Using Handheld LIBS Analyzer for Laser-Based Chromium Analysis in Elements and Alloys

Spark optical emission spectroscopy (OES) and handheld XRF are often used to study a range of alloys and elements. An alternative approach to these techniques is the laser-induced breakdown spectroscopy (LIBS). Similar to the OES technique, the LIBS method involves the creation of plasma at the surface of the material. As and when the plasma cools, spectral lines arising from different existing elements are determined. The presence of the elements is determined by the wavelength of specific spectral lines, and light intensity at a specified wavelength is linked to individual element concentration.

SciAps Handheld Analyzer

An advanced handheld analyzer called Z has been developed by SciAps, which uses the LIBS method (Figure 1). When it comes to handheld LIBS, three basic factors are important to study most alloys, particularly stainless and high temperature ferrous alloys. These factors include:

  • A high energy pulsed laser (beam rastering)
  • 50 Hz burst cleaning to prevent sample surface effects and grinding
  • Opti-Purge™ on-board argon purge to ensure a high level of accuracy, compared to air-based analysis

Z handheld analyzer

Figure 1. Z handheld analyzer

The Z handheld analyzer utilizes 6 mJ/pulse at a repetition rate of 50 Hz. For sites with limitations regarding compressed gas canister, the analyzer can be integrated for only air-burn analysis. When compared to a standard handheld XRF instrument, the Z provides a number of benefits for flow accelerated corrosion (FAC) applications. These benefits include faster analysis of chromium (Cr) at reduced level of concentrations (0.05%) which can be completed in 3 seconds.

The Z handheld is a laser-based system, eliminating any ionizing radiation such as X-rays. This means that the regulatory requirements at nuclear fueled power plants is considerably reduced. The Z analyzer not only offers a low atomic number performance (Al, Li, B, Be, Si, Si) of mobile OES analyzers, but it maintains the portability of handheld XRF analyzers.

FAC Applications

For FAC applications, it is important to determine the amount of Cr present in carbon steels in a rapid way. If the concentration of Cr is reduced to less than 0.1%, which happens to be the standard threshold value, then the speed of corrosion in carbon steel-based flow systems will increase quickly. Handheld XRF analyzers have been effectively employed for Cr analysis in carbon steels, and one such analyzer is the SciAps X.

LIBS also provides a number of benefits. The Z handheld analyzer requires a test lasting for 3 seconds to determine 0.05% of Cr, compared to the 10 seconds required for an XRF instrument to achieve a suitable accuracy at a concentration range of 0.1% in carbon steel. Most facilities, including power plants, have limited regulations when it comes to using the handheld XRF analyzer. As the Z is a laser-based device, it does not have to conform to the various regulation requirements for X-ray. Table 1 describes 10x repeats required for two concentrations of Cr.

Table 1. 10x repeats for two Cr concentrations

1018 Cr (%) 1117 Cr (%)
1 0.109 1 0.078
2 0.113 2 0.077
3 0.115 3 0.081
4 0.120 4 0.077
5 0.119 5 0.079
6 0.104 6 0.079
7 0.112 7 0.076
8 0.116 8 0.079
9 0.121 9 0.078
10 0.113 10 0.074
Average 0.114 Average 0.078
Std. Dev. 0.0054 Std. Dev. 0.002
RSD 4.7% RSD 2.3%

A carbon steel 1018 with Cr content 0.111% was one material, and a carbon steel 1117 with Cr content 0.076% was the other. Table 1 shows the repeatability data, including the typical deviation. When the 1018 alloy Cr result is applied with a confidence interval of 2 standard deviations, reliable measurement of the Cr can still be achieved over a threshold value of 0.1%. In the case of the alloy 1117, a maximum threshold value of 0.084% LIBS measurement for Cr is shown by a two sigma confidence band. Therefore, the Cr levels of concern, less than a standard threshold of 0.1%, are determined in a reliable way.

A suitable alternative to XRF, the Z handheld analyzer also generates excellent Cr results with a maximum test times of 3 seconds. Figure 2 displays the results for carbon steels, evaluating the Z analyzer results against the certified assay.

Measured Cr versus Cr assay for FAC application.

Figure 2. Measured Cr versus Cr assay for FAC application.

The Cr detection limit in 3 seconds is below 0.015%, and as noted from the correlation, the precision is relatively good. The slope has 1 to 4 major figures, with almost an offset of 0.

Conclusion

The advanced Z handheld LIBS analyzer has three major requirements to ensure an effective in-field analysis of a wide range of alloys and materials. This combination delivers excellent performance on a variety of materials such as red metals, aluminum alloys, stainless, nickel, and ferrous. With the new sample detection system, the device can be used under Class 1 conditions, removing all of the restrictive regulatory requirements of class 3b LIBS devices and X-ray.

This information has been sourced, reviewed and adapted from materials provided by SciAps, Inc.

For more information on this source, please visit SciAps, Inc.

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