Ran Zhou

Determinations of trace boron in superalloys and steels using laser-induced breakdown spectroscopy assisted with laser-induced fluorescence.

Boron (B) is widely applied in microalloying of metals. As a typical light element, however, determination of boron in alloys with complex matrix spectra is still a challenge for laser-induced breakdown spectroscopy (LIBS) due to its weak line intensities in the UV-visible-NIR range and strong spectral interference from the matrix spectra. In this study, a wavelength-tunable laser was used to enhance the intensities of boron lines selectively. The intensities of B I 208.96 nm from boron plasmas were enhanced approximately 3 and 5.8 times while the wavelength-tunable laser was tuned to 249.68 and 249.77 nm, respectively. Utilizing the selective enhancement effect, accurate determinations of trace boron in nickel-based superalloys and steels were achieved by laser-induced breakdown spectroscopy assisted by laser-induced fluorescence (LIBS-LIF), with limits of detection (LoDs) of 0.9 and 0.5 ppm, respectively. The results demonstrated that LIBS-LIF can hopefully be used in boron determinations and has great potential for improving the ability of LIBS to determine light elements in alloys with a complex matrix.

Spatially selective excitation in laser-induced breakdown spectroscopy combined with laser-induced fluorescence

Spatially selective excitation was proposed to improve excitation efficiency in laser-induced breakdown spectroscopy combined with laser-induced fluorescence (LIBS-LIF). Taking chromium (Cr) and nickel (Ni) elements in steels as examples, it was discovered that the optimal excitation locations were the center of the plasmas for the matrix of the iron (Fe) element but the periphery for Cr and Ni elements. By focusing an excitation laser at the optimal locations, not only excitation efficiency but also the analytical accuracy and sensitivity of quantitative LIBS-LIF were better than those with excitation at the plasma center in conventional LIBS-LIF. This study provides an effective way to improve LIBS-LIF analytical performance.

Spectral Interference Elimination in Soil Analysis Using Laser-Induced Breakdown Spectroscopy Assisted by Laser-Induced Fluorescence

The complex and serious spectral interference makes it difficult to detect trace elements in soil using laser-induced breakdown spectroscopy (LIBS). To address it, LIBS-assisted by laser-induced fluorescence (LIBS-LIF) was applied to selectively enhance the spectral intensities of the interfered lines. Utilizing this selective enhancement effect, all the interference lines could be eliminated. As an example, the Pb I 405.78 nm line was enhanced selectively. The results showed that the determination coefficient (R2) of calibration curve (Pb concentration range = 14-94 ppm), the relative standard deviation (RSD) of spectral intensities, and the limit of detection (LOD) for Pb element were improved from 0.6235 to 0.9802, 10.18% to 4.77%, and 24 ppm to 0.6 ppm using LIBS-LIF, respectively. These demonstrate that LIBS-LIF can eliminate spectral interference effectively and improve the ability of LIBS to detect trace heavy metals in soil.

Detection of Trace Elements in Active Luminescent Glass Using Laser-induced Breakdown Spectroscopy Combined with Laser-induced Fluorescence

Abstract In the preparation of active luminescent glass, trace elements are generally co-doped to improve the properties. To overcome the poor sensitivity of laser-induced breakdown spectroscopy (LIBS) on detecting trace elements in glass, LIBS combined with laser-induced fluorescence was utilized to detect trace Yb, Al and P. A wavelength-tunable laser was used to excited Yb ions, Al atoms, and P atoms. The transition process in laser-induced fluorescence was described. The results showed that the spectral intensities of Yb, Al and P were enhanced by 23, 50 and 8 times, respectively. LIBS sensitivity was demonstrated to be greatly improved by combining laser-induced fluorescence.

Laser-induced breakdown spectroscopy of liquid solutions: A comparative study on the forms of liquid surface and liquid aerosol

Liquid surface and liquid aerosol as the traditional liquid forms for laser-induced breakdown spectroscopy (LIBS) and inductively coupled plasma (ICP), respectively, have been used to analyze chromium (Cr) and cadmium (Cd) elements using LIBS in a liquid solution. The spectral differences, the effects of laser energy and laser frequency, the accumulated number of laser pulses, gate delay time, and the quantitative analyses for a liquid surface and a liquid aerosol were compared. The results showed that the liquid surface demonstrated a lower plasma threshold, higher optical emission intensity, and higher single-to-noise ratio. Moreover, the relative standard deviations (RSDs) of the intensities of the liquid aerosol are better than those of the liquid surface. Furthermore, the results of the quantitative analyses of Cr I 357.86 nm and Cd I 361.05 nm of the liquid surface are close to those of the liquid aerosol. The limit of detections of Cr and Cd of the liquid surface were 2.764 and 86.869  μg/mL, which were close to those of liquid aerosol, 2.847  μg/mL of Cr and 97.635  μg/mL of Cd. For both the liquid surface and liquid aerosol, the coefficient of determination R2 of the calibration curve for Cr and Cd were above 0.99, and the average RSDs of Cr and Cd of the liquid surface were 0.027 and 0.054, which were similar to the 0.020 of Cr and 0.042 of Cd of the liquid aerosol. These results suggest that both the liquid surface and aerosol have similar detection abilities for water quality monitoring.

Determination of Carbon Content in Steels Using Laser-Induced Breakdown Spectroscopy Assisted with Laser-Induced Radical Fluorescence

Carbon is a key element for steel properties but hard to be determined by laser-induced breakdown spectroscopy (LIBS). Utilizing the combination of carbon in analytes and nitrogen in ambient gas to generate carbon-nitrogen (CN) radicals, LIBS assisted with laser-induced radical fluorescence (LIBS-LIRF) was proposed to resonantly excite radicals instead of atoms in plasmas. The CN radicals in the B2Σ-A2Π band were stimulated by a 421.60 nm laser wavelength and emitted 388.34 nm fluorescence. The results show that the spectral intensity of the CN radicals was enhanced by 2 orders of magnitude using LIBS-LIRF. Then carbon content in steels was accurately and sensitively determined without spectral interference. The limits of detection (LoDs) were 0.039 and 0.013 wt % in air and nitrogen gas, respectively. The limits of quantification (LoQs) were 0.130 and 0.043 wt % in air and nitrogen gas, respectively. This work demonstrated the feasibility of LIBS to realize reliable carbon determination in steel industry.

High-sensitivity determination of cadmium and lead in rice using laser-induced breakdown spectroscopy

Stability and sensitivity of toxic elements determination is still unsatisfactory in agricultural product using laser-induced breakdown spectroscopy (LIBS). A simple and low cost sample pretreatment method named solid-liquid-solid transformation method was proposed in this work. The target analytes of cadmium (Cd) and lead (Pb) from rice samples were prepared through ultrasound assisted extraction in hydrochloric acid solution. The solution was dropped on the glass slide after centrifuging process and was further dried on a heater. Finally, the glass slide contained the analytes was carried out for LIBS determination. Compare with conventional pellet method, the spectral intensity of Cd and Pb element were enhanced significantly using LIBS. The limits of detection were 2.8 and 43.7 μg/kg, respectively. The limits of quantification were 9.3 and 145.7 μg/kg, respectively. The results demonstrated that LIBS coupled with ultrasound assisted extraction should be a promising tool to detect toxic elements in rice.

Determination of Trace Available Heavy Metals in Soil Using Laser-Induced Breakdown Spectroscopy Assisted with Phase Transformation Method

To detect available heavy metals in soil using laser-induced breakdown spectroscopy (LIBS) and improve its poor detection sensitivity, a simple and low cost sample pretreatment method named solid-liquid-solid transformation was proposed. By this method, available heavy metals were extracted from soil through ultrasonic vibration and centrifuging and then deposited on a glass slide. Utilization of this solid-liquid-solid transformation method, available Cd and Pb elements in soil were detected successfully. The results show that the regression coefficients of calibration curves for soil analyses reach to more than 0.98. The limits of detection could reach to 0.067 and 0.94 ppm for available Cd and Pb elements in soil under optimized conditions, respectively, which are much better than those obtained by conventional LIBS.

Preparation and formation mechanism of phase-controlled titanium dioxide microspheres by selective laser heating in liquid medium

An approach for the fabrication of crystal-controlled microspheres from nanoparticles is presented, in which the nanoparticles were melted to form microspheres by selective laser heating in liquid medium. As an example, anatase titanium dioxide was selected as a typical material due to its metastability. The results showed that the single-crystalline rutile spheres, amorphous titanium dioxide spheres and polycrystalline anatase spheres could be prepared from anatase titanium dioxide nanoparticles. The formation of the microspheres was investigated under a variety of irradiation wavelengths and input laser fluences, and the formation mechanisms were discussed according to three aspects: melting–quenching process, laser-induced chemical transition process and liquid-medium heat transfer process.

Long-term repeatability improvement of quantitative LIBS using a two-point standardization method

To improve long-term repeatability in quantitative analysis of laser-induced breakdown spectroscopy (LIBS), a two-point standardization (TPS) method was used to perform a standard procedure on the measured intensities of test samples before quantitative analysis. Based on a self-developed LIBS analyzer, the TPS method was used to measure trace elements such as Mn, Si, Cr, Ni, Cu, Ti, Al, V and Mo in low alloy steel samples. Quantitative validations with six test samples were performed every 24 hours for three days. The results demonstrated that the instrument drift was effectively corrected using the TPS method, and the average relative errors (AREs) of repeated measurements decreased by 45%, 32%, 3%, 16%, 15%, 54%, 11%, 11%, and 91% for Mn, Si, Cr, Ni, Cu, Mo, Al, V, and Ti elements, respectively. The long-term repeatability of quantitative LIBS was improved using the TPS method. The performance of the TPS method for different elements is mainly influenced by the characteristics of test samples, correction samples, experimental conditions, etc. In practice, the TPS method is a very promising way to improve the repeatability of quantitative LIBS.