Preparation And Structural Properties Evolution Of Low Density Fiber Reinforced Carbon Foams

Aircrafts(missiles, rockets, spacraft, etc) operate a long time at high Mach mumber in atmosphere where pneumatic thermal environment is heat enthalpy, heat flow density ande long heating time, so designing suitable thermal protection system is very important. This paper studied a composite low density carbon reinforced carbon foam composite materials. Low density, high porosity and low thermal conductivity carbon bonded carbon fiber skeleton which were impregnated by phenolic resin were pyrolysised to composite materials with superior properties.In order to get aqueous slurry, this paper used phenolic resin to impregnate the low thermal conductivity rayon carbon fiber. The density of carbon bonded carbon fiber composte materials that were prpared by filter press molding, curingand carbonization process were in 0.18~0.37g/cm3. The method of preparing materials led to the existence of anisotropic material structure. Short-cut carbon fiber distributed in layer forms in the thickness direction and distributed randomly in plane derection. The density of carbon bonded carbon fiber skeleton were 0.188g/cm3, 0.193g/cm3, 0.257g/cm3, 0.364g/cm3, thermal conductivity increased from 0.064W/(m·K) to 0.142W/(m·K), the material compression strength incresed from 1.39 MPa to 4.07 MPa, ande Young’s modulus incresed from 12.3MPa to 47.7MPaPhenolic resin impregnated carbon bonded carbon fiber composite materials were prepared by vacuum impregnation mathod. The composite material showed a similar nature "rime" phenomenon. A large number of low density, high porosity and low heat conductivity of phenolic resin are filled between carbon fibers, which are connected by the pyrolysis carbon.The composite materials form slit pore which the size of are about 40 nm, with the increase of carbon skeleton density, the pore size decrease. The heat loss of composite materials is mainly diveded into three stages: the adsorbed water evaporate and small molecular chain damage below 300℃, the weight loss is not obvious; some elements escape between 300~800℃, so the quality change is obvious; carbon pyrolysis above 800℃, so the quality change is not obvious. The higher the density, the slower the trend of the loss rate of the composite materias. Through the analysis of XRD and Raman, with the increase of temperature, the graphite structure of the material is more remarkable.The phenolic resin impregnated carbon fiber produce small molecular gas(H2, H2 O, CH4, CO). Low density carbon fiber skeleton reinforced carbon foam composite materials are produced after C/Ph are pyrolysed under different temperature(400℃, 600 ℃, 800 ℃, 1000 ℃, 1200 ℃). The density of C/C composite materials is from.0251g/cm3 to 0.376g/cm3, thermal conductivity increases from 0.044W/(m·K) to 0.211W/(m·K), compression strength increases from 1.79 MPa to 7.32 MPa, and Yang’s modulus from 3.48 MPa 630 MPa.