Effect of Melting Iron-Based Alloy Temperature on Carbon Content Observed in Laser-Induced Breakdown Spectroscopy

Our recent work has determined the carbon content in a melting ferroalloy by laser-induced breakdown spectroscopy (LIBS). The emission spectrum of carbon that we obtained in the laboratory is suitable for carbon content determination in a melting ferroalloy but we cannot get the expected results when this method is applied in industrial conditions: there is always an unacceptable error of around 4% between the actual value and the measured value. By comparing the measurement condition in the industrial condition with that in the laboratory, the results show that the temperature of the molten ferroalloy samples to be measured is constant under laboratory conditions while it decreases gradually under industrial conditions. However, temperature has a considerable impact on the measurement of carbon content, and this is the reason why there is always an error between the actual value and the measured value. In this paper we compare the errors of carbon content determination at different temperatures to find the optimum reference temperature range which can fit the requirements better in industrial conditions and, hence, make the measurement more accurate. The results of the comparative analyses show that the measured value of the carbon content in molten state (1620 K) is consistent with the nominal value of the solid standard sample (error within 0.7%). In fact, it is the most accurate measurement in the solid state. Based on this, we can effectively improve the accuracy of measurements in laboratory and can provide a reference standard of temperature for the measurement in industrial conditions.     

Wavelength Dependence in the Analysis of Carbon Content in Coal by Nanosecond 266 nm and 1064 nm Laser Induced Breakdown Spectroscopy

The wavelength dependence of laser induced breakdown spectroscopy(LIBS) in the analysis of the carbon contents of coal was studied using 266 nm and 1064 nm laser radiations.Compared with the 1064 nm wavelength laser ablation,the 266 nm wavelength laser ablation has less thermal effects,resulting in a better crater morphology on the coal pellets.Besides,the 266 nm wavelength laser ablation also provides better laser-sample coupling and less plasma shielding,resulting in a higher carbon line intensity and better signal reproducibility.The carbon contents in the bituminous coal samples have better linearity with the line intensities of atomic carbon measured by the 266 nm wavelength than those measured by the 1064 nm wavelength.The partial least square(PLS) model was established for the quantitative analysis of the carbon content in coal samples by LIBS.The results show that both of the 266 nm and 1064 nm wavelengths are capable of achieving good performance for the quantitative analysis of carbon content in coal using the PLS method.     

The Effect of an External Magnetic Field on the Plume Expansion Dynamics of Laser-Induced Aluminum Plasma

In this work,we investigated the plasma morphology induced by a Nd:YAG laser with the aim of improving the understanding of the formation and dynamics of the plasma in two cases,with and without a magnetic field.Single laser pulse production of a plasma in the absence and presence of a magnetic field was performed with an aluminum target in air.A fast photography technique was employed to obtain information about the expansion dynamics and confinement of the aluminum plasma in each case.The generation of the laser plasma was allowed to expand at two locations with different magnetic field strengths,which correspond to the strength 0.58 T in the center of two magnetic poles and 0.83 T at a distance of 4 mm from the upper pole(N).The plume showed lateral confinement at longer delays when the target was placed at the center of the two poles.When the target was placed at a distance of 4 mm from the upper pole it was observed that the plume was divided into two lobes at the initial stage and traveled towards the center of the magnetic field with further elapse of time.