Journal of the American Ceramic Society最新文献

Understanding the rheological behavior of ceramic suspensions is crucial for optimizing shaping technologies, including slip casting, injection molding, and additive manufacturing. Classical models often fail to account for temperature effects, interfacial phenomena, and nonlinear concentration effects, thereby limiting their applicability to real processing conditions. This study introduces a new empirical rheological model based on a hyperbolic sine formulation, incorporating three physically interpretable parameters: the effective Einstein limit offset (A), the mixing viscosity factor (β), and the interaction viscosity factor (C), verified in the concentration range 0–40 vol.%. Unlike conventional viscosity–concentration relationships, the proposed model captures the first measurable deviation from the dilute Einstein regime and describes the progressive nonlinear rise of relative viscosity using a compact analytical expression. The parameter β captures the effects of interfacial tension, liquid viscosity, and effective particle number density under isothermal conditions, as confirmed by its temperature and shear-dependent decrease and by its reduction in dispersant-stabilized suspensions, where steric layers diminish particle interactions. Therefore, parameter β provides a physically grounded link between the suspension structure and its rheological response. The model demonstrates excellent agreement with experimental data, outperforming five established rheological models across multiple systems and measurement conditions. These findings highlight the novelty of the proposed formulation as both a flexible fitting tool and a physically meaningful descriptor of early-stage viscosity evolution.

Garnet-structured (A₃B₅O₁₂) transparent ceramics show promising applications in fields such as lasers, phosphors, and scintillators. The introduction of high-entropy design into transparent ceramics offers a new pathway to expand the regulatory space of structure and properties in garnet materials. However, conventional powder sintering methods used for preparing high-entropy transparent ceramics face several challenges, including stringent requirements for high-quality powders, dependence on high temperature and pressure, and consequently grain coarsening. In this study, we innovatively employed the full glass crystallization method to fabricate high-entropy transparent ceramics. Through pressureless crystallization of glassy bulk at a relatively low temperature (1000°C, 2 h), a high-entropy transparent (Eu_0.2Gd_0.2Y_0.2Yb_0.2Lu_0.2)₃Al₅O₁₂-Al₂O₃ (HEAG-Al₂O₃) garnet-based nanoceramic was successfully synthesized. Crystallization kinetics analysis revealed that the bulk glass precursor of the HEAG-Al₂O₃ nanoceramic exhibits a high activation energy, with a crystallization mechanism of three-dimensional crystal growth mode accompanied by volume nucleation. The obtained high-entropy transparent ceramic consists of a HEAG primary phase and an in-situ formed Al₂O₃ secondary phase. The resulting dense three-dimensional network nanostructure, combined with nanoscale grains (< 30 nm), endow the biphasic HEAG-Al₂O₃ nanoceramics possessing excellent optical transmittance (81.4% at 780 nm) and mechanical properties even comparable to those of single crystal.

For potentially wider applications of ceramics with dislocation-tuned mechanical and functional properties, it is pertinent to achieve dislocation engineering in polycrystalline ceramics. However, grain boundaries (GBs) in general are effective barriers for dislocation glide and often result in crack formation when plastic deformation in ceramics is attempted at room temperature. To develop strategies for crack suppression, it is critical to understand the fundamental processes for dislocation–GB interaction. For this purpose, we adopt a model system of bi-crystal SrTiO₃ with a 4° tilt GB, which consists of an array of edge dislocations. Room-temperature Brinell indentation was used to generate a plastic zone at the mesoscale without crack formation, allowing for direct assessment of GB-dislocation interaction in bulk samples. Together with dislocation etch pits imaging and transmission electron microscopy analysis, we observe dislocation pileup, storage, and transmission across the low-angle tilt GB. Our experimental observations reveal new insight into dislocation–GB interaction at room temperature at the mesoscale.

Soda lime silicate glass produced by the float process is among the materials with the largest use worldwide. The manufacturing process introduces an asymmetry in the glass sheets that causes well-known modifications in terms of properties between the so-called “air side” and “tin side”. Nevertheless, not much is known about the structural changes induced by the diffusing tin ions in the network. In the present work, we show that surprisingly, the short range of the tin side is akin to that of the bulk, while the network connectivity in the air side vicinity is enhanced with a larger concentration of bridging oxygens. This correlates with a partial depletion of modifiers from the air side as detected by secondary ion mass spectrometry. On the other hand, the incorporation of tin markedly changes the medium range. In fact, the tin side is characterized by: (i) longer correlation distances, (ii) a more homogeneous structure depicted by a more reduced splitting of the medium frequency Raman features into R and R_c bands, (iii) a substantially lower amount of free volume, and (iv) a slight reduction in the average free volume size. Furthermore, the spontaneous hydration layer on the two surfaces is studied, and its effect on the free volume is discussed. These results provide new insight into the soda lime silicate glass structure and have various technological implications for processes like chemical tempering or phenomena like surface defects nucleation.

Solid solutions based on cerium dioxide are important functional materials with diverse applications, particularly in electrochemical and catalytic systems. The synthesis and application of CeO₂-based systems frequently require exposure to extreme heat, leading to a selective loss of volatile components from the solid matrix. This process significantly impacts both the material's composition and performance. However, the behavior of ceria-containing ceramics under such conditions remains poorly understood. This work focuses on investigating the thermodynamic stability of CeO₂–Al₂O₃ melts. Specimens were prepared via high-temperature solid-state synthesis (1673 K, 22.5 h) and characterized via x-ray diffraction analysis. Vaporization of the system was studied using Knudsen effusion mass spectrometry within the 2150–2720 K range. The most stable composition at 2350 K, corresponding to the minimum ΔG^m of −42.3 ± 0.7 kJ mol⁻¹, is located at (52% ± 2%) CeO₂. The system displays significant negative deviation from ideality. Among the binary CeO₂-based systems (with Al₂O₃, Gd₂O₃, Y₂O₃, and ZrO₂ as the second component), CeO₂–Al₂O₃ demonstrated the highest thermodynamic stability.

Porous β-SiAlON demonstrates unique physical and chemical properties that make it especially advantageous as a porous filter medium used under extreme operational conditions. Among the various synthesis methods, self-propagating high-temperature synthesis (SHS), also known as combustion synthesis, is recognized as one of the most energy-efficient and rapid approaches for producing of β-SiAlON powder. However, existing methodologies in the field of SHS are insufficient for producing porous β-SiAlON with predetermined shapes, porosity, and pore sizes that can be used directly without further technological processing of the combustion products. The primary objective of this study is to develop a method for synthesizing mechanically stable, porous β-SiAlON in block form, devoid of macro-defects, and possessing specific foam porosity and pore dimensions through SHS. The developed approach consists of two stages: (1) the initial structuring of the powder precursor, and (2) subsequent nitridation via SHS. The investigation showed the effects of alkali content in the initial slurry, nitrogen gas pressure, and the initial dimensions of the blocks on the combustion characteristics of the pre-structured samples. Optimal and critical synthesis parameters were determined. A comprehensive analysis of the phase composition, porosity, pore size, chemical composition, and microstructure of the synthesized samples was conducted. The porosity of the nitrided samples ranged from 37% to 77%, predominantly characterized by open porosity, with a maximum pore size of up to 24 mm. Furthermore, the study presents findings related to acid resistance, oxidation resistance, thermal shock resistance, compressive strength, and gas permeability of the synthesized porous β-SiAlON.

In this study, the laser ablation mechanisms of porous silicon nitride under different gas environments and airflow velocities were compared. The high-temperature pyrolysis characteristics of silicon nitride were integrated with thermal radiation principles to elucidate the “high-temperature ring” recorded by thermal imaging cameras during ablation. According to the dynamic evolution of temperature distribution, the temperature inflection point corresponded to the ablation initiation time. The results revealed ablation initiation times of 2.0 and 0.7 s in air and nitrogen, respectively. A comparative analysis of the morphology and spectral characteristics of silicon nitride, subjected to short-time laser irradiation in different gaseous environments, revealed the formation of an oxide layer, whose reflectivity was 20.6% higher than that of the original material, in air. This oxide layer formation resulted in the later initiation of ablation, the formation of smaller pit diameters, and in oxygen-free ablation-induced depths that exceeded those observed in air environments. Laser ablation experiments under high-speed airflow revealed that unlike the porous ablation morphology observed in static air, higher oxygen-content dendritic products formed under high-speed airflow. As airflow velocity increased from 0 to 374 m/s, the ablation pit diameter decreased from 11.2 to 6.7 mm. This study provides a reference for evaluating laser damage characteristics and laser protection capabilities of porous silicon nitride. In addition, it reveals the severe high-temperature ablation behavior of silicon nitride used as antenna radomes in high-speed aircrafts.

This paper reports that flexible composite films containing BiFeO₃ nanoparticles demonstrate substantial electrocaloric strength and adiabatic temperature change of 407 mK m MV⁻¹ and 24.4 K for a 10 wt% solid content, respectively. These values significantly surpass previously reported data. We discovered that crystallite sizes exceeding 10 nm in the polar β-phase are essential for amplifying the electrocaloric effect, allowing for easier domain motion at lower electric fields. Simulations based on Landau theory validate the electrocaloric effect in the BiFeO₃/P(VDF-TrFE) composite film, predicting it can induce a 34 K adiabatic temperature change under 120 MV m⁻¹. This finding offers a basis for selecting between high cooling performance and energy efficiency for practical applications. The research showcases a flexible composite film with potential practical applications in solid-state refrigeration technologies.

With increasing industrial emissions, mining, and agriculture, heavy metals and organic pollutants accumulate in soil. Traditional treatments are complex, inefficient, and prone to secondary pollution. Natural montmorillonite has high surface area and ion-exchange capacity, but conventional modifications carry potential risks such as structural collapse and adsorbent re-release, limiting long-term use. This study proposes a green modification method using 355 nm picosecond UV laser, exploring its regulation of montmorillonite structure and adsorption via molecular dynamics, neural networks, and experiments. Simulations show laser induces interlayer rearrangement and microfractures affecting adsorption; neural network models predict the relationship between laser parameters and performance. Experiments confirm ∼37% adsorption enhancement at 400 kHz, 0.75 J/cm², with improved surface area and porosity. This work provides theoretical and practical support for precise control and green application of montmorillonite, offering new strategies for soil remediation.