Search

Novel complex-shaped porous B 4 C supports were fabricated for use in ceramic membrane filtration applications, the processing of which is described in detail. Firstly, an extrudable ceramic paste was formulated and homogenised, containing a high content of B 4 C of super-coarse and ultrafine grades, plus water as liquid medium and various organic additives as thickener, binder, plasticiser, and lubricant. Secondly, tubular honeycomb parts (i.e. , cylinders of ∼26 mm outer diameter with 30 inner channels of 3 mm diameter each) were extruded at ∼25 bar and dried in air at 120 °C for 24 h, resulting in robust green B 4 C membrane supports without macro- or micro-defects. Thirdly, suitable debinding conditions were identified by thermogravimetry of the paste and its components, and the dry membrane supports were debinded at 700 °C for 1.5 h in high vacuum (<0.1 Pa) confirming that they retain their shape with minimal isotropic shrinkage (∼0.13–0.15 %). And fourthly, the debinded membrane supports were pressureless sintered at 2000 °C for 3 h in inert atmosphere undergoing only an additional 1 % isotropic shrinkage, resulting in B 4 C membrane supports with low apparent density (∼0.89(1) g/cm3), high porosity (∼38–39 %), open interconnected micrometre pores (in the range ∼0.5–16 μm, and d 50 ∼1.5 μm), and low skeletal density (∼2.455(1) g/cm3). Importantly, their only partial densification makes them both sufficiently strong mechanically (∼68(2) MPa compressive strength) and highly permeable to water (∼13131(418) l/(m2·h·bar) permeability at ∼1.3 bar). These attributes, together with the intrinsic lightness and durability of B 4 C ceramics, make these novel supports in principle very appealing for ceramic membrane filtration and other applications. [ABSTRACT FROM AUTHOR]

Nanostructured Y‐TZP samples with Non‐Homogeneous Yttria Distribution (NNHYD) were prepared by mixing co‐precipitated 3Y‐TZP powder (Tosoh TZ‐3Y) with yttria‐free monoclinic powder (Tosoh TZ‐0), yielding an overall yttria content of 2 mol%. The cyclic fatigue behavior of NNHYD was evaluated by Step‐Stress Accelerated Life Testing (SSALT) and mechanical cycling in a biaxial flexural strength test (BFST) setup and compared to Conventional Submicrometric 3Y‐TZP (CS). Physical, structural, microstructural, and mechanical characterizations of all groups were also evaluated and compared before and after artificial aging in autoclave. NNHYD presented a higher capacity for damage accumulation and maintenance of phase transformation potential than CS, associated with elevated resistance to the propagation of Low‐Temperature Degradation (LTD). A nanostructured 3Y‐TZP surface layer introduced in NNHYD by dip coating (DC‐NNHYD) improved resistance to LTD at the cost of reduced reliability under cyclic fatigue by increasing the stability of the tetragonal phase. This surface alteration highlights the impact of surface properties on mechanical performance. The results of this study present practical possibilities to help achieve the ideal balance between strength, toughness, and LTD resistance to improve the lifetime of zirconia‐based biomaterials. [ABSTRACT FROM AUTHOR]

Synthesis of metal oxides is typically the first step of any materials science research in a field or application involving oxides materials. However, the synthesis is rarely the prime focus in materials science, which usually describe properties and characterizations of said materials. Consequently, synthesis protocols are often given too little attention in the literature and hence poorly described. For scientists starting in the field, it becomes confusing to make the right choice of synthesis route and conditions to successfully prepare what will be the base of their research, which is a pure, single phase, complex oxide powder. With this tutorial article, we are giving basic knowledge on the underlying chemistry of oxide synthesis, and simple explanations on what motivates the need of various synthesis routes. Then, four main synthesis routes are described, namely the solid state reaction route, the Pechini route, the combustion route, and the precipitation route. For each routes, the approach is described, and the relevant parameters to be considered are developed. Finally, a step by step general protocol for each route is proposed, which can serve as a solid foundation for unexperienced researchers to become more confident when approaching metal oxide synthesis. [ABSTRACT FROM AUTHOR]

Chemical substitution, which can be iso- or heterovalent, is the primary strategy to tailor material properties. There are various ways how a material can react to substitution. Isovalent substitution changes the density of states while heterovalent substitution, i.e. doping, can induce electronic compensation, ionic compensation, valence changes of cations or anions, or result in the segregation or neutralization of the dopant. While all these can, in principle, occur simultaneously, it is often desirable to select a certain mechanism in order to determine material properties. Being able to predict and control the individual compensation mechanism should therefore be a key target of materials science. This contribution outlines the perspective that this could be achieved by taking the Fermi energy as a common descriptor for the different compensation mechanisms. This generalization becomes possible since the formation enthalpies of the defects involved in the various compensation mechanisms do all depend on the Fermi energy. In order to control material properties, it is then necessary to adjust the formation enthalpies and charge transition levels of the involved defects. Understanding how these depend on material composition will open up a new path for the design of materials by Fermi level engineering. [ABSTRACT FROM AUTHOR]

Cracks can form during the freeze‐drying of freeze cast ceramic suspensions while attempting to produce dense ceramics. The suspensions contain alumina particles dispersed in cyclohexane. The rate of drying is controlled by the pressure and temperature during drying (slow drying at atmospheric pressure and −15°C and fast drying under vacuum while the temperature slowly increases from −80°C to room temperature). X‐Ray micro‐computed tomography was used to characterize internal crack formation. Cracks were found to occur during freeze‐drying rather than during freezing. Both slow and fast drying produced cracks, although two different morphologies were observed. Mechanistic models are proposed for the formation of both types of cracks. The rate of freezing was found to influence the formation of cracks. Slow freezing tended to reduce the formation of drying cracks because the slower freezing produced a more heterogeneous distribution of particles and porous regions, which tends to allow stress to be relieved by opening up existing pores rather than forming cracks in the more homogeneous fast frozen bodies. [ABSTRACT FROM AUTHOR]

Stereolithography of ceramics remains one of the most powerful additive manufacturing routes for the creation of intricate ceramic parts. Despite its utility as a forming tool, ceramic stereolithography requires a challenging debinding stage due to the requisite high polymeric loading. Earlier research has identified both the polymeric resin composition and debinding atmosphere to be crucial factors in improving debinding performance. Here, we use a combination of thermogravimetric analysis and neutron imaging to examine samples of different compositions printed using the same processing and exposure parameters. We quantify the influence of both polyethylene glycol addition and the use of different debinding atmospheres (argon and vacuum) on the debinding behavior of ceramic pellets. Specifically, we demonstrate a method for examining the concentration gradients that develop during thermal debinding with the aid of neutron tomography. We find that at a constant heating rate of 1°C/min up to 500°C, vacuum atmosphere appears to result in a greater number of cracks as compared to the use of argon. The vacuum atmosphere led to the development of lower concentration gradients in the samples on average. The greatest improvement resulted with the addition of polyethylene glycol to the samples. This addition led to significantly less cracking and much lower concentration gradients in samples during debinding. These results prompt us to conclude that while keeping printing and exposure parameters constant, composition modification has a more significant effect on the debinding improvement than heating atmosphere. [ABSTRACT FROM AUTHOR]

Dense and homogeneous nanostructured Y-TZP ceramics were prepared by colloidal processing and 2-step sintering using commercial powders. The influence of non-homogeneous yttria distributions on mechanical properties and Low-Temperature Degradation (LTD) resistance were assessed. Physical, structural, microstructural, and mechanical characterizations of all groups were evaluated and compared before and after artificial aging. Nanostructured Y-TZP samples with non-homogeneous yttria distributions presented the highest fracture toughness and elevated fracture strength. These samples were susceptible to LTD, but with the transformed monoclinic phase fraction restricted to the near-surface region. The characterization data of nanostructured samples were compared to those of conventional 3Y-TZP. The results of this work indicate that it may be possible to prepare Y-TZP ceramics with improved mechanical properties and resistance to LTD by careful and systematic design and engineering of nanostructures. [Display omitted] [ABSTRACT FROM AUTHOR]

Introduction: Dilutely doped ferroelectric materials are of interest, as engineering these materials by introducing point defects via doping often leads to unique behavior not otherwise achievable in the undoped material. For example, B-site doping with transition metals in barium titanate (BaTiO3, or BTO) creates defect dipoles via oxygen vacancies leading enhanced polarization, strain, and the ability to tune dielectric properties. Though defect dipoles should lead to dielectric property enhancements, the effect of grain size in polycrystalline ferroelectrics such as BTO plays a significant role in those properties as well.Methods: Herein, doped BTO with 1.0% copper (Cu), iron (Fe), or cobalt (Co) was synthesized using traditional solid-state processing to observe the contribution of both defect-dipole formation and grain size on the ferroelectric and dielectric properties.Results and discussion: 1.0% Cu doped BTO showed the highest polarization and strain (9.3 μC/cm2 and 0.1%, respectively) of the three doped BTO samples. While some results, such as the aforementioned electrical properties of the 1.0% Cu doped BTO can be explained by the strong chemical driving force of the Cu atoms to form defect dipoles with oxygen vacancies and copper’s consistent +2 valency leading to stable defect-dipole formation (versus the readily mixed valency states of Fe and Co at +2/+3), other properties cannot. For instance, all three Tc values should fall below that of undoped BTO (typically 120°C–135°C), but the Tc of 1.0% Cu BTO actually exceeds that range (139.4°C). Data presented on the average grain size and distribution of grain sizes provides insight allowing us to decouple the effect of defect dipoles and the effect of grain size on properties such as Tc, where the 1.0% Cu BTO was shown to possess the largest overall grains, leading to its increase in Tc.Conclusion/future work: Overall, the 1% Cu BTO possessed the highest polarization, strain, and Tc and is a promising dopant for engineering the performance of the material. This work emphasizes the challenge of extricating one effect (such as defect-dipole formation) from another (grain size modification) inherent to doping polycrystalline BTO.

Copyright of Revista Foco (Interdisciplinary Studies Journal) is the property of Revista Foco and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The formation of advanced ceramic components with homogeneous microstructure and functional characteristics demands a suitable control of particle dispersion. Thus, the characterization of particle stability as immersed in a liquid medium is important. The present paper reports an approach to evaluate the stability of europium, thulium co-doped yttria (YET) nanoparticles by a correlation between zeta potential and Electron Paramagnetic Resonance (EPR) techniques. Based on results, YET suspensions exhibited high stability apart from pH 10, while their isoelectric point presented a slight variation from pH IEP 8.5 to 9.2 according to thulium content 0 and 2 at.%, respectively. The peak-to-peak amplitude of EPR spectra of the YET suspensions increased as pH shifted toward alkaline condition, following zeta potential curves features. The present achievements are very useful parameters to form stable suspensions based on rare-earth oxides and to advance toward new materials for radiation dosimetry. [Display omitted] • Tm, Eu co-doped yttria (YET) particles were evaluated by zeta potential (ζ) and electron paramagnetic resonance (EPR). • Tm content induces changes in surface chemistry of particles and EPR spectra. • The isoelectric point of YET compositions varied from pH IEP 8.5 to pH IEP 9.2. • YET suspensions are highly stable at pH 10.5 (ζ > 20 mV). • The mean EPR peak of YET suspensions were recorded between 160 and 165 mT. • Peak-to-peak amplitude ofYET suspensions are in accordance with zeta results. • YET suspensions exhibited slight variation g-values from 4.380 to 4.335. • EPR measurement results corroborated zeta potential findings. [ABSTRACT FROM AUTHOR]

Pure and low α-Al 2 O 3 /SiO 2 co-doped ceria specimens were prepared by conventional ceramic processing using powder metallurgy. This study investigated the effect of co-doping on the microstructural and structural properties of cerium dioxide was investigated by means of optical microscopy, scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The co-addition of alumina and silica promoted liquid phase sintering and significantly contributed to grain growth, even in the small concentrations of the present study (1 and 2 wt%). A glassy look phase precipitated at the grain boundaries, a characteristic feature of liquid phase sintering. The addition of dopants to the formulation greatly enhanced the grain growth process without disturbing the CeO 2 structure. [ABSTRACT FROM AUTHOR]

The production of porcelain tiles is increasing in Brazil besides the production of grés tiles and monoporosa is decreasing since COVID 19. Plastic clays are used in the composition of porcelain tiles to give plasticity to the pastes in the forming step. However, there is a shortage of plastic clays in south Brazil, the largest producer of porcelain tiles. Therefore, the aim of this work was to improve the plasticity of two commercially available kaolins by high-energy milling (HEM). Both kaolins were characterized before and after milling by X-ray diffraction, particle size, plasticity, and cation exchange capacity techniques. After high-energy milling, the processed kaolins were used in the composition of a commercial porcelain tile paste. The performance of the paste before and after use of the processed kaolins was determined regarding its firing shrinkage and sintering temperature. The porcelain tile compositions with the high-energy milled kaolins showed less densification during pressing and greater shrinkage after firing, but the tiles presented dimendional stability, improving the quality of the tiles.

“Lead free” piezoceramics 0.99K0.5Na0.5NbO3-0.01BiFeO3 (KNN–BF) with increasing amount of CuO (0, 0.5, 1 wt.%) were prepared through a scalable combination of High Energy Ball Milling, calcination at 900 °C and air sintering. The effect of CuO on the sintering behaviour and electrical properties of KNN–BF was investigated. The compositions examined show high-density values (>95% of TD) at their optimized sintering temperatures. Small addition of CuO (0.5 wt.%) causes an increase in the size of grains, however an excess of CuO (1 wt.%) inhibits the growth of grains due to the excess of liquid phase. The KNN–BF composition shows promising electrical properties (d33 = 150 pC/N; kp = 42%; Qm = 150) which are mainly related to the high density achieved and to the orthorhombic-tetragonal symmetry coexistence. The addition of 0.5 wt.% of CuO causes an increase in the quality factors (Qm = 235; Q(d31) = 207).

Thailand is the world's largest rice exporter, tend to continuous increasing the agricultural waste. Burning, to eliminate an agricultural waste, pollutes the air with CO and CO2 emissions which is considered by many in the science community to be a cause of global warming. However, the calcined agricultural waste with the optimum temperature, results in a rich source of active-SiO2. Active-SiO2 was reacted with sodium hydroxide (NaOH) to form sodium silicate (Na2SiO3), called as waterglass or soluble glass. Therefore, sodium silicate is often used as a deflocculant in clay-based ceramic slip production to reduce viscosity instead of adding large amounts of water. In this work, rice straw and rice husk are an agricultural waste and used as a starting material. Before used, the reaction temperature of agricultural waste is checked by using DTA-TGA technique. The waste was first calcined at 600 °C for 2 h in air to remove organic matter and produce high purity of active-SiO2. This was then added to NaOH as the starting material for Na2SiO3 synthesis. Then used synthesized Na2SiO3 as a dispersant in clay-based ceramic slip. The phase, viscosity, porosity, and particle arrangement were tested and compared with commercial grade of Na2SiO3. Sodium silicate from agricultural waste exhibited high-performance deflocculant behavior, with reduced viscosity and water demand of clay minerals. Card pack particle arrangement resulted in increased density and low porosity, and directly endowed the ceramic products with high strength. For reducing waste and environmental impact, the result suggested that sodium silicate produced from agricultural waste, can be utilized as a promising and alternative natural deflocculant to clay-based ceramic slip in the ceramic manufacturing process to decrease production costs. [ABSTRACT FROM AUTHOR]

Porous nonoxide ceramics have exhibited impressive progress in terms of synthesis and applications over the past few decades because of their unique characteristics distinguished from the oxide counterparts. From the synthetic aspect, the preceramic polymer route, where nonoxide ceramics such as carbides and nitrides are produced from molecular precursors, offers exceptional opportunities to elaborate and control the material shape as well as the micro‐ and nanostructures in concert with various techniques. This review presents monolithic ceramic materials based on various reduced phases bearing hierarchical porosity with a focus on those obtained from macroporous preceramic monoliths prepared via the one‐pot sol–gel process accompanied by spinodal decomposition. Here, we highlight two classes of preceramic inorganic–organic hybrid gels: organometallic crosslinked polymers based on poly(silsesquioxane)s and nonorganometallic hybrid networks related to Ti without Ti–C bonds. The polymer‐to‐ceramic conversion processes are discussed with concern for the crystal transition behaviors and the variation of pore properties in different length scales upon heating. In addition, although out of the preceramic polymer category, some examples of inorganic–organic nanocomposite gels with a carbonizable polymer and/or urea for yielding porous metal carbides and nitrides in a monolithic form are introduced as well, which provides extended versatility toward a variety of transition metal systems. [ABSTRACT FROM AUTHOR]

This research investigated the production of porous zinc oxide (ZnO) ceramics obtained by the replica method for water depollution by photocatalytic processes. Five photo-decolorization cycles were performed to analyze the reuse potential of the ceramics. Statistical analyses using R programming were conducted to investigate possible significant differences between them. The ceramics porosities were between 46.74 and 62.50% (depending on the composition). The most successful results were achieved in prepared ceramics from slurries containing 65% ZnO and 1% carboxymethylcellulose, in which the dye decolorization results reached 90.5% after 5 cycles, indicating a high reuse potential of these ceramics. Multivariate analysis proved the negative effect of increasing the heat treatment temperature on the evaluated properties. The best processing conditions to obtain porous ZnO ceramics by the replica technique were established through statistical tools, with very satisfactory results in the photo-decolorization potential of the investigated dye.

Metal-supported SOFC consists of metallic and ceramic multilayers. Since the cell has to be flat, interaction between the layers that results in a flat sintered layer needs to be studied. The method used here was changing the starting materials through several experiments. Here, we highlight the effects of pore former in metal slurry on the sintered half-cell multilayer of a 430L metallic support, an NiO-8YSZ anode, and an 8YSZ electrolyte. The results show that by changing the amount of pore former in the 430L metal slurry changed the sinterability of the metal layer. This change of the sinterability of the metal support affected the final warpage state of the cell. This study aid in explaining the sintering phenomena between layers of metal-supported SOFCs. [ABSTRACT FROM AUTHOR]

The present work describes a comparative study on a pool of 12 dispersants for the de‐agglomeration and stabilization of silicon carbide in aqueous suspensions with solids loading relevant for dip coating applications. As silicon carbide slurries may include sintering aids, different functional groups, molecular weight, and stabilization mechanisms were considered for the dispersants to be able to stabilize both slurry components. Additionally, pH effect, toxicity, additive compatibility, and foaming properties were considered, giving all the necessary information for developing new aqueous formulation of SiC suspensions, including advantages and disadvantages of the different candidates. Different de‐agglomeration procedures, powder surface area, and calcination temperature were also considered to study the effect of the SiC surface properties. The outcome is that slurry stabilization provided by an alkaline environment at pH larger than 8‒9 is significantly more effective than slurry stabilization by any of the tested dispersants. Alkaline environments facilitate a negative surface charge on SiC particles and provide a stable electrostatic stabilization mechanism not observed in neutral or acidic environments. One among the dispersant candidates (FA 4404) seems to broaden slightly the range of stability toward the acidic regime. Anionic surfactants or block co‐polymers tested exhibited no significant interaction with the SiC particles. [ABSTRACT FROM AUTHOR]

The effects of Yttrium-doped Barium Zirconate (BZY) synthesis steps by solid-state reaction and the number of starting reactants (2 or 3) on the characteristics of the synthesized ceramic powders were investigated. The slow diffusion rate associated with this synthesis route and the calcination steps used in this work lead to an incomplete synthesis reaction. This condition proved to be useful to improve densification during sintering for undoped samples by emulating the reactive sintering technique with transient reactions originating from the residual BaCO 3 reactant. The effects of a low concentration (1 mol%) of ZnO as sintering aid on microstructure and electrical conductivity were also investigated and used for comparison to undoped samples. Electrical properties were analyzed and correlated with microstructural and compositional characteristics. Dense undoped BZY samples (99% of relative density) with high proton conductivity (2.4 × 10 − 2 S/cm at 600 °C) were obtained by sintering at 1500 °C, while ZnO-doped samples achieved high relative density (97%) at only 1300 °C, but with lower electrical conductivity (7.8 × 10 − 3 S/cm at 600 °C). Image 1 • BZY was synthesized by solid-state reaction route using 2 or 3 reactants: BaCO 3 and 10YSZ or BaCO 3 , ZrO 2 , and Y 2 O 3. • Solid-state reactive sintering was achieved without sintering aids due to the presence of residual BaCO3 reactant. • Undoped BZY samples achieved high densities (99% of relative density) by traditional sintering at 1500 °C. • Characteristics of undoped samples were compared to samples with ZnO as sintering aid. • Undoped BZY samples presented high proton conductivity at 600 °C (2.4 × 10 − 2 S / c m). [ABSTRACT FROM AUTHOR]

• DIC highlights damage growth by means of increased crack density and crack openings for networks on monitored surfaces, whereas traditional techniques only monitor Young's modulus changes. • Tomography scans showed that cracks initiate on the surface, and then propagate toward the center of the specimen. • DIC results indicate that after the crack density reaches its maximum value, the crack opening displacements continue to increase as in-depth propagation is still active. MgO particles are added to high-alumina castables to provide in situ spinel formation at high temperatures. However, the MgO hydration upon curing may damage the material because of localized volumetric expansion. Usually, damage is evaluated by the ex situ overall measurement of Young's modulus changes during processing via Impulse Excitation Techniques. In this paper, an experimental setup was designed to use Digital Image Correlation (DIC) as an in situ alternative to evaluate damage. Tomographic scans highlighted that all cracks initiated on the sample surfaces, and propagated in the bulk in an intergranular mode. Crack initiation and growth were assessed, for different temperatures, via Surface Crack Density (SCD) measurements, and Mean Crack Opening Displacement (MCOD) fields. They provided important insights into heterogeneous expansion phenomena and crack network quantification; for example, the SCD flattened while the overall damage was still increasing. The results attested the usefulness of DIC for in-situ quantification of ceramics cracking during processing. [ABSTRACT FROM AUTHOR]

The properties of ceramic layers are not only related to the coating material but also—to a very high degree—the processing technology used. In particular, microstructure and thickness are key to the successful implementation of functional layers in application. This will be shown using yttria‐stabilized zirconia (YSZ) as an example, a highly versatile compound with high fracture toughness, high chemical and thermal stability, high biological compatibility, and high oxygen ion conductivity. For each application, specific microstructures are required, which can only be obtained by suitable processing. Herein, coating technologies for layers with thicknesses spanning the nanometer range up to several hundred micrometers, and from full density to tailored open porosity are focused. Wet processing routes, thin‐film deposition from the gas phase as well as thermal and plasma spraying are presented along with the resulting YSZ layers. [ABSTRACT FROM AUTHOR]

The effects of powder characteristics and conformation methods on green microstructure have been investigated, and microstructural evolution was analyzed based on the green density and the different sintering techniques. Colloidal processing of nanopowders with narrow particle size distribution (15 ± 5 nm) can be more problematic than dry processing and can lead to more heterogeneous microstructures. Two-step sintering can be used to obtain dense nanostructured samples with more flexibility than microwave sintering and still at lower temperatures than conventional sintering. The sinterability of Ce 0.8 Gd 0.2 O 1.9 is significantly improved by Zn addition, which can reduce sintering temperature to values as low as 800, 1150 and 1200 °C for two-step, microwave and conventional sintering, respectively, in order to achieve relative densities above 90%. Microscopic grain boundary conductivity is shown to be improved in nanostructured samples, despite the higher grain boundary density. [ABSTRACT FROM AUTHOR]

The development of a low-cost and environmentally-friendly procedure for the fabrication of silicon carbide (SiC) membranes while achieving good membrane performance is an important goal, but still a big challenge. To address this challenge, herein, a colloidal coating suspension of sub-micron SiC powders was prepared in aqueous media by employing aluminum nitrate nonahydrate as a sintering additive and was used for the deposition of a novel SiC membrane layer onto a SiC tubular support by dip-coating. The sintering temperature influence on the structural morphology was studied. Adding aluminum nitrate nonahydrate reduced the sintering temperature of the as-prepared membrane compared to conventional SiC membrane synthesis. Surface morphology, pore size distribution, crystalline structure, and chemical and mechanical stability of the membrane were characterized. The membrane showed excellent corrosion resistance in acidic and basic medium for 30 days with no significant changes in membrane properties. The pure water permeance of the membrane was measured as 2252 L h−1 m−2 bar−1. Lastly, the final membrane with 0.35 µm mean pore size showed high removal of oil droplets (99.7%) in emulsified oil-in-water with outstanding permeability. Hence, the new SiC membrane is promising for several industrial applications in the field of wastewater treatment.

Ultra‐high temperature ceramics (UHTCs) have emerged as promising materials for high‐temperature aerospace applications due to their high melting temperature and superior ablation performance. Even still, they have yet to reach their full potential due to the catastrophic brittle failure that typically accompanies the intrinsic low fracture toughness of ceramic materials. Therefore, the emerging field of UHTC ceramic matrix composites (UHTCMCs) offers the toughness benefits of a composite with the high temperature stability of UHTCs. Here, we outline work in the last decade on the processing of UHTCs with a reinforcing fiber phase for enhanced fracture toughness. Included are fibers of both carbon and silicon carbide composition in both continuous and chopped fiber lengths. Particular emphasis is given to emerging research from the last few years to highlight novel developments. [ABSTRACT FROM AUTHOR]

Open-Celled silicon carbide (SiC) foams were prepared from a mixture of a boron-modified polycarbosilane as a preceramic polymer and poly(methymetacrylate) (PMMA) microbeads as sacrificial agents. The process consists in the cross-linking of the liquid allylhydridopolycarbosilane (AHPCS, SiC precursor) with borane dimethylsulfide (BDMS, boron source) to form a solid boron-modified polycarbosilane with an adjusted cross-linking degree. The latter is mixed with PMMA microbeads (25 μm) in a 20:80 ratio and the mixture is warm-pressed at 120 °C forming consolidated green bodies to be pyrolyzed at 1000 °C under argon and to deliver open-celled SiC foams with an interconnected porosity of 73.4 vol %. These foams combine a low density with a compressive strength of 3.49 ± 0.56 MPa and a thermal and mechanical stability under argon up to 1300 °C. Ageing and microfiltration tests in the conditions of a primary loop of coolant in a Pressurized Water Reactor (PWR) showed that foams display a relatively high stability while retaining particles of 5 μm in diameter making these materials as appropriate candidates to work in separation techniques under harsh environments. [ABSTRACT FROM AUTHOR]

The influence of the sintering temperature and the dwell time on the structural, optical, and dielectric properties of [KNbO3]0.8[Ba(Ni0.5Nb0.5)O3−δ]0.2 ceramics (KBNNO) was systematically investigated. X‐ray diffraction measurements of the ceramic bodies sintered at different temperatures indicated that all samples presented a cubic‐like structure. However, the results remarkably revealed that both the sintering temperature and the dwell time are crucial factors that must be taken into account for "tuning" the optical response of the KBNNO ceramics. It was concluded that fine distortions in the (Nb,Ni)O6 octahedral site, induced by sintering temperature and dwell time, promoted subtle changes in the local crystal field and, consequently, in the optical properties of the KBNNO. The mechanisms responsible for the observed spectral features of KBNNO were discussed by considering absorbance spectra of NiNb2O6 ceramics and allowed ligand‐field transitions. The comparison between both optical spectra revealed a notable similarity between them. Since the octahedral site in KBNNO is equivalent to the nickel columbite structure, it was inferred that the spectral behavior is mainly driven by the same two contributions: one major associated to a distorted octahedral configuration and one minor related to spin‐orbit coupling effects. In accordance with X‐ray diffraction data, the temperature dependence of the dielectric properties corroborated that the KBNNO present a cubic‐like phase in the whole temperature range investigated. [ABSTRACT FROM AUTHOR]

Abstract The colloidal properties and processing of aqueous LaNi 0.6. Fe 0.4 O 3 suspensions into electrode layers with hierarchical pore sizes has been investigated by light scattering, electron microscopy and rheology. We found that the colloidal stability of the oxide particles and the resulting microstructure of the electrode layers were similar when dispersing the particles at their intrinsic pH, or when adding polyvinylpyrrolidone. The addition of the ammonium salt of poly(methaacrylic acid) resulted in a poor colloidal stability and the concentrated suspensions became viscoelastic during processing. Addition of rice starch resulted in an increase of the porosity but the cast electrode layers cracked and delaminated. [ABSTRACT FROM AUTHOR]

Chromia-forming metallic interconnects used for solid oxide cells require protective coatings to prevent chromium poisoning of other cell components. This study focuses on Mn 1.0 Co 1.9 Fe 0.1 O 4 -coated Crofer 22 H interconnects fabricated by wet powder spraying, which is a versatile, cost-effective, and scalable coating technique. The investigation and fine-tuning of relevant parameters along the process chain provide a fundamental understanding of their impact on coating quality and thermomechanical stability. The correlation with cross-sectional analysis and area-specific contact resistance (ASR) measurements supports the parameter evaluation. Mid-term thermal testing demonstrates excellent chromium retention, as well as chemical and mechanical stability of the protective layer on real component interconnect substrates. With an ASR below 10 mΩ cm2 after 1000 h at 800 °C, wet powder spraying represents a viable alternative to established but more expensive processes. • Successfully applied wet powder sprayed Cr retention layers on interconnects. • Optimization of coating parameters. • Optimization of reduction and oxidation parameters. • Dense, adhering, thin layers obtained. • Layers with respect to area resistance optimized. [ABSTRACT FROM AUTHOR]

Abstract MgO nanopowders were synthesized through the co-precipitation method with different Y 2 O 3 percentages (0, 2.5, 5, and 10 wt %). The nanocomposite powder was characterized by thermal gravimetric-differential thermal analysis (TG-DTG-DTA), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and field-emission scanning electron microscope (FESEM) analysis. Y 2 O 3 can have positive effect on synthesis and sintering of MgO Y 2 O 3 ceramic likewise particles size and densification process. Crystallite size decreased with increasing amount of Y 2 O 3 additive, and it was 32.6 nm for MgO-10%, and the average particle size by FESEM image was 52.2 nm for this sample. Lattice parameter increased (from 4.2188 to 4.2243 A0) by increasing the additive percentage from 0 to 5%, but it decreased (4.2195 A0) in 10% additive. Nanopowder was sintered by the SPS technique at 1400 °C. MgO-2.5% sample had the highest relative density (99.1%) and transmittance (15%), with an average grain size of 0.41 μm. MgO-5% sample, however, had the highest hardness (10.57 GPa), thanks to the finer average grain size (0.25 μm). Graphical abstract Image Highlights • Nanopowder prepared by the co-precipitation and formed by the SPS methods. • MgO 5%Y 2 O 3 had the highest lattice parameter and MgO 10%Y 2 O 3 had the smallest particles size. • Y 2 O 3 additive improved density and hardness in low amounts, but it decreased them in high amounts. • The best transmittance properties belonged to MgO-2.5%Y 2 O 3 sample. [ABSTRACT FROM AUTHOR]

Rare earth (RE) materials present excellent properties, which importance is recognized worldwide. Innovation approaches in energy, medicine, communication, transportation, militarism, and radiation dosimetry consist in RE based materials. As yttrium oxide (Y 2 O 3 ) exhibits intrinsic lattice characteristics that enable doping with others RE elements (Y 2 O 3 :RE), new materials with promising characteristics can be developed. This work aims to evaluate EPR response of europium-yttria (Y 2 O 3 :Eu) rods obtained by bio-prototyping. Ceramic rods containing up to 10 at.%Eu were irradiated with gamma doses from 0.001 to 150 kGy and evaluated by Electron Paramagnetic Resonance (EPR) at room temperature with X-band EPR. Based on results, Y 2 O 3 :Eu rods with 2 at.%Eu exhibited the most significant response, in which linear behavior arose from 0.001 up to 50 kGy. Fading and thermal annealing evaluations revealed that 2 at%.Eu improved dosimetric characteristics of yttria remarkably. These innovative findings afford that Y 2 O 3 :Eu is a promising material for radiation dosimetry. [ABSTRACT FROM AUTHOR]

Ceramic sheet of Na + ion-conducting solid electrolyte, Na 3 Zr 2 Si 2 PO 12 (NASICON), has been prepared by tape-casting method. Addition of 60Na 2 O-10Nb 2 O 5 -30P 2 O 5 glass as a sintering aid is crucial for fabrication of fully-densified impermeable sheet. Otherwise the gas tightness is not achieved even sintered at 1200 °C. The best preparation condition is 5 or 10 wt% grass-addition with respect to NASICON and sintering at 1000–1100 °C, which is lower by 100–200 °C than the typical densification temperature of NASICON without the additive. A sample with a thickness of 35 μm and total conductivity of 4.4 × 10 −4  S cm −1 is obtained by 5 wt% glass addition and sintering at 1100 °C for 4 h. [ABSTRACT FROM AUTHOR]

Current industrialization era stresses upon taking intensive measures to recognize and utilize sustainable, eco-friendly and high energy output generating resources, thus, shifting focus towards proton conducting fuel cells (PCFCs) for use in industrial, residential and transportation sectors. Accordingly, the following research focused on the development of a novel gadolinium-doped electrolyte material i.e. BaCe0.59Zr0.2Y0.15Gd0.06O2.97-δ (BCZYG59) for PCFCs using solid-state and wet-chemical synthesis approach. X-ray Diffraction Analysis (XRD) and Scanning Electron Microscopy (SEM) were carried out for analyzing microstructural morphology, grain-growth and characteristics, densification trends and other phase/structural transformations, whereas, electrical properties were investigated via DC conductivity testing to examine BCZYG59's feasibility as electrolyte. Homogenous cubic perovskite phase for ensuring proton conduction was achieved at 1300 °C and 1500 °C for BCZYG59 synthesized from wet-chemical and solid–state methods, respectively. These materials showed corresponding conductivity values of 3.20 × 10 −4  S cm −1 and 4.70 × 10 −4  S cm −1 at 650 °C in air with the promising prospects of exhibiting greater proton conductivity making it a fairly convincing choice among present-day electrolyte materials. [ABSTRACT FROM AUTHOR]

Innovating dosimetric materials, which includes design and development of new dosimetric materials based on rare earth oxides, is challenging. Yttrium oxide (Y2O3) is one of the most important sesquioxides and presents crystal characteristics that enable doping with rare earth ions, making it a promising material for radiation dosimetry. This paper reports on the development and measurement of Electron Paramagnetic Resonance (EPR) signal response for Y1.98Eu0.02O3micro rods that have undergone facile low-pressure hydrothermal synthesis and bio-prototyping. As- synthesized powders with narrow sub-micrometer particle size distribution with d50 of 584 nm exhibited a reactive surface, which led to the formation of stable aqueous suspensions by controlling the surface charge density of particles through alkaline pH adjustment. Ceramic samples with dense microstructure were formed by sintering at 1600 oC for 4h at ambient atmosphere. Y1.98Eu0.02O3micro rods were irradiated using a 60Co source with doses from 1 to 100 kGy, and EPR spectra were measured at room temperature in X-band microwave frequencies. Sintered samples exhibited linearity of the main EPR signal response from 10 Gy to 10 kGy. Supralinearity was observed for higher doses, which is possibly ascribed to formation of more defects. Using europium as a dopant enhanced the EPR signal of yttrium rods remarkably, due to 4f–4f transitions of the Eu3+ ion. These innovative findings make europium-doped yttrium oxide a promising material for radiation dosimetry. [ABSTRACT FROM AUTHOR]

We report on a novel type of screw conveyor dryer (SCD) with passive heating by an annular heat pipe, ‘Heat Pipe Screw Dryer’ (HPSD). It was firstly optimised, with its best performance corresponding to the lowest thermal resistances of 0.08–0.18 °C/W achieved at 11% filling ratio and in horizontal orientation. It was applied in the drying of a ceramic raw material slurry (initial moisture 33 wt. %). The highest moisture reduction of 46% (final moisture 18 wt. %) was achieved at 200 °C and 260 s. The specific moisture extraction rate (SMER) was 2.04 kg/kWh, more energy efficient than conventional dryers. Moreover, overall heat transfer coefficients were measured to be 35% higher than in a conventional steam jacketed-SCD due to the excellent thermal conductivity of the annular heat pipe. Solids build up on the surfaces increased from 3–62%, as moisture reduction increased from 10– 46%, respectively. Non-stick coating on the screw conveyor resulted in 10% fouling remediation on average. Significant potentials for even greater fouling reduction have been identified for this particular application of ceramic processing. Overall, the HPSD offers the opportunity for excellent energy recovery and space saving in drying processes, but more suitable for less fouling materials. [ABSTRACT FROM AUTHOR]

Short chained triesters of glycerol and citric acid were systematically investigated as novel dual-functional dispersants and plasticisers for use in ceramic processing. Additional systematic studies on a series of diesters having structural similarities with the citrate and glycerol triesters were performed to further assess the significance of specific functional groups for the stabilisation of suspensions. The overall purpose of this work consists in simplifying the formulation for ceramic processing slurries while at the same time limiting the environmental impact and toxicity. The use of multifunctional additives reduces the risk of unwanted interactions between different components. Additionally, the possible use of one additive in more than one role opens the opportunity for an overall reduction in the number and amount of chemicals and therefore reduction of costs and risks. For the citrate ester candidates, different alkoxy groups were tested as well as the acetylation on the hydroxyl group. The glycerol esters differed by the length of the carboxylic chain. Especially triethyl and tributyl citrate are proposed as promising dual-functional additives for ceramic processing. Specifically, for triethyl citrate the dual-function was finally demonstrated by producing a dense piece of 8YSZ through tape casting and subsequent sintering. [ABSTRACT FROM AUTHOR]

The use of rare earths (RE) as dopant of materials has led the development of advanced materials for many applications such as optical tracers, special alloys, semiconductors, as well as radiation dosimeters. The development of new dosimetric materials based on REs is a great challenge in innovation of materials. Yttria (Y 2 O 3 ) presents luminescent proprieties and is a promising material for radiation dosimetry. The present paper aims to evaluate paramagnetic defects of Y 2 O 3 rods obtained via bio-prototyping by using Electron Paramagnetic Resonance (EPR) technique at room temperature. Ceramic rods were irradiated with gamma doses from 0.001 to 150 kGy and evaluated by EPR at room temperature with X-band EPR. According to EPR results, as sintered samples exhibited an EPR signal with principal g tensor of 2.020 and maximum line width around 2.3 mT, which is ascribed to interstitial oxygen ion. Dose response behaviour exhibited two distinct dose ranges, one is from 1 to 100Gy and the second is from 0.1 to 70 kGy. Thermal annealing approaches reveal that defect centres of yttria decay significantly at high temperature. These innovative results make Y 2 O 3 a promising material for radiation dosimetry. [ABSTRACT FROM AUTHOR]

[Display omitted] • An orientation behavior of Pr 4 Ni 3 O 10 in a magnetic field was disclosed. • An ab -plane preferentially oriented Pr 4 Ni 3 O 10 cathode was formed on an electrolyte. • Both ohmic and polarization losses were reduced with oriented Pr 4 Ni 3 O 10 cathode. A textured layer of a highly conductive mixed ion–electron conductor, Pr 4 Ni 3 O 10 , with a layer structure is applicable as a cathode to intermediate-temperature solid oxide fuel cells because of the large anisotropy in its conduction properties. In the present work, an ab -plane preferentially oriented Pr 4 Ni 3 O 10 cathode was successfully fabricated on a Gd 2 O 3 -doped CeO 2 electrolyte using a magnetic orientation process in a 0.9 T magnetic field. The orientation of the Pr 4 Ni 3 O 10 cathode effectively reduced not only the ohmic loss but also the polarization loss. [ABSTRACT FROM AUTHOR]