Advanced ceramic materials with complex design have become inseparable from the current engineering applications. Due to the limitation of traditional ceramic processing, ceramic additive ...manufacturing (AM) which allows high degree of fabrication freedom has gained significant research interest. Among these AM techniques, low-cost robocasting technique is often considered to fabricate complex ceramic components. In this work, aqueous ceramic suspension comprising of commercial nano-sized yttria-stabilized zirconia (YSZ) powder has been developed for robocasting purpose. Both fully and partially stabilized YSZ green bodies with complex morphologies were successfully printed in ambient conditions using relatively low-solid-content ceramic suspensions (<38 vol%). The sintered structures were able to retain the original morphologies with >94% of the theoretical density despite its high linear shrinkage (up to 33%). The microstructure analysis indicated that dense fully and partially stabilized YSZ with grain size as small as 1.40 ± 0.53 and 0.38 ± 0.10 μm can be obtained, respectively. The sintered partially stabilized YSZ solid and porous mesh samples (porosity of macro-pores >45%) exhibited hardness up to 13.29 GPa and flexural strengths up to 242.8 ± 11.4 and 57.3 ± 5.2 MPa, respectively. The aqueous-based ceramic suspension was also demonstrated to be suitable for the fabrication of large YSZ parts with good repeatability.
The inherent disadvantage of lead‐free potassium sodium niobate (KNN)‐based ceramics is the severe temperature instability of piezoelectric charge coefficient (d33) caused by the polymorphic phase ...boundary. Herein, a new concept of structural gradient is proposed by designing compositionally graded multilayer composites with multiple successive phase transitions, to solve the challenge of the inferior temperature stability. The structural gradient ceramics exhibit a superior temperature reliability (d33 remains almost unchanged in the temperature range of 25–100 °C), far outperforming the previously reported KNN counterparts with d33 variation above 27% over the same temperature range. The synergistic contribution of the continuous phase transition, the strain gradient, and the complementary effect of each constituent layer leads to the excellent temperature stability, which is also confirmed by phase‐field simulation. These findings are expected to provide a new paradigm for functional material design with outstanding temperature stability.
A new concept of structural gradient is proposed by designing compositionally graded multilayer composite with multiple successive phase transitions. The structural gradient ceramics exhibit a superior piezoelectric temperature stability over extensively studied lead‐free piezoelectrics, and thereby achieve a new record performance.
Materials with negative permittivity need to be used at different temperatures, while the negative permittivity behavior affected by large fluctuations in temperature has seldom been studied. In this ...work, La0.5Sr0.5MnO3 ceramics were prepared by a sol-gel auto-combustion method and subsequent sintering. The negative permittivity behavior, electrical conductivity and reactance of La0.5Sr0.5MnO3 ceramics were systematically studied at various temperatures. The fluctuation in negative permittivity is less than 2.6 % and the dielectric loss (tanδ) is less than 0.2 in the temperature range of 50–600 °C. Based on the key governing properties being achieved, the present work experimentally demonstrates that La0.5Sr0.5MnO3 ceramics, as single-phase oxides, can be used as a feasible alternative metamaterial in a wide temperature range.
Stereolithography (SLA) requires the creation of stable and well dispersed ceramic suspensions with high solid loading in order to achieve dense ceramic parts. Five different dispersants used were ...stearic acid (SA), oleic acid (OA), Disperbyk (BYK), coupling agent KH560 and variquat CC 42 NS (CC). The results indicated that BYK, KH560 and OA are all capable of creating low viscosity, well dispersed suspensions with nanozirconia particles; of these 3 wt% BYK was the best option. 3 wt% BYK treated suspensions displayed shear thinning behaviour and had a viscosity of 1680 mPa s at a shear rate of 18.6 s−1. A zirconia part was fabricated using the optimized suspension and its production followed the Beer-Lambert law. After sintering, a significant shrinkage was measured (21.9% in X–Y plane and 28.9% in Z directions), the SEM image showed the sintered part offered a high level of densification.
Ceramic Electrolytes
In article number 2203663, Ritu Sahore, Xi Chelsea Chen, and co‐workers investigate the role of ceramic architecture and excess surface polymer layers in a 3D interconnected ...ceramic/polymer composite electrolyte. The cover art highlights that despite the interconnectedness, the high impedance polymer/ceramic interface at the surface is a bottleneck.
Rare earth silicate environmental barrier coatings (EBCs) are state of the art for protecting SiC ceramic matrix composites (CMCs) against corrosive media. The interaction of four pure rare earth ...silicate EBC materials Yb2SiO5, Yb2Si2O7, Y2SiO5, Y2Si2O7 and three ytterbium silicate mixtures with molten calcium‐magnesium‐aluminosilicate (CMAS) were studied at high temperature (1400°C). The samples were characterized by SEM and XRD in order to evaluate the recession of the different materials after a reaction time of 8 hours. Additionally, the coefficient of thermal expansion (CTE) was determined to evaluate the suitability of Yb silicate mixtures as EBC materials for SiC CMCs. Results show that monosilicates exhibit a lower recession in contact with CMAS than their disilicate counterparts. The recession of the ytterbium silicates is far lower than the recession of the yttrium silicates under CMAS attack. Investigation of the ytterbium silicate mixtures exposes their superior resistance to CMAS, which is even higher than the resistance of the pure monosilicate. Also their decreased CTE suggests they will display better performance than the pure monosilicate.
MWO4 tungstates (M = Zn, Mg, Ni, Co) were synthesised by calcining the mixed oxide powders at 900 C, followed by planetary milling, uniaxial pressing and sintering at 900-1200 C. The specimens were ...characterised by microstructural studies, and determinations of phase composition, density, grain size, and measurements of quality factor and relative permittivity at frequencies of 8.5-10 GHz. All materials, except MgWO4, were single phase, and all had a wolframite-like monoclinic P2/c (13) structure. All sintered at temperatures above those acceptable for use with Cu (1085 C) or Ag (960 C) electrodes. Although not fully sintered, ZnWO4 and CoWO4 exhibited satisfactorily high quality factor values of 34000 and 28900 GHz, respectively, below these temperature limits. When sintered at 1200 C, the quality factors of ZnWO4, NiWO4 and CoWO4 were 62800, 24900 and 38600 GHz, respectively. MgWO4 disintegrated on sintering at 1250 C, attributed to phase change. 14 refs.
(Bi0.5Na0.5)TiO3–BiAlO3 lead‐free materials exhibit excellent ferroelectric properties, but its depolarization temperature is relatively low which is the major obstacle limiting the material's ...practical application. In this study, the effects of Manganese (Mn) modification on the microstructure, ferroelectric properties and depolarization behavior of 0.96(Bi0.5Na0.5)(Ti1−xMnx)O3–0.04BiAlO3 ceramics were investigated. It was found that the average grain size was enlarged and ferroelectric properties were enhanced with small Mn addition, meanwhile the tangent loss decreased. The remnant polarization (Pr) of the samples reached an optimal value (~41 μC/cm2) as Mn content increased up to 0.7 mol%, whereas further addition resulted in the decrease in Pr. Moreover, appropriate Mn addition (x=0.7%) can improve the depolarization temperature from 140°C to 161°C determined from thermally stimulated depolarization currents measurement.
A multiscale structural design was innovatively adopted herein to increase the toughness of monolithic HfB2 ceramics. SiC whiskers (SiCw) and graphene oxide (GO) were used as fillers for the HfB2 ...matrix, whereas a ductile W foil was introduced as an interlayer to synthesize laminated HfB2‐SiCw‐rGO/W ceramics. Monolithic HfB2‐SiCp (particulate) and laminated HfB2‐SiCp/W ceramics were prepared using the same routes and used as controls. Following tape casting and spark plasma sintering at 1800°C, the toughness of the prepared laminated HfB2‐SiCw‐rGO/W samples was increased to 14.2 ± 0.6 MPa·m1/2, with minimal sacrifice in flexural strength (421 ± 16 MPa). Morphological analysis of the fracture surface revealed the synergistic effects of micro‐toughening (including bridging and pullout of whiskers and rGO) and macro‐toughening (including crack deflection, bifurcation, and delamination) mechanisms responsible for improving the fracture toughness of the laminated HfB2‐SiCw‐rGO/W composites.
We reported a multiscale structural design to toughen HfB2‐based ceramics. Thin metal W interlayer was introduced into laminated HfB2 ceramics for the first time to combine the strength of ceramics and the ductility of metals. Moreover, the micro‐toughening effect was enriched by incorporation of SiC whisker and rGO fillers in HfB2 matrix.
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