Ceramics

This study investigates the use of gypsum waste from civil construction as a partial substitute for cement in soil–cement formulations, aiming to produce eco-friendly bricks aligned with circular economy principles. Formulations were prepared using a 1:8 cement–soil ratio, with gypsum replacing cement in proportions ranging from 5% to 40%. The raw materials were characterized in terms of chemical composition, crystalline phases, plasticity, and thermal behavior. Specimens, molded by uniaxial pressing into cylindrical bodies and cured for either 7 or 28 days, were evaluated for compressive strength, water absorption, durability, and microstructure. Water absorption remained below 20% in all samples, with an average value of 16.20%. Compressive strength after 7 days exhibited a slight reduction with increasing gypsum content, ranging from 16.36 MPa (standard formulation) to 13.74 MPa (40% gypsum), all meeting the quality standards. After 28 days of curing, the formulation containing 10% gypsum achieved the highest compressive strength (26.7 MPa), surpassing the reference sample (25.2 MPa). Mass loss during wetting–drying cycles remained within acceptable limits for formulations incorporating up to 20% gypsum. Notably, samples with 5% and 10% gypsum demonstrated superior mechanical performance, while the 20% formulation showed performance comparable to the standard formulation. These findings indicate that replacing up to 20% of cement with gypsum waste is a technically and environmentally viable approach, supporting sustainable development, circular economy, and reduction of construction-related environmental impacts. Full article

This work shows an approach on the role of the gas mixture used in the pulsed DC plasma nitriding aiming to enhance the niobium cavitation erosion resistance through the formation of niobium nitride on the treated surfaces. For this purpose, nitriding was carried out at 1353 K (1080 °C) for 2 h, under a pressure of 1.2 kPa (9 Torr), and a 5 × 10⁻⁶ Nm³s⁻¹ (300 sccm) flow rate for three distinct gas mixtures, namely 30% N₂ + 50% H₂ + 20% Ar, 50% N₂ + 30% H₂ + 20% Ar, and 70% N₂ + 10% H₂ + 20% Ar. Surfaces were comparatively characterized before and after nitriding through scanning electron microscopy (SEM), X-ray diffractometry, 3D roughness, and nanoindentation hardness measurements. The cavitation erosion test was carried out in accordance with ASTM G32-09, obtaining the cumulative mass loss (CML) curve and the average (AER) and maximum (MER) erosion rate of the tested surfaces. Surfaces showed multiphase layers mainly constituted of ε-NbN and β-Nb₂N nitride phases, for the three distinct gas mixture conditions investigated. A CML of 25.0, 20.2, and 34.6 mg, and an AER of 1.56, 1.27, and 2.16 mg h⁻¹ was determined to the 960 min (16 h) cavitation erosion testing time, for NbN surfaces obtained at the 30% N₂, 50% N₂, and 70% N₂ gas mixture, respectively. In this case, the nominal incubation period (NIP) was 600, 650, 550 min, and the maximum erosion rate (MER) was 4.2, 3.4, and 5.1 mg h⁻¹, respectively. Finally, the enhancement of the cavitation erosion resistance, based on the NIP of the NbN surfaces, regarding the Nb substrates (with NIP of ≈100 min), was up ≈6 times, on average, thus significantly improving the cavitation erosion resistance of the niobium. Full article

The production of ultra-high-temperature ceramic parts, like ZrB₂, is very challenging, as they cannot be conventionally sintered without using significant amounts of additives, which reduce their high-temperature properties. However, it is possible to sinter these ceramics using spark plasma sintering (SPS) without additives or with minimal amounts. The challenge, then, lies in obtaining complex shapes. In this work, we report a solution for the fabrication of ZrB₂ gears through the use of PLA-printed interfaces and graphite powder. This process is relatively simple and utilizes a fused deposition modeling (FDM) printer. The pros and cons of this approach are discussed with the aim of identifying what shapes can be produced using this method. Full article

The growing demand for organic dyes across industries increases their environmental impact since wastewater containing organic dyes poses serious risks to aquatic life, human beings, and the environment. The removal of organic dye residues is a challenge for traditional wastewater treatment facilities, highlighting the need for advanced treatment techniques that balance cost-effectiveness and sustainability in the face of today’s strict environmental regulations. The use of low-cost starting materials in ceramic membrane technology has recently become more popular as a feasible option because of its affordability and effectiveness, leveraging the synergy of adsorption and filtration to improve dye removal. Recent developments in ceramic membranes derived from waste and natural materials are examined in this review paper, along with their types, mechanisms, and applications in eliminating organic dyes from wastewater. The various forms of ceramic membranes derived from waste and natural materials are classified as follows: those composed solely of inexpensive starting materials, composites of inexpensive materials, hybrids of inexpensive and commercial materials, and inexpensive materials functionalized with cutting-edge materials such as carbon nanotubes and nanoparticles. These membranes have shown promising results in lab-scale research, but their large-scale use is still limited. The factors that negate the commercialization of these membranes are also critically discussed. Finally, key challenges and future research opportunities in the development of sustainable ceramic membranes for highly efficient dye removal are highlighted. Full article

This study explores the synergistic potential of ladle slag (LS) and sunflower shell fly ash (SSFA) in alkali-activated binder systems, focusing on their chemical and mineralogical characteristics and the influence of SSFA addition on the mechanical performance of LS-based pastes. X-ray fluorescence and XRD analysis revealed that LS is rich in CaO and latent hydraulic phases such as γ-belite and mayenite, while SSFA is dominated by K₂O, SO₃, and KCl/K₂SO₄ phases, reflecting its biomass origin. Infrared spectroscopy and thermal analysis confirmed the presence of carbonate, hydroxide, and hydrate phases, with SSFA exhibiting more complex thermal behavior due to volatile-rich composition. When used alone, LS produced weak binders; however, a 10 wt% SSFA addition tripled compressive strength to nearly 30 MPa, indicating a significant activation effect. Further increases in SSFA content led to strength reduction, likely due to increased porosity and excess salts. Microstructural analysis showed that SSFA promotes the formation of AFm phases such as Friedel’s salt and hydrocalumite, altering hydration pathways and enhancing early strength through chemical activation and carbonation processes. The findings highlight the potential of combining LS and SSFA as a sustainable binder system, offering a waste-derived alternative for low-carbon construction materials. Full article

Proton-conducting ceramics have gained significant attention in various applications. Yttrium-doped barium cerium zirconate (BaCe_xZr_1−x−yY_yO_3–δ) is the state-of-the-art proton-conducting electrolyte but poses a major challenge because of its high sintering temperature. Sintering aids have been found to substantially reduce the sintering temperature of BaCe_xZr_1−x−yY_yO_3–δ. This work evaluates, for the first time, the impact of NiO and ZnO addition in three different loadings (1, 3, 5 mol%), via wet mechanical mixing, on the sintering and electrical properties of a low cerium-containing composition, BaCe_0.2Zr_0.7Y_0.1O_3–δ (BCZY). The sintering temperature remarkably dropped from 1600 °C (for pure BCZY) to 1350 °C (for NiOBCZY and ZnOBCZY) while achieving > 95% densification. In general, ZnO gave higher densification than NiO, the highest being 99% for 5 mol% ZnOBCZY. Dilatometric studies revealed that ZnOBCZY attained complete shrinkage at temperatures lower than NiOBCZY. Up to 650 °C, ZnO showed higher conductivity compared to NiO for the same loading, mostly due to a higher extent of Zn incorporation inside the BCZY lattice as seen from the BCZY peak shift to a lower Bragg’s angle in X-ray diffractograms, and the bigger grain sizes of ZnO samples compared to NiO captured in scanning electron microscopy. At any temperature, the variation in conductivity as a function of sintering aid concentration followed the orders 1 mol% > 3 mol% > 5 mol% (for ZnO) and 1 mol% < 3 mol%~5 mol% (for NiO). This difference in conductivity trends has been attributed to the fact that Zn fully dissolves into the BCZY matrix, unlike NiO which mostly accumulates at the grain boundaries. At 600 °C, 1 mol% ZnOBCZY showed the highest conductivity of 5.02 mS/cm, which is, by far, higher than what has been reported in the literature for a Ce/Zr molar ratio <1. This makes ZnO a better sintering aid than NiO (in the range of 1 to 5 mol% addition) in terms of higher densification at a sintering temperature as low as 1350 °C, and higher conductivity. Full article

The present work is the first study exploring the potential of geopolymer foams based on fayalite slag, an industrial by-product, as the primary precursor, for lightweight and fireproof construction applications. The research involved the synthesis and characterization of geopolymer foams with varying water to solid ratio, followed by testing their physical and mechanical properties. The phase composition and microstructure of the obtained geopolymer foams were examined using powder XRD, Micro-CT and SEM. The geopolymer foams at optimal water to solid ratio (0.15) demonstrated 73.2% relative porosity, 0.92 g/cm³ apparent density and 1.3 MPa compressive strength. The use of an air-entraining admixture improved compressive strength to 2.8 MPa but lowered the relative porosity to 64.5%. Real-size lightweight panel (300 × 300 × 30 mm) specimens were prepared to measure thermal conductivity coefficient (0.243 W/mK) and evaluate size effect and the reaction to direct fire. This study demonstrates the successful preparation of geopolymer foam products containing 81% fayalite slag, highlighting its potential as a lightweight, insulating and fire-resistant material for sustainable construction applications. Full article

To mitigate CO₂ emissions from raw material decomposition and reduce the consumption of natural resources, this study investigated the use of mussel and oyster shell waste as secondary raw materials in earthenware production. Mineralogical, chemical and thermal analyses confirmed their suitability as sources of bio-calcite. Specimens incorporating various replacement levels (0–100%) showed no significant differences in key properties. Plates produced with mussel-derived bio-calcite in a pilot plant exhibited comparable properties to standard ceramics, demonstrating their industrial viability. CO₂ emissions were reduced by 14% and 10% in mussel and oyster shell-based ceramics, respectively, potentially saving up to 53 kgCO₂eq/t under the European Emissions Trading System, if the shells are classified as by-products. These findings demonstrated that bivalve shell waste can effectively replace mineral calcite in earthenware products, reducing CO₂ emissions and virgin raw material consumption, diverting waste from landfills and promoting sustainability in the ceramic industry. Full article

Cylindrical targets have a high utilization rate, but are difficult to manufacture. A large hollow ITTO segment with thin walls was prepared by cold isostatic pressure and two-stage sintering. The fabrication process yielded a segment with an outer diameter of 153 mm, an inner diameter of 135 mm, and a length of 700 mm, indicating a length to thickness ratio of up to 78. The dense and uniform green bodies ensure the achievement of high density and uniformity of the sintered body throughout its volume. The segment exhibited a high relative density of about 99.5% and a low resistivity of below 3.4 × 10⁻⁴ Ω·cm. The density and resistivity illustrate a minimal inhomogeneity along the length of the segment. The segment exhibits a cubic bixbyite phase and is characterized by densely packed fine grains with an average size of several microns. Therefore, these results establish a substantial foundation for the large-scale production of cylindrical ITTO segments. Full article

Nanostructures obtained as a by-product of the electrochemical synthesis of ZrO₂ nanotube membranes have scarcely received any attention despite their enormous potential. This is mainly due to their size properties, morphology, and composition. In the present work, these nanostructures are characterized, and their potential application as an additive in PVA-based coatings is analyzed. The characterization was performed by X-ray fluorescence, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction. The results showed that the nanostructures consist of tubular fragments generated during the formation of the ZrO₂ membrane, with a dimension of 626.74 nm in width, a length of 1906.39 nm, and a clear cubic structure. The ZrO₂-PVA coating, which is prepared by using the spin coating technique, presented a uniform and homogenous particle distribution, which was later confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The optical transparency and thermal resistance were evaluated through UV-Vis spectroscopy and thermogravimetric analysis, showing that the incorporation of ZrO₂ as an additive improved its UV absorption properties and thermal stability during the pyrolysis stage. The results suggest that the ZrO₂ nanostructures enhance the thermal and protective properties of the PVA-based coatings by acting as physical barriers and stabilizers within the polymer matrix. Full article

Urban glass waste is a significant by-product of residential areas, while scrap carbon fiber is a prevalent industrial by-product. This study explores an innovative approach to valorize these materials by producing foam glass (FG) for versatile applications, particularly in construction. A key challenge in FG production is enhancing its properties to meet increasingly stringent application-specific standards. The properties of FG are intrinsically linked to its porous structure, which depends on factors such as the foaming process. The oxidation of carbon fibers at high temperatures can induce a foaming effect, creating a porous matrix in the glass. This research investigates the effect of powdered recycled carbon fiber (PRCF)—an alternative method for recovering waste carbon fiber as a foaming agent for FG. PRCF was added at concentrations of 0.5%, 1%, and 1.5% by mass relative to powdered waste glass. Increasing PRCF content enhanced foaming and improved porosity, with total porosity rising from 47.18% at 0.5% PRCF to 65.54% at 1.5% PRCF, accompanied by a 50% reduction in compressive strength and a 68% decrease in thermal conductivity. The results demonstrate the feasibility of large-scale FG production with enhanced properties, achieved without substantial additional investment and by recovering two waste materials. This process supports sustainable development by promoting waste valorization and advancing circular economy principles. Full article

This research aims to develop self-healing geopolymer concrete (SHG) to address the limitations of conventional repair methods, including reduced thermal conductivity and density, while promoting sustainable construction. The incorporation of the self-healing method (SHM), crushed brick (CB), and minced water bottles (F-PET) resulted in reduced thermal conductivity, maintenance costs, and environmental impact. This study investigated the effects of varying amounts of CB, F-PET, and SHM on several properties, including flowability, setting times, densities, ductility index (DI), and mechanical strengths, across 13 different mixtures. Additionally, water absorption (WA%), residual weight loss (WL%), and relative dynamic modulus of elasticity (RDME%) were assessed following freeze–thaw cycles, alongside SEM analysis and thermal transport measurements of the SHG mixtures. The inclusion of up to 50% CB enhanced density and thermal conductivity but negatively affected other properties. In contrast, incorporating 25% F-PET led to modest improvements in mechanical, thermal, and durability properties; however, it did not reduce density and thermal conductivity as effectively as CB. Among the three mixtures containing both CB and F-PET, the formulation with 37.5% CB and 12.5% F-PET exhibited the lowest density (1650 kg/m³) and thermal conductivity (1.083 W/m·K). The self-healing capacity of SHM was demonstrated through its ability to close cracks, facilitated by the deposition of CaCO₃ under combined durability conditions. Incorporating 2%, 3%, and 4% SHM into the 37.5% CB and 12.5% F-PET mixture significantly improved key properties, including strength, water absorption, freeze–thaw resistance, SEM characteristics, density, and thermal conductivity. The addition of 4% SHM enhanced the mechanical performance of the geopolymer concrete (GVC) after 28 days, resulting in increases of 27% in compressive strength, 40.5% in tensile strength, 81% in flexural strength, and 61.6% in ductility index. Further, the inclusion of SHM improved density, reduced WA% and WL%, and enhanced RDME% after 300 freeze–thaw cycles. Specifically, thermal conductivity decreased from 1.8 W/m·K to 0.88 W/m·K, and density reduced from 2480 kg/m³ to 1760 kg/m³. Meanwhile, WA%, WL%, and RDME% improved from 3%, 4.5%, and 45% to 2%, 2.5%, and 50%, respectively. Full article

Recent archaeological sites dating to the late 19th and early 20th centuries have rarely been studied to date. Among the 500 “glassy” beads excavated from Dohouan (Côte d’Ivoire), elemental analyses reveal that fewer than half contain abnormally high alumina contents, associated with a soda–potash–lime flux (three compositional groups). The remaining beads are typical lead-based glass. The Raman spectra of the alumina-rich beads are quite complex due to their glass–ceramic nature, combining features similar to the vitreous phase of porcelain glaze with the presence of various crystalline phases (quartz, wollastonite, calcium phosphate, calcite). Organic residues are also observed. Colors are primarily produced by transition metal ions, although some specific pigments have also been identified. These characteristics suggest that the alumina-rich beads were manufactured by pressing followed by sintering, as described in patents by Richard Prosser (1840, UK) and Jean Félix Bapterosse (1844, France). A comparison is made with beads from scrap piles at the site of the former Bapterosse factory in Briare, France. This process represents one of the earliest examples of replacing traditional glassmaking with a ceramic process to enhance productivity and reduce costs. Full article

The synergistic combination of outstanding electrical properties and exceptional thermal stability holds significant implications for advancing piezoelectric ceramic applications. In this work, lead-free ((1−x)(0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃)-xBiFeO₃ (x = 0.08, 0.10, 0.12)) ceramics were synthesized using a conventional solid-state method, with systematic investigation of phase evolution, microstructural characteristics, and their coupled effects on electromechanical performance and thermal stability. Rietveld refinement analysis revealed a rhombohedral–tetragonal (R–T) phase coexistence, where the tetragonal phase fraction maximized at x = 0.10. This structural optimization enabled the simultaneous enhancement of piezoelectricity and thermal resilience. The x = 0.10 composition achieved recorded values of d₃₃ = 132 pC/N, g₃₃ = 26.11 × 10⁻³ Vm/N, and a depolarization temperature T_d = 105 °C. These findings establish BiFeO₃ doping as a dual-functional strategy for developing high-performance lead-free ceramics. Full article

Fiber–cement composites have been increasingly studied for sustainable construction applications, but durability issues—particularly fiber degradation in alkaline environments—remain a challenge. This study aimed to evaluate the individual and combined effects of furfurylated sisal fibers and nanoclay additions on the physical and mechanical performance of autoclaved fiber–cement composites, seeking to enhance fiber durability and matrix compatibility. All the composites were formulated with CPV-ARI cement and partially replaced with agricultural limestone to reduce the environmental impact and production costs. Sisal fibers (2 wt.%) were chemically modified using furfuryl alcohol, and nanoclays—both hydrophilic and surface-functionalized—were incorporated at 1% and 5% of cement weight. The composites were characterized for physical properties (density, water absorption, and apparent porosity) and mechanical performance (flexural and compressive strength, toughness, and modulus). Furfurylation significantly improved fiber–matrix interaction, leading to higher flexural strength and up to 100% gain in toughness. Nanoclay additions reduced porosity and increased stiffness, particularly at 5%, though excessive content showed diminishing returns. The combination of furfurylated fibers and functionalized nanoclay provided the best results in maintaining a compact microstructure, reducing water absorption, and improving mechanical resilience. Optical microscopy confirmed improved fiber dispersion and interfacial bonding in composites containing furfurylated fibers and functionalized nanoclay. These findings highlight the effectiveness of integrating surface-treated natural fibers with pozzolanic additives to enhance the performance and longevity of fiber–cement composites. Full article

The chemical and microstructural transformation of the surface of a 31.5 vol.% ZrB₂-31.5 vol.% HfB₂-27 vol.% SiC-10 vol.% C_CNT ultrahigh-temperature ceramic sample (where C_CNT refers to carbon nanotubes) was studied under the influence of a subsonic N₂-plasma flow with the addition of 5 mol% methane, simulating aerodynamic heating in the atmosphere of Titan. As in the case of pure nitrogen flow, it was found that silicon carbide is removed from the surface. Zirconium and hafnium diborides are partially transformed into a Zr-Hf-B-C-N solid solution in the experiment conducted. XRD, Raman spectroscopy, and SEM-EDX analysis show that the presence of C₂ in the N₂-CH₄ plasma flow leads to surface carbonization (formation of a graphite- and diamond-like coating with a high proportion of amorphous carbon), resulting in significant changes in the microstructure and emissivity, potentially affecting the catalytic properties of the surface. Full article

This paper systematically investigated the influence of sintering atmospheres, vacuum, and oxygen, on the microstructure and optical properties of Y₂O₃ ceramics. Compared with vacuum sintering, sintering in flowing oxygen atmosphere can effectively inhibit the grain growth of Y₂O₃ ceramics at the final stage of sintering and improve the uniformity of microstructure. After hot isostatic pressing, the samples pre-sintered at oxygen atmosphere showed good in-line transmittance from a visible-to-mid-infrared wavelength range (0.4–6.0 μm) except in the range of 2.8–4.1 μm. Spectral analysis showed that an obvious broadband absorption peak (2.8–4.1 μm) of characteristic hydroxyl groups is detected in the above samples. However, before densification, a low-temperature heat treatment at 600 °C under vacuum can effectively diminish the hydroxyl groups in Y₂O₃ ceramics. However, laser experiments in the ~1 μm wavelength range showed that although the Yb:Y₂O₃ ceramic carrying hydroxyl had obvious absorption in the 2.8–4.1 μm range, it had little effect on its laser oscillation in the ~1 μm wavelength. Yb:Y₂O₃ ceramics pre-sintered in an oxygen atmosphere at 1460 °C followed by hot isostatic pressing at 1440 °C achieved 12.85 W continuous laser output at room temperature, with a laser slope efficiency of 84.4%. Full article

The aim of this study is to evaluate the apical sealing ability of novel bioceramic-based (BCB) and widely used resin-based (RB) root canal sealers in combination with traditional or bioceramic-coated gutta-percha points. A total of 92 human single-root extracted teeth were endodontically treated and divided into three groups (A, B, and C) of 30 samples based on the endodontic sealer/type of gutta-percha points/obturation method used. One tooth sample was used for the negative and positive controls (each). Group A: BCB sealer BioRoot RCS (Septodont, Saint-Maur-des-Fossés, France)/bioceramic-impregnated gutta-percha TotalFill BC points (FKG Dentaire, La Chaux-de-Fonds, Switzerland)/cold hydraulic single-cone. Group B: BioRoot RCS (Septodont, France)/traditional Protaper Gold Gutta-Percha Points (Dentsply Sirona, Charlotte, NC, USA)/cold hydraulic single-cone. Group C: RB sealer AdSeal (Meta Biomed, Cheongju, Republic of Korea)/traditional Protaper Gold Gutta-Percha Points (Dentsply Sirona, USA)/warm vertical condensation. A dye penetration method was applied, and the length of apicocoronal penetration was measured using a surgical microscope. The data were statistically analyzed to evaluate differences at the 0.05 significance level. A significant difference was found between groups A and C, p = 0.0003, and groups B and C, p = 0.003. The data analysis proved that the BCB sealer using the cold hydraulic single-cone method ensured a substantially better seal than the RB sealer using the warm vertical condensation method. The choice of the type of gutta-percha points (bioceramic-coated or regular) appeared to be unimportant. No statistical significance was found between groups A and B, which indicates that using bioceramic-coated gutta-percha points does not bring any considerable benefit in view of a no-gap root canal obturation. Full article