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    The Effect of Conversion Coated and Plated Components on the Corrosion of Cobalt Alloy Magnetic Disks

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    Common disk drive components with chromate conversion coatings or electroless nickel platings were analyzed by ion chromatography for residual levels of Cl-, F-, SO42-, and NO3-. Extraction with boiling DI water revealed levels up to several hundred ng/cm2 for these anions. When these components were placed 2 mm under a suspended cobalt-nickel-phosphorous disk in an environmental chamber at 55°C/85% RH, corrosion of the cobalt disk occurred directly over the chromated component when the total level of anions was greater than 200 ng/cm2. This accelerated corrosion did not occur in a 120-h test when the level was less than 50 ng/cm2. The amount of corrosion was found to be dependent on the separation distance between the disk and the chromated component.

    Surface analysis of the disk corrosion area exposed to a chromate conversion coating showed NiO, CoO, and an increased concentration of chlorine.


    chromate conversion coatings, electroless nickel plating, cobalt magnetic disks, corrosion, corrosion analysis

    Author Information:

    Goodson, K
    Manager, Censtor Corporation, San Jose, CA

    Cormia, R
    Manager, Surface Science Laboratories, Mountain View, CA

    Committee/Subcommittee: G01.11

    DOI: 10.1520/STP15053S