| 摘要 |
<p>A salt bath composition is provided for forming on the surface of ferrous metal, particularly pre-nitrided, parts, an Fe3O4 magnetite layer so as to protect the underlying iron against corrosion, said layer being a sealing and ordered crystal layer, thus providing a deep black coloration and a corrosion potential of more than 1 000 mV. The composition includes at least nitrate anions and sodium and lithium cations in a range of 0.1-5 % by weight of the bath, and preferably of 0.5-1.75 %. The preferred compositions contain sodium, potassium and lithium cations, and nitrate, carbonate and hydroxyl anions within the following percentage ranges: 8.5 ≤ CO32- ≤ 26, 15 ≤ NO¿3?- ≤ 41,5, 4.7 ≤ OH- ≤ 21.5. In addition to the exceptional reliability of the oxidizing treatment, the presence of lithium combined with sodium and potassium and nitrate or carbonate anions reduces the formation of carbonated slurries in the bath, probably due to the formation of low melting point ternary nitrate or carbonate compounds.</p> |
