SEDL / STP / STP1148-EB / STP15053S

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

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

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

Pages: 10    Published: Jan 1992

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Abstract

Common disk drive components with chromate conversion coatings or electroless nickel platings were analyzed by ion chromatography for residual levels of Cl^-, F^-, SO^42-, and NO^3-. 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.