Alternative Applications Using WDXRF

X-ray fluorescence (XRF) spectroscopy is an analytical technique primarily used for elemental analysis, capable of detecting elements ranging from beryllium to curium. Its key advantages include relatively simple and fast sample preparation, precise and accurate results, and long-term stability without frequent calibration. Traditionally, XRF is most commonly employed for the bulk analysis of large sample quantities.

XRF operates by irradiating a sample with primary X-rays (photons) emitted from an X-ray tube. These primary X-rays cause electrons to be ejected from the atoms within the sample, creating vacancies. To stabilize, other electrons fill these vacancies, releasing secondary (fluorescent) X-rays. The energy difference of these emitted X-rays is what the spectrometer analyzes. The position of a peak in the resulting spectrum indicates the element present (qualitative analysis), while the peak's intensity corresponds to its concentration or other values like thickness (quantitative analysis). Software packages then convert these intensities into meaningful results, often using mathematical models like the fundamental parameter approach or empirical calibrations based on reference standards.

The SQX Scatter FP method is a semi-quantitative X-ray analysis technique used for samples where the exact matrix (balance compounds) is unknown. Unlike standard SQX methods where the matrix type (e.g., metal, oxide, liquid) is generally known, SQX Scatter FP is ideal for complex, heterogeneous materials like waste, sludges, scales, or organic samples. This method utilizes the scattered radiation from the sample, particularly the inelastic (Compton) scattering effect, which is more prominent in lighter matrices. By analyzing the Compton peak, the software can estimate an average balance compound (typically light elements like hydrogen to oxygen), allowing for semi-quantitative analysis even without knowing the precise matrix.

The oil solidification method transforms liquid oil samples into a solid disc for XRF analysis. This process offers several significant benefits: it eliminates the risk of leakage and contamination within the spectrometer, which is common with liquid samples; it prevents sedimentation of particles in heavy fuels during analysis, ensuring more accurate results; it removes the need for helium atmosphere or films, both of which can be costly or difficult to obtain and can reduce intensity for light elements like sodium and magnesium. By solidifying the oil, XRF can achieve significantly better precision, especially for light elements.

UltraCarry and MicroCarry are specialized carrier materials (a paper filter for MicroCarry and a pure carrier for UltraCarry) designed to enable XRF analysis of trace elements in water samples at very low detection limits (sub-PPM to tens of PPB). Traditionally, analyzing water with XRF using liquid cells and films results in high background noise and poor detection limits, especially for light elements. With UltraCarry and MicroCarry, a small amount of water sample is deposited and dried on the carrier. This concentrates the analytes and, combined with a scatter reduction cup, significantly lowers the background signal, allowing for dramatically improved detection limits and the analysis of elements from boron to uranium, which are typically undetectable by conventional XRF water analysis.

Small spot analysis and mapping allow for the detailed examination of specific areas and elemental distributions on a sample's surface. Using a CCD camera, an image of the sample is captured, and specific areas of interest can be targeted and zoomed in on. The XRF spectrometer then performs micro-analysis on these selected spots (e.g., 0.5 or 1 mm in size). Mapping involves analyzing multiple measurement points across a defined surface area, providing a visual representation (2D or 3D) of element distribution. This capability is not just qualitative; it can also be used for quantitative analysis of elemental concentrations at various points, making it valuable for understanding material homogeneity, identifying contaminants, or analyzing intricate structures like a "CE mark" on a small component.

XRF can analyze loose powder samples in a vacuum, which is typically challenging as air in the sample cup would hinder vacuum conditions. This is achieved using special sample cups designed with two open ends. One end is sealed with a regular plastic film, and the sample is placed inside. The other end is covered with a "plankton net." This net allows air to easily escape from the sample cup when placed in a vacuum spectrometer while ensuring the powder sample remains contained. This method allows for efficient removal of air, bringing the sample closer to the measurement surface and enabling vacuum analysis. For very small or invaluable samples, a similar approach uses small "sample pans" within a liquid sample cell, allowing for easy recovery of the sample after analysis.

XRF is widely used in industries like electronics and construction for analyzing the thickness, composition, and distribution of metal coatings and thin films. It's crucial for ensuring quality, optimizing material use (especially for expensive coatings like gold), and verifying properties like corrosion resistance. The technique works by measuring the intensity of fluorescent X-rays from the coating and the substrate. As the coating thickness increases, the intensity of its characteristic X-rays rises until it reaches a "saturation level," where no further increase in intensity occurs. This saturation point represents a physical limit beyond which the XRF spectrometer cannot accurately determine the thickness because the X-rays are no longer penetrating the entire layer. The analysis uses software models to define layered structures and properties, employing either empirical calibrations (with standard samples) or fundamental parameter algorithms for quantification.