ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF COPPER AND LEAD IN SILICON-NITRIDE AND SILICON-CARBIDE BY DIRECT ATOMIZATION

A method involving atomic absorption spectrometry (AAS) with direct atomization has been developed for the determination of trace amounts of Cu and Pb in Si3N4 and SIC using a graphite furnace, The samples were ground to a particle size of less than 20 mu m and mixed with 2.5 times the amount of graphite powder in a corundum mortar. A 0.5-3 mg amount of the mixed sample was weighed in a tared graphite cup and atomized in a cup-type graphite furnace. The absorbance was determined by integration of the spectral lines in the absorbance versus time spectrum. Calibration was effected using aqueous standard solutions. The absorbance versus time spectrum of Cu shows double peaks, On the basis of the X-ray diffraction patterns and scanning electron micrographs of the Si3N4-graphite powder mixture heated at the temperature of each atomization step, the first peak could be assigned to the Cu vaporizing from Si, and the second peak to the Cu vaporizing from SIG. The results for 12 alpha-Si3N4, two beta-Si3N4 and two SIC samples were in good agreement with the values obtained by electrothermal AAS for liquid samples, The relative standard deviations for Cu (0.11-53.7 ppm m/m) and Pb (0.36-1.55 ppm m/m) are 1.6-39% (n = 5) and 4.3-17% (n = 5), respectively, The determination limits, corresponding to twice the standard deviation of the blank measurements, are 92 pg for Cu and 53 pg for Pb.