XRF is an analytical technique which can determine the chemical composition of solids, liquids and powders. It has a wide range of applications and a linearity from ppm to % range. XRF has the advantage to be a non-destructive technique and for most samples, sample preparation is hardly required. OCAS recently installed a brand new WD-XRF.
X-rays are used to excite the sample, which subsequently emits specific X-ray fluorescence. It can be used to obtain a qualitative screening of the analysed materials or after calibration to obtain a quantitative chemical composition. In between those two options, semi quantitative analyses can be obtained either by standardless analyses (based on elemental response factors determined on reference materials ) or by means of pre-calibrated packages which can be continuously optimized. Those options are mainly interesting in the development of new materials. The compositions under study haven’t been commercialized, therefore it is not straightforward to find a good set of certified reference materials needed to build an own calibration.
WD-XRF versus ED-XRF
XRF can be divided in two main categories depending on the detection method, ie wavelength (WD) or energy (ED) dispersive systems. A benchtop ED-XRF system is already available at OCAS. It can determine all elements between Na and U. In energy dispersive systems all emitted X-rays are virtually measured at once and a spectrum consists of the relative amount of X-rays per energy. In wavelength dispersive systems the X-rays are physically seperated according to wavelength and subsequently measured one by one.
As a result WD-XRF systems have higher sensitivities and a better resolution compared to ED-XRF. The higher resolution of WD-XRF means reduced spectral overlaps, leading to more accurate analyses of complex samples. In addition backgrounds are reduced, resulting in improved detection limits and sensitivity. The higher sensitivity allows to determine a full chemical composition (trace levels and percentage range) in one measurement.
The elemental range in ED-XRF systems starts at Na. In WD-XRF theoretically the elemental range starts at Be. However, the sensitivity with which the light weight elements are measured depends on the crystal selected in the configuration. In the configuration at OCAS C and N can only be measured in % range.
Typical applications of XRF
- chemical composition of solid metallic samples
- layer thickness of metallic coatings
- layer thickness organic and inorganic coatings based on a tracer element (e.g. temporary corrosion protection coatings)
- inorganic elements in liquids, such as oils, water samples, emulsions
- chemical composition of powders
“WD-XRF is an interesting technique to improve & speed-up the chemical analysis of our castings and coated products.”