Search Results (521)

Porous ceramics have been widely used in various fields. In this paper, porous ceramics with through-hole structures were prepared using a novel and eco-friendly gel casting method with carrageenan as the gelling agent. Especially, the idea of large size particle stacking is introduced into the gel casting process. By introducing large size alumina aggregates as raw materials, and small size micropowders as filling materials, micropores were directly formed after the green body was sintered. To tune the pore size, pore structure, gas permeability, the strength of the final porous ceramics, the components of the raw materials including the alumina aggregates, the filling materials, and sintering additives in the slurry were precisely designed. Porous Al₂O₃-based ceramics with high gas permeability, high flexural strength, and moderate porosity were finally obtained. Full article

To elucidate the key material parameters governing the tribological performance of ceramic composites under dry sliding against steel, this study presents a comprehensive comparative assessment of the microstructural characteristics, mechanical performance, and tribological behavior of two alumina–zirconia (Al₂O₃–ZrO₂) ceramic composites, each reinforced with a 42 vol.% carbide phase: zirconium carbide (ZrC) and tungsten carbide (WC). Specifically, tungsten carbide (WC) was selected for its exceptional bulk mechanical properties, while zirconium carbide (ZrC) was chosen to contrast its potentially different interfacial reactivity against a steel counterface. ZrC and WC were selected as reinforcing phases due to their high hardness and distinct chemical and interfacial properties, which were expected to critically affect the wear and friction behavior of the composites under demanding conditions. Specimens were consolidated via spark plasma sintering (SPS). The investigation encompassed macro- and nanoscale hardness measurements (Vickers hardness HV₁, HV₁₀; nanoindentation hardness H), elastic modulus (E), fracture toughness (K_IC), coefficient of friction (COF), and specific wear rate (W_s) under unlubricated reciprocating sliding against 100Cr6 steel at normal loads of 10 N and 25 N. The Al₂O₃–ZrO₂–WC composite exhibited an ultrafine-grained microstructure and markedly enhanced mechanical properties (HV₁₀ ≈ 20.9 GPa; H ≈ 33.6 GPa; K_IC ≈ 4.7 MPa·m^½) relative to the coarse-grained Al₂O₃–ZrO₂–ZrC counterpart (HV₁₀ ≈ 16.6 GPa; H ≈ 27.0 GPa; K_IC ≈ 3.2 MPa·m^½). Paradoxically, the ZrC-reinforced composite demonstrated superior tribological performance, with a low and load-independent specific wear rate (W_s ≈ 1.2 × 10⁻⁹ mm³/Nm) and a stable steady-state COF of approximately 0.46. Conversely, the WC-reinforced system exhibited significantly elevated wear volumes—particularly under the 25 N regime—and a higher, more fluctuating COF. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX) of the wear tracks revealed the formation of a continuous, iron-enriched tribofilm on the ZrC composite, derived from counterface material transfer, whereas the WC composite surface displayed only sparse tribofilm development. These findings underscore that, in steel-paired tribological applications of Al₂O₃–ZrO₂–based composites, the efficacy of interfacial tribolayer generation can supersede intrinsic bulk mechanical attributes as the dominant factor governing wear resistance. Full article

Objectives: The aim of this study was to compare the hardness, chemical composition, and microstructure of various self-ligating ceramic orthodontic brackets and enamel. Methods: Sixty ceramic brackets (0.022″ × 0.028″) from six different orthodontic firms (Damon^® Clear 2, Genius^® Crystal, Empower^® 2 Clear, Clarity^® Ultra, Alpine SL^® Clear, and Experience Ceramic^®) were tested using a microhardness tester and a scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS). Results: The hardness of the ceramic brackets ranged from 1969.8 to 2567.3 VH. The statistical analysis using the Kruskal–Wallis and Mann–Whitney tests revealed significant differences in microhardness between most of the ceramic brackets. Additionally, this study found that passive self-ligating brackets exhibited a significantly higher hardness than that of active self-ligating brackets (p = 0.01). The SEM analysis showed that the variations in the oxygen and alumina composition between the six bracket types were also statistically significant (p = 0.01). Conclusions: Among all of the ceramic brackets tested, Alpine^® brackets displayed the lowest hardness values, making them a potential choice for minimizing enamel damage. Notably, the hardness of self-ligating ceramic brackets was found to be at least six times greater than that of enamel, raising concerns about their potential to cause trauma to the enamel of antagonistic teeth. Consequently, the researchers recommend avoiding bonding ceramic brackets to the mandibular teeth or elevating occlusion with turbo-bites to prevent traumatic contact during treatment. Full article

Background and Objectives: Ensuring the optimal shear bond strength (SBS) is essential for the long-term success of prosthodontic restorations. Our in vitro study aimed to evaluate the SBS of three types of ceramics (feldspathic, alumina, and lithium disilicates) using three adhesive cements (Variolink Esthetic LC, Variolink Esthetic DC, and Maxcem Elite). Materials and Methods: Healthy molars were prepared, and ceramic blocks were cemented following universally accepted luting protocols. SBS tests were performed using a custom-made testing machine. A multiple linear regression model assessed the effects of ceramic type, surface treatment, and luting agent on SBS. Results: The regression model explained 61.3% of the variation in SBS values (R² = 0.613); the adjusted R² = 0.605 confirmed the model’s robustness. The global F-test was statistically significant (F = 78.96, p < 0.001). The total-etch technique (+4.47), the use of feldspathic ceramic, and 5% hydrofluoric acid treatment (+3.28) significantly affected SBS. Feldspathic ceramic and lithium disilicate showed superior performance against alumina. Light-cured and self-cured cement showed negative effects. Conclusions: Ceramic material and cement type have combined effects on SBS. Optimal results were obtained with the total-etch technique, feldspathic ceramic, 5% hydrofluoric acid treatment, and dual-cured cement. Full article

The effect of induction heating on alumina ceramics and alumina ceramic composites based on α-Al₂O₃ nanopowders (additives: SiC, Si₃N₄, SiO₂, ZrO₂) has been examined. Various factors such as the structure, grain size, distribution of elements, hardness, fracture toughness, and wear rate of hot-pressed ceramic materials were assessed. Despite achieving improved densification of alumina ceramics at a higher temperature of 1720 °C, there is a consistent trend toward a decline in hardness and fracture toughness. Heating at lower temperatures of 1300–1500 °C results in the development of a strengthened surface layer with a fine-grained structure enriched with carbon. Therefore, the wear rate behavior of such ceramics differs from the behavior of samples made at higher temperatures of 1600–1720 °C. This fact indicates the presence of a non-thermal microwave effect of induction heating. The incorporation of additives to alumina leads to the formation of novel structures with altered crack propagation patterns. The optimal ceramic composite, containing 5 wt. % SiC, displayed superior hardness and the lowest wear rate when compared to pure alumina ceramics. Across all investigated composites, a short dwell time at 1700 °C results in an enhancement of the mechanical properties. Full article

Choosing the appropriate cutting tool material is essential for enhancing machining processes because it directly affects product quality, surface finish, dimensional accuracy, tool longevity, and overall efficiency. Different materials are used for cutting tools, i.e., for cutting inserts. Due to their high hardness and high temperature resistance, ceramics cutting inserts allow for increased cutting speeds, resulting in shorter manufacturing times and reduced costs, despite being pricier than traditional cemented carbide and facing certain technical challenges due to their brittleness. Alumina-based ceramics dominate the market, accounting for about two-thirds of usage, followed by silicon nitride and zirconia. This paper provides a comprehensive overview of recent advances in alumina ceramic materials used as cutting inserts, focusing on research conducted in the last five years to optimize static and dynamic mechanical and thermal properties, wear resistance, density, etc. They ways in which the properties are altered through the incorporation of whiskers, nanoparticles, or nanotubes; the modification of the structure; the optimization of sintering parameters; and the application of advanced sintering techniques are demonstrated. The paper also addresses sustainability, environmental impact, and the management of critical raw materials associated with cutting inserts, which pertains to the future development of cutting insert materials. 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

Alumina is a polycrystalline oxide ceramic with different structures. Currently, α-alumina with a hexagonal close-packed stacking structure is mainly used for a variety of industrial applications. Alumina-based ceramics and composites have been widely used in various fields due to their excellent hardness, strength, creep resistance and good biocompatibility. However, it is difficult for Al₂O₃ ceramic components based on traditional preparation methods to meet the increasing industrial requirements, especially for applications such as precise multi-walled complex structures. Al₂O₃ ceramic additive manufacturing by vat photopolymerization 3D printing stands out owing to its ability to produce complex structures and tailored shaping accuracy/properties. The vat photopolymerization 3D printing of Al₂O₃ ceramics requires multiple steps including slurry preparation, photopolymerization shaping, debinding and sintering. Therefore, many efforts mainly focus on the strategies of optimizing the ceramic slurry formulation and the debinding/sintering process. This paper provides a scoping review to present optimization strategies for the above aspects of vat photopolymerization 3D printing, which creates a strong reference for researchers to improve the accuracy and properties of alumina parts. Finally, this review also states the main applications of Al₂O₃ ceramic components based on vat photopolymerization, and highlights the opportunities and challenges associated with this technology in the future. It is beneficial to understanding the future trends and policy directions of advanced manufacturing industry. Full article

Additive manufacturing (AM) of ceramics presents a promising approach for the production of complex sanitaryware prototypes, offering advantages in terms of cost and time to market. This study explores binder jetting (BJ) as an optimal AM technique due to its ability to process ceramic materials without thermal stress, accommodate various compositions, and produce large components without support structures. A combination of refractory cement, feldspathic sands, quartz, and calcined alumina was used to formulate 19 different compositions, ensuring adequate green strength and minimizing shrinkage during sintering. A hydration-activated binding method with a water-based binder was employed to enhance part formation and mechanical properties. The results indicate that compositions containing calcined alumina exhibited lower pyroplastic deformation, while optimized gelling agent concentrations improved green strength and dimensional accuracy. The final selected material (SA18) demonstrated high compressive strength, low shrinkage, and a surface roughness comparable to traditional sanitaryware. The application of an engobe layer improved glaze adherence, ensuring a homogeneous surface. This study highlights binder jetting as a viable alternative to traditional ceramic processing, paving the way for its adoption in industrial sanitaryware manufacturing. Full article

This study investigates the application of spinel (MgAl₂O₄) hollow fiber membranes for clarification of clove basil (Ocimum gratissimum L.) aqueous extract, a rich source of bioactive compounds. The membranes were produced using a phase-inversion and sintering method at 1350 °C, combining alumina and dolomite as raw materials. The calcination of the powder materials at 1350 °C resulted in the spinel phase formation, as indicated by the XRD analyses. The spinel hollow fiber membrane presented a hydrophilic surface (water contact angle of 74°), moderate roughness (144.31 ± 12.93 nm), and suitable mechanical strength. The ceramic membrane demonstrated a water permeability of 35.28 ± 2.46 L h⁻¹ m⁻² bar⁻¹ and a final permeate flux of 9.22 ± 1.64 L h⁻¹ m⁻² for filtration of clove basil extract at 1.0 bar. Fouling analysis identified cake formation as the dominant mechanism for flux decline. The membrane retained 44% of the total phenolic compounds and reduced turbidity by 60%, while preserving significant antioxidant capacity in the permeate. The results highlight the potential of spinel-based hollow fiber membranes as a cost-effective and efficient solution for clarifying bioactive plant extracts, offering enhanced mechanical properties and lower sintering temperatures compared to conventional alumina membranes. Full article

The rapid advancement of materials science has revolutionized total hip arthroplasty (THA), a critical orthopedic procedure aimed at restoring mobility and improving patient quality of life. This review investigates the evolution of biomaterials used in THA, analyzing their mechanical, biological, and chemical properties. The study outlines the transition from early natural materials to modern metals, polymers, and ceramics, highlighting their benefits and limitations in clinical applications. Particular emphasis is placed on the development of advanced materials such as highly cross-linked polyethylene (HXLPE), zirconia-toughened alumina (ZTA), and tantalum alloys (Ta), which demonstrate enhanced biocompatibility, wear resistance, and longevity. By examining emerging trends, including bioactive coatings and nanotechnology, this paper aims to provide a comprehensive understanding of current challenges and future directions in material selection for hip prostheses, ultimately aiming to minimize annual revision rates and improve long-term outcomes. Full article

As additive manufacturing technologies continue to gain ground in industrial applications, the need for the accurate metrological evaluation of parts produced with advanced materials becomes increasingly critical. In this context, non-contact metrology plays a key role. This research investigates the performance of conoscopic holography as an optical metrology technique for the inspection of ceramic parts manufactured by stereolithography. However, its reliability needs to be validated, especially as factors such as material properties, surface finish, and color can significantly affect measurement accuracy. Spherical artifacts in alumina were chosen as mathematically well-defined reference elements, and a representative series was produced with the best values for the printing, debinding, and sintering parameters. These spheres were first measured via contact with a coordinate measuring machine (CMM) to establish dimensional (diameter) and geometrical (form error) reference values. These parameters were then compared with measurements obtained via conoscopic holography and optimized by means of Gaussian filters. The results indicated significant dimensional (up to 60 µm) and geometrical (up to 280 µm) deviations from the CMM reference data. The investigation shows that conoscopic holography does not ensure an accurate measurement method for this additive process and ceramic material, making it impossible to achieve power and frequency settings that would allow signal-to-noise ratios above 50%. Full article

The continuous advancement of technology has led to escalating demands for superior tribological performance in industrial applications, necessitating the enhancement of ceramic materials’ frictional properties through innovative approaches. Solid-lubricant embedding is a widely employed lubrication strategy in metals. However, the challenge of machining holes on ceramic surfaces remains a significant barrier to applying this lubrication technique to ceramics. Gel casting, as a near-net-shaping process, offers several advantages, including uniform green body density, low organic content, and the capability to fabricate components with complex geometries, making it a promising solution for addressing these challenges. In this study, alumina ceramics with small surface holes designed for embedding oil-containing microcapsules were fabricated via gel casting using an N-hydroxy methylacrylamide gel system, which demonstrates lower toxicity compared to conventional acrylamide systems. The fabricated alumina ceramic materials exhibited a high density of 98.2%, a hardness of 16 GPa, and a bending strength of 276 MPa. The oil-containing microcapsules were self-synthesized using hexafluorophosphate ionic liquid as the core material and polyurea-formaldehyde as the wall material. The research results show that under conditions of using an alumina ball, sliding speed of 10 cm/min, load of 5 N, and at room temperature, the material with a microcapsule content of 15 wt% and embedded hole diameter of 1.2 mm reduced the friction coefficient from 0.696 in an unlubricated condition to 0.317. Moreover, the embedding of microcapsules further improved the wear resistance of the alumina. Full article

Drop-on-demand (DoD) printing is an additive manufacturing technique that utilizes functional inks containing nanoparticles (NPs) to fabricate electronic circuits or devices on a variety of substrates. One of the most promising applications for such technology is the aerospace industry, due to the capability of this method to fabricate custom low-weight geometric films. This work evaluates the performance of a gold (Au) nanoparticle (NP)-based film printed on a ceramic substrate for avionics applications, following the environmental temperature guidance of the Radio Technical Commission for Aeronautics (RTCA) DO-160. Experimental results show that the Au films, printed on alumina substrates, successfully survived the environmental temperature procedures for airborne equipment. The thermal coefficient of resistance (TCR) of the films was measured to be $2.7\times {10}^{-3} {°\mathrm{C}}^{-1}.$ Full article

This paper investigates grain growth and densification kinetics in alumina ceramics subjected to spark plasma sintering (SPS) and conventional pressureless sintering (CS). The findings reveal that, under both sintering conditions, grain growth primarily occurs after reaching the sintering ‘freezing point’. The analysis of densification kinetics indicates that the activation energies of densification of alumina ceramics are 173.6 KJ/mol and 261.2 KJ/mol during the early stage, and 362.2 KJ/mol and 383.7 KJ/mol in the late stage for SPS and CS conditions, respectively. Therefore, a two-step sintering method (TSS) is proposed, where SPS rapidly sinters alumina powder to reach the grain growth ‘freezing point’, and then, the sintered bodies are subjected to CS to obtain dense alumina ceramics. The results show that the flexural strength of alumina prepared using this TSS can reach 489.6 MPa, about 19% improvement over those processed solely through CS. Full article