International Journal of Applied Ceramic Technology最新文献

Alkali-activated materials (AAMs) were prepared using tungsten tailings via pressure molding and casting, and their high-temperature resistances were analyzed. Variations in their compressive strength, gel, and physical phase transformation, pore structure, and morphology at different temperatures were investigated and comparatively analyzed. Results showed that the compressive strength of both AAMs first increased and then decreased with increasing temperature. At 600°C, the pressure-molded AAM exhibited a considerably higher compressive strength (152.38 MPa) than the cast-molded AAM (42.05 MPa). Thermogravimetric–differential scanning calorimetry, XRD, and FTIR analyses showed that the pressure-molded AAM contained more gel phases than the cast-molded AAM at the same temperature. The gel phase further polymerized and decomposed at high temperatures (>800°C), forming nepheline and zeolite crystals. Mercury intrusion porosimetry and scanning electron microscopy results revealed that pressure molding increases the contact between the gel and unreacted materials, effectively reducing the porosity and densifying the AAM. The pressure-molded AAM had a considerably smaller pore diameter than the cast-molded AAM; thus, the former had considerably higher compressive strength. The porosity and pore size of the pressure-molded AAM gradually increased with the temperature, which polymerized the gel phase and eventually decomposed it; this increased its compressive strength first and then decreased.

Herein, a spinel-type high-entropy ceramics (Co_.2Cr_.2Fe_.2Mn_.2Zn_.2)₃O₄ is introduced. The obtained ceramics exhibit superior thermal stability under accelerated aging conditions at 125°C for 500 h, that is, aging drift was less than .35% for all samples sintered at temperatures (1200or–1275or . The variation of resistance is mainly attributed to the oxidation of grain boundaries and the migration of oxygen vacancies. The relationship between crystal structure evolution and aging properties was investigated using structural analysis and P–V–L bonding theory. Theoretically, the Co/Cr/Mn/Fe–O bonds at the octahedral sites in the spinel structure are more important for controlling structural stability.

High-temperature oxidation (1050°C) of Sr_.9(Zr_.9Yb_.05Y_.05)O_2.85 (SZYY) thermal barrier coatings (TBCs) by suspension plasma spraying (SPS) and growth behavior of thermally grown oxide (TGO) were investigated. When the TBCs were exposed to high temperature for a period of time (∼5 h), the BC oxidized and TGO inevitably formed between the bond coating (BC) and the ceramic top coating (TC). The high-temperature oxidation behavior of the BC is generally manifested as the growth of TGO, which has four specific stages as follows: (1) formative oxidation stage (0‒10 h), (2) rapid oxidation stage (10‒50 h), (3) stable oxidation stage (50‒100 h), and (4) complex oxidation stage (100‒200 h). The main component of early TGO is α-Al₂O₃. It has a very low oxygen ion diffusivity and provides an excellent diffusion barrier, which has a positive effect on preventing further BC oxidation. However, as the heat treatment time increased, the Al consumption and the formation of a CNS layer (NiO, Co₃O₄, and spinel) in the BC eventually led to coating failure. The working life of TBCs can be improved by improving the ceramic TC structure and the Al content of BC. SZYY-TBCs have certain potential application value.

Direct ink writing (DIW) technology supersedes traditional mold-based forming methods, significantly enhancing the fabrication of personalized and customized products with complex structures. This technology particularly excels in achieving precise control over the porosity of porous constructs. This study employs inorganic Al₂O₃ as raw material, sodium hexametaphosphate as dispersing agent, and inorganic SiO₂ micropowder as binding medium to fabricate lattice porous structures. One challenge encountered is the viscoelastic behavior of the extruded filament. When spanning the unsupported segments of the lower layer, the upper extruded filaments are susceptible to deflection or collapse, adversely affecting the porosity and dimensional fidelity of the final specimens. Experimental results revealed that a larger span and smaller modulus will cause the extruded filament to be more prone to deformation at the midpoint. The introduction of 2 wt% polyethylene glycol as a plasticizer mitigates this issue, ensuring nondeflection of the extruded filaments at a span of 6 mm. The deflection model for the extruded filament about span and modulus identifies the minimum modulus necessary to prevent or minimize deflection under given spans, which closely approximates our experimental findings, offering a valuable framework for guiding the production of high-precision, porosity-controlled porous structures.

To achieve the repeatability of aerospace thermal components, C/TaC‒SiC composites were fabricated. Cycle ablation and bending tests were carried out. After 3 × 60 s of ablation beyond 2100°C, the mechanical property retention rate was 80.9%. Interestingly, a reaction similar to “ouroboros ring,” in which the cyclic reactions of “TaC being oxidized to Ta₂O₅ and Ta₂O₅ being reduced to TaC,” occurred in the central ablation region of C/TaC‒SiC composites. On the one hand, the continuous generation of TaC could prevent liquid state Ta₂O₅ from being blown off central ablation region, playing a similar role in “water and soil conservation.” On the other hand, liquid Ta₂O₅ covered the surface of C/TaC‒SiC composites during ablation process, contributing to block the inward permeation of oxidized gases. In addition, novel “Grotto” structures were detected in the transitional ablation region of C/TaC‒SiC composites. The formation reason of the “Grotto” structure has also been discussed.

In the present study, SrTiO₃ was selected to enhance the multiferroic characteristics of Bi_0.88Sm_0.12FeO₃ (BSF) ceramics. With increasing SrTiO₃ content, the principal phase of BSF ceramic transitions from rhombohedral R3c to Pna2₁. Through DSC and dielectric analysis, it was observed that both the Curie temperature and Néel temperature decreased proportionally with the augmentation of SrTiO₃ content. When x = .1, the optimal ferroelectric performance is achieved, and the highest remanent polarization value is 55.47 µC/cm², significantly surpassing that of BSF ceramics. Moreover, the PFM test results showed that as the substitution content increased, the domains in the BSF ceramic gradually transformed from normal ferroelectric domains to polar nanomicro-domains. Magnetic and magnetoelectric results show that when x = .1, the best magnetic properties are obtained, M_r = 59.7 emu/mol. The magnetoelectric coefficient α_ME initially increased and then decreased with the increasing SrTiO₃ content, reaching its optimum magnetoelectric properties at x = .1, where α_ME = .47 mV cm^–1 Oe^–1. In summary, when the substitution amount of SrTiO₃ reaches 10%, the ferroelectric, magnetic, and magnetoelectric properties of BSF ceramics are significantly improved.

Titania nanotube (NT) arrays have been widely used as cell-supporting matrices. However, cells are always seeded on the porous surface of the NT array and have very limited interactions with each individual NT in the array. In this study, titania hollow microtubes (HMTs) were synthesized via a gelatin-template sol-gel route and then utilized as free-standing cell-supporting matrices for the first time. The resultant titania HMTs were studied by field emission scanning electron microscopy, energy-dispersed spectroscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. Each HMT was composed of rutile-type titania nanoparticles with diameters of 50–100 nm and a diameter of 50–100 µm. The results from a leaching liquor assay demonstrated good biocompatibility of titania HMTs. Each HMT has been demonstrated to independently support the adhesion and proliferation of osteoblast MC3T3-E1 cells. For comparison, titania NT arrays, not independent titania NT, only supported the adhesion of cells on their porous surface. Thus, the resultant titania HMTs are applicable to free-standing and biocompatible cell-supporting matrices.