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Preparation of Porous Materials for Backscatter Electron Imaging: Some Observations on Metallurgical Grade Coke

The preparation of porous materials for examination by backscatter electron (BSE) imaging with an SEM may be carried out by impregnating open porosity with a low melting liquid metal under pressure followed by standard polishing procedures [1]. Open porosity with sizes greater than about 25 nm can be filled using a pressure of 10 ksi in a standard mounting press adapted with o-ring holders to contain the liquid metal. Low melting Bi-Sn alloys, such as “cerrotru” (58%Sn-42%Bi), provide the best infiltrates as they tend to expand during solidification. A significant advantage of liquid metal impregnation is the ability to apply argon-ion etching to reveal microstructural detail. The main disadvantages are cost, and the difficulty in obtaining a good final polish for optical microscopy. Petrographic analysis of coke microstructure is usually conducted using optical microscopy, where cellwall thickness, mean pore size, and volume fraction (Vv) of porosity are estimated [2].