Principal processes in graphite atomisers modified by high-melting carbides

Abstract

Some properties of graphite atomisers, modified with an aqueous solution of sodium tungstate or lanthanum nitrate, were studied. The free oxygen concentration in the gas phase of the tungsten carbide modified atomiser is lower than that for a standard atomiser. The most probable reason for this change is that the tungsten carbide catalyses the oxidation of graphite by the free oxygen entrained in the argon. The decreased concentration of free oxygen is one of the reasons for the improved sensitivity obtained with the modified graphite atomisers for elements with thermostable oxides (Ge and possibly B and Si). The maximum ashing temperature for Mo was increased for graphite atomisers modified with lanthanum carbides due to the formation of the refractory La₂O₃.3MoO₃. The maximum ashing temperatures for some Mo- and Sn-containing organic extracts were increased due to the decomposition of volatile chelates and on the active sites of the modified graphite atomiser surface. From a consideration of the information in the literature and the data presented here it was concluded that the processes that occur in a graphite atomiser with a pyrolytic graphite coating and a carbide coating are very different.