COKE FORMS IN NATURE AND IN POWER UTILITIES - INTERPRETATION WITH SEM

Scanning electron microscopy (SEM) has grown to be a mature analytical technique. However, its use in coal science and technology can be mor e widely expanded. This paper is a summary showing how SEM-EDX was app lied in such diverse fields as geology and the power industry. As refl ected light microscopy, SEM is suited to the identification of textura l changes in coal conversion products. However, in contrast with refle cted light microscopy, SEM does not require sample polishing. An advan tage for many applications is that X-ray micro-analysis gives informat ion on the temperature history of heated coal. These features make SEM with energy dispersive X-ray analysis (EDX) a valuable tool in studie s of industrial and geological samples. The paper gives examples where SEM has been successfully applied. Natural coke samples were fracture d to study heating effects on coal and mineral matter. Pyrite was used as a geological thermometer, showing that 750-degrees-C was the maxim um temperature reached near the magmatic intrusion. High temperature c ombustion chars were analysed as-received, without polishing. Whole pa rticles as seen by SEM gave more information about the combustion proc ess than the polished blocks used in optical microscopy. This is becau se the effects of burn-off are more visible from the outer surface tha n from the internal structure.