| 摘要 |
Process for pickling alloy steels, copper, alloys of non-ferrous heavy metals, special alloys, titanium, zirconium, tantalum and the like by means of nitric acid baths which can also contain other acids, for example hydrofluoric acid, baths to which urea or an aqueous solution of urea has been added, characterised in that the addition of urea is directly metered by an NOx detector working continuously in the conduit through which the gases escape and by a controller, for example a PID controller, the addition being controlled to the minimum desired concentration of NOx in the gases which escape.
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