The thermal expansion of 3C-SiC in TRISO particles by high temperature X-ray diffraction

The lattice parameter change of SiC in TRISO particles prepared by chemical vapour deposition (CVD) was measured using high temperature X-ray diffraction, across a temperature range of 25-1400 °C. Al2O3 was used as the internal standard and the SiC temperature corrections were calibrated using its two independent lattice parameter values along the a- and c-axes. Experimental unit cell values of SiC at low temperatures corresponded well with those published in previous literature, but deviated systematically at higher temperatures. Thermal expansion coefficients of the CVD prepared SiC shell material are considered the most accurate and follow a linear trend with increasing temperature (α11 = 2.7706 × 10−9 T + 3.3048 × 10−6 K−1). The TRISO particles are described best using non-linear expansion coefficients. Apparent is the deviation in the SiC lattice constants of the shell material and the TRISO particles from which it originated. This could indicate a residual strain in the TRISO particles or a difference in sample displacement between the TRISO particles and the surrounding alumina standard. The room temperature lattice constant for the shell material is 4.36030 Å (SD 0.00006 Å) as compared with that of the TRISO sample of 4.35835 Å (SD 0.00006 Å) after adjusting the sample displacement to get alumina lattice constants as close to the accepted values. Residual stress of ∼300 MPa is calculated from the lattice constant differences.