Microstructural changes of phenolic resin during pyrolysis

Abstract

After curing, phenol-formaldehyde resins were postcured at 230°C in air for 32 h and then carbonized and graphitized from 300 to 2400°C. Thermal fragmentation and condensation of the polymer structure occurred above 300°C. The crystal size of the cured phenolic resins decreased with the temperature increase. Above 600°C the original resin structures disappeared completely. Below 1000°C the stack size (L c ) and crystal size (L a ) were small. Above 1000°C the L c increased with the increasing treatment temperature. The carbonized and graphitized resins were characterized using Raman spectroscopy. Below 400°C there were no carbon structures in the Raman spectra analysis. Above 500°C the G and D bands appeared. The frequency of the G band of all carbonized and graphitized samples shifted to 1600 cm Ϫ1 from the 1582 cm Ϫ1 of graphite. The D band shifted to 1330 cm Ϫ1 from the 1357 cm Ϫ1 of the imperfect carbon. The carbonized and graphitized phenolic resins could not be considered as truly glassy or amorphous carbon materials because they had some degree of order in the basal plane. However, the crystal size was very small even at 2400°C.

Effect of Firing Temperature on Mechanical Properties of Al2O3–C Sensor for Continuous Measurement of Molten Steel Temperature

“…As the firing temperature increased to 800°C, the chemical densification greatly improved and resulted in a sharp reducing of the apparent porosity to 8.8%, which is mainly due to the fast shrinkage, repacking and cross-linking of the glassy carbon. 16) With the temperature rising from 800 to 950°C, the sensor exhibited a low apparent porosity about 8.8%-8.4%, which is attributable to the slow shrinkage of the binder above 800°C. Thus, Al 2 O 3 -C sensor will obtain a low apparent porosity when it is fired under a higher temperature beyond 800°C.…”

“…Lc where λ = 0.1542 nm, k = 0.9 for Lc, k = 1.84 for La and β is the half-value width (rad) of the X-ray diffraction intensity versus the 2θ curve. 16,18) …”

“…When the firing temperature was below 600°C, the main exothermic reaction had finished and the weight of the binder reduced by 80% in total reduction. The weight loss is related to the removing volatiles such as H 2 O, phenol and cresol (LMS), CH 4 , C 2 H 6 , CO and CO 2 , 15,16) which generates a lot of pores in the binder and the boundary of the aggregates and binder. The strong exothermic reaction also happens with the weight loss and makes the polymer structure gradually transform into the glassy carbon, which result in a high porosity and a low strength of the Al 2 O 3 -C sensor in this temperature range.…”

“…It contains complicated physicochemical processes, such as removing volatiles, formation of pores, shrinkage and structure evolution. 15,16) Actually, the mechanism of Al 2 O 3 -C refractory firing is pyrolysis of the binder, while the rest compositions almost remain stable in firing. According to the firing temperature of the long nozzle, submerged nozzle and stopper rod, Al 2 O 3 -C sensor is fired at 950°C in practice.…”

Electrical Behavior of Carbon Fiber/Phenolic Composite during Pyrolysis

“…Depending on application and design requirements thermoset resins based on phenol-formaldeyde are the most used. Also, easy processing and reasonably carbon yield makes phenol-formaldyde polymers attractive for using as precursor matrix for CFRC composites 7,8 . Convertion of phenolic resin/carbon fiber composites into CFRC composites is acomplished by rupture of the original molecular structure converting the polymer matrix to an amorphous carbon material by the action of heat 9 .…”