在 XRF 熒光光譜儀中使用壓片法與直接測試粉末樣品相比有哪些優勢？

壓片制備步驟

X 射線熒光光譜 (XRF) 對樣品材料的制備高度敏感。壓縮的水泥樣品顯示出更高的信噪比，與松散的粉末形式相比，它可以檢測到最輕的元素。

當元素組成被量化時，在預期值和松散粉末樣品之間觀察到明顯的差異。當使用同一批水泥制備壓縮顆粒時，這些差異將消失。

XRF 光譜分析信號由兩部分組成：

特征波長處的 X 射線發射峰對應于分析樣品原子中發生的電子躍遷

由松散束縛的外部電子散射的 X 射線的連續背景，發射峰疊加在其上

這些特征 X 射線通常是由樣品表面以下 1-1000 µm 深度處的表面原子引起的。確切的深度取決于它的原子量。如果元素較輕，則較重的元素更難以檢測。

背景散射和發射峰的強度都受顆粒大小、礦物成分和顆粒密度的影響。然而，將樣品研磨成非常細的顆粒，然后將其壓縮成光滑平整的 XRF 顆粒可以減少背景散射并改善發射檢測。

顆粒和散粉中重元素和輕元素的比較

使用松散粉末獲得的光譜顯示出與壓縮顆粒的顯著差異。粒子顯示出更高的信噪比，這使得在背景上可以輕松檢測到最輕的元素。由于不需要薄膜，因此可以在真空條件下進行測量，從而進一步提高顆粒的性能。

準確定量最重要的是用戶可以清楚地檢測到樣品中的所有元素。在松散粉末樣品中，低估較輕的 Al、Mg 和 Na 元素會導致高估水泥中的 Fe 和 Ca。另一方面，樣品沉淀提供的定量與標準實驗室實驗確定的范圍一致。

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.