Abstract
Addition of nitric ions to the black chromium plating bath containing hydrogen silicofluoride was most effective for blackness of platings as described in the previous report (Part 2). Then, platings from the bath containing hydrogen silicofluoride and nitric ions were studied and it was observed that the bath was very stable and gave platings, having extremely good characteristics.The results obtained were as follows.(1) Thermal resistance: Resistant at 500°C for 5hr. on nickel plated substrate.(2) Adhesion: Satisfactory results in tape-test and 180° bending test.(3) Wear resistance: Lower than that of nickel platings, and much lower than that of chromium platings (equivalent to a few divisions of the latter).(4) Hardness: Lower than that of nickel platings.(5) Adhesion of paints: Satisfactory results for some kinds of paints.(6) Corrosion resistance: No rust was observed in continuous salt-spray test for 64hr.
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