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在 XRF 荧光光谱仪中使用压片法与直接测试粉末样品相比有哪些优势?

更新时间:2021-07-21      点击次数:1125

在 XRF 荧光光谱仪中使用压片法与直接测试粉末样品相比有哪些优势?

压片制备步骤


X 射线荧光光谱 (XRF) 对样品材料的制备高度敏感。压缩的水泥样品显示出更高的信噪比,与松散的粉末形式相比,它可以检测到最轻的元素。



当元素组成被量化时,在预期值和松散粉末样品之间观察到明显的差异。当使用同一批水泥制备压缩颗粒时,这些差异将消失。



XRF 光谱分析信号由两部分组成:




特征波长处的 X 射线发射峰对应于分析样品原子中发生的电子跃迁




由松散束缚的外部电子散射的 X 射线的连续背景,发射峰叠加在其上




这些特征 X 射线通常是由样品表面以下 1-1000 µm 深度处的表面原子引起的。确切的深度取决于它的原子量。如果元素较轻,则较重的元素更难以检测。




背景散射和发射峰的强度都受颗粒大小、矿物成分和颗粒密度的影响。然而,将样品研磨成非常细的颗粒,然后将其压缩成光滑平整的 XRF 颗粒可以减少背景散射并改善发射检测。




颗粒和散粉中重元素和轻元素的比较








使用松散粉末获得的光谱显示出与压缩颗粒的显着差异。粒子显示出更高的信噪比,这使得在背景上可以轻松检测到最轻的元素。由于不需要薄膜,因此可以在真空条件下进行测量,从而进一步提高颗粒的性能。

准确定量最重要的是用户可以清楚地检测到样品中的所有元素。在松散粉末样品中,低估较轻的 Al、Mg 和 Na 元素会导致高估水泥中的 Fe 和 Ca。另一方面,样品沉淀提供的定量与标准实验室实验确定的范围一致。

What are the advantages of the pressed pellet method over the direct testing of powder samples when used in XRF fluorescence spectrometers?


pressed pellet prepare steps


X-ray fluorescence spectroscopy (XRF) is highly sensitive to the preparation of sample materials. The compressed cement sample shows a higher signal-to-noise ratio, which can detect the lightest elements compared to the loose powder form.








When the elemental composition is quantified, a clear difference is observed between the expected value and the loose powder sample. These differences will disappear when the same batch of cement is used to prepare compressed granules.




The XRF spectrum analysis signal consists of two parts:




The X-ray emission peak at the characteristic wavelength corresponds to the electronic transition that occurs in the atom of the analyzed sample




Continuous background of X-rays scattered by loosely bound external electrons on which emission peaks are superimposed




These characteristic X-rays are usually caused by surface atoms at a depth of 1-1000 µm below the sample surface. The exact depth depends on its atomic weight. If the element is light, the heavier element is more difficult to detect.




The intensity of background scattering and emission peaks are both affected by particle size, mineral composition and particle density. However, grinding the sample to a very fine particle size and then compressing it into smooth and flat XRF particles can reduce background scattering and improve the detection of emissions.




Comparison of heavy and light elements in granules and loose powder








The spectra obtained using the loose powder showed a marked difference from the compressed granules. The particles show a higher signal-to-noise ratio, which allows the lightest elements to be easily detected on the background. Since no film is required, the measurement can be performed under vacuum conditions, thereby further improving the performance of the particles.




xrf pressed pellet machine




The most important thing for accurate quantification is that the user can clearly detect all the elements in the sample. In loose powder samples, the underestimation of the lighter Al, Mg and Na elements will lead to the overestimation of Fe and Ca in cement. On the other hand, the quantification provided by the sample precipitate is consistent with the range determined by standard laboratory experiments.


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