Stratos is an evolution of Malvern Panalytical’s market-leading thin film metrology software. A distinct feature of Stratos is the ability to analyze thin layers by using only bulk standards in the calibration. By doing so, one reduces the dependence on standards that are layered samples, which are often difficult to obtain or certify. Whenever available, layered standards and certified reference materials can still be added for ultimate accuracy. Stratos also makes use of a step-by-step setup guide called the Virtual Analyst which simplifies and optimizes the setup of an application. It suggests the best possible measurement conditions for a specific sample type which can be a tedious and complicated process if done manually.
An important application of Stratos is in the analysis of chrome coatings on steel. Chrome coatings are often used in the automotive industry because of their high resistance to corrosion. The coatings optimally protect the steel from premature wear and consequently extend the lifetime of important engine components.
This study demonstrates the powerful capabilities of an Axios FAST, PANalytical’s simultaneous WDXRF spectrometer, combined with the Stratos software module for determining the mass thickness of chrome coatings on steels. This is achieved using two bulk standards instead of costly in-type standards.
Axios FAST is a fully integrated simultaneous wavelength dispersive XRF spectrometer, complete with an X-Y handler and state-of-the-art software, SuperQ. It is engineered for excellence in terms of both analytical and operational performance.
X-ray tube: Rhodium anode 4 kW SST-mAX tube
Tube settings: 60 kV/66 mA
Fixed channels: Cr Kα
Shielding plate: 27 mm Rh plated
Sample holder: Stainless steel 27 mm aperture
Detector: Sealed Kr
The Cr on steel samples (as shown in Figure 1) were fitted directly into a sample cup with a 27 mm aperture.
Figure 1. Cross section of the Cr coating on a steel substrate
Calibration with the Virtual Analyst and measurement details
Based on the expected thickness and composition of the unknown samples, PANalytical’s Virtual Analyst facilitates the setup of the optimum measurement program to analyze multilayer samples. Optimum XRF lines are chosen based on the existing hardware configuration of the Axios FAST instrument. Line selection is based on the response of the XRF lines with respect to changes in thickness and composition within the expected concentration and thickness range of the unknown samples.
For this application, Cr Kα was proposed as the optimum line for the analysis. The calibration was set up using Omnian standardless software setup samples in the form of a pressed powder and a stainless steel reference material. The total measurement time was 20 seconds.
Results and discussion
Three chrome on steel samples previously analyzed wet chemically were measured and compared. The results reported in Table 1 show that Stratos is capable of accurately analyzing multilayer samples using only bulk standards. Using the bulk density of Cr, the mass thickness of 250 mg/m2 for Cr is equivalent to a layer thickness of 35 nm.
Table 1. Comparison of nominal and calculated values
In order to evaluate the instrument repeatability, the same samples were measured twenty times sequentially, with loading/unloading between each measurement. The results reported in Table 2 shows the excellent repeatability of this method.
Table 2. Results of twenty repeat measurements of Cr on steel samples
This data sheet demonstrates that Axios FAST, in combination with Stratos software is capable of performing accurate analysis of layer thicknesses of Cr coatings on steel. The excellent agreement shows that for this application the need for in-type layered standards is not necessary, which is seen as a significant advantage. The method established by using the Virtual Analyst is fast, non-destructive and permits the automatic selection of optimal measurement conditions for the analysis of thin films and multilayer samples.
The repeatability of the instrument also demonstrates that the combination Axios FAST and Stratos is an excellent solution in the production control of Cr coatings in the steel industry.