International Journal of Applied Ceramic Technology最新文献

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.

In this study, an Al₂O₃-based ceramic pastes with high solid content and low viscosity for photocuring was prepared. The effects of TiO₂/Yb₂O₃ binary sintering aid on the rheological properties, curing behavior, and bending strength of the sintered parts were systematically investigated. Ceramic samples with an intact surface and no defects were prepared through debinding in various atmospheres followed by pressure-less sintering at 1600°C. The bending strength of the sintered material was 329 MPa, which represents a 231% increase compared to the bending strength of 99.4 MPa for pure Al₂O₃ ceramic material prepared using the same process, with the highest recorded bending strength reaching 478.47 MPa. Scanning electron microscopy and X-ray diffraction analyses revealed that the binary sintering aid acts as a bridge between grains by forming a solid solution with Al₂O₃ powder at high temperatures, which decreased the pore size and number between Al₂O₃ ceramic grains, thereby enhancing the bending strength of the ceramics. The prepared ceramic pastes is expected to meet the manufacturing requirements of high-performance ceramic substrates and accelerate the development of high-performance ceramic substrate processing technology.

A more generalized approach for predicting the steady-state creep rate of ceramic fibers under extensive stress ranges is proposed. Creep rate equations derived from dimensional analysis, such as Almeida's creep equation and Arrhenius’ creep equation, were evaluated using Buckingham's method, and the corresponding π groups were determined. Subsequently, a new equation is proposed using the usual semi-empirical constants for the diffusional and power law creep phenomena, along with an additional power law exponent to account for changes in creep mechanisms at higher stresses. The proposed equation was used to fit the creep rate data of the fiber Nextel 720 at various temperatures and constant stress, which demonstrated a good fit with an adjusted R-squared of .96. Subsequently, the equation was used to predict the creep rate at constant temperature and various stresses, exhibiting an adjusted R-squared of .77 and .85, depending on the scatter of the used data. The predictive results of the proposed equation were then compared to those obtained using the Arrhenius creep equation, which tends to higher rates at high stresses. In summary, the novel equation can be more efficiently applied in predicting the creep rate of ceramic fibers across a broader spectrum of stress.

The Ti₃SiC₂/Cu composites were synthesized by spark plasma sintering (SPS) at 950°C, 1000°C, and 1050°C, and the as-formed composites were oxidized at 700°C, 800°C, and 900°C. The effects of the sintering temperature and the oxidation temperature on the anti-oxidation of the composites at high temperatures were explored. The samples were characterized by X-ray diffraction, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscope. The results indicated that the sintering temperature significantly improved the oxidation resistance of the composites. With the increase of the sintering temperature, the weight gain of the oxidation of the composites decreased and the optimum sintering temperature was 1050°C. At an identical sintering temperature, with the increase of the oxidation temperature, the weight gain of the oxidation of the composites first decreased and then it increased. Thus, when the oxidation temperature was 800°C, the composites exhibited an excellent oxidation resistance (oxidation weight gain: .0042 × 10⁻⁵ g/mm²). The anti-oxidation behavior of the composites benefited by the formation of an oxide layer. The oxide layer was composed by TiO₂, CuO, and amorphous SiO₂.

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.

TC4 titanium alloy has been widely used in the automotive field due to its exceptional properties. However, inherent defects such as low hardness and poor wear resistance for TC4 alloy limited its wider application. The microarc oxidation (MAO) technique was employed in this paper to prepare MAO coatings on TC4 titanium alloy. The microstructure, phase structure, mechanical properties, and tribological performance were systematically evaluated. The results show that the coating contains a large amount of rutile TiO₂ hard phase after MAO treatment, which significantly improves the mechanical properties of the substrate. The hardness of the MAO coating can reach 581 HV_.05. Furthermore, the synergistic lubrication effect of onion-like carbon (OLC) nanoparticles and organic molybdenum dithiocarbamate (MoDTC) in PAO oil was observed for MAO-treated TC4. Particularly, when .01 wt.% OLC is used with 1 wt.% MoDTC oil, the coefficient of friction (COF) decreases to .062, and the wear rate decreases to 4.3 × 10⁻⁷ mm³/Nm. Combined Raman and X-ray photoelectron spectroscopy (XPS) analysis indicate that OLC is deposited on coating area to form a lubricating carbon film. Additionally, OLC can promote the decomposition of MoDTC during sliding to generate a tribofilm containing MoS₂.

In this study, Ti₂O₃ thin films were successfully produced using magnetron sputtering. Through orthogonal gradient experiments, the impact of substrate temperature, sputtering vacuum, RF power, and sputtering duration on surface morphology, roughness, physical structure, and resistivity was investigated. Various analytical techniques were employed, including AFM and SEM for surface morphology observation, XRD and Raman for qualitative physical structure analysis, XPS for elemental valence examination, and the four-probe method for resistivity measurements. The study identified optimal growth conditions for Ti₂O₃ films, demonstrating a low resistivity of 2.66 × 10⁻³ Ω cm under the following conditions: RF power of 200 W, sputtering vacuum of .6 Pa, substrate temperature of 600°C, and sputtering duration of 60 min. Additionally, the sensor arrays were efficiently fabricated using the Lift-off method to evaluate the photoelectric performance of the films. A light responsiveness of approximately 6 µA/W was observed in the device when illuminated with 950 nm light for 10 s. This finding carries important implications for the use of Ti₂O₃ thin films in future photoelectric devices.