Reaction kinetics in cement, mortar and concrete is a main investigation topic to understand phenomena like alkali-silica reactions (ASR), alkali-carbonate reactions (ACR) as well as alkali-aggregate reactions (AAR). These reactions are usually studied with cross-sectional mapping of samples using microscopy or SEM-EDS. However, such results are user dependent, time consuming and the lower limit of detection are usually insufficient.

Malvern Panalyticals latest HiPer Small Spot Mapping (HiPer SSM) addition on the Zetium platform offers user-independent results that are accurate and fast. In this application note, we show how the HiPer SSM is used for elemental mapping of mortar samples. The short timeframe in which these mappings can be recorded with the HiPer SSM allow for extensive reaction studies using multiple samples.

Instrumentation

A Zetium spectrometer, configured with a 4kW SST R-mAX tube, an X-Y sample handler for faster sample throughput and advanced analytical software was used. To enable the small spot analysis, the spectrometer was equipped with an ED core and dedicated HiPer SSM optics as well as high-precision translation mechanics and a high-resolution camera for sample imaging. Our SuperQ software allows for easy application setup and the production of 2D images, while the straightforward export of data to third- party image manipulation software allows the production of 3D contoured images.

Compositional mapping of a mortar sample

The distribution of eleven elements was mapped for a mortar sample checked for quality control purposes of the used cement paste. The sample was mounted in the special sample holder and imaged using the high-resolution camera. An area of 13mm x 21mm was selected and mapped with 1,161 spots using an Omnian
standardless analysis application. Each spot was measured with a single condition (60kV, 66mA, no filter) for only 20 seconds giving a total measurement time of 6.4 hrs.

This elemental mapping was used to analyze how the cement paste was distributed between the aggregates and had interacted with them. The different types of aggregates can also be easily identified based on the coupled substitution of elements such as Ca, Si and Mg. With this application it is thus possible to monitor the elemental composition and study the reaction kinetics.

Benefits of HiPer SSM on ED core

The HiPer SSM is the latest addition to the Zetium spectrometer’s SumXcore platform. This platform provides a unique combination of wavelength dispersive (WD) and energy dispersive (ED) technologies. Where the WD core can be used to achieve uncompromised accuracy and precision for routine bulk analysis, the ED core provides fast, simultaneous and multi-element analysis on small spots.

Using the ED core for small spot mapping provides several unique advantages over alternative techniques. Compared to SEM-EDS, minimal sample preparation is required and detection limits for quantitative studies are better. Compared to microscopy, the quantitative results are not user-dependent. Finally, compared to wavelength-based small spot systems, the simultaneous measurement of elements strongly reduces measurement times and allows for identification and quantification of elements not expected. These combined advantages allows for efficient and quantitative studies on reaction kinetics on multiple samples.

Even with measurement times per spot as short as 20 seconds and using a single high-kV condition normally best suited for heavier element excitation, Na was still easily mapped down to sub-0.5% levels with the HiPer SSM. This demonstrates the benefits of the ED core mapping solution, which collects full spectra and thereby measures multiple elements simultaneously.

Conclusions

The data in this application note demonstrates that the Zetium with HiPer Small Spot Mapping can perform fast elemental small spot analysis and mapping. Such analyses contribute to a better understanding of the reaction kinetics of cement, mortar and concrete and are an ideal tool for materials research and production process troubleshooting. The Zetium with SumXcore technology brings the mapping functionality closer to where routine analyses are performed and is thus a valuable addition to a bulk sample analysis spectrometer.