Ceramics

Sintering additives play a decisive role in the densification behavior, mechanical properties, and thermal conductivity of silicon nitride ceramics. In this study, Mg₂Si and YH₂ were used as sintering additives for gas pressure sintering of silicon nitride based on the synergistic mechanism of “silicide silicon extraction-hydride dehydrogenation”. The regulation rules of the additives on ceramic densification, mechanical properties, and thermal conductivity were systematically investigated. Two optimization strategies were proposed for the technical route of replacing traditional oxide additives with non-oxide systems. (i) Rare-earth hydride YH₂ was used to replace traditional rare-earth oxides. It reacts with SiO₂ to achieve strong deoxidation and precisely regulate the liquid phase composition. (ii) Metal silicide Mg₂Si was used to replace metal oxides. It promotes the preferred growth of β-Si₃N₄ grains, consumes oxygen in the system, and reduces lattice defects. Mg₂Si introduces Si into the liquid phase, increasing the Si/O ratio, which lowers lattice oxygen content and supports higher thermal conductivity. YH₂ consumes SiO₂ on the Si₃N₄ surface, which reduces liquid phase oxygen content and inhibits lattice oxygen incorporation, promoting a liquid phase with a high N/O ratio. Compared with traditional Y₂O₃, YH₂ increases the Y₂O₃/SiO₂ ratio in the liquid phase. It promotes grain growth, reduces SiO₂ activity, and further improves the thermal conductivity of ceramics. Silicon nitride ceramics prepared by gas pressure sintering at 1750 °C with 3 wt.% Mg₂Si and 4 wt.% YH₂ composite additives exhibit the highest thermal conductivity of 87 W/(m·K), with a Vickers hardness of 14.36 GPa and a flexural strength of 643.15 MPa. This study provides an innovative idea for the preparation of high-performance silicon nitride heat dissipation substrates. Full article

Samples made from illitic clay were investigated using thermogravimetry (TG), thermodilatometry (TD) and dynamic mechanical analysis (DMA) during heating from room temperature to 300 °C. TG revealed three steps of mass loss: (a) the release of weakly bound H₂O (with the maximum rate at ~120 °C) from the pores, (b) a small mass loss event around 215 °C, (c) a small mass loss event near ~300 °C related to dehydration when H₂O molecules located in K-free sites of the illite interlayers are removed. TD indicated very small dimension changes for 20 °C → 300 °C. This behavior may result from two competing mechanisms, where the first one is regular thermal expansion and the second one is particle rearrangement caused by the removal of physically bound water. Young’s modulus initially decreases during heating up to approximately 70 °C. Young’s modulus subsequently increases exponentially, which may be explained by mechanisms analogous to those observed in the TD measurements. The activation energies derived from the exponential dependence E(t) are 5.66 kJ/mol for the temperature interval 130–200 °C and 10.96 kJ/mol for the 200–280 °C range. Full article

Lead-free piezoelectric ceramics have attracted substantial attention in environmental protection and energy storage applications due to their excellent performance. In this study, the Ba_1−xCa_xZr_0.1Ti_0.9−ySn_yO₃(BCZTS) lead-free piezoelectric ceramic system was synthesized. The effects of doping ratios of Ca and Sn, as well as sintering temperature, were systematically investigated on the phase structure, microstructure, and piezoelectric properties of BCZTS ceramics. The results showed that the Ba_0.88Ca_0.12Zr_0.1Ti_0.81Sn_0.09 ceramics synthesized with a Ca doping content of x = 12 mol% and a Sn doping content of y = 9 mol % had a homogeneous phase structure with an Orthorhombic–Tetragonal (O-T) morphotropic phase boundary (MPB) and uniform grain size. At a sintering temperature of 1300 °C, the ceramics achieved optimal piezoelectric performance, with a piezoelectric coefficient d₃₃ = 319 pC/N. These lead-free piezoelectric ceramics have superior properties compared to conventional lead-based piezoelectric ceramics in the local market, providing a novel and feasible way to replace lead-based ones in civilian applications. Full article

This work reports the synthesis, characterization, and photocatalytic performance of multifunctional spheres based on AgNP-doped TiO₂-Fe₃O₄ embedded in an alginate–chitosan biopolymeric matrix for the removal of organic contaminants from water. The composite powders exhibited a nanocrystalline structure composed of anatase TiO₂ (~20 nm) and magnetite (~25 nm), with homogeneously dispersed Ag nanoparticles, as observed by SEM. The spheres presented a mainly submicrometric particle size distribution (0.55–0.92 µm), favoring high surface area and colloidal stability. Under simulated solar irradiation, the material achieved efficient photocatalytic degradation of methylene blue, with a pseudo-first-order rate constant of 0.112 h⁻¹ and ~46% decolorization after 5 h. UV-Vis spectra showed progressive attenuation of the dye absorption band without accumulation of intermediates. Magnetic recovery tests confirmed rapid separation and reuse without performance loss. The enhanced activity is attributed to the synergistic interaction among plasmonic Ag, photocatalytic TiO₂, redox-active Fe₃O₄, and the adsorptive carbon–biopolymer matrix. The material exhibited strong antibacterial activity, achieving over 90% removal of fecal coliforms after 5 h of irradiation. Therefore, the developed AgNP-doped TiO₂-Fe₃O₄ spheres represent a sustainable, reusable, and efficient material for solar-assisted water sanitation. Full article

This study investigates the development of sustainable ceramic materials using industrial and agricultural waste from the Kyzylorda region of Kazakhstan. The research focuses on the combined use of local clay, ash from the Kyzylorda thermal power plant (TPP), and rice husk ash (RHA). Experimental investigations included the evaluation of chemical composition, linear and volumetric shrinkage, water absorption, bulk density, and compressive strength of ceramic samples fired at 950–1050 °C. Microstructural (SEM) and phase composition (XRD) analyses were performed to explain the observed behavior. The results showed that the optimal composition was 70% clay, 20% TPP ash, and 10% RHA, which demonstrated the highest compressive strength (15.45 MPa), reduced water absorption, and improved densification. The enhanced performance is attributed to partial vitrification and viscous-phase-assisted densification and the formation of crystalline phases such as mullite, cristobalite, and anorthite. The study confirms that the combined use of TPP ash and RHA enables effective recycling of local waste materials and improves the physical and mechanical properties of ceramic products. Full article

The ceramic tile industry is increasingly required to reduce its environmental impact while maintaining high technological and aesthetic standards. In this context, the use of secondary raw materials (SRMs) represents a promising strategy to decrease the consumption of virgin resources and the energy demand associated with conventional frit production. At the same time, solar-reflective engobes can contribute to passive cooling by limiting solar heat absorption and mitigating the urban heat island effect. In this study, white solar-reflective engobes were developed by incorporating at least 8 wt.% of SRMs, including various recycled glass streams, ceramic wastes, and yttria-stabilized zirconia residues. The results demonstrate that optimized formulations achieve high solar reflectance values (up to 0.79) while maintaining the technological and aesthetic requirements of industrial ceramic tiles. Recycled glasses act as effective fluxing agents, whereas waste zirconia enhances optical performance due to its strong light-scattering capability. The most promising formulations were validated at the industrial scale, confirming their applicability under real production conditions. Overall, the developed engobes represent a scalable alternative to traditional frit-based systems, enabling reduced resource consumption and supporting the development of energy-efficient ceramic surfaces. Full article

Thermal barrier coatings (TBCs) require materials with intrinsically low thermal conductivity and high grain-boundary thermal resistance to maximize the temperature gradient across the top coat. In this work, the effective thermal conductivity of more than 40 prospective TBC oxides belonging to seven structural families (YSZ/YSH, pyrochlores/fluorites A₂B₂O₇, defective fluorites A₃BO₇, fergusonite/monazite ABO₄, and perovskites ABO₃) was systematically deconvoluted into intrinsic grain thermal conductivity (k_grain) and grain-boundary (R_gb) contributions. It is shown that grain-boundary Kapitza resistance dominates heat transport in virtually all advanced oxides, contributing 60–90% to the total thermal resistance of polycrystalline samples. The lowest k_grain values (4–12 W m⁻¹ K⁻¹) are found for cerates and certain tantalates, while the highest R_gb (up to 7.2 × 10⁻⁶ m² K W⁻¹) are characteristic of high-entropy and heavily doped perovskites. Orthorhombically distorted SrCeO₃-based and high-entropy perovskites combine moderate k_grain (4.7–27.9 W m⁻¹ K⁻¹), high R_gb, and tunable thermal-expansion coefficients (10–13 × 10⁻⁶ K⁻¹), making them the most promising candidates for next-generation TBCs. These findings provide a rational basis for microstructure engineering and composition design aimed at maximizing the temperature drop across TBC layers while maintaining phase stability and CMAS resistance. Full article

This study centred on the parametric optimisation and performance prediction of NiCr/WC-Co coatings produced by high-velocity oxygen fuel (HVOF) spraying. An L18 orthogonal experimental design based on the Taguchi method and the response surface method (RSM) was adopted to examine how key process parameters affect the microstructure, phase composition and hardness of the coatings. The results revealed that analysis of variance (ANOVA) indicated that travel speed, methane flow rate, powder feed rate, and stand-off distance were the primary parameters affecting coating hardness, collectively accounting for 76.25% of the total variance. Also, the RSM model established in this study demonstrates remarkably high predictive accuracy, with a coefficient of determination (R²) of 0.985 and an average prediction error of just 1.16%. Verification experiments were also conducted under optimal conditions. The measured hardness was 1352.7 ± 75 HV, in close agreement with the predicted value of 1365 HV. The coating, which was applied using HVOF spraying, had a dense layered structure and low porosity, and the decarburisation of the tungsten carbide was extremely minimal. In addition, interfacial bonding is improved and structural defects are reduced by the addition of a NiCr intermediate layer. It is demonstrated by the results that the Taguchi-RSM method is reliable for the optimization of HVOF spraying parameters and the prediction of coating hardness. Full article

The use of zirconia as a material in the base of modern restorative dentistry is due to its high strength, biocompatibility, and improved aesthetic performance. The aim of this review is to provide an integrated and coherent overview of the recent developments in zirconia crowns by focusing on the development of materials, microstructure, digital fabrication processes, optical capabilities, and clinical performance. A survey of literature in the form of a narrative literature review was conducted in the most significant databases, such as PubMed, Scopus, Web of Science, and Google Scholar, including publications published since 2000, with a focus on systematic reviews, meta-analyses, clinical studies, and materials science studies. The results show that zirconia materials have developed beyond traditional 3Y-TZP systems, characterized by high strength and fracture toughness to high-translucency and multilayer zirconia (4Y 6Y-PSZ) systems, which provide better aesthetics at the cost of lower mechanical reliability. The implementation of CAD/CAM technologies has enhanced the accuracy of fabrication, marginal fit and reproducibility and the development of sintering, surface modification and bonding protocols has enhanced clinical performance. Recent clinical results have shown high survival rates (around 85–95 percent over 5–10 years), and the results depend on the design of the restoration, the zirconia generation, and the functional loading circumstances. Despite these developments, there are still concerns about the durability of bonding, trade-offs between translucency and strength, and long-term performance of high-translucency zirconia. The development of new technologies, such as additive manufacturing, design-aided artificial intelligence, and bioactive surface modification, is a promising avenue toward improving clinical reliability and performance. Full article

Fully dense monoclinic zirconia ceramics were successfully fabricated by pressureless sintering and/or HIP. Although monoclinic zirconia exhibits unique physicochemical properties, fabrication of fully dense polycrystalline bodies has remained challenging due to catastrophic volume expansion during the tetragonal-to-monoclinic transformation. By introducing a synergistic ternary (Ga₂O₃-ZnO-TiO₂) sintering aid, a relative density exceeding 99.6% with an average grain size of 0.5–2 µm was achieved by sintering under an oxygen atmosphere at 1070 °C for 3–100 h, well below the phase-transition temperature. X-ray diffractometry confirmed a single-phase monoclinic structure. Subsequent hot isostatic pressing at 1080 °C and 180 MPa for 2 h eliminated residual porosity, yielding a 4-point bending strength of 328 MPa, a fracture toughness of 2.7 MPa·m^0.5, and a Vickers hardness HV₁ of 805. This monoclinic zirconia ceramic exhibited ~30% total transmittance, while in-line transmittance remained below 0.1% due to intrinsic birefringence of the monoclinic lattice. These results established a low-temperature route for densifying phase-sensitive ceramics while achieving long-term stability. Full article

The structural response of ceramics to extreme deformation is of significant scientific and technological relevance since such conditions are commonly encountered during both processing and service. In this study, monoclinic zirconia was subjected to high-energy ball milling for extended durations of 80 h and 120 h, followed by annealing at 1000 °C. X-ray diffraction revealed a progressive increase in the tetragonal phase content with milling duration, while subsequent annealing promoted its consolidation alongside the principal monoclinic phase, resulting in a stable biphasic structure. The phase evolution is also evaluated through a Raman spectroscopy analysis and correlated with the morphology, mechanical properties, and surface area analyses. Scanning electron microscopy confirmed the preservation of nanoscale features in the milled and annealed specimens, in contrast to the unmilled sample, which exhibited pronounced grain coarsening. The combined presence of nanostructural stability and biphasic phase constitution underscores the efficacy of high-energy ball milling, in conjunction with thermal treatment, as an effective strategy to tailor the microstructure and phase stability of zirconia ceramics for advanced engineering applications. Full article

In this study, a multiphysics finite-element model was developed for the deposition of W–C–B coatings in a hot-wall tubular CVD reactor from a gas mixture of tungsten hexafluoride (WF₆), hydrogen (H₂), and trimethylamine borane ((CH₃)₃N:BH₃) at 550 °C and 5 Torr. The aim of this work is to deepen the understanding of reactant transport mechanisms and to optimize the process parameters for obtaining targeted tungsten carbide or boride phases. The simulations were performed in COMSOL Multiphysics (ver. 6.1) using a 2D axisymmetric formulation that couples laminar flow, heat transfer, and multicomponent diffusion, accounting for heterogeneous chemical reactions at the reactor walls. The obtained spatial distributions of reactant concentrations demonstrate precursor depletion along the reactor length. A comparison of the calculated B/W and C/W stoichiometric ratios for 13 operating conditions with experimental data confirms a transition from W and W–B phases at low trimethylamine borane (TMAB) flow rates to tungsten carbide-based coatings at higher flow rates. Furthermore, a parametric sweep was utilized to determine the optimal parameter range for the synthesis of tungsten borides. Full article

Ceramic membranes show potential for high-temperature CO₂ extraction from flue gas; nevertheless, their performance under simultaneous heat and pressure stress is not well comprehended. This research addresses the temperature-dependent CO₂/N₂ separation characteristics of a commercial ceramic membrane (pore size ~0.1–1 µm) utilizing simulated flue gas (11.8% CO₂, 74.2% N₂, 2.5% O₂, remainder CH₄) at temperatures ranging from 60 to 140 °C and pressures between 4 and 6 bar. Calibrated GC-TCD was used to quantify permeate compositions across multiple operating valve openings. With a CO₂/N₂ selectivity (α) of 0.75 at 4 bars, the maximum CO₂ enrichment peaked at 80 °C (10.8 mol%), getting close to the Knudsen diffusion limit (0.80). Selectivity decreased dramatically beyond 100 °C—α = 0.61 (100 °C), 0.45 (140 °C)—and CO₂ dropped to 5.8% at 4 bar and 2.2% at 6 bars. Viscous flow dominance was shown by the strong pressure amplification—α decreased by more than 60% from 4 to 6 bar at all temperatures. These findings emphasize the possibility of performance collapse in hot, pressured flue streams and identify the limited operating window under which Knudsen-controlled transport can be maintained. The study provides quantitative evidence of a transition in transport regime under mixed flue-gas conditions. Full article

MXenes, with a high surface area, abundant active sites, and excellent ion transport properties, have demonstrated excellent electrochemical performance. However, systematic comparisons of the structural evolution process and electrochemical performance for MXene are lacking. In this study, multilayer MXene (M-Ti₃C₂T_x) was successfully fabricated by in situ etching. During the subsequent centrifugation process, the thicker and heavier multilayer sheets settled due to their faster sedimentation rate, while the lighter, surface-functionalized monolayer sheets remained colloidally stable in the supernatant due to solvation and electrostatic repulsion, thereby achieving separation and obtaining delaminated MXene (D-Ti₃C₂T_x). Structural analysis indicates that the removal of the aluminum layer synergizes with the exfoliation of the nanosheets, significantly increasing the interlayer spacing and making the sheet structure more pronounced, and the pore structure is more abundant. Especially, in three-electrode and two-electrode systems at an identical mass loading of 5 mg on carbon paper, D-Ti₃C₂T_x delivered a higher specific capacitance, more pronounced pseudocapacitive behavior, and a superior rate capability compared to Ti₃AlC₂ and M-Ti₃C₂T_x. Such excellent electrochemical performance of D-Ti₃C₂T_x is due to the shortened ion diffusion path in the delaminated structure, which enables rapid ion migration, an extremely large specific surface area, and a mesoporous structure that provides abundant active sites. This study underscores the significant potential of D-Ti₃C₂T_x in emerging energy storage systems and offers insights into guiding MAX phase synthesis during its preparation. Full article

The effect of A-site substitution on the morphological and electrochemical properties of La_1-xSr_xMnO₃ (x = 0, 0.25, 0.50) perovskites was investigated to evaluate their potential as electrode materials for supercapacitors. X-ray diffraction analysis confirmed the formation of the perovskite structure, with minor peak shifts and distortion of crystal structure induced by Sr substitution. Scanning electron microscopy analysis revealed irregularly shaped particulate morphology across all perovskite compositions. The increasing amount of Sr as in La_0.5Sr_0.5MnO₃ (LSM-50) favored the formation of nanosized particles, and energy dispersive X-ray (EDX) analysis confirmed the presence of all constituent elements; EDX elemental mapping also showed a uniform distribution of all elements in the various perovskite compositions. Among all compositions, La_0.75Sr_0.25MnO₃ (LSM-25) possessed the highest specific capacitance (C_sp) of 483 Fg⁻¹ at 1 Ag⁻¹ current density in 3 M KOH electrolyte, as determined by electrochemical analysis. This perovskite material also exhibited a capacitance retention of 87.8% after 5000 charge–discharge cycles. Electrochemical impedance spectroscopy revealed that LSM-25 showed the lowest solution resistance (0.68 Ω*cm²) and charge transfer resistance (1.52 Ω*cm²), indicating strong electrode–electrolyte interaction. Detailed analysis of cyclic voltammetry data revealed that the predominant charge storage mechanism was diffusive in nature, with 88% of the diffusive contribution registered for LSM-25. These findings demonstrate that Sr substitution at the A-site significantly enhances the energy storage performance of LaMnO₃, making it a promising candidate for supercapacitor applications. Full article

Ceramics are widely evaluated for their extreme hardness, high-temperature stability, and corrosion resistance, which enable applications in harsh service environments. However, these same properties, high melting points, brittleness, and low thermal shock resistance, make conventional manufacturing of complex ceramic components difficult and expensive. Traditional processes often require costly diamond tooling or energy-intensive sintering and tend to produce only simple geometries, with significant waste material and risk of defects. Additive manufacturing (AM) has recently emerged as a promising route to fabricate intricate, near-net-shape ceramic parts without these drawbacks. By building components layer by layer, AM reduces the need for extensive machining and enables the fabrication of geometrically complex, near-net-shape ceramic structures with reduced material waste, although challenges such as porosity, interlayer defects, and cracking during post-processing remain. Nonetheless, ceramic AM technologies lag behind their metal and polymer counterparts, and significant challenges remain in achieving fully dense parts with reliable mechanical properties. This review provides an in-depth overview of the state of the art in ceramics and ceramic composite additive manufacturing. We detail the most widely used AM processes (stereolithography, binder jetting, material extrusion, powder bed fusion, inkjet printing, and direct energy deposition) and typical feedstock formulations for each technique. We examine the resulting mechanical properties (strength, toughness, hardness, wear resistance) and functional properties (thermal stability, dielectric behavior, biocompatibility) of additively manufactured ceramics, and discuss their current and potential engineering applications in the aerospace, defense, automotive, biomedical, and energy sectors. Persistent challenges, including porosity, shrinkage and cracking during sintering, achieving uniform microstructures, high process costs, and scalability issues, are analyzed, and we highlight promising future directions such as multi-material grading, integration of machine learning for process optimization, and sustainable manufacturing approaches. Despite significant progress, challenges remain in achieving fully dense structures, improving process reliability, and scaling ceramic AM for industrial applications, highlighting the need for further research in process optimization, material design, and multi-material integration. Full article

Porous, crystalline gamma-Al₂O₃ coatings with a thickness of (6 ± 0.5) μm and a uniform distribution of rare earth (RE) dopants are synthesized by plasma electrolytic oxidation of aluminum at a current density of 150 mA/cm² in a boric acid and borax (BB) solution containing added RE oxide particles (Ho₂O₃, Tb₄O₇, and Pr₆O₁₁) at concentrations of 1, 2, and 4 g/L. The concentration of RE oxide particles in the BB solution determines the amount of RE elements incorporated into the coatings but does not significantly affect their surface morphology, crystal structure, or light absorption properties. The coatings exhibit high absorption in the middle/near-ultraviolet region, characteristic of Al₂O₃. Typical 4f-4f transitions of Ho³⁺, Tb³⁺, and Pr³⁺ are observed in the photoluminescence spectra. Photocatalytic evaluations using methyl orange degradation under simulated solar irradiation show that RE doping significantly enhances photocatalytic efficiency. Peak degradation efficiencies are achieved at a concentration of 4 g/L for all RE oxides. After 8 h of irradiation, maximum degradation reaches 88%, 92%, and 85% with pseudo-first-order rate constants (k_app) of about 0.274 h⁻¹, 0.339 h⁻¹, and 0.232 h⁻¹ for coatings synthesized in BB with 4 g/L Ho₂O₃, Tb₄O₇, or Pr₆O₁₁, respectively. In comparison, the pristine Al₂O₃ coating achieves only about 50% degradation (k_app ≈ 0.087 h⁻¹). Photoluminescence indicates that RE³⁺ ions serve as effective charge-carrier traps, suppressing electron–hole pair recombination. RE-doped Al₂O₃ coatings demonstrate exceptional structural stability and reusability over six cycles, highlighting their potential for sustainable wastewater remediation. Full article

The traditional solid-state method was employed in this study to prepare Mn-Zn ferrite. By adjusting the sintering temperature and the MoO₃ doping ratio, the evolution of its structural and magnetic properties was systematically investigated. Fe₂O₃, MnO, and ZnO were used as the main raw materials, with MoO₃ serving as an additive. MoO₃ was doped at molar ratios ranging from 0 to 1000 ppm under experimental conditions involving a sintering temperature between 1125 °C and 1165 °C and an oxygen concentration of 1.5%. The addition of an appropriate amount of MoO₃ led to an increase in the Q value, which consequently resulted in a reduction in the loss. The formation of a single-phase spinel structure was confirmed by X-ray diffraction analysis. Observations of the surface morphology revealed that the grain size also increased with the increase in MoO₃ content, a trend consistent with the enhanced grain growth kinetics at higher MoO₃ levels. In this study, a Mn-Zn ferrite material with excellent comprehensive performance was successfully prepared under the optimal conditions of a sintering temperature of 1150 °C and a MoO₃ doping concentration of 500 ppm. A Q value of 22.3 was obtained for this material at 25 °C, while a Q value of 15.7 was obtained at 100 °C. At room temperature, a Q value of 192.4 was measured at a test frequency of 500 kHz, and a Q value of 137.2 was measured at 1 MHz. At a frequency of 500 kHz, a loss of 27.1 kW/m³ was observed at 25 °C, and a loss of 53.6 kW/m³ was observed at 100 °C. At a frequency of 1 MHz, a loss of 88.2 kW/m³ was recorded at 25 °C, while a loss of 183.7 kW/m³ was recorded at 100 °C. Additionally, the lattice constant was stabilized in the range of 8.52–8.53 Å, indicating favorable structural stability. Full article