The EDAX Low Energy X-Ray Spectrometer (LEXS) is a wavelength dispersive spectrometry (WDS) spectrometer that consists of X-ray optics capable of performing parallel beam operation. The high collection optics offer high efficiency to analyze light elements, particularly O, B, N and C, with a complete range of operation spanning from 80 eV to 2.4 keV.
This article discusses the method of using the LEXS to detect light elements found in carbide layers on steel.
High accuracy X-ray data collection for quantification is needed to understand the composition and distribution of the carbide layer on stainless steel.
The spectrometer utilized for this WDS application was the LEXS. A sequence of carbide standards were determined with a few pure elements to enable quantitative analysis of the carbide unknowns to be measured. All samples were measured using a beam current between 20 to 25 nA and an accelerating voltage of 10 kV.
Along with a Keithley Pico ammeter, a tungsten filament Scanning Electron Microscope (SEM) was used to observe the beam current. Together with the WDS data, energy dispersive spectroscopy (EDS) spectra were procured from the samples.
The concurrent acquisition of WDS and EDS data offers users the ability to apply EDS data for some of the higher atomic number samples; however, this was not done in this case. The two detectors had a takeoff angle of 35°, and the instrument’s working distance was 17 mm. This distance is specific to the instrument, and can be smaller if the SEM chamber allows.
Standards are required for precise quantification in WDS. For this research, the carbide standards Cr3C2, SiC, Cr7C3, TiC, and Fe3C were utilized. The EDS and WDS spectra gathered from the standards Fe3C and TiC are respectively illustrated in Figures 1 and 2.
Figure 1. Spectra of Fe3C. The WDS data (top) shows the C K and Fe L lines, while the EDS spectrum (bottom) shows C K, Fe L and K lines.
Figure 2. WDS (top) and EDS (bottom) spectra of TiC.
A cast iron coated with plasma spray was analyzed to demonstrate carbon coating on steel. The carbide measured approximately 2 µm wide by 10 µm long, and was tested in spot mode. Figure 3 illustrates the spectra gathered from the sample with the selectivity and high sensitivity of the WDS system clearly shown. From the quantified data, the carbide layer’s concentrations were computed by utilizing the measured standards. Table 1 shows the results.
Figure 3. WDS (top) and EDS (bottom) spectra for the carbide.
Table 1. Quantitative results for the carbide.
The LEXS has been optimized to handle low energy microanalysis. It employs innovative high collection optics (HCO), which records the maximum count rates available, offering fast X-ray analysis at the highest resolutions possible. The LEXS is exclusively designed for low energy X-ray microanalysis, offering resolutions of below 20 eV and high peak-to-background ratios for X-ray energies less than 2.5 keV. It is suitable for overcoming such overlaps as N Kα from Ti Lα and Si Kα from Ta Ma or W, with count rates adequately high that testing speed is not a limitation for this system.
The LEXS equipped with high performance optics, is suitable for testing light elements from Be K to S K. The LEXS system’s ability to establish the carbide concentration on steel is shown in the data. It undoubtedly shows that the LEXS is a unique complementary tool to an EDS system, and assists in the precise determination of light elements.
This information has been sourced, reviewed and adapted from materials provided by EDAX Inc.
For more information on this source, please visit EDAX Inc.