Finally, [l.sub.23] is equal to [b.sub23]--the interaction between the chromating time ([X.sub.2]) and the Cr(VI) content of the first rinse ([X.sub.3]).
Their analysis allows us to conclude that the best results are obtained in the low levels of pH ([X.sub.1]) and the concentration of Cr(VI) ions in the first rinse after chromating treatment ([X.sub.3]), with high amounts of chromating time ([X.sub.2]) and the time of the first rising ([X.sub.4]), while maintaining the time of the first draining ([X.sub.5]) and the second draining ([X.sub.8]) at their low levels.
The depth-profiling of the chromating layer using GDOES shows a "multilayer" structure (Figs.
If the chromating composition modifies the layer thickness, it is worth noting that the rinses play an important role in layer formation and affect the layer's morphology.
Of the eight variables considered, the best results were obtained with low pH levels and a concentration of the Cr(VI) ion in the first rinse after the chromating treatment, with high levels of chromating time and time of first rinsing, while maintaining the time of the first draining and that of the second draining at a low level.