Long spin disk lube migration

The depletion of thin surface lubricants (<5 nm) on commercially used particulate porous media with radial migration driven by air shear stress over a six-year spin period is reported. The radial thickness profile of the outer disk pack assembly surface lubricant after long spin time is characterized by nearly complete depletion near the inner diameter followed by a ramp up to a semi-stable outer annulus plateau. Inner diameter (ID) depletion does not occur on interior pack corotating surfaces because of nearly solid body air rotation near the hub and the associated reduction of air shear stresses there. Elementary modeling is done for the development of the outer pack surface profile. One such model includes surface lubricant replenishment from subsurface porosity, surface air shear stress, and effective interface slippage of the surface lubricant