X-ray fluorescence spectroscopy (XRF) is an important and well-established analytical technique within the cement industry, being used extensively for production and quality control for the elemental analysis of raw materials, alternative fuels and finished products.
Compliance with applicable industry norms is becoming increasingly important, especially when setting up new equipment and/or applications. The correct configuration, an optimized application and the appropriate sample preparation procedures are critical to the accuracy and quality of the obtainable results. The following application note demonstrates how easy and user-friendly it can be to comply with the ASTM C114-13 cement testing norm by using a Zetium spectrometer, configured with 1 kW power, together with an Eagon 2 fusion system for sample preparation.
The ASTM C114-13 norm outlines recommendations concerning maximum allowed deviations of measured results for a selection of important compounds in cement. According to this norm, two criteria apply, one for the differences between duplicates and one for the differences between the averages of the duplicates and the certified values. The maximum permissible variations in results according to the ASTM C114-13 norm are provided in Tables 2 and 3.
A Malvern Panalytical Zetium spectrometer configured with a 1 kW Rh anode, end window Super Sharp Tube (SST R) was used to carry out the measurements. The power settings of the tube ranged from 60 kV/16 mA (for heavy elements) to 25 kV/40 mA (for light elements). The total measurement time was less than 10 minutes.
Our Claisse Eagon 2 fully automatic fusion machine was used for fused bead sample preparation. An innovative (patented) design, with a two beads per cycle capacity, combines all of the advantages of both gas burner and muffle furnace technology in a fully electric system that does not require cooling water or compressed air. The Eagon 2 is completely safe to operate with a cold-to-cold safety circuit.
Sample preparation and measurement details
To prepare the cement fused beads with the Eagon 2 the recipe presented in Table 1 (dilution 1:10) was used.
Table 1. Fusion recipe details
Total time for making a pair of cement fused beads was less than 15 minutes. The bead diameter was defined by the mold used at 40 mm.
In order to demonstrate the instrument and sample preparation performance, seven international cement powder reference materials (NIST Portland SRM) were selected to produce duplicate fused bead samples. Duplicate beads were prepared and measured on different days.
Table 2 presents the concentration ranges and the the maximum difference between duplicates. Table 3 presents the concentration ranges and the deviation of the average of the duplicates from the certificatied values for all measured NIST SRM samples.
The difference between the measurements on different days is a measure of the overall precision of the method, while the difference between the average values and the certified values is a measure of the overall accuracy of the method.
When seven SRMs are used in the qualification procedure, the ASTM C114-13 norm states that a minimum of six of the seven SRMs must meet the criteria, in terms of differences between duplicates, as outlined in Table 2. Where the criteria is not met, the differences should not exceed twice the the allowed limit for a given compound.
Table 2. Differences between duplicates for all measured SRM samples compared with the C114-13 criteria
Table 3. Difference between the average of the duplicates and the certified value for all measured SRM samples compared with the C114-13 criteria
The fused bead sample preparation procedure was also tested using the Eagon 2 over a 10 day period. Table 4 shows average concentrations and the standard deviations (1σ) for 40 fused bead replicates of an ignited cement sample made with an Eagon 2 over 10 days (4 beads fused per day).
Considering that the standard deviation value includes not only sample preparation errors but also instrumental measurement errors, it can be seen that an Eagon 2 produces highly reproducible beads.
Table 4. Reproducibility test results over 10 days
The Zetium spectrometer, configured with only 1 kW power, and the Eagon 2 furnace fusion system easily meet the ASTM C114-13 norm requirements for the analysis of cement fused beads. The error that can be attributed to the spectrometer including sample preparation is small compared to the tolerances permitted by the norm. The required application know-how is embedded in the application database of the SuperQ analytical software and the fusion recipes are delivered with the Eagon 2, providing the cement industry with an efficient and reliable solution to high- quality analytical results and compliance with the most rigid norms.