Journal of the American Ceramic Society最新文献

Sodium cobaltite (Na_xCoO₂) is one of the most renowned and thermoelectrically promising p-type cobalt oxide materials, showing exceptional performance in this domain. Nonetheless, its thermal instability in air renders it unsuitable for high-temperature applications such as energy harvesting from industrial waste heat. To utilize the beneficial properties of Na_xCoO₂, microscale Na_xCoO₂ template particles of significantly larger size were effectively embedded within a thermally stable Ca₃Co_4−yO_9+δ–Na_xCoO₂–Bi₂Ca₂Co₂O₉ triple-phase matrix. This approach additionally aimed to enhance the texture and boost the thermoelectric performance of the ceramic composite. Highly textured p-type ceramic composites were fabricated via uniaxial cold-pressing and pressureless sintering in air. The unique hexagonal Na_xCoO₂ template particles, produced through molten-flux synthesis, allowed precise control over their shape and dimensions, while the matrix was synthesized via a sol–gel synthesis. The integrated Na_xCoO₂ particles of the textured composite exhibited increased thermal stability, showing no sign of decomposition at 1173 K in air, whereas the sole template particles decomposed at 1073 K during sintering. A 20 wt% template particle content in the textured composites resulted in a remarkably high and nearly temperature-independent power factor of 8.8 µW cm⁻¹ K², corresponding to an improvement of 13% compared to that of the pure matrix material.

The brittleness of oxide glasses remains a critical problem, limiting their suitability for high-performance and safety-critical applications. In this study, we attempt to address this by synthesizing nanostructures in sodium borosilicate glasses through phase separation. While most previous work on the mechanical properties of phase-separated glasses has focused on phase separation through nucleation and growth, we here create interconnected structures through spinodal decomposition. Interestingly, this leads to improvements in Vickers hardness (from 5.8 to 6.2 GPa), crack initiation resistance (from 4.9 to 8.1 N), and fracture toughness (from 0.85 to 1.09 MPa⋅m^1/2). We show that the interconnected glassy phases deflect the propagating cracks, causing the required energy for cracks to cross phase boundaries to increase when subjected to external stress. This study deepens the understanding of how to address the brittleness problem of oxide glasses and provides a promising way to design high-performance glass materials.

Borosilicate glasses possess excellent melting properties and high stability against chemical attack by aqueous solutions, enabling this glass family to be used in various fields. In this article, we design a novel glass network in order to achieve a chemically robust glass with a low melting temperature. Therefore, the substitution effect of Na₂O by MgO, Al₂O₃, Li₂O, and K₂O on the chemical durability and melting properties of sodium aluminosilicate glass (i.e., 80SiO₂‒5Al₂O₃‒15Na₂O [mol%]) was examined using a standard hydrolytic resistance test and viscosity measurement. Interestingly, we found that the partial replacement of Na₂O by Al₂O₃, Li₂O, and K₂O (i.e., 80SiO₂‒5Al₂O₃‒15Na₂O → 80SiO₂‒6.5Al₂O₃‒9Li₂O‒2.25Na₂O‒2.25K₂O) makes the glass network with chemical durability and melting properties comparable to those of the commercial borosilicate network, resulting in a low HCl consumption of 0.04 mL/g and working temperature of 1238°C (i.e., temperature at viscosity 10⁴ dPa s). The structural characterizations indicate that the high chemical stability of this glass composition originates from the abundance of SiO₄ tetrahedrons with three and four bridging oxygen in the glass network as well as the increase in cationic field strength of mixed alkali ions. These excellent melting properties and superior chemical durability of glass imply the possibility of using the mixed alkali metal oxides aluminosilicate glass together with the commercial borosilicate glass in the markets for numerous practical applications.

The oxide layer formed by ultra-high melt point oxides (ZrO₂, HfO₂) and SiO₂ glassy melt is the key to the application of traditional thermal structural materials in extremely high-temperature environment. However, the negative effect of ZrO₂ and HfO₂ phase transitions on the stability of oxide layer and rapid volatilization of low viscosity SiO₂ melt limit its application in aerospace. In this study, the ablation behavior of C_f/(CrZrHfNbTa)C‒SiC high-entropy composite was explored systematically via an air plasma ablation test, under a heat flux of 5 MW/m² at temperatures up to 2450°C. The composite presents an outstanding ablation resistance, with linear and mass ablation rates of 0.9 µm/s and 1.82 mg/s, respectively. This impressive ablation resistance is attributed to the highly stable oxide protective layer formed in situ on the ablation surface, which comprises a solid skeleton of (Zr, Hf)₆(Nb, Ta)₂O₁₇ combined with spherical particles and SiO₂ glassy melt. The irregular particles provide a solid skeleton in the oxides protective layer, which increased stability of the oxide layer. Moreover, the spherical particles have a crystal structure similar to that of Ta₂O₅ and are uniformly distributed in SiO₂ glassy melt, which hinder the flow of SiO₂ glassy melt and enhance its viscosity to a certain degree. And it reduces the volatilization of SiO₂. In summary, the stable oxide layer was formed by irregular particles oxide and the SiO₂ glassy melt with certain viscosity, thereby resulting in the impressive ablation resistance of the composite. This study fills a gap in ablation research on the (CrZrHfNbTa)C system.

This study examines and compares the impact of various interfacial modification strategies in optimizing the contact resistance between the rigid ceramic electrolyte and cathode active material (AM) in solid-state sodium-ion batteries (SSBs). All the cells are fabricated using Na_3.1V₂P_2.9Si_0.1O_12, Na_3.456Mg_0.128Zr_1.872Si_2.2P_0.8O₁₂, and Na as a cathode AM, solid electrolyte (SE) and anode, respectively. The AM/SE interface is modified by (1) wetting the interface with organic liquid electrolyte (LE), (2) slurry casting and sintering a thin layer of composite cathode, and (3) infiltrating AM precursors inside the porous SE structure followed by drying and sintering. Despite exhibiting a stable cyclability performance, the SSBs prepared using the LE modification and composite cathode approach possess a low AM loading of < 1 mg·cm⁻². On the other hand, the SSBs with infiltrated-cathode exhibit a superior discharge capacity of ∼ 102 mAh·g⁻¹ at 0.2C and less than 5% capacity fading after 50 cycles at room temperature. Notably, these cells contain a high AM loading of 2.12 mg·cm⁻². The microstructural analysis reveals the presence of AM particles inside the pores of the porous SE, allowing for the efficient insertion/removal of sodium ions. The porous scaffold of SE not only provides continuous sodium-ion conduction pathways inside the cathode structure but also renders stability by accommodating stress induced by volume change during repeated cycling. The outcomes of this work demonstrate the effectiveness of the wet-chemical infiltration technique in improving the AM loading and storage capacity performance of SSBs working at 25°C.

This study selected ZrB₂–hBN ceramics as the matrix for low-cost second-generation SiC fibers, due to their low modulus and ability to be sintered at relatively low temperatures. The resulting composites, which contained up to 30 wt.% short-chopped SiC_f, were consolidated using reactive spark plasma sintering at 1550 and 1700°C under 50 MPa for 5 min. Without needing to prepare interfaces on the SiC_f surfaces, fiber pullout, strengthening, and toughening during the fracture process were realized. By constructing the volatility phase diagram for the fiber, the microstructural changes that occurred on the fiber surfaces during sintering were successfully illustrated. Mechanical properties of ZrB₂–hBN ceramics with 10 wt.% SiC_f sintered at 1550°C still showed considerable improvements, including an elastic modulus of 187 GPa, a flexural strength of 337 ± 16 MPa, and a fracture toughness of 4.12 ± 0.25 MPa m^1/2, increases of 12.6%, 61.2%, and 118%, respectively, compared to the counterparts without adding chopped fibers. Variations in these properties were linked to the matrix porosity and SiC_f pullout behaviors, which were subsequently analyzed using the He–Hutchinson model.

The mechanical properties at microlevels are of important meaning for refractories while determining these values is of great challenges. In this contribution, a tailored grid nanoindentation test was employed to determine the micromechanical properties of low-carbon Al₂O₃–C refractories featuring reduced brittleness with in situ magnesium aluminate spinel/carbon nanotubes (MgAl₂O₄/CNTs) compound interfacial layer between the aggregate and matrix. The micromechanical properties, especially Young's modulus (E) and specific fracture energy (G_c) of the aggregate, matrix, and aggregate/matrix interface area of the refractories, were determined and compared. Statistical analysis on the nanoindentation results of the aggregate and matrix in the reference sample and the sample with interfacial layer shows high consistency, which reveals the high feasibility of the method. The median microspecific fracture energy of the aggregate/matrix interface increases from 63.67 J m⁻² of the reference group to 132.90 J m⁻² of the sample with the compound interfacial layer, which means that higher energy is needed for the initiation and propagation of microcracks within the interfacial layer, accounting for the brittleness reduction of the refractories. Consistent conclusions were drawn from the nanoindentation test at microlevels along with the macrolevel thermal shock test and wedge splitting test.

Ceramic matrix composites (CMCs) on one level are excellent materials for acoustic emission (AE) analysis. They are excellent waveguides for AE waveform transmission due to the high modulus to density ratio. CMC inelastic behavior is due to micro- and macrocrack formation from matrix crack interaction with the fibers via a relatively weak fiber/matrix interface which create ideal stress waves. Because of this, AE is an excellent detector of microcracks in general, and most importantly in the case of CMCs, the initial or lowest stress crack formation. This property can be related to long time stressed-oxidation degradation of nonoxide composites, in particular. In addition, AE has been used to effectively determine the stress distribution for matrix cracks which cause the nonlinear stress–strain behavior. However, a key to quantitatively correlating AE with sources is first and foremost to locate where the AE originated. For a tensile test, most AE comes from the near-grip region and the radius region outside the gage area of interest. Outside the gage region AE would not be considered useful data pertaining to stress/strain behavior and must be sorted out from the AE dataset. Location is determined by the difference in time of arrivals (TOAs) of waveforms received on each sensor from a given AE source. Automated TOA techniques such as threshold voltage crossing or Akaike information criteria (AIC) have limitations in overall accuracy of differences in TOA (Δt) of two different sensors required for location analysis. This study has incorporated several signal filter and enhancement techniques and an approach toward increasing the accuracy of the classic TOA techniques. First TOA was determined for the two sensors of the AE tests “manually” based on first extensional peak of the waveform, this served as the “exact” difference in TOA. Δt’s were then determined for the various filter/TOA techniques and compared to those from the manual determined Δt. The best filter/TOA techniques resulted in more than two times better accuracy (defined as percentage of events within 0.1 µs of the exact Δt) than the conventional threshold crossing or AIC technique.

The Er³⁺/Yb³⁺ co-doped tellurite glasses and glass-ceramics (GCs) containing the Gd₂Te₆O₁₅ phase were successfully fabricated via the conventional melting-quenching technique followed by a crystallization regime. The Er³⁺/Yb³⁺ co-doped tellurite glasses generated intense up-conversion green (524 and 546 nm) and red (658 nm) emissions when stimulated by a 980 nm laser. The up-conversion green emission intensity increased by 68 and 46 times with the increase of the Yb³⁺/Er³⁺ ratio, and the optimal Yb³⁺/Er³⁺ ratio was found to be 8:1. The surface crystallization process of the Gd₂Te₆O₁₅ GCs was confirmed through analysis of crystallization kinetics and microscopic morphology. The up-conversion luminescence and lifetime of Er³⁺ ions were enhanced by the precipitation of low-phonon-energy Gd₂Te₆O₁₅ crystals. The GC sample crystallized at 480°C for 4 h showed the highest luminescence intensity. The optical thermometry properties of Er³⁺ ions at thermally coupled energy levels (²H_11/2/⁴S_3/2→⁴I_15/2) were explored. The Gd₂Te₆O₁₅ GCs co-doped with 0.25 mol% Er₂O₃ and 2.0 mol% Yb₂O₃ exhibited an excellent temperature relative sensitivity (S_r) of 1.22% K⁻¹ at 293 K and a great repeatability of 98.07%. These results suggest that the Er³⁺/Yb³⁺ co-doped Gd₂Te₆O₁₅ GCs show promise for optical thermometry.