Examine reaction kinetics of mortar about 100 times faster with HiPer small spot mapping

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 is an ideal tool for materials research and production process troubleshooting.

Introduction

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 4 kW 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 13 mm x 21 mm was selected  and mapped with 1161 spots using an Omnian standardless analysis application. Each spot was measured with a single condition (60 kV, 66 mA, no filter) for only 20  seconds  giving  a  total   measurement time of 6.4 hrs.

The  distribution  and  relative concentration of eleven  measured elements are depicted in Figure 1. 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.

Figure 1. Qualitative compositional map of mortar measured for quality control purposes of the used cement paste. Sample courtesy of CEMEX.

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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 as can be seen in Figure 2. This demonstrates the benefits of the ED core mapping solution, which collects full spectra and thereby measures multiple elements simultaneously.

Figure 2a. Measured spectrum showing the Na-peak

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Figure 2b. Semi-quantitative mapping of sub-0.5% to 5 % Na 

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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.

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