Patent ID: 8430973
Filing Date: 2013-04-30
Classification: C23C

Abstract:
1. A process for the passivation of stainless steel, wherein the stainless steel is subjected firstly to a chemical treatment with an aqueous solution containing at least one polydentate complexing agent for iron and at least one oxidant, where the oxidant is able to ensure a standard potential of at least +300 mV in the solution, subsequently to a rinsing step with water and then to a heat treatment at a temperature of at least 80° C. in an oxygen-containing atmosphere, wherein the aqueous solution comprises: (a) 0.5-10% by weight of at least one hydroxycarboxylic acid having 1-3 hydroxyl groups and 1-3 carboxyl groups or a salt/salts thereof, (b) 0.2-5.0% by weight of at least one phosphonic acid having a general structure R′—PO(OH) (c) 0.1-5.0% by weight of at least one nitroarylsulfonic or nitroalkylsulfonic acid or a salt/salts thereof, (d) 0.05-1.0% by weight of at least one alkyl glycol having a general structure H—(O—CHR—CH 0.2-20% by weight of the oxidant, where the remainder of the solution is water to which optionally one or more thickeners can also be added, wherein the at least one polydentate complexing agent comprises (a), (b) and (c).