Scanning Electron Microscopy (SEM)

The Sandberg Geomaterials Department has its own in-house Hitachi Scanning Electron Microscope (SEM) fitted with a state of the art Oxford Instruments INCA energy dispersive X-Ray microanalysis system and liquid nitrogen-cooled thin-window Pentafet X-ray detector capable of light element detection.  The equipment is supervised by staff with over 20 years’ experience in SEM and associated petrographic/analytical techniques.

Capabilities

The Sandberg SEM is able to carry out very high resolution imaging but also has the additional ability to examine samples at low vacuum enabling easily damaged materials or fragile hydrated samples such as clays or polymers to be examined. High resolution low vacuum imaging in secondary electron as well as backscattered electron mode is possible using the Hitachi UVD secondary electron detector.

The microscope has a maximum resolution of 7nm (0.000007mm) and can operate at magnifications of up to x100,000 enabling the morphology of cement hydrates in concrete and clays to be revealed in great detail. The microscope also has a large sample chamber allowing samples of up to 70mm in diameter to be examined.

The SEM is fitted with a backscattered electron detector that can be used to provide images of samples that show variation in chemical composition. Materials containing elements with a high atomic mass, such as iron, appear brighter d electron images than materials containing elements with predominantly low atomic masses, such as magnesium or carbon.

Chemical analysis / X-ray Microanalysis

The Oxford Instruments INCA analysis system coupled with an X-Max 50 dry X-ray detector allows for the simultaneous analysis of multiple elements and can provide a cost-effective solution to establishing general information about the chemical composition. A typical analysis would commence with the identification of the elements present which are then analysed simultaneously and expressed as either elements or oxides.

The ability to undertake chemical analyses is indispensable for most types of SEM-based analysis. With the Sandberg SEM it is possible to make spot chemical analysis of particles as small as 1 µm (0.001mm) in diameter. Much larger areas of up to 4mm x 4mm can also be analysed. X-ray mapping can be used to show spatial distribution of elements.

Working at low accelerating voltages it is possible to obtain chemical compositions of very thin surface coatings that are less than 0.001mm thick. This ability is vital for staining investigations.

Image Analysis

The SEM has the ability to carry out image analysis based either on contrast / brightness or on chemical composition. This technique can be useful for quantifying proportions of morphological features such as microscopic voids / pores or for examining the distributions of elements such as chloride around a cracks in concrete.

Applications of Scanning Electron Microscopy

Sandberg's SEM/EDX facilities are very widely used by several departments at Sandberg for examining not only concretes, and construction materials but also in the fields of metallurgy and polymer science.

 Some examples of the use of the SEM in examining concrete and construction materials of geological origin are listed as follows:

  • Concrete, mortar, render, screed
  • Identifying causes of chemical deterioration
  • Measurement of the % of PFA or GGBS
  • Investigating chloride penetration into concrete along cracks
  • Identifying the types of binder in modern and historic construction materials
  • Investigating causes of staining
  • Detecting sulphate ingress and the early stages of sulphate attack
  • Detecting delayed ettringite formation (DEF)

 Building stone (including stone cladding)

  • Investigating causes of staining
  • Determining causes of deterioration and depths of penetration of deleterious sulphate or chloride compounds

Summary

The Sandberg SEM / EDX facility has a vast array of applications. The facilities are routinely used for analysis of:

Concrete, mortar, grout, cement, plaster, historic construction materials, building stone, rock, soil, aggregate, glass, metals and polymers.

Mike Eden

For further information contact: Mike Eden, Partner
Direct Tel: 020 7565 7077
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

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