Data for: Significant influence of Al2O3 on the flexural properties of C/C composites

In this work, we obtained high flexural strength C/C composites, and they had lower density comparing with pure C/C composites. And the high flexural strength kept in different C/C composits. However, the flexural strength of all C/C-Al2O3 composites decreased when they experienced heat treatment higher than 1500℃. And when the temperature was higher than 2100℃, the flexural strength of all C/C-Al2O3 composites was lower than pure C/C composites. The reason was that their structure changed when temperature was higher than 1500℃. In order to exlpain and repeat the high flexural strength of C/C-Al2O3 composites, 2D needle-punched carbon felts with a density of 0.4 g/cm3 were heat-treated under 2450 ℃ for 2 h and then used as starting materials. Pure CH/C composites and three different CH/C-Al2O3 composites were prepared from the 2D needle-punched carbon felts, and the content of Al2O3 in carbon felts is 4.5 wt% (CH/C-5AlO), 10.7 wt% (CH/C-10AlO) and 14.9 wt% (CH/C-15AlO) before densification. And the subsequent procedures and processes were the same as fabricating C/C- Al2O3 composites.And the flexural strength of pure CH/C composites (79.6 MPa / 84.9 MPa) was only half of that of pure C/C composites (171.01 MPa / 161.64 MPa) which the 2D needle-punched carbon felts were not heat-treated. When Al2O3 was introduced into CH/C composites, their flexural strength increased significantly and were 150.1 MPa / 142.5 MPa for CH/C-5AlO, 191.9 MPa / 197.5 MPa CH/C-10AlO and 228.8 MPa / 201.7 MPa for CH/C-15AlO.
Because the teat treatment had important influence on the flexural strength of C/C- Al2O3 composites, thermal conductivity and coefficient of thermal expansion were carried out at different temperature to study the effect of temperature on the thermo-physical properties of C/C- Al2O3 composites.The thermal diffusivity and conductivity of C/C-10AlO composites changed with the temperature in the same way between different directions. But mutations happened at about 1500 ℃, the reason was that Al2O3 reacted with C above 1500 ℃ and the microstructure changed in some way. This phenomenon also happened in the coefficient of thermal expansion of C/C-10AlO composites. The CTE of C/C-10AlO composites also kept steady before 1500 ℃, but it increased when the temperature is higher than 1500 ℃. And the CTE kept increasing with increasing temperature. The thermo-physical test indicated that the change all happened at about 1500 ℃, so it supposed that the structure and phases of C/C-Al2O3 composites changed after 1500 ℃, and then causing the decrease of their flexural strength.