ABSTRACTLaAlO3–BaSnO3 ceramics as a new microwave dielectric material were investigated in terms of optimum synthesis conditions and thereby the relative density, microstructure, solid-solution state, and dielectric properties with the addition of various sintering aids at different sintering temperatures. The dielectric properties of 0.9LaAlO3–0.1BaSnO3 (LA-0.1BS) were strongly influenced by relative density, microstructure, chemical ordering, and mixing rule of the dielectric constant. Densification of the LA-0.1BS ceramics was improved from 82.3 to 96.13% with an average grain size of around 1.9 µm at reduced sintering temperature by 250°C. The LA-0.1BS ceramics sintered with 3 mol% of Bi2O3–SiO2 (BS) showed dielectric constant (ϵr) ∼21.18 with associated dielectric loss (tan δ) ∼0.00824 and Q × f ∼1213.59 (10 GHz) which could be achieved at low sintering temperature of 1400–1450°C.

ABSTRACTThe fitness of self-glazed zirconia (SGZ) onlays fabricated with computer-aided design/computer-aided manufacturing was analysed, and conventional impressions (CIs) were compared with intraoral digital impressions (DIs). Onlay preparation was applied on a typodont left mandibular first molar to create 22 copy dies, which were divided into DI and CI groups. The marginal gap of DI-fabricated onlays was smaller than that of CI-fabricated onlays (p < 0.05). In both groups, the marginal gap was larger in the distal gingival than in other regions (p < 0.05), and a trend of decreasing marginal accuracy after thermal cycling was observed. SGZ onlays performed well for internal fitness; the overall internal gaps were 72.05 ± 8.16 and 100.96 ± 22.53 μm in Groups DI and CI, respectively. SGZ onlays exhibited clinically acceptable marginal and internal fitness values. The marginal adaptation of DI-fabricated onlays was better than that of CI-fabricated onlays.

ABSTRACTThis paper reports the 3D printing of fibre-reinforced ceramic composite with hierarchical structures. Through printing precursor formulation, short SiC fibres have been successfully incorporated into silicate materials and gradient porous hierarchical structure has been achieved for the printed parts. The mechanical testing shows a 27% improvement in impact strength, 22% improvement in flexural modulus, and 7.5% in flexural strength compared with parts without fibre reinforcement. High-resolution tomography analysis using x-ray microscopy shows that the inner structure has a porosity of 27%, while the outer layer shows a dense structure with little pores formation. This 3D printed ceramic composite with fibre-reinforcement shows high similarity to the gradient porous structures of human bone and tooth. The results indicate that 3D printing of nano/microfibre reinforced ceramic composite with hierarchical structure is a promising method to enhance the fracture toughness of ceramics and allow accurate patient-specific customisation for their implants.

ABSTRACTUniform-sized amorphous hydrous titania particles (HTPs) with nonporous or porous surface were prepared and subjected to hot-water or hydrothermal treatment to induce crystallisation of the titania phase for preparing porous titania particles with high specific surface area (SSA) and outer diameter in a micron order. Porous HTPs were crystallised under milder treatment conditions than those required to crystallise nonporous spherical HTPs. This difference was attributed to the difference in the polycondensation states of hydrous titania. The SSA of the porous titania particles crystallised by hot-water treatment at 80°C for 24 h was 216 m2 g−1, despite their micron-order particle size. This simple method can synthesise highly functional titania particles at low temperatures and is a general-purpose method for preparing porous particles for use as adsorbents, catalysts and catalyst supports.

ABSTRACTGarnet-type solid-state electrolytes are promising candidates for solid-state lithium batteries, nevertheless their ionic conductivity is still not enough for commercial applications. On the other hand, doping still is the common way to improve the ionic conductivities of these solid electrolytes. In this study, mono and dual-doped garnet-type solid electrolytes were synthesised by substituting indium (In), gallium (Ga), indium-titanium (In-Ti) and gallium-titanium (Ga-Ti) to the Li7La3Zr2O12 structure by a solid-state reaction method. The contribution of substitutions to the formation of crystal phases was investigated by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). On the other hand, morphological analyses were done by scanning electron microscope (SEM) and the ionic conductivities of the solid electrolytes were determined by electrochemical impedance spectroscopy (EIS). The study showed that while Li7-3xInxLa3Zr2O12 (for x = 0.05, 0.10, 0.15, 0.20) and Li7-3xGaxLa3Zr2O12 (for x = 0.05) samples were formed in tetragonal phase with a space group of I41/acd:2, dual substituted Li7-3xInxLa3Zr1.8Ti0.2O12 and Li7-3xGaxLa3Zr1.8Ti0.2O12 solid electrolytes for all x values were formed in cubic phase with a space group of I-43d. The highest conductivity is reached for Li6.85Ga0.05La3Zr1.8Ti0.2O12. The radial distribution function studies showed that when more In and Ga atoms take place in the sites of Li atoms, more O atoms take place in the vicinity of both substituted In and Ga atoms within the Li7La3Zr1.8Ti0.2O12 (LLZTO) crystal framework which can eventuate in a change in the conduction mechanism.

ABSTRACTIn this study, aluminosilicate fiber-embedded SiBOC matrix composite foams are realised by a simple, cost-effective and easily scalable method. Aluminosilicate wool is transformed into a compressible preform using polyvinyl alcohol as a binder. The preforms are impregnated with methylvinylborosiloxane (MVBS), followed by heat treatment at 1400°C in an inert atmosphere. The composite foam’s density, compressive strength and thermal conductivity are modulated in the ranges 0.71–0.46 g/cc, 0.79–0.39 MPa and 0.21–0.13 Wm−1K−1, respectively, by varying MVBS concentration from 29 to 54 wt.%. While the incorporation of aluminosilicate fibers was observed to lower the thermal conductivity of the composite foams, it did not contribute to their compressive strength. Exposure of the foams to air at 1300°C for 90 min didn’t change their density, while it increased the compressive strength by up to 46% due to improved fiber-matrix adhesion and rounding of cracks.

ABSTRACTZirconium diboride (ZrB2) is a typical ultra-high temperature ceramic material (UHTC). In this work, the preparation of ZrB2 by reducing zirconia (ZrO2) with calcium hexaboride (CaB6) was studied in detail. With the assistance of molten salt, the reduction rate was dramatically enhanced. Additionally, the results showed that ZrB2 products with different particle shapes were prepared by changing the type of molten salt (NaCl, KCl, MgCl2, and CaCl2). However, the particle size of products could not be properly refined when nano-ZrO2 was used as the raw material. During the process of reducing ZrO2 by CaB6, B2O3 could be formed, which would cause the loss of B source. To decrease the consumption of CaB6, Ca-assisted reduction was performed, and monophase ZrB2 was obtained. The varied morphologies of ZrB2 particles obtained by Ca-assisted reduction were the result of complex reaction mechanisms.

Published in Advances in Applied Ceramics: Structural, Functional and Bioceramics (Vol. 121, No. 5-8, 2022)

ABSTRACTCarbon fibre has excellent mechanical properties at high temperatures but weak oxidation resistance. The paper prepared the anti-oxidative silica coating on the surface of needled carbon fibre felt by the sol–gel method and discussed the effects of sol content and sintering temperature on the coatings’ performance. The phase composition, density, thermal conductivity and thermal stability of derived composites were characterised, and the structure and morphology of SiO2 coatings were also analysed by scanning electron microscopy. The results indicated that a uniform and complete coating could be formed on the fibre surface when the sol content exceeds 20%. Ceramic particles sintered below 1200°C were amorphous silica, while those sintered at 1350°C were cristobalite. Compared with other processes, 20% silica sol content or sintering at 1350°C could provide better antioxidant protection. The new coating process is significant for retarding fibre oxidation in a high-temperature environment.

ABSTRACTCarbon fibre-reinforced carbon aerogel composites (C/CAs) were prepared by using polyacrylonitrile (PAN) and phenolic (PH) carbon precursor fibres as reinforcements, respectively, then impregnated with resorcinol-formaldehyde sol, aging, solvent exchanging, CO2 supercritical drying and carbonization at 1000°C. The physical properties, structural morphology and mechanical and thermal insulation behaviour of the two kinds of composites were further compared. Pore structure analysis shows that the PH-based C/CAs have a larger specific surface area (438.92 m2·g−1) and richer mesoporous volume than the PAN-based C/CAs. Mechanical behaviour of the C/CAs has been changed, but the stronger enhancement effects belong to PAN-based C/CAs (compressive strength in xy and z-directions are 1.63±0.10 MPa and 1.22±0.19 MPa, bending strength is 3.62±0.50 MPa). However, the PH-based C/CA composites have relatively low thermal conductivities, ranging from 0.027 to 0.164 W·m−1·K−1 between 25 and 1800°C.

ABSTRACTZrO2-reinforced porous mullite ceramics were fabricated by a foam-gel casting approach using zircon (ZrSiO4) powders and alumina (Al2O3) powders as raw materials. The influence of firing temperature on the phase composition of porous samples was analysed. Based on the analysis results, the effects of a blowing agent on the physical properties, microstructure, mechanical strength and heat conductivity of ZrO2-reinforced porous mullite samples fired at 1600°C were investigated. In the present study, linear shrinkage, porosity and mean pore size of ZrO2-reinforced porous mullite ceramics increased, and volume density, mechanical strength and heat conductivity decreased. When the dosage of the blowing agent was 1.0 vol.-%, the flexural strength and compressive strength of ZrO2-reinforced porous mullite sample with 77.4% porosity respectively reached 3.0 and 10.9 MPa, and their heat conductivity was kept at 0.181 W m−1 K−1.

ABSTRACTThe composites, (1−x)(BiFe1-yLayO3)– xNaNbO3 with x = 0.25, 0.45 and y = 0.10, 0.20, are prepared by mixed oxide method. XRD analysis shows rhombohedral (hexagonal) structure at room temperature. The properties such as dielectric loss (tanδ) and dielectric constant (ϵr) of all the samples are studied. A significant improvement in dielectric constants has been observed with the rise of Lanthanum (La) content. A dielectric anomaly above 350°C is observed for all the studied materials. Further, it is observed that ac conductivity (σac) spectrum obeys universal Jonscher’s power law. The variation of σac with inverse of temperature for all the samples is found to obey the Arrhenius equation. The formation of loop in polarisation verses electric field curve establishes the ferroelectric (FE) nature of all the studied samples. Current (I)-Electric Field (E) loops is studied to show the behaviour of domain switching.

ABSTRACTIn this investigation, it was studied the effect of curing temperature on the mechanical properties of pastes made with calcium sulfoaluminate cements synthesised from industrial wastes at a relatively low temperature of 1100°C. Fluorgypsum, fly ash, aluminium slag and calcium carbonate were used as raw materials. The main phases of synthesis were calcium sulfoaluminate and gehlenite. Pastes were prepared with different water/cement ratios, 15–25 wt-% hemihydrate and cured at 20 and 40°C. It was found that with higher total amounts of sulphates and increase in temperature, compressive strength is enhanced in the first days of curing and setting times decreased. Ettringite was found to be the main reaction product forming dense structures over time. Calcium sulphates hydration changed the ettringite formation causing fluctuations in the strength development, nevertheless, in some cases the strength surpassed 40 MPa at 28 days. Microstructures and hydration products were studied by SEM and XRD.

ABSTRACTThe wear behaviour of WC-Co cemented carbide reinforced with graphene platelets (WC-Co-GPLs composite) was investigated. The tribological parameters as friction coefficient and wear rate were measured using a ball-on-plate configuration with different contact loads. The microstructures and worn surfaces of composites were studied. The WC-Co-GPLs composite exhibits significantly better tribological properties in comparison to the WC-Co which is most evident at contact load of 80 N, where the friction coefficient and wear rate of the WC-Co-GPLs composite are 0.339 and 9.27 × 10−6 mm3·(m·N)−1, respectively. The improvement in wear behaviour of WC-Co-GPLs composite is attributed to the formation of the tribofilm during the wear test and enhancement of mechanical properties of the WC-Co-GPLs composite. The pulled-out GPLs attaches on the worn surface contribute to the formation of tribofilms during tribology test, especially at higher loads. The tribofilms protect the WC-Co-GPLs from wear and guarantee the integrity of the worn surface.

ABSTRACTThe electric flash generated by an electric field aided the sintering of hydroxyapatite (HA) in relatively less time and at lower furnace temperatures than the conventional sintering method. The current work has reported a comparative study to explain thermodynamically the effects of the increasing DC electric field strength at 1000°C and 1100°C sintering furnace temperatures during flash sintering in terms of the grain growth and densification of the HA in air. The abrupt change in current density and conductivity of HA during the flash peak correlates the high grain growth and rapid densification with increasing electric field strength. The increased electric field strength reduced the power dissipation from the HA. The abrupt high-rise grain growth phenomenon during flash sintering might consist of the thermal effect and enhancement in ionic conductivity due to the application of an electric field.

ABSTRACTMonolithic self-glazed zirconia is a new type of biomimetic zirconia that has been successfully used as crown and bridge restorations in the anterior and posterior regions. It exhibits excellent biomechanics and aesthetic properties through completely digital processing technology. This case presents a young patient’s aesthetic rehabilitation with self-glazed ultra-thin zirconia veneers by closing the scattered diastema in the aesthetic zone of the anterior teeth with a fully digital workflow. The restorations exhibited excellent aesthetic outcomes with a minimally invasive concept and superior mechanical properties over glass-based ceramic veneers. The application of full-contour monolithic ultra-thin self-glazed zirconia restorations in the anterior aesthetic zone constitutes a reliable, fully digital clinical workflow.

ABSTRACTUsing a conventional sintering (CS) process, it is difficult to eliminate pore distribution across ceramic composites, resulting in mechanical properties destruction. In this study, 90%–95% of pores were reduced with the same sintering parameters by replacing CS with the cutting-edge Alumina-Graphite Powder Bath (AGPB) sintering method. Alumina-Zirconia-CNT(AZC) composites were fabricated using both AGPB and CS methods. The ceramic samples were surrounded by alumina-graphite powder particles in the AGPB method, which provided indirect homogeneous heating to the samples. This powder bath setup changed convection-radiation heat to conduction heat and produced sintered product with pore-free microstructures. The hardness of the AGPB-AZC composite was 43% higher than the CS-AZC, demonstrating the exponential property enhancement caused by cutting-edge AGPB sintering. The AGPB-AZC FESEM investigation revealed the formation of a homogenous microstructure with minimum pores, which eventually increased the hardness.

ABSTRACTThis investigation is motivated by increasing interest in polymer-diamond coatings for biomedical applications in implants and sensors. A conceptually new strategy is based on the feasibility of solubilisation of polyethyl methacrylate (PEMA) in isopropanol using 18β-glycyrrhetinic acid (GRA) and rhamnolipids (RLP) as solubilising agents. This approach offers benefits for biomedical applications by avoiding the use of traditional toxic solvents for PEMA dissolution. The ability to obtain concentrated solutions of high molecular mass polymer is a crucial factor for the development of a dip coating method. Potentiodynamic and impedance spectroscopy studies indicate that PEMA films provide corrosion protection of stainless steel in 3% NaCl solutions. The use of GRA facilitates the fabrication of films with improved protective properties. PEMA films are obtained as monolayers or multilayers of controlled film mass. Another important finding is a good dispersion of chemically inert microdiamond and nanodiamond particles using GRA and RLP. For the first time composite PEMA-diamond films are obtained using GRA and RLP as solubilising agents for PEMA and dispersing agents for diamonds in isopropanol solvent. The detailed analysis of film microstructures provides an insight into the influence of chemical structure of GRA and RLP on their interactions with PEMA and diamonds. Moreover, microstructure analysis indicates that such interactions are important for preventing defects in the composite films. The benefits of steroid-like dispersants are discussed. Composite films are obtained as monolayers with different diamond content or PEMA-diamond multilayers of different composition and film mass. The method represents a versatile strategy for the fabrication of alternating PEMA/PEMA-diamond multilayers. The benefits of the obtained microstructures for biomedical applications are discussed. The approach developed in this investigation opens an avenue for the fabrication of other polymer coatings containing various functional materials.

ABSTRACTBi2−2xLixMgxSr2Co2Oy (x = 0.05, 0.10 and 0.15) samples are prepared by a solid-state reaction at various temperatures (1033–1133 K). All X-ray diffraction peaks can be indexed as the monoclinic Bi2Sr2Co2Oy phase. The structural and thermoelectric properties of Bi2−2xLixMgxSr2Co2Oy samples are systematically investigated, depending on the sintering temperature and the Li+/Mg2+ concentration. A higher sintering temperature increases the hole concentration and hole mobility, whereas a higher Li+/Mg2+ concentration increases the hole concentration and decreases the hole mobility. As the Li+/Mg2+ concentration increases, the power factor of the samples sintered at 1033 K decreases, whereas that of the samples sintered at 1083 and 1133 K increases. Of the prepared samples, Bi1.70Li0.15Mg0.15Sr2Co2Oy sintered at 1133 K shows the largest power factor (0.25 × 10−4 W m−1 K−2) at 973 K. This power factor is 2.5 times greater than that of Bi1.70Li0.15Mg0.15Sr2Co2Oy sintered at 1033 K (0.10 × 10−4 W m−1 K−2) at 973 K.

ABSTRACTThe temperature dependence of ageing in the commercial zirconia ceramic is crucial in the applications of dental implants. This study investigated the relationship between structure and mechanical properties of the zirconia dental ceramics and their susceptibility to human body temperature in a prolonged time. Commercial samples were put into exaggerated low-temperature degradation (LTD) as per ISO standard and three-quarters of its ageing temperature to see its effect on LTD in zirconia-based ceramics. The results reveal a negligible effect of LTD on the material at a temperature lower than 134°C, which is the standard LTD temperature for zirconia.