Experimental techniques for electron microscopy studies of gas reactions with polycrystalline graphites

Abstract

In spite of the experimental difficulties involved, structural changes produced in polycrystalline graphites by gas reactions have been examined directly in these materials at high resolution. Experimental techniques are described which were found satisfactory for an exploratory investigation, using direct transmission electron microscopy, of changes in graphite microstructure produced by reactions with oxygen, carbon dioxide, water vapor, and hydrogen. This study was made using disk-shaped graphite specimens having a thin central area made by mechanical abrasion. The procedures used in the preparation, treatment, and microscopic examination of these specimens are described. Specimen treatment involved both thermal gas reactions, at temperatures between 600°C and 6000°C, and electronically-excited reactions initiated by microwave discharge. Specimen examination included weight loss determination, microstructure image study, selected-area electron diffraction analysis, measurement of X-ray emission from impurities, and repeated examination of the same specimen areas before and after treatment.