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Improvement of the thermal stability of continuous SiC fiber reinforced SiC ceramic matrix composites (SiCf/SiC CMC) by the pre-treatment of SiC fillers and the suppression of oxidation during polymer impregnation and pyrolysis (PIP) process were investigated. Dense SiCf/SiC CMCs were fabricated using the slurry infiltration and PIP process under a purified argon atmosphere. Structure and mechanical properties of the SiCf/SiC CMC heated at different temperatures were evaluated. The flexural strength of the SiCf/SiC CMC decreased only 15.3%after heating at 1400 °C, which exhibited a clear improvement compared with the literature data (49.5% loss), where severe thermal deterioration of SiCf/SiC composite occurred at high temperatures by the crystallization and decomposition of the precursor-derived ceramic matrix. The thermal stability of the SiCf/SiC CMC fabricated by PIP process was improved by the pre-treatment of SiC fillers for removing oxides and the strict atmosphere control to prevent oxidation.

The thermomechanical properties of carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC CMCs) were studied up to 2000 °C using high-temperature in situ flexural testing in argon. The CMC specimens were fabricated using an ultrahigh concentration (66 vol%) aqueous slurry containing nano-sized silicon carbide powder. The SiC powder compacts were obtained by drying the slurry and were densified using the precursor impregnation and pyrolysis (PIP) method with field assisted sintering technology/spark plasma sintering (FAST/SPS). The high relative density of the SiC green body (77.6%) enabled densification within 2.5 days using four PIP cycles. In contrast, conventional PIP processes take over 7 days. The in situ flexural strength of the Cf/SiC CMC was 434 MPa at 1750 °C, which was 84% higher than the room temperature value. The value further increased to 542 MPa at 2000 °C. Possible mechanisms to explain the excellent strength of the CMC at elevated temperatures are discussed. [ABSTRACT FROM AUTHOR]

Yttria-stabilized zirconia (YSZ) nanospheres were synthesized by calcination at 900 °C after the adsorption of Y3+ ions into the pores of a zirconium-based metal–organic framework (MOF). The synthesized 3YSZ (zirconia doped with 3 mol% Y2O3), 8YSZ (8 mol% Y2O3), and 30YSZ (30 mol% Y2O3) nanospheres were found to exhibit uniform sizes and shapes. Complex permittivity and complex permeability were carried out in K-band (i.e., 18–26.5 GHz) to determine their suitability for use as low-k materials in 5G communications. The real and imaginary parts of the permittivity of the sintered 3YSZ were determined to be 21.24 and 0.12, respectively, while those of 8YSZ were 22.80 and 0.16, and those of 30YSZ were 7.16 and 0.38. Control of the real part of the permittivity in the sintered YSZ was facilitated by modifying the Y2O3 content, thereby rendering this material an electronic ceramic with potential for use in high-frequency 5G communications due to its excellent mechanical properties, high chemical resistance, and good thermal stability. In particular, it could be employed as an exterior material for electronic communication products requiring the minimization of information loss. [ABSTRACT FROM AUTHOR]

This study assesses the influence of added iron (Fe) nanoparticles on the sinterability, microstructure, and mechanical characteristics of SiC-enforced ZrB2 ceramics. The specimens were sintered under 30 MPa at 1700 °C for 5 min using the spark plasma sintering method. The SiC-free sample presented near full density; however, the incorporation of SiC led to a ~ 3% drop of the relative density. Although SiC could remove the surface oxides, the generation of a noticeable volume of gaseous phases resulted in increasing the amount of residual porosity. According to the X-ray diffractometry, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and field emission electron probe microanalyses studies, the ZrFe2 and FeB compounds were generated as the in situ phases in the ZrB2-Fe specimen, whereas the chemical reactions among the available constituents led to the in situ generation of graphite, FeSi2, and Zr3Fe phases in the ZrB2-SiC-Fe composite. The SiC-reinforced sample achieved a Young's modulus of 480 GPa and hardness of 29.4 GPa. Finally, the nanoindentation test was simulated using a 3D axisymmetric finite element model wherein the results obtained for the finite element modeling and load–displacement curve were in good agreement with the practical results. The mean values of elastic modulus, hardness, and stiffness in practical results were found to be 480 GPa, 29.4 GPa, and 0.72 mN/nm, while the corresponding ones in simulations were 571 GPa, 21.9 GPa, and 1.51 mN/nm, respectively. [ABSTRACT FROM AUTHOR]

This study assessed the sinterability and microstructure of ZrB2-SiC-TaN and ZrB2-TaN ceramics. Spark plasma sintering at 2000 °C and 30 MPa for 5 min produced both ceramics. The relative density of ZrB2 ceramic containing TaN was 95.3%; the addition of SiC increased this value to 98.1%. SiC's contribution to the elimination of ZrB2 surface oxides was the primary factor in the advancement of densification. The in situ formation of hexagonal boron nitride at the interface of TaN and ZrB2 was confirmed by high-resolution transmission electron microscopy, field emission-electron probe microanalyzer, X-ray diffractometry, and field emission scanning electron microscopy. Moreover, the in situ graphite might be produced as a byproduct of the SiC-SiO2 process, hence boosting the reduction of oxide compounds in the ternary system. The SiC compound had the highest hardness (29 ± 3 GPa), while the ZrB2/TaN interface exhibited the greatest values of elastic modulus (473 ± 26 GPa) and stiffness (0.76 ± 0.13 mN/nm). [ABSTRACT FROM AUTHOR]