ELECTRODE BINDER PYROLYSIS AND BOND-COKE MICROSTRUCTURE.

Abstract

The pyrolysis characteristics and coke microstructure of a large variety of electrode binders have been examined. Examination techniques included (1) thermogravimetric analysis with simultaneous differential thermal analysis, (2) optical and scanning electron microscopy, (3) proton nuclear magnetic resonance analysis, and (4) bond-coke strength measurements. Coal-tar pitches exhibited more uniformity in pyrolytic behavior than the petroleum pitches studied. Petroleum binder quality varied widely from unacceptable to essentially equal that for coal-tar pitch. While early stages of pyrolysis are basically endothermic for all binders, the later stages involve several exotherms related to the carbon polymerization process. In particular, exotherms at about 430 degree C and 470 degree C were repeatedly observed, both singly and together, which appeared to be related to binder aromaticity and degree of condensation. Quinoline-insoluble levels up to at least 20% improved bond-coke microstructure by increasing disorder with minimum coke shrinkage. However, crosslinking the binder with oxidation treatments tended to produce an undesirable amount of bond shrinkage, apparently due to early solidification of the mesophase.