In Situ Hot Pressing And Properties Of Carbon/Carbon-Ceramic/Carbon Composites

In this paper, clay/carbon composites was synthesized via hydrothermal synthesis using fibrous clay and cellulose. The obtained clay/carbon composites was introduced into carbon/carbon composites, through hot press method enhances the mechanical and antioxidant properties of carbon/carbon composites. The main conclusions are given as follows:(1) Palygorskite/carbon composites were synthesized via a hydrothermal route using palygorskite and cellulose as raw materials. The obtained palygorskite/carbon composites were introduced into the carbon/carbon composites during the impregnation process. Thus the carbon/carbon-ceramic/carbon composites were in situ prepared by hot pressing method. The mechanical and antioxidant properties were studied for carbon/carbon composites using palygorskite/carbon as additives. The results show that the palygorskite/carbon converts to ceramic/carbon during hot-press pyrolysis. The ceramic/carbon enhances the mechanical properties of carbon/carbon composites by filling and bridging, and the carbon loading on the surface avoid week-binding between ceramic and pitch-based carbon matrix. Compared to that of carbon/carbon without additive, the strength and modulus are increased by 34～45% and 27～42% respectively. Meanwhile ceramic/carbon matrix in situ generated slowed down the oxidation process of matrix, then improving the oxidation resistance of the material. The mass loss of oxidation is reduced by 12～18% at 1000 ℃ in comparison of the carbon/carbon composite without additives.(2) Clay/carbon composites was obtained via hydrothermal synthesis using clay and cellulose as sources. The clay includes fibrous sepiolite and tubular halloysite. Then the obtained clay/carbon composites were introduced into carbon/carbon composites. The carbon/carbon-ceramic/carbon composites were in situ prepared by hot pressing method. The mechanical and antioxidant properties were studied. The results show the halloysite converts to γ-Al2O3 and amorphous SiO2 during heat treatment. The ceramic/carbon enhances the mechanical properties of carbon/carbon composites through making up the matrix defects. Compared to that of carbon/carbon without additive, the strength and modulus are increased by 45～73% and 152～179% respectively. The mass loss of carbon/carbon composites reduce to 34～48% because of ceramic/carbon matrix in situ which can decreased the oxidation activity site and slow down the oxidation rate. Compared to that of carbon/carbon without additive, the strength and modulus of carbon/carbon composites with sepiolite/carbon as additive are increased by 45 ～ 64% and 97～118%, respectively. The mass loss of carbon/carbon composites containing sepiolite/carbon reduce to 53～58%. The results show that the mechanical and oxidation properties were also enhanced due to the addition of clay/carbon nanocomposites (sepiolite/carbon and halloysite/carbon).(3) The halloysite/carbon was introduced into carbon/carbon composites. The pressure and the content of halloysite/carbon were investigated. The results showed that the optimum pressure is 30MPa. The strength of composites achieved maximun when the Halloysite/carbon content was 30wt%. The enhancement effect of ceramic/carbon is not obvious with the low additive of halloysite/carbon. When the halloysite/carbon content is highter, carbon matrix can not bond well with other components.