Scanning electron microscopy (SEM) allows us to examine materials at higher magnifications and with superior resolution than optical microscopes. When equipped with energy-dispersive x- ray spectrometers (EDS), the electron microscope allows in situ determinations of the chemical composition of an area of interest. DRP has extensive experience in the use of SEM/EDS methods to study microstructural aspects of cement hydration and strength development, fly ash quality and characteristics, and durability mechanisms that include sulfate attack, alkali- aggregate reactions, salt weathering and freeze-thaw damage as influenced by deicers.

DRP houses a state-of-the-art FEI Quanta 250 Environmental Scanning Electron Microscope (ESEM). The instrument can operate in high vacuum for conductive or conventionally prepared specimens; low vacuum for non-conductive specimens (without coating the surface) and ESEM mode for hydrous materials that are incompatible with high vacuum.

Numerous detectors are available for imaging. The copper wafer shown here is a low kV solid state backscatter electron detector (BSED). Other detectors include a standard Everhardt Thornley secondary electron detector (SED) and high-sensitivity gaseous SED and BSED for ESEM conditions.

Ready for lift-off. A sample that has a surface area of ~ 2500 mm2 is fixed to the sample holder and about to be loaded into the chamber.

EDS map of concrete from a sea wall undergoing a combination of alkali-silica reaction and marine water attack. The areas shown in purple, light pink and yellow represent ASR gel, the blue areas represent brucite and the reddish brown areas represent hydrotalcite.

Hard at it on the SEM...

Backscatter electron micrograph of Freidel’s salt in a void.

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