Preparation And Structure Control Of Phenolic Resin Based Carbon Foams

As a rich carbonaceous precursor for preparation of carbon foam, phenolic resin exhibits many advantages compared with mesophase pitch, such as low-cost, mild foaming conditions, low energy consumption and easy control of pore structure. Applied fundamental research was done in this paper in order to solve the defects of carbon foam preparation such as irregular pore size, cracking of pore wall and complicated technology. Concrete method has low foaming pressure and it simplifies the preparation process through foaming-carbonization one-step method, and finally high compressive strength carbon foam with regular spherical pore structure was obtained. Homogeneity of the pore structure and density of the carbon foam were effectively controlled and it provides a reference for applied fundamental research and engineering scale-up in the future. The influence laws of the parameters in carbon foam preparation were respectively studied and the main conclusions were achieved as follows:1) Foaming pressure and curing agent content are the key factor of the density and pore diameter, and heating rate is the key factor of the compressive strength and opening ratio. Carbon foams were prepared under different technological parameters, the bulk density is 0.10-0.70g/cm3, the average pore diameter is 232-322μm, the opening ratio is 75-97%;2) Homogeneity of the pore structure is manly decided by the heating rate in foaming, and it can be improved by reducing the heating rate at the price of increased average pore diameter. When heating rate was reduced from 3℃/min to 0.5℃/min, homogeneity of the pore structure was improved obviously and the average pore diameter increased from 267μm to 304μm;3) Mechanisms of the opening are divided into two kinds:One forms in the foaming stage and is decided by matching degree between foaming rate and curing rate. The other forms through the slow pyrolysis expansion process after curing, which is decided by heating rate in carbonization. The former stomata are with smooth edge and the latter are zigzag;4) Under the original pressure of 2.5MPa and carbonization temperature of 900℃, the carbon foam with optimum parameters were obtained and its average pore diameter, density and compressive strength are 268μm,0.52 g/cm3 and 18.3MPa.