Search Results (62)

Bi₆Fe₂Ti₃O₁₈ (BFTO) ceramics were synthesized via a solid-state reaction route using stoichiometric amounts of Bi₂O₃, TiO₂, and Fe₂O₃ powders. A thermal analysis of the powder mixture was conducted to optimize the heat treatment parameters. Energy-dispersive X-ray spectroscopy (EDS) confirmed the conservation of the chemical composition following calcination. Final densification was achieved through hot pressing. The crystal structure of the sintered samples, examined via X-ray diffraction at room temperature, revealed a tetragonal symmetry for BFTO ceramics sintered at 850 °C. Electron backscatter diffraction (EBSD) provided detailed insight into the crystallographic orientation and microstructure. Broadband dielectric spectroscopy (BBDS) was employed to investigate the dielectric response of BFTO ceramics over a frequency range of 10 mHz to 10 MHz and a temperature range of −30 °C to +200 °C. The temperature dependence of the relative permittivity (ε_r) and dielectric loss tangent (tan δ) were measured within a frequency range of 100 kHz to 900 kHz and a temperature range of 25 °C to 570 °C. The impedance data obtained from the BBDS measurements were validated using the Kramers–Kronig test and modeled using the Kohlrausch–Williams–Watts (KWW) function. The stretching parameter (β) ranged from ~0.72 to 0.82 in the impedance formalism within the temperature range from 200 °C to 20 °C. Full article

Textured Si₃N₄/BN composite ceramics were successfully fabricated using two-step sintering, combining pseudo-hot isostatic pressing (PHIP) and gas pressure sintering. The grain size of h-BN platelets had a significant influence on densification and mechanical and thermal properties. With an increase in h-BN grain size, the volume density of the composite ceramics gradually decreased, while flexural strength gradually increased. Meanwhile, larger h-BN platelets were more likely to trigger toughening mechanisms like large-angle deflection and greatly increase fracture toughness. Through proper selection of h-BN grain size, textured ceramics, with the addition of h-BN platelets of 1–2 μm, showed high thermal conductivity (∼92 W∙m⁻¹∙K⁻¹) and reliable mechanical properties (∼540 MPa, ∼7.5 MPa∙m^1/2, ∼11.1 GPa). Therefore, texture control is an effective means of improving the overall performance of ceramic materials. Novel textured composite ceramics thus have great potential in large-scale fabrication and directional heat dissipation applications. 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

Powders with phase composition including quasi-amorphous phases and calcium carbonate CaCO₃ in the form of calcite or aragonite and sodium halite NaCl as a reaction by-product were synthesized from 0.5M aqua solutions of sodium silicate and 0.5M aqua solutions of calcium and/or magnesium chlorides. Starting solutions were taken in quantities which could provide precipitation of hydrated calcium and/or magnesium silicates with molar ratios Ca/Si = 1 (CaSi), Mg/Si = 1 (MgSi) or (Ca+Mg)/Si = 1 (CaMgSi). Hydrated calcium and/or magnesium silicates, hydrated silica, magnesium carbonate, hydrated magnesium carbonate or hydrated magnesium silicate containing carbonate ions are suspected as components of quasi-amorphous phases presented in synthesized powders. Heat treatment of synthesized powders at 400, 600, 800 °C and pressed preceramic samples at 900, 1000, 1100 and 1200 °C were used for investigation of thermal evolution of the phase composition and microstructure of powders and ceramic samples. Mass loss of powder samples under investigation during heat treatment was provided due to evacuation of H₂O (m/z = 18), CO₂ (m/z = 44) and NaCl at temperatures above its melting point. After sintering at 1100 °C, the phase composition of ceramic samples included wollastonite CaSiO₃ (CaSi_1100); enstatite MgSiO₃, clinoenstatite MgSiO₃ and forsterite Mg₂SiO₄ (MgSi_1100); and diopside CaMgSi₂O₆ (CaMgSi_1100). After sintering at 1200 °C, the phase composition of ceramics CaSi_1200 included pseudo-wollastonite CaSiO₃. After heat treatment at 1300 °C, the phase composition of MgSi_1300 powder included preferably protoenstatite MgSiO₃. The phase composition of all samples after heat treatment belongs to the oxide system CaO–MgO–SiO₂. Ceramic materials in this system are of interest for use in different areas, including refractories, construction materials and biomaterials. Powders prepared in the present investigation, both via precipitation and via heat treatment, can be used for the creation of materials with specific properties and in model experiments as lunar regolith simulants. Full article

Lithium disilicate ceramics (LDSs) are widely used in restorative dentistry for their excellent aesthetic and mechanical properties. Variants like zirconia-reinforced lithium silicate (ZLS) and advanced lithium disilicate (ALD) were developed to enhance these characteristics. However, differences in their physical and optical properties, as well as the influence of processing techniques (heat pressing vs. CAD-CAM), remain unclear. This study aimed to evaluate the physical and aesthetic properties of LDS, ZLS, and ALD ceramics. A systematic review and meta-analysis following PRISMA guidelines were conducted. Studies published in the last ten years were retrieved from PubMed, Web of Science, Scopus, Cochrane, and Scielo. The inclusion criteria encompassed in vitro studies analyzing LDS, ZLS, and ALD ceramics with quantitative data on mechanical and aesthetic properties. Meta-analyses were performed using a random-effects model, with subgroup analyses based on ceramic type and processing technique. Twenty-two studies met the inclusion criteria. Meta-analyses showed significant differences in flexural strength, hardness, surface roughness, wear, and translucency. The processing technique influenced these properties, with CAD-CAM materials exhibiting distinct performance compared to heat-pressed ceramics. Publication bias was assessed using Egger’s test and the Trim and Fill method, and heterogeneity via meta-regression. LDS showed the highest fracture resistance and least wear, while ALD had greater roughness depth. Heat pressing enhanced hardness and reduced roughness, whereas CAD-CAM improved flexural strength. Considering these findings and study limitations, LDS appears the most suitable option for clinical use due to its superior mechanical performance. 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

This paper demonstrates a novel method for preparing electrically conductive silicon carbide (SiC) ceramics by combining hot-press sintering and nitrogen pressure heat treatment. By incorporating graphite and AlN-Y₂O₃ sintering additives, conductive SiC ceramics with intergranular regions containing Y, C, and O elements were fabricated via low-temperature hot-pressing in a hot-press furnace. Following this, the samples were subjected to heat treatment in nitrogen atmosphere at varying temperatures using a gas pressure sintering furnace. It is revealed that Y and N elements were successfully dissolved into SiC grains, enhancing electrical conductivity. Additionally, localized nitridation occurred, and the Y₂Si₄CN₆ phase—a newly identified phase in nitrided regions—was discovered for the first time, potentially contributing to reduced resistivity. After heat treatment, the sample resistivity decreased significantly from an initial 3.1 × 10⁻¹ Ω·cm to the minimum of 7.56 × 10⁻³ Ω·cm. Full article

Thermal runaway in microwave hybrid heating of ceramics is an unwanted phenomenon which damages the sintered products. The aim of the present study is to establish to what extent the pressing forces of 100, 200 and 300 MPa used in the compaction process and the optimization of the microwave heating mechanism can reduce the occurrence of thermal runaway. Modeling and simulation of temperature distributions alongside defects created by the compaction process are performed in order to evaluate their influence on the stability of MHH. Based on CT scanning, defects with dimensions from 110 to 515 μm are studied in terms of local overheating and how the thermal runaway can lead to internal arc discharge. The results show that samples compacted at 100 MPa and exposed at 600 W injected power reach temperatures peaks around 1010 °C and are affected by major cracks and large melted areas. The samples compacted at 200 and 300 MPa present similar behavior, without arc discharge, but are also affected by cracks. Based on these findings, the MHH process can be applied to sintering processes but with a reduced injected power below 300 W for samples compacted with pressing forces higher than 300 MPa. Full article

The metal injection molding (MIM) manufacturing process has made relevant advances for applications in components with complex geometries, small dimensions, and high production volumes. New technologies such as hot isostatic pressing (HIP), uniform polymer extraction, and sintering with reduced temperature variations improve metallurgical and mechanical properties. However, there are still knowledge gaps in understanding these technologies and the behavior of catalytic low-alloy steels obtained by the MIM process and cyclic applications. This study aims to analyze the behavior of Catamold 100Cr6 steel subjected to quenching and tempering heat treatment in different microhardness ranges and the effect of compressive stresses on the samples obtained by polishing using ceramic microchips. The samples were characterized using optical microscopy, scanning electron microscopy, an EDS microprobe, and X-ray diffraction and subjected to elastic return cycling and an experimental device developed to apply a 19° bending angle. The findings show a significant increase in fatigue life due to the compressive stresses (up to—430 MPa) generated by the reduction in retained austenite and surface plastic microdeformation, indicating the effectiveness of 100Cr6 Catamold steel in cyclic applications. Full article

Calcium-silicate-based ceramic composites with different CaO/SiO₂ weight ratios (10/90, 20/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/20, and 90/10) have been prepared from chicken eggshells and silica gel using attrition milling for 3 h in wet conditions and conventional pressing–heat treatment in the air at 800 °C for 1 h. The effect of the CaO/SiO₂ weight ratio and the calcination period of the eggshells on the microstructural features including apparent density, phase evolution, and morphological properties were investigated. The phase transformation of the powder mixtures after attrition milling for 3 h in ethanol with powder/ball milling mass ratio of 0.0996 (110/1104.7) revealed to have calcium hydroxide (Ca(OH)₂) as a dominate phase, which was observed to increase with the increase in calcium oxide (CaO) amount in the powder mixtures. The phase transformation of ceramic samples after heat treatment at 800 °C for 1 h, on the other hand, showed different phases depending on the CaO/SiO₂ weight ratio. The results also show a linear relationship between the CaO/SiO₂ weight ratio and apparent density when the CaO/SiO₂ ratio increase from 0.11 (10/90) to 0.67 (40/60) due to the densification of ceramics. An inversely proportional relationship was found between CaO/SiO₂ and density when the CaO/SiO₂ weight ratio increased from 0.67 (40/60) to 9 (90/10). Full article

Carbon nanotube (CNT)/graphene ceramic composites with outstanding properties are expected to replace a number of components currently used in the automotive and aerospace industries in the future. Consequently, this area of research has progressed significantly. This review paper, therefore, delves into the enhancement of ceramic properties through the integration of graphene and CNTs. These reinforcements are known to mitigate the inherent brittleness of ceramics, thereby unlocking their potential for applications in sectors requiring high mechanical reliability, such as the aerospace, automotive, and biomedical industries. By summarizing recent research, this paper outlines various preparation methods, including ball milling, heat pressing and spark plasma sintering, and discusses how these techniques contribute to improved mechanical and thermal performance. This review emphasizes the critical role of graphene and CNT ratios, sizes, and their synergistic effects in enhancing fracture toughness, machinability, and overall structural integrity. Thus, this paper provides a comprehensive overview of the current research in this area and discusses the potential of these technologies. Full article

Being a type of carbonaceous material, glassy carbon possesses thermomechanical properties akin to ceramics, offering both mechanical and chemical stability at high temperatures; therefore, it can be applied in electrochemistry and high-temperature manufacturing. However, the direct pyrolysis of a bulk precursor leads to internal pores and cracks, usually resulting in fracture. Our characterization results show that at temperatures below 400 °C, large pores do not form, and pre-carbonized glassy carbon (PGC) formed at 350 °C has a dense microstructure without cracks. It exhibits a high compressive strength of ~370 MPa and flexural strength of ~190 MPa, making it suitable for load-bearing applications. Additionally, the PGC-350 material shows small mass loss (~5%) and reasonably low thermal expansion (2.5 × 10⁻⁶/°C) when heated to 350 °C again. These properties suggest the potential of PGC for high-temperature applications. As a demonstration, PGC formed at 350 °C was employed to fabricate molds to press chalcogenide glass blanks, which exhibited favorable molding results for various surface morphologies. Full article

This paper studies the structural parameters and electrophysical properties (dielectric and piezo electric, as well as currents of thermostimulated depolarization) of samples of composition 0.20BiScO₃·0.45PbTiO₃·0.35PbMg_1/3Nb_2/3O₃ (or in short 0.20BS·0.45PT·0.35PMN) obtained by ceramic and melt-hardening methods of synthesis. In the ceramic method, the samples were obtained from the starting oxides by two-stage firing. In the melt method, amorphous precursors were first obtained from heat-treated and non-heat-treated starting oxide mixtures by melting and subsequent quenching under sharply gradient temperature conditions. Samples were obtained after grinding, pressing, and thermal annealing of the synthesized precursors, and four types of samples differing in size and shape of the intermediate precursor particles (crystallites) were obtained. The X-ray phase analysis showed that the predominant phase in the studied samples is the perovskite phase; in both types of samples, up to 5 wt.% of impurity phase with pyrochlore structure was also present. The samples of 0.20BS·0.45PT·0.35PMN exhibit dielectric properties characteristic of relaxor ferroelectrics, and the polarized samples exhibit a pronounced piezo effect with a piezo modulus value of d₃₃~200 pC/N. A comparative analysis of the properties of the samples obtained by different methods has been carried out. The essential advantage of the melt method is that its use allows obtaining varieties of four kinds of ferroelectric relaxors and reduces the time of synthesis of samples by 2–3 times. Full article

Objective: To determine the effect of grit-blasting before and after sintering on the surface roughness of zirconia and the micro-tensile bond strength of a pressable veneering ceramic to zirconia. Methods: Pre-sintered zirconia blocks (IPS e.max ZirCAD, Ivoclar) were divided into four test groups of three specimens each and a control group (‘CTR’; no surface treatment). Pre-S-30, Pre-S-50, and Pre-S-110 were grit-blasted with 30-µm SiO₂-coated Al₂O₃, 50-µm Al₂O₃ and 110-µm Al₂O₃ particles, respectively, before sintering. Post-S-30 was grit-blasted with 30-µm SiO₂-coated Al₂O₃ after sintering. For each treatment, the surface roughness was measured (Ra, Perthometer M4P, Mahr Perthen). After sintering the zirconia blocks, a liner was applied and a pressable ceramic (IPS e.max ZirPress, Ivoclar) was heat-pressed. Sixteen microbars were obtained from each block and submitted to micro-tensile bond-strength (µTBS) testing. Data were analyzed with one-way ANOVA. Any correlation between Ra and µTBS was evaluated (Sperman test). Results: Grit-blasting before sintering with 110-µm Al₂O₃ (Ra_Pre-S-110 = 3.4 ± 0.4 µm), 50-µm Al₂O₃ (Ra_Pre-S-50 = 2.3 ± 0.5 µm), and 30-µm SiO₂-coated Al₂O₃ (Ra_Pre-S-30 = 1.2 ± 0.2 µm) resulted in significantly higher roughness than grit-blasting after sintering with 30-µm SiO₂-coated Al₂O₃ (Ra_Post-S-30 = 0.5 ± 0.1 µm). The highest µTBS was measured when the sintered zirconia was grit-blasted with 30-μm SiO₂-coated Al₂O₃ (µTBS_Post-S-30 = 28.5 ± 12.6 MPa), which was significantly different from that of specimens that were grit-blasted before sintering (µTBS_Pre-S-30 = 21.8 ± 10.4; µTBS_Pre-S-50 = 24.1 ± 12.6; µTBS_Pre-S-110 = 26.4 ± 14.1) or were not grit-blasted (µTBS_CTR = 20.2 ± 11.2). Conclusions: Grit-blasting zirconia before sintering enhanced the surface roughness proportionally to the particle size of the sand used. Grit-blasting with 30-µm SiO₂-coated Al₂O₃ after sintering improved bonding of the veneering ceramic to zirconia. Clinical Significance: As grit-blasting with 30-µm SiO₂-coated Al₂O₃ after sintering improved bonding of the veneering ceramic to zirconia, it may reduce veneering ceramic fractures/chipping. Full article

Negative thermal expansion (NTE) ceramics Sm_0.85Zn_0.15MnO₃ (SZMO) and ZrMgMo₃O₁₂ (ZMMO) were selected to prepare Sm_0.85Zn_0.15MnO₃-ZrMgMo₃O₁₂/Al-20Si (SZMO-ZMMO/Al-20Si) composites using ball milling and vacuum heating-press sintering processes in this study. The synergistic effect of the SZMO and ZMMO NTE ceramic reinforcements on the microstructure, mechanical properties, and coefficient of thermal expansion (CTE) of the composites was investigated. The results show that the processes of ball milling and sintering did not induce the decomposition of SZMO or ZMMO NTE ceramic reinforcements, nor did they promote a reaction between the Al-20Si matrix and SZMO or ZMMO NTE ceramic reinforcements. However, the excessive addition of SZMO and ZMMO NTE ceramics led to their aggregation within the composite. Adding a small amount of SZMO in combination with ZMMO effectively increased hardness and yield strength while reducing CTE in the Al-20Si alloy. The improvement in strength was primarily provided by SZMO, while the inhibition effect on CTE was primarily provided by ZMMO. An evaluation parameter denoted as α was proposed to evaluate the synergy effects of SZMO and ZMMO NTE ceramic reinforcements on the mechanical properties and CTE of the composites. Based on this parameter, among all composites fabricated, adding 2.5 vol% SZMO NTE ceramic and 10 vol% ZMMO NTE ceramic resulted in an optimal balance between CTE and strength for these composites with a compressive yield strength of 349.72 MPa and a CTE of 12.55 × 10⁻⁶/K, representing a significant increase in yield strength by 79.20% compared to that of Al-20Si alloy along with a notable reduction in CTE by 26.44%. Full article