Search Results (102)

Fly ash, as the main solid waste of coal-fired power plants, is an environmental problem that needs to be solved due to its massive accumulation. The mechanical properties and optimization mechanism of lightweight aggregate concrete prepared by using new single-cylinder rotary kiln fly ash ceramic granules as aggregate were systematically investigated. Through orthogonal experimental design, combined with macro-mechanical testing and microscopic characterization techniques, the effects of cement admixture and ceramic granule admixture on the properties of concrete, such as compressive strength, split tensile strength, and modulus of elasticity, were analyzed, and the optimization scheme of key parameters was proposed. The results show that the new single rotary kiln fly ash ceramic particles significantly improve the mechanical properties of concrete by optimizing the porosity (water absorption ≤ 5%), and its 28-day compressive strength reaches 46~50.9 MPa, which is 53.3~69.7% higher than that of the ordinary ceramic concrete, and the apparent density is ≤1900 kg/m³, showing lightweight and high-strength characteristics. X-ray diffraction (XRD) analysis shows that the new ceramic grains form a more uniform, dense structure through the synergistic effect of internal mullite crystals and dense glass phase; computed tomography (CT) scanning shows that the total volume rate of cracks of the new ceramic concrete was reduced by up to 63.8% compared with that of ordinary ceramic concrete. This study provides technical support for the utilization of fly ash resources, and the prepared vitrified concrete meets the demand of green building while reducing structural deadweight (20~30%), which has significant environmental and economic benefits. Full article

This study presents a comprehensive mineralogical, chemical, and technological characterization of clay schist samples from Barrancos (southern Portugal), aiming to evaluate their suitability for sustainable ceramic production. The work integrated X-ray diffraction (XRD), X-ray fluorescence (XRF), thermal analysis (TGA, DTA, and dilatometry), and other assays. After simple dry milling, the clay schist samples’ texture supported their use in plastic ceramic pastes but indicated a need for blending with coarser materials to meet extrusion requirements. Mineralogical analysis confirmed a dominance of illite (82%–85%), with minor kaolinite and chlorite. Chemical composition revealed significant Al₂O₃ (21.65%–28.24%) and SiO₂ (52.27%–58.99%) contents, while Fe₂O₃ (4.41%–8.89%) supported their use in red ceramics. The presence of K₂O (up to 5.43%) and Na₂O (up to 1.63%) contribute to the fluxing capacity, promoting vitrification. Cation exchange capacity and specific surface area were low, consistent with the mineralogy dominated by illite and kaolinite. Thermal analysis confirmed the formation of mullite after firing at 1100 and 1150 °C, alongside residual quartz and hematite. The ceramic bodies exhibited progressive densification and strength enhancement with increasing temperature. The mixture of two selected samples showed good mechanical properties and lower porosity, with no efflorescence observed. These results underscore the potential of these schists as sustainable raw materials for ceramic production, promoting regional economic valorization and reducing environmental impact by utilizing local resources. Full article

This study investigates the potential of residual clays from a traditional ceramic-producing region in southern Portugal as raw materials for red ceramic applications. This work aims to support more sustainable ceramic practices through the local valorization of naturally available, underutilized clay resources. A multidisciplinary approach was employed to characterize clays, integrating mineralogical (XRD), chemical (XRF), granulometric, and thermal analyses (TGA/DTA/TD), as well as technological tests on plasticity, extrusion moisture, shrinkage, and flexural strength. These assessments were designed to capture both the intrinsic properties of the clays and their behavior across key ceramic processing stages, such as shaping, drying, and firing. The results revealed a broad diversity in mineral composition, particularly in the proportions of kaolinite, smectite, and illite, which strongly influenced plasticity, water demand, and thermal stability. Clays with higher fine fractions and smectitic content exhibited excellent plasticity and workability, though with increased sensitivity to drying and firing conditions. Others, with coarser textures and illitic or feldspathic composition, demonstrated improved dimensional stability and lower shrinkage. Thermal analyses confirmed expected dehydroxylation and sintering behavior, with the formation of mullite and spinel-type phases contributing to densification and strength in fired bodies. This study highlights that residual clays from varied geological settings can offer distinct advantages when matched appropriately to ceramic product requirements. Some materials showed strong potential for direct application in structural ceramics, while others may serve as additives or tempering agents in formulations. These findings reinforce the value of integrated characterization for optimizing raw material use and support a more circular, resource-conscious approach to ceramic production. Full article

A ceramic–metal composite was synthesized using sol–gel and electrospinning methods to serve as a SERS substrate. The precursors used were tetraethyl orthosilicate, aluminum nitrate, and zirconium, and polyvinylpyrrolidone was added to electrospun nonwoven fibrous membranes. The membranes were sintered, decorated with silver nanoparticles. The enhancement substrates were made of fibers of cylindric morphology with an average diameter of approximately 190 nm, a smooth surface, and 9 nm spherical particles decorating the surface of the fibers. The enhancement capacity of the substrates was tested using pyridine, methyl orange, methylene blue, crystal violet, and Eriochrome black T at different concentrations with Raman spectroscopy to determine whether the size and complexity of the analyte has an impact on the enhancement capacity. Enhancement factors of 2.53 × 10², 3.06 × 10¹, 2.97 × 10³, 4.66 × 10³, and 1.45 × 10³ times were obtained for the signal of pyridine, methyl orange, methylene blue, crystal violet, and Eriochrome black T at concentrations of 1 nM. Full article

Mining activities generate large volumes of tailings with significant environmental impact but also the potential for sustainable reuse in construction materials. This study evaluates the production of ceramic aggregates from mixtures of clay, sand, and iron ore waste subjected to thermal treatment at temperatures ranging from 600 to 1100 °C. The influence of calcination temperature on mineralogical transformations and mechanical integrity was investigated using X-ray diffraction (XRD) and the $\alpha$-Treton parameter, derived from standardized impact resistance testing. The results indicate that the formation of metakaolinite between 700 and 900 °C enhances mechanical resistance, while higher temperatures (>900 °C) lead to structural degradation, followed by partial recovery due to mullite crystallization. The $\alpha$-Treton curve exhibited clear correlation with the phase changes identified by XRD, demonstrating its applicability as a low-cost, sensitive proxy for optimizing thermal activation. A simplified methodology is proposed to optimize the thermal activation of such materials by correlating firing temperature with mineralogical evolution and mechanical integrity, contributing to the development of sustainable ceramic aggregates for pavement applications. Full article

Microstructural, mechanical and qualitative phase identification of durable mullite-based ceramics obtained by utilization of waste clay–diatomite has been studied. Mullite-based ceramics were fabricated using waste clay–diatomite from the Baroševac open-cast coal mine, Kolubara (Serbia). The raw material consists mainly of SiO₂ (70.5 wt%) and a moderately high content of Al₂O₃ (13.8 wt%). In order to achieve the stoichiometric mullite composition (3Al₂O₃-2SiO₂), the raw material was mixed with an appropriate amount of Al(NO₃)₃·9H₂O. After preparing the precursor powder, the green compacts were sintered at 1300, 1400 and 1500 °C for 2 h. During the process, rod-shaped mullite grains were formed, measuring approximately 5 µm in length and a diameter of 500 nm (aspect ratio 10:1). The microstructure of the sample sintered at 1500 °C resulted in a well-developed, porous, nest-like morphology. According to the X-ray diffraction analysis, the sample at 1400 °C consisted of mullite, cristobalite and corundum phases, while the sample sintered at 1500 °C contained mullite (63.24 wt%) and an amorphous phase that reached 36.7 wt%. Both samples exhibited exceptional compressive strength—up to 188 MPa at 1400 °C. However, the decrease in compressive strength to 136 MPa at 1500 °C is attributed to changes in the phase composition, the disappearance of the corundum phase and alterations in the microstructure. This occurred despite an increase in bulk density to 2.36 g/cm³ (approximately 82% of theoretical density) and a complete reduction in open porosity. The residual glassy phase (36.7 wt% at 1500 °C) is probably the key factor influencing the mechanical properties at room temperature in these ceramics produced from waste clay–diatomite. However, the excellent mechanical stability of the samples sintered at 1400 and 1500 °C, achieved without binders or additives and using mined diatomaceous earth, supports further research into mullite-based insulating materials. Mullite-based materials obtained from mining waste might be successfully used in the field of energy-efficient refractory materials and thermal insulators. for high-temperature applications Full article

Original compositions of electrical ceramics have been developed and tested using marshalite and wollastonite as raw materials. An analysis of the equilibrium states of the created porcelain masses at different temperatures in Na₂O-Al₂O₃-SiO₂ and K₂O-Al₂O₃-SiO₂ systems was carried out. The amount of melt in these systems was calculated based on equilibrium flux curves. The characteristics of the sintering process of the masses were identified. A scheme for the formation of key secondary needle-like mullite during the thermal treatment of the masses was outlined and the temperature intervals for the formation of intermediate compounds were found. X-ray diffraction patterns and micrographs of the synthesized samples were decoded, and the phase composition and microstructure of the samples were analyzed. The effective influence of silica component dispersion on the mineral formation processes during the sintering of the porcelain masses in model samples of feldspar compositions with quartz sand and marshalite was noted. The optimal firing temperatures for full mineral formation and structure formation have been determined, as well as the physical–mechanical and dielectric properties of the obtained ceramic samples. Full article

An aqueous mixture of three compounds (atrazine, carbamazepine, and p-chlorobenzoic acid) has been treated by photochemical processes including photolysis and photocatalysis with 10.7% TiO₂ supported on ceramic foams of mullite. Experiments were conducted in both ultrapure water and in a secondary effluent from a municipal wastewater treatment plant. Radiation at 365 nm was totally inefficient in the photolytic process carried out in ultrapure water; however, some sensitization phenomena were observed when municipal wastewater was used as a bulk matrix. In the latter case, conversion values in the range of 20–30% were obtained after 2 h. The photocatalytic process was much more effective experiencing conversions above 80% after just 80 min of reaction. The nature of the matrix used exerted a significant influence. Use of municipal wastewater slowed down the process due to the scavenging character of the natural organic matter content. Test runs in the presence of carbonates and t-butyl alcohol suggested that radical carbonates play some role in contaminant abatement, and secondary radicals generated after the t-BuOH attack by HO^● radicals should also be considered in the reaction mechanism. A pseudo-empirical mechanism of reactions sustains the experimental result obtained, acceptably modeling the effects of a water matrix, scavenger addition, and radiation volumetric photon flux. Full article

The slurry collected from the waste water resulting from ceramic tile processing contains significant amounts of quartz, kaolinite, and mullite, along with traces of iron hydroxides as observed using XRD analysis coupled with mineralogical optical microscopy (MOM). Such an admixture would be ideal for the development of ecologic building materials. Microstructural conditioning enhances the binding properties of kaolinite. Therefore, the influence of the vibration compaction of the moistened slurry at 30% humidity on the compressive strength was assessed. The compressive strength of the unvibrated sample is about 0.8 MPa with failure promoted by the microstructural unevenness. Several vibration amplitudes were tested from 20 to 40 mm. The optimal vibration mode was obtained at an amplitude of 25 mm for 10 min, ensuring a compressive strength of 2.37 MPa with a smooth and uniform failure surface involved within the binding layer as observed using SEM microscopy. The samples prepared under optimal conditions were thermally consolidated at 700, 800, and 900 °C below the mullitization temperature to ensure a low carbon footprint. XRD results reveal kaolinite dehydration in all fired samples, inducing its densification, which increases with increasing heating temperature. SEM coupled with EDS elemental investigations reveal that the dehydrated kaolinite better embeds quartz and mullite particles, ensuring a compact microstructure. The binding strength increases with the firing temperature. The mullite particles within the samples fired at 900 °C induce the partial mullitization of the dehydrated kaolinite matrix, increasing their homogeneity. The compression strength of the fired samples is temperature dependent: 4.44 MPa at 700 °C; 5.88 MPa at 800 °C, and 16.87 MPa at 900 °C. SEM fractography shows that failure occurs due to the dehydrated kaolinite matrix cracks and the quartz particles. The failure is rather plastic at low temperatures and becomes brittle at 900 °C. Reducing the firing temperature and treatment time reduces the carbon footprint of the consolidated ceramic parts. Samples fired at 700 °C exhibit a compressive strength comparable to low quality bricks, those fired at 800 °C exhibit a strength comparable to regular bricks, and those fired at 900 °C exhibit a superior strength comparable to high-quality bricks. Full article

A Miocene carbonatic clay quarried in Transylvania (Romania) has been used for more than 100 years for the production of traditional ceramic ware, bricks, and tiles. To investigate the mineralogical and microstructural changes of this clay when heated between 700 °C and 1200 °C, a combination of polarized light optical microscopy, X-ray powder diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectrometry, and Fourier transform infrared spectroscopy was applied. Primary mineral phases such as illite, muscovite, feldspar, carbonate, Fe oxyhydroxides, and quartz undergo a gradual thermal alteration and form, besides a glassy phase, a wide range of minerals such as gehlenite, clinopyroxene, feldspar, maghemite, hematite, mullite, and α-cristobalite. These firing phases can be regarded as ‘ceramic markers’. A comparison between the data obtained by several methods is discussed. The combination of the optical appearance and the microstructure on one side, and the specific associations of primary phases and ceramic markers on the other side, can be used as a ‘ceramic thermometer’ in estimating the firing temperature for ancient ceramics. Full article

This study explores the optimization of foam ceramic materials through experimental research and mathematical modeling. The goal was to enhance mechanical strength, thermal insulation, porosity, water absorption, and density by adjusting composition and firing conditions. Regression analysis and response surface methodology were used to assess the effects of loam, fly ash content, and the firing temperature. The optimal composition of 60–65% loam, 10% fly ash, and a firing temperature of 950–1000 °C yielded foam ceramics with a bulk density of 680–700 kg/m³, a compressive strength of 3.5–4 MPa, and a thermal conductivity of 0.135–0.140 W/(m·K). Controlled porosity (70–72%) enhanced insulation while maintaining structural integrity. X-ray diffraction confirmed mullite, quartz, and cristobalite phases, with mullite improving mechanical properties. This research demonstrates the potential of optimized foam ceramics for energy-efficient construction. Mathematical modeling and experimental validation provide a pathway for developing lightweight, high-performance ceramic materials. Future work should refine sintering processes, explore new additives, and evaluate the long-term performance. Full article

Mullite–corundum ceramics are pivotal in heat transfer pipelines and thermal energy storage systems due to their excellent mechanical properties, thermal stability, and chemical resistance. Establishing relationships and mechanisms through traditional experiments is time-consuming and labor-intensive. In this study, gradient boosting regression (GBR), random forest (RF), and artificial neural network (ANN) models were developed to predict essential properties such as apparent porosity, bulk density, water absorption, and flexural strength of mullite–corundum ceramics. The GBR model (R² 0.91–0.95) outperformed the RF and ANN models (R² 0.83–0.89 and 0.88–0.91, respectively) in accuracy. Feature importance and partial dependence analyses revealed that sintering temperature and K₂O (~0.25%) positively affected bulk density while negatively influencing apparent porosity and water absorption. Additionally, sintering temperature, additives, and Fe₂O₃ (optimal content ~5% and 1%, respectively) were positively related to flexural strength. This approach provided new insight into the relationships between feedstock compositions and sintering process parameters and ceramic properties, and it explored the possible mechanisms involved. Full article

Mullite, 3Al₂O₃·2SiO₂, is a material with excellent thermal and mechanical properties. Two types of waste sand, rich in impurities, were employed as precursors for mullite ceramic synthesis. Two different synthesis routes were used: (i) solid-state reactions involving a sand and bauxite mixture, and (ii) precipitation synthesis, where alumina was deposited on sand particle surfaces; the sintering process was performed at temperatures ranging from 1300 °C to 1400 °C. Mullite was obtained as the main phase when the ceramics were obtained by solid-state reactions opposite to the second method, in which a composite ceramic with a specific microstructure, i.e., sand particles embedded in a matrix formed by alumina crystals, was assessed by electronic microscopy. The main properties, i.e., the apparent density, open porosity, compressive strength and thermal expansion coefficient (CTE) of the obtained materials were influenced by the composition and microstructure as well as the sintering temperature. The ceramics in which mullite was the main phase had slightly lower CTE’s and did not exhibit any phase transition in the 20–900 °C range. The results presented in this article highlight the importance of the synthesis route correlated with the nature of the precursors, the type and amount of impurities and the sintering temperature. Full article

In-situ porous mullite ceramics with varying pore size and porosity were fabricated using 3D printing. The pore size was controlled by adjusting the size of polymethyl methacrylate (PMMA) microspheres. The effect of sintering temperature on phase evolution was also examined. Additionally, the impact of PMMA microsphere size and content on the rheological properties of the printing inks was investigated. The results indicated that alumina and microsilica fully transformed into mullite at 1550 °C. The influence of PMMA microsphere content and size on the porosity, mechanical properties, and thermal conductivity of 3D-printed porous mullite ceramics was also studied. The 3D-printed porous mullite ceramic prepared with 15 μm PMMA microspheres exhibited a porosity of 44.38%, a flexural strength of 58.53 MPa, and a thermal conductivity of 2.21 W/(m·K). This printing strategy offers a simple and effective method for fabricating porous mullite ceramics. Full article

To enhance the mechanical properties and high-temperature performance of cordierite–mullite composite ceramics, yttrium oxide (Y₂O₃), a rare earth metal oxide, was employed as a sintering aid to fabricate these composites via in situ synthesis and non-pressure sintering. This study systematically investigated the formation mechanisms of the cordierite and mullite phases and examined the effects of yttrium oxide on the densification behavior, mechanical properties, volumetric stability, and thermal shock resistance. The results indicate that incorporating yttrium oxide (1.5–6.0 wt%) not only promoted the formation of the cordierite phase but also refined the microstructure and enhanced the thermal shock stability at a sintering temperature of 1350 °C. An optimal addition of 3 wt% yttrium oxide ensures that the primary phases are cordierite and mullite, with a microstructure characterized by uniformly distributed micropores, hexagonal short-columnar cordierite, and interlocking rod-like mullite, thereby significantly improving both the mechanical properties and thermal shock stability. Specifically, the room-temperature compressive strength increased by 121%, the flexural strength increased by 177%, and, after three thermal shock cycles at 1100 °C, the retention rates for compressive and flexural strengths were 87.66% and 71.01%, respectively. This research provides a critical foundation for enhancing the mechanical properties and high-temperature service performance of cordierite–mullite saggers used in lithium battery cathode materials. Full article