Published

2022-11-01

Effects of Variations in Operating Conditions on the Preci-sion and Accuracy of Standardless Elemental Analysis of Stainless Steel by SEM-EDS

Efectos de cambios en las condiciones de operación en la precisión y la exactitud del microanálisis químico sin patrones de acero inoxidable por MEB-EDE

Keywords:

Scanning electron microscopy, Energy dispersive spectroscopy, SDD detector, Elemental analysis, Accuracy (en)
Microscopía electrónica de barrido, Espectroscopía por dispersión de energía, Detectores SDD, Microanálisis químico, Exactitud (es)

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It is a customary practice to carry out standardless elemental microanalysis by energy dispersive spectroscopy (EDS) under the very same operational conditions as those used for scanning electron microscope (SEM) imaging. In this article, EDS experiments were carried out with stainless steel (SS), varying the EDS testing operating conditions. The results showed that, if X-ray spectra are acquired under operating conditions that are very dissimilar to those optimized for microanalysis, both the detectability limit of minor species (Si, Mo, and Mn) and the uncertainty in the concentration of major alloying elements (Cr and Ni) are noticeably impaired. It was observed that, by improving the signal-to-noise (S-to-N) ratio (i.e., by increasing the accelerating voltage, beam intensity, and total acquisition time, or when the working distance is optimized), the precision of the elemental concentration increases, but the accuracy is only marginally affected. For the major alloying elements, 25% of the measurements showed a percent discrepancy higher than three times the standard deviation, which is inconsistent with a normal statistical distribution.

Es común que el microanálisis químico por espectroscopia por dispersión de energía (EDE) se realice en las mismas condiciones en las usadas para la adquisición de imágenes mediante el microscopio electrónico de barrido (MEB). En este artículo se realizaron experimentos de EDE sobre acero inoxidable, variando las condiciones de operación. Los resultados mostraron que, cuando se adquieren espectros de rayos X bajo condiciones de operación muy disímiles de aquellas optimizadas para el microanálisis, tanto la detectabilidad de las especies minoritarias (Si, Mo y MN) como la incertidumbre en la concentración de los principales elementos de aleación (Cr y Ni) se ven notoriamente afectadas. Se observó que, al mejorar la relación señal a ruido (S-R) (i.e., aumentando el voltaje de aceleración, la intensidad del haz y el tiempo de adquisición total, o cuando se optimiza la distancia de trabajo), aumenta la precisión en la concentración elemental, pero la exactitud se ve afectada solo de manera marginal. Para los elementos de aleación principales (Cr y Ni), 25% de las medidas presentaron discrepancias porcentuales mayores a tres veces la desviación estándar, lo cual no es consistente con una distribución estadística normal.

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