DETERMINATION OF TRACE AMOUNTS OF ZINC IN NICKEL-BASED HEAT-RESISTINGALLOYS BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

An analytical method has been developed for the direct determination o f trace amounts of zinc in sample solutions of nickel-based heat-resis ting alloys without any preseparation. The samples contain complex all oying elements so it is necessary to use hydrofluoric acid for their d ecomposition. The interferences from such coexisting elements Ind hydr ofluoric acid have been able to be overcome by the use of a L'vov plat form and a peak area measurement. There were no adverse effects from d iverse elements of 5 approximately 20% Co, Cr, Fe, Mo, W, Al, Mn, Nb, Ta, Ti and Zr. As for background correction an AC Zeeman effect method was found to be better than a continuum source method which showed an over correction. The established analytical procedure is as follows: 0.5 g of an alloy sample is decomposed with 4 ml nitric acid, 4 ml hyd rofluoric acid and 5 ml distilled water by heating on a hot plate and the solution is then made up to 50 ml in a polypropylene volumetric fl ask. Ten microliters of the liquid is injected onto a L'vov platform i n a graphite tube. The optimum operating conditions of AAS are ashing temperature, 650-degrees-C (20 s-20 s); atomizing temperature, 1350-de grees-C (0 s-5 s) and wavelength, 213.9 nm. Calibration solutions are prepared by adding a standard zinc solution to nickel matrix solutions . The sensitivity (absorbance, 0.0044) was 0.3 pg and the limit of det ection was 0.8 pg (3sigma of blank value) which was equivalent to 0.00 4 ppm in a sample. The proposed method is able to be applied to many k inds of nickel-based heat-resisting alloys.