Achieving high strength in porous zirconium carbide (ZrC)-based ceramics is notoriously challenging, primarily due to their high inherent porosity. Here, we present a creative, in situ synthesis strategy that utilizes anisotropic 3 mol% yttria-stabilized zirconia (YSZ) ice-templated foam as a reactive template. This novel approach yields a ZrC/YSZ composite foam with a high average axial compressive strength of 61.5 MPa at a porosity of ~70.9% at room temperature. The ZrC phase nucleates and grows for the first time within dense YSZ struts, not just on the surface. This unique reaction is intimately linked to the redistribution of Y3+ ions and the consequent tetragonal (t) to cubic (c) phase transformation in the YSZ matrix. Phase transformation in the matrix is a critical internal lever governing the mechanical properties, in some cases exceeding the influence of geometric factors. This research not only offers a new route to fabricate high-strength ultrahigh-temperature ceramic composite foams but also unveils the intricate interplay between their internal reaction chemistry and macroscopic mechanical strength.

The development of aeroengine with a high thrust-weight ratio poses great challenges for current top-coating thermal barrier coatings (TBCs) and environmental barrier coatings (EBCs) in service. Medium/high-entropy ceramics are highly promising candidate material for advanced TBCs/EBCs owing to their low thermal conductivity, high melting point, high-temperature stability, and calcium–magnesium–alumino–silicate (CMAS) resistance. Most feedstock powder used for medium/high-entropy TBCs/EBCs is prepared via traditional spray drying, which cannot fully exploit the advantages of multicomponent ceramics. The density, sphericity, inner structure, and flowability of feedstock powder affect their melting state during the thermal spraying process, which strongly affects the microstructure and properties of the deposited coatings. Therefore, the deposited coatings exhibit phase segregation, amorphous phases, and microstructure defects owing to unpredictable variations in feedstock powder with random morphologies and structures. Here, the structure and properties of feedstock powder prepared by state-of-the-art granulation technologies and their influences on the deposited coatings were systematically investigated, which can provide guidance for configuration optimization of feedstock powder and the manufacturing accuracy of the deposited coating. This review aims to bridge the gap between cutting-edge ceramics and advanced engineering technologies, thus providing concrete background knowledge and crucial guidelines for designing and developing TBCs/EBCs.

Although ZrB2-SiC (ZS) ceramics have been extensively researched for reusable space vehicles, the gaseous Si-bearing oxides are actively yielded, which limits their service for ultra-high-temperature applications (>2000 degrees C). In this work, medium-entropy oxide spiral fibers (MEOsf) with a composition of Zr0.68Y0.07Ce0.2Ti0.05O2-delta (Zr-0.68) were developed to promote the generation of oxide scale. The MEOsf-ZS composites demonstrated a low ablation rate of 0.27 mu m/s when exposed to ten 60 s cycles of oxyacetylene flame at 2150 degrees C. The first-principle calculations revealed that the MEO-Zr-0.68 exhibited minimum lattice distortion in the ferroelastic tetragonal (t) phase and a highly integrated crystal orbital overlap of the Ti-O bond, which contributed the good phase stability at high temperature. The enhanced ablation resistance of MEOsf-ZS was ascribed to the outstanding t-phase stability and structural integrity of the oxide scale. The intact MEO-glassy SiO2 oxide scale formed by capillary resistance effect of spiral geometry finally retarded the active oxidation of SiC grains.

A SO 4 2− /ZrO 2 –TiO 2 catalyst was prepared for the high-efficiency esterification of tributyl citrate from citric acid and n -butanol.

Achieving low-frequency broadband electromagnetic wave absorption in extreme environments over 2000 degrees C is challenging. Biomimetic hierarchy materials of high entropy lanthanide carbides were designed to optimize electromagnetic wave absorption. Composite microspheres of (Hf0.2Zr0.2Ti0.2Ce0.2La0.2)C1-delta and SiC embedded in pyrolytic carbon (MC/PyC) were prepared by using the electro-spray method followed by heat treatment. The specimens of MC/PyC microspheres with a thickness of 2.5 mm exhibited a minimum reflection loss value of - 48.9 dB, and electromagnetic wave absorption from 4.0 GHz to 17 GHz. The enhanced absorption capability is attributed to the synergistic effect of dielectric losses from conduction and polarization, along with magnetic losses due to eddy currents and natural resonance of the high-entropy carbides within the multiscale pores. The composition and featured microstructure MC/PyC microspheres were noteworthily stable under the 2200 degrees C oxyacetylene ablation, ensuring consistent high-performance electromagnetic wave absorption even in harsh conditions.

The relationship between the composition, structure and property is critical in selecting high entropy rare earth zirconates for thermal barrier coating applications, which has been systematically investigated in the present work. Key findings reveal that the size (radius) disorder delta R overriding mass disorder delta M and average mass M A , predominantly determine the phonon scattering coefficient and the phonon thermal conductivity. Moreover, an increase in the lattice disorder degree (xO48 f ) and the bond length of Zr-O48 f contributes to a reduction in the lattice energy, facilitating a decrease in the elastic modulus and an increase in the thermal expansion coefficient. Additionally, increasing the size disorder delta R and average mass M A at the A site leads to a smaller grain size, enhancing fracture toughness. These insights guide the design of high-entropy rare earth zirconates for next- generation thermal barrier coating materials.

Defects such as bubble pores and cracks of enamel coating accelerate failure in hydrothermal conditions. Here, a trace amount of SiB6 modified enamel coating prepared at a low sintering temperature showed promising hydrothermal corrosion resistance at 80-600 degrees C. The semi-crystalline enamel coatings modified by 1 wt% SiB6 demonstrated enhanced amorphization degree and exhibited a minimal mass change of similar to 0.01 % after 480 h. Compared to the undoped coatings, both the equivalent coating electrochemical resistance and charge transfer resistance at the coating/substrate interface were increased by 2 similar to 3 times. A significant amount of flocculent products sealed in the residual pores of the SiB6 modified enamel coating during hydrothermal reaction process, preventing gaseous H2O to migrate to the interface of the steel substrate. This study highlights the synergistic optimization of the amorphous phase and residual stress to dynamically regulate the coating hydrothermal corrosion resistance through a strategic interplay of composition and microstructure design.

This study investigates the thermal cycling oxidation and interfacial cracking behavior of thermal barrier coatings (TBCs) with NiCoCrAlFeY bond coats at 1100 degrees C, and compares it with YSZ/NiCoCrAlY TBCs. Two TBCs form continuous and dense thermally grown oxide (TGO), consisting of an outer spinel and an inner Al2O3. The spinel in YSZ/NiCoCrAlY TBCs is mainly composed of (Co, Ni)Al2O4, whereas (Ni, Co)(Fe, Cr)2O4 predominates in YSZ/NiCoCrAlFeY TBCs. Failure of TBCs is caused by cracking in ceramic layers near the top coat/TGO interface. The lifetime of YSZ/NiCoCrAlFeY TBCs is 2.8 times longer than that of YSZ/NiCoCrAlY TBCs, which is attributed to lower TGO growth rates, small amount of spinel and associated delay in the formation of larger interfacial cracking.

Ceramics containing profiled fiber-like additives (nanotubes, whiskers, etc.) show high mechanical properties. However, the toughening mechanism is debated due to its complex multi-scale microstructure. In this work, ZrB2(Z)-20 vol%SiC(S) spiral fibers (ZS(sf)) were prepared by liquid rope effect and non-solvent induced phase separation, while quantitative relation of mechanical properties and structure were investigated by using SEVNB with femtosecond lasers and in-situ 3D-XRM simulation. The ZrB2-SiC composites with hierarchy ZS(sf) exhibited a similar to 60 % increase in fracture toughness (5.45 MPa m(1/2)) compared with blank composites, while the toughening efficiency of the hierarchy ZS(sf) increased over 2 times compared to the 1D and 2D toughening additives. The ZS(sf) with a thin graphite-like layer and spiral structure with hierarchy pores provided a torsional release effect that changed brittle fracture to the pseudoplastic fracture, where topological interlocking of 3D crimped structure hindered rapid cracking propagation. Additionally, the enhanced toughness was attributed to the uniform reconstruction of the stress field induced by hierarchical inner pores. The preserved 3D topological interlocking and uniform stress reconstruction lead to the highly stable fracture toughness of the ZS(sf) composites up to 1500 degrees C.

Although ZrB 2 ‒SiC (ZS) ceramics have been extensively researched for reusable space vehicles, the gaseous Si‐bearing oxides are actively yielded, which limits their service for ultra‐high‐temperature applications (>2000°C). In this work, medium‐entropy oxide spiral fibers (MEO sf ) with a composition of Zr 0.68 Y 0.07 Ce 0.2 Ti 0.05 O 2‒ δ (Zr 0.68 ) were developed to promote the generation of oxide scale. The MEO sf ‐ZS composites demonstrated a low ablation rate of 0.27 µm/s when exposed to ten 60 s cycles of oxyacetylene flame at 2150°C. The first‐principle calculations revealed that the MEO‐Zr 0.68 exhibited minimum lattice distortion in the ferroelastic tetragonal ( t ) phase and a highly integrated crystal orbital overlap of the Ti–O bond, which contributed the good phase stability at high temperature. The enhanced ablation resistance of MEO sf ‐ZS was ascribed to the outstanding t ‐phase stability and structural integrity of the oxide scale. The intact MEO‐glassy SiO 2 oxide scale formed by capillary resistance effect of spiral geometry finally retarded the active oxidation of SiC grains.

This study investigates the oxidation behavior of Y/Hf co-doped NiCoCrAl-type EMPEAs with various Co and Cr concentrations (Ni59.6Co10Cr10Al20.4, Ni50.7Co15Cr15Al19.3 and Ni33.4Co25Cr25Al16.6 in at%) at 1100 degrees C and 1200 degrees C. After oxidation at 1100 degrees C, increasing Co and Cr contents enhances Y/Hf solubility in the beta phase, which delays the theta- to alpha-Al2O3 phase transformation and promotes the formation of larger columnar grains of alpha-Al2O3 scale, thereby reducing the oxidation rate by up to 62 %. After oxidation at 1200 degrees C, the NiCoCrAl-type EMPEAs with higher Co and Cr content show significantly better spallation resistance due to the reduction of the coefficient of thermal expansion (CTE) and Y/Hf solubility in the gamma phase. This reduction minimizes residual stress in the oxide scale and decreases the tendency for oxide intrusion at the scale/alloy interface, thereby enhancing the interfacial fracture energy. These findings provide scientific guidance for optimizing the composition of NiCoCrAl EMPEAs to enhance oxidation resistance in high-temperature applications.

Tributyl citrate, an environment-friendly and nontoxic plasticizer, is commonly synthesized via the esterification of citric acid and n-butanol. Highly effective SO4 2-/ZrO2-TiO2 catalysts were prepared by coprecipitation and impregnation for tributyl citrate production. The excellent conversion of 95.1% for citric acid and selectivity of 98.8% for tributyl citrate were achieved over a 3SO4 2-/ZrO2-TiO2 (4 : 1) catalyst with Zr/Ti mole ratio ∼4/1 under optimal reaction conditions of 120 °C and acid-to-alcohol ratio of 1/5. The textural and surface properties of the catalysts were characterized by nitrogen adsorption-desorption, XRD, pyridine-FTIR, etc. The characterization results confirmed that the addition of TiO2 promoted the formation of ZrO2 tetragonal phase to a certain extent, increased the specific surface area of the catalyst, stabilized the combination of SO4 2- and ZrO2, and reduced the loss of active sites. At the same time, the 3SO4 2-/ZrO2-TiO2 (4 : 1) catalyst has stronger acidity and higher acid content, which greatly improves the activity and stability of the catalyst. No significant decrease in the catalytic activity and selectivity were found during 10 runs. A promising solid acid catalyst with an excellent performance was developed for esterification reactions.

(La0.2Yb0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 (HEZ) has shown considerable promise as a novel thermal barrier coating material for temperatures exceeding 1300 °C. This study systematically investigates the interfacial stability of (La0.2Yb0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 with yttria-stabilized zirconia (YSZ), which is of paramount importance for its application in double-layer thermal barrier coatings. Our findings highlight that rare earth elements with a smaller radius diffuse more easily into the YSZ lattice, resulting in a broader diffusion zone. Simultaneously, the incorporation of rare earth elements into the YSZ lattice inhibits tetragonal-to-monoclinic phase transformation. Compared to La2Zr2O7/YSZ, HEZ/YSZ demonstrates superior high-temperature stability, which could be attributed to the higher fracture toughness and lower thermal expansion coefficient of HEZ, the absence of t-m transformation and the formation of a continuous gradient diffusion layer that minimizes interface stress. This study offers a practical strategy for designing materials for durable double-layer thermal barrier coating systems.

Download This Paper Open PDF in Browser Add Paper to My Library Share: Permalink Using these links will ensure access to this page indefinitely Copy URL Copy DOI

The controllable synthesis of high-entropy fluorite oxide (HEO) having large ionic radius mismatch remains a challenging due to poor understanding on nucleation. The (HfZrTiLn)-5HEO nanoparticles with 15 % ionic radius mismatch were synthesized via benzyl alcohol route at 220 degrees C-5 min in presence of PtCl4 and Fe(acac)3, exhibiting novel optical, electrical and magnetic properties. Nucleation pathways of the 5HEO at the critical temperature were elucidated by using a comparison study of conventional heating and microwave irradiation heating. Consistency of XRD patterns and STEM-EDX observation indicate that the resultant Hf-OBn monomers acted as the nucleation center of the 5HEO, determined by diffusion kinetics. The nucleation rate depended on the metal monomers assembly and esterification reaction, which was accelerated by water vapor pressure produced in-situ by 0.5 x 10(-4)mol/l PtCl4 catalyst. The Fe-metal organic cages derived from 1.5 x 10(-4)mol/l Fe (acac)(3) additive served as the structure stabilizer of Zr/Ti monomers, and prevented early hydrothermal reaction route.

In the process of long-term high temperature service, thermal barrier coatings (TBCs) will inevitably be sintered, leading to pores healing and porosity decline, which will affect the microstructure and the stability of mechanical properties of TBCs. To understand the relationship between the microstructural changes of sintered TBCs and the mechanical properties, in this work, the cross-sectional microstructure of TBCs at different sintering times were investigated by scanning electron microscopy (SEM). After calculating the porosity and pore size distribution, two-dimensional (2D) numerical models were developed for five different porosities (16% to 12%) by an improved reconstruction method with layer-by-layer labeling. Based on the results of finite element (FE) analysis after thermal cycling, it was found that the coating’s irregular pore structures lead to stress concentration, which affects the mechanical properties of the coating to a great extent. For the whole TC layer, the level of stresses increases and the absolute value of maximum stress augments significantly by 46% associated with the doubled increase of stress concentration areas with the densification of coating. For the local areas of TC layer, the changes in pore morphology led to a more complex variation in local stress fields. At the TC/BC interface, the Mises stress level tends to increase with decreasing porosity during sintering. At the TC surface, coatings with lower porosities cause higher stresses near this region. The insights gained from the numerical results contribute to a better understanding of the failure behavior of real TBCs systems and help to further remedy the deficiencies and difficulties of the experimental work.