Comparative Analysis of the Results Obtained by Different Methods of Studying the Composition of Lithium-Containing Films on Diagnostic Targets in the T-11M Tokamak Chamber

The scurf (outwash) from the working surface of the Li limiter collector exposed for a long time in the T-11M tokamak discharge is examined using modern methods of analysis. As a result of the use of the combination of the direct acid-base titration (DABT) method and a spectral analysis method, it is found that the lithium content determined by the DABT method is overestimated owing to the matrix effect in the outwash, (oxo)hydroxides of transition metals included in the composition of steel (primarily, iron), and ammonia, which is formed during hydrolysis of lithium nitride and causes overstatement of the results when determining lithium by the DABT method. The resultant amount of lithium determined by the DABT method consists of the following components: the true amount of lithium, its apparent amount due to the presence of ammonia in the flush water (outwash), and its apparent amount due to the presence of rust ((oxy)hydroxide of iron(III)) and other corrosion products of the tokamak’s first steel wall in the outwash. Selective determination of ammonia was carried out by the colorimetric method and by the back titration method, while multielement spectral analysis methods (ICP-MS/AES) made it possible to separately assess the effect of corrosion of the first wall and to provide data on the relative rate of removal of some elements from it (the highest, for phosphorus and sulfur, and significant, for tungsten and copper). Therefore, the comparison of the results of the DABT method and direct determination of the amount of lithium deposited by flame analysis taking into account the role of ammonia can be used as a qualitative indicator of the level of erosion of the first wall.