SiC Ceramics, Structure, Processing and Properties

Effects of initial α‐phase content on properties of pressureless solid‐state sintered SiC ceramics

“…The XRD patterns revealed α‐SiC (6H, 4H, 15R polytypes), and traces of B 4 C and graphite in the sintered specimens. β‐SiC (3C) was not detected in the samples because of its complete conversion to α‐phase caused by B‐doping in the SiC lattice 23 and the high sintering temperature 24 . Residual C left after the carbothermal reduction of native SiO 2 was transformed to graphite at the sintering temperature 5 .…”

“…The thermal conductivity of PSS SiC ceramics with varying initial α-phase content is shown in Figure 4. The thermal conductivity monotonically increased from 117 Wm −1 K −1 in A0 to 154 Wm −1 K −1 in A100 sample due to (1) an increased 6H-SiC content, which has a higher intrinsic thermal conductivity compared with that of 4H-SiC, 23 (2) the lower soluble impurity content of the α-SiC starting powders (Table 1), and (3) an increased relative density with increasing initial α-phase content (Table 2). 23 Soluble impurities, such as Fe and V, 40,41 act as phonon scattering sites in the SiC lattice and deteriorate the thermal conductivity.…”

“…The thermal conductivity monotonically increased from 117 Wm −1 K −1 in A0 to 154 Wm −1 K −1 in A100 sample due to (1) an increased 6H-SiC content, which has a higher intrinsic thermal conductivity compared with that of 4H-SiC, 23 (2) the lower soluble impurity content of the α-SiC starting powders (Table 1), and (3) an increased relative density with increasing initial α-phase content (Table 2). 23 Soluble impurities, such as Fe and V, 40,41 act as phonon scattering sites in the SiC lattice and deteriorate the thermal conductivity. The reported thermal conductivities of solid-state sintered SiC ceramics varies from 107 to 192 Wm −1 K −1 depending on the composition and processing conditions (Table 3).…”