Journal of the American Ceramic Society最新文献

Raman spectroscopy (RS) has attracted significant attention for the analysis of cementitious materials owing to its remarkable spatial and spectral resolution, which enable the precise investigation of chemical bonds, mineral phases, and microstructures. This review focuses on applications of RS for characterizing cement clinker compositions, monitoring hydration processes, and detecting durability issues, with a particular focus on advancements in quantitative analysis and imaging techniques in recent years. The featured Raman vibration bands are summarized, which are useful for the identification of calcium silicate-related substances. The current technical limitations of RS for investigating cementitious materials are discussed, and potential approaches to overcome these limitations are proposed. The technological innovations in RS will further enhance its efficacy and applicability for investigations of cementitious materials, thus facilitating a comprehensive understanding of the life cycle of cement across various scales of interest.

Developing high strength and tough silicon carbide (SiC) composite ceramics remains a significant challenge. Here, we report the process of synthesizing fully densified SiC/C composite ceramics using SiC@graphene (SiC@G) core–shell nanoparticles as raw materials through spark plasma sintering (SPS) at 1700°C and 45 MPa. The SiC@G nanoparticles were synthesized by the fluidized bed chemical vapor deposition (FB-CVD) method. During the sintering process, graphene coated, the surface of nanosized SiC particles exhibited high electrical and thermal conductivity, facilitating the uniform distribution of pulse current and heat and promoting the densification of SiC/C composite ceramics. For the prepared SiC/C composite ceramic, the carbon content reaches as high as 14.3 wt%, with carbon uniformly dispersed in a particulate form within the SiC matrix and stable interface bonding. Consequently, the introduction of excessive carbon does not compromise the hardness (28.8 GPa) and flexural strength (517.34 MPa) of the SiC/C composite ceramics. Furthermore, the carbon particles effectively enhance the toughness of the SiC/C composite material through mechanisms such as crack branching, bridging, and deflection, resulting in a fracture toughness of 7.38 MPa m^1/2. The preparation strategy in this study provides a novel route for sintering SiC composites with high-carbon content through nanoscale powder structure design, resulting in the attainment of high-performance lightweight composite materials.

Rare-earth hafnates are gaining attention due to their excellent high-temperature phase stability and low thermal conductivity. However, they still have shortcomings of low thermal expansion and poor calcium-magnesium-aluminum-silicate (CMAS) corrosion resistance. In this study, we employed high-entropy engineering and component design to synthesize three high-entropy hafnates (La_0.2Ce_0.2Nd_0.2Gd_0.2T_0.2)₂Hf₂O₇ (T = Dy, Ho, Tm) as well as a single-component hafnate Nd₂Hf₂O₇, with the aim of preparing thermal barrier coatings with an excellent comprehensive performance. Test results indicate that the high-entropy compositions have excellent thermal properties. The focus is on elucidating the corrosion process and failure mechanism of CMAS at 1300°C. Moreover, the analysis of residual CMAS and corrosion products was conducted to evaluate the discrepancies in CMAS corrosion behavior among the various compositions.

In this study, aluminum titanate/anorthite (Al₂TiO₅-CaAl₂Si₂O₈) ceramics were fabricated from ferrotitanium slag through phase reconstruction. Stabilization of the ceramic was achieved by migration of Mg element into Al₂TiO₅ phase. The results indicated that optimal performance was achieved with the addition of 4 wt% MgO and 60 wt% ferrotitanium slag at 1370°C. The ceramic exhibited bulk density of 3.11 ± 0.01 g/cm³, thermal storage density of 1.51 kJ/cm³, and thermal expansion coefficient of 3.40 × 10⁻⁶/°C (1000°C), respectively. Additionally, the solid solution of Mg²⁺ in the Al₂TiO₅ lattice reduced the formation of microcracks and enhanced the mass transfer process. Consequently, the sintering temperature decreased from 1415°C to 1370°C while the bending strength increased from 61.25 ± 1.05 MPa to 75.92 ± 7.72 MPa. Furthermore, finite element simulation demonstrated that higher thermal expansion led to concentrated thermal stress, potentially increasing the possibility of ceramic cracking. This research provides a new strategy for preparing low thermal expansion ceramics from titanium-containing solid waste.

H₃BO₃ was used as the sintering additive to enable Zn_0.997Cu_0.003ZrNb₂O₈ ceramics to accomplish low-temperature sintering and outstanding microwave dielectric performances. Composite ceramics were created using typical solid-state processes. The effects of added H₃BO₃ on the sintering behavior, microstructural characteristics, vibrational properties, and microwave dielectric performances of Zn_0.997Cu_0.003ZrNb₂O₈ + x wt% H₃BO₃ (2 $�\le$ x $�\le$ 8) ceramics have been systematically investigated by means of X-ray diffraction, Raman scattering spectroscopy, scanning electron microscopy, and complex chemical bond theory. The results of relative density and microscopic morphology demonstrated that the application of an adequate quantity of H₃BO₃ additive can significantly enhance sintering properties. The doped H₃BO₃ alters the inter-ionic interactions so that the structural features become intrinsic to the microwave dielectric performances. The particularly satisfactory microwave dielectric performances ($�{\epsilon }_r$ = 10.61, $��Q�\times �f�$ = 33 980 GHz, and $�{\tau }_f$ = -45.10 ppm/°C) were detected in x = 6 ceramic specimens sintered at 950°C, which would make it promising for use in modern low temperature co-fired ceramics technology.

n-type Dy-doped Ca₂MnO₄ powders with the Ruddlesden–Popper structure were synthesized by the combustion method and sintered by conventional sintering and spark plasma sintering (SPS). Conventional sintering fails to densify Ca₂MnO₄, but the addition of Li₂O proves to be a highly effective sintering additive, albeit with a detrimental impact on electrical conductivity. In contrast, SPS at 850°C for 1 min yields nanostructured, nearly fully dense samples, demonstrating superior outcomes. The dimensionless figure of merit ZT reaches 0.02 at 750°C. Additionally, the best sample exhibits a remarkable hardness value of 10.7 GPa, underlining the excellent mechanical properties achieved through this innovative approach.

In this work, the Yb₂Si₂O₇ interphase was prepared on SiC fibers using the sol–gel method. The influence of sol concentration on the morphology of the interphase was discussed. After heat treatment in argon at 1200°C for 1 h, the Yb₂Si₂O₇ was grown in situ on the fiber surface, forming an interphase layer. Then, SiC_f/Yb₂Si₂O₇/SiC minicomposites were prepared by chemical vapor infiltration (CVI). The Yb₂Si₂O₇ interphase exhibited no changes throughout the high-temperature preparation process and maintained stability and compatibility with the fiber and matrix. The tensile strength of SiC_f/Yb₂Si₂O₇/SiC minicomposites with Yb₂Si₂O₇ interphase was significantly higher than SiC_f/SiC minicomposites without interphase. The crack deflection, interfacial debonding, and fiber pullout were observed in the tensile fracture of the SiC_f/Yb₂Si₂O₇/SiC minicomposites.

0.92(K_0.5Na_0.5)NbO₃-0.02(Bi_0.8Li_0.2)TiO₃-0.06BaZrO₃ (BZ6) is a lead-free piezoelectric ceramic with excellent piezoelectric performance (such as the normalized strain $�d_{33}^{\ast }$ reaches up to 476 pm/V). Considering potential device applications, it is essential to evaluate the ceramic's resistance to electrical fatigue. The bipolar fatigue behavior of (K,Na)NbO₃ (KNN)-based lead-free piezoelectric ceramics was investigated. Comparative analysis shows that BaZrO₃-modified KNN ceramics have strong resistance to bipolar fatigue due to the coexistence of rhombohedral and tetragonal phase and the depinning of domain walls, whereas microstructural damage under mechanical stress makes pristine KNN ceramics susceptible to bipolar cycling. The hypothesis was systematically verified through the study of cycle-dependent small and large signal parameters and microscopic morphology. Our findings can guide the future design of KNN compositions with high resistance to bipolar fatigue.

The safe and secure encapsulation or immobilization of nuclear waste, particularly low to intermediate-level waste (accounting for ∼97% of the total volume of nuclear waste), has been a significant concern. Consequently, numerous studies have been conducted on various materials such as ordinary Portland cement-based, bitumen, and ceramics for the purpose of waste encapsulation/immobilization. However, these studies generally offer a broad overview of materials performance without focusing on specific radioisotopes of concern. Cesium (Cs) and strontium (Sr) are important radioactive nuclides to consider for encapsulation, but the existing studies on immobilizing these elements are fragmented and lack a comprehensive understanding. This critical review article offers a thorough qualitative and quantitative analysis to uncover the primary trends/knowledge gaps within the field. It comprehensively delves into waste classifications/management and leaching assessments, followed by an exploration of the immobilization performance and durability issues of various traditional and advanced cementitious materials including low-temperature chemically bonded ceramics such as alkali-activated matrices and Mg‒K phosphates for the immobilization of Cs and Sr. Furthermore, the review article provides fresh insights and perspectives, including recommendations for improvements, novel technologies, and future trends in this domain.

ns² ions-doped lead-free perovskites have garnered significant attention for their potential in diverse optoelectronic applications, owing to their broad emission characteristics arising from self-trapped excitons (STEs). Herein, high-performance white light-emitting diodes (WLEDs) for intelligent lighting are developed by Bi³⁺/Te⁴⁺co-doped Cs₂SnCl₆. Effective energy transfer between the dual STE emissions results in tunable broadband emissions covering the full-color region. Adjustable WLEDs containing cold- and warm-white lighting are fabricated. The WLEDs have excellent luminescent performances coupled with adjustable correlated color temperatures of 6417 and 3829 K. This versatility allows them to meet lighting demand for different scenarios, which is essential for future WLEDs to achieve healthy lighting. In addition, the excellent white light emission characteristics can also be applied in the visible light communication (VLC) system, achieving a −3 dB bandwidth of 13.3 MHz and opening eye diagrams in the data rate range of 10–60 Mbps. This work represents a significant advancement toward building intelligent health lighting applications and achieving high-quality light sources for VLC based on lead-free perovskites.