Heated Stage Scanning Electron Microscope

The use of the ElectroScan Environmental SEM allows the examination of unprepared, uncoated specimens on a heated stage up to a temperature of 1,832oF (1,000oC) in a variety of atmospheres. The most recent use of this analytical instrument was for the study of the calcination behavior of limestones. Use of this instrument enable us to observe the development of thermally-induced fractures (TIFs) during calcination. It was observed that the orientation and extent of TIFs that developed varied significantly between limestones that were identified as petrographically different. This was considered significant because the TIFs serve as large feeder pores which permit rapid influx of SO2, thereby increasing calcium utilization.

ElectroScan Environmental SEM (Model ES-30)

Photomicrographs and Description of TIFs

Before Heat Treatment	After Heat Treatment (Calcined)

In general, limestones composed primarily of micritic calcite showed limited development of TIFs. The TIFs are randomly oriented. In limestones having rhombohedral cleavage the TIFs were well ordered and more numerous. TIFs tended to develop along cleavage planes and crystal boundaries.