MAXIMUM HEATING RATES FOR PRODUCING UNDISTORTED GLASSY-CARBON WARE DETERMINED BY WEDGE-SHAPED SAMPLES

Polymeric carbon artifacts are particularly difficult to make in thick section, Heating rate, temperature, and sample thickness determine th e outcome of carbonization of resin leading to a glassy polymeric carb on ware. Using wedge-shaped samples, we found the maximum thickness fo r various heating rates during gelling (300 K-360 K), curing (360 K-40 0 K), postcuring (400 K-500 K), and precarbonization (500 K-875 K). Ex cessive heating rate causes failure, In postcuring the critical heatin g rate varies inversely as the fifth power of thickness; in precarboni zation this varies inversely as the third power of thickness. From the rmogravimetric evidence we attribute such failure to low rates of diff usion of gaseous products of reactions occurring within the solid duri ng pyrolysis, Mass spectrometry shows the main gaseous product is wate r vapor; some carboniferous gases are also evolved during precarboniza tion. We discuss a diffusion model applicable to any heat-treatment pr ocess in which volatile products are removed from solid bodies.