Microsc. Microanal. 23, 1143–1149, 2017 doi:10.1017/S1431927617012685
© MICROSCOPY SOCIETY OF AMERICA 2017
X-Ray Excited Optical Luminescence and Portable Electron Probe Microanalyzer–Cathodoluminescence (EPMA–CL) Analyzers for On-Line and On-Site Analysis of Nonmetallic Inclusions in Steel
Susumu Imashuku,* Koichiro Ono, and Kazuaki Wagatsuma Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
Abstract: The potential of the application of an X-ray excited optical luminescence (XEOL) analyzer and portable analyzers, composed of a cathodoluminescence (CL) spectrometer and electron probe microanalyzer (EPMA), to the on-line and on-site analysis of nonmetallic inclusions in steel is investigated as the first step leading to their practical use. MgAl2O4 spinel and Al2O3 particles were identified by capturing the luminescence as a result of irradiating X-rays in air on a model sample containing MgAl2O4 spinel and Al2O3 particles in the size range from 20 to 50 μm. We were able to identify the MgAl2O4 spinel and Al2O3 particles in the same sample using the portable CL spectrometer. In both cases, not all of the particles in the sample were identified because the luminescence intensities of the smaller Al2O3 in particular were too low to detect. These problems could be solved by using an X-ray tube with a higher power and increasing the beam current of the portable CL spectrometer. The portable EPMA distinguished between the MgAl2O4 spinel and Al2O3 particles whose luminescent colors were detected using the portable CL spectrometer. Therefore, XEOL analysis has potential for the on-line analysis of nonmetallic inclusions in steel if we have information on the luminescence colors of the nonmetallic inclusions. In addition, a portable EPMA–CL analyzer would be able to perform on-site analysis of nonmetallic inclusions in steel.
Key words: X-ray excited optical luminescence, cathodoluminescence, electron probe microanalyzer, nonmetallic inclusion, on-line and on-site analysis
INTRODUCTION
On-site or on-line analysis has been attracting massive attention in various fields such as industry, environmental analysis, medicine, and art. In the steelmaking industry, on-site and on-line analysis contribute to improvement in the productivity of steel (Chiba et al., 1991; Hemmerlin et al., 2001), as the analysis of steel is the time-consuming process in steelmaking (Atkinson & Shi, 2003). An especially time- consuming process is the analysis of nonmetallic inclusions in the steel (Atkinson & Shi, 2003). This is an important step to ensure the quality of the steel, because nonmetallic inclusions generate various defects in steel products (Zhang & Thomas, 2003). In the analysis of nonmetallic inclusions in steel, it is necessary to identify the amount, size, shape, and composition of nonmetallic inclusions above a dozen micrometers in size (Cramb, 1999; Goransson et al., 1999; Zhang & Thomas, 2003) because nonmetallic inclusions of those sizes will deteriorate the mechanical properties of steel, although the identification of nonmetallic inclusions below such sizes is sometimes required in a few steel products such as lead frame (Cramb, 1999). Various kinds of measurement techniques such as microscope observation, electron probe
*Corresponding author.
susumu.imashuku@
imr.tohoku.ac.jp Received June 5, 2017; accepted October 27, 2017
microanalysis (EPMA) (Belk, 1963), spark-induced atomic emission spectrometry (Goransson et al., 1999), laser microprobe mass spectrometry (Saitoh et al., 1996) are suggested for analyzing nonmetallic inclusions in steel, and their characteristics are summarized by Zhang & Thomas (2003). Among these techniques, an analytical method combined with optical microscopes and EPMA is generally used to identify the amount, size, shape, and composition of the inclusions off-line. However, it takes approximately 1 week to complete this analysis for a single sample. Spark- induced atomic emission spectrometry is suitable for a rapid analysis of nonmetallic inclusions, but it cannot identify the shapes and is off-line analysis. Thus, the productivity of steel will be substantially improved if the analysis of nonmetallic inclusions is carried out on-site or on-line. The use of portable analyzers is one of the solutions to reduce the time
for analysis of these inclusions in steel. Portable X-ray fluorescence spectrometers are already used for the elemental analysis of steel. However, these cannot identify the size and shape of nonmetallic inclusions because it is difficult to focus the X-rays on nonmetallic inclusions with sizes of only a dozen micrometers. Therefore, an alternative approach is necessary to realize on-site and on-line analysis of nonmetallic inclusions of this size range in steel. We have recently realized a portable EPMA (Imashuku et al., 2011, 2013b, 2014) and cathodoluminescence
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