Abstract
For the determination of impurities in high purity tantalum powders, atomic absorption spectrometry using a heated graphite tube as an atomizer was studied. In comparison with another method, this method has no contamination risk from the pretreatment of the sample, and the operation is performed rapidly and easily. Some factors for the determination, (1) the effect of the carrier gas flow rate on the sensitivity, (2) the effect of a state of sample on the absorption peak, (3) the relation between the spectral intensity and the duration of absorption, and (4) the relation between the spectral intensity and the furnace temperature are examined.
The more the carrier gas rate increases, the more the sensitivity decreases. The flow rate variation of 0.1 l/min. corresponds to the absorption spectral intensity variation of 5% or so. For this reason, the flow rate variation was fixed within 0.05 l/min in the determination. The relation between the spectral intensity and the duration of absorption shows that the element is vapourized more rapidly in an aqueous solution than the tantalum powder. Therefore, when the impurities at different states contained in a substance are measured, it is better to determine the elements by the use of the peak area method than the peak height method. The peak height increases with the atomizing temperature, but the peak area is a constant above a certain temperature. The resulting value does not depend on the amounts of sample, and the value from the peak area method has better accuracy than that from the peak height method. In case of copper in tantalum powders, standard relative deviation was 3.5%, and the detection limit was 5×10-11 g. The time for a determination was 5 minutes. Cr, Fe, Mn, Ni, and Si, were determined similarly.
