Search Results (140)

This article concerns the issue of contactless estimation of the complex electrical permittivity of masonry materials by means of a microwave technique in the frequency domain. The main aim of the study was to develop a method enabling the determination of the real part of relative permittivity and the electrical conductivity of ceramic building materials using microwave reflection measurements, as well as to assess the applicability of the proposed approach for moisture diagnostics in porous media. The research was performed using a reflection-mode measuring setup comprising a vector network analyser and a broadband horn antenna, while measurements were carried out in the frequency range from 1 to 6 GHz on samples of solid ceramic brick with six gravimetric moisture levels. A one-dimensional model of electromagnetic wave propagation in the material was developed, considering complex permittivity, impedance transformation, and a calibration procedure compensating for the influence of the antenna and free-space propagation. Based on the fitting of the magnitude and phase characteristics of the reflection coefficient, the electrical parameters of the tested samples were estimated. The results obtained showed an increase in both permittivity and conductivity with increasing moisture content and revealed very good agreement with the reference values determined using the time-domain method. It can be concluded that the frequency-domain microwave approach may be effectively applied for contactless and non-destructive diagnostics and estimation of the dielectric properties and moisture content in ceramic materials. Full article

In the biodegradable metal class, Mg-based alloys are considered the most promising candidates for temporary implant manufacture. However, their high corrosion rate in physiological media is considered a main drawback for clinical translation. Conversion coatings address the limitations of Mg-based alloys and provide a strategy to control corrosion and improve surface biocompatibility. In this review paper, a detailed analysis of various conversion coating techniques, including ceramic conversion coatings based on metals, polymeric conversion coatings, bioactive conversion coatings, and hybrid conversion coatings, is performed. Attention is devoted to the corrosion process and parameters, as well as to the biological response in relation to bioactivity or biocompatibility. The main angiogenic and osteogenic signaling pathways are described based on the analyzed conversion coatings, and the evolution of the cellular response is estimated. Although significant progress has been made in the field, there are still challenges associated with synchronizing Mg alloy degradation with new bone formation and with precisely guiding cell signaling responses to achieve a desired biological response. An overall conclusion of the paper consists of the fact that conversion coatings are an important topic, as they can enhance the surface of Mg-based alloys, making them prone to clinical translation. Full article

Ti₂AlC, an important member of the MAX phase family, exhibits combined metallic and ceramic characteristics, showing potential for applications in conductive composites and high-temperature structural components. However, this phase possesses a narrow thermodynamic stability window, making high-purity synthesis challenging. Conventional solid-state synthesis requires temperatures exceeding 1300 °C, where aluminum volatilization and kinetic limitations of carbon diffusion lead to impurity phases such as TiC and Ti₃AlC₂. Based on the ionic transport characteristics of molten salt media, this study employed the eutectic NaCl-KCl molten salt method to synthesize Ti₂AlC using Ti, Al, and TiC powders within the temperature range of 1000–1150 °C. Systematic investigations revealed that an optimized raw powder composition (Ti:Al:TiC = 1:1.10:0.95) at 1100 °C yielded Ti₂AlC powders with 96.1% phase purity, high crystallinity, and typical laminated structure with stable stoichiometry (Ti/Al ≈ 2:1). Furthermore, Ag/Ti₂AlC composites demonstrated excellent electrical conductivity (resistivity of 5.72 μΩ·cm) and favorable mechanical properties, validating the applicability of this synthetic route for conductive composite materials. Full article

High-temperature particulate matter (PM) filtration remains a fundamental challenge, because most fiber filters not only face the challenge of high temperatures but also suffer from an inherent trade-off between capture efficiency, pressure drop, and service life. This paper reports a hierarchical layered zirconia (ZrO₂) ceramic fiber aerogel featuring a continuous multiscale gradient. The aerogel was prepared by gradient air-blown spinning, and the resulting structure has directional order, with the fiber diameter gradually decreasing from upstream to downstream, thus forming a pore size gradient and achieving hierarchical particle interception across multiple scales. This rational design simultaneously suppresses surface clogging and reduces flow resistance, resolving the longstanding trade-off between efficiency and permeability. Consequently, this aerogel achieves an ultra-high filtration efficiency of 99.96%, a low pressure drop of 156 Pa, and a high dust-holding capacity of 101 g m⁻². The material also exhibits outstanding mechanical toughness (80% compressive strain elasticity and 25.75% tensile fracture strain) and thermal stability up to 1000 °C. Moreover, it maintains over 99.95% filtration efficiency at high temperatures and can be fully regenerated through 800 °C heat treatment. This work establishes a structure-based design paradigm for high-temperature filtration media and provides a scalable pathway for next-generation industrial flue gas purification. Full article

This in vitro study assessed the impact of coconut milk, cow milk, and soybean oil on the surface roughness (Ra) of two milled (polymer-infiltrated ceramic network (PICN), Vita Enamic (EN) and resin nanoceramic (RNC), Cerasmart (CS)) and 3D-printed (VarseoSmile Crown plus (VS)) hybrid resin–ceramic materials. Standardized rectangular specimens were prepared and subjected to cyclic immersion in the test media at 37 °C for 30 days to simulate dietary exposure. Surface roughness was measured pre- and post-aging, and statistical analysis was performed using two-way ANOVA and paired t-tests (α = 0.05). All media significantly increased Ra across all materials (p < 0.001). While coconut milk and soybean oil caused comparable roughening (Ra up to 0.155 µm), cow milk exhibited a material-specific impact. It roughened milled materials (EN and CS) (Ra: 0.147–0.154 µm) significantly more than the 3D-printed material (VS) (Ra: 0.126 µm) (p < 0.05). Notably, all post-aging Ra values remained below the clinical bacterial adhesion threshold of 0.2 µm. In conclusion, while all tested dietary media significantly degraded the surface topography of hybrid resin–ceramics, the 3D-printed hybrid resin–ceramic material demonstrated superior resistance to cow milk compared to milled alternatives. Nonetheless, plaque retention risks remain clinically acceptable for all tested materials. Full article

To clarify the influence of the media filling ratio on fine particle production during ceramic ball grinding of magnetite, magnetite ore from the fine grinding stage of an industrial concentrator was investigated under different feed size classes and media filling ratios through grinding kinetics experiments. The generation behavior of the fine and finest particle fractions during ceramic ball grinding was systematically analyzed. The results indicate that particle size fractions with sizes less than or equal to 0.150 mm exhibit pronounced zero-order production characteristics under different filling ratios, with cumulative yields showing a strong linear relationship with grinding time. This zero-order behavior is insensitive to variations in the media filling ratio. Conversely, the generation rate of the finest size fraction is significantly affected by the media filling ratio. For coarse feed sizes, the generation rate of the finest fraction initially increases and then decreases with increasing filling ratio, reaching a peak value of 6.23%/min at a filling ratio of 35%. When the feed falls below 1.18 mm, the generation rate of the finest fraction shows a strong positive correlation with the ceramic ball filling ratio. Furthermore, based on the functional relationship between the generation rate of the finest size fraction and the mill input power, an energy–size model for magnetite ceramic ball grinding was established, providing a quantitative description of the variation in the finest particle yield with respect to the input energy and media filling ratio. The findings provide a theoretical foundation for optimizing media filling ratios, enhancing fine grinding performance, and controlling overgrinding in industrial applications. Full article

Reducing the surface roughness of thermal barrier coatings (TBCs) improves engine aerodynamic efficiency and mitigates CMAS adhesion, but turbine blades’ complex geometries demand low-cost, damage-mzitigated finishing. This work employed drag finishing with spherical ceramic media, establishing a discrete element method (DEM) model to quantify abrasive trajectories, contact forces, and energy distributions, combined with surface characterization to study abrasive effects on columnar YSZ and modified GZO topcoats. Results show roughness reduction is constrained by fracture toughness and columnar unit local fracture, leading to different decay rates and late-stage improvement between YSZ and GZO. Introducing smaller abrasives enhances packing density via void filling, strengthens microscale cutting, and reduces strong normal impacts, promoting surface uniformization and suppressing localized damage. These findings guide mechanistic understanding of drag finishing on multi-material TBCs, as well as abrasive grading design and process parameter optimization. Full article

Inert media such as plastic, ceramic or zeolite are conventionally used for wastewater biofiltration. They all need microbial activation and are essentially chosen for their surface/mass ratio, since biofiltration is entirely performed within the surface biofilm. Using biodegradable media may enhance the sustainability of the system, but it should not produce decomposition-related pollutants. Due to their surface extension, peculiar microbiota and structural resistance, aquatic moss appears to be a very good support for biofilters. Thus, in this study, we evaluated aquatic moss mats as an alternative medium for biofiltration of aquaculture or aquaponic effluents. Two moss species, Taxiphyllum barbieri and Leptodictyum riparium, were tested, also for their contribution on nitrogen metabolism and potential negative effects on hydroponic plants cultivation, due to competition for nutrients. Our proof-of-concept research demonstrates equivalence in real conditions, as inert and moss media exhibited comparable rates; however, the amount of moss required can be several times lower than that of any competing media. Preliminary results suggest the possibility to integrate moss-based biofilters in aquaculture and aquaponics technologies. Full article

Ceramic balls, as an emerging grinding medium, require a systematic method for optimizing their size distribution in wet ball mills. This study proposes an innovative approach that integrates Duan’s semi-theoretical ball diameter formula with breakage statistical mechanics to determine the optimal ceramic ball size distribution. The ideal ball diameters for grinding 2.36–3.0 mm, 1.18–2.36 mm, 0.60–1.18 mm, and 0.30–0.60 mm tungsten ore were identified as 55 mm, 50 mm, 35 mm, and 20 mm, respectively. Subsequently, the optimal ball size distribution was formulated as CB3: Ø55 mm:Ø50 mm:Ø35 mm:Ø20 mm = 30%:40%:20%:10%. Comparative sieve analysis and discrete element method (DEM) simulations confirmed that the CB3 distribution yields the highest proportion of qualified particles, the most favorable collision frequency, and the greatest kinetic energy among all tested configurations. The proposed method demonstrates both accuracy and practicality, providing a theoretical foundation for the industrial application of ceramic ball grinding systems. Full article

With the advancement of aerospace equipment toward high-speed and heavy-duty applications, conventional forced lubrication systems are facing significant challenges in terms of reliability and adaptability to complex operating conditions. Porous medium materials, owing to their unique self-lubricating and oil-retention capabilities, are regarded as an ideal lubrication solution. However, their seepage behavior is governed by the strong coupling effects of microscopic pore structures and fluid physicochemical properties, the mechanisms of which remain inadequately understood, thereby severely constraining the design and application of high-performance lubricating materials. To address this, this paper systematically reviews recent research progress on seepage behavior in porous media, with the aim of establishing a correlation between microstructural characteristics and macroscopic performance. Starting from the characterization of porous media, this work comprehensively analyzes the structure–seepage relationships in porous polymers, metal foams, and porous ceramics, and constructs a multi-scale theoretical framework encompassing macroscopic continuum theories, mesoscopic lattice Boltzmann methods (LBM), pore network models, and microscopic molecular dynamics. The advantages and limitations of experimental measurements and numerical simulation approaches are also compared. In particular, this study critically highlights the current neglect of key interfacial parameters such as surface wettability and pore roughness, and proposes an in-depth investigation into the seepage mechanisms of polyimide porous cage materials based on LBM. Furthermore, the potential application of emerging research paradigms such as data-driven approaches and intelligent computing in seepage studies is discussed. Finally, it is emphasized that future efforts should focus on developing deeply integrated cross-scale simulation methodologies, strengthening multi-physics coupling and artificial intelligence-assisted research, and advancing the development of intelligent porous lubricating materials with gradient structures or stimulus-responsive characteristics. This is expected to provide a solid theoretical foundation and technical pathway for the rational design and optimization of high-performance lubrication systems. Full article

The objective of this study was to evaluate whether any coating material would have a beneficial influence on maintaining color stability and surface roughness and to what extent an uncoated resin composite can keep its original color. The study evaluated three direct composite resins (Gradia Direct Anterior A2, Tetric EvoCeram A2, Filtek Z550 A2) using 30 samples per material (1 mm thick, 14 × 10 × 1 mm). Samples were prepared in 3D-printed molds, light-cured for 40 s, and initially smoothed with abrasive paper (grit 400–2000). The surface treatments applied were as follows: group 1—polished with a brush and Compo + polishing paste, group 2—conditioned with 37% phosphoric acid, ScotchBond adhesive applied, light-cured. All samples were cleaned ultrasonically for 5 min. Initial surface roughness and color were measured with a profilometer and spectrophotometer. Samples were then immersed in distilled water (control at 37 °C), Coca-Cola and red wine (at 10 °C) with surface roughness and color changes measurements taken on days 1, 7, 14 and 90. Immersion media were refreshed weekly. The most notable color changes after immersion in coloring solutions were observed in the groups treated with Coca-Cola and red wine compared with the control group in distilled water. Tetric EvoCeram sealed and Gradia sealed maintained the greatest resistance to perceptible coloration over 90 days, while Filtek Z550 performed the poorest. Tetric EvoCeram sealed maintained the greatest color stability (ΔE < 3.5 at 90 days), whereas Filtek Z550 sealed showed early degradation. Roughness is often decreased by surface sealing. As immersion time rises, unsealed surfaces often become noticeably rougher than sealed ones. This study simulates the oral environment and the exposure of restorative materials to staining agents. As the loss of esthetic properties over time is a continuous problem, the clinical significance of this research lies in demonstrating how a restorative material could resist pigmentation, when in contact with well-known high staining beverages, in order to maintain its esthetic properties and remain suitable for long-term use in the oral cavity. Moreover, the hypothesis that a coating material would protect the resin composite surface and reduce discoloration and surface roughness was tested. Full article

Background: Gastroesophageal reflux disease (GERD) exposes restorative materials to gastric acid, which may compromise their esthetic and optical properties. Limited evidence exists regarding the performance of different CAD/CAM ceramics under acidic challenges. Methods: Forty CAD/CAM ceramic discs were prepared (n = 10 per group): high-translucency zirconia (Z; Ceramill Zolid Gen-X), lithium disilicate (E; IPS e.max CAD), zirconia-reinforced lithium silicate (S; VITA Suprinity), and hybrid ceramic (C; Cerasmart 270). Specimens were immersed in simulated gastric acid (0.06 M HCl, pH 1.2) at 37 °C for 96 h. Color difference (ΔE) and translucency parameter (ΔTP) were recorded before and after immersion using a spectrophotometer. Data were analyzed using one-way ANOVA with Tukey’s post hoc test (α = 0.05). Results: All materials exhibited changes in color and translucency after acidic immersion. Group Z demonstrated the lowest ΔE values, indicating the best color stability, whereas group C showed the highest ΔE and a significant reduction in ΔTP. Groups E and S revealed moderate but clinically acceptable changes. Intergroup differences were statistically significant (p < 0.05). Conclusions: Exposure to simulated gastric acid as in (GERD) resulted in measurable alterations in the optical properties of CAD/CAM ceramic materials. The extent of color change and translucency loss differed among the materials tested. High-translucency zirconia (Z) exhibited the greatest stability, while hybrid ceramic (C) showed the most pronounced changes. Zirconia-reinforced lithium silicate (S) and lithium disilicate (E) demonstrated moderate alterations, falling between these two extremes. Full article

This study aimed to evaluate the effect of popular beverages, coffee, matcha, and protein isolate, on the microhardness and color stability of feldspar glass ceramic (VB) and nano-ceramic hybrid composite (GD) CAD/CAM materials. Three hundred specimens were prepared and divided into control and immersion groups (water, coffee, matcha, protein). Vicker’s microhardness (HN) was recorded for the control group and post-immersion groups, while color changes were measured before and after immersion. Microhardness values (HN) and color change (ΔE00) were statistically analyzed using the Kruskal–Wallis test followed by Dunn’s post hoc test (p < 0.05). Results: The HN values of all VB and GD immersion subgroups were significantly lower than those of the control groups (p < 0.001). The VB water immersion group had a significantly lower HN than the protein and matcha immersion groups. The GD immersion groups showed no significant difference in HN between them (p > 0.05). VB had a significantly lower ΔE00 (>3.5) and higher HN (790.8 ± 123.62 kgf/mm²) than GD (175.22 ± 28.95 kgf/mm²) (p < 0.001). Coffee caused the greatest ΔE00 in both VB and GD, whereas protein caused the lowest ΔE00 in GD. Conclusion: The study revealed that the feldspar glass ceramic CAD/CAM material had higher microhardness and color stability than the nano-ceramic hybrid composite. Immersion reduces the microhardness and color stability of CAD/CAM ceramics. Matcha and protein have less impact on glass ceramic microhardness, with protein causing less discoloration in nano-ceramic hybrid composites than other immersion media. Full article

Lithium-containing zeolites are receiving significant attention due to their intriguing properties in various industrial applications, mainly related to gas separation and catalyzed processes. This paper presents an in-depth exploration of a nucleation strategy aimed at producing porous ceramic monoliths enriched with lithium zeolites. The synthesis was obtained by means of a geopolymer gel conversion, carried out by submerging either sodium- or lithium-rich geopolymers in lithium hydroxide solutions and performing a hydrothermal treatment. A full factorial design of experiments (DoE) was adopted to investigate the effect of LiOH molarity, treatment temperature, and time on the zeolite content in the samples. The most abundant and recurring zeolites obtained were Li-ABW (ABW) and lithium edingtonite (EDI). Concerning the lithium/sodium-containing systems, the competing presence of sodium directed the nucleation towards faujasite as well, together with minor amounts of other zeolites. In contrast, in pure lithium treatment media, the samples showed just ABW and EDI as the only crystalline phases. Full article

This study investigates the performance variations in chemically bonded phosphate ceramic (CBPC) cement under different media (water and 3% NaCl solution) environments subjected to varying numbers of freeze–thaw cycles, including changes in compressive strength, mass loss rate, phase composition, microstructure, external pH, and ion concentration, with the aim of elucidating its long-term durability degradation mechanisms and microstructural evolution. The results show that both the mass and compressive strength of CBPC cement first increase and then decrease with increasing freeze–thaw cycles. After 400 cycles, the compressive strength decreases by 29.91% in water and 25.16% in salt solution. The pH value rises with cycling, along with increased concentrations of K⁺, Mg²⁺, and PO₄³⁻, while Na⁺ and Cl⁻ concentrations decrease in salt solution. XRD/Rietveld analysis reveals that the content of MgKPO₄·6H₂O decreases from 28.1% to 19.5% (water) and 20.7% (salt), with a gradual reduction in crystallinity. TG/DTG and FTIR results confirm these findings, showing extensive microcracking in hydration products, which aligns with the observed macro-performance changes. Full article