Analysis of tungsten carbide coatings by infrared laser-induced argon spark with inductively coupled plasma atomic emission spectrometry

Infrared laser ablation was studied for application to the analysis of plas ma-sprayed tungsten carbide/cobalt coatings. The potential of the laser ind uced argon-spark (LINA-Spark(TM)), as a sample introduction device in induc tively coupled plasma atomic emission spectrometry was studied. The use of an IR laser along with defocusing led to laser-induced microplasma-based ab lation. The mass ablation rate, represented by the ICP emission intensity p er laser beam unit area, exhibited a flat increase in the irradiance range 2-250 GW/cm(2). A low slope (0.5) of this dependence in log-log scale gave evidence of plasma shielding. The sleep increase in the measured acoustic s ignal when focused in front of the sample, i.e. in argon, indicated a break down of argon. Consequently, considerably lower ICP emissions were observed within the same range of irradiance. The cobalt/tungsten line intensity ra tio in the ICP was practically constant from 1.5 up to at least 250 GW/cm(2 ) Acceptable precision (R.S.D. < 5%) was obtained without internal standard ization for irradiance between 2 and 8 GW/cm(2). Optimization of the laser pulse energy, repetition rate, beam focusing and sample displacement during interaction led to the Linearization of dependences of signal vs. cobalt p ercentage, at least up to the highest studied Value of 23% Co. (C) 2000 Els evier Science B.V. All rights reserved.