Spectral preprocessing to improve accuracy of quantitative detection of elemental Cr in austenitic stainless steel by laser-induced breakdown spectroscopy

Abstract

The production and consumption of austenitic stainless steel account for about 70% of stainless steel worldwide. The content of chromium (Cr) must be accurately detected and controlled to form a stable austenite structure and obtain strong properties in production. Laser-induced breakdown spectroscopy (LIBS) can be used to detect the Cr content of austenitic stainless steel in a complex production process. However, LIBS signals may be weak and unstable because the experimental signals are seriously affected by noise, self-absorption, the matrix effect, and the instability of the shot-to-shot signal, rendering the quantitative detection results inaccurate and unstable. The spectral-preprocessing methods of baseline correction and denoising can improve the accuracy of quantitative detection of LIBS. An improved segmented Hermite cubic-interpolation method is proposed herein to correct the baseline offset and produce baseline signals that are smooth and convergent (to overcome the Runge phenomenon). Empirical mode decomposition (EMD) based on the wavelet method is proposed to remove LIBS noise; this is done by exploiting the adaptivity of EMD to refine the wavelet-scaling coefficients. Compared with other denoising methods, the proposed method has good denoising evaluation indices and stability and, thus, effectively removes the noise. To verify detection accuracy, the internal standard quantitative method is used to detect the Cr content, and a cyclic-inversion prediction method is designed to verify detection stability. The results show that the correlation coefficient of the calibration curve is improved, the root-mean-square error is reduced, and the average relative error of the predicted Cr content decreases from 10.46% to 3.858%.

Enhancement of LIBS plasma and efficient collection of emitted light by open smooth triangular cavities

“…1 However, because of the inuence of the matrix effect, 2,3 self-absorption effect, the noise of the experimental instrument and experimental environment, the spectral intensity and detection sensitivity of LIBS are low and the spectral stability is poor, resulting in low detection accuracy. 4 In order to enhance spectral intensity and reliability and improve the signal-to-noise ratio, spectral enhancement techniques such as dual-pulse excitation, 5 spark discharge, 6 microwave-assisted methods, 7 magnetic connement, 8 nanoparticle enhancement 9 and spatial connement are developed. 10 All the above-mentioned methods, except spatial connement, can enhance the spectral intensity, but they require additional equipment for the standard LIBS system, complicating the operation of the LIBS system and increasing the experimental costs.…”

“…The equations of mass, momentum and energy are expressed as eqn (1)-(3) respectively. The equation of state for ideal gas is used to close the equations, as shown in eqn (4).…”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…Another example was described by Yang et al who took a different approach. 18 These authors stated that errors can be caused by noise, weak signals, selfabsorption, matrix effects and the instability of the shot-toshot signals. They used spectral pre-processing in the form of empirical mode decomposition to correct for the noise component, hence facilitating the analysis when weak signals are obtained.…”