material by residual compressive stress. It was revealed that the fracture toughness could be increased to 2.83 MPa·m^0.5 after annealing for 48 h, demonstrating its potential as thermal barrier coating materials [7]. In addition, Mannapovitch et al. compared the effectiveness of photocatalysts of nanostructured functional ceramics additives synthesized in the Big Solar Furnace and in an infrared radiation furnace and their influence on welding performance [8].

There are several research focuses on the electric properties of ceramic matrix composites, with broad application prospects in electronic devices. Molina et al. from Electrical Engineering Department, University of South Florida, combined conventional photonic thermal processing with additive manufacturing techniques and successfully fabricated Ba_0.5Sr_0.5TiO₃-based ferroelectric varactors with a maximum tunability of 60.6% at 1 GHz under an applied electric field of 25 kV/mm [9]. Swift et al. utilized sol–gel process to prepare perovskite powders. It was discovered that the introduction of calcium increases the ceramic material entropy from calculation, which further influences its conductivity [10]. Hussain et al. also focused on the ferroelectric and piezoelectric properties of perovskite-based multifunctional composite ceramics. In addition, it was discovered that ceramic composition BFBT:0.2Sn exhibits excellent remnant polarization and piezoelectric coefficient, stable impedance, and low dielectric loss [11]. In addition, Liu et al. successfully prepared a high-entropy carbide (Ti_0.2Zr_0.2Nb_0.2Hf_0.2Ta_0.2)C ceramic and obtained its thermal and electrical properties from the combination of first-principle calculations and experiments at room temperature [12].

Compared to advanced ceramics, investigations on ancient ceramics, including pottery and porcelain, hold great historical significance, which not only improves our understanding of ancient ceramic craftsmanship but also facilitates the authentication and preservation of ancient ceramic artifacts. Li et al. applied thermoluminescence pre-dose dating techniques to identify the artificial irradiation of ancient Chinese porcelain, demonstrating its reliability in porcelain authentication [13]. In addition, Li et al. analyzed the celadon samples from the Lieshan Kiln in the Northern Song and Jin Dynasties, especially the coloring mechanism of the transparent celadons. This work is important for researchers to further understand the advancement of materials and techniques in porcelain production of the Lieshan Kiln [14].

The papers published in this issue cover a broad range of ceramic microstructure investigation and regulation to improve their properties and functionality. They will be valuable for researchers interested in ceramic matrix composites, microstructure of ceramics, materials characterization, ancient ceramics, and functional ceramics with wide applications.