Effects of annealing and firing in wet hydrogen on the dielectric breakdown strengths of alumina ceramics

Abstract

Annealing and firing in wet hydrogen are widely used steps in the processing alumina-ceramic insulators that may affect their dielectric breakdown strengths (DBS). In this study, the effects of annealing (at 1300 ℃ for 7 h) and firing in wet hydrogen on the DBS of alumina ceramics (all sintered at 1650 ℃) were studied, and the underlying mechanisms were analyzed by material characterizations. Annealing reduced the DBS of the 95% alumina ceramics due to the inter-granular phase crystallization, and the reduction in the DBS could be correlated to the reduction in mechanical strength. In contrast, annealing improved the DBS of the 99% alumina ceramic without intergranular phase transformation. Firing in wet hydrogen at 1500 ℃ caused the DBS increment, which can be ascribed to the reduction in the concentrations of point defects and electrical carriers.

Synergistic Improvement of Dielectric and Thermal Conductivity Properties for Polymers Filled with Multifunctional Modified Nanowires

“…Figure shows the structure and performance of the CCTO-NWs@AO and CCTO-NWs@AO/HIPS composites. From the FTIR infrared absorption spectra shown in Figure a, obvious absorption peaks at 1401 and 889 cm –1 are attributed to the longitudinal phonon vibration of Al 2 O 3 and stretching vibration of Al–O. , The emergence of an absorption band near 1640 cm –1 is caused by the deformation vibration of H–O–H of H 2 O on Al 2 O 3 . In addition, no obvious peak in the range of 2400–3400 cm –1 corresponding to O–H further indicates the complete oxidation of Al­(OH) 3 to Al 2 O 3 after high-temperature calcination, with no Al­(OH) 3 residue on the Al 2 O 3 shell.…”

“…From the FTIR infrared absorption spectra shown in Figure 5a, obvious absorption peaks at 1401 and 889 cm −1 are attributed to the longitudinal phonon vibration of Al 2 O 3 and stretching vibration of Al− O. 43,44 The emergence of an absorption band near 1640 cm In order to further study the nanostructure of CCTO-NWs@AO, high-resolution TEM was carried out, as shown in Figure 5c. The results show that the Al 2 O 3 buffer layer with a thickness of 3 nm is continuously and uniformly grown on CCTO-NW.…”

Ethanol-Induced Flash Sintering of ZnO Ceramics at Room Temperature

“…With the development of current-or electric field-assisted sintering techniques, such as spark plasma sintering (SPS) and micro-wave sintering (MWS), it becomes possible to obtain ceramic materials at a faster speed and lower energy consumption [1][2][3]. Since being first reported by Raj et al [4] in 2010, flash sintering (FS) has been broadly applied to sinter many kinds of ceramics, including YSZ [5][6][7], Al 2 O 3 [8,9], BaTiO 3 [10,11], SiC [12], and ZnO [13,14]. According to these studies, FS makes it possible to sinter highly densified ceramics in a short time at low temperatures.…”

High Purity and High Density Ti3SiC2/Al2O3 Composites Were Prepared at High Temperature

“…Alumina ceramics, which exhibit high hardness, high chemical stability, and suitable exure strength, have attracted signi cant attention in recent years, and as a result, they have been commonly used in industry. However, their low fracture toughness limits their further development as a reliable ceramic material, therefore, the toughening and strengthening of Alumina ceramics is a research hotspot of ceramics [10][11][12][13]. The toughening of Al 2 O 3 usually involves two ways: self-toughening and composite material toughening.…”