Journal of the American Ceramic Society最新文献

Micropillar compression (microcompression) is a promising technology for studying the intrinsic strength and plasticity of macroscopically brittle ceramics. However, their ductility limits at microscopic scale have rarely been investigated. This study digests the orientation dependence of the strength and ductility of various oxide single crystals with cubic structures (9.8-mol% Y₂O₃-stabilized ZrO₂, Y₂O₃, MgAl₂O₄, and SrTiO₃) using room-temperature microcompression, electron microscopy observation, and crystal plasticity finite element method simulation. The strength and ductility of these oxides exhibited remarkable orientation dependence. Specifically, the ZrO₂ [111] and SrTiO₃ [001] pillars demonstrated substantial ductility with no visible cracks, even at nominal strains of approximately 40%. The ductility may be attributed to mechanisms suppressing slip localization without causing dislocation interlocking. Multiple-slip activation was preferred across several slip modes of ZrO₂, Y₂O₃, and MgAl₂O₄, which was attributed to the forest-cutting interactions among dislocations of different slip systems. In contrast, the ductility of SrTiO₃ required the activation of a single slip, where slip localization was suppressed by the strain transfer associated with the formation of Lüders band. The relationship between ductility and slip activation may be influenced by the competition between the Peierls mechanism and dislocation–impurity interactions.

This study investigates the quantitative distribution of iron between the two crystallographic sites of brownmillerite isolated in a previous study from four sulfate resisting (SR) Portland cement clinkers. ⁵⁷Fe Mössbauer spectroscopy was combined with powder x-ray diffraction (XRD) in order to determine the balance between Fe³⁺ and Al³⁺ ions in the tetrahedral and octahedral sites of the orthorhombic structure. Synthetic samples covering the whole composition range were studied for protocol validation.

The study examines the effect and mechanism of 3Y–ZrO₂ addition on the phase composition, microstructure, and mechanical properties of Al₂O₃–ZrO₂ ceramics. The ceramics were sintered at 1580°C for 120 min, comprising varying proportions of 20, 40, 60, and 80 wt.% of 3Y–ZrO₂. The study investigates the phase composition, phase content, microstructure, relative density, microhardness, fracture toughness, and wear rate of the ceramics. Notably, Al₂O₃–ZrO₂ ceramics demonstrated a dense surface with evenly distributed reinforcing particles in the matrix. The microhardness and wear rate of Al₂O₃–ZrO₂ ceramics declined with increased 3Y–ZrO₂ addition; in contrast, the bending strength, abrasion resistance, and fracture toughness increased with the addition of 3Y–ZrO₂. Alumina grain refinement, crack propagation inhibition, and microcrack toughening induced by tetragonal-to-monoclinic phase transformation are the primary factors influencing these changes. Meanwhile, as the content of 3Y–ZrO₂ increases, the fracture mode of Al₂O₃ shifted gradually from transgranular to intergranular, whereas ZrO₂ maintained predominantly transgranular fracture.

The first experiment on “touch-free” flash sintering, was reported in 2022, where it was shown that superposition of magnetic field could migrate the “flash” from a reactor held in Stage III of flash into a free-standing workpiece. The density of the workpiece increased with the magnetic field which was controlled by increasing the current through the induction coil. The coil was constructed from Kanthal wire which is nominally used for heating elements. Thus, the heat from the Kanthal wire raised the question of whether it or the magnetic field, was the cause of enhanced sintering. Here we present results with silver wire, which being one hundred times more conductive than Kanthal, can carry a much higher current without significant heating. The higher magnetic field obtained with silver led to nearly full density of the workpiece (> 98%). The results are presented in the form of a map with the current density ranging up to 200 mA/mm², and the induction current up to 70 A (at 60 Hz). These experiments serve to (i) allay the concern that heat from the induction coil was inducing flash in the workpiece and (ii) show the need for high induction currents to attain high density in magnetic field-assisted flash sintering experiments.

Modifications of phonon thermal conduction by perfect and extended edge dislocations in SrTiO₃ have been numerically analyzed. SrTiO₃ has a unique feature that Ti and O atoms, which form optical phonon modes at intermediate and high frequencies, dominates thermal conduction rather than Sr atoms. Dislocations reduce thermal conductivity through introducing spatial inhomogeneity, that is, nonuniform Ti–O bond strains in the network of TiO₆ octahedra. Due to the different spatial distributions of Ti–O bond strains, an extended dislocation with partial dislocations and stacking faults has a different mechanism of phonon scattering compared with perfect dislocations. The dislocations scatter phonons, most significantly for acoustic phonons, almost eliminating their contributions to thermal conduction. Consequently, optical phonons of Ti and O atoms at intermediate frequencies dominate thermal conduction when dislocations are present in SrTiO₃.

A fundamental issue in solid matter is how to accurately determine the fracture toughness. Glass is a brittle material that typically exhibits failure through brittle fracture, making it significant to know the accurate fracture toughness. The classic methods, including single-edge notched beam (SENB), single-edge V-notched beam (SEVNB), chevron notched beam (CNB), and single-edge precracked beam (SEPB), have been widely explored while suffering from limitations such as low efficiency, low preparation success rate, or large notch root radius (ρ) leading to overestimation. In this paper, we propose an effective strategy for the determination of fracture toughness of glass by employing the ultrashort pulse laser micro-machining (FSL-SEVNB). The ultrashort pulse laser is featured by exceptionally high peak power and rather short pulse widths that are on the order of femtoseconds, showing great potential for ultra-fine machining. By using the protype BK7 glass, the relation between the laser parameters and the induced microstructure is systematically studied. Importantly, the submicron-level crack with ρ ∼ 0.85 µm can be induced. This enables the achievement of high stress concentration, and as a result, the accurate determination of K_Ic. In addition, it is necessary to note that the method exhibits high comparability to SEPB. Furthermore, the strategy can reach ∼100% success rate with high efficiency (several minutes for sample preparation). The progress about ultrashort pulse laser-assisted micro-machining is believed to offer a novel perspective for extreme field applications in material characterization.

A straightforward physical mixing method was used to prepare the highly efficient TiO₂/polypyrrole (PPy) photocatalysts of hydrothermally prepared TiO₂ and PPy, obtained by the chemical oxidative polymerization, with different amounts of PPy (0, 0.5, 1, 1.5, 3, and 5 wt.%). Synthesized composites were characterized by XRPD, FTIR, FESEM, EDS, BET, and UV–Vis methods, while their photocatalytic activity was estimated towards the degradation of toxic dye Reactive Orange 16 (RO16) based on UV–Vis and TOC. XRPD showed that the TiO₂ was obtained as nanoanatase with crystallites of 26 nm. Band gap energies of the nanocomposites decreased with the PPy content increase from 3.11(3) to 2.94(3) eV. The TiO₂/1%PPy demonstrated the highest photocatalytic activity by completely degrading RO16 for 120 min under simulated solar light with degradation described by the pseudo-first reaction order with the rate constant of 0.056(5) min⁻¹. It was established that 73% of the total reactive oxidative species were h⁺ and that the photodegradation mechanism followed a slightly modified direct Z-scheme in which PPy played an active and irreplaceable role by opening a new reaction path. Besides extremely high photocatalytic efficiency, the recyclability of TiO₂/1%PPy was confirmed since no decrease in efficiency was found after several runs of photocatalysis.

Relaxation plays a critical role in all glasses, especially those that undergo heat treatments for industrial applications. However, the fundamental mechanisms of relaxation are still poorly understood, especially in industrially relevant glasses such as aluminosilicate systems. Additionally, there exists a gap between glass chemistry and theories of relaxation in glass physics, where the underlying descriptions of relaxation are not always tied to specific features of glass structure. Here, we present a comprehensive review of experimental and computational models used to study the relaxation behavior of high-temperature oxide glasses, with an emphasis on aluminosilicate glass compositions relevant to the high-tech glass industry. At the end of this review, we provide a perspective on bridging the gap between glass physics and chemistry through joint experimental and modeling approaches, as well as potential future experiments for measuring relaxation behavior below the glass transition temperature.