St Alban's based Stanger Materials Science has recently upgraded its in-house scanning electron microanalyser (SEM) to allow it to be used for the semi-quantitative analysis of a new range of materials, including paints, bricks and concrete.
Energy-dispersive x-ray (EDAX) analysis on the SEM has so far been used mainly for investigating metallurgical failures. Visual examination at depth within a specimen can reveal hidden detail such as fracture surfaces, voids, inclusions and contaminants. At magnifications up to x7,000, it is possible to isolate a particular feature in the material and subject it to semi-quantitative analysis by EDAX.
But the technique could not detect the lighter elements, anything with a lower atomic weight than sodium. Now, by installing a thinner beryllium window in the detector head, Stanger is able to detect key elements such as carbon and oxygen, widening the scope of the technique beyond metallurgy.
A frequent commission is to investigate staining on concrete floors, which may adversely affect their long-term performance. This is often carried out as part of a schedule of dilapidation, necessary when leases are sold.
Usually the staining substance is unknown. Now a small sample can be subjected to SEM-EDAX at the outset of the investigation. The resulting spectrum will highlight the elements present using a database computer package which matches known wavelength signature positions to those of major elements.
If the staining medium proves to be organic, then a more accurate analysis using techniques such as gas chromatography can be performed. If it is crystalline, then techniques such as x-ray diffraction/fluorescence and/or petrographic methods are the obvious next step. Thus the SEM acts as a valuable first stage guide to the investigation, pointing it in the right direction and cutting out the need for unnecessary testing.
Since upgrading its SEM, Stanger has also used it to identify stains in marble floors and glass fibre reinforced plastic swimming pool liners. The technique has also been used to resolve disputes by confirming what material types, for example insulating foams, have been used in a building.
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